Abstract
BackgroundEpithelial cell adhesion molecule (EpCAM) is a 40-kD type-I transmembrane protein that is frequently overexpressed in human epithelial cancers. Recent evidence implicates EpCAM in the regulation of oncogenic signaling pathways and epithelial-mesenchymal transition. Of note, multiple proteins with thyroglobulin-type-1 (TY-1) domains are known to inhibit cathepsin-L (CTSL), a cysteine protease that promotes tumor invasion and metastasis.MethodsHuman cancer sequencing studies reveal that somatic EpCAM mutations are present in up to 5.1% of tested tumors form public database search. To determine how EpCAM mutations affect cancer biology we studied C66Y, a damaging TY-1 domain mutation identified in liver cancer, as well as 13 other cancer-associated EpCAM mutations. Using in-vitro and in-vivo models, immunoprecipitations and localizations we demonstrate EpCAM inhibits CTSL activity based mutations and thereby its localization.ResultsWe demonstrate that wild type (WT) EpCAM, but not C66Y EpCAM, inhibits CTSL activity in vitro, and the TY-1 domain of EpCAM is responsible for this inhibition. WT EpCAM, but not C66Y EpCAM, inhibits tumor cell invasion in vitro and lung metastasis in vivo. In an extended panel of human cancer cell lines, EpCAM expression is inversely correlated with CTSL activity. Previous studies have demonstrated that EpCAM germline mutations can prevent EpCAM from being expressed at the cell surface. We demonstrate that C66Y and multiple other EpCAM cancer-associated mutations prevent surface expression of EpCAM. Cancer-associated mutations that prevent EpCAM cell surface expression abrogate the ability of EpCAM to inhibit CTSL activity and tumor cell invasion. ConclusionsThese studies reveal a novel role for EpCAM as a CTSL inhibitor, confirm the functional relevance of multiple cancer-associated EpCAM mutations, and suggest a therapeutic vulnerability in cancers harboring EpCAM mutations.
Overexpression of ACE2 produces antitumor effects via inhibition of angiogenesis and tumor cell invasion in vivo and in vitro
