The nuclear activity of the actin-binding Moesin protein is necessary for gene expression in Drosophila

Gas-powered extracellular vesicles promote bone regeneration

The signaling gas hydrogen sulfide (H2S) has recently been implicated in the regulation of bone remodeling and the maintenance of periodontal health. Exploring the underlying mechanisms for this regulation holds promise for the development of new treatment strategies to block bone resorption and stimulate bone regeneration. A recent study by Zhou et al. (Bioactive Materials, 2024) showed that treatment with H2S stimulated changes in the extracellular vesicles (EVs) released by M2 macrophages, enhancing their capacity to promote the osteogenic differentiation of mesenchymal stem cells in vitro. The H2S-stimulated EVs, given together with mesenchymal stem cells (MSCs), also promoted bone regeneration in vivo in a mouse calvarial critical-size defect model. This activity was linked to augmented expression of moesin, a membrane-cytoskeletal linkage protein, which was found at increased levels in EVs from cells stimulated by H2S. The study identifies a new strategy for generating EVs that are pro-osteogenic. It also uncovers a surprising role for moesin in stimulating osteogenesis in MSCs.

Phosphorylated ERM regulates meiotic maturation in mouse oocytes

The cytoskeleton of mammal oocytes provides structural support to the plasma membrane and contributes to critical cellular dynamic processes such as nuclear positioning, germinal vesicle breakdown, spindle orientation, chromosome segregation, polar body extrusion, and transmembrane signaling pathways. The ERM family (ezrin, radixin and moesin) well known as membrane-cytoskeletal crosslinkers play a crucial role in organizing plasma membrane domains through their capacity to interact with transmembrane proteins and the underlying cytoskeleton. Recent works mainly focused on the structural analysis of the ERM family members and their binding partners, together with multiple functions in cell mitosis, have significantly advanced our understanding of the importance of membrane-cytoskeletal interactions. In the present study, we documented that p-ERM was expressed and localized at cortical and nucleus during mouse oocyte meiosis. p-ERM and microfilaments were colocalized from GV to MII during mouse oocyte maturation. After being treated with cytochalasin B (CB), the F-actin was disassembled. Meanwhile, p-ERM exhibited a diffuse cytoplasmic distribution and no special staining was detected in either the oocyte membrane or condensed chromosomes. p-ERM depletion by trim-away caused the meiotic procedure arrest with a significantly lower polar body extrusion rate. Collectively, these data demonstrate that the subcellular distribution of p-ERM is correlated with microfilaments. Meanwhile, the p-ERM contributes to the first polar extrusion but does not regulate the microfilament assembly.

Moesin contributes to heat shock gene response through direct binding to the Med15 subunit of the Mediator complex in the nucleus

The members of the evolutionary conserved actin-binding Ezrin, Radixin and Moesin (ERM) protein family are involved in numerous key cellular processes in the cytoplasm. In the last decades, ERM proteins, like actin and other cytoskeletal components, have also been shown to be functional components of the nucleus; however, the molecular mechanism behind their nuclear activities remained unclear. Therefore, our primary aim was to identify the nuclear protein interactome of the single Drosophila ERM protein, Moesin. We demonstrate that Moesin directly interacts with the Mediator complex through direct binding to its Med15 subunit, and the presence of Moesin at the regulatory regions of the Hsp70Ab heat shock gene was found to be Med15-dependent. Both Moesin and Med15 bind to heat shock factor (Hsf), and they are required for proper Hsp gene expression under physiological conditions. Moreover, we confirmed that Moesin, Med15 and Hsf are able to bind the monomeric form of actin and together they form a complex in the nucleus. These results elucidate a mechanism by which ERMs function within the nucleus. Finally, we present the direct interaction of the human orthologues of Drosophila Moesin and Med15, which highlights the evolutionary significance of our finding.

FERM domain-containing proteins are active components of the cell nucleus

The FERM domain is a conserved and widespread protein module that appeared in the common ancestor of amoebae, fungi, and animals, and is therefore now found in a wide variety of species. The primary function of the FERM domain is localizing to the plasma membrane through binding lipids and proteins of the membrane; thus, for a long time, FERM domain-containing proteins (FDCPs) were considered exclusively cytoskeletal. Although their role in the cytoplasm has been extensively studied, the recent discovery of the presence and importance of cytoskeletal proteins in the nucleus suggests that FDCPs might also play an important role in nuclear function. In this review, we collected data on their nuclear localization, transport, and possible functions, which are still scattered throughout the literature, with special regard to the role of the FERM domain in these processes. With this, we would like to draw attention to the exciting, new dimension of the role of FDCPs, their nuclear activity, which could be an interesting novel direction for future research.

A bipartite NLS motif mediates the nuclear import of Drosophila moesin

The ERM protein family, which consists of three closely related proteins in vertebrates, ezrin, radixin, and moesin (ERM), is an ancient and important group of cytoplasmic actin-binding and organizing proteins. With their FERM domain, ERMs bind various transmembrane proteins and anchor them to the actin cortex through their C-terminal F-actin binding domain, thus they are major regulators of actin dynamics in the cell. ERMs participate in many fundamental cellular processes, such as phagocytosis, microvilli formation, T-cell activation and tumor metastasis. We have previously shown that, besides its cytoplasmic activities, the single ERM protein of Drosophila melanogaster, moesin, is also present in the cell nucleus, where it participates in gene expression and mRNA export. Here we study the mechanism by which moesin enters the nucleus. We show that the nuclear import of moesin is an NLS-mediated, active process. The nuclear localization sequence of the moesin protein is an evolutionarily highly conserved, conventional bipartite motif located on the surface of the FERM domain. Our experiments also reveal that the nuclear import of moesin does not require PIP2 binding or protein activation, and occurs in monomeric form. We propose, that the balance between the phosphorylated and non-phosphorylated protein pools determines the degree of nuclear import of moesin.

The MEF2A transcription factor interactome in cardiomyocytes

Transcriptional regulators encoded by the Myocyte Enhancer Factor 2 (MEF2) gene family play a fundamental role in cardiac development, homeostasis and pathology. Previous studies indicate that MEF2A protein-protein interactions serve as a network hub in several cardiomyocyte cellular processes. Based on the idea that interactions with regulatory protein partners underly the diverse roles of MEF2A in cardiomyocyte gene expression, we undertook a systematic unbiased screen of the MEF2A protein interactome in primary cardiomyocytes using an affinity purification-based quantitative mass spectrometry approach. Bioinformatic processing of the MEF2A interactome revealed protein networks involved in the regulation of programmed cell death, inflammatory responses, actin dynamics and stress signaling in primary cardiomyocytes. Further biochemical and functional confirmation of specific protein-protein interactions documented a dynamic interaction between MEF2A and STAT3 proteins. Integration of transcriptome level data from MEF2A and STAT3-depleted cardiomyocytes reveals that the balance between MEF2A and STAT3 activity exerts a level of executive control over the inflammatory response and cardiomyocyte cell survival and experimentally ameliorates Phenylephrine induced cardiomyocyte hypertrophy. Lastly, we identified several MEF2A/STAT3 co-regulated genes, including the MMP9 gene. Herein, we document the cardiomyocyte MEF2A interactome, which furthers our understanding of protein networks involved in the hierarchical control of normal and pathophysiological cardiomyocyte gene expression in the mammalian heart.

DRR1 promotes neuroblastoma cell differentiation by regulating CREB expression

BACKGROUND

Neuroblastoma is the most common cancer in infants and the most common extracranial solid tumor in childhood. DRR1 was identified to be downregulated in poorly differentiated ganglion cells from neuroblastoma model mice. However, the roles of DRR1 in neuroblastoma remain largely unclear.

METHODS

The neuroblastoma cells were induced to differentiate, and the expression of DRR1 was detected. The expression of the neuroblastoma cell differentiation markers was analyzed in DRR1 shRNA- or DRR1-expressing vector-treated neuroblastoma cells. The downstream genes of DRR1 were screened with ChIP-seq assay. Finally, TNB1 cells were infected with DRR1 shRNA and CREB expressing vector containing lentivirus, and the expression of the cell differentiation markers, cell cycle distribution and tumor growth were analyzed.

RESULTS

The expression of DRR1 was increased in differentiated neuroblastoma cells, and downregulation of DRR1 expression inhibited the differentiation of neuroblastoma cells. Further experiments indicated that CREB is a candidate downstream gene of DRR1, and it mediates neuroblastoma cell differentiation. Moreover, overexpression of CREB rescued the effect of DRR1 shRNA on cell differentiation, cell cycle distribution and tumor growth in neuroblastoma.

CONCLUSIONS

DRR1-CREB axis modulates the differentiation of neuroblastoma cells and is associated with the outcome of neuroblastoma patients.

IMPACT

DRR1 is involved in regulation of the differentiation of neuroblastoma. Binding with actin is essential for DRR1 to regulate neuroblastoma cell differentiation. CREB is a candidate downstream gene of DRR1 in regulating of the differentiation of neuroblastoma.

Detection of Actin in Nuclear Protein Fraction Isolated from Adult Drosophila Ovary

Much evidence supports the presence of cytoskeletal elements in the nucleus; however, the exact functions of these proteins in the nucleus are still uncertain. Of the cytoskeletal proteins, the activity and biological significance of nuclear actin has been the most extensively researched. It is now clear that actin performs essential tasks both in the cytoplasm and the nucleus, and that the dynamic balance between the large cytoplasmic and the significantly smaller nuclear actin pools is maintained by robust transport mechanisms. Therefore, the compartment-specific manipulation or investigation of actin has been an enormous challenge. Here, we present a protocol for the detection of actin in isolated nuclear protein fractions from Drosophila ovaries.