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Tasaki, Takafumi,Kim, Sung Tae,Zakrzewska, Adriana,Lee, Bo Eun,Kang, Min Jueng,Yoo, Young Dong,Cha-Molstad, Hyun Joo,Hwang, Joonsung,Soung, Nak Kyun,Sung, Ki Sa,Kim, Su-Hyeon,Nguyen, Minh Dang,Sun, Mi National Academy of Sciences 2013 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF Vol.110 No.10
<P>The N-end rule pathway is a proteolytic system in which destabilizing N-terminal residues of short-lived proteins act as degradation determinants (N-degrons). Substrates carrying N-degrons are recognized by N-recognins that mediate ubiquitylation-dependent selective proteolysis through the proteasome. Our previous studies identified the mammalian N-recognin family consisting of UBR1/E3α, UBR2, UBR4/p600, and UBR5, which recognize destabilizing N-terminal residues through the UBR box. In the current study, we addressed the physiological function of a poorly characterized N-recognin, 570-kDa UBR4, in mammalian development. UBR4-deficient mice die during embryogenesis and exhibit pleiotropic abnormalities, including impaired vascular development in the yolk sac (YS). Vascular development in UBR4-deficient YS normally advances through vasculogenesis but is arrested during angiogenic remodeling of primary capillary plexus associated with accumulation of autophagic vacuoles. In the YS, UBR4 marks endoderm-derived, autophagy-enriched cells that coordinate differentiation of mesoderm-derived vascular cells and supply autophagy-generated amino acids during early embryogenesis. UBR4 of the YS endoderm is associated with a tissue-specific autophagic pathway that mediates bulk lysosomal proteolysis of endocytosed maternal proteins into amino acids. In cultured cells, UBR4 subpopulation is degraded by autophagy through its starvation-induced association with cellular cargoes destined to autophagic double membrane structures. UBR4 loss results in multiple misregulations in autophagic induction and flux, including synthesis and lipidation/activation of the ubiquitin-like protein LC3 and formation of autophagic double membrane structures. Our results suggest that UBR4 plays an important role in mammalian development, such as angiogenesis in the YS, in part through regulation of bulk degradation by lysosomal hydrolases.</P>
Lee, Min Jae,Kim, Dong Eun,Zakrzewska, Adriana,Yoo, Young Dong,Kim, Su-Hyeon,Kim, Sung Tae,Seo, Jai Wha,Lee, Young Sook,Dorn, Gerald W,Oh, Uhtaek,Kim, Bo Yeon,Kwon, Yong Tae American Society for Biochemistry and Molecular Bi 2012 The Journal of biological chemistry Vol.287 No.28
<P>The N-end rule pathway is a proteolytic system in which destabilizing N-terminal amino acids of short lived proteins are recognized by recognition components (N-recognins) as an essential element of degrons, called N-degrons. In eukaryotes, the major way to generate N-degrons is through arginylation by ATE1 arginyl-tRNA-protein transferases, which transfer Arg from aminoacyl-tRNA to N-terminal Asp and Glu (and Cys as well in mammals). We have shown previously that ATE1-deficient mice die during embryogenesis with defects in cardiac and vascular development. Here, we characterized the arginylation-dependent N-end rule pathway in cardiomyocytes. Our results suggest that the cardiac and vascular defects in ATE1-deficient embryos are independent from each other and cell-autonomous. ATE1-deficient myocardium and cardiomyocytes therein, but not non-cardiomyocytes, showed reduced DNA synthesis and mitotic activity ~24 h before the onset of cardiac and vascular defects at embryonic day 12.5 associated with the impairment in the phospholipase C/PKC-MEK1-ERK axis of Gα(q)-mediated cardiac signaling pathways. Cardiac overexpression of Gα(q) rescued ATE1-deficient embryos from thin myocardium and ventricular septal defect but not from vascular defects, genetically dissecting vascular defects from cardiac defects. The misregulation in cardiovascular signaling can be attributed in part to the failure in hypoxia-sensitive degradation of RGS4, a GTPase-activating protein for Gα(q). This study is the first to characterize the N-end rule pathway in cardiomyocytes and reveals the role of its arginylation branch in Gα(q)-mediated signaling of cardiomyocytes in part through N-degron-based, oxygen-sensitive proteolysis of G-protein regulators.</P>
UBR2 mediates transcriptional silencing during spermatogenesis via histone ubiquitination
An, Jee Young,Kim, Eun-A.,Jiang, Yonghua,Zakrzewska, Adriana,Kim, Dong Eun,Lee, Min Jae,Mook-Jung, Inhee,Zhang, Yi,Kwon, Yong Tae Proceedings of the National Academy of Sciences 2010 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF Vol.107 No.5
<P>Ubiquitination of histones provides an important mechanism regulating chromatin remodeling and gene expression. Recent studies have revealed ubiquitin ligases involved in histone ubiquitination, yet the responsible enzymes and the function of histone ubiquitination in spermatogenesis remain unclear. We have previously shown that mice lacking the ubiquitin ligase UBR2, one of the recognition E3 components of the N-end rule proteolytic pathway, are infertile associated with meiotic arrest at prophase I. We here show that UBR2 localizes to meiotic chromatin regions, including unsynapsed axial elements linked to chromatin inactivation, and mediates transcriptional silencing via the ubiquitination of histone H2A. UBR2 interacts with the ubiquitin conjugating enzyme HR6B and its substrate H2A and promotes the HR6B-H2A interaction and the HR6B-to-H2A transfer of ubiquitin. UBR2 and ubiquitinated H2A (uH2A) spatiotemporally mark meiotic chromatin regions subject to transcriptional silencing, and UBR2-deficient spermatocytes fail to induce the ubiquitination of H2A during meiosis. UBR2-deficient spermatocytes are profoundly impaired in chromosome-wide transcriptional silencing of genes linked to unsynapsed axes of the X and Y chromosomes. Our findings suggest that insufficiency in UBR2-dependent histone ubiquitination triggers a pachytene checkpoint system, providing a new insight into chromatin remodeling and gene expression regulation.</P>