Identification of a Rare Germline Heterozygous Deletion Involving the Polycistronic miR-17-92 Cluster in Two First-Degree Relatives from a BRCA 1/2 Negative Chilean Family with Familial Breast Cancer: Possible Functional Implications

A Single Variant in Pri-miRNA-155 Associated with Susceptibility to Hereditary Breast Cancer Promotes Aggressiveness in Breast Cancer Cells

Variants in genes encoding for microRNAs have been associated with their deregulation in breast cancer (BC). Sequencing of microRNAs deregulated in BC was performed using DNA from Chilean patients with a strong family history and negative for mutations in BRCA1/BRCA2. Seventeen variants were identified, three of which were selected for a case-control association study: rs376491654 (miR-335), rs755634302 (miR-497), and rs190708267 (miR-155). For rs190708267 C>T, the heterozygous T allele was detected in four BC cases and absent in controls, while homozygous TT cases were not detected. Variants were modelled in silico, cloned in a plasmid, expressed in BC cell lines, and functional in vitro assays were performed. Overexpression of the miR-155-T allele increased mature miR-155-5p levels in both BC cell lines, suggesting that its presence alters pre-miR-155 processing. Moreover, BC cells overexpressing the miR-155-T allele showed increased proliferation, migration, and resistance to cisplatin-induced death compared to miR-155-C overexpressing cells. Of note, the 3′UTR of APC, GSK3β, and PPP1CA genes, all into the canonical Wnt signaling pathway, were identified as direct targets. APC and GSK3β mRNA levels decreased while PP1 levels increased. These results suggest a pathogenic role of the variant rs190708267 (miR-155) in BRCA 1/2 negative BC, conferring susceptibility and promoting traits of aggressiveness.

miR-20b-5p functions as tumor suppressor microRNA by targeting cyclinD1 in colon cancer

MicroRNA functions as an oncogenic regulator or tumor suppressor in various human tumors. Although bioinformatics analysis suggested that miRNA-20b-5p may be associated with the tumorigenesis, its role in colon cancer remains elusive. To investigate the role of miRNA-20b-5p, HCT116 cell, a human colon cancer cell line used in therapeutic research and drug screenings, was chosen as a model system for our in vitro studies. We first carried out bioinformatics and microarray analysis. To gain further mechanism insight, flow cytometry was performed to determine cell apoptosis and cell cycle, and western blot or immunohistochemistry were employed to check the expression of CCND1/CDK/FOXM1 axis in HCT116 cells. In addition, wound-healing migration assay and transwell assay were conducted to uncover the effect of miR-20b-5p on tumor migration and invasion. Finally, we examined the role of miR-20b-5p by subcutaneous xenograft mouse models. Our data have shown that miRNA-20b-5p inhibited the cell cycle, migration, and invasion in HCT116 cells, but had no effect on cell apoptosis. CyclinD1 (CCND1) was identified as a direct target of miR-20b-5p. Overexpression of miRNA-20b-5p downregulated CCND1 level in HCT-116 cells. Mechanically, the inhibition of cell cycle, migration, and invasion of CC cells mediated by miRNA-20b-5p are through regulating the CCND1/CDK4/FOXM1 axis. Furthermore, miRNA-20b-5p inhibited the tumorigenesis in Balb/c nude mice CC xenograft models. Our data demonstrated that miR-20b-5p may serve as a tumor suppressor in colon cancer by negatively regulating CCND1, implying that miR-20b-5p could be a potential therapeutic target for the treatment of colon cancer.

The dual functional role of MicroRNA-18a (miR-18a) in cancer development

The polycistronic miR-17-92 cluster is instrumental in physiological processes commonly dysregulated in cancer, such as proliferation, the cell cycle, apoptosis, and differentiation. MicroRNA-18a (miR-18a) is one of the most conserved and multifunctional miRNAs in the cluster and is frequently overexpressed in malignant tumors. Altered miR-18a expression has been found in various physiological and pathological processes, including cell proliferation, apoptosis, epithelial-mesenchymal transition (EMT), tumorigenesis, cancer invasion and metastasis. In this review, we summarized the molecular basis and regulatory targets of miR-18a in cancer development. Interestingly, miR-18a has a dual functional role in either promoting or inhibiting oncogenesis in different human cancers. The differential miRNA expression in cancers of the same organ at different stages or of various subtypes suggests that this dual function of miR-18a is independent of cancer type and may be attributed to the fundamental differences in tumorigenic mechanisms. Finally, we summarized the current clinical use of miR-18a and discussed its potential uses in cancer therapy.

The MicroRNA Family Both in Normal Development and in Different Diseases: The miR-17-92 Cluster

An increasing number of research studies over recent years have focused on the function of microRNA (miRNA) molecules which have unique characteristics in terms of structure and function. They represent a class of endogenous noncoding single-strand small molecules. An abundance of miRNA clusters has been found in the genomes of various organisms often located in a polycistron. The miR-17-92 family is among the most famous miRNAs and has been identified as an oncogene. The functions of this cluster, together with the seven individual molecules that it comprises, are most related to cancers, so it would not be surprising that they are considered to have involvement in the development of tumors. The miR-17-92 cluster is therefore expected not only to be a tumor marker, but also to perform an important role in the early diagnosis of those diseases and possibly also be a target for tumor biotherapy. The miR-17-92 cluster affects the development of disease by regulating many related cellular processes and multiple target genes. Interestingly, it also has important roles that cannot be ignored in disease of the nervous system and circulation and modulates the growth and development of bone. Therefore, it provides new opportunities for disease prevention, clinical diagnosis, prognosis, and targeted therapy. Here we review the role of the miR-17-92 cluster that has received little attention in relation to neurological diseases, cardiac diseases, and the development of bone and tumors.