The non-coding 3′-untranslated region (UTR) of genes play an important role in the regulation of microRNA (miRNA) functions, since it can bind and inactivate multiple miRNAs. Herein, we report that ectopic expression of XIAP 3′UTR increased human breast cancer cells proliferation, colony formation, migration, invasion and xenograft tumor growth and suppressed tumor cell death. To investigate this process, we further correlated the genome-wide transcriptional profiling with the gene expression alterations after transfecting XIAP 3′UTR in MCF-7 cells. We identified a robust, genome-wide mechanism of cell migration, motility and epithelial to mesenchymal transition by which mediated by a previously described cellular component movement factor FSCN1. Expression of XIAP and FSCN1 were up-regulated synergistically after transfecting XIAP 3′UTR in vitro and in vivo. Interactions between XIAP and FSCN1 appear to be a key determinant of these processes. Co-transfection with Dicer siRNA reversed the XIAP 3′UTR-mediated oncogenicity, suggesting the miRNAs might be involved in that process. Furthermore, we demonstrated that one miRNA, miR-29a-5p, can bind to both the XIAP and FSCN1 3′UTRs and play an important role in that interactions. We showed that the 3′UTR of XIAP was able to antagonize miR-29a-5p, and resulted in the increased translation of XIAP and FSCN1. Thus, our findings reveal important new insights into how XIAP 3′UTR works, suggesting that the non-coding XIAP 3′UTR serves as a competitor for miRNA binding and subsequently inactivates miRNA functions, by which XIAP 3′UTR frees the target mRNAs from being repressed.
Autophagy is a conserved multi-step lysosomal process that is induced by diverse stimuli including cellular nutrient deficiency. X-linked inhibitor of apoptosis (XIAP) promotes cell survival and recently has been demonstrated to suppress autophagy. Herein, we examined regulation of XIAP-mediated autophagy in breast cancer cells and determined the underlying molecular mechanism. To investigate this process, autophagy of breast cancer cells was induced by Earle's balanced salt solution (EBSS). We observed discordant expression of XIAP mRNA and protein in the autophagic process induced by EBSS, suggesting XIAP may be regulated at a post-transcriptional level. By scanning several miRNAs potentially targeting XIAP, we observed that forced expression of miR-23a significantly decreased the expression of XIAP and promoted autophagy, wherever down-regulation of miR-23a increased XIAPexpression and suppressed autophagy in breast cancer cells. XIAP was confirmed as a direct target of miR-23a by reporter assay utilizing the 3′UTR of XIAP. In vitro, forced expression of miR-23a promoted autophagy, colony formation, migration and invasion of breast cancer cell by down-regulation of XIAP expression. However, miR-23a inhibited apoptosis of breast cancer cells independent of XIAP. Xenograft models confirmed the effect of miR-23a on expression of XIAP and LC3 and that miR-23a promoted breast cancer cell invasiveness. Therefore, our study demonstrates that miR-23a modulates XIAP-mediated autophagy and promotes survival and migration in breast cancer cells and hence provides important new insights into the understanding of the development and progression of breast cancer.
Resistance to chemotherapy remains a major obstacle to the successful treatment of breast cancer. More than 80% of patients who receive neoadjuvant chemotherapy (NAC) do not achieve a pathological complete response. In this study, we report a novel p62 mRNA isoform with a short 3′-UTR (p62-SU, 662-nt) that is associated with chemoresistance in breast cancer cells and tissue specimens. The p62 mRNA isoform was identified by RNA sequencing with qRT-PCR, 3′-RACE, and northern blot analysis. In vitro and in vivo, ectopic expression of p62-SU promoted breast cancer cell proliferation, migration, invasion, and chemoresistance compared with the p62 mRNA isoform with a full-length 3′-UTR (p62-LU, 1,485-nt). Mechanistically, CPSF1 modulated the 3′-UTR of p62 through alternative polyadenylation. In addition, p62-SU escaped miR-124-3p-mediated repression and upregulated p62-SU protein expression, thereby inducing p62-dependent chemoresistance. These data suggest that a CPSF1-p62-miR-124-3p signaling axis is responsible for reduced sensitivity of breast cancer to chemotherapy.
X-linked inhibitor of apoptosis protein functions as an intrinsic regulator of apoptosis by inhibition of caspase activity and possesses a pivotal role in human cancer development and progression. A growing body of literature has demonstrated that microRNAs lead to the degradation or translational repression of messenger RNAs by binding to the non-coding region of messenger RNA at the 3′-untranslated region. Here, we revealed that the expression of HMGA2 is upregulated with X-linked inhibitor of apoptosis protein after transfection of X-linked inhibitor of apoptosis protein 3′-untranslated region in hepatocellular carcinoma cells, suggesting that X-linked inhibitor of apoptosis protein 3′-untranslated region serves as a competitor for microRNAs and prevent the co-targeted messenger RNA, HMGA2, from being suppressed. We further identified that let-7a-5p could bind to both the X-linked inhibitor of apoptosis protein 3′-untranslated region and HMGA2 3′-untranslated region. Moreover, we demonstrated that the forced expression of X-linked inhibitor of apoptosis protein 3′-untranslated region increases the oncogenicity of hepatocellular carcinoma cells in vitro. Cell functional analyses were performed to examine the association of HMGA2 status and X-linked inhibitor of apoptosis protein 3′-untranslated region. We have also measured the functional readout of let-7a-5p and HMGA2, an assay often employed to provide substantial evidence for the effects of X-linked inhibitor of apoptosis protein 3′-untranslated region on hepatocellular carcinoma cells. In general, our findings suggest that X-linked inhibitor of apoptosis protein 3′-untranslated region serves as a competitive endogenous RNA for HMGA2 to activate hepatocellular carcinoma progression by arresting endogenous let-7a-5p. Keywords X-linked inhibitor of apoptosis protein, HMGA2, 3′-untranslated region, microRNA, hepatocellular carcinoma Date
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