MAPK9 and hepatocellular carcinoma: As miR-642b-3p is the downstream target gene of circ_MAPK9, we then examined the expression of miR-642b-3p in 41 pairs of HCC samples by qRT-PCR, and found that miR-642b-3p expression decreased in HCC tumor tissues compared to that in adjacent normal tissues (P < 0.05, Fig. 5A).