Aspartyl-(asparaginyl) beta-hydroxylase, hypoxia-inducible factor-alpha and Notch cross-talk in regulating neuronal motility

Aspartyl-(Asparginyl)-β-Hydroxylase (AAH) promotes cell motility by hydroxylating Notch. Insulin and insulin-like growth factor, type 1 (IGF-I) stimulate AAH through Erk MAPK and phosphoinositol-3-kinase-Akt (PI3K-Akt). However, hypoxia/oxidative stress may also regulate AAH. Hypoxia inducible factor-1 alpha (HIF-1α) regulates cell migration, signals through Notch, and is regulated by hypoxia/oxidative stress, insulin/IGF signaling, and factor inhibiting HIF-1α (FIH) hydroxylation. To examine cross-talk between HIF-1α and AAH, we measured AAH, Notch-1, Jagged-1, FIH, HIF-1α, HIF-1β, and the hairy and enhancer of split 1 (HES-1) transcription factor expression and directional motility in primitive neuroectodermal tumor 2 (PNET2) human neuronal cells that were exposed to H₂O₂, or transfected with short interfering RNA duplexes (siRNA) targeting AAH, Notch-1, or HIF-1α. We found that: 1) AAH, HIF-1α, and neuronal migration were stimulated by H₂O₂; 2) si-HIF-1α reduced AAH expression and cell motility; 3) si-AAH inhibited Notch and cell migration, but not HIF-1α; and 4) si-Notch-1 increased FIH and inhibited HIF-1α. These findings suggest that AAH and HIF-1α cross-talk within a hydroxylation-regulated signaling pathway that may be transiently driven by oxidative stress, and chronically regulated by insulin/IGF signaling.