The Research On Two New Functions Of Glycoprotein PIgR

Polymeric immunoglobulin receptor (pIgR) belongs to type I trans-membrane glycoprotein. It could specifically bind to polymeric IgA or polymeric IgM, and transport them into the secretion via the process of transcytosis. On basal to apical transport across epithelial cells, the pIgR extracellular domain is cleaved, releasing secreotry component (SC) in association with pIgA. pIgR can mediate the transcytosis of polymeric IgA, and thus ensure the multiple functions of sIgA, such as luminal prevention of pathogen attachment, intracellular neutralization of viruses, and antigen secretion from lamina propria. Thus, efficient secretion of pIgR is a prerequisite of polymeric IgA-mediated mucoscal protection.pIgR is always expressed in all types of secretory epithelia, with the highest levels observed in the intestine. In human small intestine, pIgR is expressed predominantly on immature cells within crypts and at lower levels on the villi cells. The localization of pIgR and IgA suggest that absorptive columnar cells, but not other cells, are primarily responsible for sIgA secretion into the intestine. Accordingly, it is generally accepted that it is the absorptive columnar cells but not other cells, including Paneth, goblet, or endocrine cells, that account for the synthesis of the pIgR, transportation of IgA, and secretion of sIgA in the small intestine. However, it was showed that positive staining of pIgR is specifically localized in Paneth cells of the rat small intestine, which suggested the possible relationship of Paneth cells and pIgR. Paneth cells are pyramidal epithelial cells found at the base of the crypts of Lieberkühn in the small intestines of many mammalian species. Paneth cells have been commonly recognized as important effectors of intestinal innate immunity. Resent researches showed that Paneth cells were involved in intestinal inflammation. Whether Paneth cells can synthesize pIgR and participate in IgA transportation or not is an important issue for the research work of IBD. It will be helpful for the improvement of clinical therapy of IBD.Firstly, the techniques of molecular biology was use to synthesize the specific digoxigenin-labeled cRNA probe of rat and human pIgR. Then, with the specific marker of Paneth cells- lysozyme, double-labeled fluorescent immunohistochemistry and double-labeled fluorescent in situ hybridization were used to determine RNA and protein expression in rat and human small intestine. Our results showed that pIgR mRNA and protein could be detected in rat and human Paneth cells, suggested that Paneth cells could synthesize pIgR. Another noteworthy finding is that, in humans, pIgR is expressed both in absorptive cells and Paneth cells, but in rats, it is found only in Paneth cells.Although pIgR plays an essential role in mucosal immunity, it was still reported to have varied functions in the body. Previous studies indicated that pIgR was over-expressed in some epithelial tumor tissues or cells, which suggested that there might be some relationship between pIgR and epithelial tumor. But the relationship is still unclear now. Whether or not pIgR will be used as a specific marker of tumor, or will be treated as a molecular target of anti-tumor medicines hasn't been reported. It will be useful to investigate and illustrate the important role of pIgR in tumorgenesis.Firstly, MDCK- hpIgR cells which over-express human pIgR was successfully constructed with the technique of transfection. Then, the common characters of MDCK-hpIgR cells and MDCK-mock cells were detected and compared. It was shown that MDCK-hpIgR cells proliferate more quickly than MDCK-mock cells. Moreover, the shape of these cells changed significantly and they were digested easily from the flat. The cell proliferation was detected using flow cytometry, western blotting and other techniques. The results showed that MDCK-hpIgR cells have the characters of high proliferation index, increasing expression of PCNA and increasing phosphorylation of ERK1/2. Flat clone experiments confirmed that over-expression of human pIgR made MDCK cells have malignant proliferation. In mechanism of the shape change and the decrease of adhesion, the epithelial mesenchymal transition always plays an important role. EMT is the process of polar epithelia transforming into the cells capable of free movement. The main characters of EMT include the decrease of E-cadherin, the different cell framework, and the shape of mesenchymal cells. This transition allows the tumor cells shake off the cell-cell connection and to be more invadable. The results showed that the cell shape and framework formed by F-actin of MDCK-hpIgR were similar as mesenchymal cells. Over-expression of human pIgR inhibited the adhesion of MDCK cells on fibronectin, and promoted migration and invasion of them. In addition, MDCK-hpIgR cells have the molecular character of EMT- decrease expression of E-cadherin. The degree of cell malignant was tested by the soft agar clone experiment. It was shown that, in vivo, over-expression of human pIgR could promote the cells gain the ability of tumor formation. These results indicated that over-expression of human pIgR made MDCK cells have the characters of malignant proliferation and EMT, and finally be the malignant cells.In sum, Paneth cells may play a critical role in IgA-mediated acquired immunity in the gastrointestinal tract in addition to their well-recognized role in innate immunity. This will add to the accumulating evidences that Paneth cells are involved in intestinal inflammation, and, therefore, support a potential role in mucosal inflammation-driven pathologic disorders in humans. Furthermore, the new finding that over-expression of human pIgR made MDCK cells become into malignant cells, will be helpful for the future researches that promote pIgR to be a new molecular target of anti-cancer medicines.