Effects of staurosporine on cell morphology, expression of the proenkephalin gene and the secretion of [Met5]-enkephalin in bovine adrenal medullary chromaffin cells.

Treatment of bovine adrenal medullary chromaffin (BAMC) cells with staurosporine for 24 h caused the cells to elongate and flatten, and induced the formation of neurite-like outgrowth from BAMC cells; superficially the cells resembled those treated with the protein kinase C (PKC) agonist phorbol myristate acetate (PMA, 10(-7) M). The intracellular concentration of [Met5]-enkephalin (ME) was significantly increased in staurosporine-treated cells whereas the secretion of ME into the medium was significantly less than that from control cells. In addition, pretreatment of cells with staurosporine effectively inhibited the long-term stimulatory effects of other secretagogues on ME secretion. Furthermore, a 24 h exposure to staurosporine greatly increased the levels of both proenkephalin A (proENK) and its messenger RNA (mRNA). Both staurosporine and PMA increased AP-1 DNA binding activity to a similar extent. In contrast to the results with staurosporine, the structurally similar compound, K252a (10(-8) M) did not show these effects. Moreover, other PKC inhibitors, H7 (10(-5) M) and sphingosine (3.6 x 10(-5) M), did not duplicate those effects, suggesting that these long-term effects of staurosporine are independent of PKC inhibition. Staurosporine acts at the ATP binding site on many other kinases, but it is presently unclear whether the observed effects on cell morphology, proENK mRNA induction and ME secretion result from inhibition of only a single particular kinase. However, the uncoupling of proENK mRNA induction from ME secretion in these cells is unique to staurosporine and, therefore, this compound may be useful for further studies on secretion-transcription coupling.