Hypertrophic cardiomyopathy (HCM) is a genetic myocardial disease. In 20% to 30% of patients, a disease-causing variant can be identified and may also be present in relatives. Individuals carrying a p Show more
Hypertrophic cardiomyopathy (HCM) is a genetic myocardial disease. In 20% to 30% of patients, a disease-causing variant can be identified and may also be present in relatives. Individuals carrying a pathogenic variant (G+) without left ventricular hypertrophy (LVH) are classified as genotype-positive/phenotype-negative (G+/P-). Their risk of developing LVH or HCM-related events remains uncertain. The aim of the article is to describe the clinical course of G+/P- individuals during long-term follow-up. G+/P- individuals were recruited from relatives of HCM patients at a tertiary center. All underwent clinical assessment, electrocardiography (ECG), and transthoracic echocardiography (TTE). Phenotype-negative status was defined as maximal left ventricular wall thickness (MLVWT) <13 mm. HCM was diagnosed when MLVWT ≥13 mm was observed without hypertension or other hemodynamic causes. Genetic testing used targeted Sanger sequencing, with variants classified per ACMG/AMP criteria. Thirty-four individuals were classified as G+/P-; the mean age was 31.7 ± 14.8 years, and 27% were men. Variants occurred in MYBPC3 (76%) and MYH7 (24%). Most were asymptomatic (85%), and 71% had a normal ECG. Mean follow-up was 6.6 ± 3.7 years, with complete ECG and TTE data in 88%. MLVWT increased from 9.6 ± 1.6 mm to 10.7 ± 3.3 mm (p = 0.01), while other echocardiographic parameters and ECG findings remained stable. Nine individuals (26%) developed LVH after a mean of 5.1 ± 4.1 years. One patient developed nonsustained ventricular tachycardia and received a primary prevention implantable cardioverter-defibrillator. In conclusion, G+/P- individuals were young and largely asymptomatic, yet 26% progressed to HCM. These results support regular TTE and ECG surveillance to enable early identification of disease progression and guide risk stratification. Show less
Mitogen-activated protein kinases (MAPKs) are highly conserved protein kinase modules, and they control fundamental cellular processes. While the activation of MAPKs has been well studied, little is k Show more
Mitogen-activated protein kinases (MAPKs) are highly conserved protein kinase modules, and they control fundamental cellular processes. While the activation of MAPKs has been well studied, little is known on the mechanisms driving their inactivation. Here we uncover a role for ubiquitination in the inactivation of a MAPK module. Extracellular-signal-regulated kinase 5 (ERK5) is a unique, conserved member of the MAPK family and is activated in response to various stimuli through a three-tier cascade constituting MEK5 and MEKK2/3. We reveal an unexpected role for Inhibitors of Apoptosis Proteins (IAPs) in the inactivation of ERK5 pathway in a bimodal manner involving direct interaction and ubiquitination. XIAP directly interacts with MEKK2/3 and competes with PB1 domain-mediated binding to MEK5. XIAP and cIAP1 conjugate predominantly K63-linked ubiquitin chains to MEKK2 and MEKK3 which directly impede MEK5-ERK5 interaction in a trimeric complex leading to ERK5 inactivation. Consistently, loss of XIAP or cIAP1 by various strategies leads to hyperactivation of ERK5 in normal and tumorigenic cells. Loss of XIAP promotes differentiation of human primary skeletal myoblasts to myocytes in a MEKK2/3-ERK5-dependent manner. Our results reveal a novel, obligatory role for IAPs and ubiquitination in the physical and functional disassembly of ERK5-MAPK module and human muscle cell differentiation. Show less