Altered calcium-mediated cell signaling in keratinocytes cultured from patients with neurofibromatosis type 1

snRNA-seq of human cutaneous neurofibromas before and after selumetinib treatment implicates role of altered Schwann cell states, inter-cellular signaling, and extracellular matrix in treatment response

Neurofibromatosis Type 1 (NF1) is caused by loss of function variants in the NF1 gene. Most patients with NF1 develop skin lesions called cutaneous neurofibromas (cNFs). Currently the only approved therapeutic for NF1 is selumetinib, a mitogen -activated protein kinase (MEK) inhibitor. The purpose of this study was to analyze the transcriptome of cNF tumors before and on selumetinib treatment to understand both tumor composition and response. We obtained biopsy sets of tumors both pre- and on- selumetinib treatment from the same individuals and were able to collect sets from four separate individuals. We sequenced mRNA from 5844 nuclei and identified 30,442 genes in the untreated group and sequenced 5701 nuclei and identified 30,127 genes in the selumetinib treated group. We identified and quantified distinct populations of cells (Schwann cells, fibroblasts, pericytes, myeloid cells, melanocytes, keratinocytes, and two populations of endothelial cells). While we anticipated that cell proportions might change with treatment, we did not identify any one cell population that changed significantly, likely due to an inherent level of variability between tumors. We also evaluated differential gene expression based on drug treatment in each cell type. Ingenuity pathway analysis (IPA) was also used to identify pathways that differ on treatment. As anticipated, we identified a significant decrease in ERK/MAPK signaling in cells including Schwann cells but most specifically in myeloid cells. Interestingly, there is a significant decrease in opioid signaling in myeloid and endothelial cells; this downward trend is also observed in Schwann cells and fibroblasts. Cell communication was assessed by RNA velocity, Scriabin, and CellChat analyses which indicated that Schwann cells and fibroblasts have dramatically altered cell states defined by specific gene expression signatures following treatment (RNA velocity). There are dramatic changes in receptor-ligand pairs following treatment (Scriabin), and robust intercellular signaling between virtually all cell types associated with extracellular matrix (ECM) pathways (Collagen, Laminin, Fibronectin, and Nectin) is downregulated after treatment. These response specific gene signatures and interaction pathways could provide clues for understanding treatment outcomes or inform future therapies.

The Role of the Gap Junction Protein Connexin in Adrenal Gland Tumorigenesis

Gap junctions (GJs) are important in the regulation of cell growth, morphology, differentiation and migration. However, recently, more attention has been paid to their role in the pathogenesis of different diseases as well as tumorigenesis, invasion and metastases. The expression pattern and possible role of connexins (Cxs), as major GJ proteins, under both physiological and pathological conditions in the adrenal gland, were evaluated in this review. The databases Web of Science, PubMed and Scopus were searched. Studies were evaluated if they provided data regarding the connexin expression pattern in the adrenal gland, despite current knowledge of this topic not being widely investigated. Connexin expression in the adrenal gland differs according to different parts of the gland and depends on ACTH release. Cx43 is the most studied connexin expressed in the adrenal gland cortex. In addition, Cx26, Cx32 and Cx50 were also investigated in the human adrenal gland. Cx50 as the most widespread connexin, along with Cx26, Cx29, Cx32, Cx36 and Cx43, has been expressed in the adrenal medulla with distinct cellular distribution. Considerable effort has recently been directed toward connexins as therapeutically targeted molecules. At present, there exist several viable strategies in the development of potential connexin-based therapeutics. The differential and hormone-dependent distribution of gap junctions within adrenal glands, the relatively large gap junction within this gland and the increase in the gap junction size and number following hormonal treatment would indicate that gap junctions play a pivotal role in cell functioning in the adrenal gland.

Synthetic dysmobility screen unveils an integrated STK40-YAP-MAPK system driving cell migration

Integrating signals is essential for cell survival, leading to the concept of synthetic lethality. However, how signaling is integrated to control cell migration remains unclear. By conducting a "two-hit" screen, we revealed the synergistic reduction of cell migration when serine-threonine kinase 40 (STK40) and mitogen-activated protein kinase (MAPK) were simultaneously suppressed. Single-cell analyses showed that STK40 knockdown reduced cell motility and coordination by strengthening focal adhesion (FA) complexes. Furthermore, STK40 knockdown reduced the stability of yes-associated protein (YAP) and subsequently decreased YAP transported into the nucleus, while MAPK inhibition further weakened YAP activities in the nucleus to disturb FA remodeling. Together, we unveiled an integrated STK40-YAP-MAPK system regulating cell migration and introduced "synthetic dysmobility" as a novel strategy to collaboratively control cell migration.

Recent Advances in the Diagnosis and Pathogenesis of Neurofibromatosis Type 1 (NF1)-associated Peripheral Nervous System Neoplasms

The diagnosis of a neurofibroma or a malignant peripheral nerve sheath tumor (MPNST) often raises the question of whether the patient has the genetic disorder neurofibromatosis type 1 (NF1) as well as how this will impact the patient's outcome, what their risk is for developing additional neoplasms and whether treatment options differ for NF1-associated and sporadic peripheral nerve sheath tumors. Establishing a diagnosis of NF1 is challenging as this disorder has numerous neoplastic and non-neoplastic manifestations which are variably present in individual patients. Further, other genetic diseases affecting the Ras signaling cascade (RASopathies) mimic many of the clinical features of NF1. Here, we review the clinical manifestations of NF1 and compare and contrast them with those of the RASopathies. We also consider current approaches to genetic testing for germline NF1 mutations. We then focus on NF1-associated neurofibromas, considering first the complicated clinical behavior and pathology of these neoplasms and then discussing our current understanding of the genomic abnormalities that drive their pathogenesis, including the mutations encountered in atypical neurofibromas. As several neurofibroma subtypes are capable of undergoing malignant transformation to become MPNSTs, we compare and contrast patient outcomes in sporadic, NF1-associated and radiation-induced MPNSTs, and review the challenging pathology of these lesions. The mutations involved in neurofibroma-MPNST progression, including the recent identification of mutations affecting epigenetic regulators, are then considered. Finally, we explore how our current understanding of neurofibroma and MPNST pathogenesis is informing the design of new therapies for these neoplasms.

Sensitization of Ion Channels Contributes to Central and Peripheral Dysfunction in Neurofibromatosis Type 1

Neurofibromatosis type 1 (Nf1) is a progressive, autosomal disorder with a large degree of variability and severity of manifestations including neurological, cutaneous, ocular/orbital, orthopedic, and vascular abnormalities. Nearly half of Nf1 patients presents with cognitive impairment, specifically spatial learning deficits. These clinical manifestations suggest a global impairment of both central and peripheral nervous system functions in neurofibromatosis. Nf1 encodes for neurofibromin, a Ras GTPase-activating protein (Ras GAP) that has been implicated in the regulation of long-term potentiation (LTP), Ras/ERK (extracellular signal-regulated kinase) signaling, and learning in mice. Over the last decades, mice with a targeted mutation in the Nf1 gene, Nf1 ^-/- chimeric mice, Nf1 exon-specific knockout mice, and mice with tissue-specific inactivation of Nf1 have been generated to model the human Nf1 disease. These studies have implicated neurofibromin in regulation of the release of the inhibitory neurotransmitter γ-amino butyric acid (GABA) in the hippocampus and frontal lobe, which can regulate memory. Mutations in neurofibromin thus lead to perturbed ERK signaling, which alters GABA release, LTP, and subsequently leads to learning deficits. In addition to these cognitive deficits, Nf1 patients also have defects in fine and gross motor coordination as well as decreased muscle strength. Although the mechanisms underlying these motor deficits are unknown, deficits in GABAergic neurotransmission in both the motor cortex and cerebellum have been suggested. In this review, we present evidence to support the hypothesis that alterations of ion channel activity in Nf1 underscore the dysregulated neuronal communication in non-neuronal and neuronal cells that likely contributes to the clinical cornucopia of Nf1.

The Challenge of Cancer Genomics in Rare Nervous System Neoplasms: Malignant Peripheral Nerve Sheath Tumors as a Paradigm for Cross-Species Comparative Oncogenomics

Comprehensive genomic analyses of common nervous system cancers provide new insights into their pathogenesis, diagnosis, and treatment. Although analogous studies of rare nervous system tumors are needed, there are major barriers to performing such studies. Cross-species comparative oncogenomics, identifying driver mutations in mouse cancer models and validating them in human tumors, is a promising alternative. Although still in its infancy, this approach is being applied to malignant peripheral nerve sheath tumors (MPNSTs), rare Schwann cell-derived malignancies that occur sporadically, after radiotherapy, and in neurofibromatosis type 1. Studies of human neurofibromatosis type 1-associated tumors suggest that NF1 tumor suppressor loss in Schwann cells triggers cell-autonomous and intercellular changes, resulting in development of benign neurofibromas; subsequent neurofibroma-MPNST progression is caused by aberrant growth factor signaling and mutations affecting the p16(INK4A)-cyclin D1-CDK4-Rb and p19(ARF)-Mdm2-p53 cell cycle pathways. Mice with Nf1, Trp53, and/or Cdkn2a mutations that overexpress the Schwann cell mitogen neuregulin-1 or overexpress the epidermal growth factor receptor validate observations in human tumors and, to various degrees, model human tumorigenesis. Genomic analyses of MPNSTs arising in neuregulin-1 and epidermal growth factor receptor-overexpressing mice and forward genetic screens with Sleeping Beauty transposons implicate additional signaling cascades in MPNST pathogenesis. These studies confirm the utility of mouse models for MPNST driver gene discovery and provide new insights into the complexity of MPNST pathogenesis.

Partial Blindness to Submicron Topography in NF1 Haploinsufficient Cultured Fibroblasts Indicates a New Function of Neurofibromin in Regulation of Mechanosensoric

Cells sense physical properties of their extracellular environment and translate them into biochemical signals. In this study, cell responses to surfaces with submicron topographies were investigated in cultured human NF1 haploinsufficient fibroblasts. Age-matched fibroblasts from 8 patients with neurofibromatosis type 1 (NF1(+/-)) and 9 controls (NF1(+/+)) were cultured on surfaces with grooves of 200 nm height and lateral distance of 2 μm. As cellular response indicator, the mean cell orientation along microstructured grooves was systematically examined. The tested NF1 haploinsufficient fibroblasts were significantly less affected by the topography than those from healthy donors. Incubation of the NF1(+/-) fibroblasts with the farnesyltransferase inhibitor FTI-277 and other inhibitors of the neurofibromin pathway ameliorates significantly the cell orientation. These data indicate that NF1 haploinsufficiency results in an altered response to specific surface topography in fibroblasts. We suggest a new function of neurofibromin in the sensoric mechanism to topographies and a partial mechanosensoric blindness by NF1 haploinsufficiency.

Store-operated Ca2+ entry is remodelled and controls in vitro angiogenesis in endothelial progenitor cells isolated from tumoral patients

BACKGROUND

Endothelial progenitor cells (EPCs) may be recruited from bone marrow to sustain tumor vascularisation and promote the metastatic switch. Understanding the molecular mechanisms driving EPC proliferation and tubulogenesis could outline novel targets for alternative anti-angiogenic treatments. Store-operated Ca(2+) entry (SOCE), which is activated by a depletion of the intracellular Ca(2+) pool, regulates the growth of human EPCs, where is mediated by the interaction between the endoplasmic reticulum Ca(2+)-sensor, Stim1, and the plasmalemmal Ca(2+) channel, Orai1. As oncogenesis may be associated to the capability of tumor cells to grow independently on Ca(2+) influx, it is important to assess whether SOCE regulates EPC-dependent angiogenesis also in tumor patients.

METHODOLOGY/PRINCIPAL FINDINGS

The present study employed Ca(2+) imaging, recombinant sub-membranal and mitochondrial aequorin, real-time polymerase chain reaction, gene silencing techniques and western blot analysis to investigate the expression and the role of SOCE in EPCs isolated from peripheral blood of patients affected by renal cellular carcinoma (RCC; RCC-EPCs) as compared to control EPCs (N-EPCs). SOCE, activated by either pharmacological (i.e. cyclopiazonic acid) or physiological (i.e. ATP) stimulation, was significantly higher in RCC-EPCs and was selectively sensitive to BTP-2, and to the trivalent cations, La(3+) and Gd(3+). Furthermore, 2-APB enhanced thapsigargin-evoked SOCE at low concentrations, whereas higher doses caused SOCE inhibition. Conversely, the anti-angiogenic drug, carboxyamidotriazole (CAI), blocked both SOCE and the intracellular Ca(2+) release. SOCE was associated to the over-expression of Orai1, Stim1, and transient receptor potential channel 1 (TRPC1) at both mRNA and protein level The intracellular Ca(2+) buffer, BAPTA, BTP-2, and CAI inhibited RCC-EPC proliferation and tubulogenesis. The genetic suppression of Stim1, Orai1, and TRPC1 blocked CPA-evoked SOCE in RCC-EPCs.

CONCLUSIONS

SOCE is remodelled in EPCs from RCC patients and stands out as a novel molecular target to interfere with RCC vascularisation due to its ability to control proliferation and tubulogenesis.

Molecular mechanisms promoting the pathogenesis of Schwann cell neoplasms

Neurofibromas, schwannomas and malignant peripheral nerve sheath tumors (MPNSTs) all arise from the Schwann cell lineage. Despite their common origin, these tumor types have distinct pathologies and clinical behaviors; a growing body of evidence indicates that they also arise via distinct pathogenic mechanisms. Identification of the genes that are mutated in genetic diseases characterized by the development of either neurofibromas and MPNSTs [neurofibromatosis type 1 (NF1)] or schwannomas [neurofibromatosis type 2 (NF2), schwannomatosis and Carney complex type 1] has greatly advanced our understanding of these mechanisms. The development of genetically engineered mice with ablation of NF1, NF2, SMARCB1/INI1 or PRKAR1A has confirmed the key role these genes play in peripheral nerve sheath tumorigenesis. Establishing the functions of the NF1, NF2, SMARCB1/INI1 and PRKAR1A gene products has led to the identification of key cytoplasmic signaling pathways promoting Schwann cell neoplasia and identified new therapeutic targets. Analyses of human neoplasms and genetically engineered mouse models have established that interactions with other tumor suppressors such as TP53 and CDKN2A promote neurofibroma-MPNST progression and indicate that intratumoral interactions between neoplastic and non-neoplastic cell types play an essential role in peripheral nerve sheath tumorigenesis. Recent advances have also provided new insights into the identity of the neural crest-derived populations that give rise to different types of peripheral nerve sheath tumors. Based on these findings, we now have an initial outline of the molecular mechanisms driving the pathogenesis of neurofibromas, MPNSTs and schwannomas. However, this improved understanding in turn raises a host of intriguing new questions.

ORAI1 genetic polymorphisms associated with the susceptibility of atopic dermatitis in Japanese and Taiwanese populations

Atopic dermatitis is a chronic inflammatory skin disease. Multiple genetic and environmental factors are thought to be responsible for susceptibility to AD. In this study, we collected 2,478 DNA samples including 209 AD patients and 729 control subjects from Taiwanese population and 513 AD patients and 1027 control subject from Japanese population for sequencing and genotyping ORAI1. A total of 14 genetic variants including 3 novel single-nucleotide polymorphisms (SNPs) in the ORAI1 gene were identified. Our results indicated that a non-synonymous SNP (rs3741596, Ser218Gly) associated with the susceptibility of AD in the Japanese population but not in the Taiwanese population. However, there is another SNP of ORAI1 (rs3741595) associated with the risk of AD in the Taiwanese population but not in the Japanese population. Taken together, our results indicated that genetic polymorphisms of ORAI1 are very likely to be involved in the susceptibility of AD.

Image analysis of Ca2+ signals as a basis for neurotoxicity assays: promises and challenges

Free intracellular calcium ([Ca(2+)](i)) controls a wide range of cellular functions such as contraction, neurotransmitter and hormone release, metabolism, cell division and differentiation. Cytosolic Ca(2+) levels are abnormal in cells exposed to toxicants and understanding how these levels become altered may improve our ability to design high-throughput methods for the sensitive detection of cellular responses to a toxic exposure. Because Ca(2+) is involved in multiple aspects of cellular function, its role in signaling is complex. It is therefore necessary to identify the individual pathways targeted during toxicant exposure in order to use them as a tool for predictive measurements of toxicity and as targets for prevention or reversal of injury. This review illustrates several methods available for analysis of Ca(2+) responses in vitro and their applicability for understanding mechanisms of toxicity at the molecular and cellular levels. The review will also consider the usefulness of Ca(2+) imaging for predicting a unique signature for classes of toxicants. Towards this end, two methodological approaches for assessment of Ca(2+) responses to toxicants are examined: steady state measurements and complex spatial and/or temporal measurements. Each of the methods described and appropriately used results in reliable and reproducible measurements which may be applied in a high-throughput fashion to individualize in vitro assessment of cellular responses caused by toxicants.

Recent advances in Ca2+-dependent Ras regulation and cell proliferation

Our understanding of the mechanisms whereby growth factors stimulate cell proliferation through the Ras pathway stems largely from studies of the canonical pathway involving recruitment of Ras activators and inhibitors to the vicinity of receptor tyrosine kinases via phosphotyrosine-binding adaptor proteins. Ca(2+) has seldom joined the party, despite the identification of phospholipase Cgamma and Ca(2+) entry as receptor tyrosine kinase-dependent signals. Mechanisms by which Ca(2+) can directly influence Ras activity have remained relatively elusive. Similarly, the mechanisms whereby Ca(2+) modulates the cell cycle have been equally murky, and yet there are some interesting parallels in the role of Ras and Ca(2+) in cell cycle re-entry. This review focuses on a number of novel mechanisms that link Ca(2+) with the regulation of Ras activity and signaling output. Their collective discovery adds to the complexities of Ras regulation and raises further questions about the role of Ca(2+) signals in Ras-dependent cell proliferation.

Keratinocytes cultured from patients with Hailey-Hailey disease and Darier disease display distinct patterns of calcium regulation

BACKGROUND

Hailey-Hailey disease (HHD) (OMIM 16960) and Darier disease (DD) (OMIM 124200) are dominantly inherited acantholytic skin diseases, respectively, caused by mutations in the genes encoding the Golgi secretory pathway Ca2+-ATPase (SPCA1, ATP2C1) and the sarco/endoplasmic reticulum Ca2+-ATPase type 2 (SERCA2, ATP2A2) genes.

OBJECTIVES

To investigate calcium regulation in keratinocytes cultured from patients with HHD and DD by measuring intracellular calcium resting levels and the cellular responses to ATP and thapsigargin.

METHODS

The study was carried out using keratinocyte cultures established from four patients with HHD and four with DD. Calcium concentrations were measured with fluorescence ratio imaging using fura-2 loading.

RESULTS

Control and HHD keratinocytes displayed approximately the same Ca2+ levels in resting phase, while DD keratinocytes showed elevated Ca2+ levels. Application of ATP caused less pronounced elevation of intracellular calcium concentration ([Ca2+]i) in both HHD and DD keratinocytes than in control cells. HHD keratinocytes did not lower their [Ca2+]i as efficiently as control keratinocytes after treatment with thapsigargin. In addition, DD keratinocytes were practically incapable of lowering their [Ca2+]i after treatment with thapsigargin.

CONCLUSIONS

The results demonstrate that the defects in SPCA1 and SERCA2 calcium ATPases result in distinct patterns of calcium metabolism. This is also supported by the different clinical features of the diseases.

The effect of extracellular calcium concentration on calcium-mediated cell signaling in NF1 tumor suppressor-deficient keratinocytes

Capacitative calcium entry and calcium wave propagation were studied in keratinocytes from healthy volunteers and patients with type 1 neurofibromatosis (NF1) in calcium-depleted and in low calcium culture medium. In previous studies, we found evidence that mutations of the NF1 tumor suppressor gene can lead to altered calcium-mediated cell signaling in keratinocytes cultured in the presence of a high extracellular calcium concentration. The present study demonstrated that the differences between normal and NF1 keratinocytes were dependent on extracellular calcium concentration. Specifically, when keratinocytes were exposed to thapsigargin under calcium-depleted culture conditions the subsequent increase in free intracellular calcium concentration was moderate in NF1 keratinocytes compared to controls. The finding indicates lowered endoplasmic calcium stores in NF1 which may also in part explain the reduced activation signal for capacitative calcium influx and the wound-induced intracellular Ca2+ transient observed in NF1 keratinocytes maintained in culture medium containing 0.05 mM calcium. The differences between control and NF1 keratinocytes were most pronounced when the cells were cultured in the presence of a high (1.8 mM) calcium concentration. Since elevated extracellular calcium levels induce keratinocytes to form cellular contacts and lead to terminal differentiation, markedly aberrant responses of NF1 keratinocytes in the presence of a high calcium concentration may help to explain previous findings on impaired formation of cellular junctions and differentiation in NF1 deficient cells.

Local dissipation and coupling properties of cellular oscillators: a case study on calcium oscillations

Synchronised signal transduction between cells is crucial, since it assures fast and immutable information processing, which is vital for flawless functioning of living organisms. The question arises how to recognise the ability of a cell to be easily coupled with other cells. In the present paper, we investigate the system properties that determine best coupling abilities and assure the most efficient signal transduction between cells. A case study is done for intercellular calcium oscillations. For a particular diffusion-like coupled system of cellular oscillators, we determined the minimal gap-junctional permeability that is necessary for synchronisation of initially asynchronous oscillators. Our results show that dissipation is a crucial system property that determines the coupling ability of cellular oscillators. We found that low dissipation assures synchronisation of coupled cells already at very low gap-junctional permeability, whereas highly dissipative oscillators require much higher gap-junctional permeability in order to synchronise. The results are discussed in the sense of their biological importance for systems where the synchronous responses of cells were recognised to be indispensable for appropriate physiological functioning of the tissue.

Neurofibromatosis type 1 tumour suppressor gene expression is deficient in psoriatic skin in vivo and in vitro: a potential link to increased Ras activity

BACKGROUND

Neurofibromatosis type 1 (NF1) protein (neurofibromin) accelerates the inactivation of Ras-GTP in various cell types. Somatic mutations of the NF1 gene may lead to malignant transformation and uncontrolled proliferation. We have previously shown that NF1 protein expression is downregulated in psoriasis in vivo.

OBJECTIVES

To study the functional expression and distribution of NF1 mRNA and protein in vivo and in psoriatic and normal keratinocyte cultures.

METHODS

Immunohistochemistry and in situ hybridization were used to study NF1 gene and protein expression in psoriasis in vivo. Furthermore, Northern and in situ hybridizations, immunoblot and localization analyses were utilized to study NF1 mRNA and protein in vitro in keratinocyte cultures.

RESULTS

NF1 tumour suppressor gene expression was reduced in lesional psoriatic skin compared with perilesional and normal skin in vivo. The in vitro results showed that the levels of NF1 mRNA and protein were reduced in cultured psoriatic keratinocytes during cellular differentiation even after multiple passaging of the cells. Moreover, cultured nonlesional psoriatic keratinocytes were almost equally defective as lesional cells with respect to NF1 expression.

CONCLUSIONS

Our findings demonstrate that psoriatic keratinocytes maintain an altered phenotype and gene expression profile even when isolated from interaction with lymphocytes and fibroblasts, which are known to increase proliferation of keratinocytes. As NF1 protein is regarded as a Ras proto-oncogene regulator, the aberrant expression and distribution of NF1 protein and mRNA found in the present study may be causative to the previously described increased activation of Ras in psoriatic lesions, and relate to altered cellular behaviour.