Analysis of the physiological function of a newly discovered protein, parchorin, specifically expressed in water-secreting cells

这项工作是为了阐明parchorin的生理功能，我们最近纯化并克隆了parchorin。Parchorin在各种组织中参与水运动的细胞中特异性表达，如外分泌腺导管细胞、纤毛体、内耳、肾小管等。断奶后胃黏膜的parchorin含量增加，而下颌腺的parchorin含量没有增加。在乳腺中，泌乳兔的parchorin表达量高于妊娠兔。细胞分布和表达变化表明parchorin在细胞参与水分运动中起重要作用。Parchorin被认为与刺激有关，从细胞质溶胶转移到质膜。为了阐明易位机制，我们建立了一个模型系统，其中GFP-parchorin在MDCK细胞中表达。当融合细胞受到ATP或缓激肽刺激时，parchorin通过钙和蛋白激酶c介导的途径转移到质膜上。我们还发现酪蛋白激酶II磷酸化parchorin的83、338和393号丝氨酸。parchorin的突变分析表明，这些残基的磷酸化导致了蛋白质的稳定。

This work was conducted to elucidate the physiological function of parchorin, which we recently purified and cloned. Parchorin is specifically expressed in cells participating water movement in various tissues, I.e., ductal cells of exocrine glands, ciliary body, inner ear, renal tubules, etc. The amount of parchorin in the gastric mucosa, but not in the submandibular glands, increased after weaning. In the mammary gland, parchorin expression was greater in a lactating rabbit compared with a pregnant rabbit. The cellular distribution and changes in expression indicate that parchorin plays an important role in the cells participating water movement. Parchorin was suggested to translocate from cytosol to plasma membrane in association with stimulation. To elucidate the translocation mechanism, we developed a model system where GFP-parchorin was expressed in MDCK cells. When confluent cells were stimulated with ATP or bradykinin, parchorin translocated to the plasma membrane by calcium and protein kinase C-mediated pathway. We also found casein kinase II phosphorylates parchorin on its Ser83, 338, and 393. Mutational analysis of parchorin revealed that the phosphorylation of these residues resulted in the stabilization of the protein.