Proteoglycan biosynthesis is required in BC3H1 myogenic cells for modulation of vascular smooth muscle alpha-actin gene expression in response to microenvironmental signals

Vascular smooth muscle alpha-actin gene transcription during myofibroblast differentiation requires Sp1/3 protein binding proximal to the MCAT enhancer

The conversion of stromal fibroblasts into contractile myofibroblasts is an essential feature of the wound-healing response that is mediated by transforming growth factor beta1 (TGF-beta1) and accompanied by transient activation of the vascular smooth muscle alpha-actin (SmalphaA) gene. Multiple positive-regulatory elements were identified as essential mediators of basal SmalphaA enhancer activity in mouse AKR-2B stromal fibroblasts. Three of these elements bind transcriptional activating proteins of known identity in fibroblasts. A fourth site, shown previously to be susceptible to single-strand modifying agents in myofibroblasts, was additionally required for enhancer response to TGF-beta1. However, TGF-beta1 activation was not accompanied by a stoichiometric increase in protein binding to any known positive element in the SmalphaA enhancer. By using oligonucleotide affinity isolation, DNA-binding site competition, gel mobility shift assays, and protein overexpression in SL2 and COS7 cells, we demonstrate that the transcription factors Sp1 and Sp3 can stimulate SmalphaA enhancer activity. One of the sites that bind Sp1/3 corresponds to the region of the SmalphaA enhancer required for TGF-beta1 amplification. Additionally, the TGF-beta1 receptor-regulated Smad proteins, in particular Smad3, are rate-limiting for SmalphaA enhancer activation. Whereas Smad proteins collaborate with Sp1 in activating several stromal cell-associated promoters, they appear to operate independently from the Sp1/3 proteins in activating the SmalphaA enhancer. The identification of Sp and Smad proteins as essential, independent activators of the SmalphaA enhancer provides new insight into the poorly understood process of myofibroblast differentiation.

Chronic elevation of calmodulin in the ventricles of transgenic mice increases the autonomous activity of calmodulin-dependent protein kinase II, which regulates atrial natriuretic factor gene expression

Although isoforms of Ca2+/calmodulin-dependent protein kinase II (CaMKII) have been implicated in the regulation of gene expression in cultured cells, this issue has yet to be addressed in vivo. We report that the overexpression of calmodulin in ventricular myocytes of transgenic mice results in an increase in the Ca2+/calmodulin-independent activity of endogenous CaMKII. The calmodulin transgene is regulated by a 500-bp fragment of the atrial natriuretic factor (ANF) gene promoter which, based on cell transfection studies, is itself known to be regulated by CaMKII. The increased autonomous activity of CaMKII maintains the activity of the transgene and establishes a positive feed-forward loop, which also extends the temporal expression of the endogenous ANF promoter in ventricular myocytes. Both the increased activity of CaMKII and transcriptional activation of ANF are highly selective responses to the chronic overexpression of calmodulin. These results indicate that CaMKII can regulate gene expression in vivo and suggest that this enzyme may represent the Ca2+-dependent target responsible for reactivation of the ANF gene during ventricular hypertrophy.