Abstract 2647: HOXB7, a key transcriptional regulator in triple negative breast cancer progression

Despite major advances in breast cancer treatment and management one-third of women with ER-positive, and nearly 30% of women with ER-negative breast cancer will have recurrent disease within fifteen years. Our laboratory and others have accumulated a large body of evidence for the involvement of HOXB7 in various aspects of breast cancer progression: tamoxifen resistance, DNA repair, epithelial-mesenchymal transition, promotion of metastasis in a transgenic mouse model and human cells as well as angiogenesis suggesting a role for HOXB7 not only in the epithelium but also strongly implicating its control on the microenvironment of the tumor. In this project, we focused on understanding factors driven by HOXB7 that lead to triple-negative breast cancer (TNBC). In the previous studies, we found that HOXB7 expression results in the recruitment of stromal components and enhances the formation of lung metastasis in transgenic crosses of HOXB7xHER2 mice. Interestingly, HOXB7 expression was increased in MDA-MB-231 Bone and Brain metastatic cells. Therefore, we hypothesize that HOXB7, through its ability to mediate EMT and recruit pro-angiogenic molecules, is capable of promoting invasion and metastasis. In this report, we established HOXB7 overexpressing MDA-MD-231 cells. We screened secretomes from MB231-HOXB7 cells using Human Cytokine Array Q440 to quantitatively detect 440 human inflammatory factors, growth factors, chemokines, receptors, and cytokines simultaneously. We identified upregulation of IL-8, IL-6, VEGF, ARG2, CXCL1, CF XIV, Procalcitonin, Syndecan-3, AMICA, IL-11, CXCL14, ROBO3, Follistatin, SOST, and ALCAM in the secretomes from MB231-HOXB7 cells. We ranked the expression level of each factor by real-time qRT-PCR and determined that IL-8 and CXCL1 were the top candidates. We confirmed by ELISA that IL-8 and CXCL1 secreted from tumor conditioned medium (TCM) was upregulated compared to the control cells. Our data showed that the HUVEC tube formation was increased by MDA-MD-231-HOXB7 conditioned media. Furthermore, fibroblast and M2 type macrophage migration were promoted by TCM of MDA-MD-231-HOXB7 cells. Significantly, Depletion of IL-8 and CXCL1 using specific shRNAs in MDA-MD-231-HOXB7 cells decreased the HUVEC tube formation and the cell migration of fibroblast and macrophage. In addition, CXCL1 and IL-8 signaling pathway by Reparixin, an inhibitor of the CXCR1/2 abrogated the tube formation and migration induced by MDA-MD-231-HOXB7 cells. These findings implicate IL-8 and CXCL1 signaling as a critical event in HOXB7 overexpression TNBC growth and metastasis via crosstalk between cancer cells and stromal components. Citation Format: Kideok Jin. HOXB7, a key transcriptional regulator in triple negative breast cancer progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2647.