AK4 and cervical cancer: Hypoxia was reported to upregulate AK4 in human cancer cell lines such as HeLa (cervical cancer), A549 (lung carcinoma), and SHSY5Y (neuroblastoma) [30,33,35] as well as in mouse chondroprogenitor cells and immortalized HEK293 (human embryonic kidney) cells [32,33,50].