Signal Transduction II Transduction Proteins & Second Messengers

Major Signaling Highways Growth Factor/Cytokine/Adhesion –RTK –RS/TK –JAK –FAKs Steroid Hormone –Intracellular DNA binding proteins Virtually everything else –7-pass TM receptors

Typical Iconic Domain Representations and Family Groupings Receptor Non- Receptor

It's All About Phosphorylation RTKs and RS/TK directly phosphorylate each other and substrates upon ligand binding Ligand activates linked TKs indirectly 7TM receptors activate non-receptor S/T kinases

What goes on must come off Phosphatase Families

Signal Transduction Downstream of Receptor Kinases & Receptor-Linked Kinases Adaptors, Small GTPases, MAPKs

RTK Signal Transduction Components The Receptor Adaptors, GAPs, GEFs, –All contain SH2 (and usually SH3) domains (bind P-Y) –Adaptors Shc, Grb2, Nck, Crk –GAPs Ras-GAP, p120 GAP –GEFs Vav, SOS –Recruit/activate p21 GTPase family members – (Ras family) Ras, Rho, Cdc42, Rac PI3K, PLC , –Generate 2 nd messengers PI3K – phosphoinositols (PIP 2, PIP 3 ) PLC  - diacylglycerol (DAG)+ inositol phosphate (IP 2, IP 3 )

Signal Transduction Paths Downstream of Tyrosine Kinases

RTK- Ras - MAPK Pathway GAP Grb2,Shc GEF like Sos GEF

Generalized Transcriptional Activation by RTK Signaling Fig 29-6

Insulin Triggers Uptake of Glucose – How? Fig 29-7

Src – The Prototypical Non-Receptor Tyrosine Kinase SH1 – tyrosine kinase domain SH2 – phosphotyrosine binding domain SH3 – polyproline binding domain SH2 and 3 domains have been found in many other signal transduction proteins and all have a conserved structure and functionality SH1 domain found in all tyrosine kinases Fig27-3E

Adaptors: Masters of their Domains Fig phosphotyrosine binding domains polyproline binding domains Fig 27-11

Small Monomeric GTPases Dramatically different conformations of proteins depending on ligand –GTP vs GDP All have MW ~21KDa –p21 Ras Family –Ras, Rho, Cdc42 Rab family –Rab, Arf, Sar See Table 27-3 for others Fig 27-7

Activation Cycle of GTPase Fig27-8

GAPs & GEFs Have adaptor domains (SH2, SH3, PH, PTB) GEF – stimulate release of GDP from GTPase GAP – stimulate hydrolysis of GTP by GTPase Fig 27-12

Activated Ras Triggers MAP Kinase Cascade MAPK = Mitogen Activated Protein Kinases –ERK1, ERK2, etc = Extracellular signal Regulated Kinase MAPK is activated by a kinase called variably MAPK Kinase (MAPKK) or MEK (MAPK/ERK Kinase) MEK is activated by a kinase called Raf (Ras activated factor) (or MAPK Kinase Kinase) Raf is activated by Ras – not clear how yet

MAP Kinase Cascades Lead to Changes in Gene Expression Fig 29-5

TK-Linked Signal Transduction Components Receptor Non-receptor tyrosine kinases –JAKs Activate STATs (signal transducers and activators of transcription) –Src family members Src, Yes, Fyn, Lck Activated by T-cell receptors, focal adhesion kinases, and RTKs

T-cell-Receptor-Mediated Lymphocyte Activation Fig29-8

Cytokines Activate JAK-STAT Pathway Fig 29-9

RS/TK Signal Transduction Components Receptors –RII receptor binds ligand 1 st & phosphorylates RI upon heterodimerization –RI in turn phosphorylates smads Regulatory smads –Require phosphorylation by RI receptor –Interact with co-smad & translocate to nucleus Inhibitory smads –Bind to regulatory smads and block heterodimerization with co-smads Co-smads –Do not require phosphorylation

Ligands of TGF-  Superfamily Activate Smad Pathway Fig 29-10