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

Receptor

Non-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, p120GAP

– GEFs• Vav, SOS

– Recruit/activate p21 GTPase family members – (Ras family)• Ras, Rho, Cdc42, Rac

• PI3K, PLC,– Generate 2nd messengers

• PI3K – phosphoinositols (PIP2, PIP3)

• PLC - diacylglycerol (DAG)+ inositol phosphate (IP2, IP3)

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 27-12

phosphotyrosine binding domainspolyproline binding domains

Fig 27-11

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 1st & 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