Phase separation of insulin receptor substrate 1 drives the formation of insulin/IGF-1 signalosomes

PRAG1 Condensation Drives Cell Contraction Under Stress

Peak1-related, kinase-activating pseudokinase 1 (PRAG1), a member of the pseudopodium-enriched atypical kinase (PEAK) family of pseudokinases, has been reported to play a role in regulating cell morphology. However, the molecular mechanism for this function remains elusive. In this study, we demonstrate that PRAG1 forms dynamic condensates in cells mediated by its αN and αJ helices. Importantly, we found that PRAG1 condensates functioned in mediating cell contraction, while condensate-formation-deficient PRAG1 mutants lost this function. Remarkably, the formation of spherical PRAG1 condensates appears to be a common phenomenon in diverse stress models, as well as in dopaminergic (DA) neurons derived from a Parkinson's disease patient. Our findings reveal a novel mechanism through which PRAG1 drives cell contraction and suggest a potential link between aberrant PRAG1 phase separation and stress-induced cell contraction. PRAG1 condensation drives cell contraction under stress.

Artesunate: A Review of Its Potential Therapeutic Effects and Mechanisms in Digestive Diseases

Artesunate (ART), an artemisinin-derived semi-synthetic sesquiterpene lactone distinguished by its unique endoperoxide group, has become a cornerstone of clinical antimalarial therapy. Recent research has demonstrated its broad pharmacological profile, including its potent antimalarial, anti-inflammatory, anti-tumor, antidiabetic, immunomodulatory, and anti-fibrotic properties. These discoveries have significantly broadened the therapeutic scope of ART and offer new perspectives for its potential use in treating gastrointestinal disorders. Mechanistically, ART exerts significant therapeutic effects against diverse gastrointestinal pathologies-such as gastric ulcers, ulcerative colitis (UC), hepatic fibrosis (HF), gastric cancer, hepatocellular carcinoma, and colorectal cancer-via multimodal mechanisms, including cell cycle modulation, apoptosis induction, the suppression of tumor cell invasion and migration, proliferation inhibition, ferroptosis activation, and immune regulation. This review evaluates existing evidence on ART's therapeutic applications and molecular mechanisms in digestive diseases, intending to elucidate its clinical translation potential. ART emerges as a promising multi-target agent with significant prospects for improving the management of gastrointestinal disorders.

PEX11B palmitoylation couples peroxisomal dysfunction with Schwann cells fail in diabetic neuropathy

BACKGROUND

Diabetic neuropathy (DN) is a prevalent and painful complication of diabetes; however, the mechanisms underlying its pathogenesis remain unclear, and effective clinical treatments are lacking. This study aims to explore the role of peroxisomes in Schwann cells in DN.

METHODS

The abundance of peroxisomes in the sciatic nerves of mice or Schwann cells was analyzed using laser confocal super-resolution imaging and western blotting. The RFP-GFP-SKL (Ser-Lys-Leu) probe was utilized to assess pexophagy (peroxisomes autophagy) levels. To evaluate the palmitoylation of PEX11B, the acyl-resin assisted capture (acyl-RAC) assay and the Acyl-Biotin Exchange (ABE) assay were employed. Additionally, MR (Mendelian randomization) analysis was conducted to investigate the potential causal relationship between DN and MS (Multiple sclerosis).

RESULTS

There was a decrease in peroxisomal abundance in the sciatic nerves of diabetic mice, and palmitic acid (PA) induced a reduction in peroxisomal abundance by inhibiting peroxisomal biogenesis in Schwann cells. Mechanistically, PA induced the palmitoylation of PEX11B at C25 site, disrupting its self-interaction and impeding peroxisome elongation. Fenofibrate, a PPARα agonist, effectively rescued peroxisomal dysfunction caused by PA and restored the peroxisomal abundance in diabetic mice. Lastly, MR analysis indicates a notable causal influence of DN on MS, with its onset and progression intricately linked to peroxisomal dysfunction.

CONCLUSIONS

Targeting the peroxisomal biogenesis pathway may be an effective strategy for preventing and treating DN, underscoring the importance of addressing MS risk at the onset of DN.

Regulation and function of insulin and insulin-like growth factor receptor signalling

Receptors of insulin and insulin-like growth factors (IGFs) are receptor tyrosine kinases whose signalling controls multiple aspects of animal physiology throughout life. In addition to regulating metabolism and growth, insulin-IGF receptor signalling has recently been linked to a variety of new, cell type-specific functions. In the last century, key questions have focused on how structural differences of insulin and IGFs affect receptor activation, and how insulin-IGF receptor signalling translates into pleiotropic biological functions. Technological advances such as cryo-electron microscopy have provided a detailed understanding of how native and engineered ligands activate insulin-IGF receptors. In this Review, we highlight recent structural and functional insights into the activation of insulin-IGF receptors, and summarize new agonists and antagonists developed for intervening in the activation of insulin-IGF receptor signalling. Furthermore, we discuss recently identified regulatory mechanisms beyond ligand-receptor interactions and functions of insulin-IGF receptor signalling in diseases.

KPNA3 regulates histone locus body formation by modulating condensation and nuclear import of NPAT

The histone locus body (HLB) is a membraneless organelle that determines the transcription of replication-dependent histones. However, the mechanisms underlying the appropriate formation of the HLB in the nucleus but not in the cytoplasm remain unknown. HLB formation is dependent on the scaffold protein NPAT. We identify KPNA3 as a specific importin that drives the nuclear import of NPAT by binding to the nuclear localization signal (NLS) sequence. NPAT undergoes phase separation, which is inhibited by KPNA3-mediated impairment of self-association. In this, a C-terminal self-interaction facilitator (C-SIF) motif, proximal to the NLS, binds the middle 431-1,030 sequence to mediate the self-association of NPAT. Mechanistically, the anchoring of KPNA3 to the NPAT-NLS sterically blocks C-SIF motif-dependent NPAT self-association. This leads to the suppression of aberrant NPAT condensation in the cytoplasm. Collectively, our study reveals a previously unappreciated role of KPNA3 in modulating HLB formation and delineates a steric hindrance mechanism that prevents inappropriate cytoplasmic NPAT condensation.

How to drug a cloud? Targeting intrinsically disordered proteins

Biologically active proteins/regions without stable structure (i.e., intrinsically disordered proteins and regions (IDPs and IDRs)) are commonly found in all proteomes. They have a unique functional repertoire that complements the functionalities of ordered proteins and domains. IDPs/IDRs are multifunctional promiscuous binders capable of folding at interaction with specific binding partners on a template- or context-dependent manner, many of which undergo liquid-liquid phase separation, leading to the formation of membrane-less organelles and biomolecular condensates. Many of them are frequently related to the pathogenesis of various human diseases. All this defines IDPs/IDRs as attractive targets for the development of novel drugs. However, their lack of unique structures, multifunctionality, binding promiscuity, and involvement in unusual modes of action preclude direct use of traditional structure-based drug design approaches for targeting IDPs/IDRs, and make disorder-based drug discovery for these "protein clouds" challenging. Despite all these complexities there is continuing progress in the design of small molecules affecting IDPs/IDRs. This article describes the major structural features of IDPs/IDRs and the peculiarities of the disorder-based functionality. It also discusses the roles of IDPs/IDRs in various pathologies, and shows why the approaches elaborated for finding drugs targeting ordered proteins cannot be directly used for the intrinsic disorder-based drug design, and introduces some novel methodologies suitable for these purposes. Finally, it emphasizes that regardless of their multifunctionality, binding promiscuity, lack of unique structures, and highly dynamic nature, "protein clouds" are principally druggable. Significance Statement Intrinsically disordered proteins and regions are highly abundant in nature, have multiple important biological functions, are commonly involved in the pathogenesis of a multitude of human diseases, and are therefore considered as very attractive drug targets. Although dealing with these unstructured multifunctional protein/regions is a challenging task, multiple innovative approaches have been designed to target them by small molecules.

Focal cortical dysplasia II caused by brain somatic mutation of IRS-1 is associated with ERK signaling pathway activation

Somatic mutations have been identified in 10% to 63% of focal cortical dysplasia type II samples, primarily linked to the mTOR pathway. When the causative genetic mutations are not identified, this opens the possibility of discovering new pathogenic genes or pathways that could be contributing to the condition. In our previous study, we identified a novel candidate pathogenic somatic variant of IRS-1 c.1791dupG in the brain tissue of a child with focal cortical dysplasia type II. This study further explored the variant's role in causing type II focal cortical dysplasia through in vitro overexpression in 293T and SH-SY5Y cells and in vivo evaluation via in utero electroporation in fetal brains, assessing effects on neuronal migration, morphology, and network integrity. It was found that the mutant IRS-1 variant led to hyperactivity of p-ERK, increased cell volume, and was predominantly associated with the MAPK signaling pathway. In vivo, the IRS-1 c.1791dupG variant induced abnormal neuron migration, cytomegaly, and network hyperexcitability. Notably, the ERK inhibitor GDC-0994, rather than the mTOR inhibitor rapamycin, effectively rescued the neuronal defects. This study directly highlighted the ERK signaling pathway's role in the pathogenesis of focal cortical dysplasia II and provided a new therapeutic target for cases of focal cortical dysplasia II that are not treatable by rapamycin analogs.

The emerging role of receptor tyrosine kinase phase separation in cancer

Receptor tyrosine kinase (RTK)-mediated signal transduction is fundamental to cell function and drives important cellular outcomes which, when dysregulated, can lead to malignant tumour growth and metastasis. The initiation of signals from plasma membrane-bound RTKs is subjected to multiple regulatory mechanisms that control downstream effector protein recruitment and function. The high propensity of RTKs to condense via liquid-liquid phase separation (LLPS) into membraneless organelles with downstream effector proteins provides a further fundamental mechanism for signal regulation. Herein we highlight how this phenomenon contributes to cancer signalling and consider the potential impact of LLPS on outcomes for cancer patients.

Technologies for studying phase-separated biomolecular condensates

Biomolecular condensates, also referred to as membrane-less organelles, function as fundamental organizational units within cells. These structures primarily form through liquid-liquid phase separation, a process in which proteins and nucleic acids segregate from the surrounding milieu to assemble into micron-scale structures. By concentrating functionally related proteins and nucleic acids, these biomolecular condensates regulate a myriad of essential cellular processes. To study these significant and intricate organelles, a range of technologies have been either adapted or developed. In this review, we provide an overview of the most utilized technologies in this rapidly evolving field. These include methods used to identify new condensates, explore their components, investigate their properties and spatiotemporal regulation, and understand the organizational principles governing these condensates. We also discuss potential challenges and review current advancements in applying the principles of biomolecular condensates to the development of new technologies, such as those in synthetic biology.

Kinesin light chain 1 stabilizes insulin receptor substrate 1 to regulate the IGF-1-AKT signaling pathway during myoblast differentiation

The IGF signaling pathway plays critical role in regulating skeletal myogenesis. We have demonstrated that KIF5B, the heavy chain of kinesin-1 motor, promotes myoblast differentiation through regulating IGF-p38MAPK activation. However, the roles of the kinesin light chain (Klc) in IGF pathway and myoblast differentiation remain elusive. In this study, we found that Klc1 was upregulated during muscle regeneration and downregulated in senescence mouse muscles and dystrophic muscles from mdx (X-linked muscular dystrophic) mice. Gain- and loss-of-function experiments further displayed that Klc1 promotes AKT-mTOR activity and positively regulates myogenic differentiation. We further identified that the expression levels of IRS1, the critical node of IGF-1 signaling, are downregulated in Klc1-depleted myoblasts. Coimmunoprecipitation study revealed that IRS1 interacted with the 88-154 amino acid sequence of Klc1 via its PTB domain. Notably, the reduced Klc1 levels were found in senescence and osteoporosis skeletal muscle samples from both mice and human. Taken together, our findings suggested a crucial role of Klc1 in the regulation of IGF-AKT pathway during myogenesis through stabilizing IRS1, which might ultimately influence the development of muscle-related disorders.

Research progress of dihydromyricetin in the treatment of diabetes mellitus

Diabetic Mellitus (DM), a chronic metabolic disorder disease characterized by hyperglycemia, is mainly caused by the absolute or relative deficiency of insulin secretion or decreased insulin sensitivity in target tissue cells. Dihydromyricetin (DMY) is a flavonoid compound of dihydroflavonol that widely exists in Ampelopsis grossedentata. This review aims to summarize the research progress of DMY in the treatment of DM. A detailed summary of related signaling induced by DMY are discussed. Increasing evidence implicates that DMY display hypoglycemic effects in DM via improving glucose and lipid metabolism, attenuating inflammatory responses, and reducing oxidative stress, with the signal transduction pathways underlying the regulation of AMPK or mTOR/autophagy, and relevant downstream cascades, including PGC-1α/SIRT3, MEK/ERK, and PI3K/Akt signal pathways. Hence, the mechanisms underlying the therapeutic implications of DMY in DM are still obscure. In this review, following with a brief introduction of the absorption, metabolism, distribution, and excretion characteristics of DMY, we summarized the current pharmacological developments of DMY as well as possible molecular mechanisms in the treatment of DM, aiming to push the understanding about the protective role of DMY as well as its preclinical assessment of novel application.

Protein nanocondensates: the next frontier

Over the past decade, myriads of studies have highlighted the central role of protein condensation in subcellular compartmentalization and spatiotemporal organization of biological processes. Conceptually, protein condensation stands at the highest level in protein structure hierarchy, accounting for the assembly of bodies ranging from thousands to billions of molecules and for densities ranging from dense liquids to solid materials. In size, protein condensates range from nanocondensates of hundreds of nanometers (mesoscopic clusters) to phase-separated micron-sized condensates. In this review, we focus on protein nanocondensation, a process that can occur in subsaturated solutions and can nucleate dense liquid phases, crystals, amorphous aggregates, and fibers. We discuss the nanocondensation of proteins in the light of general physical principles and examine the biophysical properties of several outstanding examples of nanocondensation. We conclude that protein nanocondensation cannot be fully explained by the conceptual framework of micron-scale biomolecular condensation. The evolution of nanocondensates through changes in density and order is currently under intense investigation, and this should lead to the development of a general theoretical framework, capable of encompassing the full range of sizes and densities found in protein condensates.

VAPB-mediated ER-targeting stabilizes IRS-1 signalosomes to regulate insulin/IGF signaling

The scaffold protein IRS-1 is an essential node in insulin/IGF signaling. It has long been recognized that the stability of IRS-1 is dependent on its endomembrane targeting. However, how IRS-1 targets the intracellular membrane, and what type of intracellular membrane is actually targeted, remains poorly understood. Here, we found that the phase separation-mediated IRS-1 puncta attached to endoplasmic reticulum (ER). VAPB, an ER-anchored protein that mediates tethers between ER and membranes of other organelles, was identified as a direct interacting partner of IRS-1. VAPB mainly binds active IRS-1 because IGF-1 enhanced the VAPB-IRS-1 association and replacing of the nine tyrosine residues of YXXM motifs disrupted the VAPB-IRS-1 association. We further delineated that the Y745 and Y746 residues in the FFAT-like motif of IRS-1 mediated the association with VAPB. Notably, VAPB targeted IRS-1 to the ER and subsequently maintained its stability. Consistently, ablation of VAPB in mice led to downregulation of IRS-1, suppression of insulin signaling, and glucose intolerance. The amyotrophic lateral sclerosis (ALS)-derived VAPB P56S mutant also impaired IRS-1 stability by interfering with the ER-tethering of IRS-1. Our findings thus revealed a previously unappreciated condensate-membrane contact (CMC), by which VAPB stabilizes the membraneless IRS-1 signalosome through targeting it to ER membrane.

Phase separation enhances probability of receptor signalling and drug targeting

The probability of a given receptor tyrosine kinase (RTK) triggering a defined cellular outcome is low because of the promiscuous nature of signalling, the randomness of molecular diffusion through the cell, and the ongoing nonfunctional submembrane signalling activity or noise. Signal transduction is therefore a 'numbers game', where enough cell surface receptors and effector proteins must initially be engaged to guarantee formation of a functional signalling complex against a background of redundant events. The presence of intracellular liquid-liquid phase separation (LLPS) at the plasma membrane provides a mechanism through which the probabilistic nature of signalling can be weighted in favour of the required, discrete cellular outcome and mutual exclusivity in signal initiation.

Subcellular distribution of bone morphogenetic protein 2-inducible kinase (BMP2K): Regulation by liquid-liquid phase separation and nucleocytoplasmic shuttling

Bone morphogenetic protein 2 (BMP2)-inducible kinase (BMP2K) is induced by the cytokine BMP2, which is also implicated in the production of bone differentiation. In addition to regulating bone differentiation, BMP2K is implicated in a variety of cancers. Therefore, understanding the variables that determine where in the cell this kinase functions may help in understanding malignancies linked to BMP2K. However, the mechanisms regulating the subcellular localization of BMP2K are mainly unknown. By liquid-liquid phase separation (LLPS), BMP2K forms droplets in the cytoplasm, but how the droplets are regulated remains unclear. The reason why BMP2K localizes to the cytoplasm irrespective of having a nuclear localization signal (NLS) is also unknown. Here we show the element that controls BMP2K's LLPS and cytoplasmic localization. A glutamine-rich area is necessary for BMP2K phase separation, and droplet formation is controlled by hyperosmolarity. Cytoplasmic localization of BMP2K is managed by inhibition of NLS function through phosphorylation of Ser-1010 and by a newly found cytoplasmic localization region that antagonizes the NLS. These results will provide an important biochemical foundation for the advancement of BMP2K-related cell biology, structural biology, and pathophysiology.

The dynamic clustering of insulin receptor underlies its signaling and is disrupted in insulin resistance

Insulin receptor (IR) signaling is central to normal metabolic control and is dysregulated in metabolic diseases such as type 2 diabetes. We report here that IR is incorporated into dynamic clusters at the plasma membrane, in the cytoplasm and in the nucleus of human hepatocytes and adipocytes. Insulin stimulation promotes further incorporation of IR into these dynamic clusters in insulin-sensitive cells but not in insulin-resistant cells, where both IR accumulation and dynamic behavior are reduced. Treatment of insulin-resistant cells with metformin, a first-line drug used to treat type 2 diabetes, can rescue IR accumulation and the dynamic behavior of these clusters. This rescue is associated with metformin's role in reducing reactive oxygen species that interfere with normal dynamics. These results indicate that changes in the physico-mechanical features of IR clusters contribute to insulin resistance and have implications for improved therapeutic approaches.