Intracellular calcium mobilization induces immediate early gene pip92 via Src and mitogen-activated protein kinase in immortalized hippocampal cells

Regulation of intracellular calcium levels plays a central role in cell sur vival, proliferation, and differentiation. A cell-permeable, tumor-promotin g thapsigarin elevates the intracellular calcium levels by inhibiting endop lasmic reticulum Ca2+-ATPase. The Src-tyrosine kinase family is involved in a broad range of cellular responses ranging from cell growth and cytoskele tal rearrangement to differentiation. The immediate early gene pip92 is ind uced in neuronal cell death as well as cell growth and differentiation. To resolve the molecular mechanism of cell growth by intracellular calcium mob ilization, we have examined the effect of thapsigargin and subsequent intra cellular calcium influx on pip92 expression in immortalized rat hippocampal H19-7 cells. An increase of intracellular calcium ion levels induced by th apsigargin stimulated the expression of pip92 in H19-7 cells. Transient tra nsfection of the cells with kinase-inactive mitogen-activated protein kinas e kinase (MER) and Src kinase or pretreatment with the chemical MEK inhibit or PD98059 significantly inhibited pip92 expression induced by thapsigargin . When constitutively active v-Src or MEK was overexpressed, the transcript ional activity of the pip92 gene was markedly increased. Dominant inhibitor y Raf-l blocked the transcriptional activity of pip92 induced by thapsigari n. The transcription factor Elk1 is activated during thapsigargin-induced p ip92 expression, Taken together, these results suggest that an increase of intracellular calcium ion levels by thapsigargin stimulates the pip92 expre ssion via Raf-MEK-extracellular signal-regulated protein kinase- as well as Src kinase-dependent signaling pathways.