Properties of classic protein kinase C in human small cell lung carcinoma NCI-H345 cells

Bombesin-like peptides (BLPs) activate protein kinase C (PKC), which leads to proliferation in nonmalignant Swiss 3T3 cells. The purpose of this study was to determine if PKC expression in the classic human small cell lung carcinoma NCI-H345 cell line, which has an autocrine growth loop involving BLPs, exhibited unique properties that could result in malignant behavior. PKC activity and phorbol dibutyrate binding in NCI-H345 cells had properties similar to other reports. PKC activity in the cytosolic fraction increased to 100% as cells proliferated through lag, log, and plateau growth states. However, during the first 3 days after plating (lag growth state), 40-50% of the PKC activity was membrane associated, indicating a substantial portion in an activated form, possibly a result of BLP autocrine stimulation. NCI-H345 cells expressed the PKC isoenzymes alpha, beta, delta, sigma, and eta, but not gamma or epsilon, a pattern different from Swiss 3T3 cells or normal brain. further characterization of the Ca2+/phospholipid-dependent (classic) PKC isoenzymes, alpha and beta, showed that PKC beta was predominantly cytosolic (80%) as expected, but PKC alpha was primarily membrane associated (80-90%). Exposure of NCI-H345 cells to 200 nm phorbol 12-myristyl 13-acetate rapidly (within 2 min) decreased cytosolic PKC activity, with no change in the particulate activity, but did not alter [3H]-thymidine incorporation or subcellular distribution of PKC alpha or beta by Western blot. These results suggest altered PKC regulation in human small cell lung carcinoma NCI-H345 cells, which could contribute to their malignant behavior.