Ezrin-expressing lung adenocarcinoma cells and podoplanin-positive fibroblasts form a malignant microenvironment

Cancer cells and cancer-associated fibroblasts (CAFs) together create the tumor microenvironment, which affects malignant behavior. Lung adenocarcinomas with CAFs expressing podoplanin (PDPN) are clinically aggressive, but the molecular mechanism underlying this phenomenon has not been established. So we identified the characteristic immunophenotype of lung adenocarcinoma cells coexisting with PDPN-expressing CAFs (PDPN-CAFs) and examined how it relates to an aggressive clinicopathological outcome.

We analyzed the clinicopathological characteristics of 119 adenocarcinomas with a uniform size (2-3 cm). The expression levels of ten invasiveness-related proteins which related to cell adhesion and invasiveness, such as Ezrin, were examined in cancer cells from PDPN-CAFs (+) cases and from PDPN-CAFs (-) cases (n = 20 each). To examine the functional importance of the identified protein on the invasion phenotype, we performed wound healing and a Matrigel invasion assay using shRNA-knockdown lung adenocarcinoma cells (PC-9).

The PDPN-CAFs (+) cases had significantly higher rates of node metastasis (p < 0.01) and vascular invasion (p < 0.01). The cancer cells from the PDPN-CAFs (+) cases also had a significantly higher staining score for Ezrin (p < 0.01) than those from the PDPN-CAFs (-) cases. The migration and invasion activities of the shEzrin-induced PC-9 cells were significantly lower than those of the control cells.

Our results indicated that within a tumor microenvironment composed of PDPN-CAFs, increased Ezrin expression in cancer cells might play a key role in the invasiveness of lung adenocarcinoma.