Activation of PTPN2/TCPTP phosphatase: effects on cells of the immune system

Abstract

Protein tyrosine phosphatases (PTPs) regulate signaling and other biochemical processes through dephosphorylation of proteins at the tyrosine residue; disruption of their functioning may lead to serious diseases and disorders. Within the class I of cysteine-based PTPs, PTPRC (or CD45) is a prototype of the entire superfamily and identified as the initial link between phosphatases and the immune system. This application is focused on the protein tyrosine phosphatase N2 (PTPN2), also known as T-cell protein tyrosine phosphatase (TCPTP), which is highly homologous to PTP1B, the first non-receptor PTP identified (PTPN1). PTPN2 is an important regulator of immune cell signaling, from mouse models to human diseases, since it is a JAK-STAT pathway phosphatase ubiquitously expressed but with high expression in hematopoietic tissues. Loss of function polymorphisms of PTPN2 increase the risk of type 1 diabetes (T1D) and rheumatoid arthritis (RA) and overexpression of PTPN2 reduces inflammation in diabetic nephropathy. Recently, Dr. Nunzio Bottini's group showed that mice carrying reduced expression of PTPN2 which models the loss of function found in PTPN2-variant carrying patients, have increased severity of RA via destabilization of a disease-protective immune population of cells. These results suggested PTPN2 activation could be therapeutic in RA patients and probably other autoimmune diseases. Conversely to PTP inhibitors widely explored in the last years, the discovery of PTP activators is an incipient field of exploration for these enzymes. Thus, this project aims to investigate potential PTPN2-activating mutations identified based on similarities between the structure of PTP1B and PTPN2 and then test them in vitro as putative gain of function. Next, we will assess the effect of the mutations in key signaling pathways regulated by PTPN2 by using immune cell lines subjected to CRISPR/Cas-mediated mutation of PTPN2 under conditions of pro-inflammatory cytokines stimulation. Finally, we also plan to screen libraries of compounds searching for direct activators of PTPN2 in in vitro and possibly in cell models. The outcomes from this study will certainly establish a translational correlation between activators of PTPN2 and human immune diseases with potential therapeutic applications. (AU)