Kevin Ahern's BB 450/550 Classroom #2 for July 6 – Signaling II

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Kevin Ahern's BB 450/550 Classroom #2 for July 6 – Signaling II

I guess I’ve got the camera on so we’re located alright so request to go through this process again and I will do that to hopefully give you a big picture view of what’s happening here alright so we have a response from outside the cell that is a first messenger that has bound to an appropriate 70m receptors I said I’m not gonna talk about the receptor or what the messenger is here but suffice it to say that this process has been activated by the first messenger binding to this target sound ok now the binding of the first messenger caused a shape change in a 70 m which caused phospholipase c become activated phospholipase c in turn converted this membrane component called pip to it cleated into two pieces one piece was IP three which is the blue part that you see right there and it went down into the cytoplasm the other part that was left behind is diacylglycerol and it’s called dag and you can see with that little gray thing right there ok the movement of IP three into the cytoplasm allows it to interact with a receptor on the surface of the endoplasmic reticulum and that causes that receptor in the endoplasmic reticulum to open up it’s basically a poor open or close that’s all it does so when it binds to IP three it opens up and since there are a lot of calcium ions in here the calcium ions are allowed to leave and they come flowing out of the endoplasmic reticulum the calcium ions go and they can cause a variety of things like I said they can cause muscular contraction they don’t all have to go to this one place but in this case they’re going and binding to this enzyme called protein kinase C that’s important because the activation of protein kinase C requires two things one it but requires calcium ions which you see here and second it requires diacylglycerol which was released in the first process the combination of these two binding to protein kinase C allows protein kinase C to start phosphorylating target proteins and affecting their activity turning some of them on turning some of them off ultimately these target proteins will exert a physiological response that help it make sense okay so that’s a protein kinase c system it’s also a 70 m as i said just like the beta-adrenergic receptor system the epinephrine system was that the binding of calcium is interesting and important in the cell and the reason it’s important is as I said calcium is something that still has to be pretty careful with so calcium in high enough concentrations like a Sibyl cause DNA to precipitate the cell can’t afford to have its DNA precipitate so that’s one of the reasons we see it sequestered into organelles like endoplasmic reticulum like sarcoplasmic reticulum and even when it comes out into the cell there are proteins that will bind it and keep that free calcium concentration for being too high well you’re saying doesn’t that defeat the purpose if they bind to calcium house calcium constant concentration going to go up okay well it’s a good question part of the reason that there are proteins to bind it is some of these proteins when they bind to calcium participate in activating other proteins so calcium is a second messenger for many processes you’ve only seen one of them so far and the proteins that bind to calcium have a very common feature about them the common feature that they have is shown on the screen and they look like a hand this is called an EF hand okay the structure looks like a finger going up and a thumb coming out here’s the thumb the blue and the finger is up in yellow and the calcium ion fits right here where my little pocket is in my hand right that’s the structure of a calcium binding protein now one of the most common calcium-binding proteins we have in the cell is known as calmodulin and though it doesn’t look exactly like it here it in fact does have that binding site very much like what the EF hands figures showed us okay now what this is depicting for us is the structural change that’s happening in calmodulin when it binds a calcium okay

so here is the molokai here is the callus of the calmodulin when it’s not bound to calcium here is the calmodulin after it is bound to calcium and you’ll notice that it has a sort of a little claw like this this little claw serves to be a binding structure for target enzymes so by having calcium binding to calmodulin and calmodulin bind to target enzymes the target enzymes can be activated by calmodulin not my calcium that’s good okay so one of those target enzymes is called cam kinase it doesn’t really matter for our purpose what it is but suffice it to say that that calmodulin is the activator and it’s only activating when calcium has been released so again calcium can be the signal that the effect is modulated through calmodulin now we will see that one of the proteins involved in glycogen breakdown responds to calmodulin there are many many proteins that respond to calmodulin and in every case they’re responding to the fact that calmodulin has bound to calcium calcium is giving that signal for a process to go forwards okay well it’s time to talk about some other receptors and now i’m going to turn away from 70 ms there are hundreds of seven teams in our cells okay but i want to talk about another very important hormone signaling system that you’ve heard about and that is essential for our body and it’s the signaling system that is ultimately initiated by insulin okay so insulin is a very important hormone in the body insulin is released by our pancreas when the blood glucose levels start to rise well when do blood glucose levels start to rise after we’ve eaten a meal after we’ve gotten something that’s got a fair amount of glucose in it now there’s the first clue to you that glucose is a poison okay this body is releasing insulin and the effect of insulin is to stimulate cells to take up glucose they’re taking up glucose to lower the blood glucose concentration and that’s important because if not if we don’t lower the blood glucose concentration we will have severe effects people who have diabetes have high blood glucose levels and they get high blood glucose levels and what happens they can lose their vision they can lose their kidneys they can lose their limbs glucose is a poison well if cells are taking up a poison aren’t they going to die no when they take up glucose they make glycogen that’s why they make glycogen they take up glucose so that they are not having it out of the bloodstream where it can kill cells it kills cells by disrupting osmotic pressures inside the cell is converted to glycogen and it sits there merrily no problem so insulin is protecting the body against the harmful effects of having high concentrations of glucose in the bloodstream very important point the signaling process I’m going to describe to you tells you how that happens it suffice it to say the body doesn’t control levels of glucose the body is in deep doo-doo okay very deep doo-doo people die of diabetes people have as they say organ failure they have many problems that can arise and they arise because of the high concentrations of glucose well how does insulin exert its effects okay insulin-like all hormones insulins of first messenger remember that it’s released by the pancreas it travels into the bloodstream and it goes to target tissues those target tissues will include muscle and liver among others but for right now we’re going to talk about muscle and liver and when they hit muscle or liver cells they bind to a receptor okay they bind to a receptor so the receptor is called an insulin receptor insulin receptor is involved in a million process is probably one of the most active receptors on cells when insulin binds to the insulin receptor we’re going to see some changes that are going to happen in the receptor just like we saw changes happen in the beta adrenergic receptor except for in this case the receptor is

going to affect itself it’s going to it’s going to alter itself so what’s going to happen you’ll notice that the instant receptor is a dimer okay it exists like this in the membrane it has a cytoplasmic region down here it has an extracellular region up here the extracellular region of course is where the insulin actually binds this guy always is found in the membrane as a dimer okay but it’s not in the active form until insulin binds it so when it’s sitting there in the membrane by itself it’s not doing anything and upon activation that not what I want that is a bond the binding of insulin here’s what happens okay now this is kind of a mouthful of stuff so bear with me insulin has bound to the insulin receptor on the top scheme that’s the little green ball that you see there the binding of insulin causes the receptor to change the arrangement of the two subunits that it has the two identical subunits that arrangement is slightly changed okay so just like other proteins that we’ve seen whose shape gets changed by binding of a substrate in this case the binding of this hormone causes the insulin receptor to change the way those two subunits are interacting with each other the insulin receptor is an enzyme it’s normally inactive meaning it doesn’t catalyze anything unless insulin is their insulin causes the receptor to do something odd okay it literally forces a portion of one side of the receptor into the active site of the other now tell you what the reaction is in a minute but we’ve got these receptors are sitting here minding their own business we got an active site over here we’ve got an active site over here and neither one is doing anything because nothing is making its way into either one of them the binding of the receptor has caused one of the change shape so that a portion of the other receptor is forced into the active site of the other one so we can say in this case the one on the right is getting forced into the active site of the left the active side of the left is therefore stimulated to catalyze a reaction on this Porsche the other receptor that’s been stuck into it well what’s the reaction that it catalyzes the reaction that it catalyzes is the portion of the of the the right guy that got put into the left it’s stuck a tyrosine into the active site the action of the insulin receptor is it’s known as a tyrosine kinase more specifically it’s known as a receptor tyrosine kinase and his name would suggest a tyrosine kinase would put phosphates onto a tyrosine and the addition of the phosphate whoa the addition i was at you I thought it was above as it is this guy falling her what the addition of that phosphate to that tyrosine of the guy on the right now causes it to phosphorylate the one left so one phosphorylates the first one now that the first one they got phosphorylated oh wow I’m active i’m going to start phosphorylating the other guy and it phosphorylates the other receptor so they’ve now each mutually phosphorylated their own respective tyrosines this causes each enzyme become very active they go on a phosphorylation parade they phosphorylate each other in here they phosphorylate each other up here and the phosphorylation of this guy up here provides targets for proteins to bind okay now the rest of the events that happened in the signaling process involve both phosphorylation and binding a protein to protein to protein to protein and ultimately to activation of a kinase now I’m going to I’m going to step you through that but I want the big picture is insulins bound receptor got activated and now we’re going to start making a series of binding events that’s going to result in the activation of a target kinase okay well this phosphate up here is a target

for a protein known as IRS one in each case the phosphates that you see on all the molecules up here all of the phosphates have been placed onto tyrosines okay there are specific structures inside of some proteins that recognize only phospho tyrosine they see tyrosine they won’t bind they see phosphotyrosine they will bind so what happened was IRS one came up here and it says oh I’ve got a binding site for phosphotyrosine i bind to it okay that segment of irs-1 that bound that binds phosphotyrosine is called an sh2 domain that’s a portion of the protein that recognizes phospho tyrosine so sh2 domain right there binds to the phosphotyrosine hear this now holds the IRS one close to this enzyme and guess what this enzyme does it puts these phosphates on here that you see and it’s putting phosphates onto tyrosines again well these phosphotyrosine zar a target for another sh2 domain over here on this enzyme called phosphoinositide 3-kinase okay phosphoinositide 3-kinase phosphorylates pip 2 there’s our friend pip 2 again only in this case is putting a phosphate on instead of clipping anything and it makes pip 3 i’ll guess i will go over this again don’t worry pip three acts like a messenger for this enzyme called pdk1 pdk1 is a kinase it’s a protein kinase and it in turn phosphorylates akt to make it become active so now we’ve activated another kinase this guy down here is able to travel throughout the cell and exert its effects now I’m going to tell you what those effects are in a second you’ll start to see how this comes together in a second but before we get to those effects we have to just see this as a sequence of events that’s happening so I am going to take you through it again and hopefully clarify all right insulin is bound binding of insulin caused the receptor to basically phosphorylate itself if phosphorylated itself on both sides on tyra scenes the phosphotyrosine were targets for this protein called irs1 irs1 bound to the phosphotyrosine through its sh2 domain that brought this tail into close proximity of the enzyme which now put phosphates onto the tail the phosphates on the tail were targets for binding of the sh2 domain of phosphoinositide 3-kinase that caused the kinase to become active and start to phosphorylate pip to pip two became pip3 which was necessary for activation of pdk1 pdk1 in turn phosphorylated akt and i’ll stop for questions before i get to the stunning climax of this process everybody’s I stood with that everyone a joke okay let me think let’s see i have 1 plus my checkbook I told you my artichoke okay how about this guy’s walking along the street and he looks down and he discovers this magic vase at his feet and he looks at the magic vase he grabs it and he rubs it of course and you know what happens then genie pops out right and the genie says oh it says you know I will grant you three wishes of course what would you like and he says well he says um I want to have a billion dollars poof in his hands appears this certificate giving him 1 billion dollars in a Swiss bank account wow this is awesome okay he says well he says the genius about you

like next Oh master and he says I think I would like to be a very powerful person poof he becomes the president the biggest corporation in America wow you know Ginny says well how about number three and he says well let me think about this for my nieces I’ve got money see you’ve got power he says I want every woman to love me poof he turns into a box of chocolates bad joke okay how about a better joke I’ll give you one more okay we got we got turn all right so this is the one I was gonna tell you I couldn’t member it all right so this lady goes to this pet shop right and she decides that she wants to buy her husband a great present for his birthday anybody heard this joke okay great present for his British so it gets to the pet shop and tells the pet shop owner i want to buy my husband this really great present something different than usual and the bench upper nurses I got it for you he walks back and he brings out an iguana on a leash great big iguana Blaylock’s and she says yeah I don’t pick so that’s what I want you no choice is okay takes it back you know and he comes out and he gets got this like this 10-foot anaconda okay and he’s got it brings it out and there’s a slithering snake and everything in lady says yeah I think I want to have that around the house you know so this goes on he brings it every animal he can think of and you know she says no I don’t think it’s gonna work I don’t think it’s gonna work this goes on for quite a while finally he’s getting exasperated he says I know what you need he says you need a crutch Berg she says what’s a crunch bird he says oh you see a little Burt in the perch over there and she says yeah and he says watch this this is crunch berg chair he points over this chair and this bird jumps up off his perch and he flies over this chair and demolishes the chair writing for other lady’s eyes she says bird that’s incredible you have heard this right okay don’t give it away and he says you ain’t seen anything yet says crutch Burt desk and there’s this great big old beautiful wooden desk over in the corner and this bird flies over the desk and in in literally a minute it’s splitters she says my god she says this is amazing she says I gotta get this for my husband he’s gonna love this thing she goes walking home he’s got little bird on her finger and she walks in you know him and he said no read the paper honey I got your shopping for your birthday what is it just get the crotch bird this is crunch bird my ass okay is that the joke you heard it was different I won’t ask what your place like okay all right just make sense now we’re not we’re not done with this yet there’s more but I thought you liked you need to break before I get to the more the more is actually cool the more is simple should say simple but the more is interesting all right now what happens in this process is we’ve gone through here insulin is bound we’ve activated receptor we’ve phosphorylated these proteins we’ve localized this guy to the membrane so it can start converting to into pip3 it activated this others pip3 it activated this kinase which activated this kinase and you see several arrows you’ll notice i’m sparing you what each of those arrows do those arrows result in the movement of glucose transporter to the cell surface so what has happened insulin has stimulated the movement of glucose transporters to the cell surface and what do glucose transporters do they bring glucose into the cell this is how insulin lowers blood glucose they stimulate cells to move their receptors to the surface take glucose out of the blood stream and put it into the cell where it can be built into glycogen and thereby reduce the toxic effects of glucose makes sense ok so again it’s just a series of steps this goes to this goes to this goes to this bang we ultimately result in this happening ok um there’s an sh2 domain as the thing that binds phosphotyrosine as i told you nothing much more to say about it than that and we don’t need to worry about that ok now I’ve got what

the heck is with that I have another signaling pathway that I want to talk about that is important in cellular decisions to whether or not to divide and as we shall see these this pathway if it goes awry can cause severe problems including cancer ok so it’s important to recognize that now we’re going to think about processes that are ultimately involved in helping the cells to decide should I divide or not divide very important thing for sale to decide all right well this is part some of these are mediated through this hormone called epidermal growth factor or EGF as you see here it’s a peptide hormone just like insulin was a peptide hormone only it’s different obviously and epidermal growth factor is released there’s a structural consideration okay and I’m conscious the hormone actually that’s the receptor this I what I want hold on sorry no that’s not what I want here okay so epidermal growth factor is a hormone that binds to the epidermal growth factor receptor alright so the receptor just like the insulin receptor is a membrane protein it has an extracellular domain and it has an intracellular domain now it’s similar to the insulin receptor in that it also is a tyrosine kinase it’s a receptor tyrosine kinase what we find is that receptor tyrosine kinase a–‘s are very intimately involved in control processes in the cell insulin receptors they said does many other things you only saw the movement of the receptor here most tyrosine kinase azhar involved in important cellular controls very important saito controls and many of those controls are involved in replication or no replication epidermal growth factor receptor is called EGF receptor is the guy in yellow EGF is the lone guy in purple alright epidermal growth factor receptor is a membrane protein but in contrast to the insulin receptor it does not normally exist as a dimer in the membrane normally each one of these units is floating around the membrane all by itself only after the receptor at least the half of the receptor has bound to EGF can it bind to another half of the receptor that is also bound to EGF if there’s no EGF these guys are floating freely they’re not linked to each other you can see this little red loop here the binding of EGF to the receptor causes that red loop to stick out so they can actually interact with each other if there’s no EGF the red loop contracts and they don’t interact with each other so it’s through that red loop that there they’re held together okay what has happened here epidermal growth factor has bound to its receptor it’s bound to each half of its receptor and now as a consequence these two guys are linked and just like we saw with the insulin receptor they’re both tyrosine kinase a–‘s and they phosphorylate each other when they’re brought next to each other the phosphorylation of each other causes there to be binding sites for proteins that have guess what kind of a domain sh2 domains all right here’s an sh2 domain of this protein called group two that’s binding to the receptor herb two is interacting with this protein called SOS SOS is binding to this protein called rass and rass is becoming activated and does this look familiar like anything you’ve seen before you betcha rass is a protein it’s very much like a g-protein it’s very much like a g-protein now rass becomes activated when its gdp gets replaced by GTP and activated rass will stimulate cells to divide so when this signaling process has happened it’s a long ways before the sishen to divide happens but activated rass happens be as part of the signal to tell cells to divide so we can imagine there’s a bunch of steps after this and there are but this part right here is critical the activation of rest so the

hormone is bound the hormone the receptor phosphorylates itself this binds group to binds then SOS binds then rass binds GTP gets repeat gets replaced by GTP and wrasse is active now this is really interesting process we’re seeing now a signaling system that’s telling the cell I want you to divide if you’re a growing child for example and you need to make new bone cells this this is a great way to say we’ve got to build bigger stronger bones we’ve got to make more bones okay keep going keep going that’s signal that hormones signal to divide is tally is coming through rass now wrasse as you might imagine plays a very important role in the cell in fact all these guys play a very important role in the cell as long as everybody is playing nicely this system works very well all right I’m going to tell you in a minute what happens when this system doesn’t go very nicely well I told you that wrasse acts like a g-protein your first question should probably be does it cleave gtp and the answer is yes it does that’s how it turns itself off so this wrasse will go it will activate cell division it turns itself off and it goes back and we start this process again if necessary or if not no more division okay what happens if we screw this system up well let’s imagine a couple ways that we might screw this system up alright the most the best-known one is what happens if I make a mutant form of wrasse what if my cells suffer mutation such that wrasse is altered this is known it turns out the active site of wrasse there’s a couple of amino acids at about position 11 and 12 on the amino acid sequence that are absolutely critical for wrasse function function being cleaving gtp back to GDP acting as an inefficient enzyme alteration of either of those amino acids causes wrasse to be unable to cleave gtp this is big problem rass binds GTP it can’t turn itself off what’s it going to cause the cell to do it’s going to cause the cell to divide uncontrollably this can be one way in which we get uncontrolled growth ultimately resulting in a cancer and or a tumor rass can’t turn itself off we’ve got problems okay how else might this system gets screwed up what if we had a mutant epidermal growth factor receptor that didn’t require epidemic growth factor to interact that signal now is going to be made all the time it’s going to be making this guy was going to be making this go again we’re going to have uncontrollable growth when we look at processes that are involved in controlling growth if we screw up those processes we may be turning on growth all the time that’s a big big problem for cells okay now I want to tell you about a related protein and an interesting story relating to anti-cancer treatment okay there’s a related so I told you that the EGF receptor for example exists as monomers in the membrane okay it doesn’t normally do this until it’s bound to two of these there’s a related receptor in the cell that’s called her h er her is present in reasonably low levels but her can also interact with EGF receptor and stimulate this process at a low level this probably happens all the time regular cell division fine alright we’re not going excessive we’re not having to respond to hormones we’re just saying okay it’s time to divide her interacts with EGF receptor her doesn’t require EGF her does not require yugioh so it’s floating around in the membrane every now and then it bumps into a receptor and set ok let’s do minute this process and every now and then that selda sites to divide as long as you have a low enough level of her no problem it’s probably part of normal cell division okay well what if the cell has a mutation that causes it to make a lot of her well if you have a lot of her the likelihood her

is going to bump into EGF receptor increases the more that happens the more this process happens the more stimulation that we get the less control we have over growth and the more problems we’re going to have as a consequence over stimulation of production of her is not uncommon in breast cancer there are many mechanisms for breast cancer but one of them is that the her receptor can in fact be over stimulated to be produced a stimulating cell division way more than it should as a consequence we could imagine big problems in fact we do have big problems that’s the bad news the good news is that her related cancers are fairly easily treated thanks to a monoclonal antibody that’s been made called Herceptin anybody know anybody who’s head of Herceptin I never heard for septum okay yeah all right so Herceptin is a monoclonal antibody that’s a special kind of antibody that’s designed to bind one and only one thing and it’s designed to bind to the her receptor hmm now the beauty of this is it doesn’t bind to anything else and when given to cancer patients if they in fact have a have a tumor that results from overexpression of her it’s a very effective in essentially stopping the tumor in its tracks and be very very few side effects because it’s really designed to bind to one thing as a consequence this is one anti-cancer treatment that really works very well and doesn’t cause much in the way of other effects that happened ok so our knowledge of signaling pathways is very helpful in our understanding the progress by which cells go for uncontrollable growth ok how am i doing on time oh my goodness I’m really doing good on time staying ok all right questions about that okay moving along uh uh what else did I want to say here I guess I did show you this already but again what you saw was that was the process that led ultimately I’m sure that was insolent doctor sorry nuts eat you ok so here’s the process that happens there’s a lot of things on here I haven’t talked about you’re not responsible for all this down here but you can see that this signaling pathway is fairly complicated and we see activation of wrasse wrasse activates something called raf activate something called Mac activates kirk and these result ultimately in the phosphorylation of transcription factors that now change gene expression and gene expression change is important when a cell decides to divide it is going to have everything ready for replication all the time only when it’s ready for replication should it do that and so those genes have to be turned on at the appropriate time and that’s what this process is activated to do okay all right now I need to give you a little terminology here if you’ve heard about in other classes maybe not so I’ll make sure everybody’s heard the same stuff wrasse is an excellent example of a cellular protein that is intimately involved in important processes it’s an example of its importance is shown by the fact that if we mutate it in the appropriate place the cell loses all control it becomes it may get it is stimulated to divide uncontrolled excels have very rigorous controls on deciding to divide or not to divide but a mutated wrasse messes that up okay rass is a one of a series of actually a few hundred proteins that have such essential functions that if we screw up we screw up the ability to control division this group of proteins all has common name they’re called proto-oncogenes wrasse is a proto-oncogene explain later an oncogene is in a minute but a proto-oncogene is a gene intimately involved in cellular control and if I screw up that control the cell is going to divide uncontrollably there are hundreds of these wrasse is one example okay now when I mutate wrasse I convert it from a proto-oncogene is something we call an oncogene you probably have heard of oncogenes acha genes are called genes that cause cancer people mistakenly say that well you’re full of oncogenes your

body is already full of oncogenes your body is full of proto-oncogene they have to be mutated to become an oncogene right so if we take a normal gene that is intimately involved in controlling cell division for example we alter its function we’ve mutated it we’ve converted from a proto-oncogene into an oncogene so oncogene is a mutated proto-oncogene and that mutated proto-oncogene causes the cell to divide uncontrollably there are hundreds of these in your genome rass is a really interesting one it’s one that I always tell students it scares me I’ll tell you why it scares me okay I told you that if I mutate one of those amino acids 11 or 12 and rass I can convert rass from proto-oncogene into an oncogene in fact if i convert any one of either those amino acids into any other amino acid grass becomes an oncogene that Rask can lead to that simply that one transformation of that one amino acid in one wrasse can cause that cell to divide uncontrollably it’s been shown in mice for example that you can do exactly what I just said and cause a tumor to form of the mouse now I’m going to tell you this scare part of it and then I’m going to hopefully take away a little bit of the scare you say well what’s the chance of mutating that one thing well you know if we think about how many base pairs we have in the human genome there are 7 billion base pairs right so I’ve got if I’m going to have a mutation one in seven billion mutations you know I got plenty to spare right and if I’m if I have a mutation rate of once every let’s say 10 to the ninth okay which is about it which is about a billion also then one in a billion of one in a billion okay because what I’m going to get mutation so a billion billion is in the order of quadrillions you say well I feel pretty safe but then you realize how many trillions of cells you have in your body and how often replication is going on you’re probably making rass oncogenes fairly frequently you make them more frequently when you do things that stimulate mutagenesis these include things like smoking cigarettes they include things like going to tanning booths I am absolutely amazed and appalled at the number of young people who go to you’ll see dr. Mehra we’ll talk next term about why going to tanning booths is really nasty to your DNA it screws up the repair system should I now go out in the Sun at all no you should get a little bit of 10 it’s not like saying you shouldn’t do that but tanning booths give you short wavelengths ultraviolet light that are very mutagenic i went to a tanning booth I’m okay I only smoked one cigarette I’m okay right all right it’s a numbers game the more you you roll the dice the more likely it is you’re going to lose and so there’s one message I can communicate to my students that stay out of goddamn tanning booths okay because they’re going to be nothing but trouble for you down the line okay get off my high horse here and get back to talking about biochemistry ok any questions or comments about what I’ve said so far here No ok well I want to talk about one more system I’m actually in pretty good shape talk about one more system then we’re going to call it a day and this one other system is a very interesting and important phenomenon I’m not going to go through all the signaling so you can you can rest assured with that but it’s an important of it affects an important protein in the signaling process ok in a tight a certain type of leukemia commonly found in children ok there is a chromosomal rearrangements so cells are constantly rearranging recombining doing all kinds of things with their chromosomes one of the common rearrangements that can happen that can result in leukemia is a crossover that can happen between a region of chromosome 9 and region of human chromosome 12 this rearrangement occurs it fuses a portion of a gene called BCR with a tyrosine kinase known

as able ADL and Abel is a tyrosine kinase that is important and a signaling process it’s important in helping cells to decide whether to divide or not okay important into site helping cells to decide whether to divide or not normally able does its thing it responds to signals that phosphorylate some stuff and help cells make that decision about to divide or not to divide okay now when this recombination happens the control region of able a VCR that is the promoter region of able and the n-terminus of able is fused to the tyrosine kinase portion I’m sorry a VCR is fused to the tyrosine kinase portion of Abel so we have part of BCR here we have part of Abel here and now we’ve got a new protein well this guy turns out to act like an oncogene able by itself didn’t act like an oncogene unless you did something to it and here’s the something that you did to it it turns out that VCR is made in the cell at much higher levels than able itself is and since the control region of BCR is being fused along with BCR Abel we’re making a new gene and that new gene has tyrosine kinase activity it is very active and it is contributing the signaling process and causing a problem okay every one thing now that’s the bad news that gives rise to leukemia and causes a problem right the good news is that we actually are able to treat this cancer fairly readily with a compound that does something to this what kind of a compound do you suppose we would want to use to treat this with what’s that okay something this silence we mean by silence not quite a methyl eyes know how would we if we were designed something to stop this process from happening what would we have to do what’s that well the three combinations already happened so we’ve got the Leukemia it’s already happened we get this we’ve got this cell that’s got this thing now you’re right if we prevented that recombination from happening we wouldn’t have this problem but the recombination has happened and so now we’ve got this this protein is being made in high quantities and it’s telling the cell all the time divide divide divide we’ve got leukemia we have a problem what we want is an inhibitor of the tyrosine kinase we want this tyrosine kinase to not be able to put phosphates on tyrosine and and this is the real advantage we have is that we this is a new protein this is a protein that didn’t exist in a regular cell perhaps we can use a tyrosine kinase inhibitor that might affect this but not have effects on other tyrosine kinase right there is such an inhibitor that is known it was actually invented by a professor up at ohsu and we know what let me know what the inhibitor is it’s called gleevec GL ieve see it binds here and it appears to bind to this guy preferentially compared to other tyrosine kinase gleevec has again relatively low chemotherapy side effects because it’s working mostly on a protein that isn’t present in normal cells so thanks to gleevec a lot of childhood leukemias and other leukemias as well are in fact treatable as a result of their ability to stop this overactive signaling process from happening in the body can exert its effects okay now I have a song if you want a song a song okay the song actually requires one other signaling thing I haven’t told you so let me let me tell you what that is first so then then you’ll understand the song okay in this process okay in this process of epinephrine signaling we’ll talk later in the class about another protein that actually can stimulate the same process it’s called glucagon and we will see that that will come up in this song I believe if i recall

correctly all right this is a song to the tune of an old Simon and Garfunkel tune called the sound of silence anybody know the song okay why is that way over there okay so it’s kind of it’s fairly easy to sing if you know the tune if not just kind of hum along and we’ll go there goes biochemistry my friend it’s time to study you again mechanisms that I need to know are the things that really stress me so get these pathways planted firmly in your head hey Hearn said let’s start with epinephrine membrane proteins are well-known changed on binding this hormone rearranging cells without protest stimulating a G alpha s to go open up and displace its gdp with gtp because of epinephrine active G then moves aways stimulating at cyclase so a bunch of cyclic am p bites to kinase and then sets it free all the active sites of the kinases oh wait triphosphate because of epinephrine muscles are affected then breaking down there glycogen so they get a lot of energy in the form of lots of g1p and the synthesis that could make a glucose chain I’ll refrain because of epinephrine now I’ve reached the pathway end going from adrenaline here’s a trick I learned to get it right linking memory to flight or fried so the mechanism that’s the source of anxious fears reappears when I make up and nephron okay I thought glucagon I guess it didn’t okay so the g1 people make more sense later so all right let you guys be have fun and i will see you on a height supposed to be hot tomorrow dress accordingly see you then you