TRANSCRIPTIONAL AND POSTTRANSCRIPTIONAL MECHANISMS REGULATE HUMAN RENIN GENE-EXPRESSION IN CALU-6 CELLS

We have recently identified a human pulmonary carcinoma cell line (Cal u-6) that expresses human renin (hREN) mRNA endogenously, and we use i t herein as a model to examine the regulation of the hREN gene. Transf ection analysis of a deletion series (-2750 to -149) of hREN promoter- luciferase fusion constructs revealed the presence of multiple weak re gulatory elements within the first 1,301 bp of the 5'-flanking region and a classic silencer element within the first intron (intron A) of t he gene. The 5'-flanking regulatory domain consisted of three closely linked elements, two negative and one positive, each contributing a ce ll-specific threefold modulation of transcriptional activity. Treating Calu-6 cells with forskolin caused a 100-fold increase in steady-stat e endogenous hREN mRNA but no increase in hREN promoter activity in tr ansient transfections or in nuclear runoff transcription assays. Never theless, de novo transcription and translation were necessary for aden osine 3',5'-cyclic monophosphate (cAMP)-mediated induction, Our result s suggest that multiple regulatory elements regulate basal transcripti onal activity of the hREN gene and the increase in hREN mRNA by cAMP m ay be mediated by posttranscriptional mechanisms.