PHORBOL ESTERS REGULATE PREPROGASTRIN-RELEASING PEPTIDE MESSENGER-RNAIN SMALL-CELL LUNG-CANCER CELLS

The expression of preprogastrin-releasing peptide (GRP) mRNA was studi ed using human small cell lung cancer (SCLC) cells. By Northern analys is, preproGRP mRNA was stimulated by 4beta-phorbol 12-myristate 13alph a-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, 4alpha-PMA, had li ttle effect on preproGRP mRNA. A nuclear run-on assay indicated that 1 0(-6) M PMA increased preproGRP transcription 3-fold, whereas beta-act in and glyceraldehyde 3-phosphate dehydrogenase transcription was unal tered. In contrast, PMA had little effect on beta-actin mRNA expressio n. PMA (1 mum) in the presence of 100 mum 1-(5-isoquinolinesulfonyl)-2 -methylpiperazine (H7), a protein kinase C inhibitor, had little effec t on preproGRP mRNA. Addition of PMA after protein kinase C down-regul ation did not alter preproGRP mRNA. PMA (1 mum) caused translocation o f protein kinase C from the cytosol to the membrane of SCLC cells. Als o, 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 additio n of actinomycin D, preproGRP mRNA remained stable for 15 h. These dat a suggest that PMA induces transcription of GRP mRNA in SCLC cells.