RgpB contributes to chemoresistance in esophageal squamous cell carcinoma by preventing Cx43 degradation via inhibiting autophagosome-lysosome fusion

Abstract

To investigate the mechanism through which RgpB, a virulence factor of Porphyromonas gingivalis (Pg), induces chemoresistance in esophageal squamous carcinoma. The autophagy-regulating factors that interact with RgpB were screened by immunoprecipitation-mass spectrometry. The interaction between RgpB and the autophagy regulator TBC1D5 was investigated using co-immunoprecipitation. The impact of Pg infection on the expression of esophageal cancer cell membrane receptor molecule Cx43 was assessed using Western blotting. Immunofluorescence assay was used to analyze the relationship among Lamp1, Cx43 and TBC1D5. The effect of Pg infection on autophagosome-lysosome fusion was evaluated using autophagy double fluorescence technique. The effects of Pg infection and a Cx43 inhibitor on proliferation of esophageal cancer cells after chemotherapy were examined with plate cloning assay and CCK-8 method. Immunoprecipitation-mass spectrometry identified TBC1D5 as an autophagy regulator interacting with RgpB, and coimmunoprecipitation suggested that RgpB could directly bind to TBC1D5. In Pg-infected esophageal cancer cells, the expression of Cx43 on the cell membrane was significantly higher than that in non-infected cells. Immunofluorescence assay showed that the expression of Cx43 on the membrane of esophageal cancer cells increased significantly after Pg infection, which blocked autophagosome-lysosome fusion as shown by stubRFP-sensGFP-LC3 lentivirus study. Plate cloning assay and CCK-8 assay showed that the Cx43 inhibitor significantly attenuated the effect of Pg infection for promoting proliferation of esophageal cancer cells after chemotherapy. Pg infection in esophageal cancer blocked autophagosome-lysosome fusion in the tumor cells, thereby preventing Cx43 from lysosomal degradation and leading to chemoresistance of esophageal cancer.