Protein Kinase C Regulates Internal Initiation of Translation of the GATA-4 mRNA following Vasopressin-induced Hypertrophy of Cardiac Myocytes

Abstract

GATA-4 is a key member of the GATA family of transcription factors involved in cardiac development and growth as well as in cardiac hypertrophy and heart failure. Our previous studies suggest that GATA-4 protein synthesis may be translationally regulated. We report here that the 518-nt long 5′-untranslated region (5′-UTR) of the GATA-4 mRNA, which is predicted to form stable secondary structures (–65 kcal/mol) such as to be inhibitory to cap-dependent initiation, confers efficient translation to monocistronic reporter mRNAs in cell-free extracts. Moreover, uncapped GATA-4 5′-UTR containing monocistronic reporter mRNAs continue to be well translated while capped reporters are insensitive to the inhibition of initiation by cap-analog, suggesting a cap-independent mechanism of initiation. Utilizing a dicistronic luciferase mRNA reporter containing the GATA-4 5′-UTR within the intercistronic region, we demonstrate that this leader sequence confers functional internal ribosome entry site (IRES) activity. The activity of the GATA-4 IRES is unaffected in trans-differentiating P19CL6 cells, however, is strongly stimulated immediately following arginine-vasopressin exposure of H9c2 ventricular myocytes. IRES activity is then maintained at submaximal levels during hypertrophic growth of these cells. Supraphysiological Ca2+ levels diminished stimulation of IRES activity immediately following exposure to vasopressin and inhibition of protein kinase C activity utilizing a pseudosubstrate peptide sequence blocked IRES activity during hypertrophy. Thus, our data suggest a mechanism for GATA-4 protein synthesis under conditions of reduced global cap-dependent translation, which is maintained at a submaximal level during hypertrophic growth and point to the regulation of GATA-4 IRES activity by sarco(ER)-reticular Ca2+ stores and PKC. GATA-4 is a key member of the GATA family of transcription factors involved in cardiac development and growth as well as in cardiac hypertrophy and heart failure. Our previous studies suggest that GATA-4 protein synthesis may be translationally regulated. We report here that the 518-nt long 5′-untranslated region (5′-UTR) of the GATA-4 mRNA, which is predicted to form stable secondary structures (–65 kcal/mol) such as to be inhibitory to cap-dependent initiation, confers efficient translation to monocistronic reporter mRNAs in cell-free extracts. Moreover, uncapped GATA-4 5′-UTR containing monocistronic reporter mRNAs continue to be well translated while capped reporters are insensitive to the inhibition of initiation by cap-analog, suggesting a cap-independent mechanism of initiation. Utilizing a dicistronic luciferase mRNA reporter containing the GATA-4 5′-UTR within the intercistronic region, we demonstrate that this leader sequence confers functional internal ribosome entry site (IRES) activity. The activity of the GATA-4 IRES is unaffected in trans-differentiating P19CL6 cells, however, is strongly stimulated immediately following arginine-vasopressin exposure of H9c2 ventricular myocytes. IRES activity is then maintained at submaximal levels during hypertrophic growth of these cells. Supraphysiological Ca2+ levels diminished stimulation of IRES activity immediately following exposure to vasopressin and inhibition of protein kinase C activity utilizing a pseudosubstrate peptide sequence blocked IRES activity during hypertrophy. Thus, our data suggest a mechanism for GATA-4 protein synthesis under conditions of reduced global cap-dependent translation, which is maintained at a submaximal level during hypertrophic growth and point to the regulation of GATA-4 IRES activity by sarco(ER)-reticular Ca2+ stores and PKC. The family of GATA transcription factors regulates differentiation, growth, and survival of a wide range of cell types (1Molkentin J.D. J. Biol. Chem. 2000; 275: 38949-38952Abstract Full Text Full Text PDF PubMed Scopus (727) Google Scholar). GATA-4 is a zinc finger-containing transcription factor, which is expressed, in various mesoderm-derived tissues such as the lung, liver, gonad, and gut where it regulates tissue-specific gene expression (2Peterkin T. Gibson A. Loose M. Patient R. Sem. Cell Dev. Biol. 2005; 16: 83-94Crossref PubMed Scopus (150) Google Scholar, 3Pikkarainen S. Tokola H. Kerkela R. Ruskoaho H. Cardiovasc. Res. 2004; 63: 196-207Crossref PubMed Scopus (307) Google Scholar). Consistent with the observed expression patterns, targeted disruption of GATA-4 in mice has elucidated important functions in each of these tissues. GATA-4 is also essential for proper cardiac morphogenesis and also plays an important role as one of the transcriptional factors, which regulates the hypertrophic response in cardiac myocytes (4Liang Q. De Windt L.J. Witt S.A. Kimball T.R. Markham B.E. Molkentin J.D. J. Biol. Chem. 2001; 276: 30245-30253Abstract Full Text Full Text PDF PubMed Scopus (285) Google Scholar, 5Grepin C. Nemer G. Nemer M. Development. 1997; 124: 2387-2395Crossref PubMed Google Scholar, 6Aries A. Paradis P. Lefebvre C. Schwartz R.J. Nemer M. Proc. Natl. Acad. Sci. U. S. A. 2004; 101: 6975-6980Crossref PubMed Scopus (227) Google Scholar). Several studies suggest that GATA-4 can be regulated at both the transcriptional level and by phosphomodulation during hypertrophy (1Molkentin J.D. J. Biol. Chem. 2000; 275: 38949-38952Abstract Full Text Full Text PDF PubMed Scopus (727) Google Scholar, 7Hasegawa K. Lee S.J. Jobe S.M. Markham B.E. Kitsis R.N. Circulation. 1997; 96: 3943-3953Crossref PubMed Scopus (154) Google Scholar, 8Herzig T.C. Jobe S.M. Aoki H. Molkentin J.D. Cowley Jr., A.W. Izumo S. Markham B.E. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 7543-7548Crossref PubMed Scopus (179) Google Scholar). In cultured neonatal cardiomyocytes, electrical pacing-induced hypertrophy is associated with a significant increase in GATA-4 mRNA, suggesting a mechanism whereby total GATA-4 content is up-regulated during hypertrophy (9Xia Y. McMillin J.B. Lewis A. Moore M. Zhu W.G. Williams R.S. Kellems R.E. J. Biol. Chem. 2000; 275: 1855-1863Abstract Full Text Full Text PDF PubMed Scopus (100) Google Scholar). Increases in GATA-4 phosphorylation mediated by Raf/Mek/Erk signaling subsequent to hypertrophic agonist administration have also been demonstrated (10Morimoto T. Hasegawa K. Kaburagi S. Kakita T. Wada H. Yanazume T. Sasayama S. J. Biol. Chem. 2000; 275: 13721-13726Abstract Full Text Full Text PDF PubMed Scopus (129) Google Scholar). Our previous data (11Gera J.F. Mellinghoff I.K. Shi Y. Rettig M.B. Tran C. Hsu J.-H. Sawyers C.L. Lichtenstein A.K. J. Biol. Chem. 2004; 279: 2737-2746Abstract Full Text Full Text PDF PubMed Scopus (305) Google Scholar) suggested that the GATA-4 mRNA is also regulated at the translational level and we undertook this study to evaluate the possibility that such control may play a role in augmenting GATA-4 potency during differentiation or hypertrophy in cardiac myocytes. Most mRNAs contain 5′-UTRs 3The abbreviations used are: UTR, untranslated region; IRES, internal ribosome entry site; ORF, open reading frame; uORF, upstream open reading frame; LUC, luciferase; mTOR, mammalian target of rapamycin; ITAF, IRES trans-acting factor; eIF-2α, eukaryotic translation initiation factor 2α; AVP, arginine vasopressin; ER, endoplasmic reticulum; BiP, immunoglobin heavy chain binding protein; PKC, protein kinase C; Cdk1, cyclin-dependent kinase 1; α-MHC, α-myosin heavy chain; RACE, rapid amplification of cDNA 3The abbreviations used are: UTR, untranslated region; IRES, internal ribosome entry site; ORF, open reading frame; uORF, upstream open reading frame; LUC, luciferase; mTOR, mammalian target of rapamycin; ITAF, IRES trans-acting factor; eIF-2α, eukaryotic translation initiation factor 2α; AVP, arginine vasopressin; ER, endoplasmic reticulum; BiP, immunoglobin heavy chain binding protein; PKC, protein kinase C; Cdk1, cyclin-dependent kinase 1; α-MHC, α-myosin heavy chain; RACE, rapid amplification of cDNA that are and in which efficient cap-dependent translational initiation The and of of Scholar). the of mRNAs are and can contain upstream or such that are to In a of these translation initiation is mediated by cap-independent an internal ribosome entry site P. Dev. 2001; PubMed Scopus Google Scholar). translation initiation can during a of conditions and has been to initiation for mRNAs during differentiation, and during M. S.A. Cell 2005; PubMed Scopus Google Scholar, M. J. Biol. Chem. 2005; Full Text Full Text PDF PubMed Scopus Google Scholar, M. 2004; PubMed Scopus Google Scholar, S. S. 2001; PubMed Scopus Google Scholar, M. Cell Biol. 2005; PubMed Scopus Google Scholar). we mRNAs which or to be well translated during conditions cap-dependent translation initiation (11Gera J.F. Mellinghoff I.K. Shi Y. Rettig M.B. Tran C. Hsu J.-H. Sawyers C.L. Lichtenstein A.K. J. Biol. Chem. 2004; 279: 2737-2746Abstract Full Text Full Text PDF PubMed Scopus (305) Google Scholar, Y. A. H. Lichtenstein A. J. J. Biol. Chem. 2005; Full Text Full Text PDF PubMed Scopus Google Scholar). of these translational following exposure of to the with in the global inhibition of cap-dependent translation a to the of initiation Dev. 2001; PubMed Scopus Google Scholar). The GATA-4 has a 5′-UTR and upstream initiation PubMed Scopus Google Scholar). to the possibility of this mRNA translation in a cap-independent and contain an IRES within GATA-4 has a role in the regulation of differentiation and translation may be during differentiation G. R. J. Scholar, H. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google we the of this leader to internal initiation during this We the P19CL6 cell to the possibility that the GATA-4 mRNA translation during The P19CL6 cell is a of the cell which and A. Cell PubMed Scopus Google Scholar). GATA-4 is in these cells, is differentiation, and is to K. Y. S. T. T. A. T. T. Y. Biol. PubMed Scopus Google Scholar). GATA-4 is to be for cardiac hypertrophy we translation initiation of GATA-4 mRNA following hypertrophy of H9c2 We report here that the GATA-4 5′-UTR IRES which is stimulated during hypertrophy during Our data also suggest that GATA-4 IRES activity is with phosphorylation during hypertrophy. We that translational initiation of GATA-4 mRNA protein synthesis under conditions of reduced cap-dependent initiation during the response to vasopressin and during hypertrophic Moreover, our data suggest that Ca2+ may play a role in the stimulation of GATA-4 IRES activity a protein kinase during hypertrophy. Cell and cell and maintained in with P19CL6 cell the dicistronic reporter mRNAs by with and by and subsequent for stable expression by to under conditions by at a of in a with The of differentiation with the of as The protein kinase C cell pseudosubstrate peptide and and of the GATA-4 mRNA total H9c2 or the as by the the dicistronic the GATA-4 5′-UTR and the site of by A. of The of has been Y. A. H. Lichtenstein A. J. J. Biol. Chem. 2005; Full Text Full Text PDF PubMed Scopus Google Scholar). The GATA-4 5′-UTR also a of Biol. PubMed Scopus Google by to containing a containing an kcal/mol) P. J. Proc. Natl. Acad. Sci. PubMed Scopus (154) Google Scholar) by and immediately upstream of the in to the used in the monocistronic of in the luciferase or the GATA-4 luciferase and the to and the dicistronic used in the in by a the ORF, the intercistronic region and the and this to and by amplification of the dicistronic of and Y. A. H. Lichtenstein A. J. J. Biol. Chem. 2005; Full Text Full Text PDF PubMed Scopus Google and as The IRES and the site of to and is In of and mRNA and dicistronic and used as to in the Y. A. H. Lichtenstein A. J. J. Biol. Chem. 2005; Full Text Full Text PDF PubMed Scopus Google Scholar). mRNAs capped and used to of the cell as Y. A. H. Lichtenstein A. J. J. Biol. Chem. 2005; Full Text Full Text PDF PubMed Scopus Google Scholar). The translation with the and mRNA reporter and for by with following and and luciferase and as Biol. PubMed Scopus Google Scholar). following and luciferase luciferase are as activity of the the of R.E. 2004; PubMed Scopus Google Scholar). of the luciferase and with the or dicistronic cells. The within the used and in or H9c2 with at a of following the and in with GATA-4 protein at with of and then with protein The in and and the for in The by the and a of and of total protein with of activity the C as by the cell with and peptide in at for and and by a and as Y. A. H. Lichtenstein A. J. J. Biol. Chem. 2005; Full Text Full Text PDF PubMed Scopus Google Scholar) with the cell or in translation with of total in by and to to for the in by exposure to or by a the to the of the as (11Gera J.F. Mellinghoff I.K. Shi Y. Rettig M.B. Tran C. Hsu J.-H. Sawyers C.L. Lichtenstein A.K. J. Biol. Chem. 2004; 279: 2737-2746Abstract Full Text Full Text PDF PubMed Scopus (305) Google Scholar). in containing at of and and at for at in a an at a of The of the at the a and containing and a used in of the the in an with a for the mRNAs to in and to and with to the following and and The GATA-4 the of mRNA in Cell to study the translational control of the GATA-4 mRNA the transcriptional site to be and We used to and total or cells. The sequence in and with the 5′-UTR PubMed Scopus Google Scholar). The GATA-4 leader is and upstream initiation of which are in sequence to initiation by a the of M. Res. PubMed Scopus Google predicted a stable with We that the GATA-4 5′-UTR be inhibitory to cap-dependent and may be translated in a cap-independent this the we the GATA-4 5′-UTR immediately upstream of the luciferase open reading in a to as in In mRNAs the capped or and used to cell-free R. J. PubMed Scopus Google Scholar). in uncapped in mRNA translated as with capped in mRNAs in an uncapped containing the GATA-4 5′-UTR translated at the levels as capped mRNAs or capped mRNAs we or the initiation of capped or mRNAs in extracts. can be in translation by in the of cap-analog, while translated well at a of the that of and mRNAs of the be in the in translation data suggested that the GATA-4 5′-UTR in the mRNA or are to contain Thus, the 5′-UTR of GATA-4 can efficient translation of uncapped reporter The of the GATA-4 mRNA in in we observed that the GATA-4 mRNA well translated under conditions of reduced (11Gera J.F. Mellinghoff I.K. Shi Y. Rettig M.B. Tran C. Hsu J.-H. Sawyers C.L. Lichtenstein A.K. J. Biol. Chem. 2004; 279: 2737-2746Abstract Full Text Full Text PDF PubMed Scopus (305) Google we to a be translation in We a stable kcal/mol) P. J. Proc. Natl. Acad. Sci. PubMed Scopus (154) Google Scholar) immediately to the in to reduced the translation of the by the GATA-4 5′-UTR translation cap-dependent translation in this we the GATA-4 5′-UTR the and the translation site luciferase activity in cell then the suggesting that the GATA-4 5′-UTR can translation initiation cap-dependent is reduced within the or GATA-4 5′-UTR we the to and for luciferase activity. can be significant luciferase activity suggesting that these in the of the monocistronic reporter activity. mRNAs the GATA-4 5′-UTR within the IRES the GATA-4 5′-UTR as an IRES in we it the intercistronic region within the dicistronic mRNA reporter to the luciferase as the and the luciferase as the In the cell with the luciferase activity as with for the control a with a the IRES in these also luciferase which to with luciferase levels in the cell suggesting that the mRNA levels and the levels of cap-dependent translation of the dicistronic a stable luciferase mRNA of the for each In an to the possibility of monocistronic containing the luciferase in these dicistronic mRNAs we to by The of the mRNAs the and in in a of the with observed suggesting that the that the GATA-4 5′-UTR can translation and that the luciferase activity observed is of cap-dependent initiation of monocistronic reporter in the GATA-4 the GATA-4 5′-UTR in a dicistronic by of the the intercistronic region we the upstream of the within the dicistronic to the GATA-4 5′-UTR of the translation of the upstream also in a in luciferase We or in the cell and the levels of luciferase activity in these cells. in of the stable reduced luciferase activity by as with with the control in the cell the luciferase well translated and luciferase activity cell with the to with the control dicistronic the control for the possibility of a within the GATA-4 5′-UTR in the of the dicistronic reporter we also the GATA-4 5′-UTR in a of and luciferase activity in with this with the monocistronic significant luciferase activity data the that the GATA-4 5′-UTR of the and GATA-4 5′-UTR IRES data to this point the of an IRES within the GATA-4 5′-UTR in the of R. PubMed Scopus (100) Google Scholar, M. T. Lewis S.M. Lefebvre S. 2005; PubMed Scopus Google Scholar, Y. P. J. PubMed Scopus Google Scholar) activity or to the of monocistronic containing we to the in and dicistronic in the possibility of reporter mRNA and the of the We which the dicistronic and in and by Biol. PubMed Scopus Google Scholar). following cell and luciferase activity in the luciferase activity in with the dicistronic mRNAs containing the and and in with the dicistronic mRNA containing the IRES mRNA, as with the control In we also to luciferase expression by luciferase expression dicistronic monocistronic luciferase as a of activity or one that the region of the expression R.E. 2004; PubMed Scopus Google Scholar, R. PubMed Scopus (100) Google Scholar). Thus, the with the in can be in which with monocistronic and luciferase in a in luciferase activity while activity the dicistronic control with the the ORF, we observed a in activity with a of luciferase by a suggesting that both are translated the dicistronic with the and containing the GATA-4 5′-UTR or the IRES the within the intercistronic region, and luciferase reduced suggested that the luciferase we observed dicistronic mRNAs and these data the that the GATA-4 5′-UTR a GATA-4 IRES during of GATA-4 plays a role in differentiation J.D. Q. S.A. Dev. 1997; PubMed Scopus Google Scholar) and IRES activity has been to be stimulated during this G. R. J. we GATA-4 IRES activity in P19CL6 to P19CL6 which the mRNA for GATA-4 as well as to have expression following the of differentiation in this cell in GATA-4 expression is by of in differentiation and is by in GATA-4 mRNA levels in differentiation the that GATA-4 is regulated at the translational We then GATA-4 protein synthesis in P19CL6 during in GATA-4 protein synthesis in in differentiation by to maintained in growth expression of the cardiac of and heavy chain also observed with the of GATA-4 expression The mRNA also to be as by and unaffected by in The phosphorylation of has been to be for IRES activity under conditions differentiation, the are M. J. Biol. Chem. 2005; Full Text Full Text PDF PubMed Scopus Google Scholar, G. R. J. Scholar, J. P. M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, J. A. R. J. M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). Thus, we the phosphorylation of following the of differentiation in P19CL6 in the of by the of differentiation and by We then luciferase activity in to at various as with maintained in growth in significant increase in the of luciferase in the mRNA at following the of in the control mRNA, in luciferase observed during data suggested that initiation of GATA-4 mRNA to in P19CL6 GATA-4 IRES during of are during of and mRNA translation initiation is P. Dev. 2001; PubMed Scopus Google Scholar, S.M. M. Cell 2005; PubMed Scopus Google we GATA-4 IRES activity stimulated following the of hypertrophy in cardiac myocytes. We GATA-4 expression in H9c2 stimulated to hypertrophy by vasopressin exposure Cell PubMed Scopus Google Scholar). of H9c2 with vasopressin at of or and at Ca2+ is and is to in a rapid of protein synthesis in with phosphorylation of inhibition by of exposure to the in protein synthesis is by a stimulation of protein synthesis by of exposure J. Cell Biol. 2000; PubMed Scopus Google Scholar). hypertrophic growth by following vasopressin exposure with in cell or cell Cell PubMed Scopus Google Scholar, J. Cell Biol. 2000; PubMed Scopus Google Scholar). Thus, we the of vasopressin GATA-4 expression at and in of H9c2 with vasopressin in a increase in GATA-4 protein levels as as following exposure to the The BiP, a protein expression is to be stimulated following hypertrophy J. 2001; PubMed Scopus Google Scholar, J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google demonstrated while protein content within of exposure with hypertrophic of GATA-4 mRNA demonstrated a increase in levels by following these data of translational control of the GATA-4 mRNA following vasopressin we GATA-4 protein synthesis following exposure to the in GATA-4 protein synthesis stimulated to levels in control within of synthesis then maintained at levels during hypertrophic of GATA-4 mRNA also demonstrated of GATA-4 mRNA by of vasopressin with of the mRNA in as with at of vasopressin of the mRNA levels by the and also a increase in mRNA of GATA-4 mRNA following vasopressin exposure GATA-4 translation initiation also following vasopressin we H9c2 with and to vasopressin and luciferase at various following in luciferase activity within of vasopressin exposure and maintained levels of activity with the in GATA-4 translational and total GATA-4 protein expression following vasopressin significant in the observed in control with the following exposure to GATA-4 IRES activity of the during the hypertrophic growth following suggested that GATA-4 IRES activity stimulated during hypertrophic growth of H9c2 C for GATA-4 IRES during have activity in the of translation of mRNAs following vasopressin in H9c2 J. Cell Biol. 2000; PubMed Scopus Google Scholar, J. 2001; PubMed Scopus Google Scholar). Thus, we activity for GATA-4 IRES activity during the hypertrophic response to activity we a pseudosubstrate PKC, J. Cell Biol. 2000; PubMed Scopus Google Scholar, T. J. J. Biol. Chem. Full Text PDF PubMed Google Scholar). in H9c2 to vasopressin of within of activity by the pseudosubstrate peptide at a of H9c2 with and with vasopressin in the or of the and luciferase at various in the of to luciferase activity within of vasopressin exposure in the of increase in luciferase activity diminished by of with the of and the of cap-dependent protein synthesis by following exposure to We however, that the observed in GATA-4 IRES activity activity at following vasopressin exposure to submaximal of the luciferase in luciferase activity is with protein in Res. PubMed Scopus Google Scholar). The of to luciferase activity following exposure to vasopressin in with the pseudosubstrate suggested that activity for the of GATA-4 IRES activity following vasopressin The GATA-4 increase in protein following vasopressin exposure also by with the expression also activity following vasopressin exposure as been demonstrated J. 2001; PubMed Scopus Google Scholar). Ca2+ GATA-4 IRES the synthesis of has been demonstrated to be to Ca2+ in H9c2 following vasopressin hypertrophy J. Cell Biol. 2000; PubMed Scopus Google Scholar, J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google we Ca2+ levels GATA-4 IRES activity and protein levels following vasopressin Ca2+ levels are to Ca2+ following J. Cell Biol. 2000; PubMed Scopus Google Scholar). in of with with vasopressin in the of Ca2+ in an in luciferase activity by as with containing Ca2+ of GATA-4 protein levels also reduced in the of Ca2+ In we with the Ca2+ which Ca2+ entry and has been demonstrated to Ca2+ content of H9c2 by at the used J. Cell Biol. 2000; PubMed Scopus Google vasopressin in the stimulation of GATA-4 IRES activity and of protein levels as been observed with the data the that the IRES activity and protein expression of GATA-4 in H9c2 following vasopressin is the of Ca2+ by the Our previous studies a cap-independent mechanism of translation initiation for a of under conditions of (11Gera J.F. Mellinghoff I.K. Shi Y. Rettig M.B. Tran C. Hsu J.-H. Sawyers C.L. Lichtenstein A.K. J. Biol. Chem. 2004; 279: 2737-2746Abstract Full Text Full Text PDF PubMed Scopus (305) Google Scholar). In this report we have the mechanism of initiation of the GATA-4 mRNA and an IRES within Moreover, we have IRES activity by which the that the GATA-4 is to translation such that is We also demonstrate that the GATA-4 mRNA is to translational control during differentiation and hypertrophy. We have also demonstrated that GATA-4 IRES activity is stimulated with phosphorylation of eIF-2α, and during hypertrophic growth of following with the arginine vasopressin in a our suggest that Ca2+ stores is also for IRES activity immediately following exposure to the Our are with a in which vasopressin of in the inhibition of global cap-dependent protein synthesis to phosphorylation of eIF-2α, during which GATA-4 IRES activity is strongly stimulated as a of Ca2+ the and of PKC. The subsequent this inhibition in an increase in cap-dependent protein during the hypertrophic growth at which GATA-4 IRES activity is maintained at submaximal levels and is activity for Thus, GATA-4 protein synthesis is during hypertrophic and synthesis is maintained during hypertrophy to of for the of cell The that Ca2+ stores rapid GATA-4 IRES activity is Several are to with to mRNA T. A.K. Cell PubMed Scopus Google Scholar, A.K. 2001; PubMed Scopus Google Scholar) and we a significant increase in the mRNA levels of GATA-4 following vasopressin increase in may be the of transcription or mRNA it is also that such factors may or IRES activity in response to in Ca2+ the factors and C are to in the of Ca2+ R. M. J. J. M. Biol. PubMed Google Scholar) and in is also to be regulated by phosphorylation which to J. P. J. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, H. A. H. PubMed Scopus Google Scholar). Thus, these data Ca2+ signaling to activity. studies regulates GATA-4 IRES activity our a for activity for GATA-4 IRES during hypertrophy. Our data that the GATA-4 IRES is also during hypertrophic growth the cap-dependent initiation mechanism is Several have the for and in cardiac hypertrophy during the of cap-dependent initiation T. K. Izumo S. Circulation. PubMed Scopus Google Scholar, T. Izumo S. Circulation. 2004; PubMed Scopus Google Scholar, J. Izumo S. Res. PubMed Scopus Google Scholar, H. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, A. C. J. 2001; PubMed Scopus Google Scholar). Our data a role for the cap-independent synthesis of during this The of cap-dependent initiation may with the initiation of GATA-4 mRNA we observed in our the control of cap-independent protein synthesis suggest that mRNAs may be to translation by both cap-dependent and cap-independent conditions and that the may be P. Dev. 2001; PubMed Scopus Google Scholar, M. J. Biol. Chem. 2005; Full Text Full Text PDF PubMed Scopus Google Scholar). IRES have for initiation factors M. J. Biol. Chem. 2005; Full Text Full Text PDF PubMed Scopus Google Scholar, C. G. P. 2004; Full Text Full Text PDF PubMed Scopus Google Scholar). a cap-dependent IRES has been within the mRNA which is following M. R.E. J. Biol. Chem. 2005; Full Text Full Text PDF PubMed Scopus Google Scholar). We that during hypertrophic a is which GATA-4 IRES activity and reduced activity while conditions for cap-dependent initiation are also Several studies have demonstrated a role for phosphorylation in the regulation of G. R. J. Scholar, J. P. M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, J. A. R. J. M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). the by which phosphorylation to stimulation of IRES activity is well mechanism may be the of a IRES to efficient initiation in the of as a of have initiation translation for P. PubMed Scopus Google Scholar, P. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar). are to in a is possibility may be that phosphorylation IRES activity or of an stimulation of GATA-4 IRES activity with phosphorylation and however, the mechanism by which these may be is is that phosphorylation in or of an ITAF, which is for GATA-4 IRES activity as has been for activity is regulated by phosphorylation J. P. M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). the that the GATA-4 IRES activity during P19CL6 cell differentiation, phosphorylation that phosphorylation is to GATA-4 IRES activity for GATA-4 IRES activity may be or such as to IRES activity under this In we activity stimulated during differentiation of P19CL6 and significant Thus, it is that a or regulates GATA-4 IRES activity during hypertrophy which is during differentiation factors are for GATA-4 IRES activity under these We and for We also for J. G. Lichtenstein for