Abstract
Current anti-angiogenic therapies have changed the paradigm of treating colorectal cancer (CRC) patients with advanced diseases. However, the clinical response rate is still low at less than 10% due largely to complex angiogenic factors released by tumor cells. Exploring novel mechanisms of tumor angiogenesis and identifying alternative targets for combination therapies are therefore essential to effective inhibition of tumor vascularization and CRC development. Immunoglobulin-like transcript 4 (ILT4), initially identified as a suppressor of myeloid cell activity, is enriched in solid tumor cells. ILT4 favors tumor progression by inducing tumor malignant biologies as well as an immunosuppressive microenvironment. However, whether and how tumor-derived ILT4 orchestrates tumor angiogenesis is still undetermined. Here we found that tumor-derived ILT4 was positively correlated with microvessel density in CRC tissues. ILT4 induced the migration and tube formation of HUVECs in vitro and angiogenesis in vivo. Mechanistically, the activation of MAPK/ERK signaling and subsequent up-regulation of vascular endothelial growth factor-A (VEGF-A) and fibroblast growth factor 1 (FGF-1) were responsible for ILT4-induced angiogenesis and tumor progression. Importantly, ILT4 inhibition suppressed tumor angiogenesis and enhanced the efficacy of Bevacizumab treatment in CRC. Our study has identified a novel mechanism for ILT4-mediated tumor progression, which signals a new therapeutic target and alternative combination strategies to combat CRC.