Constitutive overexpression of cyclin D-1 in human breast epithelial cellsdoes not prevent G(1) arrest induced by deprivation of epidermal growth factor

Non-transformed human breast epithelial cell line MCF10A is dependent on ex ogenous epidermal growth factor (EGF) for continued growth. Complete G(1) a rrest was rapidly induced following EGF deprivation. The cell cycle arrest was accompanied by increased levels of p27(KIP1), a cyclin-dependent kinase inhibitor, and reduced level of cyclin D-1. This was associated with stron g inhibition of cyclin-dependent kinase 2 and cyclin D-1-associated kinase activities. Introduction of exogenous cyclin D-1 into MCF10A (MCF10AD1) cel ls resulted in an accelerated cell growth rate but did not confer colony-fo rming capacity. Cell cycle arrest was still achieved in MCF10AD1 cells foll owing EGF deprivation. In the great majority of MCF10AD1 clones, accumulati on in G(1) phase was accompanied by reduced cyclin D-1 and increased p27(KI P1) protein levels. In two clones where cyclin D-1 remained unchanged durin g G(1) arrest, it was found that more cyclin D-1 protein was bound to p27(K IP1). The data demonstrate that ectopic expression of cyclin D-1 alone coul d not transform MCF10A cells nor was it sufficient to prevent G(1) arrest i nduced by EGF deprivation.