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Hypoxia is an established hallmark of tumorigenesis. HIF-1α activation may be the prime driver of adaptive regulation of tumor cells reacting to hypoxic conditions of the tumor microenvironment. Here, we report a novel regulatory mechanism in charge of the fundamental stability of HIF-1α in solid tumor. Under hypoxic conditions, the checkpoint kinase CHK2 binds to HIF-1α and inhibits its ubiquitination, which is highly likely due to phosphorylation of a threonine residue (Thr645), a formerly uncharacterized site within the inhibitory domain. Meanwhile, HIF-1α phosphorylation induced by CHK2 promotes complex formation between HIF-1-α and the deubiquitination enzyme USP7, increasing stability under hypoxic conditions. This novel modification of the crosstalk between phosphorylation and ubiquitination of HIF-1α mediated by CHK2 enriches the post-translational modification spectrum of HIF-1α, thus offering novel insights into potential anti-angiogenesis therapies.
Bai et al. (Sat,) studied this question.