Hypoxia inducible factor-1 （HIF-1） was first discovered by Semenza et al1 in 1991 as a protein which couldspecifically bind to the oligonucleotide sequence of the erythropoietin gene enhancer. The dimmers of HIF-1 were isolated in the following year. As its subunits were found to be induced by hypoxic conditions, it was subsequently named as hypoxia inducible factor.2 HIF-1, commonly found in human and mammalian cells, also expressed in normoxic conditions. However, under physiological conditions, the intracellular HIF-1 protein soon degrades through the oxygen-dependent ubiquitin protease degradation pathway, but is stable under hypoxic conditions.3 HIF-1 is a transcription factor responding to hypoxia and includes a wide range of target gene spectrum. The expressed proteins can produce a series of reactions, including cell oxygen balance, energy metabolism, apoptosis, immune responses, cytokine production, angiogenesis, tumor invasion, and radiotherapy resistance, etc.4＇5 In recent years, more and more research has proposed that HIF-1 is a critical transcription factor in the maintenance of oxygen homeostasis and regulation of the hypoxia responses, and that HIF is the most important approach by which the hypoxia inducible gene transcription information transmitted.
