Knockdown of Musashi RNA Binding Proteins Decreases Radioresistance but Enhances Cell Motility and Invasion in Triple-Negative Breast Cancer

Abstract

The therapeutic potential of Musashi (MSI) RNA-binding proteins, important stemness-associated gene expression regulators, remains insufficiently understood in breast cancer. This study identifies the interplay between MSI protein expression, stem cell characteristics, radioresistance, cell invasiveness and migration. MSI-1, MSI-2 and Notch pathway elements were investigated via quantitative polymerase chain reaction (qPCR) in 19 triple-negative breast cancer samples. Measurements were repeated in MDA-MB-231 cells after MSI-1 and -2 siRNA-mediated double knockdown, with further experiments performed after MSI silencing. Flow cytometry helped quantify expression of CD44 and leukemia inhibitory factor receptor (LIFR), changes in apoptosis and cell cycle progression. Proliferation and irradiation-induced effects were assessed using colony formation assays. Radiation-related proteins were investigated via Western blots. Finally, cell invasion assays and digital holographic microscopy for cell migration were performed. MSI proteins showed strong correlations with Notch pathway elements. MSI knockdown resulted in reduction of stem cell marker expression, cell cycle progression and proliferation, while increasing apoptosis. Cells were radiosensitized as radioresistance-conferring proteins were downregulated. However, MSI-silencing-mediated LIFR downregulation resulted in enhanced cell invasion and migration. We conclude that, while MSI knockdown results in several therapeutically desirable consequences, enhanced invasion and migration need to be counteracted before knockdown advantages can be fully exploited.

Syndecan-1 Depletion Has a Differential Impact on Hyaluronic Acid Metabolism and Tumor Cell Behavior in Luminal and Triple-Negative Breast Cancer Cells

“…We have recently demonstrated that siRNA knockdown of the RNA binding protein, which is also a stem cell marker, Musashi (Msi) expression results in a loss of CSC features and decreases the radioresistance capacity of the triple-negative breast cancer cells. However, invasion, growth and cell motility were enhanced upon Msi knockdown [50], generating a phenocopy of Sdc-1 depletion in MDA-MB-231 cells and suggesting a functional interaction [17]. In contrast, in this study, in the triple-negative MDA-MB-231 cells, Msi2 was upregulated upon Sdc-1 depletion, suggesting a feedback loop between Sdc-1 and Msi.…”

Musashi1 Contribution to Glioblastoma Development via Regulation of a Network of DNA Replication, Cell Cycle and Division Genes

“…Cells are particularly sensitive during S phase, when the genome is replicated through a fundamental process that requires spatio-temporal coordination of many replication origins and activation of checkpoint cascades that impose cell-cycle arrest if necessary, thus preventing the propagation of damaged DNA [ 56 ]. Expanding on Msi1 function in cell cycle progression [ 3 , 26 , 57 , 58 , 59 , 60 , 61 , 62 ], we showed that Msi1 levels influence the expression of genes implicated in different stages of the cell cycle. In Msi1 KO glioblastoma cells, we observed that G1-S transition is disrupted, agreeing with an increase in expression of Msi1 targets p21 and p27 and downregulation of CDK2 and CCNE2.…”

Knockdown of the prognostic cancer stem cell marker Musashi-1 decreases radio-resistance while enhancing apoptosis in hormone receptor-positive breast cancer cells via p21WAF1/CIP1

“…It has also been linked to decreased levels of p21 WAF1/CIP1 (Wang et al 2010 ), a cyclin-dependent kinase inhibitor and, as such, a key versatile cell cycle protein that tends to inhibit breast cancer cell growth (Kreis et al 2019 ). In a previous study limited to triple-negative breast cancer (TNBC), our group first linked MSI-1 to cell death mediation, key to therapeutic success in breast cancer (Troschel et al 2020 ). In this study, we set out to understand the prognostic significance of MSI-1 expression in breast cancer and subsequently investigated ramifications of targeting MSI-1 for apoptosis and therapy resistance in hormone receptor-positive breast cancer cells.…”