Lung Carcinoma Cells Secrete Exosomal MALAT1 to Inhibit Dendritic Cell Phagocytosis, Inflammatory Response, Costimulatory Molecule Expression and Promote Dendritic Cell Autophagy via AKT/mTOR Pathway

Yanyan Liu, 1 Zhucheng Yin, 2 Ping Lu, 2 Yifei Ma, 2 Bo Luo, 3 Lanxin Xiang, 4 Wangli Zhang, 4 Yu He, 5 Xinjun Liang 2 1Division of Nephrology, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, People’s Republic of China; 2Department of Medical Oncology, Hubei Cancer Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, People’s Republic of China; 3Department of Radiotherapy, Hubei Cancer Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, People’s Republic of China; 4School of Life Science and Technology, Huazhong Agricultural University, Wuhan, Hubei, People’s Republic of China; 5Department of Orthopaedics, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, People’s Republic of ChinaCorrespondence: Xinjun Liang; Yu He Email doctorlxj@163.com; heyu6666@163.comObjective: To investigate the potential mechanism underlying the effect of lung carcinoma cell-derived exosomes on dendritic cell function.Materials and Methods: C57BL/6 (B6) mice were randomly divided into five groups: control, dendritic cell (DC), DC-NC, DC-siMALAT1, and siMALAT1. Tumor cell proliferation was measured by Ki-67 staining. LLC cells were divided into control, NC, and si-MALAT1 groups, and exosomes secreted by each group were labeled as PEX, PEXN, and PEX-si, respectively. Exosomes and autophagic vacuoles were observed by transmission electron microscopy. MALAT1 expression in LLC, A549, and Beas-2b cells was examined by RT-PCR. The expression of IFN-γ, IL-12, IL-10, and TGF-β was observed by Elisa assay. Flow cytometry was used to observe the phagocytic function of DCs, costimulatory molecule expression, and T cell proliferation and differentiation. The protein expression of p-AKT, AKT, p-mTOR, mTOR, ALIX, TSG101, and CD63 was detected by Western blot.Results: Compared with Beas-2b cells, MALAT1 expression was significantly increased in both LLC and A549 cells and in their secreted exosomes, and LLC cells showed the highest expression of MALAT1 (P < 0.05). Tumor cell proliferation and tumor volume were significantly decreased in the siMALAT1 and DC-siMALAT1 groups compared to those in the control group. DC phagocytosis, inflammatory response, costimulatory molecule expression, and T cell proliferation in the siMALAT1 and PEX-si groups were significantly enhanced (P < 0.05), while DC autophagy and T cell differentiation were reduced (P < 0.05). The levels of p-AKT, AKT, p-mTOR, and mTOR in the PEX and PEXN groups were increased compared with those in the control group, while those in the siMALAT1 and PEX-si groups were significantly decreased (P < 0.05).Conclusion: Inhibition of MALAT1 expression in LLC-derived exosomes promoted DC function and T cell proliferation and suppressed DC autophagy and T cell differentiation, suggesting that MALAT1 inhibition may be a potential strategy for the clinical treatment of lung cancer.Keywords: MALAT1, dendritic cells, AKT, mTOR, autophagy