Chronic myeloid leukemia (CML) is a myeloproliferative disease with an expansion of white blood cells. The current treatments for CML are shown not to be long-term effective because of CML stem cells' insensitivity to tyrosine kinase inhibitors. Therefore, studying more about CML stem cells is essential to understand the pathways of CML stem cell development and proliferation and finally lead to effective treatments to eliminate CML stem cells and eradicate CML. This chapter describes two methods to analyze cell cycle of CML stem cells. The rare population of CML stem cells can be identified by staining with cell surface markers, and then DNA-binding dyes Hoechst 33342 and propidium iodide (PI) are added to stain the DNA content which is changed when cells go through different phases of the cell cycle. Samples are run through the flow cytometer to be analyzed based on different absorbance and emission wavelengths of different florescent colors.
Background: Dysregulation of cell cycle progression is one of the common features of human cancer cells, however, its mechanism remains unclear. This study aims to clarify the role and the underlying mechanisms of Roquin1 in cell cycle arrest induction in breast cancer.Methods: Public cancer databases were analyzed to identify the expression pattern of Roquin1 in human breast cancers and the significant association with patient survival. Quantitative real-time PCR and western blots were performed to detect the expression of Roquin1 in breast cancer samples and cell lines. Cell counting, MTT assay, flow cytometry, and in vivo study were conducted to investigate the effects of Roquin1 on cell proliferation, cell cycle progression and tumor progression. RNA-sequencing was applied to identify the differential genes and pathways regulated by Roquin1. RNA immunoprecipitation assay, luciferase reporter assay, mRNA half-life detection, RNA affinity binding assay, and RIP-ChIP were used to explore the molecular mechanisms of Roquin1.Results: We showed that Roquin1 expression in breast cancer tissues and cell lines was inhibited, and the reduction in Roquin1 expression was associated with poor overall survival and relapse free survival of patients with breast cancer. Roquin1 overexpression inhibited breast cancer cell proliferation and induced G1/S cell cycle arrest without causing significant apoptosis. In contrast, knockdown of Roquin1 promoted breast cancer cell growth and cycle progression. Moreover, in vivo induction of Roquin1 by adenovirus significantly suppressed breast tumor growth and metastasis. Mechanistically, Roquin1 selectively destabilizing cell cycle–promoting genes, including Cyclin D1, Cyclin E1, cyclin dependent kinase 6 (CDK6) and minichromosome maintenance 2 (MCM2) through targeting the stem–loop structure in the 3’untranslated region (3’UTR) of mRNAs via its ROQ domain, leading to the downregulation of cell cycle–promoting mRNAs.Conclusions: Our findings demonstrated that Roquin1 was a novel breast tumor suppressor and could induce G1/S cell cycle arrest by selectively downregulating the expression of cell cycle–promoting genes, which might as a potential molecular target for breast cancer treatment.
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