TRANSFORMING GROWTH-FACTOR-BETA MODULATION OF THE ALPHA-1(IV) COLLAGEN GENE IN MURINE PROXIMAL TUBULAR CELLS

We have examined the expression of the alpha 1(TV) collagen gene in mu rine proximal tubular cells (MCT) to better understand how it is regul ated in parenchymal cells. Transcriptional activity was examined using luciferase reporters driven by the alpha 1(TV) promoter and varying l engths of 5'-flanking sequences. The minimal bidirectional promoter sh owed low intrinsic activity in MCT cells, but addition of upstream seq uences increased luciferase expression. Maximal activity resided withi n the first 1,200 bp upstream. A minigene construct was generated by p lacing a portion of the alpha 1(TV) first intron downstream from the p romoter region. The intronic sequences significantly decreased activit y of the promoter in MCT cells and 3T3 fibroblasts but greatly enhance d expression in murine parietal yolk sac (PYS) endodermal cells. Addit ion of transforming growth factor-beta (TGF-beta) to MCT cultures elev ated the levels of secreted type IV collagen. Treatment of either tran siently or stably transfected MCT cells with TGF-beta produced an incr ease in the levels of expression of all of the reporters tested. These data support the hypothesis that cell-specific regulation of alpha 1( N) collagen is dependent upon downstream sequences, which act to decre ase the expression of type IV collagen in tubular epithelium. The acti vity of the alpha 1(IV)) collagen gene in proximal tubular cells is in creased by TGF-beta, which acts on the domain(s) embedded within the i ntergenic bidirectional promoter.