Background:The mechanism by which SHP2 mutations cause LEOPARD syndrome is poorly understood. Results: LEOPARD syndrome mutations impair SHP2 activity but increase its propensity for an open and active conformation. Conclusion: LEOPARD syndrome SHP2 mutants bind preferentially to upstream activators to prolong substrate turnover, thus engendering gain-of-function phenotypes. Significance: The study provides a framework for understanding how individual SHP2 mutations cause diseases.
Objective To assess the frequency of cardiovascular and venous thromboembolic events in clinical studies of baricitinib, an oral, selective JAK1 and JAK2 inhibitor approved in more than 50 countries for the treatment of moderately‐to‐severely active rheumatoid arthritis (RA). Methods Data were pooled from 9 RA studies. Placebo comparison up to 24 weeks included data from 6 studies. Randomized dose comparison between baricitinib doses of 2 mg and 4 mg used data from 4 studies and from the associated long‐term extension study. The data analysis set designated “All‐bari‐RA” included all baricitinib exposures at any dose. Results Overall, 3,492 RA patients received baricitinib (7,860 patient‐years of exposure). No imbalance compared to the placebo group was seen in the incidence of major adverse cardiovascular events (MACE) (incidence rates [IRs] of 0.5 per 100 patient‐years for placebo and 0.8 per 100 patient‐years for 4 mg baricitinib), arterial thrombotic events (ATE) (IRs of 0.5 per 100 patient‐years for placebo and 0.5 per 100 patient‐years for 4 mg baricitinib), or congestive heart failure (CHF) broad term (IRs of 4.3 per 100 patient‐years for placebo and 2.4 per 100 patient‐years for 4 mg baricitinib). Deep vein thrombosis (DVT)/pulmonary embolism (PE) were reported in 0 of 1,070 patients treated with placebo and 6 of 997 patients treated with 4 mg baricitinib during the placebo‐controlled period; these events were serious in 2 of 6 patients, while all 6 had risk factors and 1 patient developed DVT/PE after discontinuation of the study drug. In the 2 mg–4 mg‐extended data analysis set, IRs of DVT/PE were comparable between the doses across event types (IRs of 0.5 per 100 patient‐years in those receiving 2 mg baricitinib and 0.6 per 100 patient‐years in those receiving 4 mg baricitinib). In the All‐bari‐RA data analysis set, the rates were stable over time, with an IR of DVT/PE of 0.5 per 100 patient‐years. Conclusion In RA clinical trials, no association was found between baricitinib treatment and the incidence of MACE, ATE, or CHF. With regard to incidence of DVT/PE, 6 events occurred in patients treated with 4 mg baricitinib, but no cases of DVT/PE were reported in the placebo group. During longer‐term evaluation, the incidence of DVT/PE was similar between the baricitinib dose groups, with consistent IR values over time, and this was similar to the rates previously reported in patients with RA.
The Src homology 2 (SH2) domain-containing protein tyrosine phosphatase 2 (SHP2) is a critical signal transducer downstream of growth factors that promotes the activation of the RAS-ERK1/2 cascade. In its basal state, SHP2 exists in an autoinhibited closed conformation because of an intramolecular interaction between its N-SH2 and protein tyrosine phosphatase (PTP) domains. Binding to pTyr ligands present on growth factor receptors and adaptor proteins with its N-SH2 domain localizes SHP2 to its substrates and frees the active site from allosteric inhibition. Germline mutations in SHP2 are known to cause both Noonan syndrome (NS) and LEOPARD syndrome (LS), two clinically similar autosomal dominant developmental disorders. NS-associated SHP2 mutants display elevated phosphatase activity, while LS-associated SHP2 mutants exhibit reduced catalytic activity. A conundrum in how clinically similar diseases result from mutations to SHP2 that have opposite effects on this enzyme’s catalytic functionality exists. Here we report a comprehensive investigation of the kinetic, structural, dynamic, and biochemical signaling properties of the wild type as well as all reported LS-associated SHP2 mutants. The results reveal that LS-causing mutations not only affect SHP2 phosphatase activity but also induce a weakening of the intramolecular interaction between the N-SH2 and PTP domains, leading to mutants that are more readily activated by competing pTyr ligands. Our data also indicate that the residual phosphatase activity associated with the LS SHP2 mutant is required for enhanced ERK1/2 activation. Consequently, catalytically impaired SHP2 mutants could display gain-of-function properties because of their ability to localize to the vicinity of substrates for longer periods of time, thereby affording the opportunity for prolonged substrate turnover and sustained RAS-ERK1/2 activation.
Background:The mechanism for the oncogenic phosphatase PRL-1 remains undefined. Results: We identified and characterized a novel PRL-1-binding protein, p115 RhoGAP. Conclusion: PRL-1 activates the ERK1/2 pathway by displacing MEKK1 from p115 RhoGAP and RhoA by preventing its interaction with p115 RhoGAP. Significance: This study offers a novel strategy for anticancer therapeutics by blocking the interaction between PRL-1 and p115 RhoGAP.
Phosphatase of regenerating liver 3 (PRL3) is suspected to be a causative factor toward cellular metastasis when in excess. To date, the molecular basis for PRL3 function remains an enigma, making efforts at distilling a concerted mechanism for PRL3-mediated metastatic dissemination very difficult. We previously discovered that PRL3 expressing cells exhibit a pronounced increase in protein tyrosine phosphorylation. Here we take an unbiased mass spectrometry-based approach toward identifying the phosphoproteins exhibiting enhanced levels of tyrosine phosphorylation with a goal to define the "PRL3-mediated signaling network." Phosphoproteomic data support intracellular activation of an extensive signaling network normally governed by extracellular ligand-activated transmembrane growth factor, cytokine, and integrin receptors in the PRL3 cells. Additionally, data implicate the Src tyrosine kinase as the major intracellular kinase responsible for "hijacking" this network and provide strong evidence that aberrant Src activation is a major consequence of PRL3 overexpression. Importantly, the data support a PDGF(␣/)-, Eph (A2/B3/B4)-, and Integrin (1/ 5)-receptor array as being the predominant network coordinator in the PRL3 cells, corroborating a PRL3-induced mesenchymal-state. Within this network, we find that tyrosine phosphorylation is increased on a multitude of signaling effectors responsible for Rho-family GTPase, PI3K-Akt, STAT, and ERK activation, linking observations made by the field as a whole under Src as a primary signal transducer. Our phosphoproteomic data paint the most comprehensive picture to date of how PRL3 drives prometastatic molecular events through Src activation. Molecular & Cellular Proteomics 12: 10.1074/mcp.M113.028886, 3759-3777, 2013.Protein-tyrosine phosphatases play critical regulatory roles during signal transduction and when deregulated cause aberrant tyrosine phosphorylation that lies at the heart of many human diseases, including cancer (1-3). The Phosphatase of Regenerating Liver (PRL) 1 phosphatases represent a unique sub-family of prenylated protein-tyrosine phosphatases comprised of three members (PRL1, 2, and 3) that share Ͼ75% of amino acid sequence identity (4 -6). A ground-breaking observation that PRL1 was an immediate early gene induced before the regeneration period of the rat liver following resection brought attention to the PRL-family as potential protooncogenes (7). Over more than two decades, research continues to provide evidence that the PRLs may play causative roles in tumorigenic and metastatic processes when aberrantly overexpressed (8).PRL3 (Ptp4a3) was first cast into the spotlight as a potential causative factor of metastasis when its transcript was found to be consistently and massively overexpressed in colorectal cancer (CRC) metastases found in the liver, whereas its expression in non-metastatic primary tumors and normal colorectal epithelium was undetectable (9). Subsequently, PRL3 transcript was found to be elevated in all metastatic lesions derived f...
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