Upstream stimulatory factor 1 regulates osteopontin expression in smooth muscle cells

Vascular smooth muscle cells (SMCs) undergo a dramatic phenotypic transitio n in response to injury and ex vivo culture that includes enhanced prolifer ation, migration, matrix deposition, and alterations in gene expression. Os teopontin is a good marker for the injury-induced SMC phenotypic state in v ivo and in vitro. To identify transcription factors that might control the regulation of osteopontin expression, we investigated cultured vascular SMC s that express high and low levels of osteopontin. Using nuclear run-on ass ays, mRNA stability studies, and deletion analysis, we demonstrate that reg ulation of osteopontin steady-state mRNA levels in SMCs occurs at the trans criptional level. Transient transfection and gel-shift analyses of osteopon tin promoter indicated that a region between -123 and +66 was involved in t he expression of osteopontin. Supershift EMSAs identified the bHLH-leucine zipper transcription factor upstream stimulatory factor-1 (USF1) as the pro tein binding to this sequence. Finally, we show that USF1 protein is induce d in vivo within 24 h of balloon angioplasty of rat carotids coordinately w ith osteopontin induction. These data suggest that USF1 governs expression of osteopontin in cultured vascular SMCs and might contribute to initial os teopontin expression observed post carotid injury and in vascular pathologi es in vivo. (C) 1999 Academic Press.