Ouabain- and Marinobufagenin-Induced Proliferation of Human Umbilical Vein Smooth Muscle Cells and a Rat Vascular Smooth Muscle Cell Line, A7r5

Abstract

Background-We studied the growth-promoting effects of 2 sodium pump-selective cardiotonic steroids, ouabain and marinobufagenin, on cultured cells from vascular smooth muscle (VSMCs) from human umbilical vein and a rat VSMC line, A7r5. Methods and Results-Both ouabain and marinobufagenin activated proliferation of these cells in a concentrationdependent manner, reflecting the cardiotonic steroid sensitivity of the specific ␣ 1 subunit contained within each cell source. The observed effective concentration ranges of both compounds was below that necessary to induce cytoplasmic ion alterations by sodium pump inhibition. Conclusions-These data indicate that the ouabain-activated proliferative effect previously observed in canine VSMCs occurs in other VSMC sources. This growth effect seems to be initiated by drug interaction with the sodium pump, reflected by the affinity of the steroid for the pump, and is independent of altered transmembrane ionic gradients. Key Words: cells Ⅲ drugs Ⅲ muscle, smooth Ⅲ vasculature T he role of the sodium pump, or Na ϩ ,K ϩ -ATPase, in the catalysis of Na ϩ and K ϩ active transport across the plasma membrane of animal cells is well documented. Recent research in this area has shown that this enzyme complex may have functions distinct from those involved in active ion transport. Significant evidence has emerged indicating that the sodium pump can also function as a transmembrane signal transducing complex (for reviews, see Xie and Askari 1 and Schoner 2 ). Studies by Kometiani et al, 3 Haas et al, 4 and Liu et al 5 have shown that low concentrations of the cardiotonic steroid ouabain activated rat cardiac myocyte hypertrophy and ERK1/2 phosphorylation and that these actions are totally independent of changes in intracellular Na ϩ and Ca 2ϩ concentrations. In addition, we have demonstrated that 0.1 to 1.0 nmol/L ouabain induced proliferation of cultured canine vascular smooth muscle cells (VSMCs) via a signaling cascade involving Src, the epidermal growth factor receptor, and ERK1/2. 6 These low concentrations of ouabain have also been shown to stimulate proliferation of human prostate smooth muscle cells. 7 Together with the recent observations of endogenous production of these species of cardiotonic steroids, 8,9 these studies suggest that they may function as autocoidal mediators of growth.VSMC proliferation has been linked to a variety of adaptive and pathophysiological responses, and a potential endogenous regulator of this function would be of considerable interest. In addition, it has been suggested that these endogenous compounds could well be a part of the cardiovascular remodeling that occurs in hypertension. 10 Thus, this study extends our previous work, because it addresses 3 critical functional issues: (1) Does the response occur in human VSMCs? (2) Do other autocoidal steroids evoke the same response? and (3) Does the response involve ligand interaction with the Na ϩ ,K ϩ -ATPase? To accomplish these goals, we have elected to assess 2 compounds, ouabain and marinobufagen...

Na,K-ATPase signal transduction triggers CREB activation and dendritic growth

“…In addition to maintaining the electrochemical gradient, the Na,K-ATPase has been shown to act as a receptor and signal transducer. Previous reports indicate that Na,K-ATPase signal transduction stimulates proliferation in smooth muscle cells (11) and apoptosis in prostate cancer cells (12). Ouabain, an endogenously synthesized hormone (13,14), is Na,K-ATPase's ligand and forms a hormone-receptor complex capable of inducing mitogen-activated protein (MAP) kinase phosphorylation (15,16) and intracellular Ca 2ϩ signaling (17)(18)(19).…”

Examination of the Cellular Mechanisms by Which Marinobufagenin Inhibits Cytotrophoblast Function

“…Xie (60) reported that in addition to promoting ion transport, Na ϩ /K ϩ -ATPase acts as a signal transducer in a cell-specific manner. Allen and co-workers (61,62) demonstrated that the cardiotonic steroid ouabain stimulates vascular smooth muscle cell proliferation, which correlates with increased epidermal growth factor transactivation and Src phosphorylation. Moreover, binding of ouabain to the sodium pump induces the phosphorylation of various MAPKs and subsequently activates the transcription factors AP-1 (activator protein-1) and NFB (63).…”

Endogenous sodium pump inhibitors, diabetes mellitus and preeclampsia

“…It has been hypothesized that the primary role of CTS during pregnancy is control of water-electrolyte balance via induction of natriuresis [3]. Growing evidence for implication of CTS including MBG, in tissue growth and differentiation [20,24,25], raises the possibility that the fetus may be a primary target for MBG. Our present data suggest that regulation of carbohydrate metabolism and modulation of glucose tolerance may also be one of the roles of MBG in pregnancy.…”