Cloning and functional study of porcine parotid hormone, a novel proline-rich protein.

A parotid gland hormone that stimulates intradentinal fluid movement is believed to play a significant role in maintaining the vitality of dentin. This hormone has been purified from porcine parotid glands and partially sequenced in our previous study (Tieche, J. M., Leonora, J., and Steinman, R. R. (1980) Endocrinology 106, 1994-2005). We now report the cloning and functional study of porcine cDNAs that code for this hormone and its complete amino acid sequence. Three cDNA clones were isolated from a porcine parotid cDNA library. The last 30 amino acids encoded by two of the cDNAs agreed with the amino acid sequence of the isolated parotid hormone. In situ hybridization and immunohistochemical staining demonstrated that the acinar cells of the parotid glands were the primary location for both the parotid hormone-related mRNAs and the translation products. A 216-bp fragment of the cDNA that contains the coding sequence for the porcine hormone was subcloned into an expression vector, and the protein expression was detected by immunoblot analysis and quantified by enzyme-linked immunosorbent assay. In addition, the 30-amino acid parotid hormone was synthesized. Both the expressed and the synthetic proteins were biologically active in that they enhanced intradentinal fluid movement as measured by intradentinal dye penetration.