Molecular cloning of gene sequences regulated by tumor promoters and mitogens through protein kinase C.

ABSTRACT

cDNA clones representing genes whose expression is modulated by treatment with mitogens and tumor promoters were isolated and characterized. TPA-S1 corresponds to an mRNA species whose abundance was increased markedly within 1 h of exposure to the tumor promoter 12-O-tetradecanoyl phorbol-13-acetate (TPA), and TPA-R1 represents an mRNA that was decreased in TPA-treated cells. The induction of TPA-S1 was blocked by actinomycin D but was not affected by cycloheximide, and it was specific for phorbol esters with tumor-promoting activity. The role of protein kinase C in the induction of TPA-S1 is supported by the following lines of evidence. (i) Agents that activated protein kinase C (TPA, platelet-derived growth factor, and diacylglycerol) also increased TPA-S1 mRNA levels. (ii) A potent PKC inhibitor blocked the induction of TPA-S1. (iii) Down-regulation of PKC activity, by treatment of cells with TPA for 24 h, resulted in a loss of responsiveness to TPA-S1 induction by subsequent TPA treatment. DNA sequence analysis of TPA-S1 predicts a cysteine-rich, secreted protein with a molecular weight of 22.6 X 10(3) that exhibits homology with sequences representing a protein with human erythroid-potentiating activity and protease inhibitory activity.