Hormonal regulation of plasminogen activator mRNA production in porcine kidney cells.

Plasminogen activator (PA) production in LLC-PK1 pig kidney cell culture is induced to high levels by calcitonin and vasopressin, both of which stimulate adenylate cyclase, or by other compounds that also raise intracellular cAMP levels. Enzyme induction is transiently sensitive to inhibition by actinomycin D, suggesting that increased concentrations of cAMP mediate the inducing effects of the hormones by enhancing the transcription of PA-mRNA sequences. We tested this hypothesis by measuring PA-mRNA sequences in the Xenopus oocyte translation system which showed a 15-20-fold enhanced PA-synthesizing capacity when supplied with poly(A)+RNA from induced cells, above that obtained from uninduced cell RNA. Changes in PA-mRNA levels measured by Northern hybridization using cloned PA-specific cDNA gave results that agreed well with those obtained from translation assays. Pretreatment with high concentrations of cycloheximide did not block calcitonin-induced PA-mRNA synthesis, indicating that PA gene activation was a primary transcriptional result of calcitonin stimulation and did not require new protein synthesis.