[Conditional medium of gastric cancer mesenchymal stem cells promotes PD-L1 expression in gastric cancer cells and tumor growth via upregulating VGLL4].

Objective To investigate whether conditional medium of gastric cancer mesenchymal stem cells (GCMSCs-CM) could up-regulate the expression of programmed death 1 ligand 1 (PD-L1) and promote gastric cancer progression by vestigial-like protein 4 (VGLL4). Methods Western blot was used to detect the expression of VGLL4 in SGC-7901, HGC-27 and MGC-803 gastric cancer cells. The expression of VGLL4 in HGC-27 and SGC-7901 cells was inhibited by being transfected with VGLL4 specific siRNA and plasmid was used to overexpress VGLL4 in SGC-7901 cells. The gastric cancer cells were divided into control group, GCMSCs-CM treatment group, VGLL4 interference or overexpression group, and VGLL4 interference followed by GCMSCs-CM treatment group. The expression of PD-L1 in each group was detected by Western blot and real time quantitative PCR (qRT-PCR). The proliferation of SGC-7901 cells was detected by colony formation assay. The migration of SGC-7901 cells was detected by Transwell migration assay. Human peripheral blood mononuclear cells adoptive NCG immunodeficiency mouse (PBMCs-NCG) subcutaneous tumor model was constructed to observe the tumor growth in mice. The mice were divided into control group, GCMSCs-CM treatment group, VGLL4 knockdown group, and VGLL4 knockdown followed by GCMSCs-CM treatment group. VGLL4 and PD-L1 mRNA levels of tumor tissue were detected by qRT-PCR. Immunohistochemical staining was used to detect the expression of VGLL4, PD-L1, ki67, CD8 and granzyme B (GZMB). Results VGLL4 is expressed in SGC-7901, HGC-27 and MGC-803 cells. The expression of PD-L1 mRNA and protein decreased significantly in SGC-7901 and HGC-27 cells transfected with siVGLL4. The expression of PD-L1 mRNA and protein was up-regulated after overexpression of VGLL4 in SGC-7901 cells. The expression of VGLL4 increased after GCMSCs-CM treatment of HGC-27 and MGC-803 cells. Inhibition of VGLL4 in HGC-27 could reverse the up-regulation of PD-L1 by GCMSCs-CM. Inhibition of VGLL4 in SGC-7901 weakened the ability of GCMSCs-CM to promote cell proliferation and migration. Knockdown of VGLL4 inhibited the effect of GCMSCs-CM in promoting tumor growth in mice and enhanced the anti-tumor immunity of PBMCs-NCG mice. Conclusion GCMSCs-CM promotes the expression of PD-L1 and tumor growth by upregulating VGLL4 in gastric cancer cells.