Background IDO1 (Indoleamine 2,3-dioxygenase 1) inhibits host anti-tumor immune response by exhausting tryptophan in tumor microenvironment, but the pathogenic mechanisms of IDO1 in gastric cancer (GC) cells need to be further explored. Methods The aim of this study was to use CCLE (Cancer Cell Line Encyclopedia) transcriptomic data of GC cell lines for WGCNA (Weighted Gene Co-expression Network Analysis) analysis, and explore the potential functions and mechanisms of IDO1 in GC progression in vitro and in vivo. Results The higher expression level of IDO1 was identified in 4 out of 7 GC cell lines. Increased IDO1 expression strongly promoted cell migration via its metabolite kynurenine and was associated with pathways of immune activation according to GSEA (Gene Set Enrichment Analysis). The functions of IDO1 were closely associated with extracellular matrix, collagen metabolic and catabolic process by WGCNA analysis. Among five hub genes ( AXL , SGCE , COL12A1 , ANTXR1 , LOXL2 ), COL12A1 and LOXL2 were upregulated in GC tissues. IDO1 disclosed positive correlation with six collagen genes by coefficient matrix diagram. Knockdown of IDO1 decreased the expression of LOXL2, COL6A1, COL6A2 and COL12A1 in GC cells in both mRNA and protein levels. Of them, knockdown of COL12A1 inhibited cell migration more apparently than knockdown of others. IDO1 and COL12A1 revealed synergistic efficacy on promoting cell migration via a positive feedback sustained by MAPK pathway. This bioprocess was mediated by IDO1 metabolite kynurenine and integrin β1. A popliteal lymph nodemetastasis model was established for verifying metastatic promotion of IDO1 and COL12A1 in GC. Conclusions IDO1 and COL12A1 synergistically promoted GC metastasis. The novel findings suggested that both IDO1 and COL12A1 may be promising targets on anti-cancer treatment in GC. Electronic supplementary material The online version of this article (10.1186/s13046-019-1318-5) contains supplementary material, which is available to authorized users.

T cell exhaustion plays critical roles in tumor immune evasion. Novel strategies to suppress immune evasion are in urgent need. We aimed to identify potential compounds to target T cell exhaustion and increase response to immune checkpoint inhibitors (ICIs). Differentially expressed genes (DEGs) were identified between tumors with different immune evasion potential by comparing the transcriptome data. DEGs were then analyzed in the Connectivity Map (CMap) platform to identify potential compounds to increase response to ICIs. Gene set enrichment analysis, LDH release assay, Chromatin immunoprecipitation (ChIP), and Co-IP were performed to explore the potential mechanisms in vitro. Patients derived organoids and humanized xenograft mouse model were utilized to validate the finding ex vivo and in vivo. We identified 25 potential compounds that may play critical roles in regulating tumor immune evasion. We further pinpointed a specific compound, dexamethasone, which shows potent anti-tumor effect in multiple cancer cell lines when cocultured with T cells. Dexamethasone can suppress T cell exhaustion by decreasing the activity of two immune checkpoints simultaneously, including PD-L1 and IDO1. Functional study shows dexamethasone can increase the sensitivity of ICIs in coculture system, 3D organoid model and humanized mouse model. Mechanism study shows dexamethasone mediated transcriptional suppression of PD-L1 and IDO1 depends on the nuclear translocation of GR/STAT3 complex. These findings demonstrate dexamethasone can suppress immune evasion by inducing GR/STAT3 mediated downregulation of PD-L1 and IDO1 pathways.

The citrullination modification (Cit) of proteins has received increasing attention in recent years. This kind of protein modification was first discovered in autoimmune diseases such as rheumatoid arthritis. The citrullination modification process is catalyzed by the peptidyl arginine deiminases (PADIs) family. A well-known citrullination of histone involves the key mechanism of neutrophil extracellular traps (NETs) of inflammation in the peripheral blood. Further studies revealed that citrullination modification of proteins also involves in carcinogenesis in human being. Citrullinated proteins disturbed the stability of proteins and caused DNA damages. There is increasing evidence that citrullinated proteins can be used as potential targets for cancer diagnosis or treatment. This review introduces the concept of citrullination modification of proteins, substrate proteins, examining methods and biological significances.