Recent advances in the discovery of protein tyrosine phosphatase SHP2 inhibitors

Src homology 2 domain-containing protein tyrosine phosphatase (SHP2) is a non-receptor protein tyrosine phosphatase encoded by the Ptpn11 gene, which regulates cell growth, differentiation and apoptosis via modulating various signaling...

Inhibition of lipid phosphatase SHIP1 expands myeloid-derived suppressor cells and attenuates rheumatoid arthritis in mice

Rheumatoid arthritis (RA) is a debilitating autoimmune disease of unknown cause, characterized by infiltration and accumulation of activated immune cells in the synovial joints where cartilage and bone destructions occur. Myeloid-derived suppressor cells (MDSCs) are of myeloid origin and are able to suppress T cell responses. Src homology 2 domain containing inositol polyphosphate 5-phosphatase 1 (SHIP1) was shown to be involved in the regulation of MDSC differentiation. The purpose of the present study was to investigate the effect of inhibition of SHIP1 on expansion of MDSCs in RA using a collagen-induced inflammatory arthritis (CIA) mouse model. In DBA/1 mice treatment with a small molecule specific SHIP1 inhibitor 3α-aminocholestane (3AC) induced a marked expansion of MDSCs in vivo. Both pre-treatment with 3AC of DBA/1 mice prior to CIA induction and intervention with 3AC during CIA progression significantly reduced disease incidence and severity. Adoptive transfer of MDSCs isolated from 3AC-treated mice, but not naïve MDSCs from normal mice, into CIA mice significantly reduced disease incidence and severity, indicating that the 3AC-induced MDSCs were the cellular mediators of the observed amelioration of the disease. In conclusion, inhibition of SHIP1 expands MDSCs in vivo and attenuates development of CIA in mice. Small molecule specific inhibition of SHIP1 may therefore offer therapeutic benefit to patients with RA and other autoimmune diseases.

Revisiting the Full Spectrum of Helicobacter pylori-Related Gastric Lymphoma

Early stage gastric diffuse large B-cell lymphomas (DLBCLs) with histological features of mucosa-associated lymphoid tissue (MALT) origin (DLBCL[MALT]) are also closely related to Helicobacter pylori (HP) infection, apart from the classical gastric MALT lymphoma, and are cured by HP eradication therapy (HPE). Whether some gastric “pure” DLBCLs (without histological features of MALT) are also HP-related is clinically very important, since this subtype of gastric lymphoma is relatively common in the population and is still universally treated with intensive systemic chemotherapy. A large proportion of early stage gastric “pure” DLBCL can achieve long-term complete remission after HPE. However, the precise mechanisms of HP-dependent (with complete regression of tumors after HPE) lymphomagenesis of gastric “pure” DLBCL, DLBCL(MALT), and MALT lymphoma remain uncertain. In the classical conception, gastric MALT lymphoma is indirectly caused by HP through T-cell stimulation, with the aid of costimulatory molecules. To explore the direct interactions between HP and lymphoma B-cells of HP-dependent gastric MALT lymphoma, DLBCL(MALT), and “pure” DLBCLs, we assessed the participation of HP-encoded cytotoxin-associated gene A (CagA) in the lymphomagenesis of these tumors. We discovered that CagA oncogenic protein and its regulated signaling molecules including phospho-Src homology-2 domain-containing phosphatase (p-SHP-2) and phospho-extracellular signal-regulated kinase (p-ERK) correlated significantly with HP-dependence of gastric MALT lymphoma. This finding supports previous observations that the CagA protein of HP can be translocated into B-cell lymphoma cells, thereby leading to survival signals. Furthermore, we demonstrated that HP-positive and CagA-expressing gastric “pure” DLBCLs behave in a less biologically aggressive manner, and have better clinical outcomes; this is a distinguishing entity, and its cell origin may include germinal center B cells. In addition, we found that the expression of CagA, p-SHP-2, and p-ERK correlated significantly with the HP-dependence of gastric DLBCL(MALT) and “pure” DLBCL. These findings indicate that the spectrum of HP-related gastric lymphomas including MALT lymphoma, DLBCL(MALT), and “pure” DLBCL, is much wider than was previously thought. Further explorations of the spectrum, lymphomagenesis, and therapeutics of HP-related gastric lymphoma are warranted.

The loops of the N-SH2 binding cleft do not serve as allosteric switch in SHP2 activation

The Src-homology-2 domain–containing phosphatase SHP2 is a critical regulator of signal transduction, being implicated in cell growth and differentiation. Activating mutations cause developmental disorders and act as oncogenic drivers in hematologic cancers. SHP2 is activated by phosphopeptide binding to the N-SH2 domain, triggering the release of N-SH2 from the catalytic PTP domain. Based on early crystallographic data, it has been widely accepted that opening of the binding cleft of N-SH2 serves as the key “allosteric switch” driving SHP2 activation. To test the putative coupling between binding cleft opening and SHP2 activation as assumed by the allosteric switch model, we critically reviewed structural data of SHP2, and we used extensive molecular dynamics (MD) simulation and free energy calculations of isolated N-SH2 in solution, SHP2 in solution, and SHP2 in a crystal environment. Our results demonstrate that the binding cleft in N-SH2 is constitutively flexible and open in solution and that a closed cleft found in certain structures is a consequence of crystal contacts. The degree of opening of the binding cleft has only a negligible effect on the free energy of SHP2 activation. Instead, SHP2 activation is greatly favored by the opening of the central β-sheet of N-SH2. We conclude that opening of the N-SH2 binding cleft is not the key allosteric switch triggering SHP2 activation.

Src Homology 2 Domain-Containing Protein Tyrosine Phosphatase Promotes Inflammation and Accelerates Osteoarthritis by Activating β-Catenin

Osteoarthritis (OA) is a chronic articular disease characterized by cartilage degradation, subchondral bone remodeling and osteophyte formation. Src homology 2 domain-containing protein tyrosine phosphatase (SHP2) has not been fully investigated in the pathogenesis of OA. In this study, we found that SHP2 expression was significantly increased after interleukin-1β (IL-1β) treatment in primary mouse chondrocytes. Inhibition of SHP2 using siRNA reduced MMP3, MMP13 levels, but increased AGGRECAN, COL2A1, SOX9 expression in vitro. On the contrary, overexpression of SHP2 exerted the opposite results and promoted cartilage degradation. Mechanistically, SHP2 activated Wnt/β-catenin signaling possibly through directly binding to β-catenin. SHP2 also induced inflammation through activating Mitogen-activated protein kinase (MAPK) and nuclear factor κB (NF-κB) pathways. Our in vivo studies showed that SHP2 knockdown effectively delayed cartilage destruction and reduced osteophyte formation in the mouse model of OA induced by destabilization of the medial meniscus (DMM). Altogether, our study identifies that SHP2 is a novel and potential therapeutic target of OA.

Niche-specific MHC II and PD-L1 regulate CD4+CD8αα+ intraepithelial lymphocyte differentiation

Conventional CD4+ T cells are differentiated into CD4+CD8αα+ intraepithelial lymphocytes (IELs) in the intestine; however, the roles of intestinal epithelial cells (IECs) are poorly understood. Here, we showed that IECs expressed MHC class II (MHC II) and programmed death–ligand 1 (PD-L1) induced by the microbiota and IFN-γ in the distal part of the small intestine, where CD4+ T cells were transformed into CD4+CD8αα+ IELs. Therefore, IEC-specific deletion of MHC II and PD-L1 hindered the development of CD4+CD8αα+ IELs. Intracellularly, PD-1 signals supported the acquisition of CD8αα by down-regulating the CD4-lineage transcription factor, T helper–inducing POZ/Krüppel-like factor (ThPOK), via the Src homology 2 domain–containing tyrosine phosphatase (SHP) pathway. Our results demonstrate that noncanonical antigen presentation with cosignals from IECs constitutes niche adaptation signals to develop tissue-resident CD4+CD8αα+ IELs.