A LINK BETWEEN CYCLIN-A EXPRESSION AND ADHESION-DEPENDENT CELL-CYCLE PROGRESSION

Cell adhesion has an essential role in regulating proliferation during the G1 phase of the cell cycle, and loss of this adhesion requirement is a classic feature of oncogenic transformation. The appearance of c yclin A messenger RNA and protein in late G1 was dependent on cell adh esion in both NRK and NIH 3T3 fibroblasts. In contrast, the expression of Cdc2, Cdk2, cyclin D1, and cyclin E was independent of adhesion in both cell lines. Transfection of NRK cells with a cyclin A complement ary DNA resulted in adhesion-independent accumulation of cyclin A prot ein and cyclin A-associated kinase activity. These transfected cells a lso entered S phase and complete multiple rounds of cell division in t he absence of cell adhesion. Thus, cyclin A is a target of the adhesio n-dependent signals that control cell proliferation.