CYCLIN D1 TRIGGERS AUTONOMOUS GROWTH OF BREAST-CANCER CELLS BY GOVERNING CELL-CYCLE EXIT

Cyclin D1 controls G(1)-associated processes, including G(0)-to-G(1) a nd G(1)-to-S transitions. This study demonstrates a novel aspect of cy clin D1 as a regulator of the transition between G(1) and G(0). Overex pression of cyclin D1 in MCF7 breast tumor cells resulted in a continu ed proliferation under low-serum conditions, whereas nonoverexpressing cells ceased to grow. This difference in growth was due to a reduced exit from G(1) to G(0) in cyclin D1-overexpressing cells. Our data the refore suggest a model in which cyclin D1 overexpression in tumor cell s is responsible for hyperproliferation under growth factor-deprived c onditions.