Neural stem cells (NSCs) reside in vivo in hypoxic environments, and NSC proliferation is enhanced in vitro under hypoxic conditions. Various adaptive responses to
hypoxia are mediated by
hypoxia-inducible factors (HIFs), a family of basic helix-loop-helix Per-Arnt-Sim (PAS)
transcription factors.
Necdin, a MAGE (
melanoma antigen) family
protein, is expressed abundantly in postmitotic neurons and possesses potent
antimitotic and antiapoptotic activities. We here report that
hypoxia induces degradation of the
necdin protein in primary NSCs by HIF-mediated
ubiquitin-
proteasome system.
Necdin was expressed in primary NSCs prepared from the ganglionic eminences of mouse embryos.
Hypoxia enhanced neurosphere formation of NSCs, in which the
necdin protein level was significantly reduced. Primary NSCs prepared from
necdin-deficient mice exhibited higher rates of proliferation and apoptosis than those from wild-type mice in normoxia, whereas there were no significant differences in the proliferation and apoptosis rates between
necdin-deficient and wild-type NSCs in
hypoxia. HIF-2α was predominantly expressed in hypoxic NSCs, where expression of HIF-responsive genes was upregulated. HIF-2α interacted with
necdin via its PAS domain, which enhanced
necdin ubiquitination. Lentivirus-mediated expression of the PAS domain in primary NSCs promoted
necdin degradation and enhanced NSC proliferation in normoxia, whereas a small-molecule inhibitor of HIF-2α translation stabilized the
necdin protein and reduced NSC proliferation in
hypoxia. These results suggest that
oxygen tension regulates the
necdin protein level in NSCs through HIF-2α-mediated proteasomal degradation to modulate their proliferation and apoptosis.