CTHRC1 promotes colorectal cancer progression by recruiting tumor-associated macrophages via up-regulation of CCL15

Abstract

Tumor-associated macrophages (TAMs) represent a key factor in the tumor immune microenvironment (TME), exerting significant influence over tumor migration, invasion, immunosuppressive features, and drug resistance. Collagen triple helix repeat containing 1 (CTHRC1), a 30 KDa protein which was secreted during the tissue-repair process, is highly expressed in several malignant tumors, including colorectal cancer (CRC). Previous studies demonstrated that CTHRC1 expression in TAMs was positively correlated to M2 macrophage polarization and liver metastasis, while our discovery suggesting a novel mechanism that CTHRC1 secreted from cancer cell could indirectly interplay with TAMs. In this study, the high expression level of CTHRC1 was evaluated in CRC based on GEO and TCGA databases. Further, CTHRC1 was detected high in all stages of CRC patients by ELISA and was correlated to poor prognosis. Multispectral imaging of IHC demonstrated that M2 macrophage infiltration was increased accompanied with CTHRC1 enrichment, suggesting that CTHRC1 may have chemotactic effect on macrophages. In vitro, CTHRC1 could have chemotactic ability of macrophage in the presence of HT-29 cell line. Cytokine microarray revealed that CTHRC1 could up-regulate the CCL15 level of HT-29, pathway analysis demonstrated that CTHRC1 could regulate CCL15 by controlling the TGFβ activation and Smad phosphorylation level. In vivo, knocking down of CTHRC1 from CT-26 also inhibits tumor formation. In conclusion, CTHRC1 could promote the chemotactic ability of macrophages by up-regulating CCL15 via TGFβ/Smad pathway; additionally, a high level of CTHRC1 could promote macrophage's M2 polarization. This discovery may be related to tumor immune tolerance and tumor immunotherapy resistance in CRC. KEY MESSAGES: CTHRC1 promotes CRC progression by up-regulating CCL15 via TGF-β/Smad pathways to further recruit tumor-associated macrophages. By the means of autocrine or paracrine, CTHRC1 can indeed promote macrophage chemotaxis and enhance the infiltration of macrophages in tumor tissues but in the presence of tumor cells. CAFs were another source of CTHRC1, indicating CTHRC1 can infiltrate tumor islet as well as the stomal and be secreted from both tumor cells and CAFs. This study validated CTHRC1 as a potential immune therapy target CRC.

Keywords: CCL15; CTHRC1; Chemokine; Colorectal cancer; Tumor microenvironment; Tumor-associated macrophages.