Myeloid-derived Suppressor Cells Secret TGF-?₁ To Promote Epithelial-mesenchymal Transition Of Lung Adenocarcinoma

Background and Objective:Despite rapid advances in clinical diagnosis and treatments,lung cancer remains the first leading cause of cancer-related deaths.Basing on histological features,lung cancer can be subdivided into four most common types:small cell lung carcinoma,lung adenocarcinoma(LAC),squamous cell carcinoma,and large cell carcinoma.The prognosis of LAC is dependent on the tumor stage at the time of diagnosis.A major reason for cancer-related mortality is the metastasis after surgery or ablation therapy,because the cascade may occur before the onset of clinical symptoms.Progress in the fight against LAC has been substantial over the last decade with the discovery of immunotherapies.However,further studies have been hampered by the complex interactions between tumor cells and the elements of tumor-associated microenvironment(TAM).During the cascade from inflammation to cancer,biological behaviors and phenotypes of tumor cells could change in response to stress such as immune surveillance,apoptosis,and physical destruction in the circulation.Epithelial-mesenchymal transition(EMT),a conserved biological event identified in embryogenesis,mediates tumor progression,including infiltration,dissemination,and planting.The proteomic features of epithelial cells undergoing EMT include the loss of epithelial markers E-cadherin,?-catenin translocation,and the acquisition of fibroblast and nuclear factors,including S100A4,Twist,and SMAD.These changes endow tumor cells with an elongated shape and enhanced motility resembling cells of mesenchymal origin.Several EMT markers are proposed as independent predictors for patients with non-small cell lung carcinoma.Transforming growth factor-?(TGF-?),appreciated as one of the most powerful driver of EMT,can synergize with JAK/STAT3 pathway and contribute to cancer cell migration and invasion.The activation of peroxisome proliferator-activated receptor-?(PPAR-?)attenuated TGF-?-induced EMT and metastasis via antagonizing Smad3,which forms a trimeric structure with Smad4 and translocates to the nucleus to regulate the expression of downstream genes.However,the roles of EMT in the metastatic progression are still a matter of debate.One of the most concerning issues is the exact cellular source of TGF-?₁.The presence of high levels of TGF-?₁ has been demonstrated in many tumors.Several types of cells,including cancer-associated myofibroblast,cancer cells,and platelet,are demonstrated as cellular sources.Immune cells stay at the crosstalk of microenvironment regulation.Malignant cells can promote the recruitment and expansion of myeloid-derived suppressor cells(MDSCs)through the secretion of chemokines,including GM-CSF,IFN?,and Cox-2.The depletion of infiltrating MDSCs hampered the progression of lung cancer.MDSCs are heterogenous and consist of granulocytic MDSCs and monocytic MDSCs.Histidine decarboxylase(Hdc)can mark a distinct subpopulation of myeloid-biased hematopoietic stem cells/progenitor cells(MB-HSC/HSPC),which differentiate into tumor-associated myeloid cells in the setting of tumor.Hdc⁺PMN-MDSCs were central to the tumorigenesis of colon cancer.Yet we have little definitive information about whether Hdc⁺PMN-MDSCs contributes to the metastasis of lung cancer.In this study,we compared the prognosis of EMT⁺metastatic LAC cases to that of EMT-negative counterparts and found that EMT may serve as a predictive parameter.Hdc⁺PMN-MDSCs were recruited into metastatic masses of transgenic murine models.Immunohistochemistry confirmed the closely spatial relationship between Hdc⁺PMN-MDSCs and EMT⁺metastatic cancer cells,raising the possibility that Hdc⁺PMN-MDSCs-derived factors may influence the behaviors of EMT⁺cells via a paracrine pattern.Hdc⁺PMN-MDSCs expressed high levels of TGF-?₁ rather than TGF-?₂ and TGF-?₃.The depletion of Hdc⁺cells or the block of Hdc⁺PMN-MDSCs-derived TGF-?₁resulted in the inhibition of metastasis.Our preliminary data further reveal the important role of Hdc⁺PMN-MDSCs in the metastatic cascade of LAC,suggesting a promising target for anti-LAC strategies.Methods:1.The retrospective research of patients with LAC showed that 58/244(23.8%)cases expressed high levels of EMT markers(Twist⁺SMAD3⁺E-cadherin^-).2.To compare the number,percentage,and spatial location of MDSCs between different groups.3.To analyse the expression of cytokines and receptors involving in MDSCs recruitment.4.Levels of TGF-?₁ in MDSCs obtained from different groups were compared to evaluate the role of MDSCs in the setting of different microenvironments.5.MDSCs-derived TGF-?₁ was inhibited in transgenic mice to explore the EMT cascade of tumor cells and metastasis.Results:1.The retrospective research of patients with LAC showed that 58/244(23.8%)cases expressed high levels of EMT markers(Twist⁺SMAD3⁺E-cadherin^-).2.Immature PMN-MDSCs infiltrate EMT⁺LAC to from aggregate.3.EMT⁺tumor tissues secreted high levels of CXCL1,CXCL5 and CCL2 to recruit PMN-MDSCs via CXCR2.4.Hdc⁺CD15⁺PMN-MDSCs secreted high level of TGF-?₁ to induce the abbarrant translocation of?-catenin into nucleus.5.The block of TGF-?₁ in Hdc⁺cells using transgenic models significantly attenuated the metastasis of LAC.Conclusion:This study provided preliminary results to show Hdc⁺PMN-MDSCs are capable of promoting the EMT transition of LAC cells,resulting in an increased risk of metastasis.Cytokines CXCL1 and CXCL5 in tumor tissues were upregulated and binded to the receptor CXCR2 to recruit Hdc⁺PMN-MDSCs,which,in turn,located around malignant cells.Hdc⁺PMN-MDSCs-derived TGF-?₁actived the EMT cascade of adjacent tumor cells via paracrine-like pattern,promoting tumor progression and metastasis.