RECEPTOR TYROSINE KINASE XMRK MEDIATES PROLIFERATION IN XIPHOPHORUS MELANOMA-CELLS

Over-expression of the oncogenic receptor tyrosine kinase (RTK) Xmrk i s sufficient to induce formation of hereditary malignant melanoma in t he fish Xiphophorus. In the melanoma tissue as well as in a melanoma-d erived cell line (PSM), the Xmrk protein shows strong tyrosine phospho rylation, indicating either ligand-independent or autocrine activation of its kinase domain. However, it is unknown whether the constitutive ly activated Xmrk receptor itself directly triggers the proliferative signals, thus leading to uncontrolled growth of the pigment cells. In order to evaluate the role of Xmrk in proliferation of melanoma cells, we inhibited its kinase activity by using a Xmrk specific tyrphostin. At a concentration of 10 mu M, tyrphostin AG555 led to a decrease of the Xmrk-induced DNA synthesis to 10% in NIH 3T3 Hm cells, whereas ser um dependent H-3-thymidine incorporation was unaffected. In fish melan oma cells, the drug efficiently blocked DNA synthesis and cellular gro wth. This anti-proliferative activity correlated with the potency of A G555 to inhibit Xmrk autophosphorylation, indicating that the Xmrk rec eptor is the major determinant of mitogenic signaling in Xiphophorus m elanoma cells. (C) 1998 Wiley-Liss, Inc.