Takafumi Tasakia,1,2, Sung Tae Kima,2, Adriana Zakrzewskaa, Bo Eun Leea, Min Jueng Kangb, Young Dong Yoob, Hyun Joo Cha-Molstadc, Joonsung Hwangc, Nak Kyun Soungc, Ki Sa Sunga, Su-Hyeon Kima,c, Minh Dang Nguyend, Ming Sune, Eugene C. Yib, Bo Yeon Kimc,3, and Yong Tae Kwona,b,3
aCenter for Pharmacogenetics and Department of Pharmaceutical Sciences, School of Pharmacy, University of Pittsburgh, Pittsburgh, PA 15261;
bWorld Class University Program, Department of Molecular Medicine and Biopharmaceutical Sciences, Graduate School of Convergence Science and Technology and College of Medicine, Seoul National University, Seoul 110-799, Korea;
cWorld Class Institute, Korea Research Institute of Bioscience and Biotechnology, Ochang, Cheongwon 363-883, Korea;
dDepartment of Clinical Neurosciences, Hotchkiss Brain Institute, University of Calgary, Calgary, AB, Canada T2N 4N1; and
eDepartment of Cell Biology, Center for Biologic Imaging, University of Pittsburgh, Pittsburgh, PA 15261
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.
cardiovascular system, ubiquitin ligase
1Present address: Medical Research Institute, Kanazawa Medical University, Ishikawa 920-0293, Japan.
2T.T. and S.T.K. contributed equally to this work.
3To whom correspondence may be addressed.
Author contributions: T.T., S.T.K., A.Z., Y.D.Y., H.J.C.-M., J.H., K.S.S., S.-H.K., M.S., E.C.Y., B.Y.K., and Y.T.K. designed research; T.T., S.T.K., A.Z., B.E.L., M.J.K., Y.D.Y., J.H., N.K.S., and M.S. performed research; M.D.N. and B.Y.K. contributed new reagents/analytic tools; T.T., S.T.K., A.Z., B.E.L., M.J.K., Y.D.Y., H.J.C.-M., J.H., N.K.S., K.S.S., S.-H.K., M.S., E.C.Y., B.Y.K., and Y.T.K. analyzed data; and T.T., S.T.K., K.S.S., S.-H.K., B.Y.K., and Y.T.K. wrote the paper.