Cellular relocalisation of protein kinase C-theta caused by staurosporine and some of its analogues

The microbial product staurosporine is a protein kinase C (PKC) inhibitor with some phorbol ester-agonistic properties. It is known to cause the translocation of the PKC isoenzymes epsilon and delta from the cellular cytosol to the membrane and nucleus. We tested the hypothesis that it also affects the cellular localisation of the novel PKC isoenzyme theta, and that staurosporine analogues, some of which are currently under clinical evaluation as potential anticancer drugs, have a similar effect. Their ability to alter PKC-theta distribution was studied in human-derived A549 lung carcinoma cells. Western blot analysis and confocal microscopy after indirect immunofluorescence staining showed that staurosporine (100 nM), like the phorbol ester 12-O-tetradecanoylphorhol-13-acetate (25 nM) caused the translocation of PKC-theta from the cytosol to the membrane and the nucleus. The bisindolylmaleimide GF 109203X mimicked staurosporine, but had a weaker effect. Ro 31-8220 and UCN-01 decreased cytosolic PKC-theta only at 1 microM. CGP 41251 had no effect on PKC-theta in either experimental design. The results show that some, but not all, staurosporine analogues share the partial phorbol ester-agonistic PKC-translocatory activity of the parent molecule.