Gastric cancer mesenchymal stem cells regulate PD-L1-CTCF enhancing cancer stem cell-like properties and tumorigenesis.

Rationale: Mesenchymal stem cells (MSCs) have been the focus of many studies because of their abilities to modulate immune responses, angiogenesis, and promote tumor growth and metastasis. Our previous work showed that gastric cancer MSCs (GCMSCs) promoted immune escape by secreting of IL-8, which induced programmed cell death ligand 1 (PD-L1) expression in GC cells. Mounting evidence has revealed that PD-L1 expression is related to intrinsic tumor cell properties. Here, we investigated whether GCMSCs maintained a pool of cancer stem cells (CSCs) through PD-L1 signaling and the specific underlying molecular mechanism. Methods: Stem cell surface markers, aldehyde dehydrogenase (ALDH) activity, migration and sphere formation abilities were tested to evaluate the stemness of GC cells. PD-L1-expressing lentivirus and PD-L1 specific siRNA were used to analyze the effects of PD-L1 on GC cells stemness. Annexin V/PI double staining was used to assess apoptosis of GC cells induced by chemotherapy. Co-Immunoprecipitation (Co-IP) and Mass spectrometry were employed to determine the PD-L1 binding partner in GC cells. PD-L1Negative and PD-L1Positive cells were sorted by flow cytometry and used for limiting dilution assays to verify the effect of PD-L1 on tumorigenic ability in GC cells. Results: The results showed that GCMSCs enhanced the CSC-like properties of GC cells through PD-L1, which led to the resistance of GC cells to chemotherapy. PD-L1 associated with CTCF to contribute to the stemness and self-renewal of GC cells. In vivo, PD-L1Positive GC cells had greater stemness potential and tumorigenicity than PD-L1Negative GC cells. The results also indicated that GC cells were heterogeneous, and that PD-L1 in GC cells had different reactivity to GCMSCs. Conclusions: Overall, our data indicated that GCMSCs enriched CSC-like cells in GC cells, which gives a new insight into the mechanism of GCMSCs prompting GC progression and provides a potential combined therapeutic target.