GENISTEIN MODULATES NEUROBLASTOMA CELL-PROLIFERATION AND DIFFERENTIATION THROUGH INDUCTION OF APOPTOSIS AND REGULATION OF TYROSINE KINASE-ACTIVITY AND N-MYC EXPRESSION

Genistein is a specific inhibitor of protein tyrosine kinase (PTK) and is considered as a therapeutic candidate for various cancers. In this paper we investigate the effects of genistein on cell, proliferation and differentiation in neuroblastoma (NB) cell lines and its possible mechanism of action. Genistein substantially inhibited the growth of f ive (N(2)A, JC, SKNSH, MSN and Lan5) of the six tumor cell lines exami ned in a dose-dependent manner with an IC50 value of similar to 5 mu g /ml, The exception was GC cells. N(2)A cells were treated with geniste in for 6 days and exhibited morphological features of differentiation, as evidenced by the development of dendritic extensions. Terminal deo xynucleotidyl transferase (TDT) histochemical staining showed a signif icant elevation in darkly stained nuclei in genistein-treated N(2)A ce lls compared with controls, indicating the occurrence of apoptosis, Fl uorescent quantitation of DNA fragments confirmed apoptosis in geniste in-treated N(2)A cells. To further elucidate the possible mechanisms b y which genistein modulates NB cell growth and differentiation we inve stigated the effect of genistein on the activities of PTK and mitogen- activated protein (MAP) kinase and N-myc proto-oncogene expression in N(2)A cells, The results showed that genistein down-regulated intrinsi c PTK activity by similar to 33% and inhibited insulin-like growth fac tor (IGF)-stimulated PTK activity by 75%. The effect of genistein on t he intrinsic activity of MAP kinase was insignificant. In addition, ge nistein significantly reduced N-myc expression in a dose-dependent fas hion. Our study suggests that genistein arrests cell growth and induce s NB cell differentiation by mediating apoptosis and modulating PTK ac tivity and N-myc proto-oncogene expression.