Expression And Functional Implication Of NcRNAs In Breast And Prostate Cancer Formation And Progression

Breast cancer and prostate cancer are one of most common malignancies and leading causes of death for women and men respectively. Their formation, progression, invasion and metastasis advance gradually and many oncogenes and tumor suppressor genes are involved, yet the underlying molecular mechanisms remain to be clarified.Non-coding RNAs are a class of functional RNA molecules which are not translated into proteins, including tRNAs, rRNAs, snRNAs, snoRNAs, piRNAs, lncRNAs and microRNAs. Published studies show that these RNAs play a critical role in regulating mRNA stability and translation, protein transportation, participating in RNA modification, influencing the structure of chromosome. Some ncRNAs are dysregulated and important for cancer formation and progression.microRNAs (miRNAs) are a class of small(19-24nucleotides (nt) in length), endogenous, non protein-coding RNAs which downregulate target gene expression by binding to complementary sites on the3’untranslated region (3’ UTR region) of specific mRNAs. miRNAs are found to be extremely conserved and represent a crucial layer of RNA-based gene expression. miRNAs control a variety of cellular functions including cell proliferation, differentiation, senescence, apoptosis and cell stemness maintenance. Dysregulation of miRNAs are reported to be highly related to multiple pathogenesis including tumorigenesis. The sophisticated network formed by miRNAs and their target genes plays an important role in cancer formation and progression.lncRNAs are a class of ncRNAs over200nt in length. lncRNAs regulate multiple biological processes including transcriptional regulation, chromatin complex formation, histone modification, RNA splicing and translation X chromosome inactivation, genome imprinting. Various clinical investigations and experimental studies demonstrate that dysregulation of ncRNAs contributes to many types of diseases, especially in cancer. Although the molecular mechanism of lncRNAs in carcinogenesis are not well documented, published studies show that ncRNAs regulate cancer cell proliferation and migration by chromatin re-structure and histone modification.miR-203is a skin sternness-inhibiting miRNA promoting epidermal differentiation by targeting to the stemness associated transcription factor ΔNp63. Dysregulation of miR-203has been found in multiple cancers. In bladder and ovarian cancers, miR-203is upregulated during carcinogenesis. Overexpression of miR-203is correlated with poor overall survival in pancreatic cancer. The promoter of miR-203gene is hypermethylated in several tumors including gastric, hematological, hepatocellular and oral cancers. Meanwhile, downregulation of miR-203plays a pivotal role in ZEB1induced epithelial-mesenchymal transition (EMT). These findings suggest that miR-203may play a causative role in tumor formation and progression and its function rely on specific type of cancers.PVT1is a lncRNA located in chromosome8q24, a frequently amplified region in cancers including breast carcinomas. In breast cancer and ovarian cancer, silenced PVT1suppresses cellular proliferation and induces cell death. Yet the regulation of PVT1has not well been documented.In our studies, we firstly aim to clarify the function of miR-203in breast cancer formation and progression. We examined the expression of miR-203in clinical breast cancer patients at first, from which we found that miR-203was significantly upregulated in breast cancer tissue compared with matched normal tissues. In breast cancer cell lines, we also found that miR-203was upregualated in cancer cells with nonmetastatic luminal A subtypes compared with normal cells and immortalized cells, while the expression of miR-203was downregulated in highly metastatic basal-like cells. At the meantime, we found that the promoter region of miR-203gene was moderately methylated in metastatic breast cancer cells while no methylation was found within its region in luminal A cells. Treatment with the5-aza-dCyd demethylating reagent in basal-like cell lines significantly restored the expression of miR-203. These results suggest that downregulation of miR-203in metastatic breast cancer cells appeared to be caused by hypermethylation of its promoter, at least partially.We further evaluated the function of miR-203in breast carcinogenesis.In basal-like breast cancer cells, ectopic expression of miR-203obviously suppressed cellular proliferation by inducing cell cycle arrest and promoting cell apoptosis and the mechanism underlying proliferation inhibition was cell-type specific. Overexpression of miR-203also inhibited invasion and migration in these cells. Bioinformatics’analysis predicted a transcription factor snail homolog2(SNAI2or SLUG) as a putative target of miR-203and this prediction was validated by expression analysis and luciferase assay. Functionally, SNAI2could rescue miR-203suppressed cellular migration in basal-like cells.These results suggest that in malignant breast cancer cells, miR-203is epigenetically suppressed and then promote tumor cell growth and invasion at least in part by upregulating SNAI2expression.After that, we further examined the role of miR-203-SNAI2regulatory pathway played in prostate cancer proliferation and migration. Similarly to other studies, we also found that miR-203was downregulated and ectopic expression of miR-203suppressed tumor growth and migration in prostate cancer. miR-203also could suppress SNAI2expression and SNAI2could rescue miR-203suppressed cellular migration in prostate cancer.At the meantime, we found that the transcription factor KLF5our lab interested could bind to the promoter region of miR-203and then upregualated miR-203expression. On the other hand, KLF5could negatively regulate SNAI2expression. Overexpression of SNAI2could rescue KLF5suppressed migration in prostate cancer.In summary, these results demonstrate that miR-203plays an important role in breast and prostate carcinogenesis. As a tumor suppressor gene, miR-203suppresses cell proliferation and migration by targeting to SNAI2in breast and prostate cancers. At the meantime the miR-203-SNAI2regulatory pathway plays a pivotal role in KLF5suppressed migration in prostate cancer.On the other hand, we found that the genotype of one SNP rs13281615nearby PVT1coding region was highly associated with PVT1expression in breast cancer. The caner tissues with the GG risk genotype in SNP rs13281615showed a higher average PVT1expression than other genotypes, and normal tissues with any genotypes. Meanwhile, frequently directional mutations of rs13281615were found in breast carcinogenesis, which resulted in loss of association of GG genotype with tumor stages and proliferative marker Ki67.Our findings afford a new clue for the regulation of PVT1.