title: Rapid response of cardiac obscurin gene cluster to aortic stenosis: differential activation of Rho-GEF and MLCK and involvement in hypertrophic growth.
abstract: Obscurin and obscurin myosin light chain kinase (MLCK) are two recently identified muscle proteins encoded by the same gene cluster. The production of obscurin, which contains a Rho-guanine exchange factor (GEF)-like sequence, and obscurin-MLCK by this cluster suggests that these novel genes may be involved in signal transduction cascades that control adaptive and compensatory responses of the heart. The goal of the present study was to investigate the transcriptional response of the obscurin gene cluster to the initiation of myocardial hypertrophy induced in mice by aortic constriction. The transcriptional activity of the obscurin genes was examined using reverse-transcriptase primed quantitative PCR. We found that the transcripts encoding the obscurin Rho-GEF and the obscurin-MLCK internal serine-threonine kinase II (SK II) domains were significantly upregulated following aortic constriction. The expression of Rho-GEF-containing transcripts at different stages of the hypertrophic growth exceeded the control levels by 2- to 6-fold. Following the induction of hypertrophy, the quantity of the SK II-encoding transcripts increased 10-fold by 24h and 16-fold by 48h, then decreased by day 7, and returned to the control level by day 56. The quantity of the carboxy terminal obscurin-MLCK transcripts encoding for SK I increased 2-fold by day 2 and returned to the control values at later stages. Immunolocalization of obscurin, which contains Rho-GEF domain, in cardiomyocytes during pharmacologically induced hypertrophic growth in vitro demonstrated that the expression was topographically associated with the growing myofibrils and with the sites of initiation and progression of myofibrillogenesis at the periphery of the sarcoplasm. This suggests that upregulation of obscurin synthesis is associated with the formation of additional amounts of contractile structures during cardiac hypertrophy. Thus, the obscurin gene cluster represents a new example of an operon that encodes differentially regulated structural and signaling proteins implicated in the control of assembly and adaptive remodeling of myofibrils during normal and hypertrophic growth.
authors.affiliation: Department of Pediatrics and Communicable Diseases, University of Michigan Medical School, Ann Arbor 48109, USA.
authors.forename: Andrei B
authors.initials: AB
authors.lastname: Borisov
authors.forename: Maide O
authors.initials: MO
authors.lastname: Raeker
authors.forename: Aikaterini
authors.initials: A
authors.lastname: Kontrogianni-Konstantopoulos
authors.forename: Kun
authors.initials: K
authors.lastname: Yang
authors.forename: David M
authors.initials: DM
authors.lastname: Kurnit
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Bloch
authors.forename: Mark W
authors.initials: MW
authors.lastname: Russell
mesh_terms: D000818:Animals; D001011:Aorta / Q000378:metabolism; D001024:Aortic Valve Stenosis / Q000378:metabolism*; D001835:Body Weight; D002478:Cells, Cultured; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics* / Q000378:metabolism*; D006984:Hypertrophy; D051379:Mice; D008856:Microscopy, Fluorescence; D005810:Multigene Family; D009124:Muscle Proteins / Q000235:genetics*; D009206:Myocardium / Q000378:metabolism; D009219:Myosin-Light-Chain Kinase / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D017434:Protein Structure, Tertiary; D064067:Rho Guanine Nucleotide Exchange Factors; D015398:Signal Transduction; D013997:Time Factors; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D015854:Up-Regulation
chemical_list: D020662:Guanine Nucleotide Exchange Factors; D009124:Muscle Proteins; D064067:Rho Guanine Nucleotide Exchange Factors; D017346:Protein Serine-Threonine Kinases; D009219:Myosin-Light-Chain Kinase