Novel regulators of the HIF pathway in Drosophila

BERTOLIN, AGUSTINA; DEKANTY, ANDRES; ROMERO, NURIA

Tabauté, Brasil

Simposio; 4th International Symposium of Developmental Biology; 2009

Latin American Society of Developmental Biology

Novel regulators of the HIF pathway in Drosophila Bertolin, Agustina1; Dekanty, Andres1; Romero, Nuria1 1 Fundación Instituto Leloir The hypoxia-inducible factors (HIFs) are a highly conserved family of transcription factors that constitute the major regulators of cellular oxygen homeostasis throughout the animal kingdom. These factors target genes that are crucial for systemic hypoxia responses, such as angiogenesis and erythropoiesis, and cellular hypoxia responses involving metabolism, proliferation, motility and autophagy. HIF is a heterodimeric DNA-binding complex composed of a constitutively expressed HIF-beta subunit and a HIF-alpha subunit that is tightly regulated through multiple mechanisms. We have previously defined a hypoxia-responsive system in Drosophila which is homologous to HIF, being the proteins Sima and Tango the functional homologues of HIF-1 alpha and beta, respectively. Although the core HIF pathway and a few canonical regulators have been extensively characterized in the past decade, a systematic loss of function screen has not been performed so far. Here we report an RNAi screen aimed to identify novel regulators of the hypoxic response. We used a Drosophila S2 cell line bearing a stably transfected luciferase reporter, which is strongly up-regulated upon exposure to hypoxia. We considered as potential regulators of the hypoxic response those genes whose interference led to a reduction of reporter activity, without affecting cell viability. The screen has allowed the identification of approximately 70 novel positive regulators of the HIF/Sima pathway.  These included several members of the PI3K signalling pathway, genes of the Brahma chromatin-remodelling complex, and members of the AAA+ family of DNA helicases. Interestingly, we have also identified dATF-4 which is considered a central component in many cellular stress-response pathways. Finally, various members of the microRNA machinery scored as positives in the screen. We focused our studies on this last group of genes, and our results show for the first time that miRNAs may act as regulators of the hypoxic response.