Ca2+-dependent binding and activation of dormant ezrin by dimeric S100P

An Extracellular/Membrane-Bound S100P Pool Regulates Motility and Invasion of Human Extravillous Trophoblast Lines and Primary Cells

Whilst S100P has been shown to be a marker for carcinogenesis, we have shown, in non-physio-pathological states, that its expression promotes trophoblast motility and invasion but the mechanisms explaining these cellular processes are unknown. Here we identify the presence of S100P in the plasma membrane/cell surface of all trophoblast cells tested, whether lines, primary extravillous (EVT) cells, or section tissue samples using either biochemical purification of plasma membrane material, cell surface protein isolation through biotinylation, or microscopy analysis. Using extracellular loss of function studies, through addition of a specific S100P antibody, our work shows that inhibiting the cell surface/membrane-bound or extracellular S100P pools significantly reduces, but importantly only in part, both cell motility and cellular invasion in different trophoblastic cell lines, as well as primary EVTs. Interestingly, this loss in cellular motility/invasion did not result in changes to the overall actin organisation and focal adhesion complexes. These findings shed new light on at least two newly characterized pathways by which S100P promotes trophoblast cellular motility and invasion. One where cellular S100P levels involve the remodelling of focal adhesions whilst another, an extracellular pathway, appears to be focal adhesion independent. Both pathways could lead to the identification of novel targets that may explain why significant numbers of confirmed human pregnancies suffer complications through poor placental implantation.

Characterizations of annexin A1-interacting proteins in apical membrane and cytosolic compartments of renal tubular epithelial cells

Annexin A1 (ANXA1) is a multifunctional calcium-binding protein that can bind to membrane phospholipids. Under high-calcium condition, ANXA1 expression increases on renal epithelial cell surface, leading to enhanced adhesion of calcium oxalate (CaOx) crystal (stone material) onto the cells. To regulate various cellular processes, ANXA1 interacts with many other intracellular protein partners. However, components of the ANXA1-interacting protein complex remain unclear. Herein, we characterized the interacting complexes of apical membrane (ApANXA1) and cytosolic (cyANXA1) forms of ANXA1 in apical membrane and cytosolic compartments, respectively, of renal epithelial cells under high-calcium condition using proteomic and bioinformatic approaches. After fractionation, the ApANXA1- and CyANXA1-interacting partners were identified by immunoprecipitation followed by nanoLC‑ESI‑Qq-TOF tandem mass spectrometry (IP-MS/MS). The ANXA1-interacting partners that were common in both apical membrane and cytosolic compartments and those unique in each compartment were then analyzed for their physico-chemical properties (molecular weight, isoelectric point, amino acid contents, instability index, aliphatic index, and grand average of hydropathicity), secondary structure (α-helix, β-turn, random coil, and extended strand), molecular functions, biological processes, reactome pathways and KEGG pathways. The data demonstrated that each set of these interacting proteins exhibited common and unique characteristics and properties. The knowledge from this study may lead to better understanding of the ApANXA1 and CyAXNA1 biochemistry and functions as well as the pathophysiology of CaOx kidney stone formation induced by high-calcium condition.

Citrullination of actin-ligand and nuclear structural proteins, cytoskeleton reorganization and protein redistribution across cellular fractions are early events in ionomycin-induced NETosis

Neutrophil extracellular traps (NETs) are web-like structures of DNA coated with cytotoxic proteins and histones released by activated neutrophils through a process called NETosis. NETs release occurs through a sequence of highly organized events leading to chromatin expansion and rupture of nuclear and cellular membranes. In calcium ionophore-induced NETosis, the enzyme peptidylargine deiminase 4 (PAD4) mediates chromatin decondensation through histone citrullination, but the biochemical pathways involved in this process are not fully understood. Here we use live-imaging microscopy and proteomic studies of the neutrophil cellular fractions to investigate the early events in ionomycin-triggered NETosis. We found that before ionomycin-stimulated neutrophils release NETs, profound biochemical changes occur in and around their nucleus, such as, cytoskeleton reorganization, nuclear redistribution of actin-remodeling related proteins, and citrullination of actin-ligand and nuclear structural proteins. Ionomycin-stimulated neutrophils rapidly lose their characteristic polymorphic nucleus, and these changes are promptly communicated to the extracellular environment through the secretion of proteins related to immune response. Therefore, our findings revealed key biochemical mediators in the early process that subsequently culminates with nuclear and cell membranes rupture, and extracellular DNA release.

Ez-Metastasizing: The Crucial Roles of Ezrin in Metastasis

Ezrin is the cytoskeletal organizer and functions in the modulation of membrane-cytoskeleton interaction, maintenance of cell shape and structure, and regulation of cell-cell adhesion and movement, as well as cell survival. Ezrin plays a critical role in regulating tumor metastasis through interaction with other binding proteins. Notably, Ezrin has been reported to interact with immune cells, allowing tumor cells to escape immune attack in metastasis. Here, we review the main functions of Ezrin, the mechanisms through which it acts, its role in tumor metastasis, and its potential as a therapeutic target.

The Role of the C-Terminal Lysine of S100P in S100P-Induced Cell Migration and Metastasis

S100P protein is a potent inducer of metastasis in a model system, and its presence in cancer cells of patients is strongly associated with their reduced survival times. A well-established Furth Wistar rat metastasis model system, methods for measuring cell migration, and specific inhibitors were used to study pathways of motility-driven metastasis. Cells expressing C-terminal mutant S100P proteins display markedly-reduced S100P-driven metastasis in vivo and cell migration in vitro. These cells fail to display the low focal adhesion numbers observed in cells expressing wild-type S100P, and the mutant S100P proteins exhibit reduced biochemical interaction with non-muscle myosin heavy chain isoform IIA in vitro. Extracellular inhibitors of the S100P-dependent plasminogen activation pathway reduce, but only in part, wild-type S100P-dependent cell migration; they are without effect on S100P-negative cells or cells expressing C-terminal mutant S100P proteins and have no effect on the numbers of focal adhesions. Recombinant wild-type S100P protein, added extracellularly to S100P-negative cells, stimulates cell migration, which is abolished by these inhibitors. The results identify at least two S100P-dependent pathways of migration, one cell surface and the other intracellularly-linked, and identify its C-terminal lysine as a target for inhibiting multiple migration-promoting activities of S100P protein and S100P-driven metastasis.

S100P contributes to promoter demethylation and transcriptional activation of SLC2A5 to promote metastasis in colorectal cancer

BACKGROUND

SLC2A5 is a high-affinity fructose transporter, which is frequently upregulated in multiple human malignant tumours. However, the function and molecular mechanism of SLC2A5 in colorectal cancer (CRC) remain unknown.

METHODS

We detected the expression levels of SLC2A5 in CRC tissues and CRC cell lines by western blotting, qRT-PCR and immunohistochemistry. CRC cell lines with stable overexpression or knockdown of SLC2A5 were constructed to evaluate the functional roles of SLC2A5 in vitro through conventional assays. An intrasplenic inoculation model was established in mice to investigate the effect of SLC2A5 in promoting metastasis in vivo. Methylation mass spectrometry sequencing, methylation specific PCR, bisulphite sequencing PCR, ChIP-qPCR and luciferase reporter assay were performed to investigate the molecular mechanism underlying transcriptional activation of SLC2A5.

RESULTS

We found that SLC2A5 was upregulated in colorectal tumour tissues. Functionally, a high level of SLC2A5 expression was associated with increased invasion and metastasis capacities of CRC cells both in vitro and in vivo. Mechanistically, we unveiled that S100P could integrate to a specific region of SLC2A5 promoter, thereby reducing its methylation levels and activating SLC2A5 transcription.

CONCLUSIONS

Our results reveal a novel mechanism that S100P mediates the promoter demethylation and transcription activation of SLC2A5, thereby promoting the metastasis of CRC.

Lipid Rafts Interaction of the ARID3A Transcription Factor with EZRIN and G-Actin Regulates B-Cell Receptor Signaling

Several diseases originate via dysregulation of the actin cytoskeleton. The ARID3A/Bright transcription factor has also been implicated in malignancies, primarily those derived from hematopoietic lineages. Previously, we demonstrated that ARID3A shuttles between the nucleus and the plasma membrane, where it localizes within lipid rafts. There it interacts with components of the B-cell receptor (BCR) to reduce its ability to transmit downstream signaling. We demonstrate here that a direct component of ARID3A-regulated BCR signal strength is cortical actin. ARID3A interacts with actin exclusively within lipid rafts via the actin-binding protein EZRIN, which confines unstimulated BCRs within lipid rafts. BCR ligation discharges the ARID3A-EZRIN complex from lipid rafts, allowing the BCR to initiate downstream signaling events. The ARID3A-EZRIN interaction occurs almost exclusively within unpolymerized G-actin, where EZRIN interacts with the multifunctional ARID3A REKLES domain. These observations provide a mechanism by which a transcription factor directly regulates BCR signaling via linkage to the actin cytoskeleton with consequences for B-cell-related neoplasia.

Neuroligin-2 dependent conformational activation of collybistin reconstituted in supported hybrid membranes

The assembly of the postsynaptic transmitter sensing machinery at inhibitory nerve cell synapses requires the intimate interplay between cell adhesion proteins, scaffold and adaptor proteins, and γ-aminobutyric acid (GABA) or glycine receptors. We developed an in vitro membrane system to reconstitute this process, to identify the essential protein components, and to define their mechanism of action, with a specific focus on the mechanism by which the cytosolic C terminus of the synaptic cell adhesion protein Neuroligin-2 alters the conformation of the adaptor protein Collybistin-2 and thereby controls Collybistin-2-interactions with phosphoinositides (PtdInsPs) in the plasma membrane. Supported hybrid membranes doped with different PtdInsPs and 1,2-dioleoyl-sn-glycero-3-{[N-(5-amino-1-carboxypentyl)iminodiacetic acid]succinyl} nickel salt (DGS-NTA(Ni)) to allow for the specific adsorption of the His6-tagged intracellular domain of Neuroligin-2 (His-cytNL2) were prepared on hydrophobically functionalized silicon dioxide substrates via vesicle spreading. Two different collybistin variants, the WT protein (CB2SH3) and a mutant that adopts an intrinsically 'open' and activated conformation (CB2SH3/W24A-E262A), were bound to supported membranes in the absence or presence of His-cytNL2. The corresponding binding data, obtained by reflectometric interference spectroscopy, show that the interaction of the C terminus of Neuroligin-2 with Collybistin-2 induces a conformational change in Collybistin-2 that promotes its interaction with distinct membrane PtdInsPs.

Promotion of the occurrence of endometrioid carcinoma by S100 calcium binding protein P

Background

Endometrial cancer, one of the most common malignant tumors, is a serious threat to women’s health. Endometrial hyperplasia is a precursor of endometrial cancer. S100 calcium binding protein P (S100P) has been found to play important roles in many types of cancer. The present study aimed to investigate the expression of S100P in endometrial cancer and its precursor lesions, and to explore the possible mechanisms.

Methods

We collected paraffin sections of normal endometrium, simple and complex non-atypical hyperplasia, atypical hyperplasia, and endometrioid carcinoma. The expression of S100P in endometrial cancer and its precancerous lesions was observed using immunohistochemistry. We also cultured primary endometrial cells and endometrial cancer cell lines (Ishikawa and RL95–2), and observed the expression of S100P in these cells. Laser confocal microscopy was used to observe the co-localization of S100P and its interacting protein Ezrin in RL95–2 cells. We employed lentiviruses to knockdown and overexpress S100P and then detected the F-actin distribution and cell invasion using phalloidin staining and Transwell assays.

Results

There was a gradual increase in the S100P signal as the disease progressed from normal endometrium and simple non-atypical hyperplasia, to complex non-atypical hyperplasia, atypical hyperplasia, and then to endometrial cancer. S100P was mainly distributed in the cytoplasm and co-localized with Ezrin in endometrial cancer cells. After knocking down S100P, F-actin aggregated in the nucleus or to the local cell membrane. Furthermore, knockdown of S100P in Ishikawa cells decreased their cell invasion capability. Meanwhile, S100P overexpression in endometrial stromal cells increased cell invasion.

Conclusions

These data suggested that S100P might be involved in the occurrence and development of endometrial cancer via interaction with Ezrin and re-organization of F-actin to promote cell invasion.

Leaflet-Dependent Distribution of PtdIns[4,5]P2 in Supported Model Membranes

Supported planar lipid bilayers (SLBs) prepared by spreading of unilamellar vesicles on hydrophilic substrates such as silicon dioxide are frequently used to investigate lipid-protein interactions by means of surface-sensitive methods. In recent years, the receptor lipid phosphatidylinositol-4,5-bisphosphate (PtdIns[4,5]P₂) became particularly important as a significant number of proteins bind to this lipid at the inner leaflet of the plasma membrane. Here, we investigated how the lipid PtdIns[4,5]P₂ distributes between the two leaflets of an SLB on SiO₂ surfaces. We prepared SLBs on SiO₂ by spreading small unilamellar vesicles and quantified the adsorption of PtdIns[4,5]P₂ binding proteins providing information about the accessibility of PtdIns[4,5]P₂. We compared protein binding to PtdIns[4,5]P₂ in SLBs with that in lipid monolayers on a 1,1,1-trimethyl-N-(trimethylsilyl)silanamine-functionalized SiO₂ surface using reflectometric interference spectroscopy and atomic force microscopy. Our results clearly demonstrate that the accessibility of PtdIns[4,5]P₂ for protein binding is reduced in SLBs compared to that in supported hybrid membranes, which is discussed in terms of PtdIns[4,5]P₂ distribution in the two leaflets of SLBs.

Biomechanical evaluation of tendon regeneration with adipose-derived stem cell

The use of Adipose-Derived Stem Cells (ADSC) has been presented as a new alternative for tendon reconstruction. Have been admitted that ADSCs are related to better outcomes when used in tendon healing. This research was designed to apply the potential of ADSCs in tendon healing. Flexor digitorum superficialis tendon lesion was performed on both legs of eleven New Zealand rabbits and them, at the same time, treated as follows: Suture alone (Group III - Suture, n:10), suture associated with ADSC (Group IV - Suture + ADSC, n:10) or without suture (Group II - SHAN, n:2). At four weeks after the tendon surgery, the animal was euthanized, and the tendon evaluated (biomechanically and macroscopically). We used 5 additional New Zealand rabbits in the control group "Group I - Control, n:10". In the macroscopic evaluation, the group with ADSC presented a more homogeneous gross morphology compared with the group III. Biomechanical testing showed a lower ultimate tensile load, stiffness and a higher cross-sectional area in the group III and IV compared with the control group. The group with ADSC showed a greater ultimate tensile load, a larger cross-sectional area and bigger deformation at the ultimate tensile load when compared to the group without ADSC. In general terms, the use of ADSCs in tendon healing have biomechanical advantages compared to the non-use of ADSCs at 4 weeks after surgery. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1281-1286, 2019.

Evaluation and validation of housekeeping genes in two contrast species of thyme plant to drought stress using real-time PCR

To decrease errors and increase accuracy and reliability of quantitative real-time PCR (qRT-PCR) results, the use of a reference gene is inevitable. Despite the industrial importance of genus Thymus, not any validated reference gene has not been reported for T. kotschyanus and T. vulgaris which could limit such investigations. In this study, the expression stability of seven housekeeping genes including Actin, Cyclophilin-18, elongation factor-1A, glyceraldehyde-3-phosphate dehydrogenase, 18S ribosomal RNA, Cullin, and Polypyrimidine tract-binding protein were evaluated in T. kotschyanus and T. vulgaris which grown at four levels of drought stress using geNorm, NormFinder, and BestKeeper algorithms. Histone deacetylase-6 (HDA-6) gene was also used for validation of evaluated reference genes. In T. vulgaris, all of the algorithms similarly ranked elongation factor-1A and glyceraldehyde-3-phosphate dehydrogenase as the two most stably expressed genes. In T. kotschyanus, only NormFinder and BestKeeper had a similar ranking and identified Actin and glyceraldehyde-3-phosphate dehydrogenase as the two most stably expressed genes, but geNorm algorithm ranked elongation factor-1A and glyceraldehyde-3-phosphate dehydrogenase as the best two reference genes. On the other hand, all algorithms ranked 18S rRNA and Cyclophilin-18 as the least stable genes in T. kotschyanus and T. vulgaris, respectively. Validation results indicated that there was a significant change (0.53-3.19 fold change) in relative expression of HDA-6 normalized by the best stable gene compare to the least ranked gene. Our study presented the first systematic validation of reference gene(s) selection in T. kotschyanus and T. vulgaris and provided useful information to obtain more accurate qRT-PCR results in these species.

S100P and Ezrin promote trans-endothelial migration of triple negative breast cancer cells

PURPOSE

Triple negative breast cancer (TNBC) patients generally have an adverse clinical outcome because their tumors often recur and metastasize to distant sites in the first 3 years after surgery. Therefore, it has become pivotal to identify potential factors associated with metastasis. Here, we focused on the effects of S100P and Ezrin on the trans-endothelial migration (TEM) of TNBC cells, as they have both been suggested to play a role in this process in other malignancies.

METHODS

The expression of S100P and Ezrin was examined by immunohistochemistry in 58 primary TNBC samples. The mRNA and protein levels of S100P and Ezrin were assessed in breast cancer-derived cell lines using qRT-PCR and Western blotting, respectively. Proliferation and migration assays were performed using TNBC-derived MFM-223 and SUM-185-PE cells transfected with S100P and Ezrin siRNAs. Two different timeframes were employed for TEM assays using TNBC-derived cells and human umbilical vein endothelial-derived cells, respectively. Correlations between the status of Ezrin^Thr-567 expression and various clinicopathological features were analyzed by immunohistochemistry.

RESULTS

We found that S100P and Ezrin double negative TNBC cases were significantly associated with a better disease-free survival. We also found that single and double siRNA-mediated knockdown of S100P and Ezrin in TNBC-derived cells significantly inhibited their TEM and destabilized the intercellular junctions of endothelial cells. In addition, we found that Ezrin^Thr-567 immunoreactivity significantly correlated with vascular invasion in TNBC patients.

CONCLUSIONS

From our data we conclude that S100P, Ezrin and Ezrin^Thr-567 are involved in the trans-endothelial migration of TNBC cells and that they may serve as potential targets in TNBC patients.

S100P enhances the motility and invasion of human trophoblast cell lines

S100P has been shown to be a marker for carcinogenesis where its expression in solid tumours correlates with metastasis and a poor patient prognosis. This protein's role in any physiological process is, however, unknown. Here we first show that S100P is expressed both in trophoblasts in vivo as well as in some corresponding cell lines in culture. We demonstrate that S100P is predominantly expressed during the early stage of placental formation with its highest expression levels occurring during the first trimester of gestation, particularly in the invading columns and anchoring villi. Using gain or loss of function studies through overexpression or knockdown of S100P expression respectively, our work shows that S100P stimulates both cell motility and cellular invasion in different trophoblastic and first trimester EVT cell lines. Interestingly, cell invasion was seen to be more dramatically affected than cell migration. Our results suggest that S100P may be acting as an important regulator of trophoblast invasion during placentation. This finding sheds new light on a hitherto uncharacterized molecular mechanism which may, in turn, lead to the identification of novel targets that may explain why significant numbers of confirmed human pregnancies suffer complications through poor placental implantation.

Adaptation and Therapeutic Exploitation of the Plasma Membrane of African Trypanosomes

African trypanosomes are highly divergent from their metazoan hosts, and as part of adaptation to a parasitic life style have developed a unique endomembrane system. The key virulence mechanism of many pathogens is successful immune evasion, to enable survival within a host, a feature that requires both genetic events and membrane transport mechanisms in African trypanosomes. Intracellular trafficking not only plays a role in immune evasion, but also in homeostasis of intracellular and extracellular compartments and interactions with the environment. Significantly, historical and recent work has unraveled some of the connections between these processes and highlighted how immune evasion mechanisms that are associated with adaptations to membrane trafficking may have, paradoxically, provided specific sensitivity to drugs. Here, we explore these advances in understanding the membrane composition of the trypanosome plasma membrane and organelles and provide a perspective for how transport could be exploited for therapeutic purposes.

New approaches targeting brown adipose tissue transplantation as a therapy in obesity

Brown adipose tissue (BAT) is raising high expectations as a potential target in the fight against metabolic disorders such as obesity and type 2 diabetes. BAT utilizes fuels such as fatty acids to maintain body temperature by uncoupling mitochondrial electron transport to produce heat instead of ATP. This process is called thermogenesis. BAT was considered to be exclusive to rodents and human neonates. However, in the last decade several studies have demonstrated that BAT is not only present but also active in adult humans and that its activity is reduced in several pathological conditions, such as aging, obesity, and diabetes. Thus, tremendous efforts are being made by the scientific community to enhance either BAT mass or activity. Several activators of thermogenesis have been described, such as natriuretic peptides, bone morphogenic proteins, or fibroblast growth factor 21. Furthermore, recent studies have tested a therapeutic approach to directly increase BAT mass by the implantation of either adipocytes or fat tissue. This approach might have an important future in regenerative medicine and in the fight against metabolic disorders. Here, we review the emerging field of BAT transplantation including the various sources of mesenchymal stem cell isolation in rodents and humans and the described metabolic outcomes of adipocyte cell transplantation and BAT transplantation in obesity.

BEST1 gene therapy corrects a diffuse retina-wide microdetachment modulated by light exposure

One of the most common forms of monogenic macular degeneration worldwide is caused by dominant or recessive bestrophinopathies associated with mutations in the BEST1 gene. Disease expression is known to start with a retina-wide electrophysiological defect leading to localized vitelliform and atrophic lesions and vision loss. To develop lasting therapies for this incurable disease, there is a need for greater understanding of the early pathophysiology before lesion formation. Here we find that the loss of retinal pigment epithelium apical microvilli and resulting microdetachment of the retina represent the earliest features of canine bestrophinopathies. We show that retinal light exposure expands, and dark adaptation contracts, the microdetachments. Subretinal adeno-associated virus-based gene therapy corrects both the vitelliform lesions and the light-modulated microdetachments.

Mutations in the BEST1 gene cause detachment of the retina and degeneration of photoreceptor (PR) cells due to a primary channelopathy in the neighboring retinal pigment epithelium (RPE) cells. The pathophysiology of the interaction between RPE and PR cells preceding the formation of retinal detachment remains not well-understood. Our studies of molecular pathology in the canine BEST1 disease model revealed retina-wide abnormalities at the RPE-PR interface associated with defects in the RPE microvillar ensheathment and a cone PR-associated insoluble interphotoreceptor matrix. In vivo imaging demonstrated a retina-wide RPE–PR microdetachment, which contracted with dark adaptation and expanded upon exposure to a moderate intensity of light. Subretinal BEST1 gene augmentation therapy using adeno-associated virus 2 reversed not only clinically detectable subretinal lesions but also the diffuse microdetachments. Immunohistochemical analyses showed correction of the structural alterations at the RPE–PR interface in areas with BEST1 transgene expression. Successful treatment effects were demonstrated in three different canine BEST1 genotypes with vector titers in the 0.1-to-5E11 vector genomes per mL range. Patients with biallelic BEST1 mutations exhibited large regions of retinal lamination defects, severe PR sensitivity loss, and slowing of the retinoid cycle. Human translation of canine BEST1 gene therapy success in reversal of macro- and microdetachments through restoration of cytoarchitecture at the RPE–PR interface has promise to result in improved visual function and prevent disease progression in patients affected with bestrophinopathies.

Activation of tissue plasminogen activator by metastasis-inducing S100P protein

S100P protein in human breast cancer cells is associated with reduced patient survival and, in a model system of metastasis, it confers a metastatic phenotype upon benign mammary tumour cells. S100P protein possesses a C-terminal lysine residue. Using a multiwell in vitro assay, S100P is now shown for the first time to exhibit a strong, C-terminal lysine-dependent activation of tissue plasminogen activator (tPA), but not of urokinase-catalysed plasminogen activation. The presence of 10 μM calcium ions stimulates tPA activation of plasminogen 2-fold in an S100P-dependent manner. S100P physically interacts with both plasminogen and tPA in vitro, but not with urokinase. Cells constitutively expressing S100P exhibit detectable S100P protein on the cell surface, and S100P-containing cells show enhanced activation of plasminogen compared with S100P-negative control cells. S100P shows C-terminal lysine-dependent enhancement of cell invasion. An S100P antibody, when added to the culture medium, reduced the rate of invasion of wild-type S100P-expressing cells, but not of cells expressing mutant S100P proteins lacking the C-terminal lysine, suggesting that S100P functions outside the cell. The protease inhibitors, aprotinin or α-2-antiplasmin, reduced the invasion of S100P-expressing cells, but not of S100P-negative control cells, nor cells expressing S100P protein lacking the C-terminal lysine. It is proposed that activation of tPA via the C-terminal lysine of S100P contributes to the enhancement of cell invasion by S100P and thus potentially to its metastasis-promoting activity.

Ezrin interacts with S100A4 via both its N- and C-terminal domains

Ezrin belongs to the ERM (ezrin, radixin, moesin) protein family that has a role in cell morphology changes, adhesion and migration as an organizer of the cortical cytoskeleton by linking actin filaments to the apical membrane of epithelial cells. It is highly expressed in a variety of human cancers and promotes metastasis. Members of the Ca2+-binding EF-hand containing S100 proteins have similar pathological properties; they are overexpressed in cancer cells and involved in metastatic processes. In this study, using tryptophan fluorescence and stopped-flow kinetics, we show that S100A4 binds to the N-terminal ERM domain (N-ERMAD) of ezrin with a micromolar affinity. The binding involves the F2 lobe of the N-ERMAD and follows an induced fit kinetic mechanism. Interestingly, S100A4 binds also to the unstructured C-terminal actin binding domain (C-ERMAD) with similar affinity. Using NMR spectroscopy, we characterized the complex of S100A4 with the C-ERMAD and demonstrate that no ternary complex is simultaneously formed with the two ezrin domains. Furthermore, we show that S100A4 co-localizes with ezrin in HEK-293T cells. However, S100A4 very weakly binds to full-length ezrin in vitro indicating that the interaction of S100A4 with ezrin requires other regulatory events such as protein phosphorylation and/or membrane binding, shifting the conformational equilibrium of ezrin towards the open state. As both proteins play an important role in promoting metastasis, the characterization of their interaction could shed more light on the molecular events contributing to this pathological process.

Identification of the interplay between SOX9 and S100P in the metastasis and invasion of colon carcinoma

Elevated expression of S100P has been detected in several tumor types and suggested to be responsible for tumor metastasis and invasion, but the upstream regulatory mechanisms promoting S100P overexpression are largely unknown. Here, we report that SOX9 was predicted and verified as a transcription factor of S100P. SOX9 and S100P were both overexpressed in colon cancer. SOX9 bound to and activated the S100P promoter. Knockdown of SOX9 expression down-regulated S100P expression, resulting in reduced invasiveness and metastasis of colon cancer cells by inhibiting the activation of receptor for advanced glycation end products (RAGE)/ERK signaling and epithelial-mesenchymal transition (EMT). Further, decreased expression of SOX9 dramatically inhibited the tumor growth and peritoneal metastasis in nude mice. More importantly, S100P was found to be critical for SOX9-mediated metastasis and invasion in colon cancer. Knockdown of S100P in SOX9-overexpressing colon cancer cells dramatically suppressed metastasis and invasion both in vitro and in mice. We also detected SOX9 and S100P expression in a tissue microarray with 90 colon cancer cases to provide their clinical relevance. There was a strong correlation between SOX9 and S100P expression in colon carcinomas. In conclusion, our results suggest that SOX9 promotes tumor metastasis and invasion through regulation of S100P expression.

Analysis of the predictive efficiency of S100P on adverse prognosis and the pathogenesis of S100P-mediated invasion and metastasis of colon adenocarcinoma

Elevated expression of S100P has been detected in several tumor types. To analyze the potential use of S100P for the prediction of colorectal cancer (CRC) metastasis and prognosis, S100P expression was detected in 125 patients with colon adenocarcinoma by immunohistochemistry, followed by correlation and survival analysis. High S100P expression was correlated with metastasis, as demonstrated by clinically relevant data, and predicted poor survival more effectively than preoperative serum carcinoembryonic antigen (CEA) and carbohydrate antigen 19-9 (CA19-9) levels in colon adenocarcinoma. Stable S100P knockdown CRC cell lines were established to elucidate the relationship between S100P expression and tumor progression in vitro and in vivo. S100P knockdown resulted in reductions in the invasiveness and metastasis of CRC cells. Xenograft growth in nude mice also demonstrated that down-regulated S100P dramatically inhibited peritoneal metastasis of CRC cells. S100P promoted the invasion and metastasis of CRC by activating RAGE/ERK signaling and promoting the epithelial-mesenchymal transition (EMT). RAGE was found to be crucial for S100P-mediated EMT in colon cancer. Knockdown of RAGE in S100P-overexpressing colon cancer cells dramatically suppressed EMT process. Our results indicate that overexpression of S100P is related with an invasive and metastatic phenotype of CRC which is EMT-involved and RAGE dependent.

The life and works of S100P - from conception to cancer

Since its discovery in 1992, the small, 10.4 kDa calcium-binding protein S100P has gained the attention of researchers from different scientific fields due to its potential roles in both healthy and neoplastic tissues. Although not ubiquitously expressed, in tissues where it is present, S100P is associated with distinct changes in cellular behaviour. In this review we have summarized the evolutionary history of S100P, its expression and involvement in implantation and human embryonic development, as well as important functions in normal tissue and cancer. Finally, we have demonstrated its pivotal role as a potential diagnostic and therapeutic target, which opens promising avenues for further fruitful research on S100P.

A novel truncated form of S100P predicts disease-free survival in patients with lymph node positive breast cancer

The calcium-binding protein S100P is overexpressed in various cancers and may contribute to the oncogenic phenotype. This study used mass spectrometry to characterize a novel 9.2-kDa C-terminally truncated form of S100P (t-S100P), and to investigate its potential prognostic value in breast cancer. Univariate analysis demonstrated the association between breast tissue t-S100P levels (n = 148) and conventional pathological markers. Across all tumor samples, high t-S100P was strongly prognostic for poor disease-free survival (P = 0.005), its efficacy confined to lymph node-positive tumors (n = 74, P = 0.007). Matrix-assisted laser desorption/ionization imaging mass spectrometry confirmed differential t-S100P abundance between breast cancer and unaffected adjacent tissue. t-S100P was exclusively located in the cell nucleus of breast cancer tissue, and full-length S100P was essentially undetectable by mass spectrometry. We conclude that t-S100P is the predominant form of S100P in breast cancer tissue and is strongly prognostic for disease-free survival in women with lymph node-positive disease.

The Na+/H+ Exchanger-3 (NHE3) Activity Requires Ezrin Binding to Phosphoinositide and Its Phosphorylation

Na⁺/H⁺ exchanger-3 (NHE3) plays an essential role in maintaining sodium and fluid homeostasis in the intestine and kidney epithelium. Thus, NHE3 is highly regulated and its function depends on binding to multiple regulatory proteins. Ezrin complexed with NHE3 affects its activity via not well-defined mechanisms. This study investigates mechanisms by which ezrin regulates NHE3 activity in epithelial Opossum Kidney cells. Ezrin is activated sequentially by phosphatidylinositol-4,5-bisphosphate (PIP2) binding and phosphorylation of threonine 567. Expression of ezrin lacking PIP2 binding sites inhibited NHE3 activity (-40%) indicating that ezrin binding to PIP2 is required for preserving NHE3 activity. Expression of a phosphomimetic ezrin mutated at the PIP2 binding region was sufficient not only to reverse NHE3 activity to control levels but also to increase its activity (+80%) similar to that of the expression of ezrin carrying the phosphomimetic mutation alone. Calcineurin Homologous Protein-1 (CHP1) is part, with ezrin, of the NHE3 regulatory complex. CHP1-mediated activation of NHE3 activity was blocked by expression of an ezrin variant that could not be phosphorylated but not by an ezrin variant unable to bind PIP2. Thus, for NHE3 activity under baseline conditions not only ezrin phosphorylation, but also ezrin spatial-temporal targeting on the plasma membrane via PIP2 binding is required; however, phosphorylation of ezrin appears to overcome the control of NHE3 transport. CHP1 action on NHE3 activity is not contingent on ezrin binding to PIP2 but rather on ezrin phosphorylation. These findings are important in understanding the interrelation and dynamics of a CHP1-ezrin-NHE3 regulatory complex.

Ezrin interacts with the scaffold protein IQGAP1 and affects its cortical localization

The cortical cytoskeleton constitutes an important subcellular structure that determines cell shape and regulates cell migration as well as membrane traffic to and from the plasma membrane. Many components of the cortical cytoskeleton have been identified including structural and scaffolding proteins, membrane-cytoskeleton linker proteins and signaling intermediates. We describe here an association of the membrane-F-actin linker protein ezrin with the scaffolding protein IQGAP1 that serves as a hub for concentrating different signaling complexes. Both, ezrin and IQGAP1 bind in a Ca²⁺-dependent manner to the EF hand protein S100P and complexes consisting of Ca²⁺-bound S100P, IQGAP1 and ezrin can be isolated by immunoprecipitation. Ezrin and IQGAP1 also interact in the absence of Ca²⁺, thus independent of S100P. Direct ezrin-IQGAP1 interaction can be shown with the purified proteins. It is mediated via the N-terminal FERM domain of ezrin and the IQ domain of IQGAP1, respectively. Ezrin and IQGAP1 colocalize in the submembraneous cytoskeleton and in cellular protrusions of human epithelial cells and knockdown of ezrin reduces the cortical localization of IQGAP1. Thus, ezrin appears to participate in recruiting IQGAP1 to the cell cortex thereby establishing a close connection between membrane-F-actin contacts and actin regulators that can be assembled by IQGAP1. This article is part of a Special Issue entitled: 13th European Symposium on Calcium.

Formation and characterization of supported lipid bilayers containing phosphatidylinositol-4,5-bisphosphate and cholesterol as functional surfaces

Solid-supported lipid bilayers (SLBs) mimicking a biological membrane are commonly used to investigate lipid-lipid or lipid-protein interactions. Simple binary or ternary lipid systems are well established, whereas more complex model membranes containing biologically important signaling lipids such as phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2) and cholesterol have not been extensively described yet. Here we report the generation of such bilayers and their relevant biophysical properties and in particular the accessibility of PI(4,5)P2 for protein binding. Ternary mixtures of POPC with 20% cholesterol and either 3 or 5 mol % dioleoyl-phosphatidylinositol-4,5-bisphosphate were probed by employing the quartz crystal microbalance and atomic force microscopy. We show that these mixtures form homogeneous solid-supported bilayers that exhibit no intrinsic phase separation and are characterized by long-term stability (>8 h). Bilayers were formed in a pH-dependent manner and were characterized by the accessibility of PI(4,5)P2 on the SLB surface as shown by the interaction with the PI(4,5)P2 binding domain of the cortical membrane-cytoskeleton linker protein ezrin. A time-dependent reduction of PI(4,5)P2 levels in the upper leaflet of SLBs was observed, which could be effectively inhibited by the incorporation of a negatively charged lipid such as phosphatidylserine. Furthermore, quartz crystal microbalance measurements revealed that cholesterol affects bilayer adsorption to the solid support.

The expression of S100P increases and promotes cellular proliferation by increasing nuclear translocation of β-catenin in endometrial cancer

There is increasing evidence suggesting that S100P has a significant role in cancer, and is associated with poor clinical outcomes. The expression of S100P mRNA and protein in endometrial cancer and normal endometrium tissues was detected by real-time quantitative RT-PCR and immunohistochemistry. Moreover, we reduced the expression of S100P in HEC-1A and Ishikawa endometrial cancer cell lines by siRNA transfection. Based on the reduced S100P mRNA expression, we measured the effects of S100P on cellular proliferation by the cell-counting kit-8. Nuclear β-catenin protein level was detected by western blotting. Cyclin D1 and c-myc mRNA expression regulated by β-catenin was detected by real-time quantitative RT-PCR. We found that the expression of S100P mRNA and protein increased in endometrial cancer tissues compared with the normal endometrium. Local S100P expression progressively increased from pathologic differenciation grade 1 to 3. After reducing the S100P expression, the cellular proliferation ability, nuclear β-catenin protein level, cyclin D1 and c-myc mRNA levels reduced. It indicated that S100P could promote cell proliferation by increasing nuclear translocation of β-catenin. The expression of S100P mRNA and protein in endometrial cancer significantly increased and is associated with pathologic differenciation grade. S100P may promote endometrial cell proliferation by increasing nuclear translocation of β-catenin.

B-cell lymphoma/leukemia 10 promotes oral cancer progression through STAT1/ATF4/S100P signaling pathway

B-cell lymphoma/leukemia 10 (BCL10) is an apoptotic regulatory protein related to advanced TNM stage and disease recurrence in oral squamous cell carcinoma (OSCC). However, the regulatory mechanism of BCL10 in OSCC progression is still unknown. Here, we showed that knockdown of endogenous BCL10 could significantly reduce cell migration and invasion abilities, retard cell proliferation by G0/G1 phase accumulation and inhibit tumorigenicity in vivo. In molecular level, we identified S100P as a crucial downstream effector of BCL10-inhibited OSCC progression by high-throughput microarray analysis. S100P messenger RNA and protein expression levels were significantly diminished in silenced-BCL10 clones, and transfected S100P expression plasmids restored migration, invasion, proliferation abilities and tumorigenicity in shBCL10 transfectants. Furthermore, we provided evidence that BCL10 regulated S100P expression through signal transducers and activators of transcription 1 (STAT1) and activating transcription factor 4 (ATF4). Knockdown of BCL10 decreased S100P promoter activity, but showed no effect in truncated STAT1/ATF4 S100P promoter.  In addition, we also found that the P50/P65 signaling pathway was involved in BCL10-enhanced OSCC progression. Restored S100P in silenced-BCL10 clones could markedly reverse P65 activation via outside-in signaling. Taken together, we discovered a novel axis of BCL10-regulated OSCC progression via STAT1/ATF4/S100P/P65 signaling, which could predict the prognosis of OSCC and will be beneficial for developing therapeutic strategy against advanced OSCC.

Phosphatidylinositol 4,5-bisphosphate alters the number of attachment sites between ezrin and actin filaments: a colloidal probe study

Direct linkage between the plasma membrane and the actin cytoskeleton is controlled by the protein ezrin, a member of the ezrin-radixin-moesin protein family. To function as a membrane-cytoskeleton linker, ezrin needs to be activated in a process that involves binding of ezrin to phosphatidylinositol 4,5-bisphosphate (PIP2) and phosphorylation of a conserved threonine residue. Here, we used colloidal probe microscopy to quantitatively analyze the interaction between ezrin and F-actin as a function of these activating factors. We show that the measured individual unbinding forces between ezrin and F-actin are independent of the activating parameters, in the range of approximately 50 piconewtons. However, the cumulative adhesion energy greatly increases in the presence of PIP2 demonstrating that a larger number of bonds between ezrin and F-actin has formed. In contrast, the phosphorylation state, represented by phosphor-mimetic mutants of ezrin, only plays a minor role in the activation process. These results are in line with in vivo experiments demonstrating that an increase in PIP2 concentration recruits more ezrin to the apical plasma membrane of polarized cells and significantly increases the membrane tension serving as a measure of the adhesion sites between the plasma membrane and the F-actin network.

Upregulation of S100P, receptor for advanced glycation end products and ezrin in malignant melanoma

S100P is a member of the S100 family. Increased levels of S100P have been documented in various malignancies. Binding of extracellular S100P to receptor for advanced glycation end products (RAGE) or coupling of intracellular S100P with a cytoskeletal protein, ezrin, play a crucial role in tumor growth, invasion and metastasis. However, little is known about the expression of S100P, RAGE and ezrin in malignant melanoma. We immunostained these three molecules in 20 primary and 20 metastatic melanomas. Samples of 20 benign nevus pigmentosus and 10 of normal skin were tested as controls. The expression levels (percentage of positively stained cells) of S100P, RAGE and ezrin were significantly higher in melanomas than in nevus pigmentosus. Moreover, slightly but significantly higher expression levels were observed in metastatic than in primary melanomas. Significant positive correlations were evident between the expression levels of S100P and RAGE, S100P and ezrin, and RAGE and ezrin, respectively. In conclusion, the coordinate upregulation of S100P, RAGE and ezrin may possibly facilitate malignant transformation of melanoma.

Solid supported membranes doped with PIP2: influence of ionic strength and pH on bilayer formation and membrane organization

Phosphoinositides and in particular L-α-phosphatidylinositol-4,5-bisphosphate (PIP2) are key lipids controlling many cellular events and serve as receptors for a large number of intracellular proteins. To quantitatively analyze protein-PIP2 interactions in vitro in a time-resolved manner, planar membranes on solid substrates are highly desirable. Here, we describe an optimized protocol to form PIP2 containing planar solid supported membranes on silicon surfaces by vesicle spreading. Supported lipid bilayers (SLBs) were obtained by spreading POPC/PIP2 (92:8) small unilamellar vesicles onto hydrophilic silicon substrates at a low pH of 4.8. These membranes were capable of binding ezrin, resulting in large protein coverage as concluded from reflectometric interference spectroscopy and fluorescence microscopy. As deduced from fluorescence microscopy, only under low pH conditions, a homogeneously appearing distribution of fluorescently labeled PIP2 molecules in the membrane was achieved. Fluorescence recovery after photobleaching experiments revealed that PIP2 is not mobile in the bottom layer of the SLBs, while PIP2 is fully mobile in the top layer with diffusion coefficients of about 3 μm(2)/s. This diffusion coefficient was considerably reduced by a factor of about 3 if ezrin has been bound to PIP2 in the membrane.

Interactome analysis reveals ezrin can adopt multiple conformational states

Ezrin, a member of the ezrin-radixin-moesin family (ERM), is an essential regulator of the structure of microvilli on the apical aspect of epithelial cells. Ezrin provides a linkage between membrane-associated proteins and F-actin, oscillating between active/open and inactive/closed states, and is regulated in part by phosphorylation of a C-terminal threonine. In the open state, ezrin can bind a number of ligands, but in the closed state the ligand-binding sites are inaccessible. In vitro analysis has proposed that there may be a third hyperactivated form of ezrin. To gain a better understanding of ezrin, we conducted an unbiased proteomic analysis of ezrin-binding proteins in an epithelial cell line, Jeg-3. We refined our list of interactors by comparing the interactomes using quantitative mass spectrometry between wild-type ezrin, closed ezrin, open ezrin, and hyperactivated ezrin. The analysis reveals several novel interactors confirmed by their localization to microvilli, as well as a significant class of proteins that bind closed ezrin. Taken together, the data indicate that ezrin can exist in three different conformational states, and different ligands "perceive" ezrin conformational states differently.

S100P expression is a novel prognostic factor in hepatocellular carcinoma and predicts survival in patients with high tumor stage or early recurrent tumors

The calcium-binding protein S100P is expressed in a variety of human cancer cells and is important in cancer cell growth and invasion. Using differential display, we found S100P is overexpressed in human hepatocellular carcinoma (HCC). We examined the expression of 305 unifocal, primary HCC tumors using immunohistochemistry. The S100P protein was expressed in 173 of the 305 (56.7%) HCC tumors. The expression of S100P correlated with female sex (P = 0.0162), high serum α-fetoprotein level (P = 0.0001), high tumor grade (P = 0.0029), high tumor stage (P = 0.0319), the presence of the p53 mutation (P = 0.0032), and the absence of the β-catenin mutation (P = 0.0489). Patients with HCC tumors that expressed S100P were more likely to have early tumor recurrence (ETR) (P = 0.0189) and lower 5-year survival (P = 0.0023). The multivariate analysis confirmed that S100P expression was an independent prognostic factor in HCC. The combinatorial analysis showed an additive unfavorable prognostic interaction between S100P expression and the p53 mutation. In contrast, the β-catenin mutation was associated with better prognosis in both S100P-positive and -negative HCCs. Furthermore, S100P expression was a predictor of survival in HCC patients with high tumor stage or ETR (P = 0.0026 and P = 0.0002, respectively). Our study indicates the expression of the S100P protein is a novel independent predictor for poor prognosis in HCC, and it is also an unfavorable prognostic predictor in HCC patients with high tumor stage or ETR.

Control of actin dynamics by allosteric regulation of actin binding proteins

The regulated assembly and organization of actin filaments allows the cell to construct a large diversity of actin-based structures specifically suited to a range of cellular processes. A vast array of actin regulatory proteins must work in concert to form specific actin networks within cells, and spatial and temporal requirements for actin assembly necessitate rapid regulation of protein activity. This chapter explores a common mechanism of controlling the activity of actin binding proteins: allosteric autoinhibition by interdomain head-tail interactions. Intramolecular interactions maintain these proteins in a closed conformation that masks protein domains needed to regulate actin dynamics. Autoinhibition is typically relieved by two or more ligand binding and/or posttranslational modification events that expose key protein domains. Regulation through multiple inputs permits precise temporal and spatial control of protein activity to guide actin network formation.

S100P expression in response to sex steroids during the implantation window in human endometrium

BACKGROUND

S100P, a protein originally detected in the human placenta, has been found to play an important role in the development and invasion of tumors. Interestingly, we have recently discovered using data mining that S100P was considerably up-regulated during the window of implantation in the human endometrium, but little further information has been available.

METHODS

Real-time PCR and immunofluorescence were performed to examine the expression and location of S100P in the human endometrium and endometrial cells. Estrogen and progesterone were added to the cultured cells to test the response of S100P to sex steroids.

RESULTS

A dramatic peak, approximately a 100-fold increase in comparison with the proliferative and early- and late-secretory phases, was observed in the endometrium during the mid-secretory phase, which corresponds to the time of embryo implantation. Progesterone regulated the expression of S100P in both primary endometrial epithelial and stromal cells, but estrogen had no significant effect.

CONCLUSIONS

The results indicate that S100P participates in the periodic change of the endometrium under the regulation of progesterone, may be used as a unique biomarker of the receptive endometrium and play an important role in embryo implantation.

S100P is a metastasis-associated gene that facilitates transendothelial migration of pancreatic cancer cells

Pancreatic ductal adenocarcinoma (PDAC) is the 5th most common cause of cancer death in the UK and the 4th in the US. The vast majority of deaths following pancreatic cancer are due to metastatic spread, hence understanding the metastatic process is vital for identification of critically needed novel therapeutic targets. An enriched set of 33 genes differentially expressed in common between primary PDAC and liver metastases, when compared to normal tissues, was obtained through global gene expression profiling. This metastasis-associated gene set comprises transcripts from both cancer (S100P, S100A6, AGR2, etc.) and adjacent stroma (collagens type I, III, and V, etc.), thus reinforcing the concept of a continuous crosstalk between the two compartments in both primary tumours and their metastases. The expression of S100P, SFN, VCAN and collagens was further validated in additional primary PDACs and matched liver metastatic lesions, while the functional significance of one of the most highly expressed genes, S100P, was studied in more detail. We show that this protein increases the transendothelial migration of PDAC cancer cells in vitro, which was also confirmed in vivo experiments using a zebrafish embryo model. Thus S100P facilitates cancer cell intravasation/extravasation, critical steps in the hematogenous dissemination of pancreatic cancer cells.

S100P immunostaining identifies a subset of peripheral-type intrahepatic cholangiocarcinomas with morphological and molecular features similar to those of perihilar and extrahepatic cholangiocarcinomas

AIMS

S100P is a calcium-binding protein that is frequently expressed in pancreatic adenocarcinoma and perihilar cholangiocarcinoma. The aim of this study was to investigate the pathological significance of the expression of S100P in peripheral intrahepatic cholangiocarcinoma (ICC).

METHODS AND RESULTS

Immunohistochemical staining was used to investigate S100P expression in 112 cases of peripheral ICC. The results were compared with those for perihilar and extrahepatic cholangiocarcinomas. Patients with S100P-positive peripheral ICC were more likely to have elevated serum levels of carcinoembryonic antigen (CEA) and CA19-9 than those with S100P-negative peripheral ICCs. All cases of peripheral ICC associated with intrahepatic lithiasis and all cases with intraductal/periductal growth patterns were positive for S100P. S100P-positive peripheral ICCs were highly associated with 'bile duct' morphology rather than cholangiolar differentiation. Nearly all cases of perihilar and extrahepatic cholangiocarcinoma were positive for S100P. Similarly to perihilar and extrahepatic cholangiocarcinomas, S100P-positive peripheral ICCs showed more frequent expression of CEA and MUC2, and were more likely to be N-cadherin-negative, than S100P-negative cases. Notably, K-RAS mutations were only detected in S100P-positive peripheral ICCs, with a frequency similar to that in perihilar and extrahepatic cholangiocarcinomas. Patients with S100P-positive peripheral ICC were more likely to have poor prognoses than those with S100P-negative tumours.

CONCLUSIONS

S100P immunostaining identifies a subset of peripheral ICC that probably originates from larger bile ducts. This subset of peripheral ICCs shares common morphological and molecular features with perihilar and extrahepatic cholangiocarcinomas.

Proteomic analysis of acquired tamoxifen resistance in MCF-7 cells reveals expression signatures associated with enhanced migration

Introduction

Acquired tamoxifen resistance involves complex signaling events that are not yet fully understood. Successful therapeutic intervention to delay the onset of hormone resistance depends critically on mechanistic elucidation of viable molecular targets associated with hormone resistance. This study was undertaken to investigate the global proteomic alterations in a tamoxifen resistant MCF-7 breast cancer cell line obtained by long term treatment of the wild type MCF-7 cell line with 4-hydroxytamoxifen (4-OH Tam).

Methods

We cultured MCF-7 cells with 4-OH Tam over a period of 12 months to obtain the resistant cell line. A gel-free, quantitative proteomic method was used to identify and quantify the proteome of the resistant cell line. Nano-flow high-performance liquid chromatography coupled to high resolution Fourier transform mass spectrometry was used to analyze fractionated peptide mixtures that were isobarically labeled from the resistant and control cell lysates. Real time quantitative PCR and Western blots were used to verify selected proteomic changes. Lentiviral vector transduction was used to generate MCF-7 cells stably expressing S100P. Online pathway analysis was performed to assess proteomic signatures in tamoxifen resistance. Survival analysis was done to evaluate clinical relevance of altered proteomic expressions.

Results

Quantitative proteomic analysis revealed a wide breadth of signaling events during transition to acquired tamoxifen resistance. A total of 629 proteins were found significantly changed with 364 up-regulated and 265 down-regulated. Collectively, these changes demonstrated the suppressed state of estrogen receptor (ER) and ER-regulated genes, activated survival signaling and increased migratory capacity of the resistant cell line. The protein S100P was found to play a critical role in conferring tamoxifen resistance and enhanced cell motility.

Conclusions

Our data demonstrate that the adaptive changes in the proteome of tamoxifen resistant breast cancer cells are characterized by down-regulated ER signaling, activation of alternative survival pathways, and enhanced cell motility through regulation of the actin cytoskeleton dynamics. Evidence also emerged that S100P mediates acquired tamoxifen resistance and migration capacity.

A proteomic view on the developmental transfer of homologous 30 kDa lipoproteins from peripheral fat body to perivisceral fat body via hemolymph in silkworm, Bombyx mori

BACKGROUND

A group of abundant proteins of ~30 kDa is synthesized in silkworm larval peripheral fat body (PPFB) tissues and transported into the open circulatory system (hemolymph) in a time-depended fashion to be eventually stored as granules in the pupal perivisceral fat body (PVFB) tissues for adult development during the non-feeding stage. These proteins have been shown to act anti-apoptotic besides being assigned roles in embryogenesis and defense. However, detailed protein structural information for individual PPFB and PVFB tissues during larval and pupal developmental stages is still missing. Gel electrophoresis and chromatography were used to separate the 30 kDa proteins from both PPFB and PVFB as well as hemolymph total proteomes. Mass spectrometry (MS) was employed to elucidate individual protein sequences. Furthermore, 30 kDa proteins were purified and biochemically characterized.

RESULTS

One- and two-dimensional gel electrophoresis (1/2D-PAGE) was used to visualize the relative changes of abundance of the 30 kDa proteins in PPFB and PVFB as well as hemolymph from day 1 of V instar larval stage to day 6 of pupal stage. Their concentrations were markedly increased in hemolymph and PVFB up to the first two days of pupal development and these proteins were consumed during development of the adult insect. Typically, three protein bands were observed (~29, 30, 31 kDa) in 1D-PAGE, which were subjected to MS-based protein identification along with spots excised from 2D-gels run for those proteomes. Gas phase fragmentation was used to generate peptide sequence information, which was matched to the available nucleotide data pool of more than ten highly homologous insect 30 kDa lipoproteins. Phylogenetic and similarity analyses of those sequences were performed to assist in the assignment of experimentally identified peptides to known sequences. Lipoproteins LP1 to LP5 and L301/302 could be matched to peptides extracted from all bands suggesting the presence of full length and truncated or modified protein forms in all of them. The individual variants could not be easily separated by classical means of purification such as 2D-PAGE because of their high similarity. They even seemed to aggregate as was indicated by native gel electrophoresis. Multistep chromatographic procedures eventually allowed purification of an LP3-like protein. The protein responded to lipoprotein-specific staining.

CONCLUSIONS

In B. mori larvae and pupae, 30 kDa lipoproteins LP1 to LP5 and L301/302 were detected in PPFB and PVFB tissue as well as in hemolymph. The concentration of these proteins changed progressively during development from their synthesis in PPFB, transport in hemolymph to storage in PVFB. While the 30 kDa proteins could be reproducibly separated in three bands electrophoretically, the exact nature of the individual protein forms present in those bands remained partially ambiguous. The amino acid sequences of all known 30 kDa proteins showed very high homology. High-resolution separation techniques will be necessary before MS and other structural analysis can shed more light on the complexity of the 30 kDa subproteome in B. mori. A first attempt to that end allowed isolation of a B. mori LP3-like protein, the complete structure, properties and function of which will now be elucidated in detail.

Glucocorticoid receptor-mediated transcriptional activation of S100P gene coding for cancer-related calcium-binding protein

S100P is a member of the S100 family of calcium-binding proteins involved in calcium sensing and signal transduction. Its abnormal expression and biological activities are linked to tumor phenotype, namely to increased survival, proliferation, invasion and metastatic propensity of tumor cells. Association of S100P with outcome of tumor treatment and preliminary data from S100P promoter analysis prompted us to study regulation of S100P expression by glucocorticoids, which are implicated in tumor response to chemotherapy. We showed that dexamethasone (DX), a representative glucocorticoid, was capable to induce activity of S100P promoter by means of increased expression, nuclear translocation, and transactivation properties of the glucocorticoid receptor (GR). Moreover, DX treatment led to decreased phosphorylation of ERK1/2, reduced transcriptional activity of AP1, and modulated activity of some additional transcription factors. We identified a promoter region responsible for DX-mediated transactivation and proved GR binding to S100P promoter. We found that the effect of DX was enhanced by partial but not complete inhibition of the MAPK/ERK pathway, supporting an active crosstalk between GR and MAPK/ERK signal transduction in control of S100P expression. On the other hand, suppression of GR mRNA level by transient siRNA expression resulted in reduced S100P transcription. The role of GR activation in S100P regulation was supported by co-expression of GR with S100P in cells treated with DX. These data suggest that S100P is a direct transcriptional target of glucocorticoid-mediated signaling in tumor cells that is activated through the interplay of GR and MAPK pathways.

Activation of F-actin binding capacity of ezrin: synergism of PIP₂ interaction and phosphorylation

Ezrin is a membrane-cytoskeleton linker protein that can bind F-actin in its active conformation. Several means of regulation of ezrin's activity have been described including phosphorylation of Thr-567 and binding of L-α-phosphatidylinositol-4,5-bisphosphate (PIP(2)). However, the relative contributions of these events toward activation of the protein and their potential interdependence are not known. We developed an assay based on solid-supported membranes, to which different ezrin mutants (ezrin T567A (inactive mutant), wild-type, and T567D (active pseudophosphorylated mutant)) were bound, that enabled us to analyze the influence of phosphorylation and PIP(2) binding on ezrin's activation state in vitro. The lipid bilayers employed contained either DOGS-NTA-Ni to bind the proteins via an N-terminal His-tag, or PIP(2), to which ezrin binds via specific binding sites located in the N-terminal region of the protein. Quantitative analysis of the binding behavior of all three proteins to the two different receptor lipids revealed that all three bind with high affinity and specificity to the two receptor lipids. Fluorescence microscopy on ezrin-decorated solid-supported membranes showed that, dependent on the mode of binding and the phosphorylation state, ezrin is capable of binding actin filaments. A clear synergism between phosphorylation and the receptor lipid PIP(2) was observed, suggesting a conformational switch from the dormant to the active, F-actin binding state by recognition of PIP(2), which is enhanced by the phosphorylation.

S100P is a novel interaction partner and regulator of IQGAP1

Ca(2+)-binding proteins of the S100 family participate in intracellular Ca(2+) signaling by binding to and regulating specific cellular targets in their Ca(2+)-loaded conformation. Because the information on specific cellular targets of different S100 proteins is still limited, we developed an affinity approach that selects for protein targets only binding to the physiologically active dimer of an S100 protein. Using this approach, we here identify IQGAP1 as a novel and dimer-specific target of S100P, a member of the S100 family enriched in the cortical cytoskeleton. The interaction between S100P and IQGAP1 is strictly Ca(2+)-dependent and characterized by a dissociation constant of 0.2 μM. Binding occurs primarily through the IQ domain of IQGAP1 and the first EF hand loop of S100P, thus representing a novel structural principle of S100-target protein interactions. Upon cell stimulation, S100P and IQGAP1 co-localize at or in close proximity to the plasma membrane, and complex formation can be linked to altered signal transduction properties of IQGAP1. Specifically, the EGF-induced tyrosine phosphorylation of IQGAP1 that is thought to function in assembling signaling intermediates at IQGAP1 scaffolds in the subplasmalemmal region is markedly reduced in cells overexpressing S100P but not in cells expressing an S100P mutant deficient in IQGAP1 binding. Furthermore, B-Raf binding to IQGAP1 and MEK1/2 activation occurring downstream of IQGAP1 in EGF-triggered signaling cascades are compromised at elevated S100P levels. Thus, S100P is a novel Ca(2+)-dependent regulator of IQGAP1 that can down-regulate the function of IQGAP1 as a signaling intermediate by direct interaction.

Natural and amyloid self-assembly of S100 proteins: structural basis of functional diversity

The S100 proteins are 10-12 kDa EF-hand proteins that act as central regulators in a multitude of cellular processes including cell survival, proliferation, differentiation and motility. Consequently, many S100 proteins are implicated and display marked changes in their expression levels in many types of cancer, neurodegenerative disorders, inflammatory and autoimmune diseases. The structure and function of S100 proteins are modulated by metal ions via Ca(2+) binding through EF-hand motifs and binding of Zn(2+) and Cu(2+) at additional sites, usually at the homodimer interfaces. Ca(2+) binding modulates S100 conformational opening and thus promotes and affects the interaction with p53, the receptor for advanced glycation endproducts and Toll-like receptor 4, among many others. Structural plasticity also occurs at the quaternary level, where several S100 proteins self-assemble into multiple oligomeric states, many being functionally relevant. Recently, we have found that the S100A8/A9 proteins are involved in amyloidogenic processes in corpora amylacea of prostate cancer patients, and undergo metal-mediated amyloid oligomerization and fibrillation in vitro. Here we review the unique chemical and structural properties of S100 proteins that underlie the conformational changes resulting in their oligomerization upon metal ion binding and ultimately in functional control. The possibility that S100 proteins have intrinsic amyloid-forming capacity is also addressed, as well as the hypothesis that amyloid self-assemblies may, under particular physiological conditions, affect the S100 functions within the cellular milieu.

The induction of S100p expression by the Prostaglandin E₂ (PGE₂)/EP4 receptor signaling pathway in colon cancer cells

BACKGROUND

Prostaglandin E₂ (PGE₂) levels are frequently elevated in colorectal carcinomas. PGE₂ is perceived via four transmembrane G protein coupled receptors (EP1-4), among which the EP4 receptor is most relevant. PGE₂/EP4-receptor interaction activates CREB via the ERK/MEK pathway. However, the downstream target genes activated by this pathway remained to be investigated.

METHODOLOGY/PRINICIPAL FINDINGS

Here, we have identified S100P (an EF-hand calcium binding protein) as a novel downstream target. We show by realtime RT-PCR that S100P mRNA levels are elevated in 14/17 (82%) colon tumor tissues as compared to paired adjacent normal colonic tissues. S100P expression is stimulated in the presence of PGE₂ in a time dependent manner at mRNA and protein levels in colon, breast and pancreatic cancer cells. Pharmacological and RNAi-mediated inhibition of the EP4 receptor attenuates PGE₂-dependent S100P mRNA induction. RNA(i)-mediated knockdown of CREB inhibits endogenous S100P expression. Furthermore, using luciferase reporter analysis and EMSA we show that mutation and/or deletion of the CRE sequence within the S100P promoter abolished PGE₂-mediated transcriptional induction. Finally, we demonstrate that RNA(i)-mediated knockdown of S100P compromised invadopodia formation, colony growth and motility of colon cancer cells. Interestingly, endogenous knock down of S100P decreases ERK expression levels, suggesting a role for ERK in regulating S100P mediated cell growth and motility.

CONCLUSIONS/SIGNIFICANCE

Together, our findings show for the first time that S100P expression is regulated by PGE₂/EP4-receptor signaling and may participate in a feedback signaling that perpetuates tumor cell growth and migration. Therefore, our data suggest that dysregulated S100P expression resulting from aberrant PGE₂/EP4 receptor signaling may have important consequences relevant to colon cancer pathogenesis.

Networking with AKAPs: context-dependent regulation of anchored enzymes

A-Kinase Anchoring Proteins (AKAPs) orchestrate and synchronize cellular events by tethering the cAMP-dependent protein kinase (PKA) and other signaling enzymes to organelles and membranes. The control of kinases and phosphatases that are held in proximity to activators, effectors, and substrates favors the rapid dissemination of information from one cellular location to the next. This article charts the inception of the PKA-anchoring hypothesis, the characterization of AKAPs and their nomenclature, and the physiological roles of context-specific AKAP signaling complexes.

Molecular Mechanism for Various Pharmacological Activities of NSAIDS

The anti-inflammatory action of non-steroidal anti-inflammatory drugs (NSAIDs) is mediated through their inhibitory effects on cyclooxygenase (COX) activity. On the other hand, NSAID use is often associated with gastrointestinal complications. The inhibition of COX by NSAIDs is not the sole explanation for the gastrointestinal side effects of NSAIDs. Furthermore, recent epidemiological studies have revealed that prolonged NSAID use reduces the risk of cancer and Alzheimer’s disease (AD) and a COX-independent unknown mechanism is suggested to be involved in these activities of NSAIDs. In this article, I review our recent work on the COX-independent mechanism involved in NSAID-induced gastric lesions and anti-tumor and anti-AD activities of NSAIDs. Using DNA microarray analysis, we found that NSAIDs affect expression of various genes in a COX-independent manner. We found that membrane permeabilization activity of NSAIDs and resulting NSAID-induced apoptosis are involved in NSAID-induced gastric lesions. On the other hand, induction of expression of tight junction-related genes and endoplasmic reticulum chaperones were suggested to be involved in anti-tumor and anti-AD, respectively, activities of NSAIDs. These results suggest that NSAIDs affect expression of various genes in a COX-independent manner, which is involved in various pharmacological activities of NSAIDs.