Corticotropin-releasing factor increases protein kinase C activity by elevating membrane-bound alpha and beta isoforms.

Corticotropin-releasing factor (CRF) has been shown to attenuate vascular leakage in injured skin, mucous membrane, muscle, lung, and brain. We previously reported that CRF increases cytosolic free calcium concentrations ([Ca2+]i), cellular cAMP, and inositol trisphosphates in human epidermoid A-431 cells. This study identified protein kinase C isoforms in A-431 cells and investigated the effect of CRF on PKC activity and isoform translocation. PKC alpha, beta, gamma, delta, and zeta isoforms were present in cytosolic and membrane fractions, but the epsilon isoform was detected only in the membrane fraction. Exposure of cells to CRF at 420 pM for 1 min increased PKC activity and led to the translocation of PKC alpha and beta isoforms from cytosol to membrane. The translocation was dependent on an increase in [Ca2+]i, because cells treated with 100 microM BAPTA-am (an intracellular Ca2+ chelator), then exposed to CRF, showed neither increases in PKC activity nor translocation of PKC isoforms. This suggests that a CRF-induced increase in [Ca2+]i mediates the increase in PKC activity.