PROTEIN-KINASE C-DEPENDENT REGULATION OF HUMAN ERYTHROLEUKEMIA (HEL) CELL SPHINGOSINE KINASE-ACTIVITY

Sphingosine kinase functions in both the catabolism of sphingosine and in signal transduction pathways utilizing sphingosine-l-phosphate, Th e regulation of sphingosine kinase activity in human erythroleukemia ( HEL) cells was investigated by treatment with several bioactive agents . Treatment of HEL cells with phorbol 12-myristate 13-acetate (PMA) ca used a time- and concentration- dependent increase in sphingosine kina se activity measured in vitro, Sphingosine kinase activity increased i n a phorbol ester- and diacylglycerol-specific manner. Staurosorine an d calphostin C, protein kinase C (PKC) inhibitors, blocked the increas e in sphingosine kinase activity, suggesting a PKC-dependent regulatio n, The effects of PMA on sphingosine kinase were dependent on transcri ption and translation. Purified PKC had no direct effect on sphingosin e kinase activity. However, these studies led to the observation that HEL cell sphingosine kinase activity is stimulated in vitro by phospha tidylserine. Interestingly, other inducers of HEL cell differentiation , dimethylsulfoxide and retinoic acid, did not affect sphingosine kina se activity. These results indicate a separate and distinct pathway of PKC-dependent sphingosine kinase activation, and suggest a role for s phingosine kinase in regulation of cell function.