circ-Keratin 6c Promotes Malignant Progression and Immune Evasion of Colorectal Cancer through microRNA-485-3p/Programmed Cell Death Receptor Ligand 1 Axis.

Recently, circular RNA was reported to be a significant participant in the development of tumorigenesis, including colorectal cancer. Therefore, we aimed to clarify the precise role of circ-keratin 6C (circ-KRT6C) in colorectal cancer progression. The relative expression levels of circ-KRT6C, microRNA-485-3p (miR-485-3p), and programmed cell death receptor ligand 1 (PDL1) were analyzed by real-time quantitative polymerase chain reaction and Western blot assays. The proliferation was assessed by cell count kit 8 and colony-forming assays. The apoptotic cells were determined by flow cytometry assay. The migration and invasion were analyzed by transwell assay. Colorectal cancer cells were cocultured with peripheral blood mononuclear cells or cytokine-induced killer cells to assess immune response. The interaction relationships among circ-KRT6C, miR-485-3p, and PDL1 were examined by dual-luciferase reporter assay. The effects of circ-KRT6C inhibition in vivo were analyzed by an animal experiment. circ-KRT6C was overexpressed in colorectal cancer tissues and cells, and its level was associated with overall survival time of patients with colorectal cancer. The suppression of circ-KRT6C suppressed growth, migration, invasion, and immune escape while stimulating apoptosis in colorectal cancer cells, which was abolished by shortage of miR-485-3p. In addition, overexpression of miR-485-3p repressed malignant progression and immune evasion of colorectal cancer by targeting PDL1, implying that PDL1 was a functional target of miR-485-3p. A xenograft experiment also suggested that circ-KRT6C inhibition could repress tumor growth in vivo. circ-KRT6C could increase PDL1 expression by functioning as an miR-485-3p sponge, which promoted malignant progression and immune evasion of colorectal cancer cells. SIGNIFICANCE STATEMENT: circ-keratin 6c could increase programmed cell death receptor ligand 1 expression by functioning as a microRNA-16-5p sponge, which promoted malignant progression and immune evasion of colorectal cancer.