Protein tyrosine phosphatase N2 regulates TNFα-induced signalling and cytokine secretion in human intestinal epithelial cells.
ABSTRACT The Crohn's disease (CD) susceptibility gene, protein tyrosine phosphatase N2 (PTPN2), regulates interferon γ (IFNγ)-induced signalling and epithelial barrier function in T₈₄ intestinal epithelial cells (IECs). The aim of this study was to investigate whether PTPN2 is also regulated by tumour necrosis factor α (TNFα) and if PTPN2 controls TNFα-induced signalling and effects in IECs.
T₈₄ IECs were used for all cell studies. Protein levels were assessed by western blotting, mRNA levels by reverse transcription-PCR (RT-PCR) and cytokine levels by ELISA. PTPN2 knock-down was induced by small interfering RNA (siRNA). Imaging was performed by immunohistochemistry or immunofluorescence.
TNFα treatment elevated PTPN2 mRNA as well as nuclear and cytoplasmic protein levels and caused cytoplasmic accumulation of PTPN2. Biopsy specimens from patients with active CD showed strong immunohistochemical PTPN2 staining in the epithelium, whereas samples from patients with CD in remission featured PTPN2 levels similar to controls without inflammatory bowel disease (IBD). Though samples from patients with active ulcerative colitis (UC) revealed more PTPN2 protein than non-IBD patients and patients with UC in remission, their PTPN2 expression was lower than in active CD. Samples from patients with CD in remission and responding to anti-TNF treatment also showed PTPN2 levels that were similar to those in control patients. Pharmacological inhibition of nuclear factor-κB (NF-κB) by BMS-345541 prevented the TNFα-induced rise in PTPN2 protein, independent of apoptotic events. PTPN2 knock-down revealed that the phosphatase regulates TNFα-induced extracellular signal-regulated kinase 1/2 (ERK1/2) and p38 phosphorylation, without affecting c-Jun N-terminal kinase (JNK), inhibitor of κB (IκB) or NF-κB phosphorylation. Loss of PTPN2 potentiated TNFα-induced secretion of interleukin 6 (IL-6) and IL-8. In TNFα- and IFNγ-co-treated cells, loss of PTPN2 enhanced protein expression of inducible nitric oxide synthase (iNOS).
TNFα induces PTPN2 expression in IECs. Loss of PTPN2 promotes TNFα-induced mitogen-activated protein kinase signalling and the induction of inflammatory mediators. These data indicate that PTPN2 activity could play a crucial role in the establishment of chronic inflammatory conditions in the intestine, such as CD.
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ABSTRACT: Crohn's disease (CD) is characterized by a breakdown of the intestinal epithelial barrier function leading to an uncontrolled immune response to bacterial antigens. Available data demonstrate that appropriate response and early host defense against invading bacteria are crucial to maintain tolerance towards commensal bacteria. When the mechanisms of early removal of invading bacteria are disturbed, a loss of tolerance and a full-blown adaptive immune reaction, which is mounted against the usually harmless commensal flora, are induced. Dysfunction of autophagy caused by genetic variations within CD susceptibility genes, such as ATG16L1 and IRGM, results in defective handling of intracellular and invading bacteria and causes prolonged survival and defective clearance of those microbes. Dysfunction of ATG16L1 and IRGM has also been shown to cause aberrant Paneth cell function and uncontrolled secretion of proinflammatory cytokines finally resulting in increased susceptibility to bacterial infection and the onset of colitis. Interestingly, autophagy can also be regulated by other CD susceptibility genes, such as NOD2 (nucleotide oligomerization domain 2) or PTPN2 (protein tyrosine phosphatase nonreceptor type 2) and the presence of the CD-associated variations within these genes results in similar effects. Taken together, more and more evidence suggests a close functional correlation between loss of tolerance and defective autophagy in CD patients. Therefore, most likely, the onset of CD is triggered by both a loss of tolerance as well as a dysfunction of autophagy, which finally results in the onset of chronic intestinal inflammation. © 2014 S. Karger AG, Basel.Digestive Diseases 01/2014; 32(4):370-7. DOI:10.1159/000358140 · 1.83 Impact Factor
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ABSTRACT: : Technological advances in the large scale analysis of human genetics have generated profound insights into possible genetic contributions to chronic diseases including the inflammatory bowel diseases (IBDs), Crohn's disease and ulcerative colitis. To date, 163 distinct genetic risk loci have been associated with either Crohn's disease or ulcerative colitis, with a substantial degree of genetic overlap between these 2 conditions. Although many risk variants show a reproducible correlation with disease, individual gene associations only affect a subset of patients, and the functional contribution(s) of these risk variants to the onset of IBD is largely undetermined. Although studies in twins have demonstrated that the development of IBD is not mediated solely by genetic risk, it is nevertheless important to elucidate the functional consequences of risk variants for gene function in relevant cell types known to regulate key physiological processes that are compromised in IBD. This article will discuss IBD candidate genes that are known to be, or are suspected of being, involved in regulating the intestinal epithelial barrier and several of the physiological processes presided over by this dynamic and versatile layer of cells. This will include assembly and regulation of tight junctions, cell adhesion and polarity, mucus and glycoprotein regulation, bacterial sensing, membrane transport, epithelial differentiation, and restitution.Inflammatory Bowel Diseases 10/2014; 20(10):1829-1849. DOI:10.1097/MIB.0000000000000090 · 5.48 Impact Factor