MicroRNA-122 (miR-122) is highly expressed in hepatocytes, where it plays an important role in regulating cholesterol and fatty-acid metabolism, and it is also a host factor required for hepatitis C virus replication. miR-122 is selectively stabilized by 3' adenylation mediated by the cytoplasmic poly(A) polymerase GLD-2 (also known as PAPD4 or TENT2).
HCV infection of thyrocytes induced the production of the chemokine CXCL-8 and the pro-inflammatory cytokines TNFα and significantly increased the expression of miR-122.
Collectively, these data suggest a model in which TNRC6B/C regulate the assembly of miR-122/Ago complexes on HCV RNA, preferentially directing miR-122/Ago2 to S1 while restricting its association with S2, thereby fine-tuning the spatial organization of miR-122/Ago2 complexes on the viral genome.
Restoration of miR-122 levels in hepatoma cells markedly enhanced the activation of interferons (IFNs) in response to a variety of viral nucleic acids or simulations, especially in response to hepatitis C virus RNA and poly (I:C).
It is shown here that this C3U variant indeed displayed higher rates of replication than that of wild-type HCV when miR-122 abundance is low in liver cells.
Taken together, our results support a model whereby hAgo2:miR-122 complexes alter the structure of the viral 5' terminus and promote formation of the HCV IRES.
Interestingly, both miR-122 supplementation and IRF3 knockout in KH cells boosted HCV replication to a similar level as in Huh-7.5 cells, suggesting that intact innate antiviral signalling and lower miR-122 expression limit HCV replication in KH cells.
However, supplementation of miR-122 molecules with compensatory mutations did not rescue these site mutants to wild-type levels, suggesting that mutation of these sequences likely disrupts an additional interaction important to the HCV life cycle, beyond direct interactions with miR-122.
In addition, we found that serum might be a more promising matrix for detecting the expression of miR-122 than plasma.<b>Conclusions:</b> Our results demonstrated that circulating miR-122 have a relatively high diagnostic value for chronic viral hepatitis detection, especially in the patients with HCV-associated chronic viral hepatitis.
These miRNAs were positively correlated with alanine aminotransferase and aspartate aminotransferase levels, and the relative expression levels were higher in hepatitis C virus-infected patients and lower in patients with Child-Pugh C cirrhosis. miR-122 and miR-885-5p levels were also positively correlated with γ-glutamyl transpeptidase concentrations. miR-21 was associated with transplant-free survival in univariate Cox regression analysis and remained independently associated with survival after adjustment for age, Child-Pugh classification, Model for End-stage Liver Disease score, and history of previous decompensation in multivariate Cox regression analysis.
Overall, our results support a model in which miR-122 stabilizes the HCV genome by shielding its 5' terminus from cellular pyrophosphatase activity and subsequent turnover by exonucleases (Xrn1/2).
Furthermore, the region spanning domains I and I' of EHcV (the 5'-proximal EHcV-specific region) improved RNA stability and provided the HCV SGR with microRNA 122 (miR-122)-independent replication capability, while EHcV domain I alone improved SGR replication and RNA stability irrespective of miR-122.
At last, we present a model for miR-122 promotion of the HCV life cycle in which miRNA annealing to the 5' UTR, in conjunction with any Ago isoform, modifies the 5' UTR structure to stabilize the viral genome and promote HCV RNA accumulation.
We produced artificial circRNA sponges in vitro that efficiently sequester microRNA-122, thereby inhibiting viral protein production in an HCV cell culture system.
In conclusion, our study suggests that DCAF1 is involved in HCV replication through regulation of miR-122 and thus provides new insights into the interaction between HCV and the host cell.