MEK-ERK pathway modulation ameliorates disease phenotypes in a mouse model of Noonan syndrome associated with the RAF1 (L613V) mutation

Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada.
The Journal of clinical investigation (Impact Factor: 13.22). 02/2011; 121(3):1009-25. DOI: 10.1172/JCI44929
Source: PubMed


Hypertrophic cardiomyopathy (HCM) is a leading cause of sudden death in children and young adults. Abnormalities in several signaling pathways are implicated in the pathogenesis of HCM, but the role of the RAS-RAF-MEK-ERK MAPK pathway has been controversial. Noonan syndrome (NS) is one of several autosomal-dominant conditions known as RASopathies, which are caused by mutations in different components of this pathway. Germline mutations in RAF1 (which encodes the serine-threonine kinase RAF1) account for approximately 3%-5% of cases of NS. Unlike other NS alleles, RAF1 mutations that confer increased kinase activity are highly associated with HCM. To explore the pathogenesis of such mutations, we generated knockin mice expressing the NS-associated Raf1(L613V) mutation. Like NS patients, mice heterozygous for this mutation (referred to herein as L613V/+ mice) had short stature, craniofacial dysmorphia, and hematologic abnormalities. Valvuloseptal development was normal, but L613V/+ mice exhibited eccentric cardiac hypertrophy and aberrant cardiac fetal gene expression, and decompensated following pressure overload. Agonist-evoked MEK-ERK activation was enhanced in multiple cell types, and postnatal MEK inhibition normalized the growth, facial, and cardiac defects in L613V/+ mice. These data show that different NS genes have intrinsically distinct pathological effects, demonstrate that enhanced MEK-ERK activity is critical for causing HCM and other RAF1-mutant NS phenotypes, and suggest a mutation-specific approach to the treatment of RASopathies.

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Available from: Benjamin G Neel, Sep 29, 2015
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    • "E-mail: Article first published online in Wiley Online Library ( 00 Month 2014 DOI 10.1002/ajmg.a.36588 Ó 2014 Wiley Periodicals, Inc. Noonan syndrome [Wu et al., 2011] "
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    ABSTRACT: Biventricular hypertrophy (BVH) is a disease state characterized by the thickening of the ventricle walls. The differential diagnosis of BVH with other congenital and familial diseases in which increased ventricle wall thickness is a prominent clinical feature is fundamental due to its therapeutic and prognostic value, mainly during infancy. We describe a 2-month-old infant presenting BVH. Using exome sequencing, we identified a novel de novo 3-bp deletion in the RAF1 gene that is located in the binding active site for the 14-3-3 peptide. Based on docking calculations, we demonstrate that this novel mutation impairs protein/target binding, thus constitutively activating Ras signaling, which is a dysregulation associated with Noonan syndrome. Finally, our study underlines the importance of molecular modeling to understand the roles of novel mutations in pathogenesis. © 2014 Wiley Periodicals, Inc.
    American Journal of Medical Genetics Part A 08/2014; 164A(8). DOI:10.1002/ajmg.a.36588 · 2.16 Impact Factor
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    • "Clinically, activating mutations in Ras and its target Raf result in Costello and Noonen syndromes respectively, both of which induce cardiomyopathy amongst other abnormalities (Lin et al., 2011; Wu et al., 2011). Induction of hypertrophy by activated Ras and Raf is ERK1/2 dependent, suggesting that this kinase is responsible for the hypertrophic response to Ras and Raf activation (Harris et al., 2004; Wu et al., 2011). However, although it has been intensively investigated, the precise role and function of activated ERK1/2 in the heart remains controversial (Bueno and Molkentin, 2002; Kehat and Molkentin, 2010). "
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    British Journal of Pharmacology 09/2012; 168(2). DOI:10.1111/j.1476-5381.2012.02195.x · 4.84 Impact Factor
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    • "Assessment of ERK/MAPK signaling in vitro and in vivo in hearts from these mice revealed increased activation of Mek1/2 and ERK1/2, suggesting that blockade of the ERK/MAPK signaling pathway in these mice could be beneficial. Indeed, treatment with the MEK inhibitor, PD0325901, blocked and reversed HCM in vivo (Wu et al. 2011). "
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    ABSTRACT: In this review, we focus on elucidating the cardiac function of germline mutations in the PTPN11 gene, encoding the Src homology-2 (SH2) domain-containing protein tyrosine phosphatase SHP2. PTPN11 mutations cause LEOPARD syndrome (LS) and Noonan syndrome (NS), two disorders that are part of a newly classified family of autosomal dominant syndromes termed "RASopathies," which are caused by germline mutations in components of the RAS/RAF/MEK/ERK mitogen activating protein kinase pathway. LS and NS mutants have opposing biochemical properties, and yet, in patients, these mutations produce similar cardiac abnormalities. Precisely how LS and NS mutations lead to such similar disease etiology remains largely unknown. Recent complementary in vitro, ex vivo, and in vivo analyses reveal new insights into the functions of SHP2 in normal and pathological cardiac development. These findings also reveal the need for individualized therapeutic approaches in the treatment of patients with LS and NS and, more broadly, patients with the other "RASopathy" gene mutations as well.
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