MMP9 and oral cavity squamous cell carcinoma: Xia et al. (2019) reported that MMP9 was a directly target of miR-149 in oral squamous cell carcinoma. Liu F. et al. (2020) observed that MMP9 was overexpressed in bladder cancer and was negatively regulated by miR-491-5p. Our study demonstrated that MMP9 was negatively associated with miR-194-3p, and circUBAP2 acts as a sponge of miR-194-3p, upregulating MMP9 expression in HCC cells (Figure 7).