Genomic organization and hypoxia inducible factor responsive regulation of teleost hsp90β gene during hypoxia stress

Background: The physiological significance of a large family of heat-shock proteins (HSPs), comprised of the cytosolic HSP90A and the endoplasmic reticulum component of HSPB, is evident in prokaryotes and eukaryotes. The HSP90A is believed to play critical roles in diverse physiological functions of cell viability and chromosomal stability including stress management. Heightened abundance of hsp90 beta transcript was documented in Channa striatus, a freshwater fish, which is capable of surviving within an extremely hypoxic environment. Methods and results: To better understand the mechanism of hsp90 beta gene expression, we investigated its genomic organization. Eleven exons were identified, including a long upstream intron with a remarkable similarity with human, but not with chicken counterpart. Dual-luciferase assays identified promoter activity in a 1366 bp 5'-flanking segment beyond the transcription initiation site. Examination detected a minimal promoter of 754 bp containing a TATA-box, CAAT-enhancer in addition to providing clues regarding other enhancer and repressor elements. The driving capability of this minimal promoter was further validated by its binding ability with TATA-box binding protein and the generation of GFP expressing transgenic zebrafish (F-2). Further, deletion of an inverted HIF (hypoxia inducible factor) motif RCGTG (upstream of the TATA-box) dramatically reduced luciferase expression in a hypoxic environment (CoCl2 treated cultivable cells) and was identified as a cis-acting HIF responsive element, necessary for the hypoxia-induced expression. Conclusions: The results obtained herein provide an insight regarding how hsp90 beta gene expression is controlled by HIF responsive element in teleost both during hypoxia stress management and normal physiological functions, and suggested that the hsp90 beta gene promoter could be used as a potential candidate for generating ornamental and food-fish transgenics.