Objective To determine the effect of denticleless E3 ubiquitin protein ligase(DTL)on the proliferation and clone formation of multiple myeloma(MM)cells and investigate the related mechanism. Methods Mononuclear cells were extracted from 34 MM patients.Mononuclear cells harvested from 14 healthy volunteers were used as controls.Quantitative polymerase chain reaction was used to detect the change of DTL at mRNA level.Furthermore,12 MM patients and 2 controls were selected,in whom the change of DTL at protein level was detected by Western blot.Human MM cell line RPMI8226 was divided into control(CON)group and DTL-short hairpin RNA(DTL-shRNA)group,which was infected with the CON and DTL-shRNA virus,respectively,for 48 hours.The infection efficiency was detected by using flow cytometry,the knock-down efficiencies at mRNA and protein levels were detected by quantitative polymerase chain reaction and Western blot,the change of cell counts in the next 0,24,48,72,96 hours were measured with CCK8 assay.The CON and DTL-shRNA cells were cultured in semisolid medium.Ten days later,inverted phase microscopy was used to measure the number of colones that contain more than 50 cells,annexin V/propidium iodide double staining to detect apoptosis,and propidium iodide staning to detect cell cycle.Finally,Western blot was empoyed to detect the phosphorylation of P65 and inhibitory subunit-κBα(IκBα)in nuclear factor-κB(NF-κB)pathway and electrophoretic mobility shift assay(EMSA)to detect the NF-κB transcriptional ability. Results The DTL expression was(1.00±0.12)and(9.36±3.71),respectively in the bone marrow mononuclear cells of healthy volunteers and in the CD138+cells of MM patients(t=3.65,P=0.0024).DTL was also highly expressed in MM CD138+positive cells at protein level.After RPMI8226 was infected by CON and DTL-shRNA virus for 48 hours,green fluorescent protein-positive cells accounted for more than 90%.The relative expression of DTL was(1.00±0.01)and(0.21±0.04)(t=33.19,P<0.0001)at mRNA level and(0.52±0.13)and(0.11±0.02)at protein level(t=5.399,P=0.0057).CCK8 revealed that CON and DTL-shRNA cells proliferated by(1.00±0.03)vs.(1.00±0.02),(2.19±0.28)vs.(1.47±0.13),(3.50±0.14)vs.(2.24±0.19),(5.43±0.41)vs.(3.08±0.14),(7.42±0.17)vs.(4.29±013)after 0,24,48,72,and 96 hours(F=24.58,P=0.001).The number of colone containing more than 50 cells was in 76±4 in CON group and 0 in DTL-shRNA group(P<0.01).The proportion of G1 stage cells was(28.61±8.64)% in CON group and(57.25±10.37)% in DTL-shRNA group(t=3.675,P=0.0213).The proportion of annexin V+in CON and DTL-shRNA groups was(3.21±0.89)% vs.(34.71±18.68)%(t=2.895,P=0.0443).After RPMI8226 was infected with CON or DTL-shRNA virus for 48 hours,the relative expression of phosphorylation P65 was(1.52±0.14)vs.(0.82±0.11)(t=6.81,P=0.0024),the P65 relative expression was(0.25±0.04)vs.(0.24±0.08)(t=0.19,P=0.85),the CON and DTL-shRNA phosphorylation-IκBα relative expression was(0.19±0.03)vs.(0.13±0.02)(t=2.882,P=0.0449),and the IκBα was(0.22±0.05)vs.(1.01±0.06)(t=17.52,P<0.0001).Detection of the transcriptional ability of DTL-shRNA NF-κB by EMSA further confirmed the down-regulation of DTL suppressed the NF-κB transcriptional ability. Conclusions DTL is highly expressed in MM cells,and down-regulation of DTL suppresses the cell proliferation,inhibit the colony formation,and induce cell apoptosis and cell cycle arrest.The effect of DTL on the biological functions of MM cells is related to the change of NF-κB pathway.