Modulation of cell rounding and apoptosis in trigeminal neurinoma cells by protein phosphatase inhibitors

Exposure of trigeminal neurinoma 476-16 cells to C2-ceramide in a serum-deprived medium induces cell rounding followed by cell death characterized by cytoplasmic shrinkage and nuclear condensation. The induction of cell rounding and death occurs in proliferating cells but not in essentially quiescent cells of confluent cultures. Trypan blue-unpermeable round cells formed as a result of ceramide treatment undergo apoptosis without ceramide in a serum-containing medium, suggesting that they are irreversibly committed to cell death. The induction of cell rounding by ceramide is inhibited by low doses of the protein-tyrosine phosphatase inhibitors, orthovanadate and pervandate, and stimulated by high doses of pervanadate. The inhibition of protein-tyrosine phosphatases interfers the induction of cell death by ceramide. The protein-serine/threonine phosphatase inhibitor calyculin A induces cell rounding in proliferating cells. This cell rounding does not lead to cell death, thus calyculin A inhibits the induction of cell death by ceramide. While orthovanadate inhibits the induction of cell rounding by calyculin A, the latter is potentiated by ceramide. A combination of ceramide and calyculin A induces cell rounding and cell death in confluent cultures. These results demonstrate that modulation of phosphorylation of the serine/threonine and tyrosine of cellular proteins is intimately involved in the process of cell rounding and apoptosis in anchorage-dependent cells.