SMOOTH-MUSCLE CELL-CYCLE AND PROLIFERATION - RELATIONSHIP BETWEEN CALCIUM INFLUX AND SARCO-ENDOPLASMIC RETICULUM CA2+ ATPSE REGULATION

The role of Ca2+ influx in the regulation of the sarco-endoplasmic ret iculum Ca2+ ATPases (SERCA) associated with intracellular Ca2+ pools w as investigated during smooth muscle cell (SMC) proliferation induced by platelet-derived growth factor (PDGF). We first; defined that the p reviously described up-regulation of the SERCA2a isoform found in vasc ular SMC after a 24-h stimulation with PDGF (Magnier, C., Papp, E., Co rvazier, E., Bredoux, R., Wuytack, F., Eggermont, F., Maclouf, J., and Enouf, J. (1992) J. Biol. Chem. 267, 15808-15815) was precisely assoc iated with SMC entry into S phase as it appeared linked with [H-3]thym idine incorporation, This was further confirmed by testing the effect of transforming growth factor-beta(1), which inhibited both aortic SMC proliferation associated with G(1) cell cycle arrest and PDGF-induced SERCA2a up-stimulation, Then, we tested the role of Ca2+ influx by us ing SR 33805, a nem Ca2+ channel blocker, which was characterized with regard to the voltage Ca2+ channel blocker nifedipine and the capacit ative entry Ca2+ blocker SKF 96865, SR 33805 was found to be the most potent inhibitor of both PDGF-induced SMC proliferation and the associ ated rise in intracellular Ca2+ concentration with IC50 values of 0.2 +/- 0.1 and 0.51 +/- 0.04 mu M, respectively, Finally, by examining in parallel both SERCA2a and SERCA2b isoforms, in terms of activity and expression we could determine that PDGF-induced stimulation of total S ERCA activity (detected by formation of the phosphorylated intermediat e, E similar to P) and of SERCA2a expression (Western blotting) were a bolished when extracellular Ca2+ entry was prevented by SR 33805, This study demonstrates that SERCA2a up-regulation is: 1) related to the G (1)/S transition step of cell cycle and 2) dependent on Ca2+ entry dur ing PDGF-induced SMC proliferation.