Nuclear Actin Polymerization Regulates Cell Epithelial-Mesenchymal Transition

Recent advances in nuclear actin research

Actin was first observed in the nucleus more than sixty years ago but research on nuclear actin did not receive significant attention for the next forty years. It only started to accelerate around the year 2000, when the first convincing experimental data emerged indicating that actin participates in essential nuclear processes. Today, we know that actin is involved in transcription, replication, DNA repair, chromatin remodeling, and participates in the determination of nuclear shape and size. In this paper we review the results of the last five years of increasingly intensive research on nuclear actin, because on one hand, the field has expanded with several new directions during this time, and on the other hand, the enrichment of our picture of nuclear actin will certainly provide a more solid foundation and new impetus for its future investigation.

Aggravated Ulcerative Colitis via circNlgn-Mediated Suppression of Nuclear Actin Polymerization

Colitis is a chronic bowel disease characterized by damage to the lining of the large intestine, with its precise underlying causes remaining incompletely understood. In this study, we provide evidence that circular RNA circNlgn plays a pivotal role in promoting the development of colitis. Colitis patients produce significant higher levels of circNlgn. Transgenic mice expressing circNlgn exhibit heightened susceptibility to colitis development and progression, primarily attributed to the presence of the protein isoform Nlgn173 encoded by circNlgn. Nlgn173 undergoes translocation into cell nuclei, where it interacts with actin, impeding the binding of actin-related protein 2 and 3 (Arp2/3) complex to actin molecules. Consequently, this leads to a reduction in actin polymerization. Mechanistically, Nlgn173 enhances tyrosine-53 phosphorylation of nuclear actin, diminishing its capacity to interact with the Arp2/3 complex and causing a decrease in filamentous actin levels. These alterations in actin dynamics result in inhibited cell cycle progression, increased apoptosis, and decreased proliferation of colonic epithelial cells, thereby exacerbating colitis development and progression. In contrast, the silencing of circNlgn or the targeted inhibition of Nlgn173 translation and nuclear translocation leads to the promotion of nuclear actin polymerization, enhanced cell survival, and reduced apoptosis and ultimately improves the outcome of colitis in vivo. Interestingly, nuclear actin polymerization is highly related with expression of PIAS3, which modulates signal transducer and activator of transcription 3 and NF-κB activity in colitis. Strategies such as circNlgn knockdown and targeting nuclear actin polymerization of the colonic epithelium may explore a novel avenue for acute ulcerative colitis clinical intervention.

Decoding the tumour-modulatory roles of LIMK2

LIM domains kinase 2 (LIMK2) is a 72 kDa protein that regulates actin and cytoskeleton reorganization. Once phosphorylated by its upstream activator (ROCK1), LIMK2 can phosphorylate cofilin to inactivate it. This relieves the levering stress on actin and allows polymerization to occur. Actin rearrangement is essential in regulating cell cycle progression, apoptosis, and migration. Dysregulation of the ROCK1/LIMK2/cofilin pathway has been reported to link to the development of various solid cancers such as breast, lung, and prostate cancer and liquid cancer like leukemia. This review aims to assess the findings from multiple reported in vitro, in vivo, and clinical studies on the potential tumour-regulatory role of LIMK2 in different human cancers. The findings of the selected literature unraveled that activated AKT, EGF, and TGF-β pathways can upregulate the activities of the ROCK1/LIMK2/cofilin pathway. Besides cofilin, LIMK2 can modulate the cellular levels of other proteins, such as TPPP1, to promote microtubule polymerization. The tumour suppressor protein p53 can transactivate LIMK2b, a splice variant of LIMK2, to induce cell cycle arrest and allow DNA repair to occur before the cell enters the next phase of the cell cycle. Additionally, several non-coding RNAs, such as miR-135a and miR-939-5p, could also epigenetically regulate the expression of LIMK2. Since the expression of LIMK2 is dysregulated in several human cancers, measuring the tissue expression of LIMK2 could potentially help diagnose cancer and predict patient prognosis. As LIMK2 could play tumour-promoting and tumour-inhibiting roles in cancer development, more investigation should be conducted to carefully evaluate whether introducing a LIMK2 inhibitor in cancer patients could slow cancer progression without posing clinical harms.

Mechanical Stimulation of Anti-Inflammatory and Antioxidant Hydrogels for Rapid Re-Epithelialization

The epithelium, an essential barrier to protect organisms against infection, exists in many organs. However, rapid re-epithelialization to restore tissue integrity and function in an adverse environment is challenging. In this work, a long-term anti-inflammatory and antioxidant hydrogel with mechanical stimulation for rapid re-epithelialization, mainly composed of the small molecule thioctic acid, biocompatible glycine, and γ-Fe2O3 nanoparticles is reported. Glycine-modified supramolecular thioctic acid is stable and possesses outstanding mechanical properties. The incorporating γ-Fe2O3 providing the potential contrast function for magnetic resonance imaging observation, can propel hydrogel reconfiguration to enhance the mechanical properties of the hydrogel underwater due to water-initiated release of Fe3+. In vitro experiments show that the hydrogels effectively reduced intracellular reactive oxygen species, guided macrophages toward M2 polarization, and alleviated inflammation. The effect of rapid re-epithelialization is ultimately demonstrated in a long urethral injury model in vivo, and the mechanical stimulation of hydrogels achieves effective functional replacement and ultimately accurate remodeling of the epithelium. Notably, the proposed strategy provides an advanced alternative treatment for patients in need of large-area epithelial reconstruction.

Salvianolic Acid B Significantly Suppresses the Migration of Melanoma Cells via Direct Interaction with β-Actin

Melanoma is the most aggressive and difficult to treat of all skin cancers. Despite advances in the treatment of melanoma, the prognosis for melanoma patients remains poor, and the recurrence rate remains high. There is substantial evidence that Chinese herbals effectively prevent and treat melanoma. The bioactive ingredient Salvianolic acid B (SAB) found in Salvia miltiorrhiza, a well-known Chinese herbal with various biological functions, exhibits inhibitory activity against various cancers. A375 and mouse B16 cell lines were used to evaluate the main targets and mechanisms of SAB in inhibiting melanoma migration. Online bioinformatics analysis, Western blotting, immunofluorescence, molecular fishing, dot blot, and molecular docking assays were carried out to clarify the potential molecular mechanism. We found that SAB prevents the migration and invasion of melanoma cells by inhibiting the epithelial-mesenchymal transition (EMT) process of melanoma cells. As well as interacting directly with the N-terminal domain of β-actin, SAB enhanced its compactness and stability, thereby inhibiting the migration of cells. Taken together, SAB could significantly suppress the migration of melanoma cells via direct binding with β-actin, suggesting that SAB could be a helpful supplement that may enhance chemotherapeutic outcomes and benefit melanoma patients.

A Novel Circular RNA circITGa9 Predominantly Generated in Human Heart Disease Induces Cardiac Remodeling and Fibrosis

Recent studies have highlighted the pivotal roles of circular RNAs (circRNAs) in cardiovascular diseases. Through high-throughput circRNA sequencing of both normal myocardial tissues and hypertrophic patients, we unveiled 32,034 previously undiscovered circRNAs with distinct cardiac expression patterns. Notably, circITGa9, a circRNA derived from integrin-α9, exhibited substantial up-regulation in cardiac hypertrophy patients. This elevation was validated across extensive sample pools from cardiac patients and donors. In vivo experiments revealed heightened cardiac fibrosis in mice subjected to transverse aortic constriction (TAC) after circITGa9 injection. We identified circITGa9 binding proteins through circRNA precipitation followed by liquid chromatography tandem-mass spectrometry. Furthermore, circRNA pull-down/precipitation assays demonstrated that increased circITGa9 expression facilitated binding with tropomyosin 3 (TPM3). Specific binding sites between circITGa9 and TPM3 were identified through computational algorithms and further validated by site-directed mutagenesis. We further showed that circITGa9 induced actin polymerization, characteristic of tissue fibrosis. Finally, we developed approaches that improved cardiac function and decreased fibrosis by delivering small interfering RNA targeting circITGa9 or blocking oligo inhibiting the interaction of circITGa9 and TPM3 into TAC mice, which is amenable for further preclinical and translational development. We conclude that elevated circITGa9 levels drive cardiac remodeling and fibrosis. By pinpointing circITGa9 as a therapeutic target, we open doors to innovative interventions for mitigating cardiac remodeling and fibrosis.