MiR-448 targets IDO1 and regulates CD8+ T cell response in human colon cancer

Qiong Lou,Junxiong Chen,Ruixian Liu,Xiangling Yang,Huiliu Tan,Kawo Chan,Nanlin Xiang,Weiqian Li,Lili Wei,Huanliang Liu,Lanlan Huang

doi:10.1186/s40425-019-0691-0

Abstract

BackgroundIndoleamine 2,3-dioxygenase 1 (IDO1) is a critical regulator of T cell function, contributing to immune tolerance. Upregulation of IDO1 has been found in many cancer types; however, the regulatory mechanisms and clinical significance of IDO1 in colon cancer are still unclear. Here, we investigated the role of dysregulated microRNA (miRNA) targeting IDO1 in the colon cancer microenvironment.MethodsWe elucidated IDO1 function by performing cell-based assays and establishing transplanted tumor models in BALB/c mice and BALB/c nude mice. We evaluated IDO1 protein expression by immunohistochemistry (IHC) in a tissue microarray (TMA) and analyzed IDO1 mRNA expression with The Cancer Genome Atlas (TCGA). We screened miRNAs targeting IDO1 by using a dual luciferase reporter assay. We tested the function of microRNA-448 (miR-448) by using western blotting (WB) and fluorescence-activated cell sorting (FACS).ResultsWe demonstrated that stable IDO1 overexpression enhanced xenograft tumor growth in BALB/c mice but not in BALB/c nude mice. We also revealed the involvement of posttranscriptional regulation of IDO1 in colon cancer by observing IDO1 protein levels and mRNA levels. Furthermore, ectopic expression of miRNA mimics suggested that miR-448 could significantly downregulate IDO1 protein expression. Notably, we proved that miR-448 suppressed the apoptosis of CD8+ T cells by suppressing IDO1 enzyme function.ConclusionOur findings indicated that IDO1 suppressed the CD8+ T cell response in colon cancer. miR-448, as a tumor-suppressive miRNA, enhanced the CD8+ T cell response by inhibiting IDO1 expression. The results provide a theoretical basis for the development of new immunotherapy for the treatment of colon cancer.

Highlights

Indoleamine 2,3-dioxygenase 1 (IDO1) is a critical regulator of T cell function, contributing to immune tolerance
Overexpression of IDO1 has no effect on migration, invasion, colony formation and proliferation of CT26 cells To determine whether IDO1 affects colon cancer cell phenotypes, we established stable IDO1 overexpression of
In summary, stable IDO1 overexpression has no effect on subcutaneous tumor growth in immune-deficient nude mice but promotes tumor growth in immune competent mice by suppressing the CD8+ T cell response

Summary

Introduction

Indoleamine 2,3-dioxygenase 1 (IDO1) is a critical regulator of T cell function, contributing to immune tolerance. Upregulation of IDO1 has been found in many cancer types; the regulatory mechanisms and clinical significance of IDO1 in colon cancer are still unclear. Exploiting tumor cell-intrinsic checkpoint expression is revolutionizing cancer immunotherapy by inducing meaningful clinical responses in many cancer types; some examples of these therapies include targeting PD1 and PDL1 [5, 7]. The depletion of Trp and accumulation of Kyn have been reported to induce effector T cell apoptosis/ dysfunction and generate immunosuppressive regulatory T cells [9]. Whether IDO1 affects the quantity of tumor-infiltrating T lymphocytes in colon cancer is not clearly defined. G. Brandacher et al reported that higher IDO1 expression significantly decreased CD3+ T lymphocytes in human CRC [11]. Ferdinande et al reported that there was no significant correlation between the level of

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