Surfactant phospholipid secretion from rat alveolar type II cells: possible role of PKC isozymes.

Protein kinase C (PKC) plays an integral role in control of many type II cell functions, including regulation of surfactant phospholipid secretion. To determine which isozymes of PKC may regulate type II cell functions, we identified those PKC isozymes activated in type II cells in association with surfactant phospholipid secretion after phorbol ester treatment. Transcripts encoding PKC-alpha, -beta, -delta, -epsilon, -eta, and -zeta were detected in type II cells by reverse transcriptase-polymerase chain reaction, whereas PKC-alpha, -beta, -delta, -eta, and -zeta were detected in type II cells by immunoblotting. PKC-alpha and -beta were only present in the cytosol in unstimulated type II cells, whereas PKC isozymes delta, eta, and zeta were found in cytosol and membrane fractions in unstimulated type II cells. 12-O-tetradecanoylphorbol-13-acetate stimulated surfactant secretion and activated PKC-alpha, -beta, -delta, and -eta isozymes in a dose-dependent manner. The inactive analogue 4alpha-phorbol 12,13-didecanoate neither activated PKC isozymes nor stimulated surfactant phospholipid secretion. PKC-zeta was not activated by any of the phorbol esters. PKC isozymes alpha, beta, delta, and eta are present in purified type II epithelial cells and are activated in a dose-dependent manner in alveolar type II cells in association with surfactant phospholipid secretion after phorbol ester treatment.