Transmembrane signaling through single-spanning receptors modulated by phase separation at the cell surface.

A wide variety of transmembrane signals are transduced by cell-surface receptors that activate intracellular signaling molecules. In particular, receptor clustering in the plasma membrane plays a critical role in these processes. Single-spanning or single-pass transmembrane proteins are among the most significant types of membrane receptors, which include adhesion receptors, such as integrins, CD44, cadherins, and receptor tyrosine kinases. Elucidating the molecular mechanisms underlying the regulation of the activity of these receptors is of great significance. Liquid-liquid phase separation (LLPS) is a recently emerging paradigm in cellular physiology for the ubiquitous regulation of the spatiotemporal dynamics of various signaling pathways. This study describes the emerging features of transmembrane signaling through single-spanning receptors from the perspective of phase separation. Possible physicochemical modulations of LLPS-based transmembrane signaling are also discussed.

Curcumin Modulates the Membrane Raft Integrity via Phase Separation and Induces CD44 Shedding in Tumor Cells.

CD44 is a transmembrane cell adhesion molecule that is cleaved by the membrane proteinase, a disintegrin and metalloproteinase 10 (ADAM10), on the cell surface via ectodomain shedding after cholesterol depletion. Lipid raft-mediated CD44 shedding is essential for cancer cell invasion. As cell-cell and cell-matrix adhesions are critical for cancer progression, lipid raft-targeting agents may be effective for cancer therapy. Here, we found that curcumin and its derivatives induced the ADAM10-mediated shedding of CD44 in tumor cells. We also found that curcumin and the derivatives are membrane-active compounds whose effect depends on its planar backbone and the spatial arrangement of methoxy groups substituted on the two aromatic rings using giant unilamellar and plasma membrane vesicles. Curcumin and its derivatives with rigid backbones and hydroxy groups exerted membrane-domain-modulating activity, which may account for their pleiotropic effects via multiple signaling pathways involving membrane receptors. This study provides a basis for the use of membrane-active compounds, such as curcuminoids, to elucidate the roles of lipid rafts in cellular signaling, regulation of membrane-bound ADAM metalloproteinases, and the development of novel membrane lipid-based therapies.

Targeting the PI3K-Akt-mTOR signaling pathway involved in vasculogenic mimicry promoted by cancer stem cells.

An accumulating body of evidence has led to the development of the cancer stem-cell (CSC) model which proposed that a subset of cells distinct from those that form the tumor mass regulated the tumor growth rate over a long period. Various types of therapy have been developed for cancer treatment. The major conventional therapies are chemotherapy, radiation therapy, and surgical excision. The other emerging therapies include targeted therapy using molecule-based agents. However, the resistance to chemotherapy and radiation therapy frequently occurs. This was most likely due to the dysregulated functioning of the multidrug efflux pumps and nucleotide repair systems resulting from the multiple interactions between the CSCs and the tumor microenvironment. Even though chimeric antigen receptor T-cell and immune checkpoint blockade therapies have succeeded remarkably for treating cancers, evidence suggested that CSCs promoted the development of resistance to these therapies and led to metastasis. The cells with stem cell-like features actively participate in vasculogenic mimicry in different types of cancer. In addition to melanoma, vasculogenic mimicry has been observed in various cancers. One of the major signaling pathways in CSCs is the phosphoinositide 3-kinase (PI3K)/Akt/PTEN pathway. PI3Ks are a family of enzymes that play a critical role in cellular growth, migration, differentiation, and vasculogenic mimicry. The PI3K-Akt pathway also plays a crucial role in epithelial-mesenchymal transition and the establishment of CSC-specific phenotypes through the PTEN/Akt mechanistic target of the rapamycin axis. Thus, targeting the PI3K pathway could be beneficial for cancer treatment through the elimination of CSCs, and such therapy might break niches which maintain the CSC, inhibit the metastasis, and suppress the recurrence of cancer.

Integrated Multimodal Omics and Dietary Approaches for the Management of Neurodegeneration.

Neurodegenerative diseases, such as Alzheimer's disease and Parkinson's disease, are caused by a combination of multiple events that damage neuronal function. A well-characterized biomarker of neurodegeneration is the accumulation of proteinaceous aggregates in the brain. However, the gradually worsening symptoms of neurodegenerative diseases are unlikely to be solely due to the result of a mutation in a single gene, but rather a multi-step process involving epigenetic changes. Recently, it has been suggested that a fraction of epigenetic alternations may be correlated to neurodegeneration in the brain. Unlike DNA mutations, epigenetic alterations are reversible, and therefore raise the possibilities for therapeutic intervention, including dietary modifications. Additionally, reactive oxygen species may contribute to the pathogenesis of Alzheimer's disease and Parkinson's disease through epigenetic alternation. Given that the antioxidant properties of plant-derived phytochemicals are likely to exhibit pleiotropic effects against ROS-mediated epigenetic alternation, dietary intervention may be promising for the management of neurodegeneration in these diseases. In this review, the state-of-the-art applications using single-cell multimodal omics approaches, including epigenetics, and dietary approaches for the identification of novel biomarkers and therapeutic approaches for the treatment of neurodegenerative diseases are discussed.

Metabolic Reprogramming toward Aerobic Glycolysis and the Gut Microbiota Involved in the Brain Amyloid Pathology.

Alzheimer's disease (AD) is characterized by the formation of senile plaques consisting of fibrillated amyloid-ß (Aß), dystrophic neurites, and the neurofibrillary tangles of tau. The oligomers/fibrillar Aß damages the neurons or initiates an intracellular signaling cascade for neuronal cell death leading to Aß toxicity. The Aß is a 4 kDa molecular weight peptide originating from the C-terminal region of the amyloid precursor protein via proteolytic cleavage. Apart from the typical AD hallmarks, certain deficits in metabolic alterations have been identified. This study describes the emerging features of AD from the aspect of metabolic reprogramming in the main pathway of carbohydrate metabolism in the human brain. Particularly, the neurons in patients with AD favor glycolysis despite a normal mitochondrial function indicating a Warburg-like effect. In addition, certain dietary patterns are well known for their properties in preventing AD. Among those, a ketogenic diet may substantially improve the symptoms of AD. An effective therapeutic method for the treatment, mitigation, and prevention of AD has not yet been established. Therefore, the researchers pursue the development and establishment of novel therapies effective in suppressing AD symptoms and the elucidation of their underlying protective mechanisms against neurodegeneration aiming for AD therapy in the near future.

Therapeutic Implications of Probiotics in the Gut Microbe-Modulated Neuroinflammation and Progression of Alzheimer's Disease.

Alzheimer's disease (AD) is characterized by the accumulation of specific proteins in the brain. A recent study revealed that manipulating gut microbiota (GM) significantly reduced tau pathology and neurodegeneration in an apolipoprotein E isoform-dependent manner. The resilience of a healthy microbiota protects it from a variety of dysbiosis-related pathologies. Convincing evidence has demonstrated the roles of GM in the pathogenesis of AD, which are partly mediated by modified microglial activity in the brain. Therefore, modulation of GM may be a promising therapeutic option for AD prevention. In addition to providing the cells with energy and affecting microglial maturation, these microbial metabolites appear to influence neuronal function. One of the potential therapeutic approaches targeting GM may involve using probiotics. Additionally, human GM and its metabolites have also become potential therapeutic targets for developing interventions for the prevention of disorders. Synbiotics and postbiotics can also be used to treat AD by modulating GM. In addition, physical activity, exercise, and physical fitness are being considered as potential nonpharmacological therapies to reduce signaling pathways related to neuroinflammation. Therefore, interventions targeting GM might be promising strategies for health promotion.

Fatty Acid Metabolites and the Tumor Microenvironment as Potent Regulators of Cancer Stem Cell Signaling.

Individual cancer cells are not equal but are organized into a cellular hierarchy in which only a rare few leukemia cells can self-renew in a manner reminiscent of the characteristic stem cell properties. The PI3K/AKT pathway functions in a variety of cancers and plays a critical role in the survival and proliferation of healthy cells under physiologic conditions. In addition, cancer stem cells might exhibit a variety of metabolic reprogramming phenotypes that cannot be completely attributed to the intrinsic heterogeneity of cancer. Given the heterogeneity of cancer stem cells, new strategies with single-cell resolution will become a powerful tool to eradicate the aggressive cell population harboring cancer stem cell phenotypes. Here, this article will provide an overview of the most important signaling pathways of cancer stem cells regarding their relevance to the tumor microenvironment and fatty acid metabolism, suggesting valuable strategies among cancer immunotherapies to inhibit the recurrence of tumors.

Pleiotropic Signaling by Reactive Oxygen Species Concerted with Dietary Phytochemicals and Microbial-Derived Metabolites as Potent Therapeutic Regulators of the Tumor Microenvironment.

The excessive generation of reactive oxygen species (ROS) plays a pivotal role in the pathogenesis of diseases. ROS are central to cellular redox regulation and act as second messengers to activate redox-sensitive signals. Recent studies have revealed that certain sources of ROS can be beneficial or harmful to human health. Considering the essential and pleiotropic roles of ROS in basic physiological functions, future therapeutics should be designed to modulate the redox state. Dietary phytochemicals, microbiota, and metabolites derived from them can be expected to be developed as drugs to prevent or treat disorders in the tumor microenvironment.

The Chemopreventive Effects of Chlorogenic Acids, Phenolic Compounds in Coffee, against Inflammation, Cancer, and Neurological Diseases.

Coffee is one of the most widely consumed beverages, which has several effects on the human body. In particular, current evidence suggests that coffee consumption is associated with a reduced risk of inflammation, various types of cancers, and certain neurodegenerative diseases. Among the various constituents of coffee, phenolic phytochemicals, more specifically chlorogenic acids, are the most abundant, and there have been many attempts to utilize coffee chlorogenic acid for cancer prevention and therapy. Due to its beneficial biological effect on the human body, coffee is regarded as a functional food. In this review article, we summarize the recent advances and knowledge on the association of phytochemicals contained in coffee as nutraceuticals, with a particular focus on phenolic compounds, their intake, and nutritional biomarkers, with the reduction of disease risk, including inflammation, cancer, and neurological diseases.

CaMK phosphatase (CaMKP/POPX2/PPM1F) inhibitors suppress the migration of human breast cancer MDA-MB-231 cells with loss of polarized morphology.

CaMK phosphatase (CaMKP/POPX2/PPM1F) is a Ser/Thr protein phosphatase that belongs to the PPM family. Accumulating evidence suggests that CaMKP is involved in the pathogenesis of various diseases, including cancer. To clarify the relationship between CaMKP activity and human breast cancer cell motility, we examined the phosphatase activity of CaMKP in cell extracts. CaMKP activity assays of the immunoprecipitates prepared from the cell extract revealed that cells exhibiting higher motility had higher CaMKP activity, with no significant differences in the specific activity being observed. Two CaMKP-specific inhibitors, 1-amino-8-naphthol-4-sulfonic acid (ANS) and 1-amino-8-naphthol-2,4-disulfonic acid (ANDS), inhibited the migration of highly invasive MDA-MB-231 breast cancer cells without significant cytotoxicity, while an inactive analog, naphthionic acid, did not. Furthermore, the cells lost their elongated morphology and assumed a rounded shape following treatment with ANS, whereas they retained their elongated morphology following treatment with naphthionic acid. Consistent with these findings, ANS and ANDS significantly enhanced the phosphorylation level of CaMKI, a cellular substrate of CaMKP, while naphthionic acid did not. The present data suggest that CaMKP could be a novel therapeutic target for cancer metastasis.

Reactive Oxygen Species, Superoxide Dimutases, and PTEN-p53-AKT-MDM2 Signaling Loop Network in Mesenchymal Stem/Stromal Cells Regulation.

Mesenchymal stromal/stem cells (MSCs) are multipotent cells that can differentiate to various specialized cells, which have the potential capacity to differentiate properly and accelerate recovery in damaged sites of the body. This stem cell technology has become the fundamental element in regenerative medicine. As reactive oxygen species (ROS) have been reported to adversely influence stem cell properties, it is imperative to attenuate the extent of ROS to the promising protective approach with MSCs’ regenerative therapy. Oxidative stress also affects the culture expansion and longevity of MSCs. Therefore, there is great need to identify a method to prevent oxidative stress and replicative senescence in MSCs. Phosphatase and tensin homologue deleted on chromosome 10/Protein kinase B, PKB (PTEN/AKT) and the tumor suppressor p53 pathway have been proven to play a pivotal role in regulating cell apoptosis by regulating the oxidative stress and/or ROS quenching. In this review, we summarize the current research and our view of how PTEN/AKT and p53 with their partners transduce signals downstream, and what the implications are for MSCs’ biology.

Implications of PI3K/AKT/PTEN Signaling on Superoxide Dismutases Expression and in the Pathogenesis of Alzheimer's Disease.

Alzheimer’s disease is a neurodegenerative sickness, where the speed of personal disease progression differs prominently due to genetic and environmental factors such as life style. Alzheimer’s disease is described by the construction of neuronal plaques and neurofibrillary tangles composed of phosphorylated tau protein. Mitochondrial dysfunction may be a noticeable feature of Alzheimer’s disease and increased production of reactive oxygen species has long been described. Superoxide dismutases (SODs) protect from excess reactive oxygen species to form less reactive hydrogen peroxide. It is suggested that SODs can play a protective role in neurodegeneration. In addition, PI3K/AKT pathway has been shown to play a critical role on the neuroprotection and inhibiting apoptosis via the enhancing expression of the SODs. This pathway appears to be crucial in Alzheimer’s disease because it is related to the tau protein hyper-phosphorylation. Dietary supplementation of several ordinary compounds may provide a novel therapeutic approach to brain disorders by modulating the function of the PI3K/AKT pathway. Understanding these systems may offer a better efficacy of new therapeutic approaches. In this review, we summarize recent progresses on the involvement of the SODs and PI3K/AKT pathway in neuroprotective signaling against Alzheimer’s disease.

Roles of oncogenes and tumor-suppressor genes in osteoclastogenesis (Review).

Osteoporosis is a bone disease that poses a tremendous burden to health care. The receptor activator of nuclear factor-κB (RANK) and its ligand (RANKL) have been a major focus of this research field. RANKL signaling not only activates a variety of downstream signaling pathways required for osteoclast development, but crosstalk with other signaling pathways also adjusts bone homeostasis both in normal physiology and in bone disease. Consequently, novel drugs specifically targeting RANK-RANKL and their signaling pathways in osteoclasts are expected to revolutionize the treatment of various bone diseases such as osteoporosis. Osteoclasts are the exclusive cells involved in bone resorption. Abnormal activation of osteoclasts can lead to reduced bone density, resulting in osteopenia, osteoporosis and other bone disorders. To date, the mechanism of how osteoclast precursors differentiate into mature osteoclasts remains elusive. Cell proliferation and cell death may be key processes in the progression as well as other cell types. Oncogene products and tumor-suppressor molecules play a pivotal role in regulating the processes, which are important in regulating the configuration of bone disorders. Based on the understanding of these processes, promising alternatives to the use of medications against osteoporosis include specific diets with plant-derived supplements to modulate the expression and/or activity of these molecules. In this review, we summarize the progress of research with a focus on the modulatory roles of oncogene products and tumor-suppressor molecules and suggest the scope of further research concerning the prevention of osteoporosis in this field.

PI3K/AKT signaling mediated by G protein­coupled receptors is involved in neurodegenerative Parkinson's disease (Review).

Parkinson's disease (PD) is a common progressive and multifactorial neurodegenerative disease, characterized by the loss of midbrain dopaminergic neurons. Numerous pathological processes including, inflammation, oxidative stress, mitochondrial dysfunction, neurotransmitter imbalance, and apoptosis as well as genetic factors may lead to neuronal degeneration. Motor deficits in PD are due mostly to the progressive loss of nigrostriatal dopaminergic neurons. Neuroprotection of functional neurons is of significance in the treatment of PD. G protein­coupled receptors (GPCRs) have been implicated in the neuroprotection against PD through the survival of dopaminergic neurons. In addition, phosphatidyl­inositol­3­kinase (PI3K)/AKT signaling has also been demonstrated to be neuroprotective. Knowledge of the mechanisms involved in this cellular protection could be critical for developing treatments to prevent this neurodegenerative disorder. In this review, we highlight the protective roles of the PI3K/AKT signaling pathway in the function of representative serotonin GPCRs. Particular attention is given to the molecular mechanisms of this pathway proposed to explain the favorable effects of food ingredients against neurodegenerative disease.

Effective PI3K modulators for improved therapy against malignant tumors and for neuroprotection of brain damage after tumor therapy (Review).

Due to the key role in various cellular processes including cell proliferation and cell survival on many cell types, dysregulation of the PI3K/AKT pathway represents a crucial step of the pathogenesis in many diseases. Furthermore, the tumor suppressor PTEN negatively regulates the PI3K/AKT pathway through its lipid phosphatase activity, which is recognized as one of the most frequently deleted and/or mutated genes in human cancer. Given the pervasive involvement of this pathway, the development of the molecules that modulate this PI3K/AKT signaling has been initiated in studies which focus on the extensive effective drug discovery. Consequently, the PI3K/AKT pathway appears to be an attractive pharmacological target both for cancer therapy and for neurological protection necessary after the therapy. A better understanding of the molecular relations could reveal new targets for treatment development. We review recent studies on the features of PI3K/AKT and PTEN, and their pleiotropic functions relevant to the signaling pathways involved in cancer progress and in neuronal damage by the therapy.

Lipid Raft-Mediated Regulation of Hyaluronan-CD44 Interactions in Inflammation and Cancer.

Hyaluronan is a major component of the extracellular matrix and plays pivotal roles in inflammation and cancer. Hyaluronan oligomers are frequently found in these pathological conditions, in which they exert their effects via association with the transmembrane receptor CD44. Lipid rafts are cholesterol- and glycosphingolipid-enriched membrane microdomains that may regulate membrane receptors while serving as platforms for transmembrane signaling at the cell surface. This article focuses on the recent discovery that lipid rafts regulate the interaction between CD44 and hyaluronan, which depends largely on hyaluronan's size. Lipid rafts regulate CD44's ability to bind hyaluronan in T cells, control the rolling adhesion of lymphocytes on vascular endothelial cells, and regulate hyaluronan- and CD44-mediated cancer cell migration. The implications of these findings for preventing inflammatory disorders and cancer are also discussed.

A novel inhibitory mechanism of MRTF-A/B on the ICAM-1 gene expression in vascular endothelial cells.

The roles of myocardin-related transcription factor A (MRTF-A) and MRTF-B in vascular endothelial cells are not completely understood. Here, we found a novel regulatory mechanism for MRTF-A/B function. MRTF-A/B tend to accumulate in the nucleus in arterial endothelial cells in vivo and human aortic endothelial cells (HAoECs) in vitro. In HAoECs, nuclear localization of MRTF-A/B was not significantly affected by Y27632 or latrunculin B, primarily due to the reduced binding of MRTF-A/B to G-actin and in part, to the low level of MRTF-A phosphorylation by ERK. MRTF-A/B downregulation by serum depletion or transfection of siRNA against MRTF-A and/or MRTF-B induced ICAM-1 expression in HAoECs. It is known that nuclear import of nuclear factor-κB (NF-κB) plays a key role in ICAM-1 gene transcription. However, nuclear accumulation of NF-κB p65 was not observed in MRTF-A/B-depleted HAoECs. Our present findings suggest that MRTF-A/B inhibit ICAM-1 mRNA expression by forming a complex with NF-κB p65 in the nucleus. Conversely, downregulation of MRTF-A/B alleviates this negative regulation without further translocation of NF-κB p65 into the nucleus. These results reveal the novel roles of MRTF-A/B in the homeostasis of vascular endothelium.

Cholesterol lowering: role in cancer prevention and treatment.

The accumulation of cholesterol is a general feature of cancer tissue, and recent evidence suggests that cholesterol plays critical roles in the progression of cancers, including breast, prostate, and colorectal cancers. The dysregulation of metabolic pathways, including those involved in cholesterol biosynthesis, is implicated in tumor development and cancer progression. Lipid rafts are highly dynamic cholesterol-enriched domains of the cell membrane, involved in various cellular functions, including the regulation of transmembrane signaling at the cell surface. It was recently demonstrated that lipid rafts also play critical roles in cancer cell adhesion and migration. This review focuses on our current understanding of how cholesterol regulation, lipid rafts, and dysregulated cholesterol biosynthesis contribute to cancer development and progression, and the therapeutic potential of cholesterol lowering for cancer prevention and treatment.

Ultrastructural analysis of nanogold-labeled cell surface microvilli in liquid by atmospheric scanning electron microscopy and their relevance in cell adhesion.

The adhesion of leukocytes circulating in the blood to vascular endothelium is critical for their trafficking in the vasculature, and CD44 is an important cell surface receptor for rolling adhesion. In this study, we demonstrate the correlative observation of CD44 distribution at the lymphocyte cell surface in liquid by fluorescence optical microscopy and immuno-electron microscopy using an atmospheric scanning electron microscope (ASEM). The ultrastructure of the cell surface was clearly imaged by ASEM using positively charged Nanogold particles. ASEM analysis demonstrated microvilli projections around the cell surface and the localization of CD44 on the microvilli. Treatment of cells with cytochalasin D resulted in a loss of the microvilli projections and concomitantly abrogated CD44-mediated adhesion to its ligand hyaluronan. These results suggest the functional relevance of microvilli in CD44-mediated rolling adhesion under shear flow.