TGF-β1 regulation of human AT1 receptor mRNA splice variants harboring exon 2

Mickey M. Martin, Jessica A. Buckenberger, Daren L. Knoell, Arthur R. Strauch, Terry S. Elton

Research output: Contribution to journalArticle

5 Scopus citations

Abstract

At least four alternatively spliced mRNAs can be synthesized from the human AT1R (hAT1R) gene that differ only in the inclusion or exclusion of exon 2 and/or 3. RT-PCR experiments demonstrate that splice variants harboring exon 2 accounts for at least 30% of all the hAT1R mRNA transcripts expressed in the human tissues investigated. Since exon 2 contains two upstream AUGs or open reading frames (uORFs), we hypothesized that these AUGs would inhibit the translation of the downstream hAT1R protein ORF harbored in exon 4. This study demonstrates that the inclusion of exon 2 in hAT1R mRNA transcripts dramatically reduces hAT1R protein levels (nine-fold) and significantly attenuates Ang II responsiveness (∼four-fold). Interestingly, only when both AUGs were mutated in combination were the hAT1R density and Ang II signaling levels comparable with those values obtained using mRNA splice variants that did not include exon 2. This observation is consistent with a model where the majority of the ribosomes likely translate uORF#1 and are then unable to reinitiate at the downstream hAT1R ORF, in part due to the presence of AUG#2 and to the short intercistronic spacing. Importantly, TGF-β1 treatment (4 ng/ml for 4 h) of fibroblasts up-regulated hAT1R mRNA splice variants, which harbored exon 2, six-fold. Since AT1R activation is closely associated with cardiovascular disease, the inclusion of exon 2 by alternative splicing represents a novel mechanism to reduce the overall production of the hAT1R protein and possibly limit the potential pathological effects of AT1R activation.

Original languageEnglish (US)
Pages (from-to)21-31
Number of pages11
JournalMolecular and Cellular Endocrinology
Volume249
Issue number1-2
DOIs
StatePublished - Apr 25 2006

Keywords

  • Alternative splicing
  • Angiotensin II receptors
  • Translational regulation

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Endocrinology

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