Tumor-derived miR-126 promotes tumor progression through immune modulation beyond the local tumor environment

Takashi Akazawa, Yu Mizote, Tomoya Ekawa, Satomi Yoshida, Yachiyo Kumamoto, Yoichiro Harada, Hisataka Ogawa, Shunichi Watanabe, Shingo Hatoya, Norimitsu Inoue, Hideaki Tahara

Epidermal growth factor-like domain 7 (EGFL7) was discovered as an extracellular matrix protein with an EGF-like domain and angiogenic and vasculogenic functions. It has also been shown to play a role in immunological evasion of tumor cells through attenuation of extravasation of immune cells by reducing the expression of cell adhesion molecules on vascular endothelial cells. Furthermore, microRNA-126 (miR-126), which is encoded within the intron of Egfl7 , has been reported to be a vasculogenic factor. However, its immune-related functions in tumors remain unclear. Here, we examined the roles of tumor-derived EGFL7 and miR-126 in in vivo tumor progression using Egfl7/Mir-126 knockout and rescue tumor cell lines. Tumor growth was significantly suppressed in Egfl7/Mir-126 -deficient cells and was restored by re-expression of miR-126, but not EGFL7. These differences in in vivo tumor growth were not observed in immunodeficient mice, suggesting the involvement of the adaptive immune system. CD4 + or CD25 + cell depletion suppressed the growth of miR-126-expressing tumors, whereas CD8 + cell depletion enhanced the growth of miR-126-deficient tumors. Histological analysis revealed an increased Foxp3 + /CD8 + cell ratio in miR-126-expressing tumors during the early phase of tumor establishment. Bilateral tumor models further demonstrated that miR-126-expressing tumors promoted the growth of contralateral miR-126-deficient tumors, and a similar effect was observed using apoptotic miR-126-expressing tumor cells In vitro analyses using extracellular vesicles derived from dying tumor cells showed the transfer of miR-126 to CD4 + T cells and a higher proportion of Foxp3 + cells. Together, these findings suggest that tumor-derived miR-126 promotes tumor progression through non-local immune modulation, potentially involving maintenance of Treg-associated populations.