Generation of diacylglycerol molecular species through cell cycle: A role for 1-stearoyl, 2-arachidonyl glycerol in the activation of nuclear protein kinase C-βII at G2/M

Protein kinase C (PKC) is a family of 11 isoenzymes that are differentially involved in the regulation of cell proliferation. PKC-betaII, a mitotic lamin kinase, has been shown previously to translocate to the nucleus at G(2)/M and this was coupled to the generation of nuclear diacylglycerol. However, it is not clear how isoenzyme selective translocation and nuclear targeting is achieved during cell cycle. To investigate further the role of nuclear diacylglycerol we measured PKC isoenzyme translocation and analysed diacylglycerol species at different stages of the cell cycle in U937 cells synchronized by centrifugal elutriation. Translocation of PKC-betaII to the membrane fraction, an indicator of activation, occurred at S and G(2)/M, although PKC-betaII was targeted to the nucleus only at G(2)/M. Levels of nuclear diacylglycerol, specifically tetraunsaturated species, increased during G(2)/M. By contrast, there were no obvious changes in nuclear phosphatidic acid species or mass. 1-stearoyl, 2-arachidonyl glycerol (SAG), the major polyunsaturated nuclear diacylglycerol, was able to activate classical PKC isoenzymes (PKC-alpha and beta), but was less effective for activation of novel isoenzymes (PKC-delta), in an in vitro PKC assay. We propose that PKC-betaII nuclear translocation during G(2)/M phase transition is mediated in part by generation of SAG at the nucleus.