Non-small cell lung cancer tumor microenvironment induces Arginase1 in neutrophils via the Toll-like receptor 2 signaling pathway

Abstract

Abstract Neutrophils dominate the tumor microenvironment of non-small cell lung cancer. Previous studies show neutrophils suppress T cells and promote immunosuppression. The objective of the current study is to identify how tumor associated neutrophils (TAN) adopt the T-cell suppressive entity after being recruited into the tumor microenvironment. In the murine lung squamous cell carcinoma autochthonous tumor model (AdCre-Lkb1fl/fl, Ptenfl/fl; LP) and subcutaneous tumor model (Lewis lung carcinoma cell line; LLC), we found that Arginase 1 (Arg1) mRNA level in TAN is drastically higher than neutrophils from the bone marrow, spleen and peripheral blood. Arg1 suppresses T cell through Arginine depletion. Whole tumor lysates from LP tumor and LLC tumor induce Arg1 level in bone marrow-derived and peripheral neutrophils from healthy B6 mice in vitro, suggesting that the tumor microenvironment alters neutrophil properties. To identify the putative molecule(s) that induce Arg1 in TAN, we used fast protein liquid chromatography (FPLC) and mass spectrometry to analyze the whole tumor lysates from LP tumor and LLC tumor. Annexin A1 and 2 are among the common molecules that appear in Arg1-inducing FPLC fraction in both LP and LLC tumor lysates. Annexin A1, A2 are involved in toll-like receptor signaling. Flow cytometry showed more than 70% of Arg1+ TAN are either TLR2 or TLR4 positive. Interestingly, only TLR2 but not TLR4 inhibition blocked Arg1 induction by whole tumor lysates in naïve neutrophils. Taken together, tumor microenvironment induces Arg1 level in neutrophils in a TLR2 dependent manner. TLR2 is a putative therapeutic target for blocking tumor associated neutrophil-mediated immunosuppression in non-small cell lung cancer.