REGULATION OF THE DROSOPHILA BHLH-PAS PROTEIN SIMA BY HYPOXIA - FUNCTIONAL EVIDENCE FOR HOMOLOGY WITH MAMMALIAN HIF-1-ALPHA

Hypoxia inducible factor-1 (HIF-1) is a heterodimeric complex of two b asic-helix-loop-helix proteins of the PAS family which is critical for oxygen-dependent expression of many mammalian genes. Regulation is me diated by the alpha subunit (HIF-1 alpha) and sequences from HIF-1 alp ha can confer hypoxia-inducible activity on a Ga14 fusion protein. To analyse conservation of this system of gene regulation between Drosoph ila and mammalian cells we constructed Ga14 fusions with a series of D rosophila basic-helix-loop-helix PAS (bHLH-PAS) proteins and tested fo r hypoxia inducibility in transfected Hep3B cells. We found that Ga14 fusions with Similar (Sima) but not other Drosophila bHLH-PAS proteins showed inducible activity following exposure to stimuli which classic ally activate mammalian HIF-1: hypoxia, cobaltous ions, and desferriox amine. We also found that Sima protein accumulated in Drosophila SL2 c ells following hypoxia. Together these findings indicate the existence of functional homologies between Sima and HIF-1 alpha, and that conse rvation is such as to enable Sima to interact with the hypoxia signal transduction system in mammalian cells. (C) 1998 Academic Press.