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PubMed2024

SUN2 mediates calcium-triggered nuclear actin polymerization to cluster active RNA polymerase II.

The nucleoskeleton is essential for nuclear architecture as well as genome integrity and gene expression. In addition to lamins, titin or spectrins, dynamic actin filament polymerization has emerged as a potential intranuclear structural element but its functions are less well explored. Here we found that calcium elevations trigger rapid nuclear actin assembly requiring the nuclear membrane protein SUN2 independently of its function as a component of the LINC complex. Instead, SUN2 colocalized and associated with the formin and actin nucleator INF2 in the nuclear envelope in a calcium-regulated manner. Moreover, SUN2 is required for active RNA polymerase II (RNA Pol II) clustering in response to calcium elevations. Thus, our data uncover a SUN2-formin module linking the nuclear envelope to intranuclear actin assembly to promote signal-dependent spatial reorganization of active RNA Pol II.

RNA Polymerase II↗

PubMed2026

Participation of the purinergic P2X7 receptor in molecular complexes in the nucleus of human chondrocytes.

In addition to the purinergic receptor P2X7R's known activity as a sensor of damage-associated molecular patterns (DAMPs), evidences support its role in maintaining tissue homeostasis. Its presence in cellular compartments other than its usual transmembrane localization suggests its involvement in specific signaling pathways. This study aimed to analyze P2X7R in the nucleus of human chondrocytes and search for potential interacting partners. Through co-immunoprecipitation and proximity ligation assay we discovered that, independent of extracellular ATP levels, P2X7R is abundantly present in both the nuclear membrane and in the nucleoplasm, where it is found in close proximity to lamin A/C (a component of the nuclear lamina), emerin (a protein involved in the assembly and disassembly of the nuclear envelope), and SUN2 (an inner nuclear membrane protein that facilitates the transmission of mechanical forces). Furthermore, chromatin immunoprecipitation revealed the participation of P2X7R in molecular complexes located in the promoter of specific genes including Sox9, TRPS1, FOXO3a, integrin β2 and connective tissue growth factor. Overall, this evidence reveals for the first time novel partners of P2X7R that place it in an intricate network that influences nuclear structure, mechanosensitivity, chromatin organization, and gene expression. Specifically, on the one hand, a close association between P2X7R and nuclear proteins participating in the LINC (Linker of Nucleoskeleton and Cytoskeleton) complex (lamin A/C, emerin, and SUN2) places it among the factors involved in mechanosignaling and the maintenance of nuclear integrity; on the other, its recruitment to specific gene promoters suggests that it may act as a transcription regulator.

Humans↗

PubMed2026

Nuclear Proteome Map of Mouse Heart Chambers.

Heart specialization involves nuclear programs; however, chamber-specific regulation of the nuclear proteome landscape remains unknown. In this study, we isolated the nucleus from four major anatomical regions of healthy mouse heart (fresh) and employed quantitative mass spectrometry-based proteomics to construct a comprehensive nuclear proteome landscape of left ventricle (LV, 2403 proteins), right ventricle (RV, 2242 proteins), left atrium (LA, 2368 proteins), and right atrium (RA, 1816 proteins). This led to the discovery of nuclear regional proteome signatures (ventricular signature, 297 proteins; atrial signature, 183 proteins) associated with oxidative metabolism and redox regulation, ferroptosis, extracellular-matrix remodeling, SUMO- and stress-responsive control and transcriptional regulation. Chamber-level analyses further identify distinct nuclear features in LV (120 proteins), LA (188 proteins), and RA (72 proteins). In addition, we defined conserved core nuclear proteome (230 proteins) shared across all anatomical regions, enriched for transcription-regulator complexes, nucleolar/ribosome-associated, RNA-processing, and chromatin-organization components. Within this core network, we report 78 transcription factors/co-factors and select nuclear, chromatin and RNA export-associated proteins, including 29 specific factors (e.g., Alpk3, Rbm14, Arglu1, Hmgb1, Myef2, Sf1) associated with the heart. Regionally, we verified spatial localization in heart of H2ac21 and Sun2 in LA and Ptbp2 in LV by immunofluorescence. This study provides insights into the chamber-resolved view of the nuclear proteome in the heart, establishes a framework for linking nuclear proteomic signatures to atrial and ventricular biology, unique features of the heart nuclear proteome landscape relative to other organs, and a baseline for studying nuclear remodeling in cardiac pathophysiology.

Animals↗