Effect of second-messenger modulators in K-562 cell differentiation: Dual action of calcium/phospholipid-dependent protein kinase in the process of differentiation

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Abstract
We investigated the roles of second messengers in K-562 cell differentiation induced by either commitment-inducing agents (Ara-C, thymidine), or a noncom-mitment-inducing agent (hemin). Cell differentiation induced by both types of agents was inhibited by dbc-AMP, staurosporine, and H-7. In contrast, OAG enhanced hemin-induced cell differentiation, but it inhibited that due to Ara-C or thymidine. When K-562 cells were incubated with 4 x 10−6M hemin or 2 x 10−7M Ara-C for 2 days, an increase of ϵ-mRNA occurred. The addition of cycloheximide (1 μg/ml) completely blocked this change, suggesting that de novo protein synthesis was necessary for the increase of ϵ-mRNA. Simultaneous treatment with Ara-C and cycloheximide for 2 days did not block either the increase of ϵ-mRNA or that of benzidine-positive cells, which were measured after 5 days of further incubation without additives. This suggested that the process of Ara-C-induced K-562 cell differentiation could be divided into two steps, i.e., a commitment step and a phenotypic expression step, and that the commitment step was at least partly resistant to cycloheximide. We investigated the roles of second messengers in each step. Our results suggested that PKC may act as a negative regulator of commitment step and as a positive regulator of the phenotypic expression. This may explain the differing effects of OAG on hemin- and Ara-C-induced K-562 cell differentiation.