词条 | Polymeric immunoglobulin receptor |
释义 |
StructurepIgR is produced among others by intestinal epithelial cells (IECs) and bronchial epithelial cells. pIgR belongs to the family of type I transmembrane proteins. The extracellular portion of the protein contains 6 domains: 5 evolutionary conserved immunoglobulin-like domains, and 1 non-homologous domain, which is involved in proteolytic cleavage of pIg-pIgR complex from the apical side of the IECs. The quite long intracellular domain of the receptor, alongside with the transmembrane region, is responsible for the transduction of highly conserved signals.[3][4] During transcytosis, an essential part of pIgR, the secretory component, is attached to the ligand and later cleaved with the ligand to form fully functioning secreted IgA.[5] FunctionPolymeric immunoglobulin receptor is responsible for transcytosis of soluble dimeric IgAs and immune complexes from the basolateral to the apical mucosal epithelial cell surface. pIgR has a strong specificity to polymeric immunoglobulins and is not responsive to monomeric immunoglobulin.[6] The ligand’s J-chain is responsible for the binding of pIgR to its ligand.[3][5] TranscytosisThe process of transporting polymeric immunoglobulins from the basolateral to apical side, known as transcytosis, is composed of several distinct steps. Transcytosis is initiated by either the binding of dimeric IgA to the receptor or the phosphorylation of Ser-664 residue of the receptor.[4] The internalization of both free and IgA-bound pIgR is mediated by clathrin coating. The internalized receptor is transported to basolateral early endosomes. The following step of transporting the pIgR across the cell (through tubulo-vesicular compartments to apical recycling endosome) is dependent on microtubules.[4] When pIgR reaches the apical membrane, proteolytic cleavage generates either a free secretory component of SC-IgA complex , which is released to the apical lumen.[3] Cleavage occurs at the junction of the transmembrane region of the receptor and domain 5.[2] Elimination of Immune ComplexespIgRs are capable of capturing IgA bound to an antigen (Immune complexes (ICs)) with identical affinity as IgA and transport them to apical side. ICs result from the capture of an antigen by an antibody. IgA ICs are formed within the mucous membranes in response to foreign invasion.[7] The accumulation of ICs on the basolateral side of mucous layers can have detrimental effects. Transcytosis of IgA ICs from the formation sites represents an important mechanism of eliminating circulating antigens and minimizing their negative effects.[7][8] RegulationCytokinetic RegulationThe expression of pIgR is critically regulated by the pro-inflammatory cytokines, such as IL-1, IL-4, TNF-α, and IFN-γ. The transcriptional regulation by different cytokines proceeds though similar pathways, involving the NF-kB feedback loop. Interaction of IL-1 and TNF-α with their receptors ultimately lead to transcriptional activation of PIGR gene due to nuclear translocation of NF-kB. NF-kB interacts with intron 1 of the PIGR gene to start pIgR mRNA synthesis.[2] Besides NF-kB pathway, the transcriptional induction also proceeds in response to IFN-γ, upregulating the expression of pIgR.[2][3] Additionally, instead of the usual antagonistic behavior, IL-4 acts synergistically with IFN-γ to induce pIgR transcription. Their combination exhibits an upregulating effect in PIGR expression because of the presence of STAT6 enhancer, the main downstream effector of IL-4, binding site in PIGR Hormonal RegulationThe level of pIgRs in the mucosal reproductive tract is highly dependent on the activity of sex hormones and correlates with estrous cycle phases. The peaks of pIgR expression at proestrus and estrus phases are due to the dominant activity of estrogen, which acts as a pIgR agonist. The low levels of pIgR during the diestrus are linked to the downregulating activity of progesterone, which peaks during this phase and is able to reverse the activity of estrogen.[10] Androgens are the agonists of pIgR expression in both male and female reproductive tissues.[2] 5’-flanking region of the Pigr gene contains a response element to glucocorticoids. This class of hormones increases the steady mRNA expression levels of pIgR of intestinal cells.[9][11] Prolactin elevates the levels of IRF-1 via Jak-STAT pathway. IRF-1 is known to be a direct agonist of pIgR expression. Considering this linkage, prolactin is believed to exhibit indirect upregulation of pIgR levels during pregnancy and lactation.[2]Pathogenic StimulationIECs express a variety of Toll-like receptors (TLRs), activation of which ultimately leads to the pIgR upregulation during the infection.[2][3] The most prominent modulators of pIgR regulation consist of TLR4 and TLR3, which recognize bacterial lipopolysaccharide and viral dsRNA respectively. TLR4, like the majority of TLRs, transduce the signal though MyD88 adaptor and execute the function via NF-kB, which stimulates the expression of pIgR by binding to intron 1 of the gene. TLR3, on the other hand, involves the regulation by the means of IRF-1, which is able to promote the transcription of PIGR gene by binding to exon 1.[9][11] References1. ^{{cite web|url=https://www.ncbi.nlm.nih.gov/sites/entrez?Db=gene&Cmd=ShowDetailView&TermToSearch=5284|title=Entrez Gene: PIGR polymeric immunoglobulin receptor|access-date=}} 2. ^1 2 3 4 5 6 7 {{cite journal | vauthors = Kaetzel CS | title = The polymeric immunoglobulin receptor: bridging innate and adaptive immune responses at mucosal surfaces | journal = Immunological Reviews | volume = 206 | pages = 83–99 | date = August 2005 | pmid = 16048543 | doi = 10.1111/j.0105-2896.2005.00278.x }} 3. ^1 2 3 4 5 {{cite journal | vauthors = Asano M, Komiyama K | title = Polymeric immunoglobulin receptor | journal = Journal of Oral Science | volume = 53 | issue = 2 | pages = 147–56 | date = June 2011 | pmid = 21712618 }} 4. ^1 2 {{cite journal | vauthors = Mostov K | title = The polymeric immunoglobulin receptor | journal = Seminars in Cell Biology | volume = 2 | issue = 6 | pages = 411–8 | date = December 1991 | pmid = 1813030 }} 5. ^1 {{Cite book|url=http://www.worldcat.org/title/kuby-immunology/oclc/820117219|title=Kuby immunology|last=Owen|first=Judith A|last2=Punt|first2=Jenni|last3=Stranford|first3=Sharon A|last4=Jones|first4=Patricia P|last5=Kuby|first5=Janis|date=2013|publisher=W.H. Freeman|isbn=9781429219198|location=New York|language=English}} 6. ^{{cite journal | vauthors = Kaetzel CS, Blanch VJ, Hempen PM, Phillips KM, Piskurich JF, Youngman KR | title = The polymeric immunoglobulin receptor: structure and synthesis | journal = Biochemical Society Transactions | volume = 25 | issue = 2 | pages = 475–80 | date = May 1997 | pmid = 9191139 | doi = 10.1042/bst0250475 | url = http://www.biochemsoctrans.org/content/25/2/475 }} 7. ^1 {{cite journal | vauthors = Kaetzel CS, Robinson JK, Chintalacharuvu KR, Vaerman JP, Lamm ME | title = The polymeric immunoglobulin receptor (secretory component) mediates transport of immune complexes across epithelial cells: a local defense function for IgA | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 88 | issue = 19 | pages = 8796–800 | date = October 1991 | pmid = 1924341 }} 8. ^{{cite journal | vauthors = Phalipon A, Corthésy B | title = Novel functions of the polymeric Ig receptor: well beyond transport of immunoglobulins | journal = Trends in Immunology | volume = 24 | issue = 2 | pages = 55–8 | date = February 2003 | pmid = 12547499 }} 9. ^1 2 {{cite journal | vauthors = Johansen FE, Kaetzel CS | title = Regulation of the polymeric immunoglobulin receptor and IgA transport: new advances in environmental factors that stimulate pIgR expression and its role in mucosal immunity | journal = Mucosal Immunology | volume = 4 | issue = 6 | pages = 598–602 | date = November 2011 | pmid = 21956244 | pmc = 3196803 | doi = 10.1038/mi.2011.37 }} 10. ^{{cite journal | vauthors = Kaushic C, Richardson JM, Wira CR | title = Regulation of polymeric immunoglobulin A receptor messenger ribonucleic acid expression in rodent uteri: effect of sex hormones | journal = Endocrinology | volume = 136 | issue = 7 | pages = 2836–44 | date = July 1995 | pmid = 7789308 | doi = 10.1210/endo.136.7.7789308 }} 11. ^1 {{cite journal | vauthors = Kaetzel CS | title = Cooperativity among secretory IgA, the polymeric immunoglobulin receptor, and the gut microbiota promotes host-microbial mutualism | journal = Immunology Letters | volume = 162 | issue = 2 Pt A | pages = 10–21 | date = December 2014 | pmid = 24877874 | pmc = 4246051 | doi = 10.1016/j.imlet.2014.05.008 }} Further reading{{refbegin | 2}}
External links
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