Serum stimulation and cell density regulate the proliferation of AsPC-1 cells through control of cyclin E and p27(KIP1) expression

Background: 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 relatio nships between growth conditions and the proliferation of AsPC-1 cells. Mat erials and Methods: AsPC-1 cells were cultured under several growth conditi ons and the proliferation of cells was studied by incorporation of H-3-thym idine. The alterations of cell-cycle-related genes were studied by immunobl otting. Results: By four consecutive days in culture, the nucleotide incorp oration of AsPC-1 cells was markedly suppressed and the suppression was ove rcome by medium change or reduction of cell density. The induction of cycli n DI by serum stimulation was observed, concomitant with the transient acti vation of extracellular signal-regulated kinases (ERKs). The most prominent changes of cell-cycle-regulating genes following consecutive culture or se rum reduction were the down-regulation of cyclin E and the induction of p27 (KIP1). The down-regulation of cyclin E was more sensitive to cell density, while the induction of p27(KIP1) was regulated by both increased cell dens ity and reduction of serum. The down-regulation of p27(KIP1) was caused by protein degradation. Conclusions: The proliferation of AsPC-1 cells was sti ll controlled by cell density and serum stimulation; nevertheless, the cell s possessed several oncogenic mutations. These results may provide a ration ale for modifying the growth environment for treatment of pancreatic cancer s.