For instance, CircPUM1, generated from the Pumilio RNA Binding Family Member 1 (PUM1) gene on human chromosome 1, was localized in the mitochondria of esophageal squamous cell carcinoma (ESCC) cell lines and stood out as a mediator of Ubiquinol-cytochrome c reductase core protein I and II (UQCRC1/2), core proteins of complex III; thus, playing a key role in ATP production. Here, UQCRC1 is linked to esophageal squamous cell carcinoma.