Knockdown of the stem cell marker Musashi-1 inhibits endometrial cancer growth and sensitizes cells to radiation.

BACKGROUND: Endometrial carcinoma is the most common gynecological cancer in Europe. Musashi-1 is known to be a key regulator of endometrial cancer stem cells and a negative prognostic marker. In the present study, we aimed to understand growth and gene expression patterns in endometrial carcinoma after Musashi-1 knockdown in vitro and in vivo. Changes in therapeutic resistance were also assessed. METHODS: First, we performed analyses to understand Musashi-1 expression patterns using The Cancer Genome Atlas database. We then proceeded to assess effects of small interfering RNA-based Musashi-1 targeting in two endometrial carcinoma cell lines, Ishikawa and KLE. After quantifying baseline changes in cell metabolism, we used MTT tests to assess chemotherapy effects and colony formation assays to understand changes in radioresistance. For mechanistic study, we used quantitative polymerase chain reaction (qPCR) and western blotting of key Musashi-1 target genes and compared results to primary tissue database studies. Finally, xenograft experiments in a mouse model helped understand in vivo effects of Musashi-1 knockdown. RESULTS: Musashi-1 is aberrantly expressed in primary tumor tissues. In vitro, silencing of Musashi-1 resulted in a strong decline in cell proliferation and radioresistance, while chemoresistance remained unchanged. Loss of Musashi-1 led to downregulation of telomerase, DNA-dependent protein kinase, the Notch pathway and overexpression of cyclin-dependent kinase inhibitor p21, the latter of which we identified as a key mediator of Msi-1 knockdown-related anti-proliferative signaling. In vivo, the anti-proliferative effect was confirmed, with Msi-1 knockdown tumors being about 40% reduced in size. CONCLUSIONS: Musashi-1 knockdown resulted in a strong decrease in endometrial cancer proliferation and a loss of radioresistance, suggesting therapeutic potential.