Lecture 7: Signaling Through Lymphocyte Receptors

Transcription

1 Lecture 7: Signaling Through Lymphocyte Receptors

2 Questions to Consider After recognition of its cognate MHC:peptide, how does the T cell receptor activate immune response genes? What are the structural motifs used by signal transduction molecules that permit specific interaction and activation of effector proteins? How do genes know what is going on in the outside environment requiring them to make their proteins at the appropriate time?

3 General Signal Transduction Concepts

4 Recognition of MHC:Peptide Complex by TCR Initiates Signaling Cascade in the T cell

5 Some Cellular Receptors Have Their Own Transduction Molecules Activated by Dimerization

6 Other Cellular Receptors Are Transduction Molecule-challenged

7 Signal Transduction Pathways Amplify the Initial Signal

8 Signal Transduction Pathways Must Have the Capacity to be Turned Off

9 Adapter Proteins Recruit Target Molecules From the Cytoplasm to Membrane-Associated Kinases

10 Src-family Kinases Are Regulated Tyrosine Kinases and Also Function as Adapter Proteins Adapter Adapter Adapter Kinase Binds to CD4/CD8 or TCR /CD3 Binds to PI3-kinase (prolinerich motif) Binds to P120/130 PI3-kinase (pyeei motif) PTK Phosphorylation of specific tyrosine residues within TCRz/CD3, CD5 P120/130 Regulates PTK activity (dephosphorylation by CD45 upregulates activity:phosphorylation by p50csk downregulates

11 Scaffolding Proteins Permit Assembly of Signaling Complexes

12 Overview of T Cell Signal Transduction

13 The T Cell Receptor Complex Consists of Eight Proteins With Unique Functions Ligand binding heterodimer or binds peptide + MHC CD3 Complex and Nonpolymorphic chains present as or dimers Intracellular - present as dimers present as a homodimer

14 Interaction Between MHC Class II:Peptide and TCR Recruits the CD4 Molecule

15 TCR-associated Proteins: src-family Kinases lck binds to CD4 and CD8 fyn binds to non-phosphorylated ITAMs SH3/SH2 domains inactive when bound to phosphorylated C-terminus activated by dephosphorylation by phosphatase such as CD45

16 Regulation of Src-family Kinases by Phosphorylation and Dephosphorylation of Activation and Inhibitory Tyrosine Sites

17 MHC:Peptide Interaction Recruits the CD45 Tyrosine Phosphatase Which Dephosphorylates and Activates Src-kinases: Fyn and Lck

18 Phosphorylation of Receptors Permits Them to Recruit Adapter Proteins That Bind Phosphotyrosine Residues

19 Role of Immunoreceptor Tyrosine- based Activation Motifs (ITAMs) Tyrosine residues on ITAMs are phosphorylated and thereby bind proteins containing SH2 domains Total of 10 ITAMs/T cell receptor complex 1 ITAM/CD3 or chain = 4 ITAMs 3 ITAMs/CD3 chain = 6 ITAMs

20 Why So Many ITAMs? Required for amplification of signal transduced by few TCR molecules Different transduction molecules bind to different ITAMs Required for association of TCR complex with actin cytoskeleton

21 Phosphorylated ITAMs Recruit ZAP70 Permitting Lck to Phosphorylate and Activate ZAP70

22 ZAP-70 Phosphorylates Scaffold Proteins LAT and SLP-76 to Activate Phospholipase C-

23 Phospholipase C- Activates Protein Kinase C and Ras-GEF (RasGRP)

24 ZAP-70 Initiates Cascade Activating Guanine-nucleotide Exchange (GEF) Factors That Activate Ras

25 Transduction of the Signal Into the Nucleus Activates Genes There are multiple pathways that transduce the signal from the cytoplasm into the nucleus Different transcription factors activate different groups of genes

26 MAP Kinase Cascade Transduces a Signal Into the Nucleus Ras activates MAP kinase kinase kinase (Raf). Raf phosphorylates serine/threonine on MAP kinase kinase (Mek) and activates it. MAP kinase kinase (Mek) phosphorylates threonine and tyrosine on MAP kinase (Erk) thereby activating it. MAP kinase (Erk) activates the Elk transcription factor which stimulates Fos gene transcription.

27 Calcium Induces the Translocation of the Transcription Factor NFAT Into the Nucleus

28 Phosphorylation of I B Releases the Transcription Factor NF B Thereby Enabling It to Translocate Into the Nucleus

29 T Cell and B Cell Activation Requires Two Signals

30 Co-stimulatory Signal Activates a Parallel MAPK Path That Activates Complementary Genes Ras activates MAP kinase kinase kinase (Raf). Raf phosphorylates serine/threonine on MAP kinase kinase (Mek) and activates it. MAP kinase kinase (Mek) phosphorylates threonine and tyrosine on MAP kinase (Erk) thereby activating it. MAP kinase (Erk) activates the Elk transcription factor which stimulates Fos gene transcription.

31 Stimulatory Signal Pathways Integrated by Production of Fos and Jun- Components of the Heterodimer AP-1 Transcription Factor

32 Broad Range of Nuclear Factors Are Activated in TCR Signal Transduction Cascade Initiation of TCR-mediated signals Biochemical intermediates Active enzymes Transcription factors Abbas- Cellular and Molecular Immunology

33 Activation of Transcription Factors To Turn on Genes by Activation of Kinases and Phosphatases Abbas- Cellular and Molecular Immunology

34 Cyclosporin and Tacrolimus Block Calcineurin Signaling and Thereby Suppress T Cell Activation

35 In 1984, Fujisawa scientists discovered tacrolimus in a soil sample taken from Mt. Tsukuba in Japan. Not long after, scientists realized that some of the properties of tacrolimus may help treat certain conditions and diseases. Eventually, they saw that this drug could be used to safely treat patients with moderate to severe eczema thus, pioneering the use of topical immunomodulators (TIMs). Protopic was the first of this new class of nonsteroid drugs approved for the treatment of moderate to severe eczema giving doctors the first prescription alternative for the treatment of moderate to severe eczema in 40 years.

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37 Cross-linking Surface Immunoglobulin Activates B Cells

38 Cross-linking Surface Immunoglobulin Activates ITAMs

39 Questions to Consider After recognition of its cognate MHC:peptide, how does the T cell receptor activate immune response genes? What are the structural motifs used by signal transduction molecules that permit specific interaction and activation of effector proteins? How do genes know what is going on in the outside environment requiring them to make their proteins at the appropriate time?