PROTEIN B61 AS A NEW GROWTH-FACTOR - EXPRESSION OF B61 AND UP-REGULATION OF ITS RECEPTOR EPITHELIAL-CELL KINASE DURING MELANOMA PROGRESSION

Epithelial cell kinase (ECK) is a receptor protein tyrosine kinase, th e role of which in melanoma biology is unclear. Were we studied the ro le of ECK during melanoma progression. ECK mRNA was overexpressed in v irtually all melanoma lines tested, and levels were significantly high er in cell lines from distant metastases than primary melanomas; melan ocytes were negative. Gene amplification was not detected in melanomas . Levels of ECK protein corresponded well with mRNA levels. B61 or LER K-1, recently identified as an ECK ligand, stimulated the growth of EC K-expressing melanoma cell lines, its first identified biological acti vity. Melanoma chemotaxis and chemoinvasion were not affected by B61. Growth of normal melanocytes was not affected. mRNA for B61 was detect ed in both melanoma cell lines and normal melanocytes. B61 was also id entified by Western blotting and ECK binding activity with the use of a BIAcore binding assay in melanoma cell-conditioned media. These resu lts suggest that B61 is an autocrine growth factor for melanomas but n ot normal melanocytes.