Ribosomal Protein S9 Expression in Multiple Myeloma and Its Effect on Cell Biological Function

Abstract

Objective To identify the expression of ribosomal protein S9(RPS9)in multiple myeloma(MM)and explore its effect on the biological characteristics of myeloma cells and the corresponding mechanisms. Methods Bone marrow mononuclear cells were harvested in 10 healthy volunteers(CON group)and bone marrow CD138 +cells from 30 MM patients(CD138+group).Quantitative polymerase chain reaction(qPCR)was performed to detect RPS9 expression at mRNA level.In three cases from CON group and 11 cases from CD138+group,Western blot was performed to detect RPS9 at protein level.GSE19784 dataset was employed to detect the relationships of RPS9 expression with the overall survival rate,nuclear factor-κB(NF-κB),small ubiquitin-like modifier(SUMO),and ubiquitin pathway.After the RPS9 knock-down vector was constructed,flow cytometry was performed to detect the infection efficiency and qPCR and Western blot to detect the knock-down efficiency.RPMI8226 was divided into CON group and RPS9-short hairpin RNA(shRNA)group,in which annexin V allophycocyanin/propidium iodide(PI)double staining was performed to detect the change of apoptosis,CCK8 to detect the proliferation change,and PI staining to detect cell cycle change.After sentrin-specific protease 1(SENP1)overexpression vector was constructed,Western blot was performed to detect the phosphorylation of P65 and inhibitory subunit-κBα(IκBα)from NF-κB pathway in CON,RPS9-shRNA,and RPS9-shRNA-SENP1 cells;in addition,annexin V/PI double staining was also performed to detect the apoptosis in these three cells. Results The relative expression of RPS9 in CON group and CD138+group was(1.00±0.12)and(5.45±0.71),respectively(t=4.291,P=0.0036).Western blot showed RPS9 expression was high in most myeloma CD138+cells.The high expression of RPS9 was associated with both extramedullary invasion and overall survival in GSE19784 dataset.After RPMI8226 was infected with CON or RPS9-shRNA lentivirus for 48 hours,flow cytometry confirmed that the infection efficiencies were above 90% in both groups.qPCR and Western blot confirmed that RPS9 expression was inhibited at both mRNA and protein levels.After RPMI8226 CON and RPS9-shRNA infected with virus for 48 hours,the proportion of annexin V-positive cells in CON and RPS9-shRNA cells was(3.47±0.37)% and(18.60±64.00)%(t=9.015,P=0.0008).The proliferation index significantly differed between CON group and RPS9-shRNA group at 72 hours(t=6.846,P=0.0024).When CON and RPS9-shRNA were infected with virus for 48 hours,the proportion of G2 phase cells was(29.28±3.42)% and(10.43±1.43)%,respectively(t=9.329,P=0.0007).The RPS9 expression was positively correlated with SENP1 in GSE19784 dataset and negatively correlated with IκBα coding gene NFKBIA.Western blot further confirmed that RPS9 knockdown inhibited the expression of SENP1,inhibited the phosphorylation of NF-κB subunit P65 and inhibitor IκBα,and promoted the expression of IκBα.Overexpression of SENP1 not only impeded this effect but also reduced RPS9-induced apoptosis. Conclusions RPS9 is highly expressed in MM CD138+cells and is associated with overall survival and extramedullary infiltration.Inhibition of RPS9 can promote apoptosis,cell cycle arrest,and proliferation of myeloma cells.RPS9 can affect the activation of NF-κB pathway and cell apoptosis through SENP1,suggesting that SENP1 may be a key factor in the biological effect of RPS9.