title: PI3-kinase is involved in mitogenic signaling by the oncogenic receptor tyrosine kinase Xiphophorus melanoma receptor kinase in fish melanoma.
abstract: Overexpression of the mutationally activated receptor tyrosine kinase Xiphophorus melanoma receptor kinase (Xmrk) initiates formation of hereditary malignant melanoma in the fish Xiphophorus. In melanoma as well as in a melanoma-derived cell line (PSM) this receptor is highly activated resulting in constitutive Xmrk-mediated mitogenic signaling. In order to analyze mitogenic signaling triggered by Xmrk a possible involvement of phosphatidylinositol 3 (PI3)-kinase in Xmrk signal transduction was examined. Constitutive binding of the p85 adapter subunit of PI3-kinase to the Xmrk receptor was detected in PSM melanoma cells. Further analyses in BHK cells expressing a Xmrk chimera (HER-mrk) showed that p85 association with the intracellular part of Xmrk was dependent on autophosphorylation of the receptor. In vitro binding studies revealed that the interaction is mediated mainly through the N-terminal SH2 domain of p85 which directly binds to a sequence motif around phosphorylated Tyr-983 in the Xmrk carboxy-terminus. In accordance with recruitment of p85 by Xmrk in PSM cells, the PI3-kinase downstream target Akt was found to be highly phosphorylated on Ser-473, indicating efficient PI3-kinase signaling in melanoma cells. PI3-kinase activation was also detected in Xiphophorus melanoma. Moreover, malignant melanomas exhibited an increased level of PI3-kinase activity which was about three times higher than that in benign pigmented lesions. Inhibition of PI3-kinase activity in PSM melanoma cells by both Wortmannin and LY294002 blocked entry into S-phase. Together these data demonstrate that PI3-kinase is a substrate of the oncogenic Xmrk receptor and plays a significant role in mitogenic signaling of melanoma cells and the formation of malignant melanoma in Xiphophorus.
authors.affiliation: Biocenter (Theodor-Boveri Institut), University of Würzburg, Würzburg, Germany. wellbrock@biozentrum.uni-wuerzburg.de
authors.forename: C
authors.initials: C
authors.lastname: Wellbrock
authors.forename: P
authors.initials: P
authors.lastname: Fischer
authors.forename: M
authors.initials: M
authors.lastname: Schartl
mesh_terms: D000595:Amino Acid Sequence; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites; D002867:Chromones / Q000494:pharmacology; D004789:Enzyme Activation; D029941:Fish Proteins; D005399:Fishes; D008546:Melanoma, Experimental / Q000201:enzymology / Q000209:etiology / Q000378:metabolism*; D008938:Mitosis; D008969:Molecular Sequence Data; D009025:Morpholines / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011485:Protein Binding; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism*; D015398:Signal Transduction; D014407:Tumor Cells, Cultured; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D002867:Chromones; D029941:Fish Proteins; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011518:Proto-Oncogene Proteins; D020794:Receptor Protein-Tyrosine Kinases; D000077191:Wortmannin; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C077101:Xmrk protein, Xiphophorus