Soluble TREM2 drives triple-negative breast cancer progression via activation of the AKT pathway

Triggering receptor expressed on myeloid cells 2 (TREM2) plays a key role in immune regulation, particularly within tumor-associated macrophages (TAMs). In triple-negative breast cancer (TNBC), TREM2⁺ TAMs have been shown to modulate the tumor microenvironment, but the role of its soluble form: soluble triggering receptor expressed on myeloid cells 2 (sTREM2), produced through proteolytic cleavage, remains unclear. In this study, we investigated the effects of sTREM2 on TNBC progression. In vitro, treatment of TNBC cells with recombinant sTREM2 or sTREM2-containing culture supernatant significantly enhanced cell proliferation, invasion, and migration. These effects were further confirmed by the use of TREM2-neutralizing antibodies, which abrogated sTREM2's tumor-promoting activities. In vivo, peri-tumoral injections of recombinant sTREM2 led to a notable acceleration of tumor growth in mouse models. Mechanistically, we found that the effects of sTREM2 were mediated through its binding to the TG2 protein in 4T1 cells, thereby activating the AKT signaling pathway. Collectively, our findings suggest that sTREM2 drives TNBC progression by enhancing critical tumor cell functions, positioning it as a potential therapeutic target for TNBC treatment.