首页> 外文期刊>American Journal of Physiology >IGFBP-3 activates TGF-beta receptors and directly inhibits growth in human intestinal smooth muscle cells.
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IGFBP-3 activates TGF-beta receptors and directly inhibits growth in human intestinal smooth muscle cells.

机译:IGFBP-3激活TGF-β受体并直接抑制人肠平滑肌细胞的生长。

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We have shown that human intestinal smooth muscle cells produce IGF-I and IGF binding protein-3 (IGFBP-3). Endogenous IGF-I acts in autocrine fashion to stimulate growth of these cells. IGFBP-3 inhibits the binding of IGF-I to its receptor and thereby inhibits IGF-I-stimulated growth. In several carcinoma cell lines and some normal cells, IGFBP-3 regulates growth independently of IGF-I. Two mechanisms for this effect have been identified: IGFBP-3 can directly activate transforming growth factor-beta (TGF-beta) receptors or it can undergo direct nuclear translocation. The aim of the present study was to determine whether IGFBP-3 acts independently of IGF-I and to characterize the mechanisms mediating this effect in human intestinal smooth muscle cells. The direct effects of IGFBP-3 were determined in the presence of an IGF-I receptor antagonist to eliminate its IGF-I-dependent effects. Affinity labeling of TGF-beta receptors (TGF-betaRI, TGF-betaRII, and TGF-betaRV) with 125I-labeled TGF-beta1 showed that IGFBP-3 displaced binding to TGF-betaRII and TGF-betaRV in a concentration-dependent fashion. IGFBP-3 stimulated TGF-betaRII-dependent serine phosphorylation (activation) of both TGF-betaRI and of its primary substrate, Smad2(Ser465/467). IGFBP-3 also caused IGF-I-independent inhibition of basal [3H]thymidine incorporation. The effects of IGFBP-3 on Smad2 phosphorylation and on smooth muscle cell proliferation were independent of TGF-beta1 and were abolished by transfection of Smad2 siRNA. Immunoneutralization of IGFBP-3 increased basal [3H]thymidine incorporation, implying that endogenous IGFBP-3 inhibits proliferation. We conclude that endogenous IGFBP-3 directly inhibits proliferation of human intestinal smooth muscle cells by activation of TGF-betaRI and Smad2, an effect that is independent of its effect on IGF-I-stimulated growth.
机译:我们已经证明人肠平滑肌细胞产生IGF-1和IGF结合蛋白3(IGFBP-3)。内源性IGF-I以自分泌方式起作用,以刺激这些细胞的生长。 IGFBP-3抑制IGF-1与其受体的结合,从而抑制IGF-1刺激的生长。在几种癌细胞系和某些正常细胞中,IGFBP-3独立于IGF-1调节生长。已经确定了产生这种作用的两种机制:IGFBP-3可以直接激活转化生长因子β(TGF-beta)受体,或者可以进行直接核转运。本研究的目的是确定IGFBP-3是否独立于IGF-I发挥作用,并表征在人肠道平滑肌细胞中介导此作用的机制。在存在IGF-I受体拮抗剂以消除其IGF-I依赖性作用的情况下确定IGFBP-3的直接作用。用125 I标记的TGF-beta1对TGF-beta受体(TGF-betaRI,TGF-betaRII和TGF-betaRV)进行亲和标记表明,IGFBP-3以浓度依赖的方式取代了与TGF-betaRII和TGF-betaRV的结合。 IGFBP-3刺激TGF-betaRI及其主要底物Smad2(Ser465 / 467)的TGF-betaRII依赖性丝氨酸磷酸化(激活)。 IGFBP-3还引起基础[3H]胸腺嘧啶核苷掺入的IGF-I独立抑制。 IGFBP-3对Smad2磷酸化和平滑肌细胞增殖的影响独立于TGF-beta1,并通过转染Smad2 siRNA消除。 IGFBP-3的免疫原化增加了基础[3H]胸苷的掺入,这表明内源性IGFBP-3抑制了增殖。我们得出的结论是,内源性IGFBP-3通过激活TGF-βRI和Smad2直接抑制人肠道平滑肌细胞的增殖,这一作用与其对IGF-I刺激的生长的影响无关。

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