The
multi-subunit GID/CTLH E3 ubiquitin ligase promotes cell proliferation
and targets the transcription factor Hbp1 for degradation.
Lampert F, et al. Elife, 2018 Jun 18. PMID 29911972, Free PMC Article Abstract
In yeast, the glucose-induced
degradation-deficient (GID) E3 ligase selectively degrades superfluous
gluconeogenic enzymes. Here, we identified all subunits of the mammalian
GID/CTLH complex and provide a comprehensive map of its hierarchical
organization and step-wise assembly. Biochemical reconstitution
demonstrates that the mammalian complex possesses inherent E3 ubiquitin
ligase activity, using Ube2H as its cognate E2. Deletions of multiple
GID subunits compromise cell proliferation, and this defect is
accompanied by deregulation of critical cell cycle markers such as the
retinoblastoma (Rb) tumor suppressor, phospho-Histone H3 and Cyclin A. We identify the negative regulator of pro-proliferative genes Hbp1 as a bonafide
GID/CTLH proteolytic substrate. Indeed, Hbp1 accumulates in cells
lacking GID/CTLH activity, and Hbp1 physically interacts and is
ubiquitinated in vitro by
reconstituted GID/CTLH complexes. Our biochemical and cellular analysis
thus demonstrates that the GID/CTLH complex prevents cell cycle exit in
G1, at least in part by degrading Hbp1. KEYWORDS: E3
ubiquitin ligase; N-end rule; S. cerevisiae; biochemistry; cell
biology; cell proliferation; chemical biology; human; metabolism; mouse;
transcription factors
