The RNA binding protein Musashi1 regulates apoptosis, gene expression and stress granule formation in urothelial carcinoma cells

Abstract

The RNA-binding protein Musashi1 (MSI1) is a marker of progenitor cells in the nervous system functioning as a translational repressor. We detected MSI1 mRNA in several bladder carcinoma cell lines, but not in cultured normal uroepithelial cells, whereas the paralogous MSI2 gene was broadly expressed. Knockdown of MSI1 expression by siRNA induced apoptosis and a severe decline in cell numbers in 5637 bladder carcinoma cells. Microarray analysis of gene expression changes after MSI1 knockdown significantly up-regulated 735 genes, but down-regulated only 31. Up-regulated mRNAs contained a highly significantly greater number and density of Musashi binding sites. Therefore, a much larger set of mRNAs may be regulated by Musashi1, which may affect not only their translation, but also their turnover. The study confirmed p21CIP1 and Numb proteins as targets of Musashi1, suggesting additionally p27KIP1 in cell-cycle regulation and Jagged-1 in Notch signalling. A significant number of up-regulated genes encoded components of stress granules (SGs), an organelle involved in translational regulation and mRNA turnover, and impacting on apoptosis. Accordingly, heat shock induced SG formation was augmented by Musashi1 down-regulation. Our data show that ectopic MSI1 expression may contribute to tumorigenesis in selected bladder cancers through multiple mechanisms and reveal a previously unrecognized function of Musashi1 in the regulation of SG formation.

Downregulation of Msi1 suppresses the growth of human colon cancer by targeting p21cip1

“…All these finding suggest that Msi1 function as an oncogene. This notion is further supported by the findings that ablation of Msi1 in gliomas (6) or bladder carcinoma cells (21) suppressed the cell cycle, and induced apoptosis and showed severe decline in cell numbers. However, Msi1 has also been proposed to have no significant effect on cell proliferation in human intestinal epithelial cells (22).…”

“…In the present study, we also found that downregulation of Msi1 inhibited the cell cycle by blocking the G 1 /S transition in 2 colon cancer cell lines. Furthermore, we found that knockdown of Msi1 upregulated the expression of p21 the findings in bladder carcinoma (21) and breast cancer (19). p21 cip1 is a universal cyclin dependent kinase (CDK) inhibitor that directly inhibits the activity of cyclin-CDK complexes, resulting in cell cycle arrest at G 0 /G 1 phase.…”

“…It has been reported that Msi1 blocked the G 1 /S phase transition of cell cycle by negative regulation of cyclin-dependent kinase (CDK) inhibitor p21 cip1 in bladder carcinoma (21) and breast cancer (19). To test whether it also occurs in colon cancer cells, p21 cip1 mRNA and protein levels were examined by qRT-PCR and western blot analysis.…”

Establishment and characterization of a bladder cancer cell line with enhanced doxorubicin resistance by mevalonate pathway activation

“…Gene expression microarray analysis and evaluation were performed with independent triplicate RNA preparations from each cell line using HG U133A GeneChips (Affymetrix, Berlin, Germany) as described previously [26]. For functional annotation, the Database for Annotation, Visualization and Integrated Discovery (DAVID), version v6.7, was used [27].…”

473: Canonical Notch signalling is inactive in urothelial carcinoma

“…The Notch receptor NOTCH1 and its ligand DLL1 are significantly down-regulated in urothelial carcinoma tissues Expression of several Notch pathway components was measured at the mRNA level by qRT-PCR in a wellcharacterized set of invasive urothelial carcinoma and normal bladder tissue samples that we had previously used for other studies [27]. Expression of NOTCH1 and NOTCH2 was significantly decreased in almost all urothelial cancers ( Figure 1A-B).…”