C. GST-pull down assay of WT and WT with 4D. GST-Atoh1 plasmids were transfected with or without Ccnd1 and Cdk4 plasmids (4D) in N2a cells. Cell lysates were pull-downed with glutathione-conjugated beads after a 6 hr treatment of 10µM MG132 and then immunoblotted with anti-poly Ubiquitin. Quantification of relative levels of poly-ubiquitin (right panel). Bars and error bars are representing as Mean ± SEM from three trials of each condition. Student T-test between WT with MG132 and WT+4D with MG132. **p < 0.01. 