p62/sequestosome 1 as a regulator of proteasome inhibitor-induced autophagy in human retinal pigment epithelial cells.

PURPOSE: The pathogenesis of age-related macular degeneration involves impaired protein degradation in retinal pigment epithelial (RPE) cells. The ubiquitin-proteasome pathway and the lysosomal pathway including autophagy are the major proteolytic systems in eukaryotic cells. Prior to proteolysis, heat shock proteins (HSPs) attempt to refold stress-induced misfolded proteins and thus prevent the accumulation of cytoplasmic protein aggregates. Recently, p62/sequestosome 1 (p62) has been shown to be a key player linking the proteasomal and lysosomal clearance systems. In the present study, the functional roles of p62 and HSP70 were evaluated in conjunction with proteasome inhibitor-induced autophagy in human RPE cells (ARPE-19). METHODS: The p62, HSP70, and ubiquitin protein levels and localization were analyzed by western blotting and immunofluorescense. Confocal and transmission electron microscopy were used to detect cellular organelles and to evaluate the morphological changes. The p62 and HSP70 levels were modulated using RNA interference and overexpression techniques. Cell viability was measured by colorimetric assay. RESULTS: Proteasome inhibition evoked the accumulation of perinuclear aggregates that strongly colocalized with p62 and HSP70. The p62 perinuclear accumulation was time- and concentration-dependent after MG-132 proteasome inhibitor loading. The silencing of p62, rather than Hsp70, evoked suppression of autophagy, when related to decreased LC3-II levels after bafilomycin treatment. In addition, the p62 silencing decreased the ubiquitination level of the perinuclear aggregates. Recently, we showed that hsp70 mRNA depletion increased cell death in ARPE-19 cells. Here, we demonstrate that p62 mRNA silencing has similar effects on cellular viability. CONCLUSIONS: Our findings open new avenues for understanding the mechanisms of proteolytic processes in retinal cells, and could be useful in the development of novel therapies targeting p62 and HSP70.

Crosstalk between Hsp70 molecular chaperone, lysosomes and proteasomes in autophagy-mediated proteolysis in human retinal pigment epithelial cells.

The pathogenesis of age-related macular degeneration involves chronic oxidative stress, impaired degradation of membranous discs shed from photoreceptor outer segments and accumulation of lysosomal lipofuscin in retinal pigment epithelial (RPE) cells. It has been estimated that a major part of cellular proteolysis occurs in proteasomes, but the importance of proteasomes and the other proteolytic pathways including autophagy in RPE cells is poorly understood. Prior to proteolysis, heat shock proteins (Hsps), agents that function as molecular chaperones, attempt to refold misfolded proteins and thus prevent the accumulation of cytoplasmic protein aggregates. In the present study, the roles of the Hsp70 molecular chaperone and proteasomal and lysosomal proteolytic pathways were evaluated in human RPE cells (ARPE-19). The Hsp70 and ubiquitin protein levels and localization were analysed by Western blotting and immunofluorescense. Confocal and transmission electron microscopy were used to detect cellular organelles and to evaluate the morphological changes. Hsp70 levels were modulated using RNA interference and overexpression techniques. Cell viability was measured by colorimetric assay. The proteasome inhibitor MG-132 evoked the accumulation of perinuclear aggregates positive for Hsp70, ubiquitin-protein conjugates and the lysosomal membrane protein LAMP-2. Interestingly, the hsp70 mRNA depletion significantly increased cell death in conjunction with proteasome inhibition. We found that the accumulation of lysosomes was reversible: a cessation of proteasome inhibition led to clearance of the deposits via a mechanism believed to include autophagy. The molecular chaperone Hsp70, proteasomes and autophagy have an important regulatory role in the protein turnover of human RPE cells and may thus open new avenues for understanding degenerative processes in retinal cells.

Characterization of the binding properties of SIRT2 inhibitors with a N-(3-phenylpropenoyl)-glycine tryptamide backbone.

SIRT2 inhibitors with a N-(3-phenylpropenoyl)-glycine tryptamide backbone were studied. This backbone has been developed in our group, and it is derived from a compound originally found by virtual screening. In addition, compounds with a smaller 3-phenylpropenoic acid tryptamide backbone were also included in the study. Binding modes for the new compounds and the previously reported compounds were analyzed with molecular modelling methods. The approach, which included a combination of molecular dynamics, molecular docking and cluster analysis, showed that certain docking poses were favourable despite the conformational variation in the target protein. The N-(3-phenylpropenoyl)-glycine tryptamide backbone is also a good backbone for SIRT2 inhibitors, and the series of compounds includes several potent SIRT2 inhibitors.

Discovering inhibitors of human sirtuin type 2: novel structural scaffolds.

A successful virtual screening experiment of novel SIRT2 inhibitors is described. Four out of 11 experimentally tested compounds showed in vitro inhibitory activity toward SIRT2 in a micromolar level, resulting in an experimental hit ratio of 36%. Two of these compounds inhibited SIRT2 with IC50 (microM) values of 51 and 91; moreover, one of the new inhibitors was comprised of an entirely new SIRT2-inhibiting structural scaffold.

N,N'-Bisbenzylidenebenzene-1,4-diamines and N,N'-Bisbenzylidenenaphthalene-1,4-diamines as Sirtuin Type 2 (SIRT2) Inhibitors.

A series of N,N'-bisbenzylidenebenzene-1,4-diamine and N,N'-bisbenzylidenenaphthalene-1,4-diamine derivatives were synthesized as inhibitors for human sirtuin type 2 (SIRT2). The design of the new compounds was based on two earlier reported hits from molecular modeling and virtual screening. The most potent compound was N,N'-bis(2-hydroxybenzylidene)benzene-1,4-diamine, which was equipotent with the most potent hit compound and well-known SIRT2 inhibitor sirtinol.

Morphogenesis of Lewy bodies: dissimilar incorporation of alpha-synuclein, ubiquitin, and p62.

The formation of Lewy bodies (LBs) and their relationship to other types of nigral inclusions associated with Parkinson disease (PD), such as pale bodies (PBs), remain poorly understood. Known constituents of LBs include alpha-synuclein (alphaS) and ubiquitin (Ub), providing windows to their morphogenesis. Additionally, p62/sequestosome 1 has been identified as a common component of neuropathological and hepatocytic inclusions. To study the formation of PD-associated nigral inclusions, we analyzed the substantia nigra of cases with abundant LBs and PBs in hematoxylin and eosin (H&E) stain, using immunohistochemistry for alphaS, Ub, and p62. We found morphologically diverse alphaS-immunoreactive deposits within neuronal perikarya and neurites. Perikaryal types extended from punctate cytoplasmic staining to variform compact (i.e. PB-type and LB-type) inclusions. Using H&E, only a small subset of the compact deposits could be unambiguously identified. Labeling for p62 was highly similar to alphaS in compact perikaryal inclusions, whereas no punctate staining or intraneuritic inclusions were detected. Ubiquitin antibodies labeled compact deposits both within perikarya and neurites. The data suggest that pathological alphaS is first evident as punctate perikaryal material that, via coalescence and incorporation of p62 and Ub, yields PB-type structures from which LB-type inclusions form in a compaction-like manner. The results also point at dissimilarities in the formation of perikaryal vs intraneuritic inclusions.

N-(3-(4-Hydroxyphenyl)-propenoyl)-amino acid tryptamides as SIRT2 inhibitors.

A series of N-(3-(4-hydroxyphenyl)-propenoyl)-amino acid tryptamides was based on a previously reported new SIRT2 inhibitor from our group, and it was designed to study if the molecular size of the compound could be reduced. The most potent compounds, N-(3-(4-hydroxyphenyl)-propenoyl)-2-aminoisobutyric acid tryptamide and N-(3-(4-hydroxyphenyl)-propenoyl)-L-alanine tryptamide, were equipotent, 30% smaller in molecular weight, and slightly more selective (SIRT2/SIRT1) than the parent compound.