Dynamic UTR Usage Regulates Alternative Translation to Modulate Gap Junction Formation during Stress and Aging

• Published in: Cell reports (Cambridge) 2019-05, Vol.27 (9), p.2737-2747.e5
• Main Authors: Zeitz, Michael J., Calhoun, Patrick J., James, Carissa C., Taetzsch, Thomas, George, Kijana K., Robel, Stefanie, Valdez, Gregorio, Smyth, James W.
• Format: Article
• Language: English
• Subjects: Aging; Animals; Animals, Newborn; Cell Communication; connexin; Connexin 43 - genetics; Female; gap junction; Gap Junctions - physiology; Humans; Male; Mice; Mice, Inbred C57BL; mRNA; Myocytes, Cardiac - cytology; Myocytes, Cardiac - metabolism; Protein Biosynthesis; Stress, Physiological; TGF-β; Transforming Growth Factor beta - genetics; Transforming Growth Factor beta - metabolism; translation; Untranslated Regions - genetics; UTR
• ISSN: 2211-1247; 2211-1247
• DOI: 10.1016/j.celrep.2019.04.114

Connexin43 (Cx43; gene name GJA1) is the most ubiquitously expressed gap junction protein, and understanding of its regulation largely falls under transcription and post-translational modification. In addition to Cx43, Gja1 mRNA encodes internally translated isoforms regulating gap junction formation, whose expression is modulated by TGF-β. Here, using RLM-RACE, we identify distinct Gja1 transcripts differing only in 5′ UTR length, of which two are upregulated during TGF-β exposure and hypoxia. Introduction of these transcripts into Gja1−/− cells phenocopies the response of Gja1 to TGF-β with reduced internal translation initiation. Inhibiting pathways downstream of TGF-β selectively regulates levels of Gja1 transcript isoforms and translation products. Reporter assays reveal enhanced translation of full-length Cx43 from shorter Gja1 5′ UTR isoforms. We also observe a correlation among UTR selection, translation, and reduced gap junction formation in aged heart tissue. These data elucidate a relationship between transcript isoform expression and translation initiation regulating intercellular communication. [Display omitted] •In aged hearts and during hypoxia or TGF-β treatment, the GJA1 mRNA 5′ UTR is truncated•Activation of P38 and ERK signal transduction pathways regulate GJA1 5′ UTR length•Truncated GJA1 5′ UTRs are sufficient to suppress internal translation of GJA1-20k•Reduced GJA1-20k expression is correlated with P38 activation in aged hearts Connexin43 gap junctions enable direct intercellular communication facilitating action potential propagation. Internal translation of connexin43 mRNA generates the truncated isoform GJA1-20k, which promotes gap junction formation. During aging, Zeitz et al. find that activation of stress-response pathways shortens connexin43 mRNA UTRs to limit GJA1-20k translation coincident with gap junction loss.