To achieve overexpression of phosphoglycerate kinase 1 (PGK1) in HEK-293T cells and screen the key site of its succinylation through constructing PGK1 overexpression vector (PGK1-WT) and four lysine site succinylation mutation vectors.

GEPIA2 database was used to analyze the expression of PGK1 mRNA in normal breast tissue (291 cases) and breast cancer tissue (135 cases) and the relationship between PGK1 expression level and the overall survival rate of breast cancer patients. Protein modification proteomics was used to detect the levels of protein succinylation in four triple negative breast cancer (TNBC) cell lines (MDA-MB-436, MDA-MB-468, MDA-MB-231, BT-549) and normal breast epithelial cells (MCF-10A); the succinylated positive and negative mutation vectors of K11, K131, K323, K361 were contructed with point mutation kit. The experiment was divided into NC, shPGK1-496, shPGK1-220, PGK1-WT groups and positive and negative mutant groups of K11, K131, K323 and K361. Real-time fluorescence quantitative polymerase chain reaction was used to detect the level of expression of PGK1 mRNA in NC, shPGK1-496 and shPGK1-220 groups. The expression levels of PGK1 proteins in NC, shPGK1-496 and shPGK1-220 groups, and the expression levels of Flag proteins in NC, PGK1-WT and four sites in positive and negative mutant groups were detected by Western blot. The key site of PGK1 succinylation was detected by co-immunoprecipitation.

Compared with normal breast tissues, the level of PGK1 mRNA was highly expressed in breast cancer tissue, and the survival time of breast cancer patients with high PGK1 expression was shorter. Four lysine sites of PGK1 in TNBC cells were hypersuccinylated. The relative expression levels of PGK1 mRNA in NC, shPGK1-496 and shPGK1-220 groups were 1.03±0.23, 0.15±0.11 and 1.42±0.69, respectively; the relative expression levels of PGK1 protein were 1.08±0.05, 0.49±0.05 and 1.28±0.01 respectively; compared with NC group, the above indexes in shPGK1-496 group were statistically different (all P<0.01). The relative expression levels of Flag protein in NC group, PGK1-WT group and positive and negative mutant groups of K11, K131, K323 site were 0, 3.43±0.09, 3.28±0.10, 2.28±0.11, 3.03±0.03, 2.79±0.11, 3.29±0.09 and 2.98±0.04, respectively; compared with the NC group, PGK1-WT group and the positive and negative mutant groups of K11, K131 and K323 had statistical differences (all P<0.01). The relative expression levels of Flag protein in NC group, PGK1-WT group and K361 positive and negative mutant group were 0, 2.58±0.11, 3.04±0.02 and 4.04±0.10, respectively; compared with NC group, PGK1-WT group and K361 positive and negative mutant group had statistical significance (all P<0.01). The levels of lysine succinylation in IgG group, PGK1-WT group and negative mutant groups of K11, K131, K323, K361 were 0, 1.53±0.12, 1.30±0.18, 1.29±0.09, 1.23±0.03 and 0.89±0.16, respectively; compared with PGK1-WT group, the negativ mutant group of K361 had statistical significance (P<0.01).

The four lysine sites of PGK1 in TNBC cells are highly succinylated, and K361 site is critical to their succinylation.