Biology subjects

Franckhauser, C.

Publications and source records attributed to Franckhauser, C..

4 recordsLinked to original sources

bioRxiv2025

Perilipin 4 repetitive region forms amyloid fibrils promoted by a genetic expansion found in myopathy patients

Lipid-binding amphipathic proteins play key roles in cellular organization, yet their conformational flexibility makes them prone to aggregation. Here we study the aggregation of perilipin 4 (PLIN4), a protein of the lipid droplet (LD)-binding perilipin family. PLIN4 contains an unusually long ([~]1000 amino acid, aa) amphipathic helix composed of tandem 33-aa repeats, which folds on the LD surface. A genetic expansion that increases the number of repeats is associated with skeletal muscle dysfunction in patients suffering from a late-onset vacuolar myopathy (MRUPAV). We show that the genetic expansion and the precise sequence of the 33 aa repeats do not significantly alter PLIN4 interaction with LDs in cells. By contrast, purified fragments of the PLIN4 repetitive region form amyloid fibrils as characterized by cryo-EM and atomic force microscopy. Repeat expansion strongly accelerates fibril formation, consistent with enhanced self-assembly driven by the accumulation of identical repeats. PLIN4 aggregation is attenuated by the presence of LDs, indicating that lipid binding modulates the balance between membrane association and self-assembly. Together, these results establish PLIN4 as a previously unrecognized amyloid-forming protein and suggest that repeat expansion enhances amyloidogenic self-assembly, providing a foundation for future studies of its role in degenerative muscle disease.

biochemistry↗

bioRxiv2024

Surface tension-driven sorting of human perilipins on lipid droplets

Perilipins (PLINs), the most abundant proteins on lipid droplets (LDs), display similar domain organization including amphipathic helices (AH). However, the five human PLINs bind different LDs suggesting different modes of interaction. We established a minimal system whereby artificial LDs covered with defined polar lipids were transiently deformed to promote surface tension. Binding of purified PLIN3 and PLIN4 AH was dependent on tension, even with polar lipids favoring packing defects, and showed an inverse correlation between protein and phospholipid densities on LDs. In contrast, PLIN1 bound readily to LDs fully covered by phospholipids; PLIN2 showed an intermediate behavior. In human adipocytes, PLIN3/4 were found in a soluble pool and relocated to LDs upon stimulation of triglyceride synthesis, whereas PLIN1 and PLIN2 localized to pre-existing LDs, consistent with the huge difference in LD avidity observed in vitro. We conclude that the PLIN repertoire is adapted to handling LDs with different surface properties. Significance statementLipid droplets (LDs) are highly dynamic organelles, whose size and surface properties vary during their life-time and also differ between different tissues. Here, we analyze the mode of binding of human perilipins (PLINs), the most abundant LD proteins, to LDs. We have developed a new reconstitution method, which shows that the purified PLIN family members have very different affinities for LDs, which might explain how they handle LDs of different dynamics in the cell.

biochemistry↗

bioRxiv2021

NF90 Interacts with Components of RISC and Modulates Association of Ago2 with mRNA

Nuclear Factor 90 (NF90) is a double-stranded RNA-binding protein involved in a multitude of different cellular mechanisms such as transcription, translation, viral infection and mRNA stability. Recent data suggest that NF90 might influence the abundance of target mRNAs in the cytoplasm through miRNA- and Argonaute 2 (Ago2)-dependent activity. Here, we identified the interactome of NF90 in the cytoplasm, which revealed several components of the RNA-induced silencing complex (RISC) and associated factors. Co-immunoprecipitation analysis confirmed the interaction of NF90 with the RISC-associated RNA helicase, Moloney leukemia virus 10 (MOV10), and other proteins involved in RISC-mediated silencing, including Ago2. Furthermore, NF90 association with MOV10 and Ago2 was found to be RNA-dependent. Glycerol gradient sedimentation of NF90 immune complexes indicates that these proteins occur in the same protein complex. At target RNAs predicted to bind both NF90 and MOV10 in their 3 UTRs, NF90 association was increased upon loss of MOV10 and vice versa, suggesting that the two proteins may compete for the binding of common target mRNAs. Interestingly, loss of NF90 led to an increase in association of Ago2 as well as a decrease in the abundance of the target mRNA. Similarly, during hypoxia, the binding of Ago2 to vascular endothelial growth factor (VEGF) mRNA increased after loss of NF90, while the level of VEGF mRNA decreased. These findings suggest a role for NF90 in the regulation of RISC-mediated silencing which stabilizes target mRNAs, such as VEGF, during cancer-induced hypoxia.

molecular biology↗

bioRxiv2020

Chromatin-associated MRN complex protects highly transcribing genes from genomic instability

The MRN-MDC1 complex plays a central role in the DNA damage response (DDR) and repair. Using Proteomics of Isolated Chromatin Fragments (PICh), we identified DDR factors, such as MDC1, among those that become highly associated with a genomic locus upon transcriptional activation. Purification of endogenous MDC1, in the absence of exogenous DNA damage, revealed its interaction with factors involved in gene expression and co-transcriptional RNA processing, in addition to DDR factors. ChIP-seq analysis showed that MDC1 interacting factors, MRE11 and NBS1 subunits of MRN, were co-localized throughout the genome and notably at TSSs and gene bodies of actively transcribing genes. Blockade of transcriptional elongation showed that binding of MRN was dependent on the RNAPII transcriptional complex rather than transcription per se. Depletion of MRN increased RNAPII abundance at TSSs and gene bodies of MRE11/NBS1-bound genes. Prolonged exposure of cells to either MRE11- or NBS1-depletion led to single nucleotide polymorphism formation across actively transcribing, MRE11 or NBS1 target genes. These data support a model by which association of the MRN complex with the transcriptional machinery constitutively scans active genes for transcription-induced DNA damage to preserve the integrity of the coding genome.

molecular biology↗