title: Control of fibroblast fibronectin expression and alternative splicing via the PI3K/Akt/mTOR pathway.
abstract: Fibronectin (FN), a ubiquitous glycoprotein that plays critical roles in physiologic and pathologic conditions, undergoes alternative splicing which distinguishes plasma FN (pFN) from cellular FN (cFN). Although both pFN and cFN can be incorporated into the extracellular matrix, a distinguishing feature of cFN is the inclusion of an alternatively spliced exon termed EDA (for extra type III domain A). The molecular steps involved in EDA splicing are well-characterized, but pathways influencing EDA splicing are less clear. We have previously found an obligate role for inhibition of the tumor suppressor phosphatase and tensin homologue on chromosome 10 (PTEN), the primary regulator of the PI3K/Akt pathway, in fibroblast activation. Here we show TGF-beta, a potent inducer of both EDA splicing and fibroblast activation, inhibits PTEN expression and activity in mesenchymal cells, corresponding with enhanced PI3K/Akt signaling. In pten(-/-) fibroblasts, which resemble activated fibroblasts, inhibition of Akt attenuated FN production and decreased EDA alternative splicing. Moreover, inhibition of mammalian target of rapamycin (mTOR) in pten(-/-) cells also blocked FN production and EDA splicing. This effect was due to inhibition of Akt-mediated phosphorylation of the primary EDA splicing regulatory protein SF2/ASF. Importantly, FN silencing in pten(-/-) cells resulted in attenuated proliferation and migration. Thus, our results demonstrate that the PI3K/Akt/mTOR axis is instrumental in FN transcription and alternative splicing, which regulates cell behavior.
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, MI 48109, USA. docew@umich.edu
authors.forename: Eric S
authors.initials: ES
authors.lastname: White
authors.forename: Rommel L
authors.initials: RL
authors.lastname: Sagana
authors.forename: Adam J
authors.initials: AJ
authors.lastname: Booth
authors.forename: Mei
authors.initials: M
authors.lastname: Yan
authors.forename: Ashley M
authors.initials: AM
authors.lastname: Cornett
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Bloomheart
authors.forename: Jessica L
authors.initials: JL
authors.lastname: Tsui
authors.forename: Carol A
authors.initials: CA
authors.lastname: Wilke
authors.forename: Bethany B
authors.initials: BB
authors.lastname: Moore
authors.forename: Jeffrey D
authors.initials: JD
authors.lastname: Ritzenthaler
authors.forename: Jesse
authors.initials: J
authors.lastname: Roman
authors.forename: Andrés F
authors.initials: AF
authors.lastname: Muro
mesh_terms: D017398:Alternative Splicing; D000818:Animals; D015153:Blotting, Western; D002465:Cell Movement; D049109:Cell Proliferation; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism*; D005353:Fibronectins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D008156:Luciferases / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D051059:PTEN Phosphohydrolase / Q000037:antagonists & inhibitors / Q000502:physiology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering / Q000494:pharmacology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases; D016212:Transforming Growth Factor beta / Q000378:metabolism
chemical_list: D005353:Fibronectins; D047908:Intracellular Signaling Peptides and Proteins; D008156:Luciferases; D051059:PTEN Phosphohydrolase; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D058570:TOR Serine-Threonine Kinases; D016212:Transforming Growth Factor beta; C546843:mTOR protein, mouse; C487757:Pten protein, mouse