The circular RNA ciRS-7 (Cdr1as) acts as a risk factor of hepatic microvascular invasion in hepatocellular carcinoma.

Purpose: Circular RNAs (circRNA) represent a novel class of widespread and diverse endogenous RNAs that regulate gene expression in mammals. microRNA-7 (miR-7) is a well-demonstrated suppressor of hepatocellular carcinoma (HCC). Recent studies have showed that one such circRNA, ciRS-7 (also termed as Cdr1as) was the inhibitor and sponge of miR-7 in the embryonic zebrafish midbrain and islet cells. However, the relationships among ciRS-7, miR-7 and clinical features of HCC remain to be clarified.

Methods: Expression levels of ciRS-7, miR-7 and three miR-7-targeted mRNAs in 108 pairs of HCC and their matched non-tumor tissues were examined by quantitative reverse transcription polymerase chain reaction (qRT-PCR). The protein production of these three miR-7-targeted mRNAs was further verified by Western blot. The relationship between ciRS-7 level and clinicopathological features as well as the recurrence of HCC patients was analyzed. The univariate and multivariate logistic regression analyses were used to detect the risk factors of hepatic microvascular invasion (MVI). The correlation among ciRS-7, miR-7 and miR-7-targeted mRNAs was evaluated using Spearman's correlation test.

Results: There was no significant difference of ciRS-7 expression levels between the HCC tissues and the matched non-tumor tissues (0.67 ± 1.49 vs. 0.44 ± 0.45, p = 0.13), and the ciRS-7 levels in more than half of HCC tissues (65 out of 108, 60.2 %) were down-regulated when compared with their matched non-tumor tissues. However, the expression of ciRS-7 was significantly correlated with the following three clinicopathological characteristics of HCC patients: age <40 years (p = 0.02), serum AFP ≥400 ng/µl (p < 0.01) and hepatic MVI (p = 0.03). Meanwhile, up-regulated ciRS-7 expression was not only an independent risk factor of hepatic MVI but also had a capable predictive ability for MVI (AUC = 0.68, p = 0.001) at the cut-off value of 0.135. Furthermore, the expression of ciRS-7 in HCC tissues with concurrent MVI was inversely correlated with that of miR-7 (r = -0.39, p = 0.007) and positively related with that of two miR-7-targeted genes [PIK3CD (r = 0.55, p < 0.001) and p70S6K (r = 0.34, p = 0.021)]. In addition, the median recurrent time of patients from higher ciRS-7 level group was shorter than that of lower ciRS-7 group (18 vs. 25 months), but no significant difference was observed (p = 0.38).

Conclusions: The expression levels of ciRS-7 were comparable between HCC and matched non-tumor tissues. However, the highly ciRS-7 expression in HCC tissues was significantly correlated with hepatic MVI, AFP level and younger age and thus partly related with the deterioration of HCC. Especially, ciRS-7 was one of the independent factors of hepatic MVI. These data suggested that ciRS-7 may be a promising biomarker of hepatic MVI and a novel therapy target for restraining MVI.