However, DEC2 knockdown effectively down-regulated HIF-1α protein levels in MNNG and 143B cell lines under normoxic conditions (Figure 2), and in all three cell lines under hypoxic conditions, indicating that in osteosarcoma cells DEC2 positively regulates HIF-1α at the post-transcriptional levels. This evidence concerns the gene BHLHE41 and osteosarcoma.