MiRNA-135a Promotes Migration And Invasion Of Breast Cancer Cell By Targeting HOXA10

MicroRNAs (miRNAs) are a class of approximately22-nuleotide-long noncoding RNAs which are expressed in many organisms. Mature miRNAs arise from one arm of endogenous hairpin transcripts primary miRNAs (pri-miRNAs) by sequential processing in the nucleus and cytoplasm. Mature miRNAs regulate target genes post-transcriptionally, by inhibiting the translation through imperfect base-pairing interaction with the3’-untranslated regions (3’-UTRs) of their respective target genes, or degrading their target mRNAs through perfect or near-perfect base pairing. An individual miRNA is capable of regulating dozens of distinct mRNAs. And it has been reviewed that more than650human miRNAs were believed to modulate about one-third of the mRNA species encoded in the genome.MiRNAs are associated with the formation and progress of many types of cancers, including breast cancer, brain cancer, chronic lymphocytic leukemia, colorectal neoplasia, hepatocellular carcinoma, lung cancer, etc. Breast cancer is one of the most common cancers in adult females and studies showed that breast cancer was also associated with the deregulation of several miRNAs. At present, the studies on miRNAs function are mainly focused on miRNAs function in the development and progress of malignant tumors through regulating expression and function of their targets.Hox genes encode transcription factors essential for regulating differentiation, and take on critical positions in embryo pattern formation, morphogenesis. Besides, several studies have also underlined the aberrant expression of specific Hox genes in numerous types of cancers, and the potential role in tumor development, invasion, and metastasis. So they are considered to be important tumor associated factors.Our strategy was based on HoxA10indicated tumor suppressive function in breast cancer. We searched for its regulative miRNA and carried out our research on mechanism and function between miRNA and its target HoxA10in breast cancer. Part1HoxA10protein usually was less or no expressed in highly invasive breast cancer cells such as MDA-MB-231cells. However, the clinical evidence showed that HoxA10mRNA expression level is high in invasive malignant tissues. This suggests the speculation that HOXA10may be regulated post-transcriptionally, such as being targeted by miRNAs, which had been no report on this before.HoxA10was predicted by bio-information analysis online and verified as a target of miR-135a. HoxA10mRNA and miR-135a are co-expressed in high invasive breast cancer cell line BT549. In order to clarify the regulation mechanism of miR-135a on HoxA10, we carried on in vitro luciferase assay, finding that miR-135a can reduce the report gene activity of HoxA10through targeting HoxA103’UTR region. And this result was confirmed by mutating the predicted miR-135a binding site at HoxA103’UTR. We also found that miR-135a inhibited HoxA10at both post-transcriptional level and transcriptional level, inducing mRNA degradation.Part2To test miR-135a function in breast cancer cells, miR-135a up-regulation and down-regulation experiments were taken on in HEK293and BT549cells respectively, but there was no observable effect on cell proliferation. As miR-135a was elevated in high invasive breast cancer cell line BT549, we inferred that miR-135a may have function on the migration and invasion of breast cancer cells. We first blocked miR-135a function by2’-O-methyl oligonucleotides (miR-135a inhibitor) in BT549, finding the decreased migration and invasion. On the other side, miRNA-135a up-regulation in breast cancer cells SKBr3and MDA-MB-231led to increased migration and invasion.What’s more, HoxA10over-expression in BT549cells caused decreasing cells invasion. And interestingly, HOXA10protein produced by full length HOXA10cDNA vector was repressed compared to the higher over-expression with deleted3’-UTR vector in miR-135a expressed BT549cells.We also found that expression level of miR-135a was elevated in breast tumors with metastasis. Above all, our results indicated that miRNA-135a is an onco-miRNA promoting migration and invasion in breast cancer by targeting HoxA103’UTR. Functional research of miR-135a on promoting migration and invasion of breast cancer cells and regulation of HoxA10offered us the potential target for diagnosis and treatment of breast cancer.