Myotrophin
regulation of cell size
cDNA sequence and characterization of the gene that encodes human myotrophin/V-1 protein, a mediator of cardiac hypertrophy.
The predominant response of the heart to sustained increased work load is development of ventricular hypertrophy, principally as a result of hypertrophy of cardiomyocytes. The molecular mechanisms and factors involved in cardiomyocyte hypertrophy are poorly understood. Myotrophin is a novel 12-kilodalton protein recently implicated as a factor associated with and able to induce cardiac hypertrophy. Cloning of rat myotrophin revealed that this protein is identical to the functionally undefined rat, murine and chicken V-1 proteins. Although human myotrophin has been purified to homogeneity, its gene has not been characterized. In this report we describe the cloning, expression, purification and characterization of the human homolog of myotrophin/V-1 protein. Sequence analysis indicators high homology (>90%) between all species at both the nucleotide and amino acid levels, and Southern blot analysis of genomic DNA from diverse species verifies that myotrophin/V-1 is a highly conserved gene. Northern analysis indicates wide-spread expression of a single human transcript, and examination of mRNA distribution in 50 human tissues by dot blot analysis indicates ubiquitous expression with relatively high expressioon in adult and fetal heart. We verify that recombinant human myotrophin produces cardiomyocyte hypertrophy, and we demonstrate for the first time that elevated levels of myotrophin/V-1 protein mRNA are expressed in human dilated cardiomyopathic hearts. We report the novel findings that myotrophin expression is elevated in ischemic hearts, and that myotrophin expression correlates positively with ventricular mass in a hypoxic rat model of induced right ventricular hypertrophy.