title: Role of BMPR2 alternative splicing in heritable pulmonary arterial hypertension penetrance.
abstract: BACKGROUND
  Bone morphogenic protein receptor 2 (BMPR2) gene mutations are the most common cause of heritable pulmonary arterial hypertension. However, only 20% of mutation carriers get clinical disease. Here, we explored the hypothesis that this reduced penetrance is due in part to an alteration in BMPR2 alternative splicing.
  
  
  RESULTS
  Our data showed that BMPR2 has multiple alternative spliced variants. Two of these, isoform-A (full length) and isoform-B (missing exon 12), were expressed in all tissues analyzed. Analysis of cultured lymphocytes of 47 BMPR2 mutation-positive heritable pulmonary arterial hypertension patients and 35 BMPR2 mutation-positive unaffected carriers showed that patients had higher levels of isoform-B compared with isoform-A (B/A ratio) than carriers (P=0.002). Furthermore, compared with cells with a low B/A ratio, cells with a high B/A ratio had lower levels of unphosphorylated cofilin after BMP stimulation. Analysis of exon 12 sequences identified an exonic splice enhancer that binds serine arginine splicing factor 2 (SRSF2). Because SRSF2 promotes exon inclusion, reduced SRSF2 expression would mean that exon 12 would not be included in final BMPR2 mRNA (thus promoting increased isoform-B formation). Western blot analysis showed that SRSF2 expression was lower in cells from patients compared with cells from carriers and that siRNA-mediated knockdown of SRSF2 in pulmonary microvascular endothelial cells resulted in elevated levels of isoform-B compared with isoform-A, ie, an elevated B/A ratio.
  
  
  CONCLUSIONS
  Alterations in BMPR2 isoform ratios may provide an explanation of the reduced penetrance among BMPR2 mutation carriers. This ratio is controlled by an exonic splice enhancer in exon 12 and its associated splicing factor, SRSF2.
authors.affiliation: Department of Pediatrics, Vanderbilt University Medical Center, Nashville, TN 37232, USA.
authors.forename: Joy
authors.initials: J
authors.lastname: Cogan
authors.forename: Eric
authors.initials: E
authors.lastname: Austin
authors.forename: Lora
authors.initials: L
authors.lastname: Hedges
authors.forename: Bethany
authors.initials: B
authors.lastname: Womack
authors.forename: James
authors.initials: J
authors.lastname: West
authors.forename: James
authors.initials: J
authors.lastname: Loyd
authors.forename: Rizwan
authors.initials: R
authors.lastname: Hamid
mesh_terms: D000328:Adult; D000368:Aged; D017398:Alternative Splicing; D052006:Bone Morphogenetic Protein Receptors, Type II / Q000235:genetics*; D065627:Familial Primary Pulmonary Hypertension; D005260:Female; D006801:Humans; D006976:Hypertension, Pulmonary / Q000235:genetics*; D008297:Male; D008875:Middle Aged; D019683:Penetrance; D020033:Protein Isoforms
chemical_list: D020033:Protein Isoforms; D052006:Bone Morphogenetic Protein Receptors, Type II