Effects of SKP1 gene interference on apoptosis and regulation mechanism of ubiquitin-proteasome system in Parkinson's disease cell model

Zhenjie SUN; Qiang TONG; Qi GAO; Ting LU; Quan CHEN; Xiangyang TIAN; Bo SUN

ABSTRACT

Objective:

To investigate the effect of interfering S-phase kinase associated protein 1 (SKP1) gene on apoptosis in Parkinson's disease(PD) cell model induced by 1-methyl-4-phenyl-pyridine ion (MPP+ ) and the mechanism of ubiquitin proteasome system degradation of α-synuclein (α-syn) influence.

Methods:

SH-SY5Y cells were divided into control group, MPP+ group, SKP1 interference group, and SKP1 interference+ MG132(UPS inhibitor) group.The cells in the control group were cultured normally. The cells in the latter three groups were incubated with MPP+ (0.5 mmol/L) for 24 h as PD model cells.The cells in SKP1 interference group were transfected with lentivirus SKP1-siRNA, and the cells in SKP1 interference+ MG132 group were transfected with lentivirus SKP1 siRNA and added with MG132 (0.5 μmol/L) for 24 h. The protein levels and mRNA levels of SKP1, microtubule-associated protein light chain 3 (LC3), lysosome-associated membrane protein (LAMP), α-syn, ubiquitin activating enzyme E1 (UBE1), parkin, and p27 in cells were detected by Western blot and RT-PCR.Flow cytometry was used to detect cell apoptosis and cycle level, and CCK-8 method was used to detect cell proliferation level.Co-immunoprecipitation method was used to explore the interaction between SKP1 and p27. SPSS 23.0 software was used for statistical analysis. One-way ANOVA was used for comparison among groups, and LSD test was used for further pairwise comparison.

Results:

RT-PCR and Western blot results showed that the mRNA levels and protein levels of autophagy related proteins and ubiquitin related proteins LC3, LAMP2, α-syn, UBE1, parkin and p27 in the four groups were statistically significant(mRNA F=99.155, 43.028, 138.464, 28.200, 22.009, 28.147, all P<0.05; F=245.517, 157.634, 315.920, 2 336.472, 477.429, 2 350.201, all P<0.05). The mRNA and protein levels of LC3, Lamp2, α-syn and p27 in SKP1 interference group were lower than those in MPP+ group (all P<0.05), while the mRNA and protein levels of UBE1 and parkin were higher than those in MPP+ group (all P<0.05). The mRNA and protein levels of LC3, α-syn and p27 in SKP1 interference+ MG132 group were higher than those in SKP1 interference group (all P<0.05), and the mRNA and protein levels of UBE1 and parkin were lower than those in SKP1 interference group (all P<0.05). The results of flow cytometry and CCK-8 method showed that the apoptosis rate and cell inhibition rate among the four groups were significantly different( F=2 749.420, 171.508, both P<0.05). The apoptosis rate of SKP1 interference group was lower than that of MPP+ group ((8.22±0.25)%, (15.30±0.21)%, P<0.05), while the cell inhibition rate of SKP1 interference group was lower than that of MPP+ group((26.31±3.73)%, (55.05±3.84)%, P<0.05). The apoptosis rate of SKP1 interference+ MG132 group ((9.49±0.07)%) was higher than that of SKP1 interference group, and the cell inhibition rate ((36.06±2.85)%) was higher than that of SKP1 interference group (both P<0.05). The results of immunoprecipitation method showed that P27 decreased after SKP1 immunoprecipitation.

Conclusion:

After SKP1 gene was interfered, the autophagy function of PD cells decreased, which may be related to parkin promoting α-syn ubiquitination, activating UBE1/ Parkin-mediated UPS pathway to degrade α-syn, and mediating P27 to inhibit apoptosis.