GOSSYPOL INHIBITION OF MITOSIS, CYCLIN D1 AND RB PROTEIN IN HUMAN MAMMARY-CANCER CELLS AND CYCLIN-D1 TRANSFECTED HUMAN FIBROSARCOMA CELLS

The antiproliferative effects of gossypol on human MCF-7 mammary cance r cells and cyclin D1-transfected HT-1060 human fibrosarcoma cells wer e investigated by cell cycle analysis and effects on the cell cycle re gulatory proteins Rb and cyclin DI. Flow cytometry of MCF-7 cells at 2 4 h indicated that 10 mu M gossypol inhibited DNA synthesis by produci ng a G(1)/S block. Western blot analysis using antihuman Rb antibodies and anti-human cyclin D1 antibodies in MCF-7 cells and high- and low- expression cyclin D1-transfected fibrosarcoma cells indicated that, af ter 6 h exposure, gossypol decreased the expression levels of these pr oteins in a dose-dependent manner. Gossypol also decreased the ratio o f phosphorylated to unphosphorylated Rb protein in human mammary cance r and fibrosarcoma cell lines. Gossypol (10 mu M) treated also decreas ed cyclin D1-associated kinase activity on histone H1 used as a substr ate in MCF-7 cells. These results suggest that gossypol might suppress growth by modulating the expression of cell cycle regulatory proteins Rb and cyclin D1 and the phosphorylation of Rb protein.