Cell Stress & Chaperones最新文献

Bone marrow contains abundant free fatty acids (FFA). Abnormal accumulation of FFAs can be triggered by pathological or physiologic conditions such as hyperlipidemia, diabetes mellitus, and menopause, leading to osteoporosis. Excess FFAs impair bone homeostasis by promoting osteoclast-mediated bone resorption and inhibiting the proliferation and differentiation of osteoblasts. C-type lectin domain family 11 member A (Clec11a) is an osteogenic growth factor that can protect islet proliferation and function against lipotoxicity. However, there is a lack of research on the function of Clec11a under bone marrow lipotoxic conditions. Here, we demonstrate that Clec11a counteracts the lipotoxicity-induced osteogenic inhibition and facilitates the proliferation and differentiation of osteoblasts. Clec11a effectively reverses palmitic acid(PA)-induced suppression of osteoblast proliferation and osteogenic differentiation, alleviates oxidative stress, and maintains mitochondrial homeostasis. Mechanistically, these protective effects of Clec11a depend on the SIRT3-SOD2 signaling axis, as the SIRT3 inhibitor 3-TYP abolishes its effects in both MC3T3-E1 cells and mouse bone marrow mesenchymal stem cells. Collectively, our findings reveal that Clec11a protects osteoblasts from PA-induced damage through regulation of the SIRT3-SOD2 signaling axis, providing mechanistic insights into bone impairment under lipotoxic conditions.

As the largest human organ, the skin experiences lifelong exposure to intrinsic/extrinsic factors that over time diminish its functional capacity and structural integrity. Skin aging involves cellular dysfunction and the loss or fragmentation of extracellular matrix (ECM) fibers, clinically presenting as wrinkles, slackening, and pigmentary abnormalities. The heat shock response (HSR) is a gene regulatory program that controls the expression of molecular chaperones associated with aging, cancer, and neurodegenerative disorders. By maintaining cellular homeostasis and facilitating DNA repair, HSR exerts protective effects against skin aging, as utilized in aesthetic technologies such as radiofrequency and focused ultrasound. This study aimed to investigate the mechanism, optimal conditions, and potential risks of short-term heat shock (HS) on the senescence process of human foreskin fibroblasts (HFF-1), providing experimental evidence to support the application of thermal stress in delaying skin aging. A replicative senescence model of HFF-1 cells was first established. Subsequently, cells were subjected to HS at 41 °C, 45 °C, and 49 °C, with a control group maintained at 37 °C. Assessments, including cell proliferation and viability assays, apoptosis analysis, reactive oxygen species (ROS) levels, Western blot, and heat shock proteins (HSPs) mRNA expression, demonstrated that 49 °C HS induced irreversible cellular damage. In contrast, 30min HS at 41 °C and 45 °C attenuated senescence-associated phenotypes to varying extents under our experimental conditions.

Heat shock protein 70 (HSP70) and its E3 ligase co-chaperone CHIP (STUB1) form a critical quality-control complex that directs client proteins toward folding or degradation. Phosphorylation of HSP70 at a conserved threonine in the C-terminal tail influences the fate of clients during cellular stress, yet the structural basis for this regulation remains unclear. Here, we present crystal structures of the CHIP tetratricopeptide repeat (TPR) domain bound to unphosphorylated and phosphorylated HSP70 C-terminal peptides at 1.6-1.9Å resolution. Phosphate occupancy at Thr636 (HSPA1A numbering) causes steric clashes and electrostatic repulsion within the TPR-binding groove, decreasing affinity by more than 10-fold, as shown by biolayer interferometry and fluorescence polarization. Molecular dynamics simulations confirm destabilization of key hydrogen bonds. A structure-guided G132N substitution in CHIP introduces new hydrogen bonds to the phosphate group, restoring affinity for phosphorylated peptides in isolated TPR domains without losing native ubiquitination activity. However, in full-length CHIP, interface modifications do not restore phosphorylation-impaired stable binding but yield only partial recovery of transient interactions in cells, indicating additional context-dependent constraints on HSP70-CHIP regulation. These findings reveal the atomic mechanism by which phosphorylation impairs HSP70-CHIP interaction during stress and demonstrate that targeted interface engineering can compensate for post-translational changes in isolated domains. Overall, the results explain how cells switch chaperone-mediated triage pathways and offer a framework for understanding how proteostasis becomes dysregulated in neurodegenerative diseases and cancer.

Heat shock protein 90 (Hsp90) is a highly conserved molecular chaperone that regulates the maturation of various client proteins. Most therapeutic studies have focused on N-terminal Hsp90 inhibitors, but these are limited by dose-escalating toxicities that are caused by induction of the heat shock response. Leonard Neckers' discovery of novobiocin as a Hsp90 C-terminal inhibitor revealed an alternative mode to Hsp90 inhibition and established the C-terminal domain (CTD) as a therapeutic target. This review highlights recent advances in Hsp90 CTD inhibition and summarizes the evolution of novobiocin-based C-terminal inhibitors. Structure-activity relationship studies are discussed, demonstrating how medicinal chemistry optimization has produced CTD modulators with selective anti-proliferative or neuroprotective activities.

Hsp90 is an abundant and essential molecular chaperone that is required for the folding and/or activity of up to 15%-20% of all yeast proteins. Hsp90 and its cochaperone Cdc37 are of interest due to their cooperative role in chaperoning oncogenic protein kinases. We previously grouped mutants in Saccharomyces cerevisiae Hsp90 into different categories based on the step of the adenosine triphosphate-dependent Hsp90 folding cycle that is disrupted. Here we used a quantitative proteomic approach to compare the impact of two different mutations that target the initial step of loading clients onto Hsp90, one in Hsp90 and one in Cdc37. We also included two Hsp90 mutants that target other steps in the folding pathway. We tested the effects at either 25°C or after a 1-h heat shock at 37°C. As expected, the Cdc37 mutant and the Hsp90 mutant that affects the loading step had similar effects, particularly on protein kinases, demonstrating the potential for using proteomics for testing the impact of alteration of the folding pathway. We also identified non-kinase proteins that may use a similar Cdc37-mediated pathway. Surprisingly, protein kinases were a small subset of the proteins impacted by Cdc37 alteration, challenging the notion that Cdc37 is a kinase-specific cochaperone. We also identified proteins that were most strongly affected by Hsc82 mutants that impact steps other than the loading step. Further analysis of how Hsp90 and cochaperones interact with these additional proteins may provide novel insights into alternative methods of client loading or other poorly understood steps in the folding cycle.