Stress-induced non-vesicular release of prothymosin-α initiated by an interaction with S100A13, and its blockade by caspase-3 cleavage

Fine structures of intrinsically disordered proteins

We report simulation studies of 33 single intrinsically disordered proteins (IDPs) using coarse-grained bead-spring models where interactions among different amino acids are introduced through a hydropathy matrix and additional screened Coulomb interaction for the charged amino acid beads. Our simulation studies of two different hydropathy scales (HPS1, HPS2) [Dignon et al., PLoS Comput. Biol. 14, e1005941 (2018); Tesei et al. Proc. Natl. Acad. Sci. U. S. A. 118, e2111696118 (2021)] and the comparison with the existing experimental data indicate an optimal interaction parameter ϵ = 0.1 and 0.2 kcal/mol for the HPS1 and HPS2 hydropathy scales. We use these best-fit parameters to investigate both the universal aspects as well as the fine structures of the individual IDPs by introducing additional characteristics. (i) First, we investigate the polymer-specific scaling relations of the IDPs in comparison to the universal scaling relations [Bair et al., J. Chem. Phys. 158, 204902 (2023)] for the homopolymers. By studying the scaled end-to-end distances ⟨RN2⟩/(2Lℓp) and the scaled transverse fluctuations l̃⊥2=⟨l⊥2⟩/L, we demonstrate that IDPs are broadly characterized with a Flory exponent of ν ≃ 0.56 with the conclusion that conformations of the IDPs interpolate between Gaussian and self-avoiding random walk chains. Then, we introduce (ii) Wilson charge index (W) that captures the essential features of charge interactions and distribution in the sequence space and (iii) a skewness index (S) that captures the finer shape variation of the gyration radii distributions as a function of the net charge per residue and charge asymmetry parameter. Finally, our study of the (iv) variation of ⟨Rg⟩ as a function of salt concentration provides another important metric to bring out finer characteristics of the IDPs, which may carry relevant information for the origin of life.

Single-cell transcriptomics identifies prothymosin α restriction of HIV-1 in vivo

Host restriction factors play key roles in innate antiviral defense, but it remains poorly understood which of them restricts HIV-1 in vivo. Here, we used single-cell transcriptomic analysis to identify host factors associated with HIV-1 control during acute infection by correlating host gene expression with viral RNA abundance within individual cells. Wide sequencing of cells from one participant with the highest plasma viral load revealed that intracellular viral RNA transcription correlates inversely with expression of the gene PTMA, which encodes prothymosin α. This association was genome-wide significant (Padjusted < 0.05) and was validated in 28 additional participants from Thailand and the Americas with HIV-1 CRF01_AE and subtype B infections, respectively. Overexpression of prothymosin α in vitro confirmed that this cellular factor inhibits HIV-1 transcription and infectious virus production. Our results identify prothymosin α as a host factor that restricts HIV-1 infection in vivo, which has implications for viral transmission and cure strategies.

Non-Vesicular Release of Alarmin Prothymosin α Complex Associated with Annexin-2 Flop-Out

Nuclear protein prothymosin α (ProTα) is a unique member of damage-associated molecular patterns (DAMPs)/alarmins. ProTα prevents neuronal necrosis by causing a cell death mode switch in serum-starving or ischemic/reperfusion models in vitro and in vivo. Underlying receptor mechanisms include Toll-like receptor 4 (TLR4) and G_i-coupled receptor. Recent studies have revealed that the mode of the fatal stress-induced extracellular release of nuclear ProTα from cortical neurons in primary cultures, astrocytes and C6 glioma cells has two steps: ATP loss-induced nuclear release and the Ca²⁺-mediated formation of a multiple protein complex and its extracellular release. Under the serum-starving condition, ProTα is diffused from the nucleus throughout the cell due to the ATP loss-induced impairment of importin α-mediated nuclear transport. Subsequent mechanisms are all Ca²⁺-dependent. They include the formation of a protein complex with ProTα, S100A13, p40 Syt-1 and Annexin A2 (ANXA2); the fusion of the protein complex to the plasma membrane via p40 Syt-1-Stx-1 interaction; and TMEM16F scramblase-mediated ANXA2 flop-out. Subsequently, the protein complex is extracellularly released, leaving ANXA2 on the outer cell surface. The ANXA2 is then flipped in by a force of ATP8A2 activity, and the non-vesicular release of protein complex is repeated. Thus, the ANXA2 flop-out could play key roles in a new type of non-vesicular and non-classical release for DAMPs/alarmins, which is distinct from the modes conducted via gasdermin D or mixed-lineage kinase domain-like pseudokinase pores.

Prothymosin α Plays Role as a Brain Guardian through Ecto-F1 ATPase-P2Y12 Complex and TLR4/MD2

Prothymosin alpha (ProTα) was discovered to be a necrosis inhibitor from the conditioned medium of a primary culture of rat cortical neurons under starved conditions. This protein carries out a neuronal cell-death-mode switch from necrosis to apoptosis, which is, in turn, suppressed by a variety of neurotrophic factors (NTFs). This type of NTF-assisted survival action of ProTα is reproduced in cerebral and retinal ischemia-reperfusion models. Further studies that used a retinal ischemia-reperfusion model revealed that ProTα protects retinal cells via ecto-F₁ ATPase coupled with the G_i-coupled P2Y₁₂ receptor and Toll-like receptor 4 (TLR4)/MD2 coupled with a Toll-IL-1 receptor domain-containing adaptor inducing IFN-β (TRIF). In cerebral ischemia-reperfusion models, ProTα has additional survival mechanisms via an inhibition of matrix metalloproteases in microglia and vascular endothelial cells. Heterozygous or conditional ProTα knockout mice show phenotypes of anxiety, memory learning impairment, and a loss of neurogenesis. There are many reports that ProTα has multiple intracellular functions for cell survival and proliferation through a variety of protein-protein interactions. Overall, it is suggested that ProTα plays a key role as a brain guardian against ischemia stress through a cell-death-mode switch assisted by NTFs and a role of neurogenesis.

Prothymosin α-derived hexapeptide prevents the brain damage and sequelae due to ischemia-hemorrhage

ProTα discovered as a necrosis-inhibitor from the conditioned medium of cortical culture also shows a potent survival action in brain and retinal ischemia/reperfusion models. The proposed mechanisms are the initial cell death mode switch from necrosis to apoptosis, which is subsequently inhibited by neurotrophic factors in vivo. It should be noted that ProTα and its derived hexapeptide P6Q completely suppress the cerebral hemorrhage induced by late tPA treatment (4.5 h) after the brain ischemia/reperfusion. Mechanisms underlying their beneficial actions may be related to the fact that ProTα inhibits the production of matrix metalloproteases (MMPs) in microglia and vascular endothelial cells. However, as P6Q inhibits MMPs in vascular endothelial cells, but not in microglia, the suppression of MMP production in endothelial cells seems to play major roles in the late tPA-induced hemorrhage. Although the tPA-treatments could enable the survival of patients with stroke, the post-stroke sequelae are the next clinical issues to be solved. The use of small peptide P6Q revealed the blockade of post-stroke pain, depression and memory-learning deficits in animal models. Furthermore, recent studies also showed that P6Q supplementation increased the viability of human induced pluripotent stem (iPS) cell-derived retinal pigment epithelium cell suspensions during the storage and P6Q attenuated the cisplatin-induced acute kidney injury.

Cell Senescence and Central Regulators of Immune Response

Pathways regulating cell senescence and cell cycle underlie many processes associated with ageing and age-related pathologies, and they also mediate cellular responses to exposure to stressors. Meanwhile, there are central mechanisms of the regulation of stress responses that induce/enhance or weaken the response of the whole organism, such as hormones of the hypothalamic-pituitary-adrenal (HPA) axis, sympathetic and parasympathetic systems, thymic hormones, and the pineal hormone melatonin. Although there are many analyses considering relationships between the HPA axis and organism ageing, we found no systematic analyses of relationships between the neuroendocrine regulators of stress and inflammation and intracellular mechanisms controlling cell cycle, senescence, and apoptosis. Here, we provide a review of the effects of neuroendocrine regulators on these mechanisms. Our analysis allowed us to postulate a multilevel system of central regulators involving neurotransmitters, glucocorticoids, melatonin, and the thymic hormones. This system finely regulates the cell cycle and metabolic/catabolic processes depending on the level of systemic stress, stage of stress response, and energy capabilities of the body, shifting the balance between cell cycle progression, cell cycle stopping, senescence, and apoptosis. These processes and levels of regulation should be considered when studying the mechanisms of ageing and the proliferation on the level of the whole organism.

A Novel S100 Family-Based Signature Associated with Prognosis and Immune Microenvironment in Glioma

Background

Glioma is the most common central nervous system (CNS) cancer with a short survival period and a poor prognosis. The S100 family gene, comprising 25 members, relates to diverse biological processes of human malignancies. Nonetheless, the significance of S100 genes in predicting the prognosis of glioma remains largely unclear. We aimed to build an S100 family-based signature for glioma prognosis.

Methods

We downloaded 665 and 313 glioma patients, respectively, from The Cancer Genome Atlas (TCGA) and Chinese Glioma Genome Atlas (CGGA) database with RNAseq data and clinical information. This study established a prognostic signature based on the S100 family genes through multivariate COX and LASSO regression. The Kaplan-Meier curve was plotted to compare overall survival (OS) among groups, whereas Receiver Operating Characteristic (ROC) analysis was performed to evaluate model accuracy. A representative gene S100B was further verified by in vitro experiments.

Results

An S100 family-based signature comprising 5 genes was constructed to predict the glioma that stratified TCGA-derived cases as a low- or high-risk group, whereas the significance of prognosis was verified based on CGGA-derived cases. Kaplan-Meier analysis revealed that the high-risk group was associated with the dismal prognosis. Furthermore, the S100 family-based signature was proved to be closely related to immune microenvironment. In vitro analysis showed S100B gene in the signature promoted glioblastoma (GBM) cell proliferation and migration.

Conclusions

We constructed and verified a novel S100 family-based signature associated with tumor immune microenvironment (TIME), which may shed novel light on the glioma diagnosis and treatment.

The macrophage-derived protein PTMA induces filamentation of the human fungal pathogen Candida albicans

Evasion of killing by immune cells is crucial for fungal survival in the host. For the human fungal pathogen Candida albicans, internalization by macrophages induces a transition from yeast to filaments that promotes macrophage death and fungal escape. Nutrient deprivation, alkaline pH, and oxidative stress have been implicated as triggers of intraphagosomal filamentation; however, the impact of other host-derived factors remained unknown. Here, we show that lysates prepared from macrophage-like cell lines and primary macrophages robustly induce C. albicans filamentation. Enzymatic treatment of lysate implicates a phosphorylated protein, and bioactivity-guided fractionation coupled to mass spectrometry identifies the immunomodulatory phosphoprotein PTMA as a candidate trigger of C. albicans filamentation. Immunoneutralization of PTMA within lysate abolishes its activity, strongly supporting PTMA as a filament-inducing component of macrophage lysate. Adding to the known repertoire of physical factors, this work implicates a host protein in the induction of C. albicans filamentation within immune cells.

The human fungal pathogen Candida albicans filaments within host macrophages, enabling its escape. Case et al. demonstrate that lysates prepared from macrophage-like cell lines and primary macrophages induce C. albicans filamentation and implicate the immunomodulatory protein prothymosin alpha (PTMA) as a trigger of filamentation produced by host immune cells.

Annexin A2 Flop-Out Mediates the Non-Vesicular Release of DAMPs/Alarmins from C6 Glioma Cells Induced by Serum-Free Conditions

Prothymosin alpha (ProTα) and S100A13 are released from C6 glioma cells under serum-free conditions via membrane tethering mediated by Ca²⁺-dependent interactions between S100A13 and p40 synaptotagmin-1 (Syt-1), which is further associated with plasma membrane syntaxin-1 (Stx-1). The present study revealed that S100A13 interacted with annexin A2 (ANXA2) and this interaction was enhanced by Ca²⁺ and p40 Syt-1. Amlexanox (Amx) inhibited the association between S100A13 and ANXA2 in C6 glioma cells cultured under serum-free conditions in the in situ proximity ligation assay. In the absence of Amx, however, the serum-free stress results in a flop-out of ANXA2 through the membrane, without the extracellular release. The intracellular delivery of anti-ANXA2 antibody blocked the serum-free stress-induced cellular loss of ProTα, S100A13, and Syt-1. The stress-induced externalization of ANXA2 was inhibited by pretreatment with siRNA for P4-ATPase, ATP8A2, under serum-free conditions, which ablates membrane lipid asymmetry. The stress-induced ProTα release via Stx-1A, ANXA2 and ATP8A2 was also evidenced by the knock-down strategy in the experiments using oxygen glucose deprivation-treated cultured neurons. These findings suggest that starvation stress-induced release of ProTα, S100A13, and p40 Syt-1 from C6 glioma cells is mediated by the ANXA2-flop-out via energy crisis-dependent recovery of membrane lipid asymmetry.

In Vitro Immunodetection of Prothymosin Alpha in Normal and Pathological Conditions

Prothymosin alpha (ProTα) is a highly acidic polypeptide, ubiquitously expressed in almost all mammalian cells and tissues and consisting of 109 amino acids in humans. ProTα is known to act both, intracellularly, as an anti-apoptotic and proliferation mediator, and extracellularly, as a biologic response modifier mediating immune responses similar to molecules termed as "alarmins". Antibodies and immunochemical techniques for ProTα have played a leading role in the investigation of the biological role of ProTα, several aspects of which still remain unknown and contributed to unraveling the diagnostic and therapeutic potential of the polypeptide. This review deals with the so far reported antibodies along with the related immunodetection methodology for ProTα (immunoassays as well as immunohistochemical, immunocytological, immunoblotting, and immunoprecipitation techniques) and its application to biological samples of interest (tissue extracts and sections, cells, cell lysates and cell culture supernatants, body fluids), in health and disease states. In this context, literature information is critically discussed, and some concluding remarks are presented.

Involvement of SNARE Protein Interaction for Non-classical Release of DAMPs/Alarmins Proteins, Prothymosin Alpha and S100A13

Prothymosin alpha (ProTα) is involved in multiple cellular processes. Upon serum-free stress, ProTα lacking a signal peptide sequence is non-classically released from C6 glioma cells as a complex with Ca²⁺-binding cargo protein S100A13. Thus, ProTα and S100A13 are conceived to be members of damage-associated molecular patterns (DAMPs)/alarmins. However, it remains to be determined whether stress-induced release of ProTα and S100A13 involves SNARE proteins in the mechanisms underlying membrane tethering of the multiprotein complex. In the present study, we used C6 glioma cells as a model of ProTα release. In pull-down assay, p40 synaptotagmin-1 (Syt-1), a vesicular SNARE, formed a hetero-oligomeric complex with homodimeric S100A13 in a Ca²⁺-dependent manner. The interaction between p40 Syt-1 and S100A13 was also Ca²⁺-dependent in surface plasmon resonance (SPR). Immunoprecipitation using conditioned medium (CM) revealed that p40 Syt-1 was co-released with ProTα and S100A13 upon serum-free stress. In in situ proximity ligation assay (PLA), Syt-1 interacted with S100A13 upon serum-free stress in C6 glioma cells. The intracellular delivery of anti-Syt-1 IgG blocked serum free-induced release of ProTα and S100A13. Serum free-induced ProTα-EGFP release was significantly blocked by botulinum neurotoxin/C1 (BoNT/C1), which cleaves target SNARE syntaxin-1 (Stx-1). In immunocytochemistry, the cellular loss of ProTα-EGFP, S100A13, and Syt-1 was also blocked by BoNT/C1. Furthermore, the intracellular delivery of anti-Stx-1 IgG or Stx-1 siRNA treatment blocked Syt-1, S100A13 and ProTα release from C6 glioma cells. All these findings suggest that SNARE proteins play roles in stress-induced non-classical release of DAMPs/alarmins proteins, ProTα and S100A13 from C6 glioma cells.

Precursors of thymic peptides as stress sensors

INTRODUCTION

A large volume of data indicates that the known thymic hormones, thymulin, thymopoietin, thymosin-α, thymosin-β, and thymic humoral factor-y2, exhibit different spectra of activities. Although large in volume, available data are rather fragmented, resulting in a lack of understanding of the role played by thymic hormones in immune homeostasis.

AREA COVERED

Existing data compartmentalizes the effect of thymic peptides into 2 categories: influence on immune cells and interconnection with neuroendocrine systems. The current study draws attention to a third aspect of the thymic peptide effect that has not been clarified yet, wherein ubiquitous and highly abundant intranuclear precursors of so called 'thymic peptides' play a fundamental role in all somatic cells.

EXPERT OPINION

Our analysis indicated that, under certain stress-related conditions, these precursors are cleaved to form immunologically active peptides that rapidly leave the nucleus and intracellular spaces, to send 'distress signals' to the immune system, thereby acting as stress sensors. We propose that these peptides may form a link between somatic cells and immune as well as neuroendocrine systems. This model may provide a better understanding of the mechanisms underlying immune homeostasis, leading thereby to the development of new therapeutic regimes utilizing the characteristics of thymic peptides.

Gγ7-specific prothymosin alpha deletion causes stress- and age-dependent motor dysfunction and anxiety

We previously showed that prothymosin alpha (ProTα) improves cerebral ischemia-induced motor dysfunction. Our recent study also demonstrated that heterozygous ProTα deletion exhibited an enhanced anxiety-like behavior in mice. However, it remains elusive which brain regions or cells are related to these phenotypes. Here we generated conditional Gγ7-specific ProTα knockout mice using G protein γ7 subunit gene (Gng7)-cre promoter to see the brain robustness roles of ProTα in the striatum and hippocampus. The younger conditional ProTα (Gng7) knockout mice at the age of 10 weeks showed no significant phenotypes in motor dysfunction in the Rotarod test and locomotor activity in the open-field test, whereas significant motor dysfunction was obtained by 15 min transient middle cerebral artery occlusion (tMCAO)-induced cerebral ischemia. The aged conditional ProTα (Gng7) knockout mice at the age of 20 weeks showed hypolocomotor activity with less center time in the open-field test and impaired motor coordination in the Rotarod test without ischemia. Thus, this study suggests that ProTα has important roles in the maintenance of motor coordination and anxiety-like behavior.

[Lysophosphatidic Acid Receptor Signaling Underlying Chronic Pain and Neuroprotective Mechanisms through Prothymosin α]

For my Ph.D. research topic, I isolated endogenous morphine-like analgesic dipeptide, kyotorphin, which mediates Met-enkephalin release, and discovered kyotorphin synthetase, a putative receptor and antagonist. Furthermore, I succeeded in purifying μ-opioid receptor and functional reconstitution with purified G proteins. After receiving my full professor position at Nagasaki University in 1996, I worked on two topics of research, molecular mechanisms of chronic pain through lysophosphatidic acid (LPA) and identification and characterization of neuroprotective protein, prothymosin α. In a series of studies, we have shown that LPA signaling defines the molecular mechanisms of neuropathic pain and fibromyalgia in terms of development and maintenance. Above all, the discovery of feed-forward system in LPA production and pain memory may contribute to better understanding of chronic pain and future analgesic drug discovery. Regarding prothymosin α, we first discovered it as neuronal necrosis-inhibitory molecule through two independent mechanisms, such as toll-like receptor and F₀/F₁ ATPase, both which protect neurons through indirect mechanisms. Prothymosin α is released by non-classical and non-vesicular mechanisms on various stresses, such as ischemia, starvation, and heat-shock. Thus it may be called a new type of neuroprotective damage-associated molecular patterns (DAMPs)/Alarmins. Heterozygotic mice showed a defect in memory-learning and neurogenesis as well as anxiogenic behaviors. Small peptide, P6Q derived from prothymosin α retains neuroprotective actions, which include blockade of cerebral hemorrhage caused by late treatment with tissue plasminogen activator in the stroke model in mice.

The Glutamate Receptor-Like Protein GLR3.7 Interacts With 14-3-3ω and Participates in Salt Stress Response in Arabidopsis thaliana

Ionotropic glutamate receptors (iGluRs) are ligand-gated cation channels that mediate fast excitatory neurotransmission in the mammalian central nervous system. In the model plant Arabidopsis thaliana, a family of 20 glutamate receptor-like proteins (GLRs) shares similarities to animal iGluRs in sequence and predicted secondary structure. However, the function of GLRs in plants is little known. In the present study, a serine site (Ser-860) of AtGLR3.7 phosphorylated by a calcium-dependent protein kinase (CDPK) was identified and confirmed by an in vitro kinase assay. Using a bimolecular fluorescence complementation and quartz crystal microbalance analyses, the physical interaction between AtGLR3.7 and the 14-3-3ω protein was confirmed. The mutation of Ser-860 to alanine abolished this interaction, indicating that Ser-860 is the 14-3-3ω binding site of AtGLR3.7. Compared with wild type, seed germination of the glr3.7-2 mutant was more sensitive to salt stress. However, the primary root growth of GLR3.7-S860A overexpression lines was less sensitive to salt stress than that of the wild-type line. In addition, the increase of cytosolic calcium ion concentration by salt stress was significantly lower in the glr3.7-2 mutant line than in the wild-type line. Moreover, association of 14-3-3 proteins to microsomal fractions was less in GLR3.7-S860A overexpression lines than in GLR3.7 overexpression line under 150 mM NaCl salt stress condition. Overall, our results indicated that GLR3.7 is involved in salt stress response in A. thaliana by affecting calcium signaling.

The Glutamate Receptor-Like Protein GLR3.7 Interacts With 14-3-3ω and Participates in Salt Stress Response in Arabidopsis thaliana

Ionotropic glutamate receptors (iGluRs) are ligand-gated cation channels that mediate fast excitatory neurotransmission in the mammalian central nervous system. In the model plant Arabidopsis thaliana, a family of 20 glutamate receptor-like proteins (GLRs) shares similarities to animal iGluRs in sequence and predicted secondary structure. However, the function of GLRs in plants is little known. In the present study, a serine site (Ser-860) of AtGLR3.7 phosphorylated by a calcium-dependent protein kinase (CDPK) was identified and confirmed by an in vitro kinase assay. Using a bimolecular fluorescence complementation and quartz crystal microbalance analyses, the physical interaction between AtGLR3.7 and the 14-3-3ω protein was confirmed. The mutation of Ser-860 to alanine abolished this interaction, indicating that Ser-860 is the 14-3-3ω binding site of AtGLR3.7. Compared with wild type, seed germination of the glr3.7-2 mutant was more sensitive to salt stress. However, the primary root growth of GLR3.7-S860A overexpression lines was less sensitive to salt stress than that of the wild-type line. In addition, the increase of cytosolic calcium ion concentration by salt stress was significantly lower in the glr3.7-2 mutant line than in the wild-type line. Moreover, association of 14-3-3 proteins to microsomal fractions was less in GLR3.7-S860A overexpression lines than in GLR3.7 overexpression line under 150 mM NaCl salt stress condition. Overall, our results indicated that GLR3.7 is involved in salt stress response in A. thaliana by affecting calcium signaling.

Comparison of the organic matrix found in intestinal CaCO3 precipitates produced by several marine teleost species

Marine bony fish poses the unique ability to hydrate from imbibed seawater. They accomplish this, in part, by the precipitation of inorganic carbonate mineral in their intestine, which lowers luminal osmotic pressure and allows for water uptake. It has recently been described that in the Gulf toadfish (Opsanus beta) this Ca(Mg)CO₃ precipitation occurs under the regulation of an organic matrix. To date no investigations have aimed to determine if this phenomenon applies more generally to marine fish. Here, intestinally derived precipitates were collected from gray snapper (Lutjanus griseus), white grunt (Haemulon plumieri), European flounder (Platichthys flesus), as well as Gulf toadfish, and their matrices were extracted. The ability of these matrices to regulate CaCO₃ production was determined using an in vitro calcification assay, which revealed that the matrix derived from each of the tested species increased precipitation at low concentrations, while inhibiting it at higher concentrations in full agreement with the earlier studies on toadfish. Matrix extracted from European flounder precipitates was then analyzed by mass spectrometry, leading to the identification of over 50 unique proteins. When the identities of these proteins were compared to previous investigation of toadfish precipitate matrix, nearly 35% were found to overlap between the flounder and toadfish analyses, suggesting conserved mechanisms of precipitation control. The effects of using different sodium hypochlorite (NaOCl) solutions during precipitate purification on the resulting organic matrix are also discussed.

Amlexanox Inhibits Cerebral Ischemia-Induced Delayed Astrocytic High-Mobility Group Box 1 Release and Subsequent Brain Damage

High-mobility group box 1 (HMGB1) is increased in the cerebrospinal fluid (CSF) and serum during the early and late phases of brain ischemia and is known to contribute to brain damage. However, detailed characterization underlying cell type-specific HMGB1 release and pathophysiological roles of extracellularly released HMGB1 in ischemic brain remain unclear. Here, we examined cell type-specific HMGB1 release and the therapeutic potential of amlexanox, an inhibitor of nonclassical release, and of an anti-HMGB1 antibody against ischemic brain damage. HMGB1 depletion from neuronal nuclei was observed within 3 hours after transient middle cerebral artery occlusion (tMCAO), whereas the intracerebroventricular (i.c.v.) pretreatment with amlexanox blocked HMGB1 release from neurons, resulting in HMGB1 redistribution in the nuclei and cytoplasm. HMGB1 was selectively released from astrocytes 27 hours after tMCAO and this HMGB1 release was blocked by late treatment with amlexanox (i.c.v.) 24 hours after tMCAO. Proximity extension assay revealed that the HMGB1 level was elevated in the CSF at 3 and 27 hours after tMCAO. This late treatment with amlexanox significantly protected the brain from ischemic damage, but its pretreatment 30 minutes before tMCAO failed to show any protection. The late treatment (i.c.v.) with anti-HMGB1 antibody 24 hours after tMCAO also ameliorated ischemic brain damage 48 hours after tMCAO. Thus, the inhibition of brain damage by late treatment with amlexanox or anti-HMGB1 antibody indicates that late HMGB1 release plays a role in the maintenance of stroke-induced brain damage, and the inhibition of this release would be a novel therapeutic target for protection of ischemic brain damage.

Extrathymic production of thymulin induced by oxidative stress, heat shock, apoptosis, or necrosis

Thymic peptides are immune regulators produced mainly in the thymus. However, thymic peptides such as thymosin-α and thymopoietin have precursors widely expressed outside the thymus, localized in cell nuclei, and involved in vital nuclear functions. In stress-related conditions, they can relocalize. We hypothesized that another thymic peptide, thymulin, could be similarly produced by non-thymic cells during stress and have a precursor therein. Non-thymic cells, including macrophages and fibroblasts, were exposed to oxidative stress, heat, apoptosis, or necrosis. Extracellular thymulin was identified in media of both cell types 2 h after exposure to stress or lethal signals. Therefore, thymulin is released by non-thymic cells. To examine possible thymulin precursors in non-thymic cells, macrophage lysates were analyzed by western blotting. Bands stained with anti-thymulin antibody were detected in two locations, approximately 60 kDa and 10 kDa, which may be a possible precursor and intermediate. All of the exposures except for heat were effective for induction of the 10 kDa protein. BLAST search using thymulin sequence identified SPATS2L, an intranucleolar stress-response protein with molecular weight of 62 kDa, containing thymulin-like sequence. Comparisons of blots stained with anti-thymulin and anti-SPATS2L antibodies indicate that SPATS2L may be a possible candidate for the precursor of thymulin.

Physiologic and pathophysiologic roles of interaction between C-type lectin-like receptor 2 and podoplanin: partners from in utero to adulthood

A platelet activation receptor, C-type lectin-like receptor 2 (CLEC-2), has been identified as a receptor for a platelet-activating snake venom, rhodocytin. CLEC-2 protein is highly expressed in platelets/megakaryocytes, and at lower levels in liver Kupffer cells. Recently, podoplanin has been revealed as an endogenous ligand for CLEC-2. Podoplanin is expressed in certain types of tumor cells, fibroblastic reticular cells (FRCs) in lymph nodes, kidney podocytes, and lymphatic endothelial cells, but not in vascular endothelial cells. CLEC-2 in platelets cannot have access to podoplanin under normal conditions, but they interact with each other under pathologic conditions or during developmental stages, and play various pathophysiologic roles. CLEC-2 facilitates hematogenous metastasis of podoplanin-expressing tumors. During development, the interaction between CLEC-2 and podoplanin in lymphatic endothelial cells or neuroepithelial cells facilitates blood-lymphatic vessel separation and cerebrovascular patterning and integrity, respectively. In adulthood, platelet CLEC-2 binding to FRCs is crucial for maintenance of the integrity of high endothelial venules in lymph nodes. Podoplanin-expressing FRC-like cells have recently been identified in the bone marrow, and facilitate megakaryocyte proliferation and proplatelet formation by binding to megakaryocyte CLEC-2. Podoplanin is inducibly expressed in liver monocytes and keratinocytes during Salmonella infection and wound healing, and regulates thrombus formation in the liver and controlled wound healing, respectively. By binding to unknown ligands, platelet CLEC-2 regulates the maintenance of vascular integrity during inflammation, thrombus stability under flow, and maintenance of quiescence of hematopoietic stem cells. Podoplanin is expressed in various cells, and additional roles of the CLEC-2-podoplanin interaction will be revealed in the future.

Neuroprotective DAMPs member prothymosin alpha has additional beneficial actions against cerebral ischemia-induced vascular damages

Prothymosin alpha (ProTα) suppresses stress-induced necrosis of cultured cortical neurons. As neuroprotection alone could not explain the long-lasting protective actions against cerebral ischemia by ProTα, we further examined whether ProTα, in addition to neuroprotective effects, has other anti-ischemic activities. When recombinant mouse ProTα (rmProTα) at 0.3 mg/kg was intravenously (i.v.) given 2 h after the start of tMCAO, all mice survived for more than 14 days. In evaluation of CD31- and tomato lectin-labeling as well as IgG and Evans blue leakage, rmProTα treatment (0.1 mg/kg) largely blocked ischemia-induced vascular damages. Therefore, rmProTα has novel beneficial effects against ischemia-induced brain damage through vascular mechanisms.

The association between S100A13 and HMGA1 in the modulation of thyroid cancer proliferation and invasion

BACKGROUND

S100A13 and high mobility group A (HMGA1) are known to play essential roles in the carcinogenesis and progression of cancer. However, the correlation between S100A13 and HMGA1 during cancer progression is not yet well understood. In this study, we determined the effects of S100A13 on HMGA1 expression in thyroid cancer cells and examined the role of HMGA1 in thyroid cancer progression.

METHODS

Stable ectopic S100A13 expression TT cellular proliferation was evaluated by nude mice xenografts assays. The effect of lentivirus-mediated S100A13 knockdown on thyroid cancer cellular oncogenic properties were evaluated by MTT, colony formation assays and transwell assays in TPC1 and SW579 cells. The effect of siRNA-mediated HMGA1 knockdown on thyroid cancer cellular proliferation and invasion were evaluated by MTT, colony formation assays and transwell assays. The tissue microarray was performed to investigate the correlation between S100A13 and HMGA1 expression in tumor tissues.

RESULTS

The ectopic expression of S100A13 could increase tumor growth in a TT cell xenograft mouse model. Moreover, lentivirus-mediated S100A13 knockdown led to the inhibition of cellular oncogenic properties in thyroid cancer cells, and HMGA1 was found to be involved in the effect of S100A13 on thyroid cancer growth and invasion. Furthermore, siRNA-mediated HMGA1 knockdown was proved to inhibit the growth of TPC1 cells and invasive abilities of SW579 cells. Clinically, it was revealed that both S100A13 and HMGA1 showed a higher expression levels in thyroid cancer cases compared with those in matched normal thyroid cases (P = 0.007 and P = 0.000); S100A13 and HMGA1 expressions were identified to be positively correlated (P = 0.004, R = 0.316) when analyzed regardless of thyroid cancer types.

CONCLUSIONS

This is the first report for the association between HMGA1 and S100A13 expression in the modulation of thyroid cancer growth and invasion. Those results would provide an essential insight into the effect of S100A13 on carcinogenesis of thyroid tumor, rending S100A13 to be potential biological marker for the diagnosis of thyroid cancer.

Subcellular dissemination of prothymosin alpha at normal physiology: immunohistochemical vis-a-vis western blotting perspective

BACKGROUND

The cell type, cell status and specific localization of Prothymosin α (PTMA) within cells seemingly determine its function. PTMA undergoes 2 types of protease proteolytic modifications that are useful in elucidating its interactions with other molecules; a factor that typifies its roles. Preferably a nuclear protein, PTMA has been shown to function in the cytoplasm and extracellularly with much evidence leaning on pathognomonic status. As such, determination of its cellular distribution under normal physiological context while utilizing varied techniques is key to illuminating prospective validation of its distinct functions in different tissues. Differential distribution insights at normal physiology would also portent better basis for further clarification of its interactions and proteolytic modifications under pathological conditions like numerous cancer, ischemic stroke and immunomodulation. We therefore raised an antibody against the C terminal of PTMA to use in tandem with available antibody against the N terminal in a murine model to explicate the differences in its distribution in brain cell types and major peripheral organs through western blotting and immunohistochemical approaches.

RESULTS

The newly generated antibody was applied against the N-terminal antibody to distinguish truncated versions of PTMA or deduce possible masking of the protein by other interacting molecules. Western blot analysis indicated presence of a truncated form of the protein only in the thymus, while immunohistochemical analysis showed that in brain hippocampus the full-length PTMA was stained prominently in the nucleus whereas in the stomach full-length PTMA staining was not observed in the nucleus but in the cytoplasm.

CONCLUSION

Truncated PTMA could not be detected by western blotting when both antibodies were applied in all tissues examined except the thymus. However, immunohistochemistry revealed differential staining by these antibodies suggesting possible masking of epitopes by interacting molecules. The differential localization patterns observed in the context of nucleic versus cytoplasmic presence as well as punctate versus diffuse pattern in tissues and cell types, warrant further investigations as to the forms of PTMA interacting partners.

Prothymosin Alpha and Immune Responses: Are We Close to Potential Clinical Applications?

The thymus gland produces soluble molecules, which mediate significant immune functions. The first biologically active thymic extract was thymosin fraction V, the fractionation of which led to the isolation of a series of immunoactive polypeptides, including prothymosin alpha (proTα). ProTα displays a dual role, intracellularly as a survival and proliferation mediator and extracellularly as a biological response modifier. Accordingly, inside the cell, proTα is implicated in crucial intracellular circuits and may serve as a surrogate tumor biomarker, but when found outside the cell, it could be used as a therapeutic agent for treating immune system deficiencies. In fact, proTα possesses pleiotropic adjuvant activity and a series of immunomodulatory effects (eg, anticancer, antiviral, neuroprotective, cardioprotective). Moreover, several reports suggest that the variable activity of proTα might be exerted through different parts of the molecule. We first reported that the main immunoactive region of proTα is the carboxy-terminal decapeptide proTα(100-109). In conjunction with data from others, we also revealed that proTα and proTα(100-109) signal through Toll-like receptor 4. Although their precise molecular mechanism of action is yet not fully elucidated, proTα and proTα(100-109) are viewed as candidate adjuvants for cancer immunotherapy. Here, we present a historical overview on the discovery and isolation of thymosins with emphasis on proTα and data on some immune-related new activities of the polypeptide and smaller immunostimulatory peptides thereof. Finally, we propose a compiled scenario on proTα's mode of action, which could eventually contribute to its clinical application.

Vascular Smooth Muscle Cells Stimulate Platelets and Facilitate Thrombus Formation through Platelet CLEC-2: Implications in Atherothrombosis

The platelet receptor CLEC-2 is involved in thrombosis/hemostasis, but its ligand, podoplanin, is expressed only in advanced atherosclerotic lesions. We investigated CLEC-2 ligands in vessel walls. Recombinant CLEC-2 bound to early atherosclerotic lesions and normal arterial walls, co-localizing with vascular smooth muscle cells (VSMCs). Flow cytometry and immunocytochemistry showed that recombinant CLEC-2, but not an anti-podoplanin antibody, bound to VSMCs, suggesting that CLEC-2 ligands other than podoplanin are present in VSMCs. VSMCs stimulated platelet granule release and supported thrombus formation under flow, dependent on CLEC-2. The time to occlusion in a FeCl3-induced animal thrombosis model was significantly prolonged in the absence of CLEC-2. Because the internal elastic lamina was lacerated in our FeCl3-induced model, we assume that the interaction between CLEC-2 and its ligands in VSMCs induces thrombus formation. Protein arrays and Biacore analysis were used to identify S100A13 as a CLEC-2 ligand in VSMCs. However, S100A13 is not responsible for the above-described VSMC-induced platelet activation, because S100A13 is not expressed on the surface of normal VSMCs. S100A13 was released upon oxidative stress and expressed in the luminal area of atherosclerotic lesions. Suspended S100A13 did not activate platelets, but immobilized S100A13 significantly increased thrombus formation on collagen-coated surfaces. Taken together, we proposed that VSMCs stimulate platelets through CLEC-2, possibly leading to thrombus formation after plaque erosion and stent implantation, where VSMCs are exposed to blood flow. Furthermore, we identified S100A13 as one of the ligands on VSMCs.

Novel Pactamycin Analogs Induce p53 Dependent Cell-Cycle Arrest at S-Phase in Human Head and Neck Squamous Cell Carcinoma (HNSCC) Cells

Pactamycin, although putatively touted as a potent antitumor agent, has never been used as an anticancer drug due to its high cytotoxicity. In this study, we characterized the effects of two novel biosynthetically engineered analogs of pactamycin, de-6MSA-7-demethyl-7-deoxypactamycin (TM-025) and 7-demethyl-7-deoxypactamycin (TM-026), in head and neck squamous cell carcinoma (HNSCC) cell lines SCC25 and SCC104. Both TM-025 and TM-026 exert growth inhibitory effects on HNSCC cells by inhibiting cell proliferation. Interestingly, unlike their parent compound pactamycin, the analogs do not inhibit synthesis of nascent protein in a cell-based assay. Furthermore, they do not induce apoptosis or autophagy in a dose- or a time-dependent manner, but induce mild senescence in the tested cell lines. Cell cycle analysis demonstrated that both analogs significantly induce cell cycle arrest of the HNSCC cells at S-phase resulting in reduced accumulation of G₂/M-phase cells. The pactamycin analogs induce expression of cell cycle regulatory proteins including master regulator p53, its downstream target p21^Cip1/WAF1, p27^kip21, p19, cyclin E, total and phospho Cdc2 (Tyr15) and Cdc25C. Besides, the analogs mildly reduce cyclin D1 expression without affecting expression of cyclin B, Cdk2 and Cdk4. Specific inhibition of p53 by pifithrin-α reduces the percentage of cells accumulated in S-phase, suggesting contribution of p53 to S-phase increase. Altogether, our results demonstrate that Pactamycin analogs TM-025 and TM-026 induce senescence and inhibit proliferation of HNSCC cells via accumulation in S-phase through possible contribution of p53. The two PCT analogs can be widely used as research tools for cell cycle inhibition studies in proliferating cancer cells with specific mechanisms of action.

Prothymosin α variants isolated from CD8+ T cells and cervicovaginal fluid suppress HIV-1 replication through type I interferon induction

Soluble factors from CD8(+) T cells and cervicovaginal mucosa of women are recognized as important in controlling human immunodeficiency virus type 1 (HIV-1) infection and transmission. Previously, we have shown the strong anti-HIV-1 activity of prothymosin α (ProTα) derived from CD8(+) T cells. ProTα is a small acidic protein with wide cell distribution, to which several functions have been ascribed, depending on its intracellular or extracellular localization. To date, activities of ProTα have been attributed to a single protein known as isoform 2. Here we report the isolation and identification of 2 new ProTα variants from CD8(+) T cells and cervicovaginal lavage with potent anti-HIV-1 activity. The first is a splice variant of the ProTα gene, known as isoform CRA_b, and the second is the product of a ProTα gene, thus far classified as a pseudogene 7. Native or recombinant ProTα variants potently restrict HIV-1 replication in macrophages through the induction of type I interferon. The baseline expression of interferon-responsive genes in primary human cervical tissues positively correlate with high levels of intracellular ProTα, and the knockdown of ProTα variants by small interfering RNA leads to downregulation of interferon target genes. Overall, these findings suggest that ProTα variants are innate immune mediators involved in immune surveillance.

A type III ACC synthase, ACS7, is involved in root gravitropism in Arabidopsis thaliana

Ethylene is an important plant hormone that regulates developmental processes in plants. The ethylene biosynthesis pathway is a highly regulated process at both the transcriptional and post-translational level. The transcriptional regulation of these ethylene biosynthesis genes is well known. However, post-translational modifications of the key ethylene biosynthesis enzyme 1-aminocyclopropane-1-carboxylate (ACC) synthase (ACS) are little understood. In vitro kinase assays were conducted on the type III ACS, AtACS7, fusion protein and peptides to determine whether the AtACS7 protein can be phosphorylated by calcium-dependent protein kinase (CDPK). AtACS7 was phosphorylated at Ser216, Thr296, and Ser299 by AtCDPK16 in vitro. To investigate further the function of the ACS7 gene in Arabidopsis, an acs7-1 loss-of-function mutant was isolated. The acs7-1 mutant exhibited less sensitivity to the inhibition of root gravitropism by treatment with the calcium chelator ethylene glycol tetraacetic acid (EGTA). Seedlings were treated with gradient concentrations of ACC. The results showed that a certain concentration of ethylene enhanced the gravity response. Moreover, the acs7-1 mutant was less sensitive to inhibition of the gravity response by treatment with the auxin polar transport inhibitor 1-naphthylphthalamic acid, but exogenous ACC application recovered root gravitropism. Altogether, the results indicate that AtACS7 is involved in root gravitropism in a calcium-dependent manner in Arabidopsis.

Neuron-specific non-classical release of prothymosin alpha: a novel neuroprotective damage-associated molecular patterns

Prothymosin alpha (ProTα), a nuclear protein devoid of signal sequence, has been shown to possess a number of cellular functions including cell survival. Most recently, we demonstrated that ProTα is localized in the nuclei of neurons, while it is found in both nuclei and cytoplasm in the astrocytes and microglia of adult brain. However, the cell type-specific non-classical release of ProTα under cerebral ischemia is yet unknown. In this study, we report that ProTα is non-classically released along with S100A13 from neurons in the hippocampus, striatum and somatosensory cortex at 3 h after cerebral ischemia, but amlexanox (an anti-allergic compound) reversibly blocks this neuronal ProTα release. We found that none of ProTα is released from astrocytes and microglia under ischemic stress. Indeed, ProTα intensity is increased gradually in astrocytes and microglia through 24 h after the cerebral ischemia. Interestingly, Z-Val-Ala-Asp fluoromethyl ketone, a caspase 3 inhibitor, pre-treatment induces ProTα release from astrocytes in the ischemic brain, but this release is reversibly blocked by amlexanox. However, Z-Val-Ala-Asp fluoromethyl ketone as well as amlexanox has no effect on ProTα distribution in microglia upon cerebral ischemia. Taken together, these results suggest that only neurons have machineries to release ProTα upon cerebral ischemic stress in vivo.

Intracellular and extracellular cytokine-like functions of prothymosin α: implications for the development of immunotherapies

Prothymosin α (ProTα) is a 12.5-kDa, highly acidic protein widely distributed in different cell types expressed intracellularly and extracellularly. ProTα does not contain a secretion-signal sequence and is released by a nonclassical secretory pathway with a cargo protein. New findings on the extracellular function of ProTα have yielded exciting insights into the cytokine-like functions of this host protein that stimulates type I interferon via Toll-like receptor 4. Here, we discuss the intracellular function of ProTα, how new findings of cytokine-like activities of ProTα aid our understanding of mechanisms that direct ProTα functions, and the potential application of these new insights to the development of immunotherapies.

Prothymosin-α interacts with mutant huntingtin and suppresses its cytotoxicity in cell culture

Huntington disease (HD), a fatal neurodegenerative disorder, is caused by a lengthening of the polyglutamine tract in the huntingtin (Htt) protein. Despite considerable effort, thus far there is no cure or treatment available for the disorder. Using the approach of tandem affinity purification we recently discovered that prothymosin-α (ProTα), a small highly acidic protein, interacts with mutant Htt (mHtt). This was confirmed by co-immunoprecipitation and a glutathione S-transferase (GST) pull-down assay. Overexpression of ProTα remarkably reduced mHtt-induced cytotoxicity in both non-neuronal and neuronal cell models expressing N-terminal mHtt fragments, whereas knockdown of ProTα expression in the cells enhanced mHtt-caused cell death. Deletion of the central acidic domain of ProTα abolished not only its interaction with mHtt but also its protective effect on mHtt-caused cytotoxicity. Additionally, overexpression of ProTα inhibited caspase-3 activation but enhanced aggregation of mHtt. Furthermore, when added to cultured cells expressing mHtt, the purified recombinant ProTα protein not only entered the cells but it also significantly suppressed the mHtt-caused cytotoxicity. Taken together, these data suggest that ProTα might be a novel therapeutic target for treating HD and other polyglutamine expansion disorders.

Regulation of non-classical FGF1 release and FGF-dependent cell transformation by CBF1-mediated notch signaling

FGF1, a widely expressed proangiogenic factor involved in tissue repair and carcinogenesis, is released from cells through a non-classical pathway independent of endoplasmic reticulum and Golgi. Although several proteins participating in FGF1 export were identified, genetic mechanisms regulating this process remained obscure. We found that FGF1 export and expression are regulated through Notch signaling mediated by transcription factor CBF1 and its partner MAML. The expression of a dominant negative (dn) form of CBF1 in 3T3 cells induces transcription of FGF1 and sphingosine kinase 1 (SphK1), which is a component of FGF1 export pathway. dnCBF1 expression stimulates the stress-independent release of transduced FGF1 from NIH 3T3 cells and endogenous FGF1 from A375 melanoma cells. NIH 3T3 cells transfected with dnCBF1 form colonies in soft agar and produce rapidly growing highly angiogenic tumors in nude mice. The transformed phenotype of dnCBF1 transfected cells is efficiently blocked by dn forms of FGF receptor 1 and S100A13, which is a component of FGF1 export pathway. FGF1 export and acceleration of cell growth induced by dnCBF1 depend on SphK1. Similar to dnCBF1, dnMAML transfection induces FGF1 expression and release, and accelerates cell proliferation. The latter effect is strongly decreased in FGF1 null cells. We suggest that the regulation of FGF1 expression and release by CBF1-mediated Notch signaling can play an important role in tumor formation.

The IL1alpha-S100A13 heterotetrameric complex structure: a component in the non-classical pathway for interleukin 1alpha secretion

Interleukin 1α (IL1α) plays an important role in several key biological functions, such as angiogenesis, cell proliferation, and tumor growth in several types of cancer. IL1α is a potent cytokine that induces a wide spectrum of immunological and inflammatory activities. The biological effects of IL1α are mediated through the activation of transmembrane receptors (IL1Rs) and therefore require the release of the protein into the extracellular space. IL1α is exported through a non-classical release pathway involving the formation of a specific multiprotein complex, which includes IL1α and S100A13. Because IL1α plays an important role in cell proliferation and angiogenesis, inhibiting the formation of the IL1α-S100A13 complex would be an effective strategy to inhibit a wide range of cancers. To understand the molecular events in the IL1α release pathway, we studied the structure of the IL1α-S100A13 tetrameric complex, which is the key complex formed during the non-classical pathway of IL1α release.