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

本工作旨在阐明parchorin的生理功能，我们最近纯化和克隆。Parchorin在参与各种组织中的水运动的细胞中特异性表达，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parchorin的含量增加，而下颌下腺中没有。在乳腺中，parchorin的表达是更大的哺乳期兔相比，怀孕的兔子。细胞分布和表达的变化表明parchorin在参与水分运动的细胞中起重要作用。Parchorin被认为与刺激有关，从细胞质转移到质膜。为了阐明易位机制，我们开发了一个模型系统，其中GFP-parchorin在MDCK细胞中表达。当用ATP或缓激肽刺激汇合细胞时，parchorin通过钙和蛋白激酶C介导的途径转运到质膜。我们还发现酪蛋白激酶II磷酸化parchorin的Ser 83，338和393。parchorin的突变分析表明，这些残基的磷酸化导致蛋白质的稳定。

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.