Ignarski, M. | Search bioRxiv

bioRxiv2024

A VHL-1/HIF-1/SQRD1/COL-88 axis links extracellular matrix formation with longevity in Caenorhabditis elegans

The extracellular matrix (ECM) is a pivotal three-dimensional network crucial for tissue organization, cellular communication, and fundamental cellular processes, where collagens are the major chemical entity in amount. ECM deregulation is directly involved with several pathologies, such as tumour growth and invasiveness, atherosclerosis, and diabetic nephropathy. Mutations in the von Hippel-Lindau tumour suppressor (pVHL) cause VHL syndrome, a multi-tumour syndrome commonly associated with clear cell renal carcinoma (ccRCC). Loss of pVHL is associated with the activation of hypoxia-inducible factor (HIF) signaling. Mutation of VHL-1 in the nematode Canorhabditis elegans has been shown to increase lifespan and stress resistance. Interestingly, considering recent findings on the involvement of collagens in the regulation of lifespan, we also observed these animals to show defects in body morphology in a HIF-1 dependent manner. Based on this finding, we established a link between HIF-1 activation upon loss of VHL-1 and ECM defects associated with alterations in collagen expression. An RNAi screen examining genes upregulated in vhl-1 mutant worms revealed the sulfide quinone oxidoreductase sqrd-1 to mediate the change in body morphology. SQRD-1 is essential to the HIF-1 dependent increase in several collagen genes. One of these genes, col-88, partly mediates both the impact of loss of VHL-1 on lifespan extension and body length. The downregulation of the uncharacterised col-88 partially restores lifespan extension and reduces body size of vhl-1/sqrd-1 to vhl-1(ok161) single mutant. This study contributes to the increasing body of evidence linking lifespan extension and the ECM and now implicates this axis in hypoxia-signaling. These findings are of special interest considering the role of ECM integrity in tumour growth and metastasis. Author SummaryThe extracellular matrix and its composing collagens are associated with a wide number of diseases, including cancer. The von Hippel-Lindau tumour suppressor (pVHL) is known to work by regulating the Hypoxia Inducible Factor (HIF) to help the organism to adapt to lack of oxygen. Mutations in pVHL are associated with clear cell renal carcinoma (ccRCC). Interestingly, a small number of studies have shown that pVHL can be directly associated with collagens, a function that is independent of its classical role regulating HIF. However, there is no further knowledge about which role the hypoxia pathway has when it comes to extracellular matrix formation and function, what would be useful since the invasiveness of cancers, such as ccRCC, are directly connected to their matrix/collagen composition. Here we observed that the model organism C. elegans has drastically different collagen composition and body size upon a mutation on its vhl-1 gene. Furthermore, a protein previously only known to be involved in sulfide metabolism, SQRD-1, connects body size and lifespan in this animal model, revealing a surprising link between the hypoxia pathway and sulfur metabolism to control lifespan. Further studies could target sulfur metabolism in ccRCC to modulate collagen production and tumour invasiveness.

genetics↗

bioRxiv2022

RNA-mediated nucleosome depletion is required for elimination of transposon-derived DNA.

Small RNAs are known to mediate silencing of transposable elements and other genomic loci, increasing nucleosome density and preventing undesirable gene expression. Post-zygotic development of the Paramecium somatic genome requires elimination of thousands of transposon remnants (IESs) and transposable elements that are scattered throughout the germline genome (Garnier et al. 2004). The elimination process is guided by Piwi-associated small RNAs and leads to precise cleavage at IES boundaries (Bouhouche et al. 2011; Furrer et al. 2017). Previous research suggests that small RNAs induce heterochromatin formation within IESs, which, in turn, is required for DNA elimination (Liu et al. 2007). Here we show that IES recognition and precise excision is facilitated by recruitment of a homolog of a chromatin remodeler ISWI, which depletes target genomic regions of nucleosomes, making the chromatin accessible for DNA cleavage. ISWI knockdown in Paramecium leads to pronounced inhibition of DNA elimination. Furthermore, nucleosome profiling indicates that ISWI is required for IES elimination in nucleosome-dense genomic regions, while other IESs do not require small RNAs or ISWI for excision. ISWI silencing notably also reduces DNA elimination precision, resulting in aberrant excision at alternative IES boundaries. In summary, we demonstrate that chromatin remodeling that increases DNA accessibility together with small RNAs are necessary for efficient and precise DNA elimination in Paramecium.

molecular biology↗

bioRxiv2018

The RNA-binding protein AATF coordinates rRNA maturation

AATF is a central regulator of the cellular outcome upon p53 activation, a finding that has primarily been attributed to its function as a transcription factor. Recent data showed that AATF is essential for ribosome biogenesis and plays a role in rRNA maturation. AATF has been implicated to fulfil this role through direct interaction with rRNA and was identified in several RNA-interactome capture experiments. Here, we provide a first comprehensive analysis of the RNA bound by AATF using CLIP-sequencing. Interestingly, this approach shows predominant binding of the 45S pre-ribosomal RNA precursor molecules. Furthermore, AATF binds to mRNAs encoding for ribosome biogenesis factors as well as snoRNAs. These findings are complemented by an in-depth analysis of the protein interactome of AATF containing a large set of proteins known to play a role in rRNA maturation with an emphasis on the protein-RNA-complexes known to be required for the generation of the small ribosomal subunit (SSU). In line with this finding, the binding sites of AATF within the 45S rRNA precursor localize in close proximity to the SSU cleavage sites. Consequently, our multilayer analysis of the protein-RNA interactome of AATF reveals this protein to be an important hub for protein and RNA interactions involved in ribosome biogenesis.

molecular biology↗