Circular RNAs (circRNAs) are considered as key regulators of cancer biology. Recently, cMTO1 (a circRNA derived from MTO1 gene, hsa_circ_0007874) has been demonstrated to act as a tumor suppressor in hepatocellular carcinoma (HCC). However, the roles of cMTO1 in liver fibrosis are largely unknown.
Expressions and roles of cMTO1 were examined
cMTO1 was shown to be reduced in the liver from patients with cirrhosis. In addition, cMTO1 was down-regulated in the mouse fibrotic livers as well as activated hepatic stellate cells (HSCs). Restoring of cMTO1 led to a reduction in HSC proliferation. Results of immunofluorescence analysis showed that cMTO1 suppressed the expressions of α-SMA and type I collagen. cMTO1 was found to be expressed in the cytoplasm of HSCs. Further studies confirmed that cMTO1 and miR-181b-5p were co-located in the cytoplasm. Interestingly, there was an interaction between cMTO1 and miR-181b-5p. Results of luciferase reporter assays and pull down assays confirmed that miR-181b-5p could bind to cMTO1. cMTO1-inhibited HSC activation was blocked down by miR-181b-5p or PTEN. Meanwhile, PTEN was a target of miR-181b-5p.
cMTO1 inhibits HSC activation, at least in part, through miR-181b-5p-mediated PTEN expression. Our results also suggest that cMTO1 may be a novel therapeutic target in liver fibrosis.