Comprehensive Analysis of Proteasomal Complexes in Mouse Brain Regions Detects ENO2 as a Potential Partner of the Proteasome in the Striatum

Abstract

Defects in the activity of the proteasome or its regulators are linked to several pathologies including neurodegenerative diseases. We hypothesize that proteasome heterogeneity and its selective partners vary across brain regions and have a large impact on proteasomal catalytic activities. Using neuronal cell cultures and brain tissues obtained from mice, we compared proteasomal activities from two distinct brain regions affected in neurodegenerative diseases, the striatum and the hippocampus. The results indicated that proteasome activities and their responses to proteasome inhibitors are determined by their subcellular localizations and their brain regions. Using a iodixanol gradient fractionation method, proteasome complexes were isolated, followed by proteomic analysis for proteasomal interaction partners. Proteomic results revealed gamma enolase (ENO2), a known proteasome partner, has more a nity to proteasome complexes puri ed from the striatum than to those from the hippocampus. These results highlight a potential key role for non-proteasomal partners of proteasome regarding the diverse activities of the proteasome complex recorded in several brain regions.

Multifunctional roles of γ-enolase in the central nervous system: more than a neuronal marker

“…γ-Enolase, predominantly located in the cytosol of brain cells, participates in glycolysis, but in a lesser extent than α-enolase [ 58 ]. Moreover, γ-enolase was reported to be interacting with centrosome and proteasome [ 72 , 73 ], however is notably absent from the nucleus [ 74 , 75 ]. Furthermore, γ-enolase was shown to be transported within axons as components of the slow component b complex, indicating a structured organization rather than free diffusion in the cytoplasm [ 76 ].…”

“…γ-Enolase is expressed in lung and nervous tissues and located in the cytosol and on the cell membrane, involved in glycolysis and neural development, but is absent from the nucleus. β-Enolase is found in liver and muscle tissues and present in the cytosol, engaging in glycolysis and interacting with sarcomeric troponin, affecting muscle contraction and the epithelial-mesenchymal transition (EMT) process [8,13,25,31,45,58,64,[66][67][68][69][70][71][72][73][74][75][76][77][78][79][80][81][82][83] β-enolase, which is primarily expressed in muscle tissue; and γ-enolase, which is mostly expressed in neural tissues (Fig. 1) [25].…”

“…α-enolase Cytosol Glycolysis, heat-shock protein interaction [25,66,67] Cytoskeleton Myogenesis, stress-induced contraction [13,31] Nucleus Suppression of c-myc [68] Mitochondrial membrane RNA chaperone activity, membrane potential stabilization [69,70] The outer side of the cell membrane Plasminogen binding receptor [8,64,71] Extracellular space (exosomes) Plasminogen binding receptor [8,64,71] γ-enolase Cytosol Glycolysis, centrosome interaction; proteasome interaction [58,72,73] Cytoskeleton Integration and transport within the axonal cytoskeletal structure [76] Nucleus Absent [74,75] The inner side of the cell membrane Cell survival, neurite outgrowth [78][79][80][81] The outer side of the cell membrane Neurite outgrowth [77] β-enolase Cytosol Glycolysis, sarcomere troponin interaction, interference with EMT process [45,82,83] significantly influence the specificity of serum NSE [121]. A potential solution could be an introduction of a hemolysis correction factor or a preliminary hemolysis index [87,122,123].…”