Biology subjects

Boban, M.

Publications and source records attributed to Boban, M..

3 recordsLinked to original sources

bioRxiv2026

Proteasome-dependent degradation and nucleus-vacuole junctions sustain proteostasis during acute glucose starvation

How protein quality control is maintained during acute metabolic stress remains poorly understood. In budding yeast, abrupt glucose depletion rapidly lowers ATP levels and leads to the formation of chaperone-containing inclusions, suggesting that ATP-dependent degradation of misfolded proteins may be compromised when energy becomes limiting. Here we find that selective degradation of misfolded proteins remains active during acute glucose starvation despite reduced cellular ATP levels. Using model misfolded substrates in yeast Saccharomyces cerevisiae, we show that misfolded proteins continue to be efficiently degraded throughout both early and late phases of acute glucose depletion. This degradation requires the proteasome and depends on its functional 19S regulatory particle, indicating that ATP-dependent proteasomal activity persists during metabolic stress. We further find that nucleus-vacuole junctions (NVJs) promote efficient degradation during prolonged glucose starvation, revealing a role for organelle contact sites in supporting proteostasis under energy limitation. Together, these findings indicate that cells preserve proteasome-mediated proteostasis during acute glucose starvation, while NVJ membrane contact sites help sustain degradation capacity when metabolic resources are scarce.

cell biology↗

bioRxiv2024

Quiescent cells maintain active degradation-mediated protein quality control requiring proteasome, autophagy and nucleus-vacuole junctions

Many cells spend a major part of their life in quiescence, a reversible state characterized by a distinct cellular organization and metabolism. In glucose-depleted quiescent yeast cells, there is a metabolic shift from glycolysis to mitochondrial respiration, and a large fraction of proteasomes are reorganized into cytoplasmic granules containing disassembled particles. Given these changes, the operation of protein quality control (PQC) in quiescent cells, in particular the reliance on degradation-mediated PQC and the specific pathways involved, remains unclear. By examining model misfolded proteins expressed in glucose-depleted quiescent yeast cells, we found that misfolded proteins are targeted for selective degradation requiring functional 26S proteasomes. This indicates that a significant pool of proteasomes remains active in degrading quality control substrates. Misfolded proteins were degraded in a manner dependent on the E3 ubiquitin ligases Ubr1 and San1, with Ubr1 playing a dominant role. In contrast to exponentially growing cells, the efficient clearance of certain misfolded proteins additionally required intact nucleus-vacuole junctions (NVJ) and Cue5-independent selective autophagy. Our findings suggest that proteasome activity, autophagy, and NVJ-dependent degradation operate in parallel. Together the data demonstrate that quiescent cells maintain active PQC that relies primarily on selective protein degradation. The necessity of multiple degradation pathways for the removal of misfolded proteins during quiescence underscores the importance of misfolded protein clearance in this cellular state.

cell biology↗

bioRxiv2018

Human neuroblastoma SH-SY5Y cells treated with okadaic acid express phosphorylated high molecular weight tau immunoreactive protein species

Recent data suggest that early stages of Alzheimers disease (AD) are characterized by an abnormally high phosphorylation of microtubule-associated protein tau and truncation of its C-terminus. Tau hyperphosphorylation may result from the downregulation of phosphatases, especially protein phosphatase 2A. In an attempt to model and analyze these molecular events we treated SH-SY5Y cells with okadaic acid (OA), an inhibitor of protein phosphatases. In addition to the low molecular weight tau, such treatment lead to the appearance of heat-stable protein species with apparent high molecular weight around 100 kDa, which were immunoreactive to tau antibodies against phosphorylated Ser202 and phosphorylated Ser396. Based on the observation that high molecular weight tau-immunoreactive proteins (HMW-TIP) correspond to the predicted size of two monomers of tau, one possibility is that HMW-TIP represent tau oligomers. The absence of HMW-TIP detection by anti-total tau antibodies used may be a consequence of epitope masking, or a combination of epitope masking and protein truncation. We noted the stability of HMW-TIP in the presence of strong denaturing agents, such as urea and guanidine, as well as upon partial dephosphorylation by the alkaline phosphatase. Moreover, as HMW-TIP did not dissociate the presence of {beta}-mercaptoethanol, it was also independent from disulfide bonds. Taken together, these data show that OA treatment of SH-SY5Y cells induces the appearance of HMW-TIP, which may represent tau oligomer or tau-crossreactive phospho-proteins. Our findings have implications for further studies of tau under the conditions of protein phosphatase downregulation.

neuroscience↗