title: A nucleus-targeted alternately spliced Nix/Bnip3L protein isoform modifies nuclear factor κB (NFκB)-mediated cardiac transcription.
abstract: Several Bcl2 family proteins are expressed both as mitochondrial-targeted full-length and as cytosolic truncated alternately spliced isoforms. Recombinantly expressed shorter Bcl2 family isoforms can heterotypically bind to and prevent mitochondrial localization of their full-length analogs, thus suppressing their activity by sequestration. This "sponge" role requires 1:1 expression stoichiometry; absent this an alternate role is suggested. Here, RNA sequencing revealed coordinate regulation of BH3-only protein Nix/Bnip3L (Nix) and its alternately spliced soluble form (sNix) in hearts, but relative sNix/Nix expression of ∼1:10. Accordingly, we examined other putative functions of sNix. Although Nix expressed in H9c2 rat myoblasts localized to mitochondria, sNix showed variable cytoplasmic and nuclear distribution. Tumor necrosis factor α (TNFα) induced rapid and complete sNix nucleoplasmic translocation concomitant with nuclear translocation of the p65/RelA subunit of NFκB. sNix co-localized and co-precipitated with p65/RelA after TNFα stimulation; TNFα-induced sNix nuclear translocation did not occur in p65/RelA null murine embryonic fibroblasts. ChIP sequencing of TNFα-stimulated H9c2 cells revealed sNix suppression of p65/RelA binding to a subset of weaker DNA binding sites, accounting for its ability to alter gene expression in cultured cells and in vivo mouse hearts. These findings reveal TNFα-stimulated cytoplasmic-nuclear shuttling of the alternately spliced non-mitochondrial Nix isoform and uncover a role for sNix as a modulator of TNFα/NFκB-stimulated cardiac gene expression. Transcriptional co-regulation of sNix and Nix, combined with sNix posttranslational regulation by TNFα, comprises a previously unknown mechanism for molecular cross-talk between extrinsic death receptor and intrinsic mitochondrial apoptosis pathways.
authors.affiliation: Center for Pharmacogenomics, Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
authors.forename: Yun
authors.initials: Y
authors.lastname: Chen
authors.forename: Keith F
authors.initials: KF
authors.lastname: Decker
authors.forename: Dali
authors.initials: D
authors.lastname: Zheng
authors.forename: Scot J
authors.initials: SJ
authors.lastname: Matkovich
authors.forename: Li
authors.initials: L
authors.lastname: Jia
authors.forename: Gerald W
authors.initials: GW
authors.lastname: Dorn
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000502:physiology; D017398:Alternative Splicing / Q000502:physiology*; D000818:Animals; D002460:Cell Line; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000502:physiology; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008817:Mice, Mutant Strains; D024101:Mitochondrial Proteins / Q000235:genetics / Q000378:metabolism*; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism*; D032386:Myoblasts, Cardiac / Q000166:cytology / Q000378:metabolism*; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D051996:Transcription Factor RelA / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic / Q000502:physiology*; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000378:metabolism
chemical_list: C505650:BNIP3 protein, rat; C505659:BNIP3L protein, rat; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; D009124:Muscle Proteins; C501741:Nix protein, mouse; D020033:Protein Isoforms; D011518:Proto-Oncogene Proteins; C498144:Rela protein, mouse; C498145:Rela protein, rat; D051996:Transcription Factor RelA; D014409:Tumor Necrosis Factor-alpha
keywords: Bcl-2 Family Proteins; Cardiovascular Disease; Gene Regulation; NF-kappa B (NF-KB); Tumor Necrosis Factor (TNF); sNix