E2f4/P107 Complex Regulates Chemotherapy Resistance In Human Colorectal Cancer Stem Cells

Most cancer patients experience disease progression despite one or multiple lines of treatment with cytotoxic chemotherapy. Evidence from human trials and in vivo experiments on patient-derived xenograft (PDX) tumor lines indicates that cancer stem cells (CSCs) can survive chemotherapy treatment. However, the mechanism of chemotherapy resistance in CSCs is not fully elucidated. To identify new mechanisms of the drug-resistance in colorectal cancer, we used gene-expression microarrays to examine the gene expression profile of CSCs and non-CSCs in four human PDX models of colorectal cancer, both before-and-after treatment with cytotoxic chemotherapy. The gene-expression data were analyzed using Independent Component Analysis (ICA) followed by Transcription Factor Target Genes (TFTG) enrichment analysis, which identified the transcription factor E2F4 as a candidate regulator of chemotherapy resistance in colorectal CSCs. E2F4 was predominantly expressed in the CSC-enriched cell population (CD44+/CD166+ human colorectal cancer cells). E2F4 knock-down sensitizes cancer cells to chemotherapy in three different PDX tumors as well as HT29 cells. Co-immunoprecipitation experiments showed that E2F4 forms a complex with p107 and DP-1, which also contributed to the chemotherapy resistance. Simultaneous knock-down of both E2F4 and p107 enhanced chemotherapy sensitivity more than E2F4 knock-down alone. In normal intestinal crypt cells E2F4 was dispensable for chemotherapy resistance. ChIP-seq and RNA-seq experiments revealed that LDHA is a key downstream target of E2F4. LDHA knock-down sensitizes cancer cells to chemotherapy. High LDHA expression in tumor tissues was an independent poor prognostic factor in colorectal cancer patients (n=466), as well as in non-small cell lung cancer (n=1,926) and breast cancer (n=3,554). Thus, the E2F4/p107-LDHA pathway represents a novel therapeutic target to overcome chemotherapy resistance in CSCs. Citation Format: Junichi Matsubara, Yong F. Li, Piero Dalerba, Debashis Sahoo, Taichi Isobe, Russ B. Altman, Michael F. Clarke. E2F4/p107 complex regulates chemotherapy resistance in human colorectal cancer stem cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 81. doi:10.1158/1538-7445.AM2017-81