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

人们已经认识到，除了离子渗透外，各种生理功能还可以受到阴离子通道(CFTR，ClC等)的调节。在细胞膜上表达。其中，CLCA蛋白具有多种功能，在分泌、细胞黏附、分化和肿瘤抑制等方面发挥作用。我们假设rCLCA与接头或支架蛋白形成不同的分子复合体(转运体)来发挥这种多功能。我们发现，大鼠CLCA同源物的全长(rCLCAl-f)负责调节依赖于Ca^&lt；2&gt；的Cl~-转运。最近，我们提出了rCLCA1-f在大鼠下颌下腺(SMG)导管系统跨上皮氯离子转运中的生理作用的体内证据。这种异构体在早期和循环中的内体中表达，并用其特定的标记进行标记。然后，我们描述了大鼠rCLCA剪接异构体(rCLCAl-t)的独特表达和生理功能。RCLCA1-t比rCLCA1-f更大程度地削弱了细胞的黏附，并与RACK1(活化C激酶受体)有关，据报道RACK1与β_1-整合素相互作用，促进细胞黏附。免疫组织化学显示rCLCA1-t定位于大鼠SMG排泄管基底层未分化细胞的核周区。这些结果表明，rCLCA mRNA的细胞特异性剪接可能是由于上皮细胞之间形成了不同类型的转运体而导致了生理功能的差异。

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.