Successful anti-tumor immunotherapeutic approaches are improving survival in many malignancies but not all patients respond to these interventions, and several also relapse. This may result from an immunosuppressive tumor microenvironment (TME) that contributes towards tumor growth and metastasis while dampening anti-tumor immune responses. We have recently demonstrated that the metalloproteinases (MMPs) are produced within the TME. This production is associated with several cancers and can compromise tumor infiltrating lymphocyte (TILs) function. In particular, MMP-2 modulates dendritic cell (DC) function to skew T cells towards a deleterious T helper 2 (TH2) phenotype. MMP-2 was shown to inhibit Interleukin-12 (IL-12) and up-regulate OX40L expression thereby promoting TH2 function. Significantly, MMP-2 triggers Toll-like receptor 2 (TLR2) stimulation and NFκB activation, to promote OX40L expression and inflammatory cytokine production.
Based on these results, the main purpose of this study is to dissect MMP-2s signaling via TLRs in the TME, which could promote immune suppression and tumor growth. We aim to access the signaling pathways downstream of the MMP-2/TLR2 axis in mouse bone marrow derived cells and immortalized cell lines. We also plan to evaluate MMP-2's role in T cell skewing in vivo and how this could affect tumor growth in the context of mouse B16 F1-induced melanomas. And finally we want to dissect the MMP-2/TLR signaling complex and identify the interactions between MMP-2, TLR2 and other proteins.
We stimulated mouse primary cells or cell lines with MMP2, TLR agonists and appropriate controls in vitro and measured inflammatory cytokine secretion by cytometric bead array (CBA). Our preliminary results suggest that similar to our previous findings in humans, mouse bone marrow-derived DCs and Macrophages respond to MMP-2 and secrete pro-inflammatory cytokines such as Tumor Necrosis Factor (TNF) α and IL-6. Furthermore we found that in mouse immortalized bone marrow macrophage cell lines (Im-BMs), MMP-2 signaling is not only TLR2-, but also TLR4- and MyD88-dependent. While TLR2-/- and TLR4-/- Im-BMs do not show impaired TNFα secretion in response to MMP2, TLR2-/-/TLR4-/- double knockout cells demonstrate compromised signaling. Similarly MyD88-/- cells and TRIF-/-/MyD88-/- also showed impaired signaling whereas TRIF-/- cells did not, suggesting that MMP-2 signaling is mainly MyD88 dependent.
Altogether, our data suggests an important role for the MMP-2/TLR axis in immune cell signaling that could be of importance in promoting tumor growth and eventually metastasis. Our results revealed that in mouse cells, TLR4 is also needed for MMP-2 signaling, which suggests species-specific requirements of the MMP-2 signaling pathway. Previous work has shown that targeting TLRs and endogenous alarmins are beneficial for control of tumor growth, thus targeting MMP-2 in the TME might be an additional way to control immune suppression in the TME.
Citation Format: Luciana Ribeiro Muniz, Mansi Saxena, Nina Bhardwaj. Matrix metalloproteinase-2 and Toll-like receptors modulating immune responses in the tumor microenvironment. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr B169.
- ©2016 American Association for Cancer Research.