title: Overexpression of HAX-1 protects cardiac myocytes from apoptosis through caspase-9 inhibition.
abstract: Caspase-9 is a critical regulator of mitochondria-mediated apoptosis. We found that adult cardiac myocytes, but not nonmyocytes, have high caspase-9 expression, and exhibit relative resistance to caspase-9-induced cell death. Thus, we hypothesized that cardiac myocytes possess factors that resist apoptosis. Through a yeast two-hybrid screening of adult human heart cDNA library, we identified HS-1 associated protein-1 (HAX-1), a 35-kD BH-domain containing protein localized to the mitochondria as one of the molecules that interacts with caspase-9. Recombinant HAX-1 protein inhibited caspase-9 processing in a dose-dependent manner in a cell-free caspase activation assay. Overexpression of HAX-1 in adult cardiac myocytes conferred 30% protection from apoptosis as compared with the control. Suppression of HAX-1 expression using siRNA-HAX-1 resulted in significant cell death in adult cardiac myocytes, suggesting the importance of HAX-1 in cardiac myocyte resistance to apoptotic stimulation. On apoptotic stimulation, some caspase-9 translocated to the mitochondria and co-localized with HAX-1, confirming the spatial proximity of caspase-9 and HAX-1. In summary, HAX-1 is a newly identified anti-apoptotic factor and its mechanism of action is through caspase-9 inhibition.
authors.affiliation: Cardiovascular Division, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Mass 02215, USA.
authors.forename: Yuchi
authors.initials: Y
authors.lastname: Han
authors.forename: Yee-Shiuan
authors.initials: YS
authors.lastname: Chen
authors.forename: Zhilin
authors.initials: Z
authors.lastname: Liu
authors.forename: Natalya
authors.initials: N
authors.lastname: Bodyak
authors.forename: Debra
authors.initials: D
authors.lastname: Rigor
authors.forename: Egbert
authors.initials: E
authors.lastname: Bisping
authors.forename: William T
authors.initials: WT
authors.lastname: Pu
authors.forename: Peter M
authors.initials: PM
authors.lastname: Kang
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000328:Adult; D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D053453:Caspase 9; D020169:Caspases / Q000172:deficiency / Q000378:metabolism; D004789:Enzyme Activation; D005260:Female; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D008929:Mitochondria, Heart; D032342:Muscle Cells / Q000166:cytology / Q000502:physiology*; D011506:Proteins / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011994:Recombinant Proteins / Q000302:isolation & purification / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C104759:HAX1 protein, human; D011506:Proteins; D011994:Recombinant Proteins; C506433:CASP9 protein, human; C506434:Casp9 protein, mouse; C506435:Casp9 protein, rat; D053453:Caspase 9; D020169:Caspases