Sapkota, O. | bioRxiv Science

bioRxiv2026

The glycine-arginine-rich motif of 53BP1 modulates RNA interactions necessary for its liquid-liquid phase separation during DNA Damage Response

The DNA damage response relies on the rapid assembly of repair factors into foci with properties of liquid-liquid phase separation, driven by de novo transcription of damage-induced RNAs. 53BP1 is a key component of these condensates, yet the molecular determinants driving this process remain unknown. Here, through computational, structural and in vitro approaches, we identify the oligomerization domain of 53BP1 and its glycine-arginine-rich (GAR) motif as crucial for RNA interactions and phase separation. Biophysical characterization reveals that 53BP1-RNA condensates can progressively mature into a more stable state, and that GAR mutants display aberrant material properties. Using a cellular model of telomere fusion events, we demonstrate that the GAR motif is essential for 53BP1-mediated DNA repair, which depends on the combined contributions of RNA binding and appropriate condensate biophysical properties. Therefore, RNA-driven 53BP1 condensation is functionally required to maintain genome integrity.

biophysics↗

bioRxiv2022

Regulation of oxidative phosphorylation by Nuclear myosin 1 protects cells from metabolic reprogramming and tumorigenesis in mice

Metabolic reprogramming is one of the hallmarks of tumorigenesis. Using a combination of multi-omics, here we show that nuclear myosin 1 (NM1) serves as a key regulator of cellular metabolism. As part of the nutrient-sensing PI3K/Akt/mTOR pathway, NM1 forms a positive feedback loop with mTOR and directly affects mitochondrial oxidative phosphorylation (OXPHOS) via transcriptional regulation of mitochondrial transcription factors TFAM and PGC1. NM1 depletion leads to suppression of PI3K/Akt/mTOR pathway, underdevelopment of mitochondria inner cristae, and redistribution of mitochondria within the cell, which is associated with reduced expression of OXPHOS genes, decreased mitochondrial DNA copy number and deregulated mitochondrial dynamics. This leads to metabolic reprogramming of NM1 KO cells from OXPHOS to aerobic glycolysis and with a metabolomic profile typical for cancer cells, namely, increased amino acid-, fatty acid-, and sugar metabolism, and increased glucose uptake, lactate production, and intracellular acidity. We show that NM1 KO cells form solid tumors in a nude mouse model even though they have suppressed the PI3K/Akt/mTOR signaling pathway suggesting that the metabolic switch towards aerobic glycolysis provides a sufficient signal for carcinogenesis. We suggest that NM1 plays a key role as a tumor suppressor and that NM1 depletion may contribute to the Warburg effect at the early onset of tumorigenesis.

cell biology↗