The human HIF (hypoxia-inducible factor)-3alpha gene is a HIF-1 target gene and may modulate hypoxic gene induction.
HIF (hypoxia-inducible factor)-3alpha is the third member of the HIF transcription factor family. Whereas HIF-1alpha and -2alpha play critical roles in the cellular and systemic adaptation to hypoxia, little is known about the regulation and function of HIF-3alpha. At least five different splice variants may be expressed from the human HIF-3alpha locus that are suggested to exert primarily negative regulatory effects on hypoxic gene induction. In the present paper, we report that hypoxia induces the human HIF-3alpha gene at the transcriptional level in a HIF-1-dependent manner. HIF-3alpha2 and HIF-3alpha4 transcripts, the HIF-3alpha splice variants expressed in Caki-1 renal carcinoma cells, rapidly increased after exposure to hypoxia or chemical hypoxia mimetics. siRNA (small interfering RNA)-mediated HIF-alpha knockdown demonstrated that HIF-3alpha is a specific target gene of HIF-1alpha, but is not affected by HIF-2alpha knockdown. In contrast with HIF-1alpha and HIF-2alpha, HIF-3alpha is not regulated at the level of protein stability. HIF-3alpha protein could be detected under normoxia in the cytoplasm and nuclei, but increased under hypoxic conditions. Promoter analyses and chromatin immunoprecipitation experiments localized a functional hypoxia-responsive element 5' to the transcriptional start of HIF-3alpha2. siRNA-mediated knockdown of HIF-3alpha increased transactivation of a HIF-driven reporter construct and mRNA expression of lysyl oxidase. Immunohistochemistry revealed an overlap of HIF-1alpha-positive and HIF-3alpha-positive areas in human renal cell carcinomas. These findings shed light on a novel aspect of HIF-3alpha as a HIF-1 target gene and point to a possible role as a modulator of hypoxic gene induction.
Tanaka
Tetsuhiro
T
Department of Nephrology and Hypertension, University Clinic Erlangen, Loschgestrasse 8, D-91054 Erlangen, Germany.
Wiesener
Michael
M
Bernhardt
Wanja
W
Eckardt
Kai-Uwe
KU
Warnecke
Christina
C
D051017:Apoptosis Regulatory Proteins; D051792:Basic Helix-Loop-Helix Proteins; D015687:Cell Hypoxia / Q000235:genetics / Q000502:physiology*; D002460:Cell Line; D045744:Cell Line, Tumor; D047369:Chromatin Immunoprecipitation; D005786:Gene Expression Regulation; D006801:Humans; D051793:Hypoxia-Inducible Factor 1 / Q000235:genetics / Q000378:metabolism*; D015151:Immunoblotting; D007150:Immunohistochemistry; D011401:Promoter Regions, Genetic / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics / Q000502:physiology; D012097:Repressor Proteins; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
D051017:Apoptosis Regulatory Proteins; D051792:Basic Helix-Loop-Helix Proteins; D051793:Hypoxia-Inducible Factor 1; D034741:RNA, Small Interfering; D012097:Repressor Proteins; D014157:Transcription Factors; C116973:HIF3A protein, human