Protein kinase C regulates internal initiation of translation of the GATA-4 mRNA following vasopressin-induced hypertrophy of cardiac myocytes.
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 Ca(2+) 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 Ca(2+) stores and PKC.
Sharma
Anushree
A
Department of Research & Development, Greater Los Angeles Veterans Affairs Healthcare System, Los Angeles, California 91343.
Masri
Janine
J
Department of Research & Development, Greater Los Angeles Veterans Affairs Healthcare System, Los Angeles, California 91343.
Jo
Oak D
OD
Department of Research & Development, Greater Los Angeles Veterans Affairs Healthcare System, Los Angeles, California 91343.
Bernath
Andrew
A
Department of Research & Development, Greater Los Angeles Veterans Affairs Healthcare System, Los Angeles, California 91343.
Martin
Jheralyn
J
Department of Research & Development, Greater Los Angeles Veterans Affairs Healthcare System, Los Angeles, California 91343.
Funk
Alexander
A
Department of Research & Development, Greater Los Angeles Veterans Affairs Healthcare System, Los Angeles, California 91343.
Gera
Joseph
J
Department of Research & Development, Greater Los Angeles Veterans Affairs Healthcare System, Los Angeles, California 91343; Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles, California 90048. Electronic address: gera@ucla.edu.
D006332:Cardiomegaly / Q000201:enzymology / Q000473:pathology; D045744:Cell Line, Tumor; D050991:GATA4 Transcription Factor / Q000096:biosynthesis / Q000235:genetics*; D006367:HeLa Cells; D006801:Humans; D032383:Myocytes, Cardiac / Q000201:enzymology* / Q000473:pathology*; D014176:Protein Biosynthesis; D011493:Protein Kinase C / Q000502:physiology*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D014667:Vasopressins / Q000633:toxicity*
D050991:GATA4 Transcription Factor; D012333:RNA, Messenger; D014667:Vasopressins; D011493:Protein Kinase C