Empéripolèse des cellules de lymphomes humains Ramos par les fibroblastes
Fibroblasts (Fbs) often represent the majority of stromal cells within tumors. A “cafocentric” view of the tumor microenvironment (MET) hypothesizes that the dynamic and reciprocal interactions between tumor cells and cancer-associated fibroblasts (CAFs) may enhance the metastatic potency of tumor cells. Very few studies investigated a physical interaction between Fbs and tumor cells within the tumor stroma. Using flow cytometry and blocking antibodies, we demonstrated that a human lymphoma cell line Ramos could interact with Fbs through the couple α4β1/VCAM-1. We observed a dose-dependent increased interaction after tumor necrosis factor-α (TNF-α) stimulation which correlated with increased VCAM-1 expression. A similar observation was made after VCAM-1 overexpression by transfection. Further investigations by confocal microscopy revealed the engulfment of Ramos into the cytoplasm of Fbs, a process called emperipolesis which mostly corresponds to transcellular migration and involves the clustering of  the α4 sub-unit and VCAM-1 and the involvement of vimentin intermediate filaments at the transmigration cups. We visualized this cell-in-cell penetration by real time-lapse video-microscopy, which confirmed an active cellular process. Finally, we used α4β1 polystyrene coated-beads as a mimetic model to further confirm the precedent results. Our results showed that Ramos lymphoma cells can interact with and further transmigrate through Fbs by an active cellular process, the emperipolesis which involves the couple of receptors α4β1/VCAM-1. This crosstalk between Fbs and tumor cells through emperipolesis may modulate tumor cells escape from the primary tumor and support the "seed and soil" hypothesis as well as a possible involvement in tumor drug resistance. This fibroblastic permeability can be modulated by inflammation and the CAFs may react as endothelial cells and should be considered as a future target in the MET. Tumor cells may selectively search for new metastatic niches where VCAM-1 expression was already induced. Our results strengthen the growing idea that Fbs and tumor cell integrins may serve as suitable targets in the development of antagonist-based cancer therapy.
VCAM-1 VLA-4 Ramos Tumor microenvironment Tumor stroma Cancer-associated-fibroblasts Vimentin Lymphoma cells Transcellular migration