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Submitted on April 1, 2004
Revised on October 7, 2004
Accepted on October 18, 2004
From the Institut für Physiologie (B.-J.T.) and Center for Cardiovascular Research (A.D.), Charite (B.-J.T., A.D., V.R.-Z.), University-Medicine Berlin; Deutsches Herzzentrum Berlin (R.P., R.H., V.R.-Z.); and Institut für Experimentelle Innere Medizin (T.K.), Otto-von-Guericke-Universität Magdeburg, Germany.
* To whom correspondence should be addressed. E-mail: anke.doller{at}charite.de.
Collagen types I and III, coded by COL1A1/COL1A2 and COL3A1 genes, are the major fibrillar collagens produced by fibroblasts, including cardiac fibroblasts of the adult heart. Characteristic for different cardiomyopathies is a remodeling process associated with an upregulation of collagen synthesis, which leads to fibrosis. We report identification of three mRNA-binding proteins, heterogeneous nuclear ribonucleoprote (hnRNP) A1, E1, and K, as positive effectors of collagen synthesis acting at the post-transcriptional level by interaction with the 3'-untranslated regions (3'-UTRs) of COL1A1, 1A2, and 3A1 mRNAs. In vitro, binding experiments (electromobility shift assay and UV cross-linking) reveal significant differences in binding to CU- and AU-rich binding motifs. Reporter gene cell transfection experiments and RNA stability assays show that hnRNPs A1, E1, and K stimulate collagen expression by stabilizing mRNAs. Collagen synthesis is activated via the angiotensin II type 1 (AT1) receptor. We demonstrate that transforming growth factor-
1, a major product of stimulated AT1 receptor, does not activate solely collagen synthesis but synergistically the synthesis of hnRNP A1, E1, and K as well. Thus, post-transcriptional control of collagen synthesis at the mRNA level may substantially be caused by alteration of the expression of RNA-binding proteins. The pathophysiological impact of this finding was demonstrated by screening the expression of hnRNP E1 and K in cardiovascular diseases. In the heart muscle of patients experiencing aortic stenosis, ischemic cardiomyopathy, or dilatative cardiomyopathy, a significant increase in the expression of hnRNP E1 and K was found between 1.5- and 4.5-fold relative to controls.
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