EpCAM activates the ERK-EGR1 signaling axis and promotes TNF-α-induced the progression of anaplastic thyroid cancer.

backgroundEpithelial cell adhesion molecule (EpCAM) is a pleotropic transmembrane glycoprotein comprising an extracellular domain (EpEX), a single transmembrane domain, and an intracellular domain (EpICD). For several types of cancer, high EpCAM expression is associated with tumor progression, metastasis, immune evasion, and overall poor prognosis. A rare but aggressive form of thyroid cancer, anaplastic thyroid cancer (ATC), has a mean survival time of only 3–6 months after diagnosis.

methodsThe levels of EpEX and EpICD cleavage in clinical patient samples was evaluated by using tissue microarray. Capture enzyme-linked immunosorbent assay (ELISA) was conducted to explore the of shedding EpEX and TNF-α. Western blotting and qRT-PCR was taken to determine the expression of proteins in ATC cell lines. RNA-seq was conducted, and differential gene expression and gene set enrichment analyses were subsequently performed to identify EpCAM knockout–associated molecular alterations and affected biological pathways. The functions of EpCAM or EpEX in ATC were investigated by proliferation, invasion, and stemness analysis. The combined therapy was validated via a tail vein injection method for the metastasis ATC models.

resultsIn this study, we observed that ATC samples typically exhibited a marked loss of membrane EpEX along with increased nuclear and cytoplasm accumulation of EpICD, as compared to non-ATC samples. Furthermore, we found that EpEX induced phosphorylation of EGFR, HGFR and Wnt receptors in ATC cells to promote cell growth, invasion and stemness activity. EpCAM signaling also increases TNF-α expression and induces TNF-α cleavage, and clarify the crosstalk between EpCAM and TNF-α to regulate ERK-EGR1 axis signaling. The inhibition of EpCAM signaling suppressed regulated intramembrane proteolysis (RIP) of EpCAM and shedding of the EpEX and EpICD in ATC cells. Combined treatment of EpAb2-6 and BRAF inhibitor dabrafenib coordinately induced apoptosis, while also inhibiting invasion, stemness and lung metastasis, and prolong survival in an animal model of metastatic ATC.

conclusionsThis study uncovers the molecular mechanisms underlying promotion of anaplastic thyroid cancer (ATC) tumor progression by EpCAM signaling via the ERK-EGR1-TNF-α axis. Our findings suggest that the EpCAM neutralizing antibody may improve the therapeutic efficacy of BRAF inhibitor, dabrafenib, in ATC.