Hypoxia-inducible Factor-1-dependent Overexpression of Myeloid Cell Factor-1 Protects Hypoxic Cells against tert-Butyl Hydroperoxide-induced Apoptosis

Increased levels of Mcl-1 (myeloid cell factor-1) have
been reported in several cancers, suggesting an important
role played by Mcl-1 in cancer cell survival. Mcl-1 is
an anti-apoptotic protein shown to delay or block apoptosis.
In this work, using semiquantitative immunofluorescence,
real-time PCR, and RNase protection assay,
an increase in Mcl-1 expression was detected in hepatoma
HepG2 cells incubated under hypoxia or in the
presence of cobalt chloride. Through analysis of the
Mcl-1 promoter sequence, a putative HIF-1 (hypoxiainducible
factor-1) binding site was identified. A Mcl-1
promoter fragment containing this hypoxia-responsive
element was able to bind HIF-1 in vitro. It also induced
hypoxia-dependent transcription of a luciferase reporter
gene, which was suppressed by anti-HIF-1 short
interfering RNA. Finally, overexpression of Mcl-1 protected
HepG2 cells against apoptosis induced by tertbutyl
hydroperoxide as shown by inhibition of caspase-3
activation and DNA fragmentation. All these data suggest
a potential anti-apoptotic role of HIF-1 that could
protect cells against apoptosis under hypoxia by overexpression
of the Mcl-1 protein.