IRBIT, an inositol 1,4,5-trisphosphate receptor-binding protein, specifically binds to and activates pancreas-type Na+/HCO3- cotransporter 1 (pNBC1)
IRBIT, an inositol 1,4,5-trisphosphate receptor-binding protein, specifically binds to and activates pancreas-type Na+/HCO3- cotransporter 1 (pNBC1)
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DOI：
10.1073/pnas.0602250103
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发表时间：
2006-06-20
影响因子：
11.1
通讯作者：
Mikoshiba, Katsuhiko
中科院分区：
文献类型：
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作者：
Shirakabe, Kyoko;Priori, Giuseppina;Mikoshiba, Katsuhiko
肌醇1,4,5-三磷酸（IP3）受体（IP(3)Rs）是位于细胞内Ca2+储存的IP3门控Ca2+通道。我们之前发现了一个IP3R结合蛋白，称为IP3R结合蛋白与IP3释放（IRBIT）。由于IP3的生理浓度会使IRBIT从IP3R中释放出来，因此我们假设IRBIT是IP3R中释放的一种信号分子，并根据IP3的产生调节下游靶分子。因此，在本研究中，我们尝试鉴定IRBIT的靶分子，并成功鉴定出Na+/HCO(3)（-）共转运体1 （NBC1）为IRBIT结合蛋白。在NBC1的两个主要剪接变体，胰腺型NBC1 （pNBC1）和肾型NBC1 （kNBC1）中，IRBIT被发现特异性结合pNBC1而不结合kNBC1。IRBIT结合到n端pnbc1特异性结构域，其结合依赖于IRBIT多个丝氨酸残基的磷酸化。此外，对非洲爪蟾卵母细胞的电生理分析表明，pNBC1需要IRBIT的共表达才能表现出与kNBC1相当的实质性活性，而kNBC1则独立于IRBIT表现出实质性活性。这些结果强烈提示pNBC1是IRBIT的靶分子，IRBIT通过pNBC1在pH调节中发挥重要作用。此外，我们的研究结果提出了通过IRBIT调节NBC1变体具有不同生理作用的可能性。
Inositol 1,4,5-trisphosphate (IP3) receptors (IP(3)Rs) are IP3-gated Ca2+ channels that are located on intracellular Ca2+ stores. We previously identified an IP3R binding protein, termed IP3R binding protein released with IP3 (IRBIT). Because IRBIT is released from IP3R by physiological concentrations of IP3, we hypothesized that IRBIT is a signaling molecule that is released from IP3R and regulates downstream target molecules in response to the production of IP3. Therefore, in this study, we attempted to identify the target molecules of IRBIT, and we succeeded in identifying Na+/HCO(3)(-)cotransporter 1 (NBC1) as an IRBIT binding protein. Of the two major splicing variants of NBC1, pancreas-type NBC1 (pNBC1) and kidney-type NBC1 (kNBC1), IRBIT was found to bind specifically to pNBC1 and not to bind to kNBC1. IRBIT binds to the N-terminal pNBC1-specific domain, and its binding depends on the phosphorylation of multiple serine residues of IRBIT. Also, an electrophysiological analysis in Xenopus oocytes revealed that pNBC1 requires coexpression of IRBIT to manifest substantial activity comparable with that of kNBC1, which displays substantial activity independently of IRBIT. These results strongly suggest that pNBC1 is the target molecule of IRBIT and that IRBIT has an important role in pH regulation through pNBC1. Also, our findings raise the possibility that the regulation through IRBIT enables NBC1 variants to have different physiological roles.