title: Mitochondrial apoptosis-induced channel (MAC) function triggers a Bax/Bak-dependent bystander effect.
abstract: Collateral spread of apoptosis to nearby cells is referred to as the bystander effect, a process that is integral to tissue homeostasis and a challenge to anticancer therapies. In many systems, apoptosis relies on permeabilization of the mitochondrial outer membrane to factors such as cytochrome c and Smac/DIABLO. This permeabilization occurs via formation of a mitochondrial apoptosis-induced channel (MAC) and was mimicked here by single-cell microinjection of cytochrome c into Xenopus laevis embryos. Waves of apoptosis were observed in vivo from the injected to the neighboring cells. This finding indicates that a death signal generated downstream of cytochrome c release diffused to neighboring cells and ultimately killed the animals. The role of MAC in bystander effects was then assessed in mouse embryonic fibroblasts that did or did not express its main components, Bax and/or Bak. Exogenous expression of green fluorescent protein-Bax triggered permeabilization of the outer membrane and apoptosis in these cells. Time-lapse videos showed that neighboring cells also underwent apoptosis, but expression of Bax and/or Bak was essential to this effect, because no bystanders were observed in cells lacking both of these MAC components. These results may guide development of novel therapeutic strategies to selectively eliminate tumors or minimize the size of tissue injury in degenerative or traumatic cell death.
authors.affiliation: Department of Basic Sciences, New York University College of Dentistry, New York, New York, USA.
authors.forename: Pablo M
authors.initials: PM
authors.lastname: Peixoto
authors.forename: Jennifer K
authors.initials: JK
authors.lastname: Lue
authors.forename: Shin-Young
authors.initials: SY
authors.lastname: Ryu
authors.forename: Brian N
authors.initials: BN
authors.lastname: Wroble
authors.forename: Jill C
authors.initials: JC
authors.lastname: Sible
authors.forename: Kathleen W
authors.initials: KW
authors.lastname: Kinnally
mesh_terms: D000818:Animals; D017209:Apoptosis; D024201:Bystander Effect; D002478:Cells, Cultured; D045304:Cytochromes c / Q000494:pharmacology; D004625:Embryo, Nonmammalian; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D008845:Microinjections; D014982:Xenopus laevis; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000378:metabolism*; D051028:bcl-2-Associated X Protein / Q000378:metabolism*
chemical_list: D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein; D045304:Cytochromes c