title: Nonmyofilament-associated troponin T3 nuclear and nucleolar localization sequence and leucine zipper domain mediate muscle cell apoptosis.
abstract: Troponin T (TnT) plays a major role in striated muscle contraction. We recently demonstrated that the fast skeletal muscle TnT3 isoform is localized in the muscle nucleus, and either its full-length or COOH-terminus leads to muscle cell apoptosis. Here, we further explored the mechanism by which it enters the nucleus and promotes cytotoxicity. Amino acid truncation and substitution showed that its COOH-terminus contains a dominant nuclear/nucleolar localization sequence (KLKRQK) and the basic lysine and arginine residues might play an important role in the nuclear retention and nucleolar enrichment of KLKRQK-DsRed fusion proteins. Deleting this domain or substituting lysine and arginine residues (KLAAQK) resulted in a dramatic loss of TnT3 nuclear and nucleolar localization. In contrast, the GATAKGKVGGRWK domain-DsRed construct localized exclusively in the cytoplasm, indicating that a nuclear exporting sequence is possibly localized in this region. Additionally, we identified a classical DNA-binding leucine zipper domain (LZD) which is conserved among TnT isoforms and species. Deletion of LZD or KLKRQK sequence significantly reduced cell apoptosis compared to full-length TnT3. We conclude that TnT3 contains both a nuclear localization signal and a DNA-binding domain, which may mediate nuclear/nucleolar signaling and muscle cell apoptosis.
authors: Department of Internal Medicine, Section on Gerontology and Geriatric Medicine, Wake Forest School of Medicine, 1 Medical Center Boulevard, Winston-Salem, NC 27157, USA.
authors: Tan
authors: T
authors: Zhang
authors: Alexander
authors: A
authors: Birbrair
authors: Osvaldo
authors: O
authors: Delbono
mesh_terms: D000818:Animals; D017304:Annexin A5 / Q000378:metabolism; D017209:Apoptosis / Q000502:physiology*; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism*; D005434:Flow Cytometry; D016350:Leucine Zippers / Q000502:physiology; D051379:Mice; D032342:Muscle Cells / Q000166:cytology* / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D019913:Nuclear Localization Signals / Q000502:physiology; D020107:Troponin T / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D017304:Annexin A5; D019913:Nuclear Localization Signals; D020107:Troponin T
references: Exp Cell Res. 2013 Jan 1;319(1):45-63
references: 22999866
references: Mol Cell Biol. 2001 Apr;21(8):2779-89
references: 11283257
references: Circ Res. 2010 Jul 23;107(2):305-15
references: 20522802
references: Results Probl Cell Differ. 2002;36:171-90
references: 11892279
references: Cell. 1992 Feb 21;68(4):699-708
references: 1739975
references: Mol Cell Biol. 1990 Dec;10(12):6565-77
references: 2247074
references: Am J Physiol Heart Circ Physiol. 2009 Jul;297(1):H283-92
references: 19395545
references: Physiol Rev. 2000 Apr;80(2):853-924
references: 10747208
references: J Cell Sci. 2009 May 1;122(Pt 9):1401-9
references: 19366726
references: Annu Rev Biochem. 1999;68:687-728
references: 10872464
references: FEBS Lett. 1994 Nov 7;354(2):183-6
references: 7957921
references: Science. 1989 Nov 17;246(4932):911-6
references: 2683088
references: Pflugers Arch. 2010 Apr;459(5):725-35
references: 20069312
references: Annu Rev Physiol. 1996;58:447-81
references: 8815803
references: PLoS One. 2011 Feb 03;6(2):e16816
references: 21304812
references: Age (Dordr). 2013 Apr;35(2):353-70
references: 22189912
references: Science. 1989 Aug 11;245(4918):646-8
references: 2503872
references: Differentiation. 2012 Mar;83(3):106-15
references: 22364878
references: Science. 2009 Apr 3;324(5923):98-102
references: 19342590
references: J Biol Chem. 2012 Mar 9;287(11):8621-32
references: 22275354
references: Science. 2001 Jun 8;292(5523):1910-5
references: 11397945
references: Pflugers Arch. 2012 Apr;463(4):615-24
references: 22249494
references: J Biol Chem. 1995 Sep 29;270(39):22721-30
references: 7559397
references: Histochem Cell Biol. 2009 Mar;131(3):425-34
references: 19039601
references: Proc Natl Acad Sci U S A. 2011 Sep 27;108(39):16265-70
references: 21914846
references: Trends Biochem Sci. 1991 Dec;16(12):478-81
references: 1664152
references: Proc Natl Acad Sci U S A. 2012 Feb 28;109(9):E544-52
references: 22323606
references: Nucleic Acids Res. 2010 Nov;38(21):7388-99
references: 20663773
references: Stem Cell Res. 2013 Jan;10(1):67-84
references: 23128780
references: J Cell Biol. 2009 Mar 23;184(6):771-6
references: 19289796
references: Biochem J. 2009 Jul 29;422(1):53-60
references: 19496756
references: Biophys J. 2008 Apr 15;94(8):3178-88
references: 18178643
references: J Cell Sci. 2009 Aug 1;122(Pt 15):2623-31
references: 19567471
references: Mol Cell Biol. 2008 Oct;28(20):6290-301
references: 18678645
references: Histochem Cell Biol. 2008 Jan;129(1):13-31
references: 18046571