Fig 2: Loss of UBE2G1 blocked the degradation of cereblon neomorphic substrates induced by cereblon-modulating agents.(A and B) Immunoblot analysis of OPM2-Cas9 cells expressing non-targeting, UBE2G1-specific or CRBN-specific sgRNA. Cells were treated with LEN, POM or CC-220 for 16 hr (A) or CC-885 for 4 hr (B) at the indicated concentrations. (C) Immunoblot analysis of 293T parental or UBE2G1-/- cells treated with BRD4 PROTACs dBET1 or MZ1 at the indicated concentrations for 16 hr. (D) Immunoblot analysis of OPM2 parental or UBE2G1-/- cells treated with 100 µg/ml cycloheximide with or without 1 µM POM pretreatment for half an hour. Cells were harvested at the indicated time points. All results shown in this figure are representative of three independent experiments.

Fig 3: Identification of UBE2G1 as the most critical ubiquitin E2 enzyme that mediates the pomalidomide-induced degradation of IKZF1.(A) Schematic showing the design of the CRISPR screen to identify E2 enzyme(s) regulating the CM-induced degradation of ePL-tagged IKZF1 in 384-well array format. (B) Chemiluminescent measurement of ePL-IKZF1 protein expression level in U937_Cas9_ePL-IKZF1 parental cells or cells expressing non-targeting or UBE2G1-specific sgRNAs. Cells were treated with POM at the indicated concentrations for 16 hr. Data are presented as mean ± SD, n = 4 technical replicates. (C) Immunoblot analysis of U937_Cas9 parental or UBE2G1-/- cells with or without stable expression of UBE2G1 wild-type or C90S mutant. Cells were treated with POM at the indicated concentrations for 16 hr. Result is representative of three independent experiments.10.7554/eLife.40958.008Figure 1—source data 1.ePL luminescence signal shown in Figure 1B.

Fig 4: UBE2G1 loss confers resistance to lenalidomide and pomalidomide in myeloma cell lines.(A) Effect of LEN (top panel) and POM (bottom panel) on proliferation of myeloma cell lines. Cell proliferation was determined by CTG. Data are presented as mean ± SD, n = 3 technical replicates. (B) Immunoblot analysis of myeloma cell lines used in (A). (C and D) Proliferation (C) and immunoblot analysis (D) of SKMM2 cells transduced with lentiviral vectors encoding GFP, UBE2G1 and UBE2G1-C90S. Cells were treated with DMSO vehicle control, LEN or POM at the indicated concentrations for 5 days (C) or 16 hr (D). In (C), cell proliferation was determined by CTG, and data are presented as mean ± SD, n = 3 technical replicates. All results shown in this figure are representative of three independent experiments.10.7554/eLife.40958.024Figure 6—source data 1.CTG luminescence signal shown in Figure 6A,C.

Fig 5: UBE2G1-deficient OPM2 myeloma cells are resistant to lenalidomide and pomalidomide but remain sensitive to CC-220 at clinical relevant concentrations.(A and B) Cell proliferation (A) and immunoblot analysis (B) of OPM2-Cas9 cells transduced with lentiviral vectors expressing non-targeting, UBE2G1-specific or CRBN-specific sgRNAs. Cells were treated DMSO vehicle control, LEN, POM or CC-220 at the indicated concentrations for 5 days (A) or 16 hr (B). In (A), cell proliferation was determined by CTG, and data are presented as mean ± SD, n = 3 technical replicates. All results shown in this figure are representative of three independent experiments.10.7554/eLife.40958.028Figure 7—source data 1.CTG luminescence signal shown in Figure 7A.