The Role of Forkhead Box Q1 Transcription Factor in Anticancer Effects of Withaferin A in Breast Cancer

Elimination of both rapidly dividing epithelial mammary cancer cells as well as breast cancer stem-like cells (bCSC) is essential for maximizing antitumor response. Withaferin A (WA), a small molecule derived from a medicinal plant (Withania somnifera), is highly effective in reducing burden and/or incidence of breast cancer in vivo in various preclinical models. We have shown previously that suppression of breast cancer incidence by WA administration in a rat model is associated with a decrease in self-renewal of bCSC but the underlying mechanism is still elusive. This study investigated the role of forkhead box Q1 (FoxQ1) transcription factor in antitumor responses to WA. Exposure of MDA-MB-231 and SUM159 cells to WA resulted in downregulation of protein and mRNA levels of FoxQ1 as well as inhibition of its transcriptional activity. FoxQ1 overexpression in SUM159 and MCF-7 cells resulted in a marked protection against WA-mediated inhibition of bCSC as judged by flow cytometric analysis of CD49f^high population and mammosphere assay. RNA-sequencing analysis revealed upregulation of many bCSC-associated genes by FoxQ1 overexpression in SUM159 cells, including IL8 whose expression was decreased by WA treatment in SUM159 and MCF-7 cells. FoxQ1 was recruited to the promoter of IL8 that was inhibited significantly by WA treatment. On the other hand, WA-mediated inhibition of cell proliferation or migration was not affected by FoxQ1 overexpression. The FoxQ1 overexpression partially attenuated WA-mediated G₂–M phase cell cycle arrest in SUM159 cells only. These results indicate that FoxQ1 is a target of WA for inhibition of bCSC fraction.

Prevention Relevance: Withaferin A (WA) is highly effective in reducing burden and/or incidence of breast cancer in various preclinical models. However, the mechanism underlying breast cancer prevention by WA is not fully understood. This study shows a role for FoxQ1 in antitumor response to WA.