ACTIVATION OF PHOSPHATIDYLINOSITOL 3-KINASE BY PROLACTIN IN NB2 CELLS

In the present studies, using anti-phosphotyrosine (PY20) and PI3-kina se (p85) antibodies, we have shown that PRL causes activation of phosp hatidyl inositol 3-kinase (PI3-kinase) in vitro in a dose- and time-de pendent manner in Nb2 cells. PRL activated PI3-kinase was completely i nhibited by LY294002 (1 mu g/ml). Stimulation of the cells with PRL al so increased tyrosine phosphorylation of the 85-kDa regulatory subunit . Moreover, in vitro kinase assay followed by SDS-PAGE protein separat ion demonstrated the phosphorylation of several other proteins besides the p85. However, no direct association between p85 and JAK2 tyrosine kinase was observed. These results indicate, for the first time, the involvement of PI3-kinase in PRL-stimulated Nb2 cell growth. (C) 1996 Academic Press. Inc.