Biology subjects

Pajares, M. A.

Publications and source records attributed to Pajares, M. A..

7 recordsLinked to original sources

bioRxiv2024

Lysosomal function, resistance to stress and repair are compromised by expression of the Alexander disease GFAP R239C mutant

Intermediate filaments are critical regulators of cell responses and organizers of cellular structures. GFAP (glial fibrillary acidic protein) is an intermediate filament protein mainly expressed in astrocytes. GFAP mutations are associated with Alexander disease (AxD), a type of leukodystrophy that causes degeneration of astrocytes and ultimately neurodegeneration. AxD astrocytes display protein aggregation, proteostasis defects and altered organelle homeostasis. We previously showed that expression of GFAP AxD mutants in astrocytes provoked mitochondrial alterations and oxidative stress. Here we have used an astrocytoma cell model to explore the impact of GFAP AxD mutants on the lysosomal degradation pathway. Expression of GFAP AxD mutants in this model elicits marked alterations in lysosomal distribution. Cells expressing the GFAP R239C mutant display defective lysosomal activity and intraluminal acidification. Lysosomes are primary sites of oxidative damage. Moreover, expression of GFAP R239C increases susceptibility of lysosomes to oxidative stress, resulting in a greater loss of lysosomal "mass" and compromised membrane integrity, as revealed by increased intraluminal recruitment of galectins, with respect to cells expressing GFAP wt. Notably, lysosomes in GFAP R239C expressing cells are also more vulnerable to chemically-induced rupture. Interestingly, lysosomes of cells expressing GFAP wt are able to rapidly recover after removal of the damaging agent. In sharp contrast, recovery of acidic vesicles is severely impaired in cells expressing GFAP R239C, suggesting a defect in lysosomal repair. Taken together, our results show that expression of the GFAP AxD mutant is sufficient to deeply perturb lysosomal distribution, function and repair. These alterations could contribute to proteostasis defects and cellular toxicity in AxD.

cell biology↗

bioRxiv2023

Intracellular pH modulates vimentin remodeling in response to oxidants

Vimentin plays key roles in cell mechanosensing, cytoskeletal crosstalk and stress responses, and is finely tuned by posttranslational modifications. The vimentin single cysteine residue, C328, is a hotspot for modification and essential for filament remodeling by oxidants and electrophiles. With a pKa near physiological pH, C328 reactivity could be sensitive to cellular pH fluctuations. Here, we show that C328 modifications and vimentin reorganization by various reactive agents are modulated in response to pH variations. Lowering intracellular pH prevents, whereas intracellular alkalinization potentiates vimentin network disruption by oxidative and electrophilic species, including diamide, hydrogen peroxide and hydroxynonenal. The protective effect associated with low pH is selective for vimentin since it does not preclude oxidant-elicited disruption of actin or tubulin structures. Vimentin C328A and C328H mutants are resistant to disruption under all pH conditions, which highlights the importance of the thiol group at this position for the sensitizing effect of alkaline pH. Chemogenetic and optogenetic modulation of cellular pH allow spatiotemporal tuning of vimentin susceptibility to oxidants, suggesting the potential role of pH in the regulation of vimentin organization at precise locations. Alkalinization and generation of reactive oxygen species cooperate at the cell front during migration. We show that vimentin disassembly at cell edges of migrating fibroblasts, and lamellipodia formation, are affected by pH changes and the presence of C328. We propose that vimentin C328 could behave as a coincidental pH and redox responsive element, contributing to the precise regulation of vimentin assembly by the concert of these factors, illustrating the pH dependence of cysteine-mediated redox signaling.

cell biology↗

bioRxiv2023

Vimentin cysteine 328 modifications finely tune network organization and influence actin remodeling under oxidative and electrophilic stress

Cysteine residues can undergo multiple posttranslational modifications with diverse functional consequences, potentially behaving as tunable sensors. The intermediate filament protein vimentin has important implications in pathophysiology, including cancer progression, infection, and fibrosis, and maintains a close interplay with other cytoskeletal structures, such as actin filaments and microtubules. We previously showed that the single vimentin cysteine, C328, is a key target for oxidants and electrophiles. Here, we demonstrate that structurally diverse cysteine-reactive agents, including electrophilic mediators, oxidants and drug-related compounds, disrupt the vimentin network eliciting morphologically distinct reorganizations. As most of these agents display broad reactivity, we pinpointed the importance of C328 by confirming that local perturbations introduced through mutagenesis provoke structure-dependent vimentin rearrangements. Thus, GFP-vimentin wild type (wt) forms squiggles and short filaments in vimentin-deficient cells, the C328F, C328W, and C328H mutants generate diverse filamentous assemblies, and the C328A and C328D constructs fail to elongate yielding dots. Remarkably, vimentin C328H structures resemble the wt, but are strongly resistant to electrophile-elicited disruption. Therefore, the C328H mutant allows elucidating whether cysteine-dependent vimentin reorganization influences other cellular responses to reactive agents. Electrophiles such as 1,4-dinitro-1H-imidazole and 4-hydroxynonenal induce robust actin stress fibers in cells expressing vimentin wt. Strikingly, under these conditions, vimentin C328H expression blunts electrophile-elicited stress fiber formation, apparently acting upstream of RhoA. Analysis of additional vimentin C328 mutants shows that electrophile-sensitive and assembly-defective vimentin variants permit induction of stress fibers by reactive species, whereas electrophile-resistant filamentous vimentin structures prevent it. Together, our results suggest that vimentin acts as a break for actin stress fibers formation, which would be released by C328-aided disruption, thus allowing full actin remodeling in response to oxidants and electrophiles. These observations postulate C328 as a "sensor" transducing structurally diverse modifications into fine-tuned vimentin network rearrangements, and a gatekeeper for certain electrophiles in the interplay with actin.

cell biology↗

bioRxiv2021

Immunolocalization studies of vimentin and ACE2 on the surface of cells exposed to SARS-CoV-2 Spike proteins

The Spike protein from SARS-CoV-2 mediates docking of the virus onto cells and contributes to viral invasion. Several cellular receptors are involved in SARS-CoV-2 Spike docking at the cell surface, including ACE2 and neuropilin. The intermediate filament protein vimentin has been reported to be present at the surface of certain cells and act as a co-receptor for several viruses; furthermore, its potential involvement in interactions with Spike proteins has been proposed. Here we have explored the binding of Spike protein constructs to several cell types using low-temperature immunofluorescence approaches in live cells, to minimize internalization. Incubation of cells with tagged Spike S or Spike S1 subunit led to discrete dotted patterns at the cell surface, which showed scarce colocalization with a lipid raft marker, but consistent coincidence with ACE2. Under our conditions, vimentin immunoreactivity appeared as spots or patches unevenly distributed at the surface of diverse cell types. Remarkably, several observations including potential antibody internalization and adherence to cells of vimentin-positive structures present in the extracellular medium exposed the complexity of vimentin cell surface immunoreactivity, which requires careful assessment. Notably, overall colocalization of Spike and vimentin signals markedly varied with the cell type and the immunodetection sequence. In turn, vimentin-positive spots moderately colocalized with ACE2; however, a particular enrichment was detected at elongated structures positive for acetylated tubulin, consistent with primary cilia, which also showed Spike binding. Thus, these results suggest that vimentin-ACE2 interaction could occur at selective locations near the cell surface, including ciliated structures, which can act as platforms for SARS-CoV-2 docking.

cell biology↗

bioRxiv2021

Elucidating vimentin interaction with zinc ions and its interplay with oxidative modifications through crosslinking assays and molecular dynamics simulations

The intermediate filament protein vimentin is involved in essential cellular processes, including cell division and stress responses. Vimentin oxidative modifications impact network reorganization and its single cysteine residue, Cys328, acts as a redox sensor. Vimentin binds zinc, which influences its assembly by undefined mechanisms. Here, results from combined biochemical and molecular dynamics studies support that zinc ions interact with Cys328 in its thiolate form, whereas Glu329 and Asp331 stabilize zinc coordination. Vimentin oxidation can induce disulfide crosslinking, implying a close proximity of cysteine residues in certain vimentin associations, validated by our computational models. Notably, micromolar zinc concentrations selectively prevent Cys328 alkylation and crosslinking. These effects are not mimicked by magnesium, consistent with the fewer magnesium ions hosted at the cysteine region. Altogether, our results pinpoint the region surrounding Cys328, highly conserved in type III intermediate filaments, as a hot spot for zinc binding, which modulates Cys328 reactivity and vimentin assembly.

biochemistry↗

bioRxiv2019

Amoxicillin inactivation by thiol-catalyzed cyclization reduces protein haptenation and antibacterial potency

Serum and cellular proteins are targets for the formation of adducts with the {beta}-lactam antibiotic amoxicillin. This process could be important for the development of adverse, and in particular, allergic reactions to this antibiotic. In studies exploring protein haptenation by amoxicillin, we observed that reducing agents influenced the extent of amoxicillin-protein adducts formation. Consequently, we show that thiol-containing compounds, including dithiothreitol, N-acetyl-L-cysteine and glutathione, perform a nucleophilic attack on the amoxicillin molecule that is followed by an internal rearrangement leading to amoxicillin diketopiperazine, a known amoxicillin metabolite with residual activity. The effect of thiols is catalytic and can render complete amoxicillin conversion. Interestingly, this process is dependent on the presence of an amino group in the antibiotic lateral chain, as in amoxicillin and ampicillin. Furthermore, it does not occur for other {beta}-lactam antibiotics, including cefaclor or benzylpenicillin. Biological consequences of thiol-mediated amoxicillin transformation are exemplified by a reduced bacteriostatic action and a lower capacity of thiol-treated amoxicillin to form protein adducts. Finally, modulation of the intracellular redox status through inhibition of glutathione synthesis influenced the extent of amoxicillin adduct formation with cellular proteins. These results open novel perspectives for the understanding of amoxicillin metabolism and actions, including the formation of adducts involved in allergic reactions.

pharmacology and toxicology↗

bioRxiv2018

Vimentin filaments interact with the mitotic cortex allowing normal cell division

The vimentin network displays remarkable plasticity to support basic cellular functions. Here, we show that in several cell types vimentin filaments redistribute to the cell periphery during mitosis, forming a robust scaffold interwoven with cortical actin and affecting the mitotic cortex properties. Importantly, the intrinsically disordered tail domain of vimentin is essential for this redistribution, which allows normal mitotic progression. A tailless vimentin mutant forms curly bundles, which remain entangled with dividing chromosomes leading to mitotic catastrophes or asymmetric partitions. Serial deletions of the tail domain induce increasing impairments of cortical association and mitosis progression. Disruption of actin, but not of microtubules, mimics the impact of tail deletion. Pathophysiological stimuli, including HIV-protease and lipoxidation, induce similar alterations. Interestingly, filament integrity is dispensable for cortical association, which also occurs in vimentin particles. These results unveil novel implications of vimentin dynamics in cell division by means of its interplay with the mitotic cortex.

cell biology↗