Abstract. P-cadherin is a subclass of Ca2+-dependent cell-cell adhesion molecules present in mouse placenta, where its localization suggests a function of connecting the embryo to the uterus (Nose, A., and M. Takeichi. 1986. J. Cell Biol. 103:2649-2658. We recently identified a human cadherin detected by an mAb capable of disrupting cell-cell adhesion of A-431 cells, and found that it was closely related immunochemically to mouse P-cadherin. Curiously, this cadherin was undetectable in human placenta by immunohistochemical examination (Shimoyama, Y., S. Hirohashi, S. Hirano, M. Noguchi, Y. Shimosato, M. Takeichi, and O. Abe. 1989. Cancer Res. 49:2128-2133. We here report the cloning and sequencing of a cDNA clone encoding the human homologue of mouse P-cadherin. The deduced amino acid sequence of the human P-cadherin consists of 829 amino acids and shows striking homology with mouse P-cadherin. On Northern blot analysis, human P-cadherin was scarcely expressed in human placenta in contrast to mouse P-cadherin, which was abundantly expressed in mouse placenta throughout pregnancy, and it was shown that E-cadherin, but not P-cadherin, was the major cadherin molecule in human placenta. Moreover, NIH3T3 cells transfected with human P-cadherin cDNA expressed the functional cadherin molecule, which was identical to the cadherin we had previously identified using the mAb, showing that this molecule really does mediate cell-cell adhesion and that the cadherin we detected immunochemically is undoubtedly human P-cadherin. The results obtained in this study support the idea that P-cadherin plays little role, if any, in Ca2+-dependent cell-cell binding in human placental tissue at least after several weeks of pregnancy.
CADHERINS are integral membrane glycoproteins responsible for Ca2+-dependent cell-cell adhesion. At present it is known that they constitute a gene family consisting of at least three subclasses, E-, N-, and P-cadherin. In developing embryos, each subclass shows a unique spatiotemporal pattern of expression that coincides with the movement and rearrangement of cell collectives, suggesting that cadherins play a key role in morphogenetic events (for review, see reference 22). Recent studies using cells transfected with cadherin cDNAs have demonstrated experimentally that cadherin molecules are directly involved in ceU-ceU binding (2, 15), and that they can control cell sorting in vitro (18). Their cell-cell binding function is mediated not by a ligand-receptor complex but occurs in a homophilic manner (2) in cooperation with certain cytoskeletal components (15).We recently reported the establishment of two mAbs recognizing two human cadherins, which are distinct from each other in terms of immunological specificity, molecular weight, and tissue distribution (20). One of them showed a broad spectrum of expression in epithelial tissues with few exceptions, and was subsequently identified as human E-cadherin, which is possibly identical to cell-CAM 120/80 (1). In contrast, the tissue distribution of the other ca...