BRYOSTATIN-1 (BRYO1)-INDUCED MONOCYTIC DIFFERENTIATION IN THP-1 - HUMAN LEUKEMIA-CELLS IS ASSOCIATED WITH ENHANCED C-FYN TYROSINE KINASE AND M-CSF RECEPTORS

Bryostatin 1 (bryo1), a naturally occurring macrocyclic lactone derive d from the marine bryozoan Bugula neritina is a potent protein kinase C (PKC) activator. In this report, we investigated the role of c-fyn p rotein, a src-related protein tyrosine kinase (PTK), during bryo1-indu ced monocytic differentiation in a human leukemia cell line, THP-1. Br yo1 treatment for 24 h inhibited the proliferation of THP-1 cells and caused a major fraction of them to become adherent cells with distinct monocyte/macrophage features and enhanced expression of M-CSF recepto rs (M-CSFR), a hallmark of mature macrophages. The THP-1 cells in cont rol cultures expressed low but detectable levels of c-fyn proteins. Tr eatment of THP-1 cells with bryo1 resulted in an enhanced expression o f c-fyn proteins, but not c-lyn proteins, another member of the src- f amily of kinases. The bryo1 treatment also enhanced the levels of both c-fyn tyrosine kinase and autophosphorylation activities in THP-1 cel ls. Using a combined immunoprecipitation and immunoblot analysis, bryo 1 was shown to promote an enhanced association between c-fyn kinase an d M-CSFR. The inducing activity of bryo1 was associated with PKC activ ation; treatment of THP-1 cells with bryo1 led to a rapid and transien t elevation of total PKC activity in THP-1 cells. These results show t hat enhanced expression and activation of fyn kinases are critical eve nts associated with monocytic differentiation induced by bryo1 in THP- 1 cells. Our findings may be of clinical relevance, as bryo1 has been used in clinical trials of cancer patients. (C) 1997 Elsevier Science Ltd.