A unique combination of plasma membrane Ca2+-ATPase isoforms is expressed in islets of Langerhans and pancreatic beta-cell lines.
A unique combination of plasma membrane Ca2+-ATPase isoforms is expressed in islets of Langerhans and pancreatic beta-cell lines.
复制标题
质膜 Ca2 -ATP 酶亚型的独特组合在胰岛和胰腺 β 细胞系中表达。
作者：
A. Váradi;E. Molnár;S. Ashcroft
细胞内游离Ca 2+浓度的变化调节胰腺β细胞的胰岛素分泌。β细胞内陡峭的Ca 2+梯度的存在需要专门的Ca 2+排除系统的存在。在这项研究中，我们已经确定了质膜Ca ~（2+）-ATP酶（PMCAs），它将Ca ~（2+）从细胞质中挤出。在啮齿动物胰腺α-和β-细胞系中，以及在人类和大鼠胰岛中，使用大鼠PMCA钙调蛋白结合区侧翼引物进行逆转录PCR，研究PMCA亚型特异性mRNA表达。PMCA 1和2的表达模式在不同物种和胰岛细胞类型中是保守的，因为大鼠和人胰岛以及所有测试的细胞系都含有1b和2b形式。然而，PMCA 4亚型以细胞类型特异性方式表达，因为β细胞仅表达PMCA 4 b，而在含有α、β、δ和多肽分泌细胞的胰岛中，PMCA 4a和4 b同时存在。未获得PMCA 3表达的证据。β细胞钙泵蛋白的表征表明，它与红细胞PMCA有几个相似之处。它是一种P型ATP酶;其磷酸化中间体被La 3+稳定;它与PMCA特异性抗体反应;并且它不是N-糖基化的。然而，β细胞PMCA的分子量高于红细胞;这种差异可以通过PMCA 2形式的主要翻译（其分子量比红细胞PMCA 1和4蛋白高3-8 kDa）或通过可能的序列插入来解释。因此，功能不同的PMCA亚型（1b，2b，4 b）的独特组合参与β细胞中的Ca 2+稳态。
Changes in free intracellular Ca2+ concentration regulate insulin secretion from pancreatic beta-cells. The existence of steep Ca2+ gradients within the beta-cell requires the presence of specialized Ca2+ exclusion systems. In this study we have characterized the plasma membrane Ca2+-ATPases (PMCAs) which extrude Ca2+ from the cytoplasm. PMCA isoform- and subtype-specific mRNA expression was investigated in rodent pancreatic alpha- and beta-cell lines, and in human and rat islets of Langerhans using reverse-transcription PCR with primers flanking the calmodulin-binding region of rat PMCA. The expression pattern of PMCA 1 and 2 was conserved in different species and islet-cell types since both rat and human islets of Langerhans and all cell lines tested contained the 1b and 2b forms. PMCA 4 isoform subtypes, however, were expressed in a cell-type-specific manner since beta-cells expressed PMCA 4b only, whereas in islets of Langerhans, which contain alpha, beta, delta and polypeptide-secreting cells, PMCA 4a and 4b were simultaneously present. No evidence was obtained for the expression of PMCA 3. Characterization of the beta-cell Ca2+-pump protein showed that it shared several similarities with the erythrocyte PMCA. It is a P-type ATPase; its phosphorylated intermediate was stabilized by La3+; it reacted with a PMCA-specific antibody; and it was not N-glycosylate. However, the beta-cell PMCA had a higher molecular mass than that of the erythrocyte; this difference could be explained by either predominant translation of the PMCA2 form, which has a molecular mass 3-8 kDa higher than the erythrocyte PMCA 1 and 4 proteins, or by a possible sequence insertion. Thus a unique combination of functionally distinct PMCA isoforms (1b, 2b, 4b) participates in Ca2+ homoeostasis in the beta-cell.