Michael Y. Sherman

Hsp70–Bag3 complex is a hub for proteotoxicity-induced signaling that controls protein aggregation

Significance This work dissects how cells monitor failure of proteasomes and trigger signaling responses defining whether cells survive proteotoxic stress or undergo apoptosis. The monitoring mechanism involves detection of a buildup of abnormal polypeptides released from ribosomes. Accordingly, the system simultaneously monitors effectiveness of several major processes, including protein synthesis, folding, and degradation. A special scaffold complex composed of heat shock protein 70 (Hsp70) and its cofactor Bcl-2–associated athanogene 3 (Bag3) links accumulation of abnormal polypeptide species with a number of protein kinases involved in various signal-transduction pathways. A startling finding is that an Hsp70–Bag3–regulated kinase, LATS1, regulates very early events of formation of protein aggregates; thus protein aggregation appears to be a tightly regulated process rather than the simple collapse of abnormal proteins. Protein abnormalities in cells are the cause of major pathologies, and a number of adaptive responses have evolved to relieve the toxicity of misfolded polypeptides. To trigger these responses, cells must detect the buildup of aberrant proteins which often associate with proteasome failure, but the sensing mechanism is poorly understood. Here we demonstrate that this mechanism involves the heat shock protein 70–Bcl-2–associated athanogene 3 (Hsp70–Bag3) complex, which upon proteasome suppression responds to the accumulation of defective ribosomal products, preferentially recognizing the stalled polypeptides. Components of the ribosome quality control system LTN1 and VCP and the ribosome-associated chaperone NAC are necessary for the interaction of these species with the Hsp70–Bag3 complex. This complex regulates important signaling pathways, including the Hippo pathway effectors LATS1/2 and the p38 and JNK stress kinases. Furthermore, under proteotoxic stress Hsp70–Bag3–LATS1/2 signaling regulates protein aggregation. We established that the regulated step was the emergence and growth of abnormal protein oligomers containing only a few molecules, indicating that aggregation is regulated at very early stages. The Hsp70–Bag3 complex therefore functions as an important signaling node that senses proteotoxicity and triggers multiple pathways that control cell physiology, including activation of protein aggregation.

Author Correction: Cancer cell responses to Hsp70 inhibitor JG-98: Comparison with Hsp90 inhibitors and finding synergistic drug combinations

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

Translation inhibition corrects aberrant localization of mutant alanine-glyoxylate aminotransferase: possible therapeutic approach for hyperoxaluria

Primary hyperoxaluria type 1 is a severe kidney stone disease caused by abnormalities of the peroxisomal alanine-glyoxylate aminotransferase (AGT). The most frequent mutation G170R results in aberrant mitochondrial localization of the active enzyme. To evaluate the population of peroxisome-localized AGT, we developed a quantitative Glow-AGT assay based on the self-assembly split-GFP approach and used it to identify drugs that can correct mislocalization of the mutant protein. In line with previous reports, the Glow-AGT assay showed that mitochondrial transport inhibitors DECA and monensin increased peroxisomal localization of the mutant. Here, we demonstrate that prolonged treatment with the translation elongation inhibitor emetine, a medicinal alkaloid used in treatment of amoebiasis, corrected G170R-AGT mislocalization. Furthermore, emetine reduced the augmented oxalate level in culture media of patient-derived hepatocytes bearing the G170R mutation. A distinct translation inhibitor GC7 had a similar effect on the mutant Glow-AGT relocalization indicating that mild translation inhibition is a promising therapeutic approach for primary hyperoxaluria type 1 caused by AGT misfolding/mistargeting.Key messages• There is no effective conservative treatment to decrease oxalate production in PH1 patients.• Chemical chaperones rescue mislocalization of mutant AGT and reduce oxalate levels.• We have developed an assay for precise monitoring of the peroxisomal AGT.• Inhibition of translation by emetine reroutes the mutant protein to peroxisome.• Mild translation inhibition is a promising cure for conformational disorders.

p62 /SQSTM1 coding plasmid prevents age related macular degeneration in a rat model

P62/SQSTM1, a multi-domain protein that regulates inflammation, apoptosis, and autophagy, has been linked to age-related pathologies. For example, previously we demonstrated that administration of p62/SQSTM1-encoding plasmid reduced chronic inflammation and alleviated osteoporosis and metabolic syndrome in animal models. Herein, we built upon these findings to investigate effect of the p62-encoding plasmid on an age-related macular degeneration (AMD), a progressive neurodegenerative ocular disease, using spontaneous retinopathy in senescence-accelerated OXYS rats as a model. Overall, the p62DNA decreased the incidence and severity of retinopathy. In retinal pigment epithelium (RPE), p62DNA administration slowed down development of the destructive alterations of RPE cells, including loss of regular hexagonal shape, hypertrophy, and multinucleation. In neuroretina, p62DNA prevented gliosis, retinal thinning, and significantly inhibited microglia/macrophages migration to the outer retina, prohibiting their subretinal accumulation. Taken together, our results suggest that the p62DNA has a strong retinoprotective effect in AMD.