[Qualitative difference of mitochondrial subproteoms of brain RPN10- and RPN13-binding proteins]

Proteasome Interactome and Its Role in the Mechanisms of Brain Plasticity

Abstract

Proteasomes are highly conserved multienzyme complexes responsible for proteolytic degradation of the short-lived, regulatory, misfolded, and damaged proteins. They play an important role in the processes of brain plasticity, and decrease in their function is accompanied by the development of neurodegenerative pathology. Studies performed in different laboratories both on cultured mammalian and human cells and on preparations of the rat and rabbit brain cortex revealed a large number of proteasome-associated proteins. Since the identified proteins belong to certain metabolic pathways, multiple enrichment of the proteasome fraction with these proteins indicates their important role in proteasome functioning. Extrapolation of the experimental data, obtained on various biological objects, to the human brain suggests that the proteasome-associated proteins account for at least 28% of the human brain proteome. The proteasome interactome of the brain contains a large number of proteins involved in the assembly of these supramolecular complexes, regulation of their functioning, and intracellular localization, which could be changed under different conditions (for example, during oxidative stress) or in different phases of the cell cycle. In the context of molecular functions of the Gene Ontology (GO) Pathways, the proteins of the proteasome interactome mediate cross-talk between components of more than 30 metabolic pathways annotated in terms of GO. The main result of these interactions is binding of adenine and guanine nucleotides, crucial for realization of the nucleotide-dependent functions of the 26S and 20S proteasomes. Since the development of neurodegenerative pathology is often associated with regioselective decrease in the functional activity of proteasomes, a positive therapeutic effect would be obviously provided by the factors increasing proteasomal activity. In any case, pharmacological regulation of the brain proteasomes seems to be realized through the changes in composition and/or activity of the proteins associated with proteasomes (deubiquitinase, PKA, CaMKIIα, etc.).

[Comparative analysis of proteins associated with 26S and 20S proteasomes isolated from rabbit brain and liver]

We have isolated fractions of 26S and 20S proteasomes were from the rabbit liver and the brain. According to mass spectrometric (MS) analysis, the 26S proteasome fractions from these organs contained catalytic and regulatory subunits characteristic of the proteasome core and regulatory subunits. The 20S fractions of brain and liver proteasomes contained only catalytic proteasome subunits. In addition to proteasome subunits, the isolated fractions contained components of the ubiquitin-proteasome system, ubiquitinated proteins, enzymes that play an important role in metabolic processes, cytoskeletal components, signaling, regulatory, and protective proteins, as well as proteins regulating gene expression, cell division, and differentiation. The abundance of a number of proteasome-associated proteins was comparable or exceeded the abundance of intrinsic proteasome components. About a third of the proteins common to all studied fractions (26S and 20S of brain and liver proteasomes) belong to the group of multifunctional proteins. Selective biosensor validation confirmed the affinity binding of proteins (aldolase, phosphoglycerate kinase) identified during MS analysis to the brain 20S proteasome. Comparison of the subproteomes of the 26S and 20S brain proteasomes showed that removal of components of the regulatory (19S) subparticles caused almost two-fold increase in the total number of individual proteins associated with the core part of the proteasome (20S). In the liver, the number of proteins associated with the core part of the proteasome remained basically unchanged after the removal of the components of the regulatory (19S) subparticles. This indicates that in the brain and, possibly, in other organs, proteins of the regulatory (19S) subunit play an important role in the formation of the proteasome interactome.

[Changes in the mitochondrial subproteome of mouse brain Rpn13-binding proteins induced by the neurotoxin MPTP and the neuroprotector isatin]

Mitochondrial dysfunction and ubiquitin-proteasome system (UPS) failure contribute significantly to the development of Parkinson's disease (PD). The proteasome subunit Rpn13 located on the regulatory (19S) subparticle play an important role in the delivery of proteins, subjected to degradation, to the proteolytic (20S) part of proteasome. We have previously found several brain mitochondrial proteins specifically bound to Rpn13 (Buneeva et al. (2020) Biochemistry (Moscow), Supplement Series B: Biomedical Chemistry, 14, 297-305). In this study we have investigated the effect of the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and the neuroprotector isatin on the mitochondrial subproteome of Rpn13-binding proteins of the mouse brain. Administration of MPTP (30 mg/kg) to animals caused movement disorders typical of PD, while pretreatment with isatin (100 mg/kg, 30 min before MPTP) reduced their severity. At the same time, the injection of MPTP, isatin, or their combination (isatin + MPTP) had a significant impact on the total number and the composition of Rpn13-binding proteins. The injection of MPTP decreased the total number of Rpn13-binding proteins in comparison with control, and the injection of isatin prior to MPTP or without MPTP caused an essential increase in the number of Rpn13-binding proteins, mainly of the functional group of proteins participating in the protein metabolism regulation, gene expression, and differentiation. Selected biosensor validation confirmed the interaction of Rpn13 subunit of proteasome with some proteins (glyceraldehyde-3-phosphate dehydrogenase, pyruvate kinase, histones H2A and H2B) revealed while proteomic profiling. The results obtained testify that under the conditions of experimental MPTP-induced parkinsonism the neuroprotective effect of isatin may be aimed at the interaction of mitochondria with the components of UPS.