Mitogenic modulation of Ca²⁺‐activated K⁺ channels in proliferating A7r5 vascular smooth muscle cells

Abstract

Modulation of Ca2+‐activated K+ channels (KCa) has been implicated in the control of proliferation in vascular smooth muscle cells (VSMC) and other cell types. In the present study, we investigated the underlying signal transduction mechanisms leading to mitogen‐induced alterations in the expression pattern of intermediate‐conductance KCa in VSMC. Regulation of expression of IKCa/rKCa3.1 and BKCa/rKCa1.1 in A7r5 cells, a cell line derived from rat aortic VSMC, was investigated by patch‐clamp technique, quantitative RT–PCR, immunoblotting procedures, and siRNA strategy. PDGF stimulation for 2 and 48 h induced an 11‐ and 3.5‐fold increase in rKCa3.1 transcript levels resulting in a four‐ and seven‐fold increase in IKCa currents after 4 and 48 h, respectively. Upregulation of rKCa3.1 transcript levels and channel function required phosphorylation of extracellular signal‐regulated kinases (ERK1/2) and Ca2+ mobilization, but not activation of p38‐MAP kinase, c‐Jun NH(2)‐terminal kinase, protein kinase C, calcium‐calmodulin kinase II and Src kinases. In contrast to rKCa3.1, mRNA expression and functions of BKCa/rKCa1.1 were decreased by half following mitogenic stimulation. Downregulation of rKCa1.1 did not require ERK1/2 phosphorylation or Ca2+ mobilization. In an in vitro‐proliferation assay, knockdown of rKCa3.1 expression by siRNA completely abolished functional IKCa channels and mitogenesis. Mitogen‐induced upregulation of rKCa3.1 expression is mediated via activation of the Raf/MEK‐ and ERK‐signaling cascade in a Ca2+‐dependent manner. Upregulation of rKCa3.1 promotes VSMC proliferation and may thus represent a pharmacological target in cardiovascular disease states characterized by abnormal cell proliferation. British Journal of Pharmacology (2006) 148, 909–917. doi:

KCa3.1 channels mediate the increase of cell migration and proliferation by advanced glycation endproducts in cultured rat vascular smooth muscle cells

“…Upregulation of K Ca 3.1 channels has been found to promote excessive VSMC proliferation and migration induced by either mitogens (platelet-derived growth factor and EGF) or balloon catheter injury. [13][14][15] However, it is unknown whether AGEs is involved in the K Ca 3.1 channel regulation. In the present study, we demonstrated that AGE-BSA increased K Ca 3.1 current density and enhanced K Ca 3.1 channel protein expression in AGEs and K Ca 3.1 channels Li-Mei Zhao et al cultured rat VSMCs.…”

“…K Ca 3.1 channels are the predominant Ca 2 þ -activated K þ channels in proliferative smooth muscle cells but not in mature contractile cells. [11][12][13][14] The expression of K Ca 3.1 channels is increased in VSMCs in coronary arteries from patients and in aortas of ApoE À / À mice with atherogenesis, and K Ca 3.1 channel blocker markedly slows down the development of atherosclerosis in ApoE À / À mice. 16 However, reports related to the regulation of K Ca 3.1 channels are limited in diabetes.…”

“…[11][12][13][14] Inhibition of K Ca 3.1 channels by the selective blocker TRAM-34 is found to inhibit proliferation mediated by plateletderived growth factor in VSMCs and decrease the development of restenosis. 15 Local delivery of TRAM-34 via balloon catheter prevents ion channel phenotype switching (K Ca 1.1 to K Ca 3.1) in VSMCs of coronary artery and reduces subsequent restenosis.…”

Renal fibrosis is attenuated by targeted disruption of K Ca 3.1 potassium channels

“…Interestingly, mitogens such as bFGF, PDGF, or VEGF have been found to distinctly up-regulate K Ca 3.1 in several cell types (15,21). Conversely, we and others have recently demonstrated in models of experimental angiogenesis (15), post-interventional arterial restenosis (17,19), atherosclerosis (26), and endometrial cancer (27), that selective pharmacological inhibition or knockdown of K Ca 3.1 suppresses mitogen-driven cell proliferation and ameliorates disease progression.…”

“…Whereas the first directly mediate Ca 2ϩ inflow, the latter regulate membrane potential and thus provide the driving force for Ca 2ϩ entry (13). In particular, the intermediate-conductance K Ca (K Ca 3.1) has been shown to play an important role in promoting mitogenesis in several tissues such as the endothelium (15,16), vascular smooth muscle (17)(18)(19), and T lymphocytes (20) as well as in several cell lines including A7r5 neonatal aortic smooth muscle cells (21), 10T1/2-MRF4 myogenic fibroblasts (22,23), HMEC-1 dermal endothelial cells (15), and some cancer cell lines (24,25).…”