In HCC tissues, miRNAs could be an oncogene and as a tumor suppressor. Such as miR-655-3p, functioning as a suppressor in HCC [
23]. And it is apparent that experimentally dependent evidence supports the role of miR-31-5p as an oncogene and as a tumor suppressor [
24]. However, the exact functions still remain unclear. In HCC, there is a trend of poor prognosis following the deletion of the fragile site where miR-31-5p is encoded [
25]. Microarrays were used to find dysregulated gene expression between HCC and normal liver tissues which in regulation of HCC progression [
26]. Current research has determined that miR-31-5p expression in some other cancers promotes resistance to platinum-based or other ways therapy in vitro, such as radiotherapy [
25,
27]. Besides that, a previous study provided a rich source of proteins for identification of drug resistant-related biomarkers, such as ANXA2, which was found to overcome drug resistance in neuroblastoma [
28]. However, little is known about the role of miR-31-5p in vivo and the role of miR-31-5p expression in OXA-based therapy. The data from this study indicate that the loss of miR-31-5p in HCC tumors may confer a chemosensitive phenotype in vitro and in vivo. Hence, potential pleiotropic alterations due to the suppression of miR-31-5p may modulate the ability of OXA to enter the cellular environment [
29]. In contrast to the initial hypothesis, the data support the alternative hypothesis that miR-31-5p loss in HCC confers a positive prognostic influence. miR-31-5p appears to mediate resistance relying upon the regulation of intracellular transport, which seems to be the potential mechanism [
29]. Dependence upon nuclear transport has previously been noted in breast cancer and malignant pleural mesothelioma, and the associations between the altered transport of platinum-containing agents within the cellular environment and resistance to therapy have been comprehensively reviewed [
30]. The intracellular accumulation of chemotherapeutics has been comprehensively reviewed [
31]. In light of the higher overall amount of OXA in miR-31-5p-expressing cells (Fig.
1d) and the reduction in the concentration of platinum in the nuclear fraction (Fig.
1c), the question remained as to how the cells were able to survive an increased intracellular concentration of OXA. We further investigated whether PARP1 was a direct target of miR-31-5p in HCC. The western blot assay showed that miR-31-5p overexpression inhibited PARP1 protein expression in HCC cells (Fig.
4a,
d). In addition, the luciferase reporter assay showed that miR-31-5p could significantly decrease luciferase activity by binding directly to the 3’ UTR of PARP1 (Fig.
6a,
c). Moreover, PARP1 was upregulated in HCC tissues and cell lines, and PARP1 expression was inversely correlated with miR-31-5p expression in HCC tissues (Fig.
4d and
e). In summary, these results suggested that PARP1 upregulation in HCC was due to miR-31-5p dysregulation. Moreover, miR-31-5p can prevent the nuclear localization of PARP1 (Figs.
4c,
5c). Furthermore, PARP1 was transported to the nucleus by miR-31-5p expression and OXA exposure, which is in accordance with OXA resistance. These data suggest that miR-31-5p can mediate OXA resistance. Previous studies informed us that miRNAs can mediate cellular sequestration through the mediation of multidrug-resistant proteins and the alteration of calcium signaling [
32‐
34]. In this study, further fractionation of cellular components revealed a change in lysosomal accumulation, which promoted the expression of possible drug transporters that were bound to lysosomes. This phenomenon made us question whether miR-31-5p-expressing cells had a higher aggregate concentration of lysosomes. The lysosomally bound drug transporter ABCB9 has been identified as a modulator of resistance, with up- or downregulation of the protein enhancing or reducing the response to therapeutics, respectively. Surprisingly, whereas ABCB9 expression appears to be increased in miR-31-5p-overexpressing cells, which display a more resistant phenotype, this phenotype may not be replicated upon manipulation of ABCB9 in miR-31-null Hep3B cells. In addition, there is a sensitizing effect to OXA treatment. Dong et al. [
20] examined the relationship between miR-31 and ABCB9. However, there is an elevation in ABCB9 protein levels associated with the miR-31-mediated chemoresistant phenotype. Contextually, this association may be explained by the pleiotropic effect of microRNAs, including miR-31-5p, targeting the mRNA of a transcription factor that regulates ABCB9. In short, the increase in miR-31-5p expression may lead to the downregulation of a potential negative regulator of transcription, thereby releasing a transcriptional brake, which may lead to an increase in the expression of target proteins such as ABCB9. As this study showed, miR-31-5p-mediated resistance to OXA may arise through protein–protein interactions. Interestingly, we observed that higher PARP1 expression was associated with lower miR-31-5p expression. Further study is required to characterize these interactions in detail; the co-IP results may support the role of PARP1 and ABCB9 interaction, but the function is not clearly understood. As Fig.
7 shows, the level of PARP1 binding to ABCB9 was much lower in the miR-31-5p-overexpressing Hep3B cells and HCC tissues(Figure). Intriguingly, the binding of these proteins can be slightly restored in OXA-treated HCC cells and tissues in which miR-31-5p is overexpressed. In summary, our data suggest that miR-31-5p mediates PARP1 through protein-protein interaction between PARP1 and ABCB9, thereby increasing OXA resistance in HCC. In other words, miRNA may promote enhanced sensitivity to OXA-based chemotherapeutics and improve patient outcomes.