BMI1 and cancer: Some of the genes that are upregulated by HH signaling are associated with stemness, such as Nanog, OCT4, SOX2, and the polycomb complex protein, BMI-1 (also known as polycomb group RING finger protein 4 [PCGF4] or RING finger protein 51 [RNF51]), which implicates HH signaling in the determination of the cancer stem cell phenotype (Tsao et al., 2019).