Figure 3.

MS28 effectively degrades cyclin D1 in a VHL-, CDK6-, and UPS-dependent manner. (A) Left, VHL KO rescues the MS28-induced degradation of cyclin D1 and CDK4/6. Calu-1 cells were transduced with lentivirus containing VHL-targeting sgRNA or an empty vector. Antibiotic-selected cells were checked for VHL expression (Top: WB results confirm CRISPR-mediated VHL KO in Calu-1 cells), followed by treatment with MS28 for 8 h. Right, quantification of cyclin D1 and CDK4/6 abundance in the indicated experimental groups. P-values for each protein were calculated between the mock and VHL KO groups (indicated by bar) within each concentration. (B) Left, CDK6 KD via siRNA rescues the MS28-induced degradation of cyclin D1. Calu-1 cells were transfected with CDK6-targeting siRNA for 2 days, followed by treatment with MS28 for 8 h. Right, quantification of cyclin D1 abundance in the indicated experimental groups. P-values were calculated between the control and CDK6 KD group within each MS28 concentration. (C) VHL coelutes with cyclin D1-CDK6 in the presence of MS28. His-tagged CDK6 was immobilized on cobalt agarose resin and incubated overnight along with cyclin D1. The VCB complex was added the next day with either DMSO or MS28. Pretreatment with MG132 (D) or MLN4924 (E) rescues the MS28-induced degradation of cyclin D1 and CDK4/6. Quantification of cyclin D1 and CDK4/6 abundance are listed aside. For each protein, p-values were calculated between groups indicated by the lines above the bars. Calu-1 cells were pretreated with MG132 or MLN4924 for 1 h, followed by treatment with MS28 for 8 h. WB results shown in panels A–E are representative of at least two independent experiments. ****P < 0.0001, ***P < 0.001, **P < 0.01, and *P < 0.05.