Positive Feedback Regulation between KLF5 and XPO1 Promotes Cell Cycle Progression of Basal like Breast Cancer.

Basal-like breast cancer (BLBC), overlapping with the subgroup of estrogen receptor (ER), progesterone receptor (PR), and HER2 triple-negative breast cancer, has the worst prognosis and limited therapeutics. The XPO1 gene encodes nuclear export protein 1, a promising anticancer target which mediates nucleus-cytoplasm transport of nuclear export signal containing proteins such as tumor suppressor RB1 and some RNAs. Despite drugs targeting XPO1 are used in clinical, the regulation of XPO1 expression and functional mechanism is poorly understood, especially in BLBC. This study finds that KLF5 is a transcription factor of XPO1, which increases RB1 nuclear export and cell proliferation in BLBC cells. Furthermore, XPO1 interacts with the RNA-binding protein PTBP1 to export FOXO1 mRNA to cytoplasm and thus activates the FOXO1-KLF5 axis as a feedback. This work demonstrates that XPO1 inhibitor KPT-330 in combination with CDK4/6 inhibitor additively suppressed BLBC tumor growth in vivo. These results reveal a novel positive feedback regulation loop between KLF5 and XPO1 and provide a novel treatment strategy for BLBC.