Human secreted proteins SLURP-1 and SLURP-2 control the growth of epithelial cancer cells via interactions with nicotinic acetylcholine receptors

Inflammation-Related Immune-Modulatory SLURP1 Prevents the Proliferation of Human Colon Cancer Cells, and Its Delivery by Salmonella Demonstrates Cross-Species Efficacy against Murine Colon Cancer

This study investigates the anticancer properties of the α7-nAChR antagonist SLURP1 with a specific focus on its effect as an inflammation modulator on human colorectal cancer cell lines Caco2, Colo320DM, and H508 cells. The investigation includes the evaluation of cell cycle arrest, cell migration arrest, endogenous expression of SLURP1 and related proteins, calcium influx, and inflammatory responses. The results demonstrate that SLURP1 not only inhibits cell proliferation but also has the potential to arrest the cell cycle at the G1/S interface. The impact of SLURP1 on cell cycle regulation varied among cell lines, with H508 cells displaying the strongest response to exogenous SLURP1. Additionally, SLURP1 affects the nuclear factor kappa B expression and effectively reverses inflammatory responses elicited by purified lipopolysaccharides in H508 and Caco2 cells. This study further confirmed the expression of human SLURP1 by Salmonella, under Ptrc promoter, through Western blot analysis. Moreover, Salmonella secreting SLURP1 revealed a significant tumor regression in a mouse CT26 tumor model, suggesting the cross-species anticancer potential of human SLURP1. However, further investigations are required to fully understand the mechanisms underlying SLURP1's ability to prevent cancer proliferation and its protective function in humans.

Selective targeting of α7 nicotinic acetylcholine receptor by synthetic peptide mimicking loop I of human SLURP-1 provides efficient and prolonged therapy of epidermoid carcinoma in vivo

α7-Type nicotinic acetylcholine receptor (α7-nAChR) promotes the growth and metastasis of solid tumors. Secreted Ly6/uPAR-Related Protein 1 (SLURP-1) is a specific negative modulator of α7-nAChR produced by epithelial cells. Here, we investigated mechanisms of antiproliferative activity of recombinant SLURP-1 in epidermoid carcinoma A431 cells and activity of SLURP-1 and synthetic 21 a.a. peptide mimicking its loop I (Oncotag) in a xenograft mice model of epidermoid carcinoma. SLURP-1 inhibited the mitogenic pathways and transcription factors in A431 cells, and its antiproliferative activity depended on α7-nAChR. Intravenous treatment of mice with SLURP-1 or Oncotag for 10 days suppressed the tumor growth and metastasis and induced sustained changes in gene and microRNA expression in the tumors. Both SLURP-1 and Oncotag demonstrated no acute toxicity. Surprisingly, Oncotag led to a longer suppression of pro-oncogenic signaling and downregulated expression of pro-oncogenic miR-221 and upregulated expression of KLF4 protein responsible for control of cell differentiation. Affinity purification revealed SLURP-1 interactions with both α7-nAChR and EGFR and selective Oncotag interaction with α7-nAChR. Thus, the selective inhibition of α7-nAChRs by drugs based on Oncotag may be a promising strategy for cancer therapy.

Differentially Expressed Genes, miRNAs and Network Models: A Strategy to Shed Light on Molecular Interactions Driving HNSCC Tumorigenesis

Head and neck squamous cell carcinoma (HNSCC) is among the most common cancer worldwide, accounting for hundreds thousands deaths annually. Unfortunately, most patients are diagnosed in an advanced stage and only a percentage respond favorably to therapies. To help fill this gap, we hereby propose a retrospective in silico study to shed light on gene-miRNA interactions driving the development of HNSCC. Moreover, to identify topological biomarkers as a source for designing new drugs. To achieve this, gene and miRNA profiles from patients and controls are holistically reevaluated using protein-protein interaction (PPI) and bipartite miRNA-target networks. Cytoskeletal remodeling, extracellular matrix (ECM), immune system, proteolysis, and energy metabolism have emerged as major functional modules involved in the pathogenesis of HNSCC. Of note, the landscape of our findings depicts a concerted molecular action in activating genes promoting cell cycle and proliferation, and inactivating those suppressive. In this scenario, genes, including VEGFA, EMP1, PPL, KRAS, MET, TP53, MMPs and HOXs, and miRNAs, including mir-6728 and mir-99a, emerge as key players in the molecular interactions driving HNSCC tumorigenesis. Despite the heterogeneity characterizing these HNSCC subtypes, and the limitations of a study pointing to relationships that could be context dependent, the overlap with previously published studies is encouraging. Hence, it supports further investigation for key molecules, both those already and not correlated to HNSCC.

α7- and α9-Containing Nicotinic Acetylcholine Receptors in the Functioning of Immune System and in Pain

Nicotinic acetylcholine receptors (nAChRs) present as many different subtypes in the nervous and immune systems, muscles and on the cells of other organs. In the immune system, inflammation is regulated via the vagus nerve through the activation of the non-neuronal α7 nAChR subtype, affecting the production of cytokines. The analgesic properties of α7 nAChR-selective compounds are mostly based on the activation of the cholinergic anti-inflammatory pathway. The molecular mechanism of neuropathic pain relief mediated by the inhibition of α9-containing nAChRs is not fully understood yet, but the role of immune factors in this process is becoming evident. To obtain appropriate drugs, a search of selective agonists, antagonists and modulators of α7- and α9-containing nAChRs is underway. The naturally occurring three-finger snake α-neurotoxins and mammalian Ly6/uPAR proteins, as well as neurotoxic peptides α-conotoxins, are not only sophisticated tools in research on nAChRs but are also considered as potential medicines. In particular, the inhibition of the α9-containing nAChRs by α-conotoxins may be a pathway to alleviate neuropathic pain. nAChRs are involved in the inflammation processes during AIDS and other viral infections; thus they can also be means used in drug design. In this review, we discuss the role of α7- and α9-containing nAChRs in the immune processes and in pain.

Extracellular Vesicles Derived from Metastatic Melanoma Cells Transfer α7-nAChR mRNA, Thus Increasing the Surface Expression of the Receptor and Stimulating the Growth of Normal Keratinocytes

We have previously shown that extracellular vesicles secreted by metastatic melanoma cells stimulate the growth, migration, and stemness of normal keratinocytes. This study showed for the first time that extracellular vesicles secreted by the metastatic melanoma cell lines mel H, mel Kor, and mel P contain, both at the mRNA and protein levels, the α7-type nicotinic acetylcholine receptor (α7-nAChR), which is involved in the regulation of the oncogenic signaling pathways in epithelial cells. Incubation with the vesicles secreted by mel H cells and containing the highest amount of mRNA coding α7-nAChR increased the surface expression of α7-nAChR in normal Het-1A keratinocytes and stimulated their growth. Meanwhile, both of these effects disappeared in the presence of α-bungarotoxin, an α7-nAChR inhibitor. A bioinformatic analysis revealed a correlation between the increased expression of the CHRNA7 gene coding α7-nAChR in patients with metastatic melanoma and a poor survival prognosis. Therefore, extracellular vesicles derived from metastatic melanoma cells can transfer mRNA coding α7-nAChR, thus enhancing the surface expression of this receptor and stimulating the growth of normal keratinocytes. Targeting of α7-nAChR may become a new strategy for controlling the malignant transformation of keratinocytes.

Mambalgin-2 Inhibits Lung Adenocarcinoma Growth and Migration by Selective Interaction With ASIC1/α-ENaC/γ-ENaC Heterotrimer

Lung cancer is one of the most common cancer types in the world. Despite existing treatment strategies, overall patient survival remains low and new targeted therapies are required. Acidification of the tumor microenvironment drives the growth and metastasis of many cancers. Acid sensors such as acid-sensing ion channels (ASICs) may become promising targets for lung cancer therapy. Previously, we showed that inhibition of the ASIC1 channels by a recombinant analogue of mambalgin-2 from Dendroaspis polylepis controls oncogenic processes in leukemia, glioma, and melanoma cells. Here, we studied the effects and molecular targets of mambalgin-2 in lung adenocarcinoma A549 and Lewis cells, lung transformed WI-38 fibroblasts, and lung normal HLF fibroblasts. We found that mambalgin-2 inhibits the growth and migration of A549, metastatic Lewis P29 cells, and WI-38 cells, but not of normal fibroblasts. A549, Lewis, and WI-38 cells expressed different ASIC and ENaC subunits, while normal fibroblasts did not at all. Mambalgin-2 induced G2/M cell cycle arrest and apoptosis in lung adenocarcinoma cells. In line, acidification-evoked inward currents were observed only in A549 and WI-38 cells. Gene knockdown showed that the anti-proliferative and anti-migratory activity of mambalgin-2 is dependent on the expression of ASIC1a, α-ENaC, and γ-ENaC. Using affinity extraction and immunoprecipitation, mambalgin-2 targeting of ASIC1a/α-ENaC/γ-ENaC heteromeric channels in A549 cells was shown. Electrophysiology studies in Xenopus oocytes revealed that mambalgin-2 inhibits the ASIC1a/α-ENaC/γ-ENaC channels with higher efficacy than the ASIC1a channels, pointing on the heteromeric channels as a primary target of the toxin in cancer cells. Finally, bioinformatics analysis showed that the increased expression of ASIC1 and γ-ENaC correlates with a worse survival prognosis for patients with lung adenocarcinoma. Thus, the ASIC1a/α-ENaC/γ-ENaC heterotrimer can be considered a marker of cell oncogenicity and its targeting is promising for the design of new selective cancer therapeutics.

Extracellular Vesicles Derived from Acidified Metastatic Melanoma Cells Stimulate Growth, Migration, and Stemness of Normal Keratinocytes

Metastatic melanoma is a highly malignant tumor. Melanoma cells release extracellular vesicles (EVs), which contribute to the growth, metastasis, and malignancy of neighboring cells by transfer of tumor-promoting miRNAs, mRNA, and proteins. Melanoma microenvironment acidification promotes tumor progression and determines EVs’ properties. We studied the influence of EVs derived from metastatic melanoma cells cultivated at acidic (6.5) and normal (7.4) pH on the morphology and homeostasis of normal keratinocytes. Acidification of metastatic melanoma environment made EVs more prooncogenic with increased expression of prooncogenic mi221 RNA, stemless factor CD133, and pro-migration factor SNAI1, as well as with downregulated antitumor mir7 RNA. Incubation with EVs stimulated growth and migration both of metastatic melanoma cells and keratinocytes and changed the morphology of keratinocytes to stem-like phenotype, which was confirmed by increased expression of the stemness factors KLF and CD133. Activation of the AKT/mTOR and ERK signaling pathways and increased expression of epidermal growth factor receptor EGFR and SNAI1 were detected in keratinocytes upon incubation with EVs. Moreover, EVs reduced the production of different cytokines (IL6, IL10, and IL12) and adhesion factors (sICAM-1, sICAM-3, sPecam-1, and sCD40L) usually secreted by keratinocytes to control melanoma progression. Bioinformatic analysis revealed the correlation between decreased expression of these secreted factors and worse survival prognosis for patients with metastatic melanoma. Altogether, our data mean that metastatic melanoma EVs are important players in the transformation of normal keratinocytes.

Secreted Ly-6/uPAR-related protein-1 (SLURP1) is a pro-differentiation factor that stalls G1-S transition during corneal epithelial cell cycle progression

PURPOSE

Previously we demonstrated that the secreted Ly-6/uPAR related protein-1 (SLURP1), abundantly expressed in the corneal epithelium (CE) and secreted into the tear fluid, serves as an anti-inflammatory and anti-angiogenic molecule. Here we describe the Slurp1-null (Slurp1X-/-) mouse corneal phenotype for the first time.

METHODS

We compared the 10-week-old wild type (WT) and Slurp1X-/- mouse corneal (i) histology by hematoxylin-eosin and periodic acid-Schiff's reagent staining, (ii) cell proliferation by immunostaining for Ki67, (iii) cell adhesion molecules by immunostaining for desmosomal and tight junction proteins, (iv) barrier function by fluorescein staining and (v) wound-healing by epithelial debridement. Effect of SLURP1 on cell cycle was quantified in human corneal limbal epithelial (HCLE) cells engineered to express SLURP1 (HCLE-SLURP1).

RESULTS

WT and Slurp1X-/- corneal histology was largely comparable, other than a few loosely attached superficial cells in Slurp1X-/- corneas. Compared with the WT, Slurp1X-/- corneas displayed (i) increase in Ki67+ cells, (ii) altered expression and/or localization of tight junction proteins Tjp1 and Pard3, and desmosomal Dsp, (iii) increased superficial fragility and (iv) slower CE wound healing. HCLE-SLURP1 cells displayed (i) decrease in Ki67+ cells, (ii) increased cell number doubling time, (iii) stalling in G1-S phase transition during cell cycle, and (iv) downregulation of cyclins CCNE and CCND1/D2, cyclin-dependent kinases CDK4 and CDK6, and upregulation of CDK inhibitor p15/CDKN2B.

CONCLUSIONS

Collectively, these results elucidate that Slurp1X-/- CE cell homeostasis is altered and suggest that SLURP1 is a pro-differentiation factor that stalls G1-S transition during cell cycle progression by downregulating cyclins and upregulating p15/CDKN2B.

Mambalgin-2 Inhibits Growth, Migration, and Invasion of Metastatic Melanoma Cells by Targeting the Channels Containing an ASIC1a Subunit Whose Up-Regulation Correlates with Poor Survival Prognosis

Melanoma is an aggressive cancer characterized by the acidification of the extracellular environment. Here, we showed for the first time that extracellular media acidification increases proliferation, migration, and invasion of patient-derived metastatic melanoma cells and up-regulates cell-surface expression of acid-sensitive channels containing the ASIC1a, α-ENaC, and γ-ENaC subunits. No influence of media acidification on these processes was found in normal keratinocytes. To control metastatic melanoma progression associated with the ASIC1a up-regulation, we proposed the ASIC1a inhibitor, -mambalgin-2 from Dendpoaspis polylepis venom. Recombinant analog of mambalgin-2 cancelled acidification-induced proliferation, migration, and invasion of metastatic melanoma cells, promoted apoptosis, and down-regulated cell-surface expression of prooncogenic factors CD44 and Frizzled 4 and phosphorylation of transcription factor SNAI. Confocal microscopy and affinity purification revealed that mambalgin-2 interacts with heterotrimeric ASIC1a/α-ENaC/γ-ENaC channels on the surface of metastatic melanoma cells. Using the mutant variant of mambalgin-2 with reduced activity toward ASIC1a, we confirmed that the principal molecular target of mambalgin-2 in melanoma cells is the ASIC1a subunit. Bioinformatic analysis confirmed up-regulation of the ASIC1 expression as a marker of poor survival prognosis for patients with metastatic melanoma. Thus, targeting ASIC1a by drugs such as mambalgin-2 could be a promising strategy for metastatic melanoma treatment.

SLURP-1 Controls Growth and Migration of Lung Adenocarcinoma Cells, Forming a Complex With α7-nAChR and PDGFR/EGFR Heterodimer

Secreted Ly6/uPAR-related protein 1 (SLURP-1) is a secreted Ly6/uPAR protein that negatively modulates the nicotinic acetylcholine receptor of α7 type (α7-nAChR), participating in control of cancer cell growth. Previously we showed, that a recombinant analogue of human SLURP-1 (rSLURP-1) diminishes the lung adenocarcinoma A549 cell proliferation and abolishes the nicotine-induced growth stimulation. Here, using multiplex immunoassay, we demonstrated a decrease in PTEN and mammalian target of rapamycin (mTOR) kinase phosphorylation in A549 cells upon the rSLURP-1 treatment pointing on down-regulation of the PI3K/AKT/mTOR signaling pathway. Decreased phosphorylation of the platelet-derived growth factor receptor type β (PDGFRβ) and arrest of the A549 cell cycle in the S and G2/M phases without apoptosis induction was also observed. Using a scratch migration assay, inhibition of A549 cell migration under the rSLURP-1 treatment was found. Affinity extraction demonstrated that rSLURP-1 in A549 cells forms a complex not only with α7-nAChR, but also with PDGFRα and epidermal growth factor receptor (EGFR), which are known to be involved in regulation of cancer cell growth and migration and are able to form a heterodimer. Knock-down of the genes encoding α7-nAChR, PDGFRα, and EGFR confirmed the involvement of these receptors in the anti-migration effect of SLURP-1. Thus, SLURP-1 can target the α7-nAChR complexes with PDGFRα and EGFR in the membrane of epithelial cells. Using chimeric proteins with grafted SLURP-1 loops we demonstrated that loop I is the principal active site responsible for the SLURP-1 interaction with α7-nAChR and its antiproliferative effect. Synthetic peptide mimicking the loop I cyclized by a disulfide bond inhibited ACh-evoked current at α7-nAChR, as well as A549 cell proliferation and migration. This synthetic peptide represents a promising prototype of new antitumor drug with the properties close to that of the native SLURP-1 protein.

Regulation of Immune Functions by Non-Neuronal Acetylcholine (ACh) via Muscarinic and Nicotinic ACh Receptors

Acetylcholine (ACh) is the classical neurotransmitter in the cholinergic nervous system. However, ACh is now known to regulate various immune cell functions. In fact, T cells, B cells, and macrophages all express components of the cholinergic system, including ACh, muscarinic, and nicotinic ACh receptors (mAChRs and nAChRs), choline acetyltransferase, acetylcholinesterase, and choline transporters. In this review, we will discuss the actions of ACh in the immune system. We will first briefly describe the mechanisms by which ACh is stored in and released from immune cells. We will then address Ca²⁺ signaling pathways activated via mAChRs and nAChRs on T cells and B cells, highlighting the importance of ACh for the function of T cells, B cells, and macrophages, as well as its impact on innate and acquired (cellular and humoral) immunity. Lastly, we will discuss the effects of two peptide ligands, secreted lymphocyte antigen-6/urokinase-type plasminogen activator receptor-related peptide-1 (SLURP-1) and hippocampal cholinergic neurostimulating peptide (HCNP), on cholinergic activity in T cells. Overall, we stress the fact that ACh does not function only as a neurotransmitter; it impacts immunity by exerting diverse effects on immune cells via mAChRs and nAChRs.

Biochemical Basis of Skin Disease Mal de Meleda: SLURP-1 Mutants Differently Affect Keratinocyte Proliferation and Apoptosis

Mal de Meleda is an autosomal recessive palmoplantar keratoderma associated with mutations in a gene encoding SLURP-1. SLURP-1 controls growth, differentiation, and apoptosis of keratinocytes by interaction with α7-type nicotinic acetylcholine receptors. SLURP-1 has a three-finger structure with a β-structural core (head) and three prolonged loops (fingers). To determine the role of SLURP-1 mutations, we produced 22 mutant variants of the protein, including those involved in Mal de Meleda pathogenesis. All mutants except R71H, R71P, T52A, R96P, and L98P were produced in the folded form. SLURP-1 reduces the growth of Het-1A keratinocytes; thus, we studied the influence of the mutations on its antiproliferative activity. Mutations in loops I and III led to the protein inactivation, whereas most mutations in loop II increased SLURP-1 antiproliferative activity. Alanine substitutions of R96 and L98 residues located in the protein head resulted in the appearance of additional pro-apoptotic activity. Our results agree with the diversity of Mal de Meleda phenotypes. Using obtained functional data, the SLURP-1/α7 type nicotinic acetylcholine receptor complex was modeled in silico. Our study provides functional and structural information about the role of the SLURP-1 mutations in Mal de Meleda pathogenesis and predicts SLURP-1 variants, which could drive the disease.

CHRNA5 belongs to the secondary estrogen signaling network exhibiting prognostic significance in breast cancer

PURPOSE

Cholinergic signals can be important modulators of cellular signaling in cancer. We recently have shown that knockdown of nicotinic acetylcholine receptor subunit alpha 5, CHRNA5, diminishes the proliferative potential of breast cancer cells. However, modulation of CHRNA5 expression in the context of estrogen signaling and its prognostic implications in breast cancer remained unexplored.

METHODS

Meta-analyses of large breast cancer microarray cohorts were used to evaluate the association of CHRNA5 expression with estrogen (E2) treatment, estrogen receptor (ER) status and patient prognosis. The results were validated through RT-qPCR analyses of multiple E2 treated cell lines, CHRNA5 depleted MCF7 cells and across a breast cancer patient cDNA panel. We also calculated a predicted secondary (PS) score representing direct/indirect induction of gene expression by E2 based on a public dataset (GSE8597). Co-expression analysis was performed using a weighted gene co-expression network analysis (WGCNA) pipeline. Multiple other publicly available datasets such as CCLE, COSMIC and TCGA were also analyzed.

RESULTS

Herein we found that CHRNA5 expression was induced by E2 in a dose- and time-dependent manner in breast cancer cell lines. ER^- breast tumors exhibited higher CHRNA5 expression levels than ER⁺ tumors. Independent meta-analysis for survival outcome revealed that higher CHRNA5 expression was associated with a worse prognosis in untreated breast cancer patients. Furthermore, CHRNA5 and its co-expressed gene network emerged as secondarily induced targets of E2 stimulation. These targets were largely downregulated by exposure to CHRNA5 siRNA in MCF7 cells while the response of primary ESR1 targets was dependent on the direction of the PS-score. Moreover, primary and secondary target genes were uncoupled and clustered distinctly based on multiple public datasets.

CONCLUSION

Our findings strongly associate increased expression of CHRNA5 and its co-expression network with secondary E2 signaling and a worse prognosis in breast cancer.

Efficient screening of ligand-receptor complex formation using fluorescence labeling and size-exclusion chromatography

Evidence of a complex formation is a crucial step in the structural studies of ligand-receptor interactions. Here we presented a simple and fast approach for qualitative screening of the complex formation between the chimeric extracellular domain of the nicotinic acetylcholine receptor (α7-ECD) and three-finger proteins. Complex formation of snake toxins α-Bgtx and WTX, as well as of recombinant analogs of human proteins Lynx1 and SLURP-1, with α7-ECD was confirmed using fluorescently labeled ligands and size-exclusion chromatography with simultaneous absorbance and fluorescence detection. WTX/α7-ECD complex formation also was confirmed by cryo-EM. The proposed approach could easily be adopted to study the interaction of other receptors with their ligands.

Structural Diversity and Dynamics of Human Three-Finger Proteins Acting on Nicotinic Acetylcholine Receptors

Ly-6/uPAR or three-finger proteins (TFPs) contain a disulfide-stabilized β-structural core and three protruding loops (fingers). In mammals, TFPs have been found in epithelium and the nervous, endocrine, reproductive, and immune systems. Here, using heteronuclear NMR, we determined the three-dimensional (3D) structure and backbone dynamics of the epithelial secreted protein SLURP-1 and soluble domains of GPI-anchored TFPs from the brain (Lynx2, Lypd6, Lypd6b) acting on nicotinic acetylcholine receptors (nAChRs). Results were compared with the data about human TFPs Lynx1 and SLURP-2 and snake α-neurotoxins WTX and NTII. Two different topologies of the β-structure were revealed: one large antiparallel β-sheet in Lypd6 and Lypd6b, and two β-sheets in other proteins. α-Helical segments were found in the loops I/III of Lynx2, Lypd6, and Lypd6b. Differences in the surface distribution of charged and hydrophobic groups indicated significant differences in a mode of TFPs/nAChR interactions. TFPs showed significant conformational plasticity: the loops were highly mobile at picosecond-nanosecond timescale, while the β-structural regions demonstrated microsecond-millisecond motions. SLURP-1 had the largest plasticity and characterized by the unordered loops II/III and cis-trans isomerization of the Tyr39-Pro40 bond. In conclusion, plasticity could be an important feature of TFPs adapting their structures for optimal interaction with the different conformational states of nAChRs.

Recombinant Analogue of the Human Protein SLURP-1 Inhibits the Growth of U251 MG and A172 Glioma Cells

The alpha7 nicotinic acetylcholine receptor (α7-nAChR) is considered a promising pharmacological target for the carcinoma therapy. We have previously shown that the recombinant analogue of the human protein SLURP-1 (rSLURP-1) effectively inhibits the growth of carcinomas of various origins via the interaction with α7-nAChR and down-regulation of expression of this receptor. Expression of α7-nAChR is increased in gliomas compared to healthy human brain tissues; however, the role of this receptor in the gliomas development is poorly understood. It was shown for the first time that rSLURP-1 significantly inhibits the growth of glioma model cells U251 MG and A172 up to ∼70%, which is comparable with the effect of α-bungarotoxin, a selective α7-nAChR inhibitor. The half-maximum effective concentrations of rSLURP-1 for U251 MG and A172 cells were 2.82 ± 0.2 and 8.9 ± 0.3 nM, respectively. Coincubation of U251 MG cells with rSLURP-1 and the nAChR inhibitor mecamylamine attenuates the antiproliferative activity of rSLURP-1, indicating nAChR as a molecular target for the rSLURP-1 action in gliomas.

α5-nAChR and survivin: Two potential biological targets in lung adenocarcinoma

Recent studies have shown that the overexpression of α5 nicotinic acetylcholine receptor (α5-nAChR) is associated with nicotine-related lung carcinogenesis. Survivin is one of the biomarkers of a worse prognosis for smoking-related lung cancer. The aim of this study is to investigate the association of α5-nAChR, survivin, and clinical outcomes in lung adenocarcinoma (LUAD). We analyzed the expression level and correlation of CHRNA5 (encoding α5-nAChR) and BIRC5 (encoding survivin) in LUAD with The Cancer Genome Atlas data set. The relationship between overall survival (OS) and the expression of CHRNA5 or/and BIRC5 was evaluated by the Kaplan-Meier method and Cox proportional hazards model. Moreover, our results showed that the expression of α5-nAChR mediated survivin expression in lung cancer cells and in lung tumor xenografts. Relationships between the expression of α5-nAChR and/or survivin with clinical-pathological characteristics were analyzed using LUAD tissue samples. The results showed that expression of α5-nAChR was correlated with survivin expression in vitro and in vivo. The group coexpressing α5-nAChR and survivin had a worse prognosis than other subgroups in LUAD (p < .05). In conclusion, ascertaining the expression of both α5-nAChR and survivin provides a better measure of prognosis for LUAD patients. The combined inhibition of α5-nAChR and survivin may be a promising multitargeted gene therapeutic strategy in LUAD diagnosis.

Three-finger proteins from snakes and humans acting on nicotinic receptors: Old and new

The first toxin to give rise to the three-finger protein (TFP) family was α-bungarotoxin (α-Bgt) from Bungarus multicinctus krait venom. α-Bgt was crucial for research on nicotinic acetylcholine receptors (nAChRs), and in this Review article we focus on present data for snake venom TFPs and those of the Ly6/uPAR family from mammalians (membrane-bound Lynx1 and secreted SLURP-1) interacting with nAChRs. Recently isolated from Bungarus candidus venom, αδ-bungarotoxins differ from α-Bgt: they bind more reversibly and distinguish two binding sites in Torpedo californica nAChR. Naja kaouthia α-cobratoxin, classical blocker of nAChRs, was shown to inhibit certain GABA-A receptor subtypes, whereas α-cobratoxin dimer with 2 intermolecular disulfides has a novel type of 3D structure. Non-conventional toxin WTX has additional 5th disulfide not in the central loop, as α-Bgt, but in the N-terminal loop, like all Ly6/uPAR proteins, and inhibits α7 and Torpedo nAChRs. A water-soluble form of Lynx1, ws-Lynx1, was expressed in E. coli, its ¹ H-NMR structure and binding to several nAChRs determined. For SLURP-1, similar information was obtained with its recombinant analogue rSLURP-1. A common feature of ws-Lynx1, rSLURP-1, and WTX is their activity against nAChRs and muscarinic acetylcholine receptors. Synthetic SLURP-1, identical to the natural protein, demonstrated some differences from rSLURP-1 in distinguishing nAChR subtypes. The loop II fragment of the Lynx1 was synthesized having the same µM affinity for the Torpedo nAChR as ws-Lynx1. This review illustrates the productivity of parallel research of nAChR interactions with the two TFP groups.

αO-Conotoxin GeXIVA Inhibits the Growth of Breast Cancer Cells via Interaction with α9 Nicotine Acetylcholine Receptors

The α9-containing nicotinic acetylcholine receptor (nAChR) is increasingly emerging as a new tumor target owing to its high expression specificity in breast cancer. αO-Conotoxin GeXIVA is a potent antagonist of α9α10 nAChR. Nevertheless, the anti-tumor effect of GeXIVA on breast cancer cells remains unclear. Cell Counting Kit-8 assay was used to study the cell viability of breast cancer MDA-MD-157 cells and human normal breast epithelial cells, which were exposed to different doses of GeXIVA. Flow cytometry was adopted to detect the cell cycle arrest and apoptosis of GeXIVA in breast cancer cells. Migration ability was analyzed by wound healing assay. Western blot (WB), quantitative real-time PCR (QRT-PCR) and flow cytometry were used to determine expression of α9-nAChR. Stable MDA-MB-157 breast cancer cell line, with the α9-nAChR subunit knocked out (KO), was established using the CRISPR/Cas9 technique. GeXIVA was able to significantly inhibit the proliferation and promote apoptosis of breast cancer MDA-MB-157 cells. Furthermore, the proliferation of breast cancer MDA-MB-157 cells was inhibited by GeXIVA, which caused cell cycle arrest through downregulating α9-nAChR. GeXIVA could suppress MDA-MB-157 cell migration as well. This demonstrates that GeXIVA induced a downregulation of α9-nAChR expression, and the growth of MDA-MB-157 α9-nAChR KO cell line was inhibited as well, due to α9-nAChR deletion. GeXIVA inhibits the growth of breast cancer cell MDA-MB-157 cells in vitro and may occur in a mechanism abolishing α9-nAChR.

Recombinant Analogue of the Human Protein SLURP-1 Inhibits the Growth of Multicellular Spheroids Reconstructed from Carcinoma Cells

In the present study we showed that the recombinant analogue of the SLURP-1 protein effectively inhibits the growth of a 3D model of tumors-multicellular spheroids reconstructed from human epidermoid carcinoma A431 cells and human lung adenocarcinoma A549 cells. The combined application of rSLURP-1 with gefitinib (inhibitor of epidermal growth factor receptor (EGFR)) leads to the synergistic antiproliferative effect on spheroids from A431 cells. The results obtained suggest the possibility for design of first-in-class anticancer drugs based on recombinant SLURP-1.

Human secreted protein SLURP-1 abolishes nicotine-induced proliferation, PTEN down-regulation and α7-nAChR expression up-regulation in lung cancer cells

Human Ly-6/uPAR-related protein-1 (SLURP-1) is an allosteric negative modulator of the α7-type nicotinic acetylcholine receptor (α7-nAChR), one of the key receptors promoting nicotine-induced proliferation of lung cancer cells. Incubation of lung adenocarcinoma A549 cells with recombinant SLURP-1 (rSLURP-1) at concentrations >10 nM resulted in the significant decrease of the cell growth (~70%), while treatment of normal lung-derived WI-38 fibroblasts with rSLURP-1 did not influence the cell proliferation up to 1 μM of the protein. rSLURP-1 fully abolished the nicotine-induced increase of the cell proliferation, down-regulation of the expression of PTEN (the negative regulator of the AKT pathway, controlling the growth, survival, and proliferation of cancer cells), and up-regulation of the α7-nAChR expression in the A549 cells. Using the siRNA against α7-nAChR and inhibitors of different cell-surface receptors, we showed that rSLURP-1 antiproliferative effect in A549 cells is connected with α7-nAChR, epidermal growth factor receptors, and β-adrenergic receptors. Moreover, we found that downstream effectors of rSLURP-1 are IP3 receptors and the STAT3 transcription factor. Implication of the IP3 receptors and PTEN in the rSLURP-1 antiproliferative activity points on the AKT-mediated signaling pathway. Co-application of rSLURP-1 with gefitinib and bortezomib (currently used anticancer drugs) resulted in an additive suppression of the A549 cells proliferation up to ~44% and 35%, respectively. Thus, rSLURP-1 could be considered a promising prototype of drugs to prevent nicotine-induced pathologies and cancer treatment.

Differential Expression of Nicotine Acetylcholine Receptors Associates with Human Breast Cancer and Mediates Antitumor Activity of αO-Conotoxin GeXIVA

Nicotinic acetylcholine receptors (nAChRs) are membrane receptors and play a major role in tumorigenesis and cancer progression. Here, we have investigated the differential expression of nAChR subunits in human breast cancer cell lines and breast epithelial cell lines at mRNA and protein levels and the effects of the αO-conotoxin GeXIVA, antagonist of α9α10 nAChR, on human breast cancer cells. Reverse transcription polymerase chain reaction (PCR) demonstrated that all nAChR subunits, except α6, were expressed in the 20 tested cell lines. Real time quantitative PCR (QRT-PCR) suggested that the mRNA of α5, α7, α9 and β4 nAChR subunits were overexpressed in all the breast cancer cell lines compared with the normal epithelial cell line HS578BST. α9 nAChR was highly expressed in almost all the breast cancer cell lines in comparison to normal cells. The different expression is prominent (p < 0.001) as determined by flow cytometry and Western blotting, except for MDA-MB-453 and HCC1395 cell lines. αO-conotoxin GeXIVA that targeted α9α10 nAChR were able to significantly inhibit breast cancer cell proliferation in vitro and merits further investigation as potential agents for targeted therapy.

Alpha7 nicotinic acetylcholine receptors in lung inflammation and carcinogenesis: Friends or foes?

The lung tissue expresses the cholinergic system including nicotinic acetylcholine receptors (nAChRs) which included in many physiologic and pathologic processes. Mounting evidence revealed that these receptors have important roles in lung carcinogenesis via modulating either stimulatory or inhibitory signaling pathways. Among different members of nicotinic receptors family, alpha7-subtype of nAChR (α7nAChR) is a critical mediator involved in both inflammatory responses and cancers. Several studies have shown that this receptor is the most powerful regulator of responses that stimulate lung cancer processes such as proliferation, angiogenesis, metastasis, and inhibition of apoptosis. Moreover, aside from its roles in the regulation of cancer pathways, there is growing evidence indicating that α7nAChR has profound impacts on lung inflammation through the cholinergic anti-inflammatory pathway. Regarding such diverse effects as well as the critical roles of nicotine as an activator of α7nAChR on lung cancer pathogenesis, its modulation has emerged as a promising target for drug developments. In this review, we aim to highlight the detrimental as well as the possible beneficial influences of α7nAChR downstream signaling cascades in the control of lung inflammation and cancer-associated properties. Consequently, by considering the significant global burden of lung cancer, delineating the complex influences of α7 receptors would be of great interest in designing novel anticancer and anti-inflammatory strategies for the patients suffering from lung cancer.

Water-soluble variant of human Lynx1 induces cell cycle arrest and apoptosis in lung cancer cells via modulation of α7 nicotinic acetylcholine receptors

Lynx1 is the first three-finger prototoxin found in the mammalian central nervous system. It is a GPI-anchored protein modulating nicotinic acetylcholine receptors (nAChRs) in the brain. Besides the brain, the Lynx1 protein was found in the lung and kidney. Endogenous Lynx1 controls the nicotine-induced up-regulation of the expression of α7 type nAChRs in lung adenocarcinoma A549 cells as well as the cell growth. Here, we analyzed the Lynx1 expression in the set of human epithelial cells. The Lynx1 expression both at the mRNA and protein level was detected in normal oral keratinocytes, and lung, colon, epidermal, and breast cancer cells, but not in embryonic kidney cells. Co-localization of Lynx1 with α7-nAChRs was revealed in a cell membrane for lung adenocarcinoma A549 and colon carcinoma HT-29 cells, but not for breast adenocarcinoma MCF-7 and epidermoid carcinoma A431 cells. The recombinant water-soluble variant of Lynx1 without a GPI-anchor (ws-Lynx1) inhibited the growth of A549 cells causing cell cycle arrest via modulation of α7-nAChRs and activation of different intracellular signaling cascades, including PKC/IP₃, MAP/ERK, p38, and JNK pathways. A549 cells treatment with ws-Lynx1 resulted in phosphorylation of the proapoptotic tumor suppressor protein p53 and different kinases participated in the regulation of gene transcription, cell growth, adhesion, and differentiation. Externalization of phosphatidylserine, an early apoptosis marker, observed by flow cytometry, confirmed the induction of apoptosis in A549 cells upon the ws-Lynx1 treatment. Our data revealed the ability of ws-Lynx1 to regulate homeostasis of epithelial cancer cells.

Lynx Prototoxins: Roles of Endogenous Mammalian Neurotoxin-Like Proteins in Modulating Nicotinic Acetylcholine Receptor Function to Influence Complex Biological Processes

The cholinergic system modulates many biological functions, due to the widespread distribution of cholinergic neuronal terminals, and the diffuse release of its neurotransmitter, acetylcholine. Several layers of regulation help to refine and control the scope of this excitatory neurotransmitter system. One such regulatory mechanism is imparted through endogenous toxin-like proteins, prototoxins, which largely control the function of nicotinic receptors of the cholinergic system. Prototoxins and neurotoxins share the distinct three finger toxin fold, highly effective as a receptor binding protein, and the former are expressed in the mammalian brain, immune system, epithelium, etc. Prototoxins and elapid snake neurotoxins appear to be related through gene duplication and divergence from a common ancestral gene. Protein modulators can provide a graded response of the cholinergic system, and within the brain, stabilize neural circuitry through direct interaction with nicotinic receptors. Understanding the roles of each prototoxin (e.g., lynx1, lynx2/lypd1, PSCA, SLURP1, SLURP2, Lypd6, lypd6b, lypdg6e, PATE-M, PATE-B, etc.), their binding specificity and unique expression profile, has the potential to uncover many fascinating cholinergic-dependent mechanisms in the brain. Each family member can provide a spatially restricted level of control over nAChR function based on its expression in the brain. Due to the difficulty in the pharmacological targeting of nicotinic receptors in the brain as a result of widespread expression patterns and similarities in receptor sequences, unique interfaces between prototoxin and nicotinic receptor could provide more specific targeting than nicotinic receptors alone. As such, this family is intriguing from a long-term therapeutic perspective.

Acetylcholine signaling system in progression of lung cancers

The neurotransmitter acetylcholine (ACh) acts as an autocrine growth factor for human lung cancer. Several lines of evidence show that lung cancer cells express all of the proteins required for the uptake of choline (choline transporter 1, choline transporter-like proteins) synthesis of ACh (choline acetyltransferase, carnitine acetyltransferase), transport of ACh (vesicular acetylcholine transport, OCTs, OCTNs) and degradation of ACh (acetylcholinesterase, butyrylcholinesterase). The released ACh binds back to nicotinic (nAChRs) and muscarinic receptors on lung cancer cells to accelerate their proliferation, migration and invasion. Out of all components of the cholinergic pathway, the nAChR-signaling has been studied the most intensely. The reason for this trend is due to genome-wide data studies showing that nicotinic receptor subtypes are involved in lung cancer risk, the relationship between cigarette smoke and lung cancer risk as well as the rising popularity of electronic cigarettes considered by many as a "safe" alternative to smoking. There are a small number of articles which review the contribution of the other cholinergic proteins in the pathophysiology of lung cancer. The primary objective of this review article is to discuss the function of the acetylcholine-signaling proteins in the progression of lung cancer. The investigation of the role of cholinergic network in lung cancer will pave the way to novel molecular targets and drugs in this lethal malignancy.

Nicotinic acetylcholine receptors

This themed section of the British Journal of Pharmacology is the product of a conference that focussed on nicotinic ACh receptors (nAChRs) that was held on the Greek island of Crete from 7 to 11 May 2017. 'Nicotinic acetylcholine receptors 2017' was the fourth in a series of triennial international meetings that have provided a regular forum for scientists working on all aspects of nAChRs to meet and to discuss new developments. In addition to many of the regular participants, each meeting has also attracted a new group of scientists working in a fast-moving area of research. This themed section comprises both review articles and original research papers on nAChRs.

LINKED ARTICLES

This article is part of a themed section on Nicotinic Acetylcholine Receptors. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.11/issuetoc/.

Human secreted proteins SLURP-1 and SLURP-2 control the growth of epithelial cancer cells via interactions with nicotinic acetylcholine receptors

BACKGROUND AND PURPOSE

Nicotinic acetylcholine receptors (nAChRs) are a promising target for development of new anticancer therapies. Here we have investigated the effects of the endogenous human proteins SLURP-1 and SLURP-2, antagonists of nAChRs, on human epithelial cancer cells.

EXPERIMENTAL APPROACH

Growth of epithelial cancer cells (A431, SKBR3, MCF-7, A549, HT-29) exposed to SLURP-1, SLURP-2, mecamylamine, atropine, timolol and gefitinib was measured by the WST-1 test. Expression levels of SLURP-1, α7-nAChR and EGF receptors and their distribution in cancer cells were studied by confocal microscopy and flow cytometry. Secretion of endogenous SLURP-1 by A431 cells under treatment with recombinant SLURP-1 was analysed by Western-blotting.

KEY RESULTS

SLURP-1 and SLURP-2 significantly inhibited growth of A431, SKBR3, MCF-7 and HT-29 cells at concentrations above 1 nM, to 40-70% of the control, in 24 h. Proliferation of A549 cells was inhibited only by SLURP-1. The anti-proliferative activity of SLURPs on A431 cells was associated with nAChRs, but not with β-adrenoceptors or EGF receptors. Action of gefitinib and SLURPs was additive and resulted almost complete inhibition of A431 cell proliferation during 24 h. Exposure of A431 cells to recombinant SLURP-1 down-regulated α7-nAChR expression and induced secretion of endogenous SLURP-1 from intracellular depots, increasing its concentration in the extracellular media.

CONCLUSIONS AND IMPLICATIONS

SLURPs inhibit growth of epithelial cancer cells in vitro and merit further investigation as potential agents for anticancer therapy.

LINKED ARTICLES

This article is part of a themed section on Nicotinic Acetylcholine Receptors. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.11/issuetoc.