The Mechanisms Of TDO2 Signaling Pathway In Regulating The Polarization Of Macrophage And ESCC Progression

The number of esophageal cancer(EC)is the sixth most common cancer and the fourth most common death cancer in China with an estimated 320,000 new cases and 300,000 deaths in 2020,according to the latest estimates on the global burden of cancer released by the International Agency for Research on Cancer(IARC).Esophageal squamous cell carcinoma(ESCC)is the cancer with Chinese characteristics,accounting for 90～95%EC cases in China and with low 5-year survival rates,the lack of treatment options and poor prognosis.Even though immunotherapy has achieved great success in management of multiple malignancies,only a small subset of patients with ESCC have acquired clinical benefits.Therefore,it is of great importance to discover novel therapeutic targets and strategies for ESCC.Tryptophan(Trp)is an essential amino acid for humans.The major metabolic pathway of Trp is the kynurenine pathway(KP),involving in the depression,schizophrenia,irritable bowel syndrome(IBS),inflammatory bowel disease(IBD),pancreatitis and tumor.The rate-limiting enzymes indoleamine 2,3-dioxygenase 1(IDO1),indoleamine 2,3-dioxygenase 2(IDO2),tryptophan 2,3-dioxygenase 2(TDO2)and axyl hydrocarbon receptor(AHR)have been shown to expressed in cancer cells,which could thus not only improve cancer cells proliferation,migration and invasion,but also modulate immune cell homeostasis to immune evasion,resulting in tumor progression and metastasis.For IDO2 with low catalytic efficiency for L-Trp,IDO1 and TDO2 have been considered as promising antitumor targeting,therefore,numerous effects have focused on them.Even high similarity of their catalytic domains revealed by protein crystallography studies,there still existed many differences between IDO1 and TDO2.There was a much higher difference to the expression of TDO2 between ESCC tissues and paired peritumor tissues than that of IDO1,according to our previous tissue microarray analysis and GEO dataset.These results prompted us to investigate the factors affecting the tumorigenicity of TDO2.Although the clinical relevance of TDO2 upregulation in ESCC has been reported and TDO2 overexpression was associated with stemness,the underlying mechanism leading to immune tolerance in ESCC progression by TDO2 has not been elucidated yet.The expression level of TDO2 was higher in esophageal tumor tissues than peritumor tissues by microarray.The similar result was also verified by qRT-PCR,GEO dataset and immunohistochemistry staining in clinical samples of ESCC.We also found that the upregulation of TDO2 was significantly correlated with gender,TNM stage,lymph node metastasis and over all survival of patients,indicating that the aberrantly overexpression TDO2 may play an important role in promoting ESCC and could be an important prognosticator in patients with ESCC.To better clarify the role of TDO2 in the carcinogenesis and progress of ESCC,TDO2-overexpressing sublines were established.We can infer that TDO2-mediated KYN production promotes ESCC cells proliferation and migration via AHR pathway,resulting in promoting ESCC tumorigenesis and the progression in primary tumor of ESCC.We also found IL-8 production upregulated by TDO2-AHR pathway from the results of qRT-PCR and ELISA experiments,promoting the polarization and infiltration of M2 macrophage in tumor.To investigate the specific mechanism of TDO2 in ESCC,ESCC cells were treated with exogenous KYN.It was found that TDO2-induced KYN-AHR would trigger AKT/GSK-3β/IL-8 signal pathway to promote esophageal squamous cell carcinoma progression.In summary,these findings provide evidence that TDO2 is an important molecule participating in the aberrant activation of AKT/GSK-3β/IL-8 signaling pathway,suggesting that TDO2 could be a potential therapeutic target and a prognostic marker against ESCC.