CLOCK and hepatocellular carcinoma: Indeed, a reciprocal interaction between the clock genes and the HIF-1α transcriptional programs seems evident given that HIF-1α can bind the promoter region of clock genes and control their transcription, at least in muscle cells [101], and, conversely, HIF-1α is a direct transcriptional target of the orthologue of Clock gene, NPAS2, in hepatocellular carcinoma [102].