REGULATION OF THE ALPHA-1(I) COLLAGEN PROMOTER IN VASCULAR SMOOTH-MUSCLE CELLS - COMPARISON WITH OTHER ALPHA-1(I) COLLAGEN-PRODUCING CELLS IN TRANSGENIC ANIMALS AND CULTURED-CELLS

We have previously reported that the expression of the ColCAT3.6 trans gene containing 3.5 kilobases (kb) of alpha 1(I) collagen (COL1A1) pro moter sequence fused to the chloramphenicol acetyltransferase (CAT) re porter gene paralleled the expression of the endogenous gene in severa l connective tissues. We report here that the activity of the reporter gene in aorta from 7-day-old transgenic mice is 10-64-fold lower than in tendon or bone, whereas the endogenous gene is highly expressed in all three tissues. In contrast, the COL1A1 minigene containing 2.3 kb of upstream sequence, the first five exon/intron units, the last six exon/intron units, and 2 kb of 3'-flanking sequence showed high CAT ac tivity in aorta. These results suggest that cia sequences found in Col CAT3.6 mediate high levels of COL1A1 expression in bone and tendon, bu t not in vascular smooth muscle cells (VSMC), whereas sequences locate d within the minigene, but not found in ColCAT3.6, mediate VSMC-specif ic expression. Analysis of promoter activity in cultured cells derived from transgenic tissues further suggests the presence of VSMC-specifi c regulatory domains. Transient transfection studies, however, failed to shows differential regulation. These differences stress the importa nce of not relying exclusively on transient transfection data when map ping tissue-specific regulatory domains.