Park 2 for CMB

Park 2 1/9/07

Handouts given in class will be posted. He is talking about signaling pathways from membrane to nucleus. There is an infinite number of them. Yesterday we looked at one example of glucocorticoid to receptor to promoter to activate gene expression. Then talked about thyroid hormone. Make sure you review these for the test.
Today we will talk about growth factors, cytokines, TNF, etc that bind to receptors. Lots of principles once you get into the nucleus (such as chromatin remodeling, coactivator recruitment, etc) are same. He has picked a few examples out to show us. Representative examples.
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cAMP discovered in late 60s by Southerland- Nobel prize. System in liver- glucagon or epinephrine activate receptor, to adenylyl cyclase, to cAMP. For our purposes, PKA can move into nucleus to activate gene expression. PKA goes into nucleus and phosphorylates a transcription factor. This is one way cAMP can convey message into nucleus.
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CREB has BR (binding region), leucine zipper, transactivation element. CREB present in most tissues. Mediates induction of many genes.
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PKA phosphorylates Ser 133 of CREB. PKA comes in, phosphorylates CREB, then coactivator CBP is recruited.
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Schema on next slide. Schema are useful for helping you memorize complex processes, so pay attention to this slide. Also consider that Dr. Rao wants us to know details about this process, too. (Editorial note)
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Think about CBP- think about histone acetylation and DNA accessibility
CBP has HAT activity.
14- WARNING- He likes the PEPCK MODEL SYSTEM.
PEPCK can be a model for how CREB will work. PEPCK (PEP carboxykinae) catalyses oxalocetate to phosphoenolpyruvate reaction (from gluconeogenesis) to contribute to hyperglycemia in diabetes.
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CREB is bound to promoter. Add glucagons to cell, generate cAMP, PKA phosphorylates CREB, rapid induction PEPCK gene expression results. Within 10 minutes you can begin to see increase in PEPCK mRNA.Pretreat with cortisol, then add glucagons- much larger response due to cortisol and CREB acting together.
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Growth factor receptors:
Growth factor receptors and insulin receptors share a lot of characteristics. For all except insulin they are all RTKs. Dimerization, autophosphorylation, activated receptor recruits other signaling molecules, they go to nucleus.2 factors are PI3K and Ras/RAF.
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Insulin Receptor is a preformed dimer, unlike the RTKs.
PTB is phosphotyrosine binding domain. SH3 and SH2 also recognize phosphotyrosines.
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See notes for definitions of domains.
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P110 produces phosphatidylinositols.
PKB is Akt.
Everything so far is at membrane. PTEN is commonly mutated in cancer to be inactive in order that the cell may constitutively activate formation of PIP3. PTEN acts in regulation by dephosphorylation of PIP3.
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Almost all growth factors activate MAPK pathway. Insulin activates PKB and MAPK pathway.
PEPCK is highly regulated by a lot of things. How does insulin inhibit?
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Acts with glucocorticoids and CREB. Insulin acts via PKB activation to go to nucleus and phosphorylate forkhead transcription factor or FOXO1. CBP comes off promoter and decreases PEPCK transcription.
Coactivators leave, inhibit expression.
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ChIP Identifies factors bound to promoter in vivo.
Note that many factors are stimulated by insulin- he showed us one that is inhibitory.
Remember many growth factors act by activating MAPK.
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Epidermal growth factor induces hundreds of genes including fos/jun.
SRF is serum response factor, which binds to serum response element to activate fos gene.
MAPK goes into nucleus as a dimer to phosphorylate transcription factor TCF and serum response factor- which bind to promoter. Fos and jun are also transcription factors, so when they are made, they can bind to other genes to help initiate transcription.
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JAK2 phosphorylates EpoR, recruits STAT by an SH2 domain, STAT phosphorylates, dimerizes, NLS exposed, activates transcription.
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TNFalpha induces NFkappaB. TNF receptor activates i-kB kinase, which leads to ubiquitination and degradation of I-kB, allowing NFkB to move into nucleus with exposed NLS so it can activate genes.
His notes are thorough.