Fig. 5: Defects in cytoplasm-to-nucleus shuttling of bulk proteins exacerbate cell death in Huntington’s disease cells.
From: Nuclear proteasomes buffer cytoplasmic proteins during autophagy compromise
a, Real-time CellTox Green fluorescence as a result of cell death is monitored by Incucyte in a time-dependent manner. Exacerbated cell death by combined inhibition of autophagy and proteasome (SBI and MG, respectively) in HTT125Q-derived neurons. These graphs do not show error bars, which make the graphs less clear. The raw data are shown in the data files with P values. When we compute areas under the curve for three biological replicates, then SBI versus SBI + MG in Cont iPS cell-derived neurons P = 0.029; SBI versus SBI + MG in HTT125Q-derived neurons P = 0.049; SBI in Cont versus HTT125Q-derived neurons P = 0.078; MG in Cont versus HTT125Q-derived neurons P = 0.036; SBI + MG in Cont versus HTT125Q-derived neurons P = 0.016 (one-tailed paired t-test). b, Left graph: enhanced cell death caused by combined inhibition of autophagy and proteasome in mouse striatal cells expressing Q7/Q111 compared with each inhibitor alone. Right graph: increased cell death caused by autophagy inhibition (SBI) in Q7/Q111 compared with Q7/Q7 striatal cells (expanded scale from the same data in the left-hand graph to clarify effects of SBI to enable ease of comparison). When we compute areas under the curve for four biological replicates normalized to DMSO values showing Q7/Q7 and Q7/Q111 striatal cells treated with proteasome inhibitor MG132 (MG, 2 µM), autophagy inhibitor SBI (5 µM) and/or both (SBI + MG) in a time-dependent manner, then SBI versus SBI + MG (in Q7/Q7 cells): P = 0.036, SBI versus SBI + MG (in Q7/Q111 cells): P = 0.015, SBI in Q7/Q7 versus Q7/Q111: P = 0.274, MG in Q7/Q7 versus Q7/Q111: P = 0.024, SBI + MG in Q7/Q7 versus Q7/Q111: P = 0.029 (one-tailed paired t-test). c, Schematic summary for our study. Cytoplasmic substrates accumulating during autophagy depletion move into the nucleus via nuclear pores to be degraded by nuclear proteasomes. In the HD context, defective cytoplasm-to-nuclear transport enhances susceptibility to autophagy inhibition leading to cell dysfunction. Source numerical data are available in source data.
