Effect of unloading on type I myosin heavy chain gene regulation in rat soleus muscle

• Published in: Journal of applied physiology (1985) 2005-04, Vol.98 (4), p.1185-1194
• Main Authors: Giger, Julia M, Haddad, Fadia, Qin, Anqi X, Zeng, Ming, Baldwin, Kenneth M
• Format: Article
• Language: English
• Subjects: Adaptation, Physiological - physiology; Amino Acid Substitution; Animals; Binding sites; Biological and medical sciences; Female; Fundamental and applied biological sciences. Psychology; Gene expression; Gene Expression Regulation - physiology; Hindlimb Suspension - methods; Muscle, Skeletal - physiology; Muscular system; Mutagenesis, Site-Directed; Myosin Type I - physiology; Rats; Rats, Sprague-Dawley; Recombinant Proteins - metabolism; Rodents; Signal transduction; Striated muscle. Tendons; Vertebrates: osteoarticular system, musculoskeletal system; Weight-Bearing - physiology
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.01099.2004

Department of Physiology and Biophysics, University of California, Irvine, California Submitted 1 October 2004 ; accepted in final form 8 December 2004 Slow-twitch soleus, a weight-bearing hindlimb muscle, predominantly expresses the type I myosin heavy chain (MHC) isoform. However, under unloading conditions, a transition in MHC expression occurs from slow type I toward the fast-type isoforms. Transcriptional processes are believed to be involved in this adaptation. To test the hypothesis that the downregulation of MHC 1 in soleus muscle following unloading is controlled through cis element(s) in the proximal region of the promoter, the MHC 1 promoter was injected into soleus muscles of control rats and those subjected to 7 days of hindlimb suspension. Mutation analyses of six putative regulatory elements within the –408-bp region demonstrated that three elements, an A/T-rich, the proximal muscle-type CAT ( e3), and an E-box (–63 bp), play an important role in the basal level of MHC 1 gene activity in the control soleus and function as unloading-responsive elements. Gel mobility shift assays revealed a diminished level of complex formation of the e3 and E-box probes with nuclear extract from hindlimb suspension soleus compared with control soleus. Supershift assays indicated that transcriptional enhancer factor 1 and myogenin factors bind the e3 and E-box elements, respectively, in the control soleus. Western blots showed that the relative concentrations of the transcriptional enhancer factor 1 and myogenin factors were significantly attenuated in the unloaded soleus compared with the control muscle. We conclude that the downregulation of MHC 1 in response to unloading is due, in part, to a significant decrease in the concentration of these transcription factors available for binding the positive regulatory elements. direct gene transfer; promoter; gel mobility shift assay; pre-messenger ribonucleic acid Address for reprint requests and other correspondence: J. M. Giger, Dept. of Physiology and Biophysics, Univ. of California-Irvine, D-346, Med Sci I, Irvine, CA 92697 (E-mail: jmeehan{at}uci.edu )