Biology subjects

Schwarzmayr, T.

Publications and source records attributed to Schwarzmayr, T..

4 recordsLinked to original sources

bioRxiv2020

Adaptive mitochondrial regulation of the proteasome

The proteasome is the main proteolytic system for targeted protein degradation in the cell. Its function is fine-tuned according to cellular needs. Regulation of proteasome function by mitochondrial metabolism, however, is unknown. Here, we demonstrate that mitochondrial dysfunction reduces the assembly and activity of the 26S proteasome in the absence of oxidative stress. Impaired respiratory complex I function leads to metabolic reprogramming of the Krebs cycle and deficiency in aspartate. Aspartate supplementation activates assembly and activity of 26S proteasomes via transcriptional activation of the proteasome assembly factors p28 and Rpn6. This metabolic adaptation of 26S proteasome function involves sensing of aspartate via the mTORC1 pathway. Metformin treatment of primary human cells similarly reduced assembly and activity of 26S proteasome complexes, which was fully reversible and rescued by supplementation of aspartate or pyruvate. Of note, respiratory dysfunction conferred resistance towards the proteasome inhibitor Bortezomib. Our study uncovers a fundamental novel mechanism of how mitochondrial metabolism adaptively adjusts protein degradation by the proteasome. It thus unravels unexpected consequences of defective mitochondrial metabolism in disease or drug-targeted mitochondrial reprogramming for proteasomal protein degradation in the cell. As metabolic inhibition of proteasome function can be alleviated by treatment with aspartate or pyruvate, our results also have therapeutic implications.

cell biology↗

bioRxiv2020

Maintenance of epithelial traits and resistance to mesenchymal reprogramming promote proliferation in metastatic breast cancer

Despite important advances in the treatment of breast cancer, the 5-year survival rate for patients with distant metastasis remains less than 30%. Metastasis is a complex, multi-step process beginning with local invasion and ending with the outgrowth of systemically disseminated cells into actively proliferating metastases that ultimately cause the destruction of vital organs. It is this last step that limits patient survival and, at the same time, remains the least understood mechanistically. Here, we focus on understanding determinants of metastatic outgrowth using metastatic effusion biopsies from stage IV breast cancer patients. By modelling metastatic outgrowth through xenograft transplantation, we show that tumour initiation potential of patient-derived metastatic breast cancer cells across breast cancer subtypes is strongly linked to high levels of EPCAM expression. Breast cancer cells with high EPCAM levels are highly plastic and, upon induction of epithelial-mesenchymal transition (EMT), readily adopt mesenchymal traits while maintaining epithelial identity. In contrast, low EPCAM levels are caused by the irreversible reprogramming to a mesenchymal state with concomitant suppression of metastatic outgrowth. The ability of breast cancer cells to retain epithelial traits is tied to a global epigenetic program that limits the actions of EMT-transcription factor ZEB1, a suppressor of epithelial genes. Our results provide direct evidence that maintenance of epithelial identity is required for metastatic outgrowth while concomitant expression of mesenchymal markers enables plasticity. In contrast, loss of epithelial traits is characteristic of an irreversible mesenchymal reprogramming associated to a deficiency for metastatic outgrowth. Collectively, our data provide a framework for the intricate intercalation of mesenchymal and epithelial traits in metastatic growth.

cancer biology↗

bioRxiv2018

Epstein-Barr virus reprograms human B-lymphocytes immediately in the pre-latent phase of infection

Epstein-Barr virus (EBV) is a human tumor virus and a model of herpesviral latency. The virus efficiently infects resting human B-lymphocytes and induces their continuous proliferation in vitro, which mimics certain aspects of EBVs oncogenic potential in vivo. This seminal finding was made 50 years ago, but how EBV activates primary human B-lymphocytes and how lymphoblastoid cell lines (LCLs) evolve from the EBV-infected lymphocytes is uncertain. We conducted a systematic time-resolved longitudinal study of cellular functions and transcriptional profiles of newly infected naive primary B-lymphocytes. EBV reprograms these human cells comprehensively and globally. Rapid and extensive transcriptional changes occur within 24 hours of infection and precede any metabolic and phenotypic changes. Within the next 48 hours, the virus activates the cells, changes their phenotypes with respect to cell size, RNA and protein content and induces metabolic pathways to cope with the increased demand for energy, supporting an efficient cell cycle entry on day three post infection. The transcriptional program that EBV initiates consists of three waves of clearly discernable clusters of cellular genes that peak on day one, two, or three and regulate RNA synthesis, metabolic pathways and cell division, respectively. Upon the onset of cell doublings on day four the cellular transcriptome appears to be completely reprogrammed to support the activated and proliferating cell, but three additional clusters of EBV regulated genes adjust the infected immune cells to fine-tune cell signaling, migration, and immune response pathways, eventually. Our study reveals that more than 98 % of the 13,000 expressed genes in B-lymphocytes are regulated upon infection demonstrating that EBV governs the entire biology of its target cell.

microbiology↗

bioRxiv2018

MAU2 and NIPBL variants in Cornelia de Lange syndrome reveal MAU2-independent loading of cohesin and uncover a protective mechanism against early truncating mutations in NIPBL

Cornelia de Lange syndrome (CdLS) is a rare developmental disorder caused by mutations in genes related to the cohesin complex. For its association with chromatin, cohesin depends on a heterodimer formed by NIPBL and MAU2, which interact via their respective N-termini. Variants in NIPBL are the main cause of CdLS and result in NIPBL haploinsufficiency.\n\nUsing CRISPR, we generated cells homozygous for an out-of-frame duplication in NIPBL. Remarkably, alternative translation initiation rescued NIPBL expression in these cells and produced an N-terminally truncated NIPBL that lacks MAU2-interaction domain, causing a dramatic reduction of MAU2 protein levels. Strikingly, this protective mechanism allows nearly normal amounts of cohesin to be loaded onto chromatin in a manner that is independent of functional NIPBL/MAU2 complexes and therefore in contrast to previous findings.\n\nWe also report the first pathogenic variant in MAU2, a deletion of seven amino acids important for wrapping the N-terminus of NIPBL within MAU2. The mutation causes dramatic reduction of MAU2 heterodimerization with NIPBL, hence undermining the stability of both proteins.\n\nOur data confirm NIPBL haploinsufficiency as the major pathogenic mechanism of CdLS and give new insights into the molecular mechanisms responsible for this neurodevelopmental disorder. Our work also unveils an alternative translation-based mechanism that protects cells from out-of-frame variants of NIPBL and that may be of relevance in other genetic conditions.

molecular biology↗