Serum stimulation and cell density regulate the proliferation of AsPC-1 cells through control of cyclin E and p27KIP1...

Cellular proliferation in normal cells is tightly regulated by environmental conditions. Growth factors stimulate proliferation while cell confluence inhibits it. Human pancreatic cancer AsPC-1 cells were believed to escape from these restrictions because they possessed several mutations which promote cell proliferation. In this study, we focused on the relationships between growth conditions and the proliferation of AsPC-1 cells.

AsPC-1 cells were cultured under several growth conditions and the proliferation of cells was studied by incorporation of 3H-thymidine. The alterations of cell-cycle-related genes were studied by immunoblotting.

By four consecutive days in culture, the nucleotide incorporation of AsPC-1 cells was markedly suppressed and the suppression was overcome by medium change or reduction of cell density. The induction of cyclin D1 by serum stimulation was observed, concomitant with the transient activation of extracellular signal-regulated kinases (ERKs). The most prominent changes of cell-cycle-regulating genes following consecutive culture or serum reduction were the down-regulation of cyclin E and the induction of p27KIP1. The down-regulation of cyclin E was more sensitive to cell density, while the induction of p27KIP1 was regulated by both increased cell density and reduction of serum. The down-regulation of p27KIP1 was caused by protein degradation.

The proliferation of AsPC-1 cells was still controlled by cell density and serum stimulation; nevertheless, the cells possessed several oncogenic mutations. These results may provide a rationale for modifying the growth environment for treatment of pancreatic cancers.