Abstract
Dicer is the key component in the miRNA pathway. Degradation of Dicer protein is facilitated during vaccinia virus (VV) infection. A C-terminal cleaved product of Dicer protein was detected in the presence of MG132 during VV infection. Thus, it is possible that Dicer protein is cleaved by a viral protease followed by proteasome degradation of the cleaved product. There is a potential I7 protease cleavage site in the C-terminus of Dicer protein. Indeed, reduction of Dicer protein was detected when Dicer was co-expressed with I7 protease but not with an I7 protease mutant protein lack of the protease activity. Mutation of the potential I7 cleavage site in the C-terminus of Dicer protein resisted its degradation during VV infection. Furthermore, Dicer protein was reduced dramatically by recombinant VV vI7Li after the induction of I7 protease. If VV could facilitate the degradation of Dicer protein, the process of miRNA should be affected by VV infection. Indeed, accumulation of precursor miR122 was detected after VV infection or I7 protease expression. Reduction of miR122 would result in the suppression of HCV sub-genomic RNA replication, and, in turn, the amount of viral proteins. As expected, significant reduction of HCVNS5A protein was detected after VV infection and I7 protease expression. Therefore, our results suggest that VV could cleave Dicer protein through I7 protease to facilitate Dicer degradation, and in turn, suppress the processing of miRNAs. Effect of Dicer protein on VV replication was also studied. Exogenous expression of Dicer protein suppresses VV replication slightly while knockdown of Dicer protein does not affect VV replication significantly.
Highlights
MicroRNAs are a group of small noncoding RNAs about 22 nt in length that downregulate gene expression by either of the two posttranscriptional mechanisms: mRNA cleavage or translational repression [1]. miRNAs have been implicated in a vast array of cellular processes including cell differentiation, proliferation and apoptosis [2]
Our results in this study showed that Dicer protein was reduced in vaccinia virus (VV)-infected cells (Fig. 1), and in turn, the processing and the function of miR122 were blocked (Figs. 4 and 5)
A recent report indicated that Dicer protein was suppressed in VV-infected cells that was associated with a universal reduction of host miRNAs expression [20]. miRNAs have been implicated in a vast array of cellular processes including cell proliferation and apoptosis [2]
Summary
MicroRNAs (miRNAs) are a group of small noncoding RNAs about 22 nt in length that downregulate gene expression by either of the two posttranscriptional mechanisms: mRNA cleavage or translational repression [1]. miRNAs have been implicated in a vast array of cellular processes including cell differentiation, proliferation and apoptosis [2]. MicroRNAs (miRNAs) are a group of small noncoding RNAs about 22 nt in length that downregulate gene expression by either of the two posttranscriptional mechanisms: mRNA cleavage or translational repression [1]. The resulting processed pre-miRNA is recognized by exportin-5 and transited to the cytoplasm [8, 9], where it is cleaved by Dicer protein [10,11,12,13]. The miRNA generated by Dicer is incorporated into the RNA-induced silencing complex (RISC) containing Argonaute proteins (Ago1–Ago4) [2, 14]. Ago-bound miRNA serves as a guide to recognize cellular mRNA so as to either induce their degradation and/or inhibit their translation [1, 2, 14].
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