Exosomal PIK3CB promotes PD-L1 expression and malignant transformation in esophageal squamous cell carcinoma.

Esophageal squamous cell carcinoma (ESCC), which accounts for 90% of esophageal carcinomas, seriously endangers human health. Worse still, the 5-year overall survival of ESCC is approximately 20%. Elucidation of the potential mechanism and exploration of promising drugs for ESCC are urgently needed. In this study, a high level of exosomal PIK3CB protein was found in the plasma of ESCC patients, which might indicate a poor prognosis. Moreover, a significant Pearson's correlation was observed at the protein level between exosomal PIK3CB and exosomal PD-L1. Further study revealed that cancer cell-intrinsic and exosome-derived PIK3CB promoted the transcriptional activity of the PD-L1 promoter in ESCC cells. Moreover, treatment with exosomes with lower levels of exosomal PIK3CB decreased the protein level of the mesenchymal marker ß-catenin while increasing that of the epithelial marker claudin-1, indicating the potential regulation of epithelial-mesenchymal transition. Consequently, the migratory ability and cancer stemness of ESCC cells and the growth of tumors formed by ESCC cells were decreased with the downregulation of exosomal PIK3CB. Therefore, exosomal PIK3CB plays an oncogenic role by promoting PD-L1 expression and malignant transformation in ESCC. This study may provide new insight into the inherent biological aggressiveness and the poor response to currently available therapies of ESCC. Exosomal PIK3CB may be a promising target for the diagnosis and therapy of ESCC in the future.