Topic 26: Signaling through enzyme-coupled receptors

What is an outcome of signaling through enzyme-coupled receptors

• can dramatically enhance tumor growth

  • with growth factors (GFs) present —> proliferation and expansion (occupy more space than w/o GFs)

What activated receptor tyrosine kinases (RTKs)?

• ligand-induced dimerization & trans-autophosphorylation

  • signal protein indices receptor dimerization

  • kinase domains in cytoplasmic tails phosphorylate each other

  • creates scaffold for signaling proteins that bind phospho-Tyr

Different intracellular signaling proteins bind to different phosphotyrosines via what?

• via SH2 domains

How is SH2 domain binding determined?

• determined by the presence of phosphorylated tyrosine AND specific amino acid chains nearby

what do SH3 domains bind to?

• bind to proline-rich stretched in other signaling proteins

what two binding sites do SH2 domains have?

• P-Tyr binding sites: all have

• specific binding sites for adjacent amino acids: (can vary from one SH2 domain to the next)

what is expressed in a cell types normally lacking PDGF receptor & WT PDGFR

• proliferation and migration

  • PLC gamma able to to activate via binding to Tyr

what is expressed in a cell type normally lacking PDGF receptor & Mutant PDGFR

• proliferation only

  • PLC gamma doesnt activare cause no phosphate to bind to on Phe as there is no autophsophorylation on Phe resides

    • Conclsuion: PLC gamma is required for migration but not proliferation

what triggers a Ras-MAP kinase module?

• EGFR activation

Not sure I understand this fully? Need to know whole process??

What can fluorescence resonance energy transfer (FERET) monitor?

• can monitor Ras activity in live cells

How does FRET monitor Ras activity in live cells?

• Upon activation of Ras, the red fluorescent-labeled GTP binds to the yellow fluorescent labeled Ras

• FRET allows blue light to generate red fluorescence only when the fluorophores are very close to each other

What does FRET reveal about the Ras activation downstream of EGF?

• that Ras activation is typically short lived

  • a variety of negative feedback mechanisms limit the duration of signaling

Physiological Downregulation of RAS-MAPK module

• it is essential for controlling cell proliferation, differentiation, and survival, preventing over activation that can lead to disease.

• This down-regulation occurs primarily through complex negative feedback loops, primarily mediates by the activated effector ERK itself, and the action of GTPase Activating Proteins (GAPs) that inactivate RAS

GTPase- deficient Ras keeps Ras-MAP kinase stuck on resulting in?

• cell cycle progression

How does the lack of GTPase affect the activity of Ras?

• lack of GTPase activity makes Ras continutively active

What allows multiple MAP kinase modules to operate in parallel in the same cell?

• scaffold proteins

  • help to limit inappropriate crosstalk between signaling pathways with shared components

What can kinase-dead mutants function as and how does it affect signaling?

• they can function as dominant negative inhibitors of signaling

What happens when over-expressed kinase-dead mutant takes up space on the scaffold?

• blocks access of wild type kinase A

What can cleave PIP2? What can phosphorylate it?

• cleaved by phospholipase C

• phosphorylated by PI 3-kinase

PI(4,5)P2 is a key intermediate in 2 different types of signaling

What does PIP3 do for PH domain proteins such as Akt?

• PIP3 creates a plasma membrane

What is PTEN and what is its function?

• it is a phosphatase that degrades PIP3

• functions as a tumor suppressor

In the PIP3 pathways, the outcome is a release of protein BcI2. What does active Bcl2 do?

• Active Bcl2 inhibits apoptosis

How are GPCRs and RTK signaling similar?

• GPCRs and RTK signaling can converge on common downstream targets