Translocation of Protein kinase C-βII in astrocytes requires organized actin cytoskeleton and is not accompanied by synchronous RACK1 relocation

Protein kinase C (PKC)-βII is the most abundant PKC isoform in astrocytes. Upon activation, this isoform of PKC translocates from the cytosol to the plasma membrane (PM). In this study, we investigated in astrocytes the modality of PKC-βII translocation as far as the participation of the receptor for activated C kinase-1 (RACK1) and the requirement for intact cytoskeleton in the process. In astrocytes, Western blots and immunocytochemistry coupled to confocal microscopic quantitative analysis showed that after 5 min of phorbol-12-myristate-13-acetate (PMA) exposure, native PKC-βII, but not PKC-βI, is relocated efficiently from the cytosol to the PM. Translocation of PKC-βII was not associated with synchronous RACK1 relocation. Furthermore, the quantity of PM-associated PKC-βII that co-immunoprecipitated with PM-bound RACK1 increased following PMA exposure, indicating a post activation binding of the two proteins in the PM. Because RACK1 and PKC-βII relocation seemed not to be synchronous, we hypothesized that an intermediate interaction with the cytoskeleton was taking place. In fact, we were able to show that pharmacological disruption of actin-based cytoskeleton greatly deranged PKC-βII translocation to the PM. The requirement for intact actin cytoskeleton was specific, because depolymerization of tubulin had no effect on the ability of the kinase to translocate to the PM. These results indicate that in astrocytes, RACK1 and PKC-βII synchronous relocation is not essential for relocation of PKC-βII to the PM. In addition, we show for the first time that the integrity of the actin cytoskeleton plays a specific role in PKC-βII movements in these cells. We hypothesize that in glial cells, rapidly occurring changes of actin cytoskeleton arrangement may be involved in the fast reprogramming of PKC targeting to specific PM location to phosphorylate substrates in different cellular locations. Published 2003 Wiley-Liss, Inc.