Differences in regulation of alpha 1(I) collagen promoter in vascular smooth muscle cells in transfection studies and transgenic mice.

It has previously been shown that the expression of a transgene containing 3.5 kb of alpha 1(l) 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 low. In contrast, the same promoter construct showed comparable activity in a variety of transiently transfected smooth muscle and fibroblastic cells. In order to compare the activity of the transiently transfected 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 while 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 dis 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 regulation of tissue specific expression.