Castro-Obregon, S. | Search bioRxiv

bioRxiv2021

Nucleophagy contributes to genome stability though TOP2cc and nucleolar components degradation

The nuclear architecture of mammalian cells can be altered as a consequence of anomalous accumulation of nuclear proteins or genomic alterations. Most of the knowledge about nuclear dynamics comes from studies on cancerous cells. How normal, healthy cells maintain genome stability avoiding accumulation of nuclear damaged material is less understood. Here we describe that primary mouse embryonic fibroblasts develop a basal level of nuclear buds and micronuclei, which increase after Etoposide-induced DNA Double-Stranded Breaks. These nuclear buds and micronuclei co-localize with autophagic proteins BECN1 and LC3 and with acidic vesicles, suggesting their clearance by nucleophagy. Some of the nuclear alterations also contain autophagic proteins and Type II DNA Topoisomerases (TOP2A and TOP2B), or nucleolar protein Fibrillarin, implying they are also targets of nucleophagy. We propose that a basal nucleophagy contributes to genome and nuclear stability and also in response to DNA damage and nucleolar stress.

cell biology↗

bioRxiv2020

Programmed cell senescence in the mouse developing spinal cord and notochord

Programmed cell senescence is a cellular process that seems to contribute to morphogenesis during embryo development, in addition to cell proliferation, migration, differentiation and programmed cell death, and has been observed in evolutionary distant organisms like mammals, amphibians and fish. Programmed cell senescence is a phenotype similar to stress-induced cellular senescence, characterized by the expression of cell cycle inhibitors such as CDKN1A/p21, increased activity of a lysosomal enzyme with beta-galactosidase activity (coined senescence-associated beta-galactosidase) and, most importantly, secretion of growth factors, interleukins, chemokines, metalloproteases, etc., collectively known as a senescent-associated secretory phenotype that instructs surrounding tissue. How wide is the distribution of programmed cell senescence during mouse development and its specific mechanisms to shape the embryo are still poorly understood. Here, we investigated whether markers of programmed cell senescence are found in the developing mouse spinal cord and notochord. We found discrete areas and developmental windows with high senescence-associated beta galactosidase in both spinal cord and notochord; expression of CDKN1A/p21 was documented in epithelial cells of the spinal cord and the notochord. Treatment of mice embryos developed ex-utero in the presence of the senolytic ABT-263 resulted in decrease senescence-associated beta-galactosidase activity and number of motoneurons. Our data suggest that several cell types undergo programmed cell senescence in developing spinal cord and notochord contributing to morphogenesis. Contribution to the Field StatementCellular senescence is a state in which cells no longer divide but have the remarkable ability to secrete signaling molecules that alter the tissue where they reside. In adults, this state is typically induced by stress situations that cause DNA damage so cells with altered genome do not multiply. Senescent cells also form when a tissue is injured; they help to regenerate damaged tissue and contribute to wound healing. Phagocytic cells eliminate them when their function is done, having a transient existence. During vertebrate development some cells acquire a very similar phenotype, coined programmed cell senescence, and interestingly they have been found in regions that organize the pattern of development of some organs. How wide is the distribution of programmed cell senescence during development and how they help to shape the embryo are still poorly understood. We discovered in mice embryos different types of cells with senescent features located in particular regions of the developing nervous system: where motoneurons form and in a region that secrete molecules that instruct the embryo where different types of neurons will be created. We propose that programed cell senescence contributes to the morphogenesis of the nervous system.

developmental biology↗

bioRxiv2019

The nuclear receptor NR4A1 is regulated by SUMO modification to induce autophagic cell death

NR4A is a nuclear receptor protein family whose members act as sensors of cellular environment and regulate multiple processes such as metabolism, proliferation, migration, apoptosis, and autophagy. Since the ligand binding domains of these receptors have no cavity for ligand interaction, their function is most likely regulated by protein abundance and post-translational modifications. In particular, NR4A1 is regulated by protein abundance, phosphorylation, and subcellular distribution (nuclear-cytoplasmic translocation), and acts both as a transcription factor and as a regulator of other interacting proteins. SUMOylation is a post-translational modification that can affect protein stability, transcriptional activity, alter protein-protein interactions and modify intracellular localization of target proteins. In the present study we evaluated the role of SUMOylation as a posttranslational modification that can regulate the activity of NR4A1 to induce autophagy-dependent cell death. We focused on a model potentially relevant for neuronal cell death and demonstrated that NR4A1 needs to be SUMOylated to induce autophagic cell death. We observed that a triple mutant in SUMOylation sites has reduced SUMOylation, increased transcriptional activity, altered intracellular distribution, and more importantly, its ability to induce autophagic cell death is impaired.\n\nSummary StatementThe modification of the nuclear receptor NR4A1 by SUMO regulates its transcriptional activity, intracellular localization and is required to induce autophagic cell death.

biochemistry↗