Constitutive overexpression of cyclin D1 in human breast epithelial cells does not prevent G1 arrest induced by deprivation of epidermal growth factor

Non-transformed human breast epithelial cell line MCF10A is dependent on exogenous epidermal growth factor (EGF) for continued growth. Complete G(1) arrest 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 strong inhibition of cyclin-dependent kinase 2 and cyclin D-1-associated kinase activities. Introduction of exogenous cyclin D-1 into MCF10A (MCF10AD1) cells resulted in an accelerated cell growth rate but did not confer colony-forming capacity. Cell cycle arrest was still achieved in MCF10AD1 cells following EGF deprivation. In the great majority of MCF10AD1 clones, accumulation in G(1) phase was accompanied by reduced cyclin D-1 and increased p27(KIP1) protein levels. In two clones where cyclin D-1 remained unchanged during G(1) arrest, it was found that more cyclin D-1 protein was bound to p27(KIP1). The data demonstrate that ectopic expression of cyclin D-1 alone could not transform MCF10A cells nor was it sufficient to prevent G(1) arrest induced by EGF deprivation.