IDENTIFICATION OF HYPOXIA RESPONSE ELEMENTS THAT REGULATE THE EXPRESSION OF 'FATIGA', THE DROSOPHILA OXYGEN SENSOR

ACEVEDO JULIETA M; CENTANIN LAZARO; DEKANTY ANDRÉS; WAPPNER PABLO

Viena, Austria,

Congreso; 20th European Drosophila Research Conference; 2007

IMP-IMBA Research Center Vienna

In response to oxygen deprivation cells induce a transcriptional adaptive response, characterized by a change in gene expression, which is in turn mediated by the transcription factor HIF-1. HIF-1 is an á/â heterodimeric  transcription factor that binds to Hypoxia Response Elements (HREs) at the enhancer region of its target genes. In normoxia HIF1- á is rapidly degraded, while in hypoxia the protein is stabilized. Degradation occurs at the 26S proteasome, after the protein has been ubiquitinated. HIF-1á ubiquitination requires prior hydroxylation of 2 key prolyl residues, in a reaction catalized by specific prolyl-4-hydroxylases (PHDs), which utilize O2 as a co-substrate for the reaction. Previous work of our laboratory has led to the identification of Sima and Fatiga (Fga) as the Drosophila homologues of HIF-1á and PHD, respectively. We have found that 3 fga transcripts (fgaA, fgaB and fgaC) are generated by a combination of alternative splicing and alternative initiation of transcription. Here we show that under hypoxia or upon over expression of Sima transcriptional induction of fga B and fga C transcripts occur, suggesting that fga is a Sima target gene. We have used luciferase-based reporter assays in S2 cells to dissect the 5’ upstream regulatory region of the fga gene, searching for functional HREs. We have identified one HRE located 759 bp upstream to the transcription initiation site which was capable of conferring hypoxia inducibility of the reporter both in S2 cells and in transgenic lines. Our results suggest the occurrence of a negative feed-back loop that limits the amount of available Sima protein, through the upregulation of the oxygen sensor.