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我们最近纯化和克隆的Parclin的生理功能。Parclin特异性地表达于各种组织中参与水分运动的细胞，即外分泌腺、睫状体、内耳、肾小管等的导管细胞。断奶后，胃粘膜中Parclin的含量增加，但颌下腺中Parclin的含量没有增加。在乳腺中，与怀孕的兔子相比，哺乳期的兔子的parclin表达更多。细胞的分布和表达的变化表明，副花青素在细胞参与水分运动中起着重要作用。Parclin被认为是在刺激时从胞浆转移到质膜上。为了阐明转位机制，我们建立了一个在MDCK细胞中表达GFP-parclin的模型系统。当融合细胞被三磷酸腺苷或缓激肽刺激时，parclin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在其Ser83、338和393上磷酸化Parclin。Parclin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.