Biology subjects

Kampinga, H. H.

Publications and source records attributed to Kampinga, H. H..

10 recordsLinked to original sources

bioRxiv2026

The Heat shock protein 70 machinery is crucial in the production of infectious chikungunya virus progeny

Over the past decades, chikungunya virus (CHIKV), a re-emerging arthropod-borne alphavirus, has caused outbreaks in many (sub)tropical regions, but also in more temperate regions of the world, including Europe. CHIKV poses a significant health burden due to high infection rates during epidemics, symptom progression into chronic arthritic manifestations, and the lack of specific antiviral treatments. Multiple studies have shown that several viruses rely on host molecular chaperones, particularly the central Heat shock protein 70 (Hsp70), for replication. Hsp70s are guided by co-chaperones that drive their functionality and specificity. Here, we used chemical inhibitors of Hsp70-co-chaperone interactions to study the role of this molecular chaperone machinery in CHIKV replication. Our findings revealed that Hsp70 inhibition significantly reduces the CHIKV infectious particle production without affecting host-cell viability. Inhibition of the Hsp70-co-chaperone interaction primarily impedes the post-RNA replication stages of the CHIKV infectious cycle, affecting viral protein expression and reducing both the number and infectivity of released virions. Moreover, Hsp70 inhibition displayed antiviral activity in skin explants. Together, these results suggest that targeting the Hsp70 network could be a viable antiviral strategy against CHIKV infections. Author summaryAs obligatory intracellular parasites, viruses rely entirely on the machinery of the host cell to produce new viral particles. In our study, we investigated whether a specific group of host proteins, known as molecular chaperones, is important for the replication of chikungunya virus (CHIKV), a reemerging mosquito-borne virus that can cause long-lasting joint pains and lacks specific antiviral treatments. We focused on one key family of molecular chaperones, called Heat shock protein 70s (Hsp70s), which supports protein folding and quality control in cells. We used chemical compounds to block Hsp70 function and observed that CHIKV replication was strongly reduced, while host cells remained healthy. We found that Hsp70 is especially important in the later stages of the virus life cycle, where it helps produce viral proteins and new infectious virus particles. When Hsp70 was blocked, fewer and less infectious virus particles were produced. We also showed that this effect holds true in biopsies of mouse skin tissue, which mimics the initial site of infection. These findings identify Hsp70 as an important host factor for CHIKV that may serve as a potential target for new antiviral therapies.

microbiology↗

bioRxiv2023

Tertiary structure and conformational dynamics of the anti-amyloidogenic chaperone DNAJB6b at atomistic resolution

DNAJB6b is a molecular chaperone of the heat shock protein network, shown to play a crucial role in preventing aggregation of several disease-related intrinsically disordered proteins. Despite its importance in maintaining cellular homeostasis, the structure-functional relationship of DNAJB6b is not yet known. Using homology modeling and microsecond-long all-atom molecular dynamics (MD) simulations, we show that monomeric DNAJB6b is a transiently interconverting protein cycling between three states: a closed state, an open state (both abundant), and a novel, less abundant extended state. Interestingly, the reported regulatory autoinhibitory anchor between helix V in the G/F1 region and helices II/III of the J-domain, which obstructs the access of Hsp70 to the J-domain remains present in all three states. This possibly suggests a mechanistically intriguing regulation in which DNAJB6b only becomes exposed when loaded with substrates that require Hsp70 processing. Our MD results of DNAJB6b carrying mutations in the G/F1 region that are linked to limb-girdle muscular dystrophy type D1 (LGMDD1) show that this G/F1 region becomes highly dynamic, pointing towards a spontaneous release of the autoinhibitory helix V from helices II/III. This would increase the probability of non-functional Hsp70 interactions to DNAJB6b without substrates. Our cellular data indeed confirm that non-substrate loaded LGMDD1 mutants have aberrant interactions with Hsp70.

biophysics↗

bioRxiv2023

DNAJB8 oligomerization is mediated by an aromatic-rich motif that is dispensable for substrate activity

J-domain protein (JDP) molecular chaperones have emerged as central players that maintain a healthy proteome. The diverse members of the JDP family function as monomers/dimers and a small subset assemble into micron-sized oligomers. The oligomeric JDP members have eluded structural characterization due to their low-complexity, intrinsically disordered middle domains. This in turn, obscures the biological significance of these larger oligomers in protein folding processes. Here, we identified a short, aromatic motif within DNAJB8, that drives self-assembly through {nu}-{nu} stacking and determined its X-ray structure. We show that mutations in the motif disrupt DNAJB8 oligomerization in vitro and in cells. DNAJB8 variants that are unable to assemble bind to misfolded tau seeds more specifically and retain capacity to reduce protein aggregation in vitro and in cells. We propose a new model for DNAJB8 function in which the sequences in the low-complexity domains play distinct roles in assembly and substrate activity. HIGHLIGHTSDNAJB8 oligomerization is mediated by a short phenylalanine-based motif in the S/T domain Mutation of a single phenylalanine yields a monomeric form of DNAJB8 Monomeric DNABJ8 binds to an aggregation-prone substrate Monomeric DNAJB8 retains substrate aggregation prevention activity

biophysics↗

bioRxiv2022

Nuclear poly-glutamine aggregates rupture the nuclear envelope and hinder its repair

Huntingtons disease (HD) is caused by a poly-glutamine expansion of the huntingtin protein, resulting in the formation of poly-glutamine aggregates. The mechanisms of toxicity that result in the complex HD pathology remain only partially understood. Here we show that nuclear polyglutamine aggregates deform the nuclear envelope (NE) and induce NE ruptures that are often repaired incompletely. These ruptures coincide with deformations of the nuclear lamina and lead to lamina scar formation. Expansion microscopy enabled resolving the ultrastructure of nuclear aggregates and revealed polyglutamine fibrils sticking into the cytosol at rupture sites, suggesting a mechanism for incomplete repair. These findings implicate nuclear polyQ aggregate-induced loss of NE integrity as a potential contributing factor to Huntingtons disease and other polyglutamine diseases. One-sentence summaryAggregates associated with Huntingtons Disease induce ruptures of the nuclear envelop that compromise its barrier function

cell biology↗

bioRxiv2022

In vivo suppression of polyglutamine aggregation via co-condensation of the molecular chaperone DNAJB6

Amyloidogenic protein aggregation is a hallmark of several human neurodegenerative conditions, including Alzheimers, Parkinsons, and Huntingtons disease (HD). Mutations and/or environmental stresses trigger conformational transition of specific proteins to amyloids, conferring them with gain of toxic function, which eventually leads to cell death in distinct brain areas. Cumulative data indicate that modulation of specific molecular chaperones can alleviate many of the pathological features of protein aggregation diseases. We previously showed that the Hsp70 co-chaperone DNAJB6 is among the strongest suppressors of amyloid aggregation, and that moderate DNAJB6 overexpression significantly extents lifespan of a mouse model of aggressive HD pathology. DNAJB6 alone delays amyloidogenic aggregation in vitro by several orders of magnitude at substoichiometric ratios, but its activity in cells is less efficient, albeit still markedly superior to most known anti-amyloidogenic agents. This suggests that downstream PQC factors are necessary for full DNAJB6-mediated suppression of aggregation in vivo, which might have to be co-stimulated in therapeutic strategies targeting DNAJB6 action. We explored here the PQC pathways required for optimal DNAJB6 inhibition of polyglutamine (polyQ) aggregation, focusing on the two main cellular proteolytic machineries: proteasomes and macroautophagy. Unexpectedly, DNAJB6 activity was largely insensitive to chemical blockage of either degradative pathway. Instead, live cell imaging unveiled a co-condensation mechanism of DNAJB6 with mobile polyQ assemblies. DNAJB6 was not required for polyQ condensation, but its expression increased the percentage of cells with mobile condensates by a factor of 3, suggesting that DNAJB6 prevents polyQ condensates to convert from the soluble to the solid state. This in turn, may keep the polyQ peptides competent for (regulated) degradation and accessible to factors allowing its extraction from the condensed state.

cell biology↗

bioRxiv2022

Cellular aging impedes stress-activation of a crucial JDP-Hsp70 protein disaggregase

The collapse of protein homeostasis manifests itself in a toxic protein aggregation cascade, which is associated with degenerative diseases and aging. To solubilize aggregates, dedicated protein disaggregases exist in unicellular organisms, but these have no nuclear/cytosolic orthologs in metazoa. Alternative metazoan disaggregation machines have been described, but how these are operated and regulated in vivo remained unknown. We show that protein disaggregases are functionally diversified in human cells to efficiently target different types of stress-induced aggregates in sequential and temporally distinct phases. In particular, we show the selective assembly of an Hsp70-DNAJA1-DNAJB1 trimeric disaggregase that forms during late phase of stress recovery., i.e., after VCP-dependent solubilization of non-native proteins that accumulate in cellular condensates such as nucleoli or stress granules. When activated, the trimeric disaggregase provides resistance to stress toxicity and contributes to amyloid disposal. Strikingly, this disaggregase collapses early in cells undergoing replicative aging with important underlining pathophysiological consequences.

cell biology↗

bioRxiv2021

The molecular chaperone DNAJB6 provides surveillance of FG-Nups and is required for interphase nuclear pore complex biogenesis

Biogenesis of nuclear pore complexes (NPCs) includes the formation of the permeability barrier composed of phenylalanine-glycine-rich nucleoporins (FG-Nups) that regulate the selective passage/crossing of biomolecules. The FG-Nups are intrinsically disordered and prone to liquid-liquid phase separate1,2 and aggregate when isolated3. It has remained largely unclear how FG-Nups are protected from making inappropriate interactions during NPC biogenesis. We found that DNAJB6, a molecular chaperone of the heat shock protein network, formed foci next to NPCs. The number of these foci decreases upon removal of proteins involved in the early steps of interphase NPC biogenesis. Reversely, when this process is stalled in the last steps, the number of DNAJB6-containing foci increases and they could be identified as herniations at the nuclear envelope (NE). Immunoelectron tomography showed that DNAJB6 localizes inside the lumen of the herniations arising at NPC biogenesis intermediates. Interestingly, loss of DNAJB6 results in annulate lamellae, which are structures containing partly assembled NPCs associated with disturbances in NPC biogenesis. We find that DNAJB6 binds to FG-Nups and can prevent the aggregation of the FG-region of several FG-Nups in cells and in vitro. Together, our data show that DNAJB6 provides quality control during NPC biogenesis and is the first molecular chaperone that is involved in the surveillance of native intrinsically disordered proteins, including FG-Nups.

molecular biology↗

bioRxiv2021

Targeting DNA topoisomerases or checkpoint kinases results in an overload of chaperone systems, triggering aggregation of a metastable subproteome

A loss of the checkpoint kinase ATM leads to impairments in the DNA damage response, and in humans causes cerebellar neurodegeneration, and a high risk to cancer. A loss of ATM is also associated with increased protein aggregation. The relevance and characteristics of this aggregation are still incompletely understood. Moreover, it is unclear to what extent other genotoxic conditions can trigger protein aggregation as well. Here, we show that targeting ATM, but also ATR or DNA topoisomerases result in a similar, widespread aggregation of a metastable, disease-associated subfraction of the proteome. Aggregation-prone model substrates, including Huntingtin exon1 containing an expanded polyglutamine repeat, aggregate faster under these conditions. This increased aggregation results from an overload of chaperone systems, which lowers the cell-intrinsic threshold for proteins to aggregate. In line with this, we find that inhibition of the HSP70 chaperone system further exacerbates the increased protein aggregation. Moreover, we identify the molecular chaperone HSPB5 as a potent suppressor of it. Our findings reveal that various genotoxic conditions trigger widespread protein aggregation in a manner that is highly reminiscent of the aggregation occurring in situations of proteotoxic stress and in proteinopathies.

molecular biology↗

bioRxiv2021

Salt Inducible Kinase activation and IRE1-dependent intracellular ATP depletion to form Sec bodies in Drosophila cells.

The phase separation of the non-membrane bound Sec bodies occurs in Drosophila S2 cells by coalescence of components of the ER exit sites under the stress of amino-acid starvation. Here we address which signaling pathways cause Sec body formation. We find that two pathways are critical. The first is a SIK dependent pathway induced by salt (NaCl) stress in a necessary and sufficient manner. The second is the activation of IRE1 (one of the key kinases mediating the Unfolded Protein Response) by absence of amino- acids, which partly leads to the depletion of intracellular ATP. However, IRE1 activation is not sufficient to induce Sec body formation and needs to be combined to salt stress. This works pioneers the role of SIK in phase transition and re-enforces the role of IRE1 as a metabolic sensor for the level of circulating amino-acids.

cell biology↗

bioRxiv2020

DNAJB chaperones inhibit aggregation of destabilised proteins via a C-terminal region distinct from that used to prevent amyloid formation

Disturbances to protein homeostasis (proteostasis) can lead to protein aggregation and inclusion formation, processes associated with a variety of neurodegenerative disorders. DNAJBs are molecular chaperones previously identified as potent suppressors of disease-related protein aggregation. In this work, we over-expressed a destabilised isoform of firefly luciferase (R188Q/R261Q Fluc; FlucDM) in cells to assess the capacity of DNAJBs to inhibit inclusion formation. Co-expression of all DNAJBs tested significantly inhibited the intracellular aggregation of FlucDM. Moreover, we show that DNAJBs suppress aggregation by supporting the Hsp70-dependent degradation of FlucDM via the proteasome. The serine-rich stretch in DNAJB6 and DNAJB8, essential for preventing fibrillar aggregation, is not involved in the suppression of FlucDM inclusion formation. Conversely, deletion of the C-terminal TTK-LKS region in DNAJB8, a region not required to suppress polyQ aggregation, abolished its ability to inhibit inclusion formation by FlucDM. Thus, our data suggest that DNAJB6 and DNAJB8 possess two distinct domains involved in the inhibition of protein aggregation, one responsible for binding to {beta}-hairpins that form during amyloid formation and another that mediates the degradation of destabilised client proteins via the proteasome. Summary statementSpecialised DNAJB molecular chaperones are potent suppressors of protein aggregation and interact with different types of client proteins via distinct C-terminal regions

cell biology↗