| Research Abstract |
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.
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