Effect of myeloid-derived suppressor cells on guanylate binding protein 1 in promoting the proliferation of glioma U87 cells and its mechanism / 肿瘤研究与临床

ABSTRACT

Objective:To investigate the effect of myeloid-derived suppressor cells (MDSC) on guanylate binding protein 1 (GBP1) in promoting the proliferation of glioma U87 cells and its mechanism.Methods:Glioma cells U87 with GBP1 overexpression (U87-GBP1) and control cells U87-Lacz transfected with empty vector were used as experimental cells. The mRNA and protein expressions of GBP1 and chemokine (C-C motif) ligand 2 (CCL2) in two groups of cells were detected by reverse transcription-quantitative polymerase chain reaction (RT-qPCR), Western blot and enzyme linked immunosorbent assay (ELISA), and the proliferation of U87 cells were detected by CCK-8. CD14 + monocytes and CD3 + T lymphocytes were isolated from peripheral blood of healthy people by immunomagnetic beads. The CD14 + monocytes were treated with culture medium of U87-Lacz cells or U87-GBP1 cells, and then the cells were divided into U87-Lacz culture medium group and U87-GBP1 culture medium group. The proportion of MDSC in CD14 + monocytes was analyzed by flow cytometry. CD14 + monocytes treated by two culture medium groups were cocultured with activated CD3 + T lymphocytes, and flow cytometry was used to detect the proliferation of activated CD3 + T lymphocytes. Monocytes untreated by U87 cells culture medium or activated CD3 + T lymphocytes were used as the control group. CD14 + monocytes were treated with U87-Lacz or U87-GBP1 cell culture medium anti-human CCL2 antibody, which were U87-Lacz+anti-CCL2 culture medium group and U87-GBP1 + anti-CCL2 culture medium group, and the proportion of MDSC in CD14 + monocytes was analyzed by flow cytometry. U87-GBP1 and U87-Lacz cells were inoculated into BALB/c nude mice to cause tumors in the brain. One week later, they were divided into chemokine (C-C motif) receptor 2 (CCR2) inhibitor RS504393 treatment group (U87-Lacz + RS nude mice group and U87-GBP1+RS nude mice group) and untreated control group (U87-Lacz nude mice group and U87-GBP1 nude mice group). After 30 days, the mice were sacrificed and the brain, spleen and bone marrow were isolated. Hematoxylin-eosin (HE) staining was used to observe the transplanted tumors in the brain of nude mice, and the volume of transplanted tumor was calculated, and flow cytometry was used to detect the proportion of MDSC in the tissues. Results:The protein expression of GBP1 in U87-GBP1 cells was significantly higher than that in U87-Lacz cells, but there was no significant difference in cell proliferation level between the two groups in vitro ( P > 0.05). The proportion of MDSC in U87-GBP1 culture medium group was significantly higher than that of U87-Lacz culture medium group [(7.75±0.80)% vs. (4.50±0.08)%], and both groups were higher than that of control group [(2.55±0.31)%)] ( F = 18.27, P = 0.002). The percentage of activated CD3 + T lymphocytes in U87-GBP1 culture medium group was lower than that in U87-Lacz culture medium group [(47.38±0.08)% vs. (61.70±5.05)%, P = 0.040]. The relative expression of CCL2 mRNA in U87-GBP1 cells and the expression level of CCL2 protein in U87-GBP1 cell culture medium [30.66±0.17 and (1 005.00±12.23) ng/L] were higher than those in U87-Lacz cells [1.29±0.15 and (111.60±11.44) ng/L] (both P < 0.01), the proportions of MDSC in U87-Lacz + anti-CCL2 culture medium group and U87-GBP1 + anti-CCL2 culture medium group was lower than those in U87-Lacz culture medium group and U87-GBP1 culture medium group (all P < 0.05). The volume of transplanted brain tumor in U87-GBP1 nude mice group was larger than that in U87-Lacz nude mice group; the volume of transplanted brain tumor in U87-GBP1 + RS nude mice group and U87-Lacz + RS nude mice group increased more slowly than the corresponding nude mice group without treatment, and the differences were statistically significant (all P < 0.05); the proportions of MDSC in transplanted brain tumor, spleen and bone marrow in U87-GBP1 nude mice group were higher than those in U87-Lacz nude mice group, and the proportions of MDSC in each tissue of U87-GBP1 + RS nude mice group and U87-Lacz + RS nude mice group were lower than those in the untreated by RS504393 corresponding nude mice group, and the differences were statistically significant (all P < 0.05). Conclusion:GBP1 might increase the expression of CCL2 in glioma U87 cells and recruit MDSC to form immunosuppression in glioma microenvironment, thus promoting the proliferation of glioma U87 cells in vivo.