DIFFERENCES IN REGULATION OF ALPHA-1(I) COLLAGEN PROMOTER IN VASCULARSMOOTH-MUSCLE CELLS IN TRANSFECTION STUDIES AND TRANSGENIC MICE

It has previously been shown that the expression of a transgene contai ning 3.5 kb of alpha 1(I) collagen (COL1A1) promoter sequence fused to the chloramphenicol acetyl transferase (CAT) reporter gene (ColCAT3.6 ) paralleled the expression of the endogenous type I collagen gene in bone, tendon and skin whereas the expression in aorta was extremely lo w. In contrast, the same promoter construct showed comparable activity in a variety of transiently transfected smooth muscle and fibroblasti c cells. In order to compare the activity of the transiently transfect ed and the ''endogenous'' transgene from a transgenic animal, in this study, vascular smooth muscle cells (VSMC) were isolated from ColCAT3. 6 transgenic animals and used in a transfection assay. The endogenous transgene remained inactive in primary cultures of transgenic VSMC whi le transiently transfected ColCAT3.6 cells had comparable activity to NIH3T3 fibroblasts, primary rat tendon fibroblasts or primary rat VSMC . The immortalized cell line SM3T3, derived from the aorta of ColCAT3. 6 transgenic mice did not express endogenous transgene but did express stably transfected ColCAT3.6 to levels similar to NIH3T3 fibroblasts or osteoblastic ROS17/2.8 cells. This result stresses the influence of transgene history, possibly its passage through the germline, in regu lation of tissue specific expression.