Reciprocal regulation of forkhead box C1 and L1 cell adhesion molecule contributes to triple-negative breast cancer progression

Abstract Purpose: Forkhead box C1 (FOXC1) may act as a therapeutic target for triple-negative breast cancer (TNBC) but without a comprehensive understanding of its regulations, especially at the upstream. L1 cell adhesion molecule (L1CAM) is a transmembrane glycoprotein that may involve in brain metastasis. Indicated by a positive correlation between FOXC1 and L1CAM transcripts, this study aims to further examine their relation in the process of TNBC. Methods: FOXC1 and L1CAM transcripts were downloaded fromtwo public datasets, and their proteins were examined in four TNBC cell lines. FOXC1 and L1CAM were separately knocked down in BT549 cells; L1CAM was overexpressed in BT549-shFOXC1, MDA-MB-231, and HCC1937 cells. CCK-8, transwell and wound healing assays were conducted in these cells, so was immunohistochemical staining in tumors. Results: L1CAM and FOXC1 transcripts were positively correlated in public datasets. BT549-shFOXC1 cells showed a decreased L1CAM expression both at the transcriptional and protein levels. Intriguingly, BT549-siL1CAM cells displayed decreased FOXC1 proteins, but exerted little effect on FOXC1 transcripts. Conversely, overexpression of L1CAM resulted in upregulation of FOXC1 protein without substantial change in FOXC1 mRNA, that consistently observedin BT549-shFOXC1, MDA-MB-231-L1CAM and HCC1937-L1CAM cells. Additionally, decreased or increased capacities of cell proliferation, migration, and invasion were seen along with down- or up-regulation of FOXC1 or L1CAM. Finally, a positive correlation between L1CAM and FOXC1 proteins was observed in human TNBC tumors. Conclusion: FOXC1 and L1CAM display coregulation at the protein level but not mRNA level to positively affect cell proliferation, migration and invasion in TNBC.