title: Internal translation of the connexin 43 transcript.
abstract: BACKGROUND
  Connexin 43 (Cx43), the most widely expressed gap junction protein, is associated with a number of physiological and pathological conditions. Many functions of Cx43 have been shown to be independent of gap junction formation and only require the expression of Cx43 C-terminal fragments. Recent evidence demonstrated that naturally occurring C-terminal isoforms can be generated via internal translation.
  
  
  RESULTS
  Here, we confirm that C-terminal domains of Cx43, particularly the major 20-kDa isoform, can be independently generated and regulated by internal translation of the same single GJA1 gene transcript that encodes full-length Cx43. Through direct RNA transfection experiments, we provide evidence that internal translation is not due to a bona fide cap-independent IRES-mediated mechanism, as upstream ribosomal scanning or translation is required. In addition to the mTOR pathway, we show for the first time, using both inhibitors and cells from knockout mice, that the Mnk1/2 pathway regulates the translation of the main 20-kDa isoform.
  
  
  CONCLUSIONS
  Internal translation of the Cx43 transcript occurs but is not cap-independent and requires translation upstream of the internal start codon. In addition to the PI3K/AKT/mTOR pathway, the major 20-kDa isoform is regulated by the Mnk1/2 pathway. Our results have major implications for past and future studies describing gap junction-independent functions of Cx43 in cancer and other pathological conditions. This study provides further clues to the signalling pathways that regulate internal mRNA translation, an emerging mechanism that allows for increased protein diversity and functional complexity from a single mRNA transcript.
authors.forename: Clàudia
authors.initials: C
authors.lastname: Salat-Canela
authors.forename: Marta
authors.initials: M
authors.lastname: Sesé
authors.forename: Cristina
authors.initials: C
authors.lastname: Peula
authors.forename: Santiago
authors.initials: S
authors.lastname: Ramón y Cajal
authors.affiliation: Molecular Pathology, Hospital Universitari Vall d'Hebron - Institut de Recerca (VHIR), Universitat Autònoma de Barcelona, Passeig Vall d'Hebron 119-129, Barcelona 08035, Spain. trond.aasen@vhir.org.
authors.forename: Trond
authors.initials: T
authors.lastname: Aasen
mesh_terms: D000818:Animals; D002460:Cell Line; D018031:Connexin 43 / Q000235:genetics / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D014176:Protein Biosynthesis; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism*; D058570:TOR Serine-Threonine Kinases
chemical_list: D018031:Connexin 43; C543076:GJA1 protein, mouse; D020033:Protein Isoforms; D012333:RNA, Messenger; C546843:mTOR protein, mouse; D017346:Protein Serine-Threonine Kinases; D058570:TOR Serine-Threonine Kinases