The distribution of protein kinase C in human leukocytes is altered in microgravity

Abstract

Protein kinase C (PKC) is an ubiquitous enzyme that mediates intracellular signal transduction in eukaryotes. Jurkat and U937 cells were exposed to microgravity during a Space Shuttle flight and stimulated with a radiolabeled phorbol ester (3H-PDBu) that specifically activates and labels several PKC isoforms. Both the total amount of 3H-PDBu labeling per cell and the relative distribution of labeling between subcellular compartments were altered in microgravity compared to onboard and ground 1 g control samples. The amount of total phorbol ester labeling per cell was increased approximately twofold in microgravity samples when compared with onboard 1 g samples for both cell lines. The subcellular distribution of PKC in the cytosol and nuclear fractions appeared 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 observed between labeling levels in the membrane fraction in both cell types. Interleukin-1beta synthesis by U937 cells was markedly decreased in microgravity when compared to the onboard 1 g control, suggesting that the observed alterations in PKC distribution may have functional consequences. The results may have important implications for the effect of gravity on cellular signal transduction.

Suppressed PHA activation of T lymphocytes in simulated microgravity is restored by direct activation of protein kinase C

“…Although some studies suggest there may be a microgravityinduced PKC defect [44][45][46][47], we were able to fully activate T cells to proliferate in simulated microgravity with PMA and ionomycin. These pharmacological agents bypass mechanisms at the cell surface and impart their effect inside the cell: PMA by mimicking 1,2-diacylglycerol (DG) and activating the serine/ threonine kinase PKC; ionomycin by increasing the cytoplasmic free calcium ion concentration [41].…”

Signal Transduction in Primary Human T Lymphocytes in Altered Gravity During Parabolic Flight and Clinostat Experiments

“…During space flights and in microgravity analogues, dysregulation of T cell function has been observed in a multitude of studies [7,8,13,14,15,16,17,18,19,20,45,46]. We found a rapid decrease of CD3 and IL-2R surface expression and reduced p-LAT after 20 seconds of altered gravity during parabolic flight, decreased CD3 surface expression, reduced ZAP-70 abundance and increased histone H3-acetylation in activated T lymphocytes after 5 minutes of clinorotation and a transient downregulation of CD3 and stable downregulation of IL-2R during 60 minutes of clinorotation.…”

Proteomics and genomics of microgravity

“…PKC and protein kinase A (PKA) are early regulators of T-cell activation (10). Although some studies suggest that there may be a microgravity-induced PKC defect (19,27,94), the impairment in the T-cell activation process has been found to be upstream of PKC activation (23,113). However, the translocation of individual PKC isoforms ␤ II, ␦, and ⑀ is differentially altered under microgravity (40, 46).…”