Loss of EP2 receptor subtype in colonic cells compromise epithelial barrier integrity by altering claudin-4.
Prostaglandin E2 (PGE2) is a bioactive lipid mediator that exerts its biological function through interaction with four different subtypes of E-Prostanoid receptor namely EP1, EP2, EP3 and EP4. It has been known that EP2 receptor is differentially over-expressed in the epithelia of inflamed human colonic mucosa. However, the significance of the differential expression in altering epithelial barrier function is not known. In this study, we used Caco-2 cells expressing EP2 receptor, either high (EP2S) or low (EP2A), as a model epithelia and determined the barrier function of these cell monolayers by measuring the trans epithelial resistance (TER). Basal TER of EP2A (but not EP2S) monolayer was significantly lower suggesting a loss of colonic epithelial barrier integrity. In comparison, the TER of wild type Caco-2 was decreased in response to an EP2 receptor specific antagonist (AH-6809) indicating an important role for EP2 receptor in the maintenance of epithelial barrier function. The decrease TER in EP2A monolayer corresponded with a significant loss of the tight junction (TJ) protein claudin-4 without affecting other major TJ proteins. Similarly, EP2 receptor antagonism/siRNA based silencing significantly decreased claudin-4 expression in EP2S cells. Surprisingly, alteration in claudin-4 was not transcriptionally regulated in EP2A cells but rather undergoes increased proteosomal degradation. Moreover, among the TER compromising cytokines examined (IL-8, IL-1β, TNF-α, IFN-γ) only IFN-γ was significantly up regulated in EP2A cells. However, IFN-γ did not significantly decreased claudin-4 expression in Caco-2 cells indicating no role for IFN-γ in degrading claudin-4. We conclude that differential down-regulation of EP2 receptor play a major role in compromising colonic epithelial barrier function by selectively increasing proteosomal degradation of claudin-4.
Department of Microbiology, Immunology and Infectious Diseases, University of Calgary, Calgary, Alberta, Canada.
Manigandan
M
Lejeune
Department of Microbiology, Immunology and Infectious Diseases, University of Calgary, Calgary, Alberta, Canada.
France
F
Moreau
Department of Microbiology, Immunology and Infectious Diseases, University of Calgary, Calgary, Alberta, Canada.
Kris
K
Chadee
D000527:Alprostadil / Q000031:analogs & derivatives / Q000494:pharmacology; D018938:Caco-2 Cells; D002463:Cell Membrane Permeability / Q000187:drug effects; D062506:Claudin-4 / Q000378:metabolism*; D016207:Cytokines / Q000378:metabolism; D015536:Down-Regulation / Q000187:drug effects; D006801:Humans; D007371:Interferon-gamma / Q000378:metabolism / Q000494:pharmacology; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D058307:Receptors, Prostaglandin E, EP2 Subtype / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D019108:Tight Junctions / Q000187:drug effects / Q000378:metabolism; D044004:Xanthones / Q000494:pharmacology
D062506:Claudin-4; D016207:Cytokines; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D058307:Receptors, Prostaglandin E, EP2 Subtype; D044004:Xanthones; C053876:6-isopropoxy-9-oxoxanthene-2-carboxylic acid; D007371:Interferon-gamma; D000527:Alprostadil; C048491:butaprost