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17 pags., 9 figs., 1 tab., Repair of injured DNA relies on nucleosome dismantling by histone chaperones and de-phosphorylation events carried out by Protein Phosphatase 2A (PP2A). Typical histone chaperones are the Acidic leucine-rich Nuclear Phosphoprotein 32 family (ANP32) members, e.g. ANP32A, which is also a well-known PP2A inhibitor (a.k.a. IPP2A). Here we report the novel interaction between the endogenous family member B—so-called ANP32B—and endogenous cytochrome c in cells undergoing camptothecin-induced DNA damage. Soon after DNA lesions but prior to caspase cascade activation, the hemeprotein translocates to the nucleus to target the Low Complexity Acidic Region (LCAR) of ANP32B; in a similar way, our group recently reported that the hemeprotein targets the acidic domain of SET/Template Activating Factor-Iβ (SET/TAF-Iβ), which is another histone chaperone and PP2A inhibitor (a.k.a. IPP2A). The nucleosome assembly activity of ANP32B is indeed unaffected by cytochrome c binding. Like ANP32A, ANP32B inhibits PP2A activity and is thus herein referred to as IPP2A. Our data demonstrates that ANP32B-dependent inhibition of PP2A is regulated by respiratory cytochrome c, which induces long-distance allosteric changes in the structured N-terminal domain of ANP32B upon binding to the C-terminal LCAR. In agreement with the reported role of PP2A in the DNA damage response, we propose a model wherein cytochrome c is translocated from the mitochondria into the nucleus upon DNA damage to modulate PP2A activity via its interaction with ANP32B., This work was supported by the Spanish Ministry of Science, Innovation and Universities (BFU2012-31670, BFU2015-71017, PGC2018-096049- BI00), Spanish Ministry of Education and Professional Training (FPU013/04373 to FRR, FPU016/01513 to AVC), Regional Government of Andalusia (BIO198, US-1254317 US/JUNTA/FEDER,UE, US- 1257019 US/JUNTA/FEDER,UE, P18-FR-3487 and P18–HO-4091), Ramon Areces Foundation, Biointeractomics Platform (cicCartuja, Seville) and the Microscopy and NMR Services at CITIUS (University of Seville). MPG is funded by a postdoctoral grant from the Spanish Association Against Cancer Scientific Foundation (FC AECC)

Cell signaling mechanisms modulate gene expression in response to internal and external stimuli. Cellular adaptation requires a precise and coordinated regulation of the transcription and translation processes. The post-transcriptional control of mRNA metabolism is mediated by the so-called RNA-binding proteins (RBPs), which assemble with specific transcripts forming messenger ribonucleoprotein particles of highly dynamic composition. RBPs constitute a class of trans-acting regulatory proteins with affinity for certain consensus elements present in mRNA molecules. However, these regulators are subjected to post-translational modifications (PTMs) that constantly adjust their activity to maintain cell homeostasis. PTMs can dramatically change the subcellular localization, the binding affinity for RNA and protein partners, and the turnover rate of RBPs. Moreover, the ability of many RBPs to undergo phase transition and/or their recruitment to previously formed membrane-less organelles, such as stress granules, is also regulated by specific PTMs. Interestingly, the dysregulation of PTMs in RBPs has been associated with the pathophysiology of many different diseases. Abnormal PTM patterns can lead to the distortion of the physiological role of RBPs due to mislocalization, loss or gain of function, and/or accelerated or disrupted degradation. This Mini Review offers a broad overview of the post-translational regulation of selected RBPs and the involvement of their dysregulation in neurodegenerative disorders, cancer and other pathologies

The alternative reading frame (ARF) protein is crucial in the cellular response to oncogenic stress, being likewise the second most frequently inactivated gene in a wide spectrum of human cancers. ARF is usually sequestered in the nucleolus by the well-known oncogenic nucleophosmin (NPM) protein and is liberated in response to cell damage to exhibit its tumor-suppressor ability. However, the mechanism underlying ARF activation is unknown. Here we show that mitochondria-to-nucleus translocation of cytochrome c upon DNA damage leads to the break-off of the NPM-ARF ensemble and subsequent release of ARF from the nucleoli. Our structural and subcellular data support a molecular model in which the hemeprotein triggers the extended-to-compact conformation of NPM and competes with ARF for binding to NPM.

Cytochrome c (Cc) is a protein that functions as an electron carrier in the mitochondrial respiratory chain. However, Cc has moonlighting roles outside mitochondria driving the transition of apoptotic cells from life to death. When living cells are damaged, Cc escapes its natural mitochondrial environment and, once in the cytosol, it binds other proteins to form a complex named the apoptosome-a platform that triggers caspase activation and further leads to controlled cell dismantlement. Early released Cc also binds to inositol 1,4,5-triphosphate receptors on the ER membrane, which stimulates further massive Cc release from mitochondria. Besides the well-characterized binding proteins contributing to the proapoptotic functions of Cc, many novel protein targets have been recently described. Among them, histone chaperones were identified as key partners of Cc following DNA breaks, indicating that Cc might modulate chromatin dynamics through competitive binding to histone chaperones. In this article, we review the ample set of recently discovered antiapoptotic proteins-involved in DNA damage, transcription, and energetic metabolism-reported to interact with Cc in the cytoplasm and even the nucleus upon DNA breaks.

Over the past decade, evidence has emerged suggesting a broader role for cytochrome c (Cyt c) in programmed cell death. Recently, we demonstrated the ability of Cyt c to inhibit the nucleosome assembly activity of histone chaperones SET/template-activating factor Iß and NAP1-related protein during DNA damage in humans and plants respectively. Here, we hypothesise a dual concentration-dependent function for nuclear Cyt c in response to DNA damage. We propose that low levels of highly cytotoxic DNA lesions - such as double-strand breaks - induce nuclear translocation of Cyt c, leading to the attenuation of nucleosome assembly and, thereby, increasing the time available for DNA repair. If DNA damage persists or is exacerbated, the nuclear Cyt c concentration would exceed a given threshold, causing the haem protein to block DNA remodelling altogether., This work was supported by the Spanish Ministry of Economy, Industry and Competitiveness (BFU2015‐71017/BMC), the Andalusian Government (BIO198), the Ramón Areces Foundation and the European Regional Development Fund (FEDER). AVC is recipient of an FPU Fellowship from the Spanish Ministry of Education, Culture and Sports (FPU16/01513).