Molecular Basis of Gain-of-Function LEOPARD Syndrome-Associated SHP2 Mutations

Abstract

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.

Regulatory Mechanisms and Novel Therapeutic Targeting Strategies for Protein Tyrosine Phosphatases

“…The answer to this question came from the realization that disease-causing Ptpn11 mutations modify not only the phosphatase activity of SHP2 but also its molecular switch regulatory mechanism that could dictate phenotypic outcome. 167–168 …”

“…Additional biophysical and computational analyses suggest that in comparison to native SHP2, the LS mutants display a greater tendency to switch from an autoinhibited closed conformation to a catalytically competent open state. 167–168 …”

Growth patterns of patients with Noonan syndrome: correlation with age and genotype

“…From a biochemical point of view, it has been shown that NScausing mutations induce hyperactivation of the phosphatase (gain-of-function mutation), while NSML-associated mutations result in reduced Shp2 catalytic activity (inactivating mutation) (7,8). How NS-Shp2 and NSML-Shp2 mutants can result in related syndromes while displaying opposite biochemical effects is still a matter of debate (9). Interestingly, a differential impact of these mutants on the phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway has been causally linked to the development of hypertrophic cardiomyopathy, which is preferentially found in patients with NSML (10,11).…”

Low-dose dasatinib rescues cardiac function in Noonan syndrome

“…Accordingly, NS-associated SHP2 mutants that are crippled in their ability to localize via their SH2 domains fail to manifest pathophysiological signaling (18). PTPN11-associated SHP2 mutations exist in an "open" conformation (20,21). Thus, both NS and NSML mutants are endowed with enhanced binding capacity through their SH2 domains to upstream receptor and adaptor proteins, which results in the acquisition of "gain-of-function" properties.…”