THE DISTRIBUTION OF PROTEIN-KINASE-C IN HUMAN-LEUKOCYTES IS ALTERED IN MICROGRAVITY

Protein kinase C (PKC) is an ubiquitous enzyme that mediates intracell ular signal transduction in eukaryotes. Jurkat and U931 cells were exp osed to microgravity during a Space Shuttle flight and stimulated with a radiolabeled phorbol ester (H-3-PDBu) that specifically activates a nd labels several PKC isoforms, Both the total amount of H-3-PDBu labe ling per cell and the relative distribution of labeling between subcel lular compartments were altered in microgravity compared to onboard an d ground 1 g control samples, The amount of total phorbol ester labeli ng per cell was increased approximately twofold in microgravity sample s when compared with onboard Ig samples for both cell lines, The subce llular distribution of PKC in the cytosol and nuclear fractions appear ed to be correlated with the applied acceleration, In both cell types the relative amount of phorbol ester labeling in the nuclear fraction decreased with applied acceleration, whereas the labeling in cytosolic fraction increased with g level, No significant differences were obse rved between labeling levels in the membrane fraction in both cell typ es, Interleukin-1 beta Synthesis by U931 cells was markedly decreased in microgravity when compared to the onboard 1 g control, suggesting t hat the observed alterations in PKC distribution may have functional c onsequences, The results may have important implications for the effec t of gravity on cellular signal transduction.