Atypical CRM1-dependent nuclear export signal mediates regulation of hypoxia-inducible factor-1α by MAPK

Abstract

Hypoxia-inducible factor 1 (HIF-1) is the key transcriptional activator of hypoxia-inducible genes and an important anti-cancer target. Its regulated subunit, HIF-1α, is controlled by oxygen levels and major signaling pathways. We reported previously that phosphorylation of Ser641/643 by p42/44 MAPK is essential for HIF-1α nuclear accumulation and activity. We now show that a fragment of HIF-1α (amino acids 616-658), termed MAPK target domain, contains a nuclear export signal (NES), which has atypical hydrophobic residue spacing. Localization, reporter gene, and co-immunoprecipitation assays demonstrate that the identified NES interacts with CRM1 in a phosphorylation-sensitive manner. Furthermore, disruption of the NES (I637A/L638A/I639A) restores nuclear localization and activity of nonphosphorylated HIF-1α and renders it largely resistant to inhibition of MAPK, an effect reproduced by a phosphomimetic mutation (S641E). As these data predict, overexpression of wild-type or mutant (S641A/S643A) MAPK target domain in HeLa cells modulates the activity and subcellular distribution of endogenous HIF-1α. We suggest that control of HIF-1α nuclear transport represents an important MAPK-dependent regulatory mechanism. © 2008 by The American Society for Biochemistry and Molecular Biology, Inc.