The Krüppel-like zinc finger transcription factor, GLI-similar 1, is regulated by hypoxia-inducible factors via non-canonical mechanisms

GLI-similar 1 (GLIS1) is important for the reprogramming of fibroblasts into induced pluripotent stem cells (iPSCs). However, the molecular mechanisms of regulation of GLIS1 expression remain unclear. We have therefore examined GLIS1 expression in various cancer cell lines and demonstrated that GLIS1 expression was dramatically increased under hypoxic conditions. Importantly, GLIS1 expression was significantly attenuated in VHL-overexpressing renal cell carcinoma cells compared to the VHL-deficient parent control. Moreover, promoter analysis demonstrated that GLIS1 transcription was regulated by hypoxia through a hypoxia-inducible factors (HIFs)-dependent mechanism. Co-transfection experiments revealed that HIF-2α had greater potency on the GLIS1 promoter activation than HIF-1α. Subsequent studies using wild-type and mutant HIF-2α demonstrated that DNA binding activity was not necessary but TADs were critical for GLIS1 induction. Finally, co-transfection experiments indicated that HIF-2α cooperated with AP-1 family members in upregulating GLIS1 transcription. These results suggest that the hypoxic signaling pathway may play a pivotal role in regulating the reprogramming factor GLIS1, via non-canonical mechanisms involving partner transcription factor rather than by direct HIF transactivation.