title: Thoracic aortic aneurysm (TAAD)-causing mutation in actin affects formin regulation of polymerization.
abstract: More than 30 mutations in ACTA2, which encodes α-smooth muscle actin, have been identified to cause autosomal dominant thoracic aortic aneurysm and dissection. The mutation R256H is of particular interest because it also causes patent ductus arteriosus and moyamoya disease. R256H is one of the more prevalent mutations and, based on its molecular location near the strand-strand interface in the actin filament, may affect F-actin stability. To understand the molecular ramifications of the R256H mutation, we generated Saccharomyces cerevisiae yeast cells expressing only R256H yeast actin as a model system. These cells displayed abnormal cytoskeletal morphology and increased sensitivity to latrunculin A. After cable disassembly induced by transient exposure to latrunculin A, mutant cells were delayed in reestablishing the actin cytoskeleton. In vitro, mutant actin exhibited a higher than normal critical concentration and a delayed nucleation. Consequently, we investigated regulation of mutant actin by formin, a potent facilitator of nucleation and a protein needed for normal vascular smooth muscle cell development. Mutant actin polymerization was inhibited by the FH1-FH2 fragment of the yeast formin, Bni1. This fragment strongly capped the filament rather than facilitating polymerization. Interestingly, phalloidin or the presence of wild type actin reversed the strong capping behavior of Bni1. Together, the data suggest that the R256H actin mutation alters filament conformation resulting in filament instability and misregulation by formin. These biochemical effects may contribute to abnormal histology identified in diseased arterial samples from affected patients.
authors: Department of Pediatrics, Roy A. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242, USA.
authors: Lindsey E
authors: LE
authors: Malloy
authors: Kuo-Kuang
authors: KK
authors: Wen
authors: Alyson R
authors: AR
authors: Pierick
authors: Elesa W
authors: EW
authors: Wedemeyer
authors: Sarah E
authors: SE
authors: Bergeron
authors: Nicole D
authors: ND
authors: Vanderpool
authors: Melissa
authors: M
authors: McKane
authors: Peter A
authors: PA
authors: Rubenstein
authors: Heather L
authors: HL
authors: Bartlett
mesh_terms: D008841:Actin Cytoskeleton / Q000235:genetics / Q000378:metabolism*; D000199:Actins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D019943:Amino Acid Substitution; D001014:Aortic Aneurysm / Q000235:genetics / Q000378:metabolism*; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology; D006801:Humans; D008840:Microfilament Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008954:Models, Biological; D020125:Mutation, Missense; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D053778:Thiazolidines / Q000494:pharmacology
chemical_list: C541116:ACTA2 protein, human; D000199:Actins; C105191:Bni1 protein, S cerevisiae; D019086:Bridged Bicyclo Compounds, Heterocyclic; D008840:Microfilament Proteins; D029701:Saccharomyces cerevisiae Proteins; D053778:Thiazolidines; C037067:latrunculin A