Mutant Protein Tyrosine Phosphatase Non-Receptor Type 2 Increases Permeability of Intestinal Epithelial Barrier Function

Mutations in Protein Tyrosine-Phosphatase Non-Receptor Type 2 (PTPN2) were found by Genome-Wide Association Studies (GWAS) to be associated with the onset and progression of the chronic intestinal inflammatory conditions, Crohn's disease and ulcerative colitis, collectively known as Inflammatory Bowel Disease (IBD). PTPN2 negatively regulates signaling pathways induced by the pro-inflammatory cytokine interferon-gamma (IFN- [gamma]). IFN-[gamma] is clinically important due to its critical role in IBD pathogenesis, which includes increasing permeability of the intestinal epithelial lining. A recent study by our laboratory demonstrated that PTPN2 knock-down in intestinal epithelial cells permits enhanced signaling by IFN-[gamma], and increased permeability of epithelial monolayers. Specifically, increased phosphorylation of downstream signaling targets such as signal transducer and activator of transcription-1 (STAT1) was observed, accompanied by enhanced expression of an IBD-associated pore-forming protein, claudin-2 (CLD2), that increases epithelial barrier permeability. Here, I detail the production of a cell line that stably expresses dominant-negative TC45 (a splice-variant of PTPN2) via lentiviral transduction, in order to better evaluate the consequences of dysfunctional PTPN2 regulation. I observed trafficking disturbances in the TC45 mutant potentially providing an explanation for dysregulation of PTPN2 and its link to barrier dysfunction. My results support earlier findings of increased phosphorylated STAT1 and subsequent increase in CLD-2. The cell line also displays a concurrent decrease in matriptase-1, a protease responsible for rapid turnover of CLD-2, indicating that this normally protective pathway is TC45-dependent. These studies offer new insights into the mechanisms through which PTPN2 mutations may explain in part the pathophysiological features of chronic IBD