captioning provided bydisability access services at oregon state university. [classroom chatter] ahern: okay, folks,let's get started. student: let's get started! ahern: i like that attitude. [class laughing] ahern: i looked atthe calendar today and realized that nextfriday we have an exam.
also, that's dad's weekend so it's good to getthis out of the way, huh? maybe have dad cometake your exam for you? maybe not have dad cometake your exam for you? [ahern laughs] okay, today i'm goingto finish up signaling and i will get talking a littlebit about the considerations for metabolic controls andthis involves gibbs free energy and i'll give yousome things about that.
the tas have been going through and probably gotten throughwith you in recitations, the considerations and problemsolving for gibbs free energy and so, as always, if youhave questions or problems or concerns, come seeme and i'll be happy to work with you as well. last time, i spent some timegetting ready to talk about how it is that, how it is thatthe beta adrenergic receptor and epinephrine playvery important roles
in increasing blood glucose. and this is very important. we have an emergency,when we need to escape, we need to do something, or we need to havemuscular contraction. having a supply ofglucose, excuse me, in our blood streamis very important. as i also referredto in class last time, glucose in our bodiesis essentially a poison
that when we have toomuch glucose in our blood stream, we havevery severe side effects. people who havediabetes for example have an insulin responsesystem that is either absent, in which case they havetype 1 diabetes, or, and there's othermanifestations besides what i'm going to tell you, or they have a cellularsystem in their body that is not respondingproperly to glucose.
i'm sorry, not respondingproperly to insulin. so the normal responseof the body to insulin is that binding of theinsulin to the insulin receptor will cause cellsto take in glucose. we'll see at themolecular level today how that happensand why that happens, or why it happens isbecause glucose is a poison. and so if we don't decreaseour blood glucose levels after we've had a meal,
then they go very high andas i mentioned last time, what this can causeis severe problems that people who havediabetes experience. may involve kidney failure,it may involve blindness, it may involve the longeryou have this amputation. people who have diabetesover a long period of time not uncommonly haveamputated limbs. so it's very, verysevere consequence of having bloodglucose level go high.
so it's important thenthat we spend some time talking about howit is that insulin causes cells to take up glucose. and so not surprisingly, there is a signalingpathway that's involved. the signaling pathway, infact the signaling pathways that i'm going todescribe to you today do not, underlinenot, involve 7tms. so 7tms we remember were the7 transmembrane domain proteins
like the betaadrenergic receptor, like the angiotensin receptorthat we're involved in causing cells toactivate a g protein, that means that the things i'mgoing to talk to you about today do not involve g proteins. no g proteins involved. okay, so insulin isa relatively simple molecule. what you see on the screenis a depiction of insulin. it's comprised of twochains that are covalently
linked togetherby disulfite bonds. disulfite bonds you can seeright there and down here. and those disulfite bonds are what hold thetwo chains together. so first of all we can saythat insulin has quaternary structure and interestinglythe way that insulin is made is insulin is madeas one long chain. then it folds and thedisulfite bonds form, then protease clipsoff some of the segments
so that you're only leftwith two linear pieces, kind of like what yousee on the screen here holding everything together. now insulin manifests itseffects on target cells by binding to a specificinsulin receptor. so the insulinreceptor is a protein that's located in themembrane of target cells and it has a structurethat looks schematically like what you see on the screen.
the top part of this imageis the outer part of the cell. the bottom part of the image isthe inner portion of the cell. the insulin receptorexists as a dimer normally. we'll see the epidermalgrowth factor receptor that i will show youin a little bit exists as a dimer only when it bindsto the epidermal growth factor. the insulin receptoris different. it exists as a dimer but thebinding of insulin to this dimer causes some drasticchanges to happen to it
that cause insulin to ultimatelybring glucose into the cell. now, like the other receptorswe saw the other day, insulin as imentioned is a hormone just like epinephrineis a hormone. hormones don't make it into, at least the one'swe're talking about, don't make it into target cells. so insulin doesn'tmake it into the cell. it causes all of its effects
by causing some changeswithin the insulin receptor. now the insulin receptoris a transmembrane protein as you can see here. it has some differentcomponents to it here. there's an alpha subunit,there's the beta subunit. and these worktogether to communicate the information into the cell. so how does this process work? well, it turns outthat insulin receptor
is a special kind of kinase. i talked before abouta different kinase. i talked about protein kinase a, i talked about protein kinase c. and these were kinasesthat we found dissolved in the cytoplasm of the cell. the insulin receptoris a kinase as well. you can see it'simbedded in a membrane. and, in addition, thiskinase is different
than protein kinasea and protein kinase c and it is a tyrosine kinase. it's a tyrosine kinase. so it's a membranebound tyrosine kinase. now, a tyrosine kinase,as its name tells you, is a kinase that puts phosphates onto target tyrosine residues. it puts tyrosinesonto target residues. now, what's interesting andodd about the insulin receptor
and many receptors thatare membrane bound exist like the insulin receptor does, is that the insulinreceptor is a tyrosine kinase but it's normally, whenyou see it in a state like you see it here,it's completely inactive. and this tyrosine kinaseends up activating itself. how does it do that? well, the binding ofinsulin on the external part of the receptor causes a shape
change like you've seen before. now, before the bindingof that insulin occurs, the tyrosine kinaseportions are down here. each side has a tyrosinekinase activity in it. but each side is unableto function because of the way that thesecatalytic sites are oriented with respect to each other. they're just sittingthere doing nothing. binding the insulincauses a shape change
that allows one ofthe tyrosine kinases to phosphorylate the other one. so there's a shape change. this now placesinto the active site of one of theportions of the dimer. it puts the targettyrosine into there. well, the phosphorylation,let's say we're phosphorylating the right in this case, thephosphorylation of the right one now causes it to become active.
and so it turns around andphosphorylates the left one. so now they're both fully active. they're able to do their thing. as a result of that, there'sa series of phosphorylations that happen up and downthese beta subunits. so several target tyrosineswill get phosphorylated on these beta residues. that's an essential componentof the insulin signaling. so first of all, we haveto jump start everything,
we jump start it byputting one phosphate on, then we go back and fourth,back and fourth, back and fourth, and get phosphatesall over there. everybody with me? now, what happens as a result, here's the tyrosinekinase first of all. there's the sidechain of tyrosine, there's the additionof a phosphate, and again like we've seen before,
this changes this guywhich is largely an oh group into something thathas a negative charge. not surprisingly,that negative charge may change again itself theshape of the protein in some way. and that causes all theother changes to happen that i've been talking about. now, you can see on thisreceptor right here that this phosphorylation induces apretty big change in shape. here is this guybefore phosphorylation
and look how far this has moved over here after phosphorylation. so the shape change that'shappening as a result of the phosphorylation ofthose tyrosines is inducing a pretty good size movementinside of this protein. there's a term thatwe use for this, i haven't given it to you andi should give to you at this point. it's called receptor mediatedtyrosine kinase, or rmtk. this is a receptor, theinsulin receptor's receptor,
meditated tyrosine kinase. and we will see, we won't actuallygo into them in this class, we'll talk about one other one. but there are many receptormediated tyrosine kinases that we find in cells. many, many. and they all play importantroles in signaling. well how does insulinsignaling work? so far you've seen how thereceptor gets activated.
what is involved in signalingthrough the insulin receptor? well, now you see this a littlebit more clearly, hopefully. you can see there'sa lot of the guys, lot of things thatare involved here. first of all, we seethat this is the receptor that has bound to insulin. and once it is bound to insulin, there's this crossphosphorylation that happens across the beta unitsof the insulin receptor.
one of these phosphotyrosines,as you can see here, is a binding target fora protein known as irs-1. that's not in internalrevenue service. it does better things than theinternal revenue service does. there's another one called irs-2 that will also do thisthat's not shown here. but this guy, this is a protein, in fact everything yousee on here are proteins. this protein bindsto phosphotyrosine.
it has a domain that werefer to as a sh2 domain. an sh2 domain isa common structure that we find in many proteinsthat is capable of recognizing and binding to phosphotyrosine. this is a phosphotyrosine. this now is a perfecttarget for irs-1. well, this bringing of irs-1in place allows it to become phosphorylated on itstyrosines as well, so again, we have have thisphosphorylation picnic
that's going on here as it were. and these phosphorylatedsites become targets for another protein. it's another enzyme, as youcan see it's another kinase, phosphoinositide 3-kinase. so when we had the beta adrenergicreceptor, we saw movement. we saw this g proteinmoving back and fourth to adenylate kinase. and we saw the cyclickamp moving in the cell.
all these things are happeningright here in this one site. we'll see right here alittle bit of movement, but for our purposes,essentially everything is happening at the same place. well what happens here? what is this protein? this protein is known asphosphoinositide 3-kinase. it also has a sh2 domain and it binds to aphosphotyrosine on irs-1.
so we're making kindof a big sandwich here if you want to thinkabout it that way. this enzyme, as you can see, catalyzes the formationof a molecule called pip3. now pip2 you've seen before. pip2 was involved in thecleavage reaction of phospholipase c that i talked about on monday. if i take pip2 andinstead of cleaving it, i put an additional phosphateon to it, i make pip3.
i've put an additionalphosphate onto this molecule. and yes, pip3 is actingas a second messenger. pip3 is able to travel inthe membrane, as is pip2. they move in themembrane very readily. and it moves in the membraneand it itself is a target for binding by pdk1. pdk1 is pip3 dependentprotein kinase. so we see kinase,kinase, kinase, kinase. we see this cascade thatwe've talked about before.
this was a tyrosinekinase that got activated. this is a phosphoinositidekinase that got activated. this is a kinase that'sgetting activated, and we'll see that thispdk1 phosphorylates this important protein known as akt. yeah? student: that catalyzesthe reaction of pip2 to 3? ahern: the green guycatalyzes the conversion of pip2 into pip3,you're exactly right.
yes, sir? student: is irs-1 the only one [inaudible]? ahern: irs-1 is simplya bridge in this scheme. it's simply a bridge. student: it's notimportant to [inaudible]? ahern: nope. student: is there anamplification that happens during this process orwill it always be together? ahern: a very good question.
is there any amplificationthat occurs in this process? the main amplificationactually occurs right here where this guy canphosphorylate a lot of pip2s, but you don't see the samesort of cascading amplification that we've talked about before. that's a very,very good question. well, we've gonehere, here, here, we've got a proteinkinase that's active. this protein kinase isgoing to phosphorylate.
this protein known as akt. akt plays many roles in the cell and mercifully not going to showyou all the roles in the cell, nor am i going to showyou the series of proteins that it phosphorylates,that phosphorylates, that phosphorylates, thatphosphorylates, that phosphorylates. but, i will tell youwhat the end result of this phosphorylation is. akt is a kinase as well.
and this enzyme willstimulate ultimately a change in the trafficking ofproteins in the cell. what does that mean? well trafficking, it refersto the movement of proteins. when we talked aboutthe endoplasm reticulum and the golgiapparatus the other day, and i said that theseglycoproteins have various licenseplates on them that tells the cellwhere they should go.
should they go to the membrane? should they getexported out of the cell? that's trafficking. those guys getmoved into the cell according to instructionsthat are on them. this guy here isaltering the trafficking. what does it do? it changes one importantprotein where it goes. the important protein thatit changes is known as glut,
g-l-u-t. and as we'll talk later,there are several gluts. glut stands forglucose transporter. now, what this pathway isdoing is it's taking glut, which is found normallyin the cytoplasm, and it's movingit to the membrane. and since glucose, i'm sorry,since glut has the property of transporting glucose, thecell starts taking up glucose. now, that's a lot of stepsthat you needed to know.
yes, okay. you need to know the steps. but that's a lot of steps toget glucose inside of the cell. as a result of this,cells start taking glucose out of the blood stream,and when they take glucose out of the blood stream, theyare reducing blood glucose, reducing the toxiceffects of glucose, and getting it to the cellthat might either burn it or store it in theform of glycogen.
so insulin ultimately is counteringthe effects of epinephrine. it's countering. epinephrine isincreasing blood glucose, insulin is reducingblood glucose. we see that they're doingvery different mechanisms, but those are theresults of the action of those different hormones. and yes, insulin is a hormone. it's a peptide hormone,meaning it's a protein
that's a hormone. okay, so i'll stop and takequestions at that point. or give you a chanceto catch your breath. yes, ma'am? student: since the glutgoes from the cytoplasm into the membrane, and ittakes glucose and with it, it counteractsepinephrine you said? ahern: yes, so whather question was, 'glut, because it's going tomembrane, is taking in glucose
and that taking in ofglucose is countering the actions of epinephrine, the answer to thatquestion was yes. question? student: was it changed by akt? ahern: so her question is,"is glut changed by akt?" glut's location ischanged by the pathway that's stimulated by akt. there's severalkinases that act before
we ever get to that change. and all that's happening is glutis having its location changed from the cytoplasmto the membrane. question over here, lawrence? student: this pt table [inaudible]? ahern: pdk1 phosphorylatesakt, that's correct. student: and that of course, affects blood...? ahern: i'll tell you what,everyone is curious about the steps, maybe i'll makeyou memorize them.
no, i won't makeyou memorize them, but let me show you theoverview of the pathway, okay? student: no! ahern: yeah, so i'vetaken you down to, oh, they've changed it this time. i've taken you down to here. you can see that there's actuallyseveral steps that's involved ultimately in moving thetransporter to surface. they used to have a figurein the old book that showed
like 20 steps thatgot us down to there. you wouldn't wantto know the 20 steps. student: so what doesamplification mean here? ahern: i'm sorry? student: what doesamplification mean? ahern: what doesamplification mean? student: yeah, in this diagram. ahern: here? student: yeah.
ahern: so amplificationis simply, well, i think it's a littlemisleading here. if we activate the receptor,then we're essentially activating the phosphorylationof many, many things. for the figure i've shown you,we're only looking at one thing, that's why i'm saying there'snot really an amplification there. the insulin receptoris involved in phosphorylating many things. we're looking atone at the moment.
there's other things that itcan phosphorylate and activate. we're not looking at those. so let's leave thatamplification out for the moment. yes, back here? student: the cell has away of releasing the insulin and stopping the wholephosphorylation process or? ahern: yeah, so how doesthe cell stop this process? that's a very good question. just like we saw before,
we have to have a way of gettinginsulin out of the membrane. the cell has to have a wayof handling that insulin and yes it does. and that's, again,beyond the scope of what we're goingto talk about here. was there another question? i thought i saw a hand. that's what's involved inthe insulin signaling pathway. as i said, the receptoris involved in many things.
the insulin receptor is one that, if you take my molecularmedicine class in the fall, i'm sorry in the winter term, i'll talk a littlemore about that. it is a very importantreceptor that's involved in a lot of things,including phenomena as diverse as aging and cancer. so the insulin receptor hasits fingers in a lot of pies, an awful lot of pies.
haha, glucose, you see. alright, i don't think weneed to talk about that. alright, so that'sthe insulin receptor and the insulin signaling pathway that we will talk about here. i want to talk aboutanother receptor mediated tyrosine kinase. and this is one that binds tothe epidermal growth factor. the epidermal growth factoris a hormone and like insulin,
it has a receptorthat it binds to. the receptor is membrane bound. and the receptor isa tyrosine kinase. so it binds to insulin, i'msorry epidermal growth factor, or egf, binds tothe egf receptor. there's a schematicdiagram of it, i don't like the schematicdiagram as much as i like this. now, i earlier pointed outthat the insulin receptor exists as a dimer all the time.
the epidermal growthfactor receptor does not. you see it in the dimerform only when the receptor has bound to epidermalgrowth factor. so we can see that here'sone half of the receptor that's bound toepidermal growth factor. here's another half the receptor and only after both of theseguys have bound epidermal growth factor do theydimerize as we see here. now, there's a figurethat's in your book
and i don't like the figure as much as i likethis little schematic. you see this little redsort of loops that are here? these red loops are themajor shape changes that occur upon binding of theepidermal growth factor. so before the epidermal growthfactor binds to the receptor, this loop is sort offolded over onto this thing so they can't interact. but the binding of thereceptor, i'm sorry,
binding of the epidermgrowth factor by the receptor causes them toliterally stick out and touch with the next one. that's how they dimerize. so the system is set up so thatthe receptors don't dimerize until they have both boundto an epidermal growth factor. well what happenswith the binding? upon the binding, verymuch like what we saw with the insulin receptor,these kinases,
which are inactive,become active. one phosphorylates the other,phosphorylates the other, phosphorylates the other,phosphorylates the other, and you see that we geta series of tyrosines with phosphates on them. those tyrosines withphosphates on them are targets for anotherprotein known as grb-2. and grb-2 has a sh2 domainjust like we saw before. it's recognizing and bindingto a phosphorylated tyrosine.
grb-2, like we saw withirs-1, serves as a bridge. excuse me, theother side of grb-2 binds to thisprotein known as sos. sos now, here's a g protein. it's not really a gprotein like we saw before. it's a differentkind of a g protein. so the beta adrenergicreceptor had what we classify as a pure g protein. this protein called ras isa very interesting protein.
it's like a g protein buttechnically it's not the same thing. so i wasn't lying toyou earlier when i said we don't have g proteinsinvolved at this point. ras is one of the mostinteresting proteins in your cells. you see that, like a gprotein, it binds to gdp and like a g protein,when it gets activated, drops the gdp and picks up a gtp. so for all apparentpurposes out here, it's functioning kindof like a g protein.
now, the g proteins we talkedabout before either activate phospholipase c oractivated adenylate kinase. ras instead activities a signalingpathway series of events. one of which ultimatelystimulates a cell to divide. and ras has many, manypathways it can affect. but one of those isstimulating the cell to divide. yes? student: so did sos activate ras? ahern: right, so the bindingof the sos to the grb-2,
good question, the bindingof the sos to the grb-2 cause a shape change the in sos? the shape change in the soscaused the change in ras, which was the dumping of thegdp and the replacement by gtp. and as a result, wehave an activated ras. so we can see in this pathwaythat here's a growth factor. a growth factor is ahormone, in this case it's a peptide hormone, that'sstimulating a cell to divide. that's what growth is all about.
not surprising. multi cellular organismsneed to control their growth. i want my left leg tobe at least approximately the length of my right leg. i know there's a little bitof difference in how long legs are but i want them to beapproximately the same length. i want to have the controlso that i'm determining when cell division in mybones is occurring. if i do that and icontrol that growth,
then i will be reasonablysymmetrical in my appearance. now this protein ras, as i saidis one of the most interesting proteins that wefind inside of cells. it is an example ofa class of proteins of which there are a few hundredthat play very critical roles in this decision todivide or not to divide. they're involved, these proteins that i'm getting readyto describe to you play very critical roles in signalingand usually in some level
affect the decision todivide or not to divide. this class of proteins hasa name, it's very important, they're called protooncogenes. proto, p-r-o-t-o dashoncogene, o-n-c-o-g-e-n-e. well what is a protooncogene? a protooncogene is aprotein intimately involved in cellular control. usually by a signaling pathway. that intimate nature of itsaction in controlling the cell
is essential for thecell to function properly. it's essential for thecell to function properly. if it doesn't function properly, if the protooncogenedoesn't function properly, it behaves as what werefer to as an oncogene. an oncogene has another name. it's a gene that causes cancer. now, how does a protooncogenebecome an oncogene? the most common way in whichthat occurs is mutation.
if we mutate the coding sequencefor ras, we may convert it so that it no longerperforms its normal function. it may stimulate the cellto divide uncontrollably. when i mutate a protooncogene,i can make an oncogene. so the differencebetween a protooncogene and an oncogene is a mutation. unmutated equals protooncogene. mutated equals oncogene. it can lead touncontrolled division.
there are many examples,there are several hundred protooncogenes that are known. and normally, they functionexactly as they're supposed to. they're supposed to controlwhether a cell divides or not divides in response tothe signals that it's getting. but when they mutate, wecan have real problems. that's why we worryabout mutagens. cigarette smoking,pollution in our air, pollution in our water,
junk that we'reeating in our food. these things may favor mutation,mutation of dna in general, you're increasing the chancesthat you're going to cause a protooncogene tobecome an oncogene. now in the case ofras, i'm going to tell you exactly what happens. there are many examplesthough of different mutations that can happen. and i'll show you one otherone after i finish with ras.
ras, like the class of g protein, i don't want to saylike other proteins, but like the class of gproteins, is a very bad enzyme. remember i said that the gproteins were bad enzymes, bad in the sense thatthey're very inefficient at breaking down gtp. ras is the same way. ras will cleave gtp, andas we can see in the scheme, when gtp gets cleaved,ras is no longer active,
it goes back to here. as long as ras is active,it's going to stimulate the cell to divide. one of the mutationsin ras that converts it from a protooncogeneinto an oncogene affects the ability of rasto break down gtp. it affects the abilityof ras to break down gtp. now in the case of ras,it's a fairly small protein. there are two, it's actuallythree, but two that we focus on,
two critical amino acidsat the active site of ras. positions 11 and 12. you don't need toknow those numbers. mutations at eitherone of those amino acids that converts that intoany other amino acid causes ras to beunable to cleave gtp. yowza. any mutation can do that. that can involvea single base pair
change in the coding sequenceof ras at that position. now, if you want tothink about why you want clean water and cleanair and good food, and you don't want to smoke,and all of these various things, ras is a really goodthing to think about. there are animal systemsthat have been shown that they can induce a tumorby making a single base change in the coding of ras. now the formation of thetumor is a complex process.
i'm not going to say ina human being that's necessarily what's going to happen. i can tell you thatmaking ras mutated is not a good career move. in general, mutatingprotooncogenes are not good career moves at all. you're asking for troubleif you start doing that. so be careful what you eat,be careful what you drink, think about the environment,think about your health,
because these thingsreally are very important in your survival. student: [inaudible] require3 or 4 separate mutations that would disable likeapoptosis and induce constitutive cell division? ahern: so his question is, doesn't the formationof a tumor require several independent,separate mutations? and there are thousands, tensof thousands of mechanisms
that can lead to a tumor. you are correct. that's why i say i'm not talkingabout necessarily in one sense, but at least insome animal systems, that has been shownto be possible to do. so you got to be careful. you don't know. i mean how many, is it2, is it 3, is it 20? if there are some systemsthat you could do where
you might take 2 or 3 ofthe right type of mutation, or maybe the wrongtype of mutation, you don't want to mess with that. student: but if asingle cellular signal just activated rasconstitutively, wouldn't you still add a regular activelike a p51 that would initiate apoptosis and... ahern: okay, so, let'stalk about apoptosis later. what he's askingabout is a phenomenon
where cells commit suicide. and you are right, there arechecking mechanisms in cells that will help preventcells from becoming out of control growth. so the mutationof proto-oncogenes is a necessary step forformation of a tumor. so i'm only telling youone way by doing this. apoptosis is one wayof preventing that, but again, let's save that until
we talk about apoptosis, okay? because there's manyfactors to consider. but i want you to be leftwith the gravity of this, which is that mutatingyour protooncogenes is not the best thing to do. yes, neil? student: how does the cellgo into uncontrolled division? ahern: how does a cell gointo uncontrolled division? well, okay, you guys reallywant to get into this here.
so cells controltheir cell cycle. in multicellular organisms,we see the cell cycle that they go through,there's a synthetic phase, a mitotic phase, andthere are resting phases, and there are specificproteins that will allow movementthrough those phases. so when we haveuncontrolled growth, we do not have regulationof those phases. that can involve, again,multiple steps in the process.
so i'm just talking aboutone mutation here, folks. so i'm not going to gothrough the whole cell cycle, but the point is that themore protooncogenes we mutate, the more likely we're going tohave something that we don't want. student: so does the gtpplay a role in the deactivating, so when it mutates thegtp is broken down...? ahern: okay, so i'm not surei understand the question, but the point is that once it'sbound to gtp, it's activated. so there's no role ofgtp or gdp because all
that we have to haveis this activated. if the ras cannot break it down, then it's always inthe activated state. the only shut off mechanismis the breaking down the gtp. i'm sorry, maybe i didn'tunderstand your question, but if i we can't breakthis down, it's on. it's on. okay. so that's a pretty important,pretty cool system to understand.
there's a long set of steps i didn't take youall the way through. there we activatedras, ras activities raf, activities mek, activities erk, and phosphorylatestranscription factors. phosphorylatestranscription factors. transcription factors of proteins that bind to dna thatactivate transcription. if we turn on the wrong genes,
getting back to neil'squestion back over here, if we turn on the wronggenes that are otherwise stopping cell cycle, nowthey're starting cell cycle, we can have uncontrolled growth. so i know i'm givingyou a very sort of black box image of this,but the point is the to we lose control of the system here,everything else that follows can be a reallybig problem for us. ba-da-ba-da.
the last things i wantto talk about with respect to signaling and then i'monly going to talk about one of these and that'sthis guy right here, bcr-abl. this one's an interestingone and it's interesting particularly for peoplewho live in oregon, interestingly enough. and this thing thatyou see on the screen is a way of making anoncogene from a protooncogene. now i talked aboutwell, we mutate.
maybe the dna polymerasedoesn't copy something properly. another way of havingchanges happen that are the equivalent of mutationare to have recombination. you guys have learned aboutrecombination in biology i'm sure. this happens when two dnasthat were not originally together get linked togetherby a cross over phenomenon. a very common, i shouldn'tsay very common, but a relatively commoncross over that can occur that is a recombinationalevent that can occur,
occurs between two genesknown as bcr and abl. abl is a receptor, i'm sorry, abl is a tyrosine kinaseinvolved in signaling. it's a tyrosine kinaseinvolved in signaling. bcr is another gene that'sup here on chromosome 22, abl is on chromosome 9. cross over events thatbring these two guys together happen as i say relativelycommonly, not every day, but relatively commonlyto make something
that we call bcr-abl. what happens in thiscase is that the abl gene gets linked toa portion of bcr gene. so the bcr genes here, wesee the bcr gene in red. we see this portion of theabl that gets linked to it. and we make essentiallya new protein. now if we completely alterthe function of the protein, it probably wouldn't causetoo much of a problem. however, this fusionkeeps the tyrosine kinase
activity of ablin the active form. this guy is stilla tyrosine kinase and abl is involved in telling cellsto divide or not to divide. the result of thisfusion gives a phenomenon that's very interesting. when we talk next termabout gene expression, we'll talk about how muchtranscription of a gene occurs. we can imagine that somegenes might have on average, let's say 1,000 copiesof its messenger rna made.
another gene that's useda lot might have 20,000 copies of its messenger rna made. bcr, it turns out,has a lot more copies of its self made than abl does. abl only has a fewcopies made normally. so what's happening asa result of this fusion is abl is being brought underthe transcriptional control of the bcr gene. so now instead of having justa few messenger rnas for abl,
the cell is flooded with them. well you've got, if youhave thousands and thousands more than youwould normally have, each one of those hasmore opportunity to get activated and to activatecellular division. so here's a case wherethe amount of a protein that we're making, theamount of the protein that we're making isaffecting the cell's ability to control itself.
now we've got an awfullot of this stuff here. that's the bad news. this mutation happensin a type of leukemia. it happens in a type ofleukemia known as cml. the good news is thatthere's a pretty darn good treatment for it. and the pretty darn goodtreatment was actually invented at ohsu. now, it involves a drugthat inhibits this enzyme.
it is a tyrosinekinase inhibitor. in the back of your mindsi hope you were thinking, do tyrosine kinase inhibitorshave effects on cells? and the answer is they can. inhibiting this tyrosinekinase is one way of keeping this tyrosinekinase under control. because if this guydoesn't have the ability to phosphorylate tyrosines,it's going to in fact not be stimulatingthat cell to divide.
we have a better way of handlingthis mutation in this cell. the tyrosine kinaseinhibitor that was invented at ohsu was known asgleevec, g-l-e-e-v-e-c. it's very effective againstthis type of mutation, or this type of alteration,and interestingly enough, this gleevec doesn'thave many side effects. why? well, it turns outthat it really binds to this fused protein verywell and this fused protein
isn't found in regular cells. so when we think aboutan anti-cancer drug and we think about somethingthat we want few side effects, we would really like tobe able to target something that occurs in cancercells but doesn't occur in other cells and gleevecactually does this quite well on this particular fusion. so in this case, thefusion actually gave us a unique target thata regular cell doesn't have.
it's something we think ofa magic bullet or a silver bullet that is targeted ata cell that is in trouble. questions about that? i brought you guys to silence. wow. student: will cellularsystems still recognize like in this case, a new protein, that it will recognizeit as foreign? ahern: are their cellular systemsthat recognize this as foreign?
the cell would have no way ofrecognizing it's a foreign thing. when we think aboutrecognizing foreign vs. natural, we're talking aboutthe immune system which is workingoutside of cells. so no, there's not away of recognizing this. good question, though. okay, so we're getting late. maybe we should singa song and call it a day. i've got a signaling song.
anybody here likesimon and garfunkel? alright. this is one of my favoritesimon and garfunkel songs. i'm an old guy. come on here. oh, wrong one. it's called "thetao of hormones." it's to the tune of"the sound of silence." lyrics: biochemistry my friend
it's time to study you again mechanisms that i need to know are the things thatreally stress me so get these pathwaysplanted firmly in your head ahern said let'sstart with epinephrine. membrane proteins are well known changed on binding this hormone rearranging selveswithout protest stimulating a g alpha s
to go open up anddisplace its gdp with gtp, got too high there because of epinephrine active g then moves a ways stimulating ad cyclase so a bunch of cyclic amp binds to kinase andthen sets it free all the active sitesof the kinases await triphosphate
because of epinephrine. muscles are affected then breaking down their glycogen so they get wad of energy in the form oflots of g-1-p and the synthases thatcould make a glucose chain all refrain now i've reached the pathway end going from adrenaline
here's a trick i learnedto get it right linking memory toflight or fright so the mechanismthat's the source of anxious fears reappears when i make epinephrine. i had a little bit ofthat fear at the end there. alright, take care guys. [class clapping] [end]
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