Disease relevance of MYH6

• A human cardiac myosin heavy-chain (MHC) gene, cloned in a charon 4A phage, was isolated using two rat cardiac pCMHC DNA clones (pCMHC26: alpha-MHC type; and pCMHC5: beta-MHC type) as probes and shown to correspond to cardiac myosin heavy-chain of the alpha-type [1].
• Atrial fibrillation was accompanied by a significant shift from the fast alpha-MHC isoform to the slow beta-MHC isoform, whereas both donor and failing ventricular tissue contained almost exclusively the beta-MHC isoform [2].
• Cardiac myosin heavy chain (myhca) is the major autoantigen associated with autoimmune myocarditis both in humans and in experimental autoimmune myocarditis (EAM) in mice [3].
• CONCLUSION: Cardiac hypertrophy and failure cause downregulation of the endogenous alpha-MHC as well as cardiac specific overexpression of the transgene directed by an alpha-MHC promoter [4].
• These results suggest that even mild chronic myocardial thyrotoxicosis, such as may occur in human hyperthyroidism, can cause tachycardia and associated changes in high energy phosphate compounds independent of an increase in SERCA II and alpha-MHC [5].

High impact information on MYH6

• In both tissues, for example, the expression of the gene coding for a fast myosin (MHCf in skeletal muscle, alpha-MHC in ventricles) is repressed and that of the gene coding for a slow myosin (beta-MHC in both tissues) is stimulated [6].
• The major new findings were that (a) both nonfailing intact and explanted human ventricular myocardium expressed substantial amounts of alpha-myosin heavy chain mRNA (alpha-MHC, 23-34% of total), and (b) in heart failure alpha-MHC was downregulated (by 67-84%) and beta-MHC gene expression was upregulated [7].
• Wild-type alpha MHC transfected into COS cells forms structures previously shown to be arrays of thick filaments, which also resemble myosin structures observed early in differentiation of muscle cells [8].
• The element within the alpha-MHC promoter responsible for induction by T3 is located approximately 160 base pairs from the transcription initiation site [9].
• Accordingly, T3-responsiveness and tissue-specific expression of human and rat alpha-MHC/chloramphenicol acetyltransferase fusion constructs have been compared in rat fetal heart cells, L6E9 myoblasts and myotubes, 3T3 fibroblasts, and HeLa cells [10].

Chemical compound and disease context of MYH6

• We show alpha-MHC to be significantly repressed in cardiac hypertrophy and restored to normal on testosterone supplementation [11].

Biological context of MYH6

• Based on these data, the four loci were mapped within an approximately 600-kb region with the following centromere to telomere order: D14S283, D14S990, MYH6, and MYH7 [12].
• Our previous report demonstrated that two human cardiac alpha- and beta-myosin heavy-chains (MHCs) which correspond to MYH6 and MYH7 respectively, according to Human Gene Mapping nomenclature, were mapped to human chromosome 14 and that human cardiac and skeletal MHC genes do not cosegregate [13].
• CONCLUSIONS: This study suggests that mutations in MYH6 may cause a spectrum of phenotypes ranging from DCM to HCM [14].
• All MYH6 mutations were distributed in highly conserved residues, were predicted to change the structure or chemical bonds of alphaMyHC, and were absent in at least 300 control chromosomes from an ethnically similar population [14].
• Three heterozygous MYH6 missense mutations were identified in DCM probands (P830L, A1004S, and E1457K; 4.3% of probands) [14].

Anatomical context of MYH6

• Together, these results reveal that (i) PUR proteins participate in transcriptional as well as translational regulation of alpha-MHC expression in cardiac myocytes and (ii) ERP may be involved in cardiac-restricted expression of the alpha-MHC gene by preventing its expression in non-muscle cells [15].
• The alpha-MHC type cardiac genomic DNA clone and the beta-MHC type cardiac cDNA clone were used as probes in the Southern analysis of human genomic DNA from human-Chinese hamster or human-mouse somatic cell hybrids [16].
• Constructs encoding wild-type rat alpha MHC and seven corresponding FHC missense mutants were transfected into COS cells [8].
• In the current study, we evaluated two methods for the enumeration and phenotypic characterization of myhca-specific CD4+ T cells during the course of EAM [3].
• Concomitant surface marker analysis in the CFC assay revealed the prototypical effector phenotype of myhca-specific Th1 cells during the acute phase of the disease [3].

Associations of MYH6 with chemical compounds

• No modifications were observed in myosin function evaluated by in vitro motility assay, whereas the administration of L-thyroxine (100 micrograms/kg intraperitoneally daily) to CMPH was able to reinduce the ventricular expression of the alpha MHC isoform (5-fold increase) [17].
• After birth, thyroid hormone induces expression of alpha-MHC mRNA and inhibits expression of the beta-MHC gene [18].
• Furthermore, ascorbic acid induced the expression of cardiac genes, including GATA4, alpha-MHC, and beta-MHC in untransfected ES cells in a developmentally controlled manner [19].
• The series includes L243 IgG1 (alpha-MHC Class II) lacking a CH3 domain pair (DeltaCH3-IgG1), single-chain Fv fusion proteins with Fc or a hinge-CH2 domain, Fc with/out a hinge, and a single CH2 domain [20].
• Treatment of hypothyroid rats with amiodarone had no significant effect on beta-MHC or Spot 14 mRNAs, but a further reduction in alpha-MHC mRNA, compared with the untreated hypothyroid state, was evident [21].

Physical interactions of MYH6

• Electrophoretic mobility shift assay showed that the in vitro translation product of the rat USF1 cDNA bound to the alpha-MHC HME motif and was recognized by an antibody to hUSF1 [22].

Regulatory relationships of MYH6

• VEGF (20 ng/ml) significantly enhanced alpha-MHC, cTn-I, and Nkx2.5 expression in differentiated ESCs [23].

Other interactions of MYH6

• Layer-specific differential expression was validated at both mRNA and protein level for MYH3, MYH6, and ACTN3 [24].
• The positive TRE for T(3)-stimulation of alpha-MHC is an imperfect direct repeat located in the proximal promoter of the gene [18].
• A molecular mechanism by which contractile function modulates alpha-MHC transcriptional activity may involve signaling via phosphorylation of USF1 [25].
• Our data suggest that IGF-1 may not protect myocardial performance when its hypertrophic effect aggravates the reduction of alpha-MHC [26].
• METHODS AND RESULTS: To examine this hypothesis, we used RNase protection assay to measure mRNA levels of TRs in failing left ventricles that exhibited a fetal pattern of gene expression, ie, decreased expression of alpha-MHC with increased beta-MHC expression compared with left ventricles from age-matched controls [27].

Analytical, diagnostic and therapeutic context of MYH6

• In situ hybridization of 3H-labeled human cardiac alpha-MHC probe to normal human metaphase chromosome independently confirmed this result [13].
• We have obtained the 5820 nucleotide sequence encoding all 1939 amino acids of the human cardiac alpha-myosin heavy chain (alpha-MHC), as established by dideoxy sequencing of cloned cDNA, genomic DNA and polymerase chain reaction (PCR) amplification products [28].
• We used flow cytometry to determine the expression of alpha-myosin heavy chain (alpha-MHC), cardiac troponin I (cTn-I), and Nkx2.5 in differentiated ESCs [23].
• Northern blot analysis of normal and failing hearts detected sense mRNA for beta-MHC, but not alpha-MHC suggesting no functionally relevant levels of alpha-MHC mRNA exist in the human ventricle [29].
• Investigation of RNA by reverse transcription polymerase chain reaction (RT-PCR) detected an antisense RNA transcript for beta-MHC but none for alpha-MHC [29].

References