Previously we investigated the role of PKC isoforms in the regulation of myeloid cell differentiation and apoptosis using the promyeloid cell line U937. Activation of PKC-β by the deoxyphorbol DOPPA, induced only a proportion of these cells to undergo apoptosis. Hence investigations were undertaken to study the regulation of isoenzymes in the various stages of the cell cycle. U937 cells were split into the Gl, S and G2/M fractions of the cell cycle using centrifugal elutriation. Initially PKC translocation of whole cells was assessed to determine the activation state of the major U937 cell PKC isoenzymes (a, βl, 0 and Q. The results showed an increase in membrane associated PKC-a and -βl in Gl, the increased activation of PKC-β l was also seen in G2/M. Further investigations centred on the relative levels of Diacylglycerol (DAG) and specific DAG species in the G l, S and G2/M fractions. DAG levels were highest at G2/M. Analysis of individual DAG species by HPLC showed that l-stearoyl-2-arachidonyl-sn-gIycerol was significantly increased at Gl. We conclude that isoenzymes of PKC show differential expression and activation in the phases of cell cycle and that DAG species generated at specific stages of cell cycle may be involved in the differential activation of PKC isoenzymes. Moreover selective and persistent activation of PKC isoenzymes, including PKC-β 1, at an inappropriate stage of the cell cycle could induce apoptosis.
ASJC Scopus subject areas