INHIBITION BY GENISTEIN OF PROLACTIN-INDUCED NB2 LYMPHOMA CELL MITOGENESIS

Tyrosine kinase activation in mediating the mitogenic action of prolac tin (PRL) has been evaluated. Use was made of genistein, a tyrosine ki nase antagonist, and cultured rat Nb2 lymphoma cells, i.e. the lactoge n-dependent Nb2-11 line and a lactogen-independent subline, Nb2-SFJCD1 . Genistein was found to be a potent growth-inhibitor for both lines, inhibiting H-3-thymidine incorporation in Nb2-11 and Nb2-SFJCD1 cells with IC(50)s of 4.2 and 6.7 mu g/ml, respectively. Genistein also inhi bited expression and translation of the heat shock protein 70 gene and pp40 protein substrate phosphorylation which, in Nb2-11 cells, follow ed PRL addition within minutes. Genistein inhibition of DNA synthesis in G(1)-arrested Nb2-11 cells was most pronounced if the agent was add ed within 1 h of PRL treatment. The results indicate that, while both Nb2 cell lines have a general growth requirement for tyrosyl phosphory lation, the early, PRL-induced tyrosine kinase activation is a compone nt of the PRL mitogenic signal transduction pathway.