siRNA-mediated inhibition of the stemness-related Musashi pathway affects LIF receptor expression and prometastatic motility of human MDA-MB-231 breast cancer cells

Introduction: The RNA-binding proteins Musashi-1 and Musashi-2 have been reported to maintain stem cell function and differentiation and to promote tumorigenesis by repressing translation of particular target mRNAs (1,2). Musashi proteins regulate the Notch signaling pathway via inhibition of numb, a protein inducing Notch endocytosis and subsequent degradation. We here evaluate the potential role and interplay of Musashi-1 and -2 on stemness-related gene expression and on the metastatic potential of breast cancer cells in vitro.

Methods: MDA-MB-231 breast cancer cells were transiently transfected with Musashi-1 and -2 siRNA as well as control siRNA. 48 hours after transfection, we conducted real-time-PCR experiments. 72 hours after transfection, colony forming experiments as well as video microscopy were performed.

Results: Real-time-PCR analysis of a panel of stemness-related markers showed a significant down-regulation of Notch-1 and the notch-dependent transcription factor Hes2 upon Musashi depletion. In addition, LIFR (leukemia inhibitory factor receptor), which has been reported to affect the YAP-Hippo-Pathway associated with tumor growth and metastasis in human breast cancer (3), was significantly downregulated. In colony formation assays and digital holographic video microcopy analysis, we were able to show a significant increase in motility of the Musashi-depleted transfected cells.

Conclusions: While interference with the Musashi-Notch pathway may reduce response to stemness-related cytokine signaling, it may enhance the metastatic potential of the triple negative breast cancer cell line MDA-MB-231.

References:

1. Nishimoto Y and Okano H. Cell Res. 20:1083 – 5 (2010)

2. Götte M et al. Int J Cancer Int J Cancer. 129:2042 – 9 (2011)

3. Chen D et al. Nat Med. 18:1511 – 7 (2012)