Antisense Inhibition of Protein Kinase Cα Reverses the Transformed Phenotype in Human Lung Carcinoma Cells

Abstract

The protein kinase C (PKC) family, which functions through serine/threonine kinase activity, is involved in signal transduction pathways necessary for cell proliferation and differentiation. Its critical role in processes relevant to neoplastic transformation and tumor invasion renders PKC a potentially suitable target for anticancer therapy. To explore whether antisense blocking of PKCα would inhibit the neoplastic properties in tumor cells, human lung carcinoma LTEPa-2 cells were transfected with a recombinant plasmid, pXJ41-CKPα, with PKCα cDNA inserted in the antisense orientation. In LT.AS4 cell clones stably expressing antisense PKCα mRNA, the amounts of PKCα protein and total PKC activity were decreased when compared to control cells. The expression of antisense PKCα markedly inhibited the cell proliferation rate, colony forming efficiency in soft agar, and tumorigenecity in nude mice. Furthermore, the mRNA levels of oncogenes (Ha-ras, c-jun, and c-fos) were seen to decrease to varying degrees. Reduced DNA binding activity of transcription factor AP-1 was also observed using gel shift analysis, suggesting that one major molecular mechanism by which PKCα can exert its effects on cell growth and transformation is through regulation of AP-1 transcription factor activity. Taken together, these data provide evidence for the ability of antisense PKCα expression to reverse the transformed phenotype of human lung carcinoma cells and support the development of PKCα inhibitors for the clinical treatment of cancers.