[PHPS1 enhances PD-L1 serine phosphorylation by regulating ROS/SHP-2/AMPK activity to promote apoptosis of oral squamous cell carcinoma cells].

OBJECTIVES

To investigate the mechanism of PHPS1 for promoting apoptosis of oral squamous cell carcinoma cells and the role of AMPK in regulating tumor angiogenesis under hypoxic conditions.

METHODS

Human oral squamous cell carcinoma Ca9-22 cells cultured in hypoxic conditions (1% O) were inoculated subcutaneously in 16 nude mice, which were divided into control group and PHPS1 group (8) for treatment with 10% DMSO and 10% PHPS1 respectively. Tumor growth in the mice was monitored till 14 days after the treatment, and the xenografts were examined pathologically using HE staining. In Ca9-22 cells cultured in 1% O, the effect of PHPS1, compound C (an AMPK inhibitor), and their combination on expressions of SHP-2, AMPK, HIF-1α, PD-L1, caspase-8, caspase-3 and BAX were evaluated using Western blotting.

RESULTS

In the tumor-bearing nude mice, PHPS1 treatment significantly inhibited tumor growth and neovascularization. HE staining showed significantly reduced tumor angiogenesis in PHPS1-treated mice. In Ca9-22 cells in hypoxic cultures, PHPS1 treatment significantly decreased the expression levels of SHP-2, HIF-1α, PD-L1, ERK2, STAT3 and VEGF and increased the expression of AMPK. The inhibitory effects of PHPS1 on HIF-1α and PD-L1 were obviously attenuated by the addition of compound C. PHPS1 also enhanced the expressions of caspase-3, caspase-8 and Bax proteins and increased the phosphorylation levels of PD-L1 and S195 in Ca9-22 cells, and these effects were effectively attenuated by compound C.

CONCLUSIONS

PHPS1 can enhance PD-L1 serine phosphorylation by regulating SHP-2/AMPK activity to promote apoptosis of oral squamous cell carcinoma cells under hypoxic conditions.