title: Cross talk between receptor guanylyl cyclase C and c-src tyrosine kinase regulates colon cancer cell cytostasis.
abstract: Increased activation of c-src seen in colorectal cancer is an indicator of a poor clinical prognosis, suggesting that identification of downstream effectors of c-src may lead to new avenues of therapy. Guanylyl cyclase C (GC-C) is a receptor for the gastrointestinal hormones guanylin and uroguanylin and the bacterial heat-stable enterotoxin. Though activation of GC-C by its ligands elevates intracellular cyclic GMP (cGMP) levels and inhibits cell proliferation, its persistent expression in colorectal carcinomas and occult metastases makes it a marker for malignancy. We show here that GC-C is a substrate for inhibitory phosphorylation by c-src, resulting in reduced ligand-mediated cGMP production. Consequently, active c-src in colonic cells can overcome GC-C-mediated control of the cell cycle. Furthermore, docking of the c-src SH2 domain to phosphorylated GC-C results in colocalization and further activation of c-src. We therefore propose a novel feed-forward mechanism of activation of c-src that is induced by cross talk between a receptor GC and a tyrosine kinase. Our findings have important implications in understanding the molecular mechanisms involved in the progression and treatment of colorectal cancer.
authors.affiliation: Department of Molecular Reproduction, Development and Genetics, Indian Institute of Science, Bangalore 560012, India.
authors.forename: Nirmalya
authors.initials: N
authors.lastname: Basu
authors.forename: Rashna
authors.initials: R
authors.lastname: Bhandari
authors.forename: Vivek T
authors.initials: VT
authors.lastname: Natarajan
authors.forename: Sandhya S
authors.initials: SS
authors.lastname: Visweswariah
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D000081247:CSK Tyrosine-Protein Kinase; D002453:Cell Cycle; D045744:Cell Line, Tumor; D003110:Colonic Neoplasms / Q000378:metabolism* / Q000473:pathology; D018450:Disease Progression; D004789:Enzyme Activation; D006162:Guanylate Cyclase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D000074261:Receptors, Enterotoxin; D050705:Receptors, Guanylate Cyclase-Coupled; D018000:Receptors, Peptide / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D019061:src-Family Kinases
chemical_list: D018000:Receptors, Peptide; D019000:Phosphotyrosine; D011505:Protein-Tyrosine Kinases; D000081247:CSK Tyrosine-Protein Kinase; D019061:src-Family Kinases; C000631346:CSK protein, human; D006162:Guanylate Cyclase; D000074261:Receptors, Enterotoxin; D050705:Receptors, Guanylate Cyclase-Coupled