Differential Regulation of the Muscle-specific GLUT4 Enhancer in Regenerating and Adult Skeletal Muscle

We have reported a novel functional co-operation among MyoD, myocyte enhancer factor-2 (MEF2), and the thyroid hormone receptor in a muscle-specific enhancer of the rat GLUT4 gene in muscle cells. Here, we demonstrate that the muscle-specific enhancer of the GLUT4 gene operates in skeletal muscle and is muscle fiber-dependent and innervation-independent. Under normal conditions, both in soleus and in extensor digitorum longus muscles, the activity of the enhancer required the integrity of the MEF2-binding site. Cancellation of the binding site of thyroid hormone receptor enhanced its activity, suggesting an inhibitory role. Muscle regeneration of the soleus and extensor digitorum longus muscles caused a marked induction of GLUT4 and stimulation of the enhancer activity, which was independent of innervation. During muscle regeneration, the enhancer activity was markedly inhibited by cancellation of the binding sites of MEF2, MyoD, or thyroid hormone receptors. Different MEF2 isoforms expressed in skeletal muscle (MEF2A, MEF2C, and MEF2D) and all members of the MyoD family had the capacity to participate in the activity of the GLUT4 enhancer as assessed by transient transfection in cultured cells. Our data indicate that the GLUT4 enhancer operates in muscle fibers and its activity contributes to the differences in GLUT4 gene expression between oxidative and glycolytic muscle fibers and to the GLUT4 up-regulation that occurs during muscle regeneration. The activity of the enhancer is maintained in adult muscle by MEF2, whereas during regeneration the operation of the enhancer depends on MEF2, myogenic transcription factors of the MyoD family, and thyroid hormone receptors. We have reported a novel functional co-operation among MyoD, myocyte enhancer factor-2 (MEF2), and the thyroid hormone receptor in a muscle-specific enhancer of the rat GLUT4 gene in muscle cells. Here, we demonstrate that the muscle-specific enhancer of the GLUT4 gene operates in skeletal muscle and is muscle fiber-dependent and innervation-independent. Under normal conditions, both in soleus and in extensor digitorum longus muscles, the activity of the enhancer required the integrity of the MEF2-binding site. Cancellation of the binding site of thyroid hormone receptor enhanced its activity, suggesting an inhibitory role. Muscle regeneration of the soleus and extensor digitorum longus muscles caused a marked induction of GLUT4 and stimulation of the enhancer activity, which was independent of innervation. During muscle regeneration, the enhancer activity was markedly inhibited by cancellation of the binding sites of MEF2, MyoD, or thyroid hormone receptors. Different MEF2 isoforms expressed in skeletal muscle (MEF2A, MEF2C, and MEF2D) and all members of the MyoD family had the capacity to participate in the activity of the GLUT4 enhancer as assessed by transient transfection in cultured cells. Our data indicate that the GLUT4 enhancer operates in muscle fibers and its activity contributes to the differences in GLUT4 gene expression between oxidative and glycolytic muscle fibers and to the GLUT4 up-regulation that occurs during muscle regeneration. The activity of the enhancer is maintained in adult muscle by MEF2, whereas during regeneration the operation of the enhancer depends on MEF2, myogenic transcription factors of the MyoD family, and thyroid hormone receptors. The GLUT4 glucose transporter gene is expressed mainly in muscle and adipose cells. GLUT4 expression is exquisitely regulated in skeletal muscle so that its level determines the whole-body glucose disposal in response to insulin. GLUT4 is differentially expressed in oxidative and glycolytic muscle fibers in the rat (1Kern M. Wells J.A. Stephens J.M. Elton C.W. Friedman J.E. Tapscott E.B. Pekala P.H. Dohm G.L. Biochem. J. 1990; 270: 397-400Crossref PubMed Scopus (219) Google Scholar, 2Camps M. Castello A. Munoz P. Monfar M. Testar X. Palacin M. Zorzano A. Biochem. J. 1992; 282: 765-772Crossref PubMed Scopus (133) Google Scholar, 3Neufer P.D. Carey J.O. Dohm G.L. J. Biol. Chem. 1993; 268: 13824-13829Abstract Full Text PDF PubMed Google Scholar), undergoes up-regulation in muscle by thyroid hormones (4Castello A. Cadefau J. Cusso R. Testar X. Hesketh J.E. Palacin M. Zorzano A. J. Biol. Chem. 1993; 268: 14998-15003Abstract Full Text PDF PubMed Google Scholar, 5Weinstein S.P. O'Boyle E. Haber R.S. Diabetes. 1994; 43: 1185-1189Crossref PubMed Scopus (104) Google Scholar, 6Torrance C.J. Devente J.E. Jones J.P. Dohm G.L. Endocrinology. 1997; 138: 1204-1214Crossref PubMed Scopus (83) Google Scholar), and is repressed by muscle denervation (7Block N.E. Menick D.R. Robinson K.A. Buse M.G. J. Clin. Investig. 1991; 88: 1546-1552Crossref PubMed Scopus (79) Google Scholar, 8Coderre L. Monfar M.M. Chen K.S. Heydrick S.J. Kurowski T.G. Ruderman N.B. Pilch P.F. Endocrinology. 1992; 131: 1821-1825Crossref PubMed Scopus (66) Google Scholar, 9Castelló A. Rodriguez-Manzaneque J.C. Camps M. Pérez-Castillo A. Testar X. Palacín M. Santos A. Zorzano A. J. Biol. Chem. 1994; 269: 5905-5912Abstract Full Text PDF PubMed Google Scholar), in experimental diabetes (2Camps M. Castello A. Munoz P. Monfar M. Testar X. Palacin M. Zorzano A. Biochem. J. 1992; 282: 765-772Crossref PubMed Scopus (133) Google Scholar, 10Slieker L.J. Sundell K.L. Heath W.F. Osborne H.E. Bue J. Manetta J. Sportsman J.R. Diabetes. 1992; 41: 187-193Crossref PubMed Scopus (81) Google Scholar, 11Richardson J.M. Balon T.W. Treadway J.L. Pessin J.E. J. Biol. Chem. 1991; 266: 12690-12694Abstract Full Text PDF PubMed Google Scholar) or in response to cyclic AMP treatment (12Viñals F. Ferré J. Fandos C. Santalucía T. Testar X. Palacín M. Zorzano A. Endocrinology. 1997; 138: 2521-2529Crossref PubMed Scopus (0) Google Scholar). In addition, agonists of AMP-activated protein kinase enhance GLUT4 transcription in a muscle fiber-dependent manner (13Buhl E.S. Jessen N. Schmitz O. Pedersen S.B. Pedersen O. Holman G.D. Lund S. Diabetes. 2001; 50: 12-17Crossref PubMed Scopus (162) Google Scholar, 14Zheng D. MacLean P.S. Pohnert S.C. Knight J.B. Olson A.L. Winder W.W. Dohm G.L. J. Appl. Physiol. 2001; 91: 1073-1083Crossref PubMed Scopus (245) Google Scholar). As to the regulation of GLUT4 gene transcription, different studies performed in transgenic mice have shown that a 5′-flanking region of 1154 bp in the GLUT4 gene is sufficient to drive muscle-, heart-, and adipose tissue-specific GLUT4 expression (15Liu M.L. Olson A.L. Moye-Rowley W.S. Buse J.B. Bell G.I. Pessin J.E. J. Biol. Chem. 1992; 267: 11673-11676Abstract Full Text PDF PubMed Google Scholar, 16Olson A.L. Pessin J.E. J. Biol. Chem. 1995; 270: 23491-23495Abstract Full Text Full Text PDF PubMed Scopus (60) Google Scholar). In addition, several regulatory elements have been identified within this region. Initial studies performed in cultured muscle cells identified the region -522/-402 as necessary for muscle-specific expression and a myocyte enhancer factor-2 (MEF2) 1The abbreviations used are: MEF2, myocyte enhancer factor-2; EDL, extensor digitorum longus; TRα1, thyroid hormone receptor; TRE, thyroid hormone receptor element; MRF, myogenic regulatory factor; CAT, chloramphenicol acetyltransferase; TK, thymidine kinase; T3, triiodothyronine.-binding site that was critical for its transcriptional activity (17Liu M.L. Olson A.L. Edgington N.P. Moye-Rowley W.S. Pessin J.E. J. Biol. Chem. 1994; 269: 28514-28521Abstract Full Text PDF PubMed Google Scholar). Disruption of this MEF2-binding site ablated tissue-specific GLUT4 expression in transgenic mice (18Thai M.V. Guruswamy S. Cao K.T. Pessin J.E. Olson A.L. J. Biol. Chem. 1998; 273: 14285-14292Abstract Full Text Full Text PDF PubMed Scopus (180) Google Scholar). Recently, it has been suggested that the transcriptional coactivator peroxisome proliferator activator protein-γ co-activator-1 participates in GLUT4 gene transcription by interacting with MEF2 transcription factors (19Michael L.F. Wu Z. Cheatham R.B. Puigserver P. Adelmant G. Lehman J.J. Kelly D.P. Spiegelman B.M. Proc. Natl. Acad. Sci. U. S. A. 2001; 98: 3820-3825Crossref PubMed Scopus (544) Google Scholar). The Krüppel-like factor, KLF15, binds to a site near the MEF2-binding element and induces GLUT4 gene expression in 3T3-L1 cells (20Banerjee S.S. Feinberg M.W. Watanabe M. Gray S. Haspel R.L. Denkinger D.J. Kawahara R. Hauner H. Jain M.K. J. Biol. Chem. 2002; 277: 34322-34328Abstract Full Text Full Text PDF PubMed Scopus (24) Google Scholar). Another relevant region is located at -742/-712 relative to the transcription initiation site. Different factors such as NF1 (nuclear factor I) (21Cooke D.W. Lane M.D. J. Biol. Chem. 1999; 274: 12917-12924Abstract Full Text Full Text PDF PubMed Scopus (64) Google Scholar) and a partially protein Knight J.B. Cao K.T. M.V. Olson A.L. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar) to this region. NF1 to participate in the of on GLUT4 gene expression in adipose cells (21Cooke D.W. Lane M.D. J. Biol. Chem. 1999; 274: 12917-12924Abstract Full Text Full Text PDF PubMed Scopus (64) Google Scholar) and the protein binding activity to with the MEF2-binding site Knight J.B. Cao K.T. M.V. Olson A.L. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). In addition, a region located between and of the has been reported to a which to as a in in N. M. T. Diabetes. 1999; PubMed Scopus Google Scholar). We have reported co-operation between MyoD, MEF2, and the thyroid hormone receptor that in the of an muscle-specific enhancer in the rat GLUT4 gene which is in both and skeletal muscle T. H. Palacin M. Zorzano A. J. Biol. 2001; PubMed Scopus (66) Google Scholar). In the skeletal muscle and in a of the GLUT4 enhancer on the of MyoD, MEF2, and and the integrity of binding is in with the capacity of the and the thyroid response element in the enhancer to MyoD and thyroid hormone T. H. Palacin M. Zorzano A. J. Biol. 2001; PubMed Scopus (66) Google Scholar, C.J. S.J. Pessin J.E. Dohm G.L. Endocrinology. 1997; 138: PubMed Scopus Google Scholar). we have shown that in the of MyoD, MEF2, and induces the expression of the GLUT4 gene T. H. Palacin M. Zorzano A. J. Biol. 2001; PubMed Scopus (66) Google Scholar). In this we that the enhancer in skeletal muscle in and that its activity depends on the muscle is during muscle regeneration, and is independent of innervation. and and the by the of of that the to in the rat GLUT4 5′-flanking region. The the enhancer so that both of the enhancer to the the or a is a that the of regulatory of on the transcription of the gene by the region of the thymidine kinase gene J. Biol. Chem. 1991; 266: Full Text PDF PubMed Google Scholar). of the which in the of binding sites for transcription by in the a of the for the The of the enhancer the site of the by the used for the The and of the in all was by The expression for MyoD, and rat muscle regulatory H. E. N. Olson D. and S. F. The of was an expression The expression for MEF2C, and P. of at J. and Olson D. Muscle and regeneration was in by of as M. M.V. A. M. S. 1994; PubMed Scopus (162) Google Scholar). was by the in the of and or soleus or extensor digitorum longus muscles with at treatment as M. M.V. A. M. S. 1994; PubMed Scopus (162) Google Scholar). We have shown that gene is at the muscle is of is at M. M.V. A. M. S. 1994; PubMed Scopus (162) Google Scholar). at and in in muscles by of by to gene The was to that by J. R. D. J.M. P. D. D. Proc. Natl. Acad. Sci. U. S. A. 1999; PubMed Scopus Google Scholar). of or expression was used to for transfection at transfection and in in Muscle and gene activity and was by data for protein on muscle and was and cultured as F. Fandos C. T. J. Testar X. Palacin M. Zorzano A. J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar). with the transfection enhancer to the activity was in as F. Fandos C. T. J. Testar X. Palacin M. Zorzano A. J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar). with the an expression the of the T. H. Palacin M. Zorzano A. J. Biol. 2001; PubMed Scopus (66) Google Scholar). activity was in to the of was with the protein was to was was by as J. J. Clin. Investig. 98: PubMed Scopus Google Scholar). was performed as A. Rodriguez-Manzaneque J.C. Camps M. Pérez-Castillo A. Testar X. Palacín M. Santos A. Zorzano A. J. Biol. Chem. 1994; 269: 5905-5912Abstract Full Text PDF PubMed Google Scholar). of protein or muscles was to GLUT4 and the of the by and was the as by and P. N. Biochem. PubMed Scopus Google Scholar). had an was at in the of and to the of was on a and on The in and in was with by to the integrity of to the of of and to was performed as reported (4Castello A. Cadefau J. Cusso R. Testar X. Hesketh J.E. Palacin M. Zorzano A. J. Biol. Chem. 1993; 268: 14998-15003Abstract Full Text PDF PubMed Google Scholar). The rat for a M. of was with by The of the GLUT4 in Muscle in and Muscle have reported that the enhancer the transcriptional activity of the GLUT4 gene in muscle cells in T. H. Palacin M. Zorzano A. J. Biol. 2001; PubMed Scopus (66) Google Scholar). Here, we the of this enhancer in in rat skeletal In the or the a by adult rat soleus of oxidative muscle and extensor digitorum longus of glycolytic muscle Our data indicate that the enhancer is in both in soleus and in muscles and the activity of the enhancer was that of the The data indicate that the enhancer activity was in soleus muscle in transfection with a the enhancer is in skeletal muscles, and soleus a activity muscles is with GLUT4 gene expression in soleus with muscles (1Kern M. Wells J.A. Stephens J.M. Elton C.W. Friedman J.E. Tapscott E.B. Pekala P.H. Dohm G.L. Biochem. J. 1990; 270: 397-400Crossref PubMed Scopus (219) Google Scholar, 2Camps M. Castello A. Munoz P. Monfar M. Testar X. Palacin M. Zorzano A. Biochem. J. 1992; 282: 765-772Crossref PubMed Scopus (133) Google Scholar, 3Neufer P.D. Carey J.O. Dohm G.L. J. Biol. Chem. 1993; 268: 13824-13829Abstract Full Text PDF PubMed Google Scholar). Muscle the of the GLUT4 skeletal muscle is to by of cells. cells by and and muscle The myogenic factors MyoD and during muscle regeneration, whereas and a induction D. Biol. 1997; PubMed Scopus Google Scholar). has been suggested that during muscle regeneration, the activity of MEF2 is enhanced R.L. J.C. Biochem. J. 1997; PubMed Scopus Google Scholar). this we the of muscle regeneration on GLUT4 enhancer this we the enhancer activity in or soleus or muscles at of the enhancer to the a marked stimulation of transcriptional activity during regeneration data the GLUT4 enhancer was to a activity was enhanced muscle regeneration Muscle regeneration marked stimulation of the GLUT4 enhancer activity in muscles The GLUT4 of Muscle denervation a marked of GLUT4 in skeletal muscles (7Block N.E. Menick D.R. Robinson K.A. Buse M.G. J. Clin. Investig. 1991; 88: 1546-1552Crossref PubMed Scopus (79) Google Scholar, 8Coderre L. Monfar M.M. Chen K.S. Heydrick S.J. Kurowski T.G. Ruderman N.B. Pilch P.F. Endocrinology. 1992; 131: 1821-1825Crossref PubMed Scopus (66) Google Scholar, 9Castelló A. Rodriguez-Manzaneque J.C. Camps M. Pérez-Castillo A. Testar X. Palacín M. Santos A. Zorzano A. J. Biol. Chem. 1994; 269: 5905-5912Abstract Full Text PDF PubMed Google Scholar). we the of denervation in the activity of the GLUT4 this or soleus and muscles by with the and activity was at differences between and in soleus or muscles Under conditions, GLUT4 expression was by denervation in both muscle We the of denervation on enhancer activity in this soleus or muscles to in the or of innervation. gene in muscles that the activity of the enhancer was independent of in both soleus and muscles of GLUT4 in on the regulatory of the GLUT4 we the of muscle regeneration on GLUT4 this soleus and muscles to by in the or of innervation. different of initiation of regeneration, muscles and GLUT4 protein and by and We in muscles adult that to denervation for of GLUT4 protein was of regeneration with adult GLUT4 protein markedly to of regeneration and to a induction of GLUT4 protein at denervation was to of GLUT4 expression during the regeneration and of the of the was induction of GLUT4 was with regeneration, which was during so that at In addition, of GLUT4 at of regeneration markedly in the during muscle regeneration GLUT4 is markedly and whereas an GLUT4 induction is independent of at it on muscle innervation. Different of the GLUT4 in and in the elements that for the activity of the enhancer in adult and in In we soleus and muscles with different of the enhancer in the the MEF2-binding or the in cultured cells has that the used the binding sites T. H. Palacin M. Zorzano A. J. Biol. 2001; PubMed Scopus (66) Google Scholar). in soleus and in muscles adult we a of to the transcriptional of the Cancellation of the the transcriptional activity of the enhancer in soleus or In of the MEF2-binding site caused a marked of the activity of the enhancer both in soleus and in muscles of the the transcriptional activity of the enhancer in soleus and muscles suggesting that the thyroid hormone a in adult We the of the GLUT4 enhancer during muscle regeneration. this we or soleus or muscles with the different of the Cancellation of the or the caused a marked in the activity of the enhancer in or soleus or muscles and which is in to we in adult muscle In with the in adult of the MEF2-binding site caused a marked of the activity of the enhancer in or soleus or muscles and of in the MEF2, and on the activity of the muscle enhancer in extensor digitorum longus muscles muscles in with the the enhancer or at the MEF2 or with a as a transfection of muscles and activity was expressed as a of enhancer the with the enhancer Different MEF2 or on the GLUT4 have shown that and MyoD the muscle-specific GLUT4 enhancer and that with MyoD and on the activity of the enhancer in muscle and cells T. H. Palacin M. Zorzano A. J. Biol. 2001; PubMed Scopus (66) Google Scholar). on the of the and the MEF2 element in the of the activity of the muscle-specific GLUT4 enhancer in the muscle different conditions, we MEF2 isoforms expressed in and S. Pessin J.E. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar), or myogenic or the In studies cells with MEF2C, or or in with MyoD MEF2C, and on In addition, all MEF2 isoforms with MyoD and Under conditions, was in with or with MyoD was by and We with different MEF2 isoforms the of the functional with MyoD or of cells with expression for and in the of MyoD and the enhancer to with which the in the of transfection with and in the of MyoD and the enhancer activity to to of the and the of the In experimental we cells with different of expression for members of the MyoD family of MRF, and In we used MyoD or as and in MyoD or and on a of the which was with the of MyoD of caused a of the enhancer cells maintained in the of whereas a was in the of In addition, and both and the enhancer with and with The by or was to that of MyoD we the of with in the enhancer on the integrity of the as we have reported for MyoD T. H. Palacin M. Zorzano A. J. Biol. 2001; PubMed Scopus (66) Google Scholar). transient studies a or a of the enhancer a of expression for the transcription that both the of or MyoD on the enhancer activity as as the between and or MyoD and by the data demonstrate that the integrity of the is required for the of the protein family on the activity of the muscle-specific GLUT4 enhancer and the of the functional of the different members of the family with MEF2 and on the muscle-specific GLUT4 The of this indicate that the muscle-specific GLUT4 enhancer located at operates in in the expression of GLUT4 in skeletal contributes to the differences in GLUT4 expression in glycolytic and oxidative muscle and is in muscles in which GLUT4 is In adult the activity of the enhancer an MEF2-binding and the an inhibitory role. during muscle regeneration, the MEF2 the and the in a the the activity of the enhancer is independent of muscle both in adult muscle and during muscle regeneration. We have that the muscle-specific GLUT4 enhancer is by MyoD, MEF2, and in muscle and cells in and that this the integrity of the elements T. H. Palacin M. Zorzano A. J. Biol. 2001; PubMed Scopus (66) Google Scholar). In addition, of the MEF2-binding element or the caused a of transcriptional in cultured T. H. Palacin M. Zorzano A. J. Biol. 2001; PubMed Scopus (66) Google Scholar). In this we that in adult skeletal normal conditions, the activity of the muscle-specific GLUT4 enhancer is maintained by the MEF2-binding and so cancellation of the element a of In addition, we have that the enhancer is to the TRE, so that its cancellation the activity of the The of the MEF2-binding site was reported in a transgenic in which a marked of the transcriptional activity by bp of the 5′-flanking region of GLUT4 gene was in adipose or in muscles of the MEF2-binding site (18Thai M.V. Guruswamy S. Cao K.T. Pessin J.E. Olson A.L. J. Biol. Chem. 1998; 273: 14285-14292Abstract Full Text Full Text PDF PubMed Scopus (180) Google Scholar). is to that the the activity of the enhancer normal in adult muscle on the the of to is to the induction of GLUT4 gene expression in muscle S.P. O'Boyle E. Haber R.S. Diabetes. 1994; 43: 1185-1189Crossref PubMed Scopus (104) Google Scholar, 6Torrance C.J. Devente J.E. Jones J.P. Dohm G.L. Endocrinology. 1997; 138: 1204-1214Crossref PubMed Scopus (83) Google in addition, the of in rat skeletal muscle within the F. G. 1999; PubMed Scopus Google Scholar), to to thyroid hormone receptors. In the that the muscle-specific GLUT4 enhancer inhibited the in skeletal muscle In with adult muscle regeneration caused a in the of operation of the GLUT4 during muscle regeneration, cancellation of the elements the MEF2-binding the and the TRE, the activity of the with the that an The different shown by the GLUT4 enhancer that the of the enhancer in adult skeletal whereas it is in is with the expression of in skeletal muscle during adult R. A. Proc. Natl. Acad. Sci. U. S. A. 1991; 88: PubMed Scopus Google Scholar, M. 1995; PubMed Scopus Google Scholar) and with induction during regeneration D. Biol. 1997; PubMed Scopus Google Scholar). In addition, data a inhibitory of the in adult muscle and a during regeneration. of the activity of the muscle-specific GLUT4 enhancer is that its activity is in adult skeletal normal conditions, with the activity that it at of the transcription MEF2, and the of up-regulation of GLUT4 gene transcription of this enhancer by an in the of expression or activity of such transcription We have that the activity of the enhancer is in soleus in muscles, which to the differences in GLUT4 gene expression and gene transcription that between oxidative and glycolytic muscles (1Kern M. Wells J.A. Stephens J.M. Elton C.W. Friedman J.E. Tapscott E.B. Pekala P.H. Dohm G.L. Biochem. J. 1990; 270: 397-400Crossref PubMed Scopus (219) Google Scholar, 2Camps M. Castello A. Munoz P. Monfar M. Testar X. Palacin M. Zorzano A. Biochem. J. 1992; 282: 765-772Crossref PubMed Scopus (133) Google Scholar, 3Neufer P.D. Carey J.O. Dohm G.L. J. Biol. Chem. 1993; 268: 13824-13829Abstract Full Text PDF PubMed Google Scholar). We that the of in the activity of the enhancer in response to in the MEF2 or was in both muscle data that oxidative muscles a activity of the muscle-specific GLUT4 enhancer glycolytic muscles as a of a activity of the MEF2-binding site. is in with that the soleus muscle a expression of and and a level and activity muscle R. R.S. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar). The of skeletal muscle the of cells. cells that between the of the and the of muscle cells the and which the muscle We that muscle regeneration treatment a induction of GLUT4 which is with the that GLUT4 is with in cultured cells F. Fandos C. T. J. Testar X. Palacin M. Zorzano A. J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar, P. F. Testar X. Palacin M. Zorzano A. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). with a stimulation of the muscle-specific GLUT4 enhancer relative to the muscle and with the functional operation of all elements and We that conditions, the enhancer is induction of myogenic D. Biol. 1997; PubMed Scopus Google Scholar, Z. A. J. Muscle 2001; PubMed Scopus Google Scholar) and by of the MEF2 factors R.L. J.C. Biochem. J. 1997; PubMed Scopus Google Scholar). In this we have that all members of the protein family to with MEF2 and thyroid hormone in the of the muscle-specific GLUT4 on the that muscle regeneration muscle it is that the muscle-specific GLUT4 enhancer participates in the induction of GLUT4 that occurs during in skeletal muscle (4Castello A. Cadefau J. Cusso R. Testar X. Hesketh J.E. Palacin M. Zorzano A. J. Biol. Chem. 1993; 268: 14998-15003Abstract Full Text PDF PubMed Google Scholar, T. Camps M. A. P. A. Testar X. Palacin M. Zorzano A. Endocrinology. 1992; PubMed Scopus Google Scholar, C. S. J. Physiol. 1992; Google Scholar). is that muscle denervation a of muscle GLUT4 gene expression (7Block N.E. Menick D.R. Robinson K.A. Buse M.G. J. Clin. Investig. 1991; 88: 1546-1552Crossref PubMed Scopus (79) Google Scholar, 8Coderre L. Monfar M.M. Chen K.S. Heydrick S.J. Kurowski T.G. Ruderman N.B. Pilch P.F. Endocrinology. 1992; 131: 1821-1825Crossref PubMed Scopus (66) Google Scholar, 9Castelló A. Rodriguez-Manzaneque J.C. Camps M. Pérez-Castillo A. Testar X. Palacín M. Santos A. Zorzano A. J. Biol. Chem. 1994; 269: 5905-5912Abstract Full Text PDF PubMed Google Scholar) of repressed transcription J.P. Tapscott E.B. Olson A.L. Pessin J.E. Dohm G.L. J. Appl. Physiol. 1998; PubMed Scopus Google Scholar). In this we have shown that muscle denervation is to the activity of the muscle-specific GLUT4 enhancer in soleus or in muscles, we have a to In addition, during muscle regeneration, the of at an of the induction of GLUT4 whereas denervation caused a marked of GLUT4 expression muscles in the activity of the muscle-specific GLUT4 data indicate that the muscle-specific GLUT4 enhancer a in the of GLUT4 gene expression that occurs during muscle denervation or the that occurs during muscle regeneration. N. D.W. Lane O. Biochem. 267: PubMed Scopus Google Scholar) have the region of the GLUT4 gene in the regulation of GLUT4 transcription by muscle which to C. S. J. Physiol. 1992; Google Scholar) and is of the muscle-specific GLUT4 In that the muscle-specific GLUT4 enhancer operates at a level in adult In addition, it a that on GLUT4 transcription with GLUT4 such as during muscle regeneration, during and in the of the of skeletal in by a expression of myogenic MEF2, and thyroid hormone receptors. In adult skeletal muscle and normal conditions, the enhancer operates at a by MEF2 transcription factors and inhibited by the TRE, and participates in the differences in GLUT4 gene expression between oxidative and glycolytic muscle In the enhancer operates at a by MEF2, and thyroid hormone receptors. Under all of conditions, the activity of the enhancer is independent of muscle innervation. We for