CALL FOR PAPERS Cellular Mechanisms of Tissue Fibrosis A novel -adrenergic response element regulates both basal and agonist- induced expression of cyclin-dependent kinase 1 gene in cardiac fibroblasts

Gaspard GJ, MacLean J, Rioux D, Pasumarthi KB. A novel -adrenergic response element regulates both basal and agonistinduced expression of cyclin-dependent kinase 1 gene in cardiac fibroblasts. Am J Physiol Cell Physiol 306: C540–C550, 2014. First published January 29, 2014; doi:10.1152/ajpcell.00206.2013.—Cardiac fibrosis, a known risk factor for heart disease, is typically caused by uncontrolled proliferation of fibroblasts and excessive deposition of extracellular matrix proteins in the myocardium. Cyclin-dependent kinase 1 (CDK1) is involved in the control of G2/M transit phase of the cell cycle. Here, we showed that isoproterenol (ISO)-induced cardiac fibrosis is associated with increased levels of CDK1 exclusively in fibroblasts in the adult mouse heart. Treatment of primary embryonic ventricular cell cultures with ISO (a nonselective -adrenergic receptor agonist) increased CDK1 protein expression in fibroblasts and promoted their cell cycle activity. Quantitative PCR analysis confirmed that ISO increases CDK1 transcription in a transient manner. Further, the ISO-responsive element was mapped to the proximal 100-bp sequence of the CDK1 promoter region using various 5=-flanking sequence deletion constructs. Sequence analysis of the 100-bp CDK1 minimal promoter region revealed two putative nuclear factor-Y (NF-Y) binding elements. Overexpression of the NF-YA subunit in primary ventricular cultures significantly increased the basal activation of the 100-bp CDK1 promoter construct but not the ISO-induced transcription of the minimal promoter construct. In contrast, dominant negative NF-YA expression decreased the basal activity of the minimal promoter construct and ISO treatment fully rescued the dominant negative effects. Furthermore, site-directed mutagenesis of the distal NF-Y binding site in the 100-bp CDK1 promoter region completely abolished both basal and ISO-induced promoter activation of the CDK1 gene. Collectively, our results raise an exciting possibility that targeting CDK1 or NF-Y in the diseased heart may inhibit fibrosis and subsequently confer cardioprotection.