Phorbol esters regulate preprogastrin-releasing peptide messenger RNA in small cell lung cancer cells.

The expression of preprogastrin-releasing peptide (GRP) mRNA was studied using human small cell lung cancer (SCLC) cells. By Northern analysis, preproGRP mRNA was stimulated by 4 beta-phorbol 12-myristate 13 alpha-acetate (PMA) in a concentration- and time-dependent manner in these cells. In cell line NCI-H209, the addition of 10(-6) M PMA increased a 0.9-kb mRNA after 8 h. An inactive phorbol ester, 4 alpha-PMA, had little effect on preproGRP mRNA. A nuclear run-on assay indicated that 10(-6) M PMA increased preproGRP transcription 3-fold, whereas beta-actin and glyceraldehyde 3-phosphate dehydrogenase transcription was unaltered. In contrast, PMA had little effect on beta-actin mRNA expression. PMA (1 microM) in the presence of 100 microM 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H7), a protein kinase C inhibitor, had little effect on preproGRP mRNA. Addition of PMA after protein kinase C down-regulation did not alter preproGRP mRNA. PMA (1 microM) caused translocation of protein kinase C from the cytosol to the membrane of SCLC cells. Also, PMA (10(-6) M) stimulated and H7 (10(-4) M) reduced SCLC growth in vitro. When new synthesis of preproGRP mRNA was blocked by the addition of actinomycin D, preproGRP mRNA remained stable for 15 h. These data suggest that PMA induces transcription of GRP mRNA in SCLC cells.