AP-1-mediated chromatin looping regulates ZEB2 transcription: new insights into TNFα-induced epithelial-mesenchymal transition in triple-negative breast cancer

Abstract

The molecular determinants of malignant cell behaviour in triple-negative breast cancer (TNBC) are poorly understood. Recent studies have shown that regulators of epithelial-mesenchymal transition (EMT) are potential therapeutic targets for TNBC. In this study, we demonstrate that the inflammatory cytokine TNFα induces EMT in TNBC cells via activation of AP-1 signaling and subsequently induces expression of the EMT regulator ZEB2. We also show that TNFα activates both the PI3K/Akt and MAPK/ERK pathways, which act upstream of AP-1. We further investigated in detail AP-1 regulation of ZEB2 expression. We show that two ZEB2 transcripts derived from distinct promoters are both expressed in breast cancer cell lines and breast tumor samples. Using the chromosome conformation capture assay, we demonstrate that AP-1, when activated by TNFα, binds to a site in promoter 1b of the ZEB2 gene where it regulates the expression of both promoter 1b and 1a, the latter via mediating long range chromatin interactions. Overall, this work provides a plausible mechanism for inflammation-induced metastatic potential in TNBC, involving a novel regulatory mechanism governing ZEB2 isoform expression.

AP-1 Is a Key Regulator of Proinflammatory Cytokine TNFα-mediated Triple-negative Breast Cancer Progression

“…We show here that, in highly invasive breast cancer cells, AP-1/proinflammatory signaling potently increases cell invasion. Consistent with this observation, we previously reported that TNF␣/AP-1 signaling induces EMT in TNBC cells (14). Our results indicate a critical role for AP-1 signaling potentiates TNF␣-driven tumor aggressiveness.…”

“…ON-TARGET plus NINJ1 siRNA pool (LQ-017671-00-0002), ON-TARGET plus RELA siRNA pool (LQ-003533-00-0002) and ON-TARGET plus NFKB1 siRNA pool (LQ-003520-00-0002) were purchased from Dharmacon. Transfection was conducted as described previously (14). The empty vector pCMV6-Entry and pCMV6-Ninj1 expression vector were purchased from Origene.…”

“…Cells-We previously demonstrated that the inflammatory cytokine TNF␣ triggered EMT of TNBC cells through AP-1-induced ZEB2 up-regulation (14). However, the AP-1 signaling network responsive to TNF␣ remains largely unexplored.…”

PCP4/PEP19 promotes migration, invasion and adhesion in human breast cancer MCF-7 and T47D cells

“…EMT plays a critical role in organ development, tissue remodeling, and in cancer invasion and metastasis [22–24]. Many studies have linked EMT to the invasive and metastatic potential of breast cancer cells [25, 26]. A feature of EMT is suppression of E-cadherin expression, which disrupts cell-cell adhesion and activates signaling pathways that control cell migration, invasion, and metastasis [27, 28].…”

Zeb2: A multifunctional regulator of nervous system development

“…Indeed, human ZEB2 mRNAs initiate from two distinct promoters, 1a or 1b, that are located $2.2 kb apart. The transcription factor AP-1, when activated by TNFa, binds to a specific site in promoter 1b to concomitantly regulate the transcription of both promoter 1b and 1a, the latter via mediation of long range chromatin interactions (Qiao et al, 2015). The complexity of the Zeb2 5 0 UTR is increased by the presence of a large intron which contains an internal ribosomal entry site (IRES).…”