Regulation of Drosophila hypoxia-inducible factor (HIF) activity in SL2 cells: identification of a hypoxia-induced variant isoform of the HIFalpha homolog gene similar.

Abstract

Although hypoxia-inducible factor-alpha (HIFalpha) subunit-specific hydroxylation and proteolytic breakdown explain the binary switch between the presence (hypoxia) and absence (normoxia) of HIFs, little is known of the mechanisms that fine-tune HIF activity under constant, rather than changing, oxygen tensions. Here, we report that the Drosophila HIFalpha homolog, the basic helix-loop-helix/PAS protein Sima (Similar), in hypoxic cultures of SL2 cells is expressed in full-length (fl) and splice variant (sv) isoforms. The following evidence supports the role of flSima as functional HIFalpha and the role of SL2 HIF as a transcriptional activator or suppressor. The pO(2) dependence of Sima abundance matched that of HIF activity. HIF-dependent changes in candidate target gene expression were detected through variously effective stimuli: hypoxia (strong) > iron chelation, e.g. desferrioxamine (moderate) >> transition metals, e.g. cobalt approximately normoxia (ineffective). Sima overexpression augmented hypoxic induction or suppression of different targets. In addition to the full-length exon 1-12 transcript yielding the 1510-amino acid HIFalpha homolog, the sima gene also expressed, specifically under hypoxia, an exon 1-7/12 splice variant, which translated into a 426-amino acid Sima truncation termed svSima. svSima contains basic helix-loop-helix and PAS sequences identical to those of flSima, but, because of deletion of exons 8-11, lacks the oxygen-dependent degradation domain and nuclear localization signals. Overexpressed svSima failed to transactivate reporter genes. However, it attenuated HIF (Sima.Tango)-stimulated reporter expression in a dose-dependent manner. Thus, svSima has the potential to regulate Drosophila HIF function under steady and hypoxic pO(2) by creating a cytosolic sink for the Sima partner protein Tango.

• Authors: Thomas A Gorr, Takeshi Tomita, Pablo Wappner, H Franklin Bunn
• Journal: The Journal of biological chemistry (J Biol Chem) Vol. 279 Issue 34 Pg. 36048-58 (Aug 20 2004) ISSN: 0021-9258 [Print] United States
• PMID: 15169765 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, P.H.S.)

Chemical References

• Carrier Proteins
• DNA-Binding Proteins
• Drosophila Proteins
• HIF1A protein, human
• Hypoxia-Inducible Factor 1, alpha Subunit
• Sima protein, Drosophila
• Transcription Factors
• tgo protein, Drosophila
• Aryl Hydrocarbon Receptor Nuclear Translocator

Topics

• Amino Acid Sequence
• Animals
• Aryl Hydrocarbon Receptor Nuclear Translocator
• Carrier Proteins (genetics, metabolism)
• Cell Hypoxia
• Cell Line
• DNA-Binding Proteins (genetics, metabolism)
• Drosophila (metabolism)
• Drosophila Proteins (genetics, metabolism)
• Gene Expression Regulation
• Humans
• Hypoxia-Inducible Factor 1, alpha Subunit
• Molecular Sequence Data
• Sequence Homology
• Signal Transduction
• Transcription Factors (genetics, metabolism)