title: Intron retention generates a novel Id3 isoform that inhibits vascular lesion formation.
abstract: The expression of intron-containing messages has been shown to occur in a variety of diseases including lactic acidosis, Cowden Syndrome, and several cancers. However, it is unknown whether these intron-containing messages result in protein production in vivo. Indeed, intron-containing RNAs are typically retained in the nucleus, targeted for degradation, or are repressed translationally. Here, we show that during vascular lesion formation in rats, an alternative isoform of the helix-loop-helix transcription factor Id3 (Id3a) generated by intron retention is abundantly expressed. We demonstrate that Id3 is expressed early in lesion formation when the proliferative index of the neointima is highest and that Id3 promotes smooth muscle cell (SMC) proliferation and S-phase entry and inhibits transcription of the cell-cycle inhibitor p21(Cip1). Using an Id3a-specific antibody developed by our laboratory, we show that Id3a protein is induced during vascular lesion formation and that Id3a expression peaks late when the proliferative index is low or declining and extensive apoptosis is observed. Furthermore, Id3a fails to promote SMC growth and S-phase entry or to inhibit p21(Cip1) promoter transactivation. In contrast, Id3a stimulates SMC apoptosis and inhibits endogenous Id3 production. Adenoviral delivery of Id3a inhibited lesion formation in balloon-injured rat carotid arteries in vivo. These data describe a novel feedback loop whereby intron retention generates an Id3 isoform that acts to limit SMC growth during vascular lesion formation, providing the first evidence that regulated intron retention can modulate a pathologic process in vivo.
authors.affiliation: Cardiovascular Division, Department of Internal Medicine, and Cardiovascular Research Center, University of Virginia Health Sciences Center, Charlottesville, 22908, USA. .
authors.forename: Scott T
authors.initials: ST
authors.lastname: Forrest
authors.forename: Kurt G
authors.initials: KG
authors.lastname: Barringhaus
authors.forename: Demetra
authors.initials: D
authors.lastname: Perlegas
authors.forename: Marie-Louise
authors.initials: ML
authors.lastname: Hammarskjold
authors.forename: Coleen A
authors.initials: CA
authors.lastname: McNamara
mesh_terms: D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D002455:Cell Division; D002467:Cell Nucleus / Q000378:metabolism; D002470:Cell Survival; D002478:Cells, Cultured; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000378:metabolism; D005091:Exons; D018014:Gene Transfer Techniques; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D051796:Inhibitor of Differentiation Proteins; D007438:Introns; D008297:Male; D008957:Models, Genetic; D032389:Myocytes, Smooth Muscle / Q000378:metabolism; D009363:Neoplasm Proteins / Q000737:chemistry*; D011401:Promoter Regions, Genetic; D020033:Protein Isoforms; D012313:RNA / Q000378:metabolism; D012326:RNA Splicing; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D016196:S Phase; D013997:Time Factors; D015533:Transcriptional Activation; D014162:Transfection
chemical_list: C493958:Cdkn1a protein, rat; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D051796:Inhibitor of Differentiation Proteins; D009363:Neoplasm Proteins; D020033:Protein Isoforms; D012333:RNA, Messenger; C075640:ID3 protein, human; D012313:RNA