Brian D. Cain

Endothelin-1 gene regulation

Over two decades of research have demonstrated that the peptide hormone endothelin‐1 (ET‐1) plays multiple, complex roles in cardiovascular, neural, pulmonary, reproductive, and renal physiology. Differential and tissue‐specific production of ET‐1 must be tightly regulated in order to preserve these biologically diverse actions. The primary mechanism thought to control ET‐1 bioavailability is the rate of transcription from the ET‐1 gene (ednl). Studies conducted on a variety of cell types have identified key transcription factors that govern ednl expression. With few exceptions, the cts‐acting elements bound by these factors have been mapped in the ednl regulatory region. Recent evidence has revealed new roles for some factors originally believed to regulate ednl in a tissue or hormone‐specific manner. In addition, other mechanisms involved in epigenetic regulation and mRNA stability have emerged as important processes for regulated ednl expression. The goal of this review is to provide a comprehensive overview of the specific factors and signaling systems that govern ednl activity at the molecular level.—Stow, L. R., Jacobs, M. E., Wingo, C. S., Cain, B. D. Endothelin‐1 gene regulation. FASEB J. 25, 16–28 (2011). www.fasebj.org

The Circadian Protein Period 1 Contributes to Blood Pressure Control and Coordinately Regulates Renal Sodium Transport Genes

The circadian clock protein period 1 (Per1) contributes to the regulation of expression of the &agr; subunit of the renal epithelial sodium channel at the basal level and in response to the mineralocorticoid hormone aldosterone. The goals of the present study were to define the role of Per1 in the regulation of additional renal sodium handling genes in cortical collecting duct cells and to evaluate blood pressure (BP) in mice lacking functional Per1. To determine whether Per1 regulates additional genes important in renal sodium handling, a candidate gene approach was used. Immortalized collecting duct cells were transfected with a nontarget small interfering RNA or a Per1-specific small interfering RNA. Expression of the genes for &agr;-epithelial sodium channel and Fxyd5, a positive regulator of Na, K-ATPase activity, decreased in response to Per1 knockdown. Conversely, mRNA expression of caveolin 1, Ube2e3, and ET-1, all negative effectors of epithelial sodium channel, was induced after Per1 knockdown. These results led us to evaluate BP in Per1 KO mice. Mice lacking Per1 exhibit significantly reduced BP and elevated renal ET-1 levels compared with wild-type animals. Given the established role of renal ET-1 in epithelial sodium channel inhibition and BP control, elevated renal ET-1 is one possible explanation for the lower BP observed in Per1 KO mice. These data support a role for the circadian clock protein Per1 in the coordinate regulation of genes involved in renal sodium reabsorption. Importantly, the lower BP observed in Per1 KO mice compared with wild-type mice suggests a role for Per1 in BP control as well.

Regulation of αENaC expression by the circadian clock protein Period 1 in mpkCCDc14 cells

The epithelial sodium channel (ENaC) mediates the fine-tuned regulation of external sodium (Na) balance. The circadian clock protein Period 1 (Per1) is an aldosterone-induced gene that regulates mRNA expression of the rate-limiting alpha subunit of ENaC (αENaC). In the present study, we examined the effect of Per1 on αENaC in the cortex, the site of greatest ENaC activity in the collecting duct, and examined the mechanism of Per1 action on αENaC. Compared to wild type mice, Per1 knockout mice exhibited a 50% reduction of steady state αENaC mRNA levels in the cortex. Importantly, siRNA-mediated knockdown of Per1 decreased total αENaC protein levels in mpkCCD(c14) cells, a widely used model of the murine cortical collecting duct (CCD). Per1 regulated basal αENaC expression and participated in the aldosterone-mediated regulation of αENaC in mpkCCD(c14) cells. Because circadian clock proteins mediate their effects as part of multi-protein complexes at E-box response elements in the promoters of target genes, the ability of Per1 to interact with these sequences from the αENaC promoter was tested. For the first time, we show that Per1 and Clock are present at an E-box response element found in the αENaC promoter. Together these data support an important role for the circadian clock protein Per1 in the direct regulation of αENaC transcription and have important implications for understanding the role of the circadian clock in the regulation of renal function.

Cell-cycle-specific biosynthesis of the photosynthetic membrane of Rhodopseudomonas sphaeroides Structural implications

Structural changes association with the intracytoplasmic membrane during the cell cycle of the photosynthetic bacterium Rhodopseudomonas sphaeroides have been studied by freeze-fracture electron microscopy. The isolated intracytoplasmic membrane vesicles, chromatophores, were fused in order to obtain large fracture faces, allowing more precise measurements and statistical analysis of both intramembrane particle density and size determinations. The intramembrane particle density of the protoplasmic face (PF) of the intracytoplasmic membrane, (from 4970 to 8290/micrometers 2), was shown to be a linear function of the protein/phospholipid ratio (from 2.5 to 5.1, w/w) of the intracytoplasmic membrane. Under constant light intensity, both the average particle size and particle size distribution remained unchanged during the cell cycle. These results provide the structural basis for the earlier reported cell-cycle-specific variations in both protein/phospholipid ratio and alternation in phospholipid structure of the intracytoplasmic membrane of R. sphaeroides during photosynthetic growth. The average particle diameter in the PF face of the intracytoplasmic membrane was 8.25, 9.08 and 9.75 nm at incident light intensities of 4000, 500 and 30 ft X cd, respectively. When chromatophores were fused with small, unilamellar liposomes, the intramembrane particle density decreased as input liposome phospholipid increased, whereas the particle size remained constant and particle distribution became random.