Down-regulation of PARP1 by miR-891b sensitizes human breast cancer cells to alkylating chemotherapeutic drugs

MicroRNAs as a clue to overcome breast cancer treatment resistance

Breast cancer is the most frequent cancer in women worldwide. Despite the improvement in diagnosis and treatments, the rates of cancer relapse and resistance to therapies remain higher than desirable. Alterations in microRNAs have been linked to changes in critical processes related to cancer development and progression. Their involvement in resistance or sensitivity to breast cancer treatments has been documented by different in vivo and in vitro experiments. The most significant microRNAs implicated in modulating resistance to breast cancer therapies are summarized in this review. Resistance to therapy has been linked to cellular processes such as cell cycle, apoptosis, epithelial-to-mesenchymal transition, stemness phenotype, or receptor signaling pathways, and the role of microRNAs in their regulation has already been described. The modulation of specific microRNAs may modify treatment response and improve survival rates and cancer patients' quality of life. As a result, a greater understanding of microRNAs, their targets, and the signaling pathways through which they act is needed. This information could be useful to design new therapeutic strategies, to reduce resistance to the available treatments, and to open the door to possible new clinical approaches.

Genetic variant rs10251977 (G>A) in EGFR-AS1 modulates the expression of EGFR isoforms A and D

Tyrosine kinase inhibitor is an effective chemo-therapeutic drug against tumors with deregulated EGFR pathway. Recently, a genetic variant rs10251977 (G>A) in exon 20 of EGFR reported to act as a prognostic marker for HNSCC. Genotyping of this polymorphism in oral cancer patients showed a similar frequency in cases and controls. EGFR-AS1 expressed significantly high level in tumors and EGFR-A isoform expression showed significant positive correlation (r = 0.6464, p < 0.0001) with reference to EGFR-AS1 expression levels, consistent with larger TCGA HNSCC tumor dataset. Our bioinformatic analysis showed enrichment of alternative splicing marks H3K36me3 and presence of intronic polyA sites spanning around exon 15a and 15b of EGFR facilitates skipping of exon 15b, thereby promoting the splicing of EGFR-A isoform. In addition, high level expression of PTBP1 and its binding site in EGFR and EGFR-AS1 enhances the expression of EGFR-A isoform (r = 0.7404, p < 0.0001) suggesting that EGFR-AS1 expression modulates the EGFR-A and D isoforms through alternative splicing. In addition, this polymorphism creates a binding site for miR-891b in EGFR-AS1 and may negatively regulate the EGFR-A. Collectively, our results suggested the presence of genetic variant in EGFR-AS1 modulates the expression of EGFR-D and A isoforms.

ChrXq27.3 miRNA cluster functions in cancer development

MicroRNAs (miRNAs) regulate the expression of their target genes post-transcriptionally; thus, they are deeply involved in fundamental biological processes. miRNA clusters contain two or more miRNA-encoding genes, and these miRNAs are usually coexpressed due to common expression mechanisms. Therefore, miRNA clusters are effective modulators of biological pathways by the members coordinately regulating their multiple target genes, and an miRNA cluster located on the X chromosome q27.3 region has received much attention in cancer research recently. In this review, we discuss the novel findings of the chrXq27.3 miRNA cluster in various types of cancer.

The chrXq27.3 miRNA cluster contains 30 mature miRNAs synthesized from 22 miRNA-encoding genes in an ~ 1.3-Mb region. The expressions of these miRNAs are usually negligible in many normal tissues, with the male reproductive system being an exception. In cancer tissues, each miRNA is dysregulated, compared with in adjacent normal tissues. The miRNA-encoding genes are not uniformly distributed in the region, and they are further divided into two groups (the miR-506-514 and miR-888-892 groups) according to their location on the genome. Most of the miRNAs in the former group are tumor-suppressive miRNAs that are further downregulated in various cancers compared with normal tissues. miR-506-3p in particular is the most well-known miRNA in this cluster, and it has various tumor-suppressive functions associated with the epithelial–mesenchymal transition, proliferation, and drug resistance. Moreover, other miRNAs, such as miR-508-3p and miR-509-3p, have similar tumor-suppressive effects. Hence, the expression of these miRNAs is clinically favorable as prognostic factors in various cancers. However, the functions of the latter group are less understood. In the latter group, miR-888-5p displays oncogenic functions, whereas miR-892b is tumor suppressive. Therefore, the functions of the miR-888–892 group are considered to be cell type- or tissue-specific.

In conclusion, the chrXq27.3 miRNA cluster is a critical regulator of cancer progression, and the miRNAs themselves, their regulatory mechanisms, and their target genes might be promising therapeutic targets.

Salidroside inhibits the growth, migration and invasion of Wilms' tumor cells through down-regulation of miR-891b

AIMS

Salidroside is a major functional component of Rhodiola rosea L. with a lot of pharmacological effects, including anti-tumor. The present work aimed to explore whether Salidroside could also exhibit anti-tumor functions in Wilms' tumor.

MAIN METHODS

WIT49 and RM1 cells were treated by various doses of Salidroside. CCK-8 assay, flow cytometry detection, colony formation assay, Transwell assay, RT-qPCR and Western blot analysis were conducted to measure WIT49 and RM1 cells proliferation, apoptosis, migration and invasion. The expression changes of miR-891b in response to Salidroside treatment were tested by RT-qPCR. Rescue assays were performed to test whether miR-891b was a downstream effector of Salidroside. Finally, the involvement of PI3K/AKT/mTOR and NF-κB signaling pathways was studied.

KEY FINDINGS

Salidroside with concentration of 80 μM significantly reduced WIT49 and RM1 cells viability, survival capacity, migration and invasion, and significantly induced apoptosis. Meanwhile, down-regulation of Cyclin D1, MMP-2 and Vimentin, up-regulations of p53 and p21, as well as cleavage of caspase-3 and -9 were observed in Salidroside-treated cell. miR-891b was down-regulated by Salidroside. And Salidroside did not suppress WIT49 and RM1 cells growth, migration and invasion when miR-891b was overexpressed. Also, the deactivation of PI3K/AKT/mTOR and NF-κB pathways induced by Salidroside was reversed by miR-891b overexpression.

SIGNIFICANCE

Salidroside inhibits Wilms' tumor cells growth, migration and invasion via down-regulating miR-891b, which leads to the deactivation of PI3K/AKT/mTOR and NF-κB signaling pathways.