INHIBITION OF CYCLIN-D CDK ACTIVITY IN CELL-CYCLE ARREST OF SWISS 3T3CELLS BY CERES-18, A NOVEL CELL REGULATORY SIALOGLYCOPEPTIDE

CeReS-18 is a unique negative regulator of cell proliferation with a w ide array of target cells, To elucidate the mechanism by which CeReS-1 8 mediates cell growth inhibition, the possibility that CeReS-18 alter s the function of G1 cyclins and their respective cyclin-dependent kin ases (cdks) has been examined in mouse fibroblasts (Swiss 3T3) synchro nized by CeReS-18, We show here that cyclin D-associated cdk activity is significantly inhibited in the CeReS-18-treated cells. Correspondin g to the inhibited cdk function, we demonstrate a low expression of cy clin D in mid G(1) determined by Western blot analysis, and cyclin D w as greatly reduced in the immunocomplex recovered with antibody to cdk 4 and cdk6, Previously, we have shown that the retinoblastoma suscepti bility gene product (pRb), a key substrate of cyclin D-cdk complex, wa s maintained in the hypophosphorylated state in the CeReS-18-inhibited cells. We conclude here that cyclin D/cdk4,6/pRb is the major pathway by which CeReS-18 mediates cell cycle arrest. (C) 1998 Academic Press .