Thymopoietin (lamina-associated polypeptide 2) gene mutation associated with dilated cardiomyopathy

Abstract

Thymopoietin or TMPO (indicated by its alternative gene symbol, LAP2, in this work) has been proposed as a candidate disease gene for dilated cardiomyopathy (DCM), since a LAP2 product associates with nucleoplasmic lamins A/C, which are encoded by the DCM gene LMNA. We developed a study to screen for genetic mutations in LAP2 in a large collection of DCM patients and families. A total of 113 subjects from 88 families (56 with familial DCM (FDC) and 32 with sporadic DCM) were screened for LAP2 mutations using denaturing high-performance liquid chromatography and sequence analysis. We found a single putative mutation affecting the LAP2alpha isoform in one FDC pedigree. The mutation predicts an Arg690Cys substitution (c.2068C>T; p.R690C) located in the C-terminal domain of the LAP2alpha protein, a region that is known to interact with lamin A/C. RT-PCR, Western blot analyses, and immunolocalization revealed low-level LAP2alpha expression in adult cardiac muscle, and localization to a subset of nuclei. Mutated Arg690Cys LAP2alpha expressed in HeLa cells localized to the nucleoplasm like wild-type LAP2alpha, with no effect on peripheral and nucleoplasmic lamin A distribution. However, the in vitro interaction of mutated LAP2alpha with the pre-lamin A C-terminus was significantly compromised compared to the wild-type protein. LAP2 mutations may represent a rare cause of DCM. The Arg690Cys mutation altered the observed LAP2alpha interaction with A-type lamins. Our finding implicates a novel nuclear lamina-associated protein in the pathogenesis of genetic forms of dilated cardiomyopathy.

Proteins that associate with lamins: Many faces, many functions

“…LAP2α is linked to a laminopathy-type dilated cardiomyopathy, and loss of LAP2α-lamin A binding was observed for the mutated protein in vitro [114]. This finding again argues that disease-causing mutations in lamin A and LAP2α impair the functions of the nucleoplasmic complex.…”

Lamina-associated Polypeptide 2-α Forms Homo-trimers via Its C Terminus, and Oligomerization Is Unaffected by a Disease-causing Mutation

“…For GFP-LAP2␣ carrying the DCM mutation, vector gAG43 was constructed by shuttling wild-type LAP2␣ cDNAs from gAG41 (18) into GFP destination vector pcDNA-DEST53 by the LR reaction (Invitrogen). The bacterial expression vectors encoding His-tagged LAP2␣ fragments are described elsewhere (16).…”

“…The Self-association of LAP2␣ Is Not Affected by a Diseaselinked Mutation-A mutation in the extreme C terminus of LAP2␣ has been linked to dilated cardiomyopathy in humans (18). The molecular mechanism of this disease is currently unknown, but we have shown that the disease-linked mutation in LAP2␣ decreased its binding affinity for lamins A and C. Therefore, we wondered whether the mutation could also interfere with the self-association of LAP2␣ molecules and whether this could contribute to the cellular defect in patient cells.…”

“…Although LAP2␣ can interact with BAF and DNA via its common LEM and LEM-like motifs, its C terminus was shown to be essential and sufficient for chromatin association during mitosis (16,17). Intriguingly, a mutation causing an amino acid substitution (Arg-690 to Cys) near the C terminus of LAP2␣ has been associated with dilated cardiomyopathy (DCM) (18), a condition also known to be caused by mutations in the LMNA gene (5). The mutation altered the observed LAP2␣ interaction with A-type lamins in vitro and may represent a rare cause of DCM.…”

Mouse models of the laminopathies

“…To date, diseases affecting striated muscle comprise about 60% of the laminopathies. Of note, only ~50% of patients diagnosed with AD-EDMD or EDMD have EMD or LMNA mutations, indicating that mutations in other genes, perhaps those encoding proteins that interact with the lamins (e.g., LAP2), may account for the remaining 50% of patients [17,18].…”