Abstract P6-03-11: Interleukin-enhancer binding factor 2 expression associates with chemotherapy response in triple-negative breast cancer
Authors: Bustos Matias A , Zhang Xiaoqing , Hoon Dave SB 
Published: March 2020

Background: Triple-Negative Breast Cancer (TNBC) is one of the aggressive breast cancer (BC) subtype and the most difficult to treat once metastasis occurs. The lack of hormone receptors prevents the usage of standard targeted therapy; moreover the heterogeneity of the TNBC subtype and the high risk of metastasis worsens the problem. Systemic chemotherapy is one of the best option to treat metastatic TNBC. However, the response to chemotherapy treatment is variable and tumors develop resistance. Enhancing the expression of specific splicing factors which generate gene variants is a mechanism the TNBC tumor cells to promote resistance. Interleukin-enhancer binding factor 2 (ILF2) is an RNA binding protein (RBP) involved in RNA metabolism and tumorigenesis. We hypothesize that the binding of the splicing factor Y-Box Binding Protein 1 (YBX1) to ILF2 generates alternative splicing of genes involved in DNA-Damage Response (DDR), in particular after chemotherapy treatment. Methods and Results: To test our hypothesis, we utilized KMplot software (http://kmplot.com/analysis/). Of clinical importance, Relapsed-Free Survival (RFS) after 5 years was analyzed for BC patients with basal subtype. High ILF2 expression determined poorer prognosis in patients with basal subtype and high ILF2 expression (upper quartile, n=154) compared to rest of the patients (n=464) (Log-rank test p=0.0032, HR= 1.53 (1.15-2.03)); furthermore when considered only patients receiving chemotherapy with high ILF2 expression (n=75) compared to rest of the patients (n=224) the prognosis was worst (Log-rank test p=0.000077, HR= 2.11 (1.44-3.07)). In assessing the potential relation of ILF2 expression and BC subtypes, we reviewed the BC TCGA and METABRIC dataset to assess ILF2 expression. A significant higher expression of ILF2 in primary tumors (n=1041) and metastatic (n=7) BC than normal tissue (n=113) was observed using TCGA; similar results were obtained using METABRIC dataset. Moreover, BC primary tumors with basal-like (n=98) subtype presented the highest ILF2 expression compare to other BC subtypes. Likewise, we demonstrated that enhanced expression of ILF2 is associated with copy number amplification in TNBC. In order to select models of TNBC, we profiled TNBC cell lines using western blot; TNBC cells presented higher levels of ILF2 expression than a normal-like cells. Then, using lentiviral transduction we generated stable clones overexpressing ILF2 in MDA-MB-231 cell lines. By functional assays, we demonstrated that higher ILF2 expression enhanced cell growth rates. To identify proteins interacting with ILF2 in TNBC, we performed immunoprecipitation assays and showed that ILF2 interacts with YBX1 in TNBC cell lines. Moreover, in TNBC patients ILF2 and YBX1 expression positively correlate. To validate our findings, we performed immunohistochemistry analysis for ILF2 in a TMA (100 BC and 10 normal breast tissues) and showed that patients with TNBC subtype displayed significantly enhanced ILF2 expression. Conclusions: ILF2 is highly expressed in TNBC cell lines and tumor tissues. ILF2 interacts with YBX1 in TNBC cells. In vitro models showed that overexpression of ILF2 promotes tumor growth. Clinically, increased ILF2 is associated with poorer prognosis and increased chance to relapse in patients with basal subtypes receiving chemotherapy treatment.

Citation Format: Matias A Bustos, Xiaoqing Zhang, Dave SB Hoon. Interleukin-enhancer binding factor 2 expression associates with chemotherapy response in triple-negative breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P6-03-11.