C-MET

By Tanay SurkundRoll no : 60

Guide: Mrs. Poonam Advani

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C-MET -The Receptor Tyrosine Kinase

Proto-oncogene coding for the C-MET protein Protein essential for organ protection and wound

healing. Activation of MET gives rise to the invasive

growth programme. Abnormal MET activation causes cancer growth in

areas such as the kidneys ,lungs ,stomach ,liver, and brain.

Found in the epithelial tissues of all the above mentioned organs.

HGF is the only known ligand

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C-MET protein Disulphide linked

heterodimer, which results from cleavage of a precursor at a furin site.

It is a trans-membrane protein and consists of :

1) Extracellular region: which consists of the alpha and beta chains, the sema domain, the MRS and the immunoglobulin structures.

2) Intracellular region: which consists of the juxtramembrane segment, the tyrosine kinase domain and the C-terminal region which comprises 2 crucial tyrosines.

Signalling activity on formation of a dimer.

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C-MET Protein structureExtracellular region

Extracellular region– It consists of an alpha and a beta

chain. The latter is much longer and spans the entire ectodomain,transmembrane helix and cytoplasmic portion.The alpha region is joined to the beta chain by a disulphide linkage.

– The alpha portion and the first 212 residues of the beta chain are sufficient for ligand binding with HGF/SF.

– This region is homologous to the sema domain of the semaphorin axon guidance system and folds into a beta propeller structure.

– The rest of the ectodomain consists of a cysteine rich sequence, Met related sequence(MRS), followed by glycine-proline rich (G-P) repeats and four unusual immunoglobluin structures.

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C-MET Protein Structure Intracellular RegionIt consists of 3 regions:1. A Juxtramembrane segment consisting of:

A serine residue which on phosphorylation by protein kinase or calcium calmodulin dependant kinases,downregulates the receptor kinase activity.

A Tyrosine(Tyr 1003) that binds to ubiquitin ligase Cbl, which is responsible for Met polyubiquination,endocytosis and degradation.

2. The Tyrosine kinase domain, bearing tyrosine 1234 and tyrosine 1235 which cause transphopshorylation of other tyrosine residues on the other MET molecule of the dimer.

3. The C-terminal region comprises 2 crucial tyrosines inserted in a degenerative motif that represents a multisubstrate docking site capable of recruiting several downstream adaptors containing Src-homology 2(SH2) domain.

Met receptor as most receptor tyrosine kinases use different tyrosines to bind to specific signalling molecules.The 2 docking sites are essential for signal transduction both invitro and invivo.

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MET Signaling Pathway I. Components

MET receptor bears 2 unique bidendate docking sites which comprimise tyrosine residues Tyrosine 1349(Y1349) and Tyrosine 1356.For Steric reasons,two substrates cannot bind simultaneously to the bidendate site of one Met molecule.

When transphosphorylated by the Kinase domains, they bind to Gab-1, Grb-2, phosphatidinylinositol-3-kinase(PI3K) and others.Most of these components contain Src-homology-2(SH2) domain binding sites which mediate the reactions.

SH2 is the largest class of pTyr- recognition domains, and typicallty bind a phosphorylated tyrosine residue in the context of a longer peptide motif with a target protein.

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MET Signaling PathwayII. Transducer binding with Gab-1

Versatile, Scaffolding adaptor protein

Most crucial binding substrate.

Phosphorylation causes binding to the Shp2,PI3K,phospholipase C and crk in which they act downstream and the Ras and Raf upstream.(MAPK componenets)

Shp2 upregulates the MAPK and Erk pathway.

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MET signalling pathwayIII. Pathway activation and functions.

Activation of the MAPK/ERK pathway: – Cell proliferation through

activation of pBR and Cdk6. Both of which are important in cell cycle progression.

– Activation of Fibronectin( Wound healing)

– Activation of Integrins- leads to cell adhension and is regulated by FAKs.(Cell adhesion and migration)

Activation of the Pi3K/Akt pathway:– Anti-apoptosis by deactivation

of Bad or through a Caspase-9 cleavage.

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MET signalling pathwayIII. Pathway activation and functions.

Activation of the Ras pathway which consecutively activate the RHO, RAC1 and CDC42 pathway: – Cytoskeletal

rearrangement via the arp2/3 complexes

– Cell mobility via formation of lamellopodia by actin rearrangement

– Cadherin rearrangement

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Dysregulation of MET receptor tyrosine kinase in the formation of invasive growth

tumours. Increased MET expression has been found in papillary carcinomas

of the thyroid gland, in carcinomas of colon, pancreas, and ovary, in osteogenic sarcomas, and in other types of cancer. Point mutations in MET have been identified in hereditary and sporadic papillary renal carcinomas , hepatocellular and gastric carcinomas and head and neck squamous carcinomas.

There are 3 mechanisms by which tumours are formed due to the met receptor.– Ligand dependant mechanisms of MET activation– Ligand independant mechanisms of MET activation– MET transactivation by other membrane receptors

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Dysregulation of MET receptor tyrosine kinase in the formation of invasive growth

tumours. Ligand Dependant mechanisms of met activation

– Tumor cells express both MET and HGF setting an autocrine loop in which, secreted HGF binds to the MET receptor and causes the activation of its downstream signaling pathways thus enhancing tumor growth and invasive behavior.

– Such loops have been detected in gliomas, osteosarcomas, and mammary, prostate, breast, lung and other carcinomas.

– This mechanism of tumor formation is not only dependant on MET and HGF but also on the enzymes responsible for the proteolytic activation of HGF from the single chain precursor molecule pro-HGF.A number of serine proteases, including urokinase type plasminogen activator and coagulation factor XII have been detected in some tumors.

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Dysregulation of MET receptor tyrosine kinase in the formation of invasive growth

tumours. Ligand Independent mechanisms of MET activation

– MET overexpression– Gene Rearrangement (TPR-MET)– Absence of negative regulators– Missense Mutations

MET transactivation via other membrane receptors– CD44 cell surface receptors present for hyaluronic acid– Integrins– Ron receptors

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CANCER THERAPIES TARGETTING HGF/MET

MET kinase inhibitors– K252a(Fermentek) – ARQ-197(ArQule)– XL880(Exlixis)– PHA-6657572(Pfizer)

HGF inhibitors– NK4– Neutralizing anti-HGF

antibodies– Uncleavable HGF

DECOY MET– CGEN241

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CANCER THERAPIES TARGETTING HGF/MET

IMMUNOTHERAPY TARGETTING MET– PASSIVE IMMUNOTHERAPY

DN30 OA-5D5

– ACTIVE IMMUNOTHERAPY INTERFERONS INTERLEUKINS

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References www.nature.com www.PubMED.com- journals MET,METASTASIS,MOTILITY-Carmen Birchmeier*,Walter Birchmeier‡,

Ermanno Gherardi§ and George F.Vande Woude. 2003 Nature Publishing Group

Hepatocyte Growth Factor Establishes Autocrine and Paracrine Feedback Loops for the Protection of SkinCells after UV Irradiation. Journal of Investigative Dermatology (2007), Volume 127

Potent and selective inhibitors of the Met [hepatocyte growth actor/scatter factor (HGF/SF) receptor] tyrosine kinase block HGF/SF-induced tumor cell growth and invasion.LETTERS TO NATURE.

Anti-apoptotic signaling by hepatocyte growth factor by Met via the phosphatidylinositol 3-kinaseyAkt and mitogen-activated protein kinase pathways.PNAS

Transcriptional activation of the Hepatocyte Growth Factor receptor (c-met) gene by its ligand (Hepatocyte Growth Factor) is mediated through AP-1. Oncogene (2000) ã 2000 Macmillan Publishers Ltd.

www.pnas.org Invasive growth: from development to metastasis. J. Clin. Invest.

109:857–862 (2002). DOI:10.1172/JCI200215392.

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References Dysregulation of Met receptor tyrosine kinase activity in

invasive tumors. J. Clin. Invest. 109:863–867 (2002). DOI:10.1172/JCI200215418.

The Met tyrosine kinase receptor in development and cancer. Cancer Metastasis Rev (2008) 27:85–94 DOI 10.1007/s10555-007-9107-6.

"Severe diabetes, age-dependent loss of adipose tissue, and mild growth deficiency in mice lacking Akt2/PKB beta" Journal of Clinical Investigation Volume 112

Phosphatidylinositol 3-kinase regulates the induction of long-term potentiation through extracellular signal-related kinase-independent mechanisms. The Journal of neuroscience : the official journal of the Society for Neuroscience .

GTP-binding proteins of the Rho/Rac family: regulation, effectors and functions in vivo.". Bioessays 29 (4): 356–370.doi:10.1002/bies.20558. PMID 17373658.

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