FOXC1-induced non-canonical WNT5A-MMP7 signaling regulates invasiveness in triple-negative breast cancer

Triple-negative breast cancer (TNBC) has high rates of local recurrence and distant metastasis, partially due to its high invasiveness. The Forkhead box C1 (FOXC1) transcription factor has been shown to be specifically overexpressed in TNBC and associated with poor clinical outcome. How TNBC's high invasiveness is driven by FOXC1 and its downstream targets remains poorly understood. In the present study, pathway-specific PCR array assays revealed that WNT5A and matrix metalloproteinase-7 (MMP7) were upregulated by FOXC1 in TNBC cells. Interestingly, WNT5A mediates the upregulation of MMP7 by FOXC1 and the WNT5A-MMP7 axis is essential for FOXC1-induced invasiveness of TNBC cells in vitro. Xenograft models showed that the lung extravasation and metastasis of FOXC1-overexpressing TNBC cells were attenuated by knocking out WNT5A, but could be restored by MMP7 overexpression. Mechanistically, FOXC1 can bind directly to the WNT5A promoter region to activate its expression. Engineered DNA-binding molecule-mediated chromatin immunoprecipitation (enChIP), coupled with mass spectrometry, identified FOXC1-interacting proteins including a group of heterogeneous nuclear ribonucleoproteins involved in WNT5A transcription induction. Finally, we found that WNT5A activates NF-kappa B signaling to induce MMP7 expression. Collectively, these data demonstrate a FOXC1-elicited noncanonical WNT5A signaling mechanism comprising NF-kappa B and MMP7 that is essential for TNBC cell invasiveness, thereby providing implications toward developing an effective therapy for TNBC.