Molecular mechanism of "transportsomes" involved in Ca^<2+-> activated Cl^- transport

人们已经认识到，除离子渗透外，各种生理功能都可以通过阴离子通道（CFTR，CLC等）进行调节。在细胞膜上表达。其中，CLCA蛋白已被证明是多功能的，具有例如分泌、细胞粘附、分化和肿瘤抑制作用的作用。我们假设rCLCA与衔接蛋白或支架蛋白形成不同的分子复合物（转运体）来发挥这种多功能。我们发现大鼠CLCA同源物（rCLCAl-f）的全长负责调节Ca^2+依赖性Cl^-转运。最近，我们提出了rCLCA 1-f在大鼠下颌下腺（SMG）导管系统跨上皮Cl^-转运中的生理作用的体内证据。这种异构体在由其特异性标记物标记的早期和再循环内体中表达。然后，我们描述了一个独特的表达和生理功能的剪接异构体的大鼠rCLCA（rCLCAl-t）。与rCLCAl-f相比，rCLCAl-t对细胞粘附的抑制作用更强，并与RACK 1（receptor for activated C kinase）结合，后者与β_1-integrin相互作用，促进细胞粘附。免疫组化显示rCLCA 1-t位于大鼠SMG排泄管基底未分化细胞的核周区域。这些表明，rCLCA mRNA的细胞特异性剪接可能有助于生理功能的差异，可能是由于上皮细胞之间形成不同类型的转运体。

It has been recognized that various physiological function, in addition to ion permeation, can be regulated by anion channels (CFTR, CLC etc.) expressed on cell membrane. Among them, CLCA proteins have been shown to be multifunctional, with roles in, for example, secretion, cell adhesion, differentiation, and tumor suppressing action. We hypothesized that rCLCA make distinct molecular complexes (transportsome) with adaptor or scaffold proteins to exert such multifunctions. We found that full-length of a rat CLCA homologue (rCLCAl-f) is responsible for modulating Ca^<2+>-dependent Cl^- transport. More recently, we presented in vivo evidence of a physiological role for rCLCA1-f in transepithelial Cl^- transport in the ductal system of rat submandibular gland (SMG). This isoform was expressed in early and recycling endosomes labeled by their specific markers. We then described a distinct expression and physiological function of a splicing isoform of rat rCLCA (rCLCAl-t). rCLCAl-t weakened cell attachment to a greater extent than rCLCAl-f did, and was found to associate with RACK1 (receptor for activated C kinase) which is reported to interact with β_1-integrin and to promote cell adhesion. Immunohistochemistry revealed rCLCA1-t to be located in the perinuclear region of the basal, undifferentiated cells of the rat SMG excretory duct. These suggest that cell-specific splicing of rCLCA mRNA may contribute to the differences in physiological function probably due to formation of distinct types of transportsome among epithelial cells.