A127

The protein kinase C (PKC) family consists of structurally related serine-threonine kinases that influence drug resistance and cell survival in various cancers. In this study we identified that two of the classical PKC isoforms, PKC-α and PKC-β that played an important role in cell survival of non-small cell lung cancer (NSCLC) cells. Various NSCLC cells (H1734, A549, H226, H1703, H292) expressed high levels of phosphorylated PKC-α, PKC-β and PKC-μ when compared to normal human tracheobronchial epithelial (NHTBE) cells. The levels of phosphorylated PKC-δ or PKC-ζ, ι/λ were reduced in NSCLC when compared to NHTBE. Knock down of protein kinase expression by small interfering (si) RNAs, siPKCβ alone or by combined siPKCα/β and to a lesser extent by siPKCα alone inhibited the expression of the cAMP response element (CRE)-binding protein (CREB) transcription factor in H1734 NSCLC cell line. Immunofluorescence analysis revealed that knock-downs also induced changes in the phosphorylation of PKCβ and CREB as well as the translocation of the nuclear CREB to the cytoplasm. Phosphorylation of kinases upstream of CREB including ERK1/2 and RSK was also observed by Western blotting following the knock down of protein kinases. The expression of survival genes Bcl-2 and Bcl-xl were also reduced by siPKCβ or siPKCα/β, which was accompanied by the induction of DNA fragmentation and apoptosis measured by TUNEL. Treatment of H1734 cells with siPKCβ inhibits cell proliferation up to 50%, which did not occur using siPKCα. Finally, combining the siPKCβ with other drugs increased the sensitivity of H1734 cells to cytotoxcicty. These data illustrate the usefulness of using siRNA directed against PKCβ alone or by combined siPKCα/β to suppress the growth of lung tumor cells that selectively overexpress PKCβ and sensitize them to other drugs which may be useful in a prevention setting for high risk populations to reduce the level of cytotoxic drugs.

[Fifth AACR International Conference on Frontiers in Cancer Prevention Research, Nov 12-15, 2006]