Polycomb-group complex 1 acts as an E3 ubiquitin ligase for Geminin to sustain hematopoietic stem cell activity.
Polycomb-group (PcG) genes encode multimeric nuclear protein complexes, PcG complex 1 and 2. PcG complex 2 was proved to induce transcription repression and to further methylate histone H3 at lysine-27 (H3K27). Subsequently PcG complex 1 is recruited through recognition of methylated H3K27 and maintains the transcription silencing by mediating monoubiquitination of histone H2A at lysine-119. Genetic evidence demonstrated a crucial role for PcG complex 1 in stem cells, and Bmi1, a member of PcG complex 1, was shown to sustain adult stem cells through direct repression of the INK4a locus encoding cyclin-dependent kinase inhibitor, p16CKI, and p19ARF. The molecular functions of PcG complex 1, however, remain insufficiently understood. In our study, deficiency of Rae28, a member of PcG complex 1, was found to impair ubiquitin-proteasome-mediated degradation of Geminin, an inhibitor of DNA replication licensing factor Cdt1, and to increase protein stability. The resultant accumulation of Geminin, based on evidence from retroviral transduction experiments, presumably eliminated hematopoietic stem cell activity in Rae28-deficient mice. Rae28 mediates recruiting Scmh1, which provides PcG complex 1 an interaction domain for Geminin. Moreover, PcG complex 1 acts as the E3 ubiquitin ligase for Geminin, as we demonstrated in vivo as well as in vitro by using purified recombinant PcG complex 1 reconstituted in insect cells. Our findings suggest that PcG complex 1 supports the activity of hematopoietic stem cells, in which high-level Geminin expression induces quiescence securing genome stability, by enhancing cycling capability and hematopoietic activity through direct regulation of Geminin.
Ohtsubo
Motoaki
M
Department of Stem Cell Biology, Research Institute for Radiation Biology and Medicine, Hiroshima University, Hiroshima 734-8553, Japan.
Yasunaga
Shin'ichiro
S
Ohno
Yoshinori
Y
Tsumura
Miyuki
M
Okada
Satoshi
S
Ishikawa
Nobutsune
N
Shirao
Kenichiro
K
Kikuchi
Akira
A
Nishitani
Hideo
H
Kobayashi
Masao
M
Takihara
Yoshihiro
Y
D000818:Animals; D018797:Cell Cycle Proteins / Q000378:metabolism*; D004261:DNA Replication; D004268:DNA-Binding Proteins / Q000378:metabolism; D064248:Geminin; D015972:Gene Expression Regulation, Neoplastic; D006412:Hematopoietic Stem Cells / Q000166:cytology*; D006801:Humans; D007313:Insecta; D051379:Mice; D008957:Models, Genetic; D009687:Nuclear Proteins / Q000378:metabolism*; D063146:Polycomb-Group Proteins; D012097:Repressor Proteins / Q000378:metabolism / Q000502:physiology*; D025801:Ubiquitin / Q000737:chemistry; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*
C467199:CDT1 protein, human; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C577995:GMNN protein, human; D064248:Geminin; C577997:Gmnn protein, mouse; D009687:Nuclear Proteins; D063146:Polycomb-Group Proteins; D012097:Repressor Proteins; C498645:Ris2 protein, mouse; C570430:Scmh1 protein, mouse; D025801:Ubiquitin; D044767:Ubiquitin-Protein Ligases