Abstract 1566: Correlation between SHP2 phosphatase activity and Hypertrophic Cardiomyopathy
Background: Hypertrophic cardiomyopathy (HCM) is a common inherited cardiac disease and a major cause of sudden death. In Noonan syndrome (NS) and LEOPARD syndrome (LS), HCM is most frequent cardiac phenotype. Recent studies revealed that both syndromes are caused by mutations in the PTPN11 gene which encodes for the protein-tyrosin phosphataes, SHP2. However, it is still unproven that this gene is involved in the pathogenesis of HCM in NS and LS.The aim of this study is to investigate possible correlation between mutant SHP2 phosphatase activity and types and severity of HCM.
Method: Patients (n=25) with NS or LS and HCM were screened for mutations in the PTPN11 gene. The detected mutations were cloned into a pcDNA4 myc-His vector containing human SHP2 and transfected into Cos7 cells. The transfected cells were lysed after 72 hours and immunoprecipitated SHP2 was assayed for phosphatase activity. All patients with mutation were precisely examined by echocardiography.
Result: In the 25 patients examined, we identified six SHP2 mutations (8 patients; seven NS and one LS). Three of six mutations showed increased phosphatase activity as previously reported. Interestingly, we identified three mutants (Y279C, N308S, Q510E) in which the levels of phosphatase activity were almost the same or diminished compared to that in wild type (WT) (0.6 to 2.7 fold). To confirm loss of phosphatase activity, we measured phosphatase activity in truncated SHP2 mutants, which showed no activation of the enzyme as seen in WT. Moreover, all our patients with loss-of-function SHP2 mutants exhibited more marked HCM than those with gain of function. In summary, SHP2 mutants in the NS and LS demonstrate not only gain-of-function but also loss-of-function. Severe HCM might be related to SHP2 mutants with low phosphatase activity. SHP2 signaling pathways in cardiomyocyte that contribute to the pathogenesis of HCM must be studied further.