SPRR2A expression in cholangiocarcinoma increases local tumor invasiveness but prevents metastasis

Cholangiocarcinoma morbidity and mortality is attributable to local invasiveness and regional lymph node and distant organ metastasis. Cholangiocarcinoma progression follows a series of sequential events that resemble wound healing reactions: local invasion resembles the epithelial migration phase involving epithelial-mesenchymal transition (EMT); colonization at distant sites resembles epithelial restitution seen during the reverse process, mesenchymal-epithelial transition (MET). In this study we compare the in vivo local and metastatic growth potential of cholangiocarcinoma cell lines with respect to expression of a novel pSTAT3-dependent, biliary epithelial cell wound healing protein, small proline-rich protein 2A (SPRR2A). SPRR2A has been associated with local aggressiveness, but decreased metastatic capabilities in other cancers. Stable SPRR2A transfection into two cholangiocarcinoma cell lines (SG231 and HuCCT-1), previously shown by us to induce permanent EMT, resulted in local aggressiveness but an inability to form metastases. In contrast, SPRR2A-negative epithelial control cells showed relatively poor local aggressiveness, but readily formed metastatic tumors. Post-intrasplenic injection cell tracking showed that: (a) mesenchymal (SPRR2A+) cells were not trapped in the liver, but were rapidly cleared through mesenteric lymph nodes and did not form metastases; whereas (b) epithelial (SPRR2A-) controls were primarily entrapped within MUC-1-associated liver "micro-infarcts" that later evolved into metastatic colonies. SPRR2A-associated tumor behavior was mimicked by MUC1 shRNA, which induced EMT and, like SPRR2A+ cells, showed reduced metastatic capabilities. Cholangiocarcinoma local invasion involves EMT processes, whereas MET and MUC1 expression promote metastasis. A better understanding of disease progression should help target treatment for this deadly neoplasm.