Overview Clustering Phosphorylation Signal trasduction - - PDF document

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Overview Clustering Phosphorylation Signal trasduction - - PDF document

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1/26/2005 Mario J. Grijalva, Ph.D. (pronounced gree-HALL-va) Irvine 333 3-2192 grijalva@ohio.edu http://www.oucom.ohiou.edu/dbms-grijalva/teaching.htm 1/26/2005 MICR 415A / 515ABios 1 486A/586A Signaling through lymphocyte receptors

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Mario J. Grijalva, Ph.D.

(pronounced gree-HALL-va)

Irvine 333 3-2192 grijalva@ohio.edu http://www.oucom.ohiou.edu/dbms-grijalva/teaching.htm

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Signaling through lymphocyte receptors

  • Overview
  • Clustering
  • Phosphorylation
  • Signal trasduction
  • Receptor signaling pathways

– Antigen receptors – Other signaling pathways

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Overview

  • Cells communicate with their

environment through surface receptors

  • Receptors recognize and bind

molecules

  • Binding creates intracellular signals

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Signals Alter Cell behavior Response

–Cell activation –Cell death –Cell secretion

How the recognition of an stimuli effects changes on the cell? “The Cell”

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Cytotoxic T cell

virus

APC CTL CD8+ APC Th 1 Cytokines Cell killing

X

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Signal transduction:

“Conversion of signal from one form to another” Th CD8+

  • Signal activates intracellular biochemical cascades
  • Activation of transcription factors
  • Expression (or repression) of genes
  • Changes on behavior of cell

APC

Extracellular signal “tickles” receptor

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Signal Transduction

Transmission of a physical signal into a biochemical signal Extracellular receptor binding => activation of gene expression

  • Binding to 1 receptor => no signal
  • Binding to 2 receptors

Cross linking => weak signal

  • Binding many receptors

Large cross linking => strong signal

Clustering

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Clustering

1.- Cross-linking of receptors leads to Clustering/aggregation

Fig 6.1

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Why clustering?

  • Receptors complexes have extracellular

and intracellular components

  • Clustering brings together the

intracellular components of the receptor complex

  • The physical proximity of the

intracellular components triggers the initiation of the signaling cascade

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  • Clustering leads to

intracellular signaling

  • Phosphorylation of Proteins

Receptor associated tyrosine kinases

  • Transphosphorylation
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Phosphorylation by protein kinases

  • Protein kinases Phosphorylate proteins

– Rapid – No new synthesis of proteins – Reversible by phosphatases

  • Enzyme Phosphorylated = Active
  • Enzyme de-phosphorylated = Inactive

– Phosphorylation creates new binding sites for other proteins

  • Phosphorylation creates SH2 & SH3 binding domains
  • Inmobilize cytosolic proteins that are only active if bound to

membrane

  • Increase the local concentration of proteins – amplification of

the signal

  • Only tyrosine, serine, threonine and histidine

residues can be phosphorylated

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Adaptor molecules

  • Phosphorylation creates binding sites for
  • ther molecules.
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Adaptor molecules = bridges

Phosphorylation creates a SH2 binding domain – Adaptor molecules containing an SH2 domain – These molecules also have SH3 domains – Downstream proteins bind to the SH3 domain and get activated

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Phospholipase C - γ (PLC- γ)

  • Contains 2 SH2 domains
  • PLC- γ binds to the adaptor molecule

bound to the receptor complex

  • Phosphorylation of (PLC- γ) activates

the enzyme

  • Activated PLC- γ propagates and

amplifies the signal

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Membrane phospholipid Catabolism

Intracellular signaling molecules carry the signal onward and amplify it. Phospholipase C - γ (PLC- γ)

  • Phosphatidylinositol-bisphosphate (PIP2)
  • diacylglycerol (DAG)
  • Inositol triphosphate (IP3)

IP3 opens Ca2+ channels that allow entry from ER. Ca2+ activates calmodulin DAG activates PKC

Figure 6.4

PIP2 DAG +IP3 PLC- γ

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G-Protein activation

  • GEFs also bind to adaptor molecules
  • GEFs activate G-Proteins
  • G proteins activate the MAP Kinase cascade => activation of transcription

factors

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Signaling…

Protein tyrosine kinases Activation of GTP-binding proteins MAP & Jun Kinases Activation of Transcription Factors Ca++; Protein kinase C Membrane phospholipid Catabolism (PLC) Regulatory sequences Expression of proteins (cytokines, receptors, etc)

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Receptor complex structure

Immunoreceptor tyrosine-beased activation motifs (ITAMS)

– Ag receptors are associated with invariant accessory proteins – Variable chains provide specificity (short cytoplasmic tail) – Invariant accessory proteins participate in 1. Transport of receptor to the membrane 2. Signaling (long cytoplasmic tail) – ITAMS = immunoreceptor tyrosine-based activation motifs 1. Composed of 2 tyrosine residues

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Receptor structure

  • Figs. 6.7; 6.8

Immunoreceptor tyrosine-beased activation motifs (ITAMS)

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First steps

  • Clustering brings

together ITAMS

  • In B-cells ITAMS are

phosphorylated by Src family kinases (Blk, Fyn, Lyn)

  • In T cells Lck,

associated with CD4 & CD8 co-receptor molecules also phosphorylates ITAMS

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Signaling: Protein phosphorylation initiates signaling cascade

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Other signaling pathways

  • Cytokines
  • Toll Like Receptors
  • Fas-Fas ligand
  • Apaf1 activation

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Cytokine signaling

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Fas - Fas ligand

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Cytocrome C leakage

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Lecture slides index:

http://www.oucom.ohiou.edu/dbms- grijalva/Teaching/