Casein kinase 1 regulates human hypoxia-inducible factor HIF-1.
Hypoxia-inducible factor 1 (HIF-1), a transcriptional activator that mediates cellular response to hypoxia and a promising target of anticancer therapy, is essential for adaptation to low oxygen conditions, embryogenesis and tumor progression. HIF-1 is a heterodimer of HIF-1alpha, expression of which is controlled by oxygen levels as well as by various oxygen-independent mechanisms, and HIF-1beta (or ARNT), which is constitutively expressed. In this work, we investigate the phosphorylation of the N-terminal heterodimerization (PAS) domain of HIF-1alpha and identify Ser247 as a major site of in vitro modification by casein kinase 1delta (CK1delta). Mutation of this site to alanine, surprisingly, enhanced the transcriptional activity of HIF-1alpha, a result phenocopied by inhibition or small interfering RNA (siRNA)-mediated silencing of CK1delta under hypoxic conditions. Conversely, overexpression of CK1delta or phosphomimetic mutation of Ser247 to aspartate inhibited HIF-1alpha activity without affecting its stability or nuclear accumulation. Immunoprecipitation and in vitro binding experiments suggest that CK1-dependent phosphorylation of HIF-1alpha at Ser247 impairs its association with ARNT, a notion also supported by modeling the structure of the complex between HIF-1alpha and ARNT PAS-B domains. We suggest that modification of HIF-1alpha by CK1 represents a novel mechanism that controls the activity of HIF-1 during hypoxia by regulating the interaction between its two subunits.
Kalousi
Alkmini
A
Laboratory of Biochemistry, School of Medicine, University of Thessaly, Mezourlo 41110, Larissa, Greece.
Mylonis
Ilias
I
Politou
Anastasia S
AS
Chachami
Georgia
G
Paraskeva
Efrosyni
E
Simos
George
G
D000595:Amino Acid Sequence; D048148:Casein Kinase Idelta / Q000235:genetics / Q000378:metabolism*; D015687:Cell Hypoxia / Q000502:physiology; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D051793:Hypoxia-Inducible Factor 1 / Q000235:genetics / Q000378:metabolism*; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D015533:Transcriptional Activation
C497442:HIF1A protein, human; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D009687:Nuclear Proteins; D014157:Transcription Factors; D048148:Casein Kinase Idelta