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Background: SNRPD1 is a spliceosome-associated protein and has previously been implicated with important roles in cancer development. Methods: Through analyzing the differential expression patterns and clinical association of splicing associated genes among tumor and tumor adjacent samples across different tumors and among different breast cancer subtypes, we identify the tumor promotive role of SNRPD1 using multiple publicly available datasets. Through pathway, gene ontology enrichment analysis and network construction, we linked the onco-therapeutic role of SNRPD1 with cell cycle. Via a series of experimental studies including knockdown assay, qPCR, western blotting, cell cycle, drug response assay, we confirmed the higher expression of SNPRD1 at both gene and protein expression levels in triple negative breast cancer cells, as well as its roles in promoting cell cycle and chemotherapy response. Results: Our study revealed that SNRPD1 over-expression was significantly associated with genes involved in cell cycle, cell mitosis and chromatin replication, and silencing SNRPD1 in breast cancer cells could lead to halted tumor cell growth and cell cycle arrest at the G0/G1 stage. We also found that triple negative breast cancer cells with reduced SNRPD1 expression lost certain sensitivity to doxorubicin whereas luminal cancer cells did not. Conclusions: Our results suggested the prognostic value of SNRPD1 on breast cancer survival, its potential as the therapeutic target halting cell cycle progression for breast cancer control, and warranted special attention on the combined use of doxorubicin and drugs targeting SNRPD1. [ABSTRACT FROM AUTHOR]

MicroRNAs (miRNAs) play an important role in regulating cancer stem cell (CSC). Previous studies have shown that microRNA-221/222 (miR-221/222) cluster are involved in the propagation of breast cancer stem cell (BCSC), however, the underlying molecular mechanisms are still not fully understood. In this study, we found that miR-221/222 were overexpressed in highly aggressive breast cancer MDA-MB-231 cells, that are enriched in markers for epithelial-mesenchymal transition (EMT) and BCSCs, than in MCF-7 cells. Phosphatase and tensin homolog (PTEN) was confirmed to be the target of miR-221/222 in breast cancer cells. MiR-221/222 enhanced breast cancer cell growth, migration and invasion by downregulating PTEN. Importantly, both ectopic expression of miR-221/222 and PTEN knockdown increased the mammosphere formation capacity and the expression of the stemness marker ALDH1. MiR-221/222 lentivirus vector infected MCF-7 cells produced larger subcutaneous tumors, while shRNA vector of PTEN showed similar trend. Along with the downregulation of PTEN caused by miR-221/222 in the breast cancer cells and the xenograft tumor tissues, Akt phosphorylation (p-Akt), NF-κB p65 and phosphorylated p65 (p-p65), and cyclooxygenase-2 (COX-2) were all overexpressed compared to the negative control. Taken together, our findings indicate that miR-221/222 play a critical role in the propagation of BCSCs and tumor growth possibly through targeting PTEN, which in turn activating the Akt/NF-κB/COX-2 pathway. MiR-221/222 might represent the potential target of breast cancer therapy. [ABSTRACT FROM AUTHOR]

Background The miR-221/222 cluster has been discovered to function as oncogene in human malignancies including breast cancer. However, the role of miR-221/222 in the self-renewal of breast cancer stem cells (BCSCs) is not fully understood. In this study, we examined the impact and mechanism of miR-221/222 on the breast cancer cell viability, migration and invasion, and propagation of BCSCs. Methods Human breast cancer cell line MCF-7 was transfected with miR-221/222 mimics or inhibitors to overexpress or knock down miR-221/222 respectively using Lipofactamine 2000. The biological effects of miR-221 and miR-222 were then assessed by cell proliferation assay, colony formation assay and transwell chamber assays. CD44/CD24 staining and mammosphere formation assay were performed to evaluate the ability of BCSCs self-renewal. Potential target gene phosphatase and tensin homolog (PTEN) and its downstream effector, phosphorylated Akt (p-Akt) were identified by Western blot and qRT-PCR methods. Results PTEN, a tumor suppressor gene, was confirmed as a target of miR-221/222 in breast cancer cell line MCF-7. Downregulation of PTEN by miR-221/222 increased the phosphorylation of Akt. Enforced expression of miR-221/222 promoted breast cancer cell proliferation, migration and invasion via targeting PTEN/Akt pathway. Importantly, ectopic expression of miR-221/222 enriched the proportion of CD44 + /CD24 − BCSCs and improved the mammosphere formation capacity through targeting PTEN/Akt pathway. Blocking the endogenous miR-221/222 restored PTEN expression and subsequently decreased Akt phosphorylation, and thereby reversed this phenotype. Conclusions Our results suggested that miR-221/222 enhance breast cancer growth, migration and invasion, meanwhile propagate the self-renewal of BCSCs. This is achieved possibly through targeting PTEN/Akt pathway. miR-221/222 might be a novel therapeutic candidate for human breast cancer. [ABSTRACT FROM AUTHOR]