Cytoskeleton-associated protein tyrosine phosphorylation involved in induction of differentiation in mouse melanoma cells

The malignancy of a cancer is due partly to its poor differentiation. Genistein, a protein tyrosine kinase inhibitor, is found to induce the highly malignant B16-BL6 mouse melanoma cells to differentiate to mature phenotypes. When Triton X-100 insoluble fraction of the differentiated cells is prepared and analyzed, tyrosine phosphorylation levels of three cytoskeleton-associated proteins (65, 60 and 53 ku respectively) are found to decrease dramatically. But no any change is found when phosphotyrosine contents of the cytosol fraction or the total cellular protein preparations are evaluated. It is concluded that cytoskeleton-associated protein tyrosine phosphorylation may be involved in the control of differentiation of cancer cells. The decrease of phosphotyrosine contents of cytoskeleton-associated proteins may be one of the important mechanisms underlying the differentiation induction of cancer cells by anticancer agents.