Semaphorin 7a promotes spreading and dendricity in human melanocytes through beta1-integrins

SEMA7A as a Novel Prognostic Biomarker and Its Correlation with Immune Infiltrates in Breast Cancer

Background

The role of Semaphorin 7a (SEMA7A) in the initiation and progression of different types of cancerous lesions has been extensively studied. However, the prognostic significance of SEMA7A, specifically in breast cancer (BC), lacks clarity.

Methods

We conducted an evaluation on the relationship between SEMA7A and the prognosis, immune invasion and tumor mutation burden in different types of cancer by analyzing data from The Cancer Genome Atlas database. The present study focused on investigating the expression level, mutation, immune correlation and coexpression of SEMA7A in BC, utilizing various databases such as the University of Alabama at Birmingham Cancer data analysis portal, cBioPortal and tumor immune estimation resource. Survival analysis was carried out using the Kaplan-Meier Plotter. Furthermore, we employed the R software package to generate receiver operating characteristic (ROC) curves and nomograms. Notably, P<0.05 was considered to indicate statistical significance.

Results

Using pancancer analysis, it has been observed that the expression of SEMA7A is elevated in various types of cancer and is strongly correlated with the prognosis of different cancer types. SEMA7A also exhibits a significant association with the tumor mutation burden of diverse types of cancer. Moreover, SEMA7A displays a notable increase in BC cases, and was indicated to have a substantial association with the abundance of immune infiltration. In-depth survival analysis demonstrated that elevated levels of SEMA7A expression are notably linked to shorter overall survival and distant metastasis-free survival among patients with BC. The efficiency of SEMA7A as a reliable prognostic biomarker for BC has been substantiated by the validation of ROC curves and nomograms.

Conclusion

SEMA7A has the potential to function as a prognostic indicator for BC, and its correlation with immune infiltration in BC is significant.

miR-25-5p in exosomes derived from UVB-induced fibroblasts regulates melanogenesis via TSC2-dominated cellular organelle dysfunction

BACKGROUND

Few reports have confirmed whether exosomes derived from fibroblasts can regulate the process of melanogenesis. We wondered whether exosomes derived from fibroblasts could have a potent regulatory effect on melanogenesis and explored the underlying mechanisms.

OBJECTIVE

This study aimed to find the role of fibroblasts in melanocytes and revealed the related mechanisms.

METHODS

RT-qPCR, Western blot analysis were conducted to measure the RNA and protein expression level of various related genes. miRNA sequencing, mass spectrum analysis and subsequent bioinformatics analysis were employed to find the underlying targets. Zebrafish were employed to measure the melanin synthesis related process in vivo. Furthermore, electron microscopy, ROS measurement and dual-luciferase reporter assay were adopted to investigate the relationship between these processes.

RESULTS

We found that exosomes derived from human primary dermal fibroblasts were internalized by human primary melanocytes and MNT1 cells and that the melanin content and the expression of melanin synthesis-related proteins TYR and MITF was inhibited by exosomes derived from UVB-induced human primary dermal fibroblasts. The miRNA expression profile in secreted exosomes changed significantly, with miR-25-5p identified as capable of regulating TSC2 expression via the CDS region. The miR-25-5p-TSC2 axis could affect the melanin content through subsequent cellular organelle dysfunction, such as mitochondrial dysfunction, endoplasmic reticulum stress and dysregulation of lysosomal cysteine proteases.

CONCLUSION

We unveiled a novel regulatory role of fibroblasts in melanocytes, facilitated by the secretion of exosomes. miR-25-5p within exosomes plays a pivotal role in regulating melanogenesis via TSC2-induced cellular organelle dysfunction.

col1a2+ fibroblasts/muscle progenitors finetune xanthophore countershading by differentially expressing csf1a/1b in embryonic zebrafish

Animals evolve diverse pigment patterns to adapt to the natural environment. Countershading, characterized by a dark-colored dorsum and a light-colored ventrum, is one of the most prevalent pigment patterns observed in vertebrates. In this study, we reveal a mechanism regulating xanthophore countershading in zebrafish embryos. We found that csf1a and csf1b mutants altered xanthophore countershading differently: csf1a mutants lack ventral xanthophores, while csf1b mutants have reduced dorsal xanthophores. Further study revealed that csf1a is expressed throughout the trunk, whereas csf1b is expressed dorsally. Ectopic expression of csf1a or csf1b in neurons attracted xanthophores into the spinal cord. Blocking csf1 signaling by csf1ra mutants disrupts spinal cord distribution and normal xanthophores countershading. Single-cell RNA sequencing identified two col1a2+ populations: csf1ahighcsf1bhigh muscle progenitors and csf1ahighcsf1blow fibroblast progenitors. Ablation of col1a2+ fibroblast and muscle progenitors abolished xanthophore patterns. Our study suggests that fibroblast and muscle progenitors differentially express csf1a and csf1b to modulate xanthophore patterning, providing insights into the mechanism of countershading.

The Involvement of Semaphorins in the Pathogenesis of Skin Diseases

Semaphorins belong to a group of membrane and secretory proteins that act as ligands for several receptor families and are involved in modulating cell signaling pathways. They bind multimeric receptor complexes on the cell membrane to exert their effects and initiate unique intracellular signal transduction cascades. These proteins can influence several processes that are very important for cell function, such as cell division and differentiation. Semaphorins are involved in cell migration, apoptosis, cell adhesion, aggregation, and numerous immune processes due to their immunoregulatory effects. Semaphorins are expressed in keratinocytes, which is why they have become a target for studies on the pathogenesis of skin diseases. Most studies to date on the role of semaphorins in the pathogenesis of skin diseases have been carried out in cellular or animal models, and there are few clinical studies evaluating the role of semaphorins in the pathogenesis and therapy of skin diseases. In this narrative review, we summarized the current state of knowledge on the role of semaphorins in the pathogenesis of skin diseases and their potential importance as targets for therapy. We also tried to present the key findings and weaknesses of previous research in this field. The novelty of this article lies in the comprehensive presentation of the role of semaphorins in the pathogenesis of skin diseases, including the results of studies on cell cultures and animal models, elucidating the mechanisms and signaling pathways through which semaphorins affect the development of skin diseases, as well as on the presentation of the results of existing clinical trials evaluating the role of semaphorins in the pathogenesis of skin diseases, and as potential therapeutic targets.

SEMA7a primes integrin α5β1 engagement instructing fibroblast mechanotransduction, phenotype and transcriptional programming

Integrins are cellular receptors that bind the extracellular matrix (ECM) and facilitate the transduction of biochemical and biophysical microenvironment cues into cellular responses. Upon engaging the ECM, integrin heterodimers must rapidly strengthen their binding with the ECM, resulting in the assembly of force-resistant and force-sensitive integrin associated complexes (IACs). The IACs constitute an essential apparatus for downstream signaling and fibroblast phenotypes. During wound healing, integrin signaling is essential for fibroblast motility, proliferation, ECM reorganization and, ultimately, restoration of tissue homeostasis. Semaphorin 7A (SEMA7a) has been previously implicated in post-injury inflammation and tissue fibrosis, yet little is known about SEMA7a's role in directing stromal cell, particularly fibroblast, behaviors. We demonstrate that SEMA7a regulates integrin signaling through cis-coupling with active integrin α5β1 on the plasma membrane, enabling rapid integrin adhesion strengthening to fibronectin (Fn) and normal downstream mechanotransduction. This molecular function of SEMA7a potently regulates fibroblast adhesive, cytoskeletal, and migratory phenotype with strong evidence of downstream alterations in chromatin structure resulting in global transcriptomic reprogramming such that loss of SEMA7a expression is sufficient to impair the normal migratory and ECM assembly phenotype of fibroblasts resulting in significantly delayed tissue repair in vivo.

Two novel CreERT2 transgenic mouse lines to study melanocytic cells in vivo

The skin of adult mammals protects from radiation, physical and chemical insults. While melanocytes and melanocyte-producing stem cells contribute to proper skin function in healthy organisms, dysfunction of these cells can lead to the generation of malignant melanoma - the deadliest type of skin cancer. Addressing cells of the melanocyte lineage in vivo represents a prerequisite for the understanding of melanoma on cellular level and the development of preventive and treatment strategies. Here, the inducible Cre-loxP-system has emerged as a promising tool to specifically target, monitor and modulate cells in adult mice. Re-analysis of existing sequencing data sets of melanocytic cells revealed that genes with a known function in neural cells, including neural stem cells (Aldh1L1 and Nestin), are also expressed in melanocytic cells. Therefore, in this study we explored whether the promoter activity of Nestin and Aldh1L1 can serve to target cells of the melanocyte lineage using the inducible CreER^T2 -loxP-system. Using an immunohistochemical approach and different time-points of analysis, we were able to map the melanocytic fate of recombined stem cells in the adult hair follicle of Nestin-CreER^T2 and Aldh1L1-CreER^T2 transgenic mice. Thus, we here present two new mouse models and propose their use to study and putatively modulate adult melanocytic cells in vivo.

Thy-1-Integrin Interactions in cis and Trans Mediate Distinctive Signaling

Thy-1 is a cell surface glycosylphosphatidylinositol (GPI)-anchored glycoprotein that bears a broad mosaic of biological roles across various cell types. Thy-1 displays strong physiological and pathological implications in development, cancer, immunity, and tissue fibrosis. Quite uniquely, Thy-1 is capable of mediating integrin-related signaling through direct trans- and cis-interaction with integrins. Both interaction types have shown distinctive roles, even when interacting with the same type of integrin, where binding in trans or in cis often yields divergent signaling events. In this review, we will revisit recent progress and discoveries of Thy-1–integrin interactions in trans and in cis, highlight their pathophysiological consequences and explore other potential binding partners of Thy-1 within the integrin regulation/signaling paradigm.

Crosstalk with keratinocytes causes GNAQ oncogene specificity in melanoma

Different melanoma subtypes exhibit specific and non-overlapping sets of oncogene and tumor suppressor mutations, despite a common cell of origin in melanocytes. For example, activation of the Gα_q/11 signaling pathway is a characteristic initiating event in primary melanomas that arise in the dermis, uveal tract, or central nervous system. It is rare in melanomas arising in the epidermis. The mechanism for this specificity is unknown. Here, we present evidence that in the mouse, crosstalk with the epidermal microenvironment actively impairs the survival of melanocytes expressing the GNAQ^Q209L oncogene. We found that GNAQ^Q209L, in combination with signaling from the interfollicular epidermis (IFE), stimulates dendrite extension, leads to actin cytoskeleton disorganization, inhibits proliferation, and promotes apoptosis in melanocytes. The effect was reversible and paracrine. In contrast, the epidermal environment increased the survival of wildtype and Braf^V600E expressing melanocytes. Hence, our studies reveal the flip side of Gα_q/11 signaling, which was hitherto unsuspected. In the future, the identification of the epidermal signals that restrain the GNAQ^Q209L oncogene could suggest novel therapies for GNAQ and GNA11 mutant melanomas.

Participation of keratinocyte- and fibroblast-derived factors in melanocyte homeostasis, the response to UV, and pigmentary disorders

Human epidermal melanocytes play a central role in sensing the environment and protecting the skin from the drastic effects of solar ultraviolet radiation and other environmental toxins or inflammatory agents. Melanocytes survive in the epidermis for decades, which subjects them to chronic environmental insults. Melanocytes have a poor self-renewal capacity; therefore, it is critical to ensure their survival with genomic stability. The function and survival of melanocytes is regulated by an elaborate network of paracrine factors synthesized mainly by epidermal keratinocytes and dermal fibroblasts. A symbiotic relationship exists between epidermal melanocytes and keratinocytes on the one hand, and between melanocytes and dermal fibroblasts on the other hand. Melanocytes protect epidermal keratinocytes and dermal fibroblasts from the damaging effects of solar radiation, and the latter cells synthesize biochemical mediators that maintain the homeostasis, and regulate the stress response of melanocytes. Disruption of the paracrine network results in pigmentary disorders, due to abnormal regulation of melanin synthesis, and compromise of melanocyte survival or genomic stability. This review provides an update of the current knowledge of keratinocyte- and fibroblast-derived paracrine factors and their contribution to melanocyte physiology, and how their abnormal production is involved in the pathogenesis of common pigmentary disorders.

SEMAPHORINS and their receptors: focus on the crosstalk between melanoma and hypoxia

Hypoxia, a condition of oxygen deprivation, is considered a hallmark of tumor microenvironment regulating several pathways and promoting cancer progression and resistance to therapy. Semaphorins, a family of about 20 secreted, transmembrane and GPI-linked glycoproteins, and their cognate receptors (plexins and neuropilins) play a pivotal role in the crosstalk between cancer and stromal cells present in the tumor microenvironment. Many studies reported that some semaphorins are involved in the development of a permissive tumor niche, guiding cell-cell communication and, consequently, the development and progression, as well as the response to therapy, of different cancer histotypes, including melanoma.

In this review we will summarize the state of art of semaphorins regulation by hypoxic condition in cancer with different origin. We will also describe evidence about the ability of semaphorins to affect the expression and activity of transcription factors activated by hypoxia, such as hypoxia-inducible factor-1. Finally, we will focus our attention on findings reporting the role of semaphorins in melanocytes transformation, melanoma progression and response to therapy. Further studies are necessary to understand the mechanisms through which semaphorins induce their effect and to shed light on the possibility to use semaphorins or their cognate receptors as prognostic markers and/or therapeutic targets in melanoma or other malignancies.

The involvement of semaphorin 7A in tumorigenic and immunoinflammatory regulation

Semaphorins, a large group of highly conserved proteins, consist of eight subfamilies that are widely expressed in vertebrates, invertebrates, and viruses and exist in membrane-bound or secreted forms. First described as axon guidance cues during neurogenesis, semaphorins also perform physiological functions in other organ systems, such as bone homeostasis, immune response, and tumor progression. Semaphorin 7A (SEMA7A), also known as CDw108, is an immune semaphorin that modulates diverse immunoinflammatory processes, including immune cell interactions, inflammatory infiltration, and cytokine production. In addition, SEMA7A regulates the proliferation, migration, invasion, lymph formation, and angiogenesis of multiple types of tumor cells, and these effects are mediated by the interaction of SEMA7A with two specific receptors, PLXNC1 and integrins. Thus, SEMA7A is intimately related to the pathogenesis of multiple autoimmune and inflammation-related diseases and tumors. This review focuses on the role of SEMA7A in the pathogenesis of autoimmune disorders, inflammatory diseases, and tumors, as well as the underlying mechanisms. Furthermore, strategies targeting SEMA7A as a potential predictive, diagnostic, and therapeutic agent for these diseases are also addressed.

miR-19a/b and miR-20a Promote Wound Healing by Regulating the Inflammatory Response of Keratinocytes

Persistent and impaired inflammation impedes tissue healing and is a characteristic of chronic wounds. A better understanding of the mechanisms controlling wound inflammation is needed. In this study, we show that in human wound-edge keratinocytes, the expressions of microRNA (miR)-17, miR-18a, miR-19a, miR-19b, and miR-20a, which all belong to the miR-17∼92 cluster, are upregulated during wound repair. However, their levels are lower in chronic ulcers than in acute wounds at the proliferative phase. Conditional knockout of miR-17∼92 in keratinocytes as well as injection of miR-19a/b and miR-20a antisense inhibitors into wound edges enhanced inflammation and delayed wound closure in mice. In contrast, conditional overexpression of the miR-17∼92 cluster or miR-19b alone in mice keratinocytes accelerated wound closure in vivo. Mechanistically, miR-19a/b and miR-20a decreased TLR3-mediated NF-κB activation by targeting SHCBP1 and SEMA7A, respectively, reducing the production of inflammatory chemokines and cytokines by keratinocytes. Thus, miR-19a/b and miR-20a being crucial regulators of wound inflammation, the lack thereof may contribute to sustained inflammation and impaired healing in chronic wounds. In line with this, we show that a combinatory treatment with miR-19b and miR-20a improved wound healing in a mouse model of type 2 diabetes.

The intervention of valproic acid on the tumorigenesis induced by an environmental carcinogen of PAHs

This study investigated whether valproic acid (VPA, a histone deacetylase inhibitor) can interfere with the carcinogenicity of polycyclic aromatic hydrocarbons (PAHs). A typical representative compound of PAHs, 7,12-Dimethylbenz[a]anthracene (DMBA), was used to induce rat breast cancer. The results showed that therapeutic concentration of VPA (50 and 100 mg/kg) delayed the occurrence of tumors, reduced tumor formation rate and attenuated tumors growth, and have a protective effect on normal tissues. The macrophage-mediated inflammatory response was found to be associated with the observed effect of VPA. In addition, we screened and validated a possible gene, Sema3c, which was involved in DMBA-induced breast cancer development and can be inhibited by VPA.

Secretome Analysis of Host Cells Infected with Toxoplasma gondii after Treatment of Human Epidermal Growth Factor Receptor 2/4 Inhibitors

Toxoplasma gondii, a ubiquitous, intracellular parasite of the phylum Apicomplexa, infects an estimated one-third of the human population as well as a broad range of warm-blooded animals. We have observed that some tyrosine kinase inhibitors suppressed the growth of T. gondii within host ARPE-10 cells. Among them, afatinib, human epithermal growth factor receptor 2 and 4 (HER2/4) inhibitor, may be used as a therapeutic agent for inhibiting parasite growth with minimal adverse effects on host. In this report, we conducted a proteomic analysis to observe changes in host proteins that were altered via infection with T. gondii and the treatment of HER2/4 inhibitors. Secreting proteins were subjected to a procedure of micor basic reverse phase liquid chromatography, nano-liquid chromatography-mass spectrometry, and ingenuity pathway analysis serially. As a result, the expression level of heterogeneous nuclear ribonucleoprotein K, semaphorin 7A, a GPI membrane anchor, serine/threonine-protein phosphatase 2A, and calpain small subunit 1 proteins were significantly changed, and which were confirmed further by western blot analysis. Changes in various proteins, including these 4 proteins, can be used as a basis for explaining the effects of T. gondii infections and HER2/4 inhibitors.

Semaphorin 7A: A novel marker of disease activity in Gaucher disease

Gaucher disease (GD) is a recessively inherited lysosomal storage disorder in which sphingolipids accumulates in the macrophages that transform into Gaucher cells. A growing body of evidence indicates that red blood cells (RBCs) represent important actors in GD pathophysiology. We previously demonstrated that altered RBC properties including increased Lyso-GL1 levels, dyserythropoiesis, and iron metabolism defect in GD patients contribute to anemia and hyperferritinemia. Since RBC defects also correlated well with markers of GD severity and were normalized under enzyme replacement therapy (ERT), the identification of molecules that are deregulated in GD RBCs represents an important issue in the search of pertinent markers of the disease. Here, we found a decreased expression of the GPI-anchored cell surface protein Semaphorin 7A (Sema7A) in RBCs from untreated GD (GD UT) patients, in parallel with increased levels of the soluble form in the plasma. Sema7A plays a role in neural guidance, atherosclerosis, and inflammatory diseases and represents a promigratory cue in physiological and pathological conditions. We showed that the decreased expression of Sema7A in RBCs correlated with their abnormal properties and with markers of GD activity. Interestingly, ERT restored the level of Sema7A to normal values both in RBCs and in plasma from GD patients. We then proposed that SemaA7A represents a simple and pertinent marker of inflammation in GD. Finally, because Sema7A is known to regulate the activity of immune cells, the increased level of soluble Sema7A in GD patients could propagate inflammation in several tissues.

Semaphorins in Angiogenesis and Autoimmune Diseases: Therapeutic Targets?

The axonal guidance molecules, semaphorins, have been described to function both physiologically and pathologically outside of the nervous system. In this review, we focus on the vertebrate semaphorins found in classes 3 through 7 and their roles in vascular development and autoimmune diseases. Recent studies indicate that while some of these vertebrate semaphorins promote angiogenesis, others have an angiostatic function. Since some semaphorins are also expressed by different immune cells and are known to modulate immune responses, they have been implicated in autoimmune disorders such as multiple sclerosis, rheumatoid arthritis, systemic lupus erythematosus and systemic sclerosis. We conclude this review by addressing strategies targeting semaphorins as potential therapeutic agents for angiogenesis and autoimmune diseases.

Semaphorin 7a participants in pterygium by regulating vascular endothelial growth factor

AIM

To investigate the relationship between semaphorin 7a expression and cell proliferation and migration in pterygium fibroblasts.

METHODS

Twenty-six patients with surgically diagnosed pterygium were enrolled, including 15 cases of primary pterygium and 11 cases of recurrent pterygium. In addition, 12 cases of normal conjunctival tissue were collected. The expression of semaphorin 7a in normal conjunctival tissue, primary pterygium and recurrent pterygium was detected by real-time polymerase chain reaction. Recurrent pterygium fibroblasts were isolated and cultured, and the expression of semaphorin 7a was silenced by small interfering RNA (siRNA) interference technique. Furthermore, the effects of si-semaphorin 7a interference on the mRNA and protein levels of β1-integrin, vascular endothelial growth factor A (VEGFA) and vascular endothelial growth factor receptor (VEGFR), and on fibroblast proliferation were analyzed. Transwell assay was used to detect the effect of semaphorin 7a interference on fibroblast migration.

RESULTS

Semaphorin 7a was highly expressed in the primary pterygium and recurrent pterygium samples than that of the normal conjunctival tissue. Compared with the primary pterygium, the expression of semaphoring 7a in the recurrent pterygium samples was significantly increased (P<0.05). The mRNA and protein expression levels of β1-integrin, VEGFA and VEGFR were decreased after si-semaphorin 7a transfection, and as well as the cell proliferation and migration.

CONCLUSION

Semaphorin 7a might play important roles in the pathogenesis of pterygium by affecting the expression of β1-integrin, VEGFA and VEGFR.

Semaphorin-7A on Exosomes: A Promigratory Signal in the Glioma Microenvironment

Exosomes are one of the most important mediators of the cross talk occurring between glioma stem cells (GSCs) and the surrounding microenvironment. We have previously shown that exosomes released by patient-derived glioma-associated stem cells (GASC) are able to increase, in vitro, the aggressiveness of both GSC and glioblastoma cell lines. To understand which molecules are responsible for this tumour-supporting function, we performed a descriptive proteomic analysis of GASC-exosomes and identified, among the others, Semaphorin7A (SEMA7A). SEMA7A was described as a promigratory cue in physiological and pathological conditions, and we hypothesised that it could modulate GSC migratory properties. Here, we described that SEMA7A is exposed on GASC-exosomes’ surface and signals to GSC through Integrin β1. This interaction activates focal adhesion kinase into GSC and increases their motility, in our patient-based in vitro model. Our findings suggest SEMA7A-β1-integrin as a new target to disrupt the communication between GSCs and the supporting microenvironment.

Studies of postpartum mammary gland involution reveal novel pro-metastatic mechanisms

Postpartum involution is the process by which the lactating mammary gland returns to the pre-pregnant state after weaning. Expression of tumor-promotional collagen, upregulation of matrix metalloproteinases, infiltration of M2 macrophages, and remodeling of blood and lymphatic vasculature are all characteristics shared by the involuting mammary gland and breast tumor microenvironment. The tumor promotional nature of the involuting mammary gland is perhaps best evidenced by cases of postpartum breast cancer (PPBC), or those cases diagnosed within 10 years of most recent childbirth. Women with PPBC experience more aggressive disease and higher risk of metastasis than nulliparous patients and those diagnosed outside the postpartum window. Semaphorin 7a (SEMA7A), cyclooxygenase-2 (COX-2), and collagen are all expressed in the involuting mammary gland and, together, predict for decreased metastasis free survival in breast cancer. Studies investigating the role of these proteins in involution have been important for understanding their contributions to PPBC. Postpartum involution thus represents a valuable model for the identification of novel molecular drivers of PPBC and classical cancer hallmarks. In this review, we will highlight the similarities between involution and cancer in the mammary gland, and further define the contribution of SEMA7A/COX-2/collagen interplay to postpartum involution and breast tumor progression and metastasis.

Semaphorin 7A Promotes Macrophage-Mediated Lymphatic Remodeling during Postpartum Mammary Gland Involution and in Breast Cancer

Postpartum mammary gland involution is a tissue remodeling event that occurs in all mammals in the absence of nursing or after weaning to return the gland to the pre-pregnant state. The tissue microenvironment created by involution has proven to be tumor promotional. Here we report that the GPI-linked protein semaphorin 7A (SEMA7A) is expressed on mammary epithelial cells during involution and use preclinical models to demonstrate that tumors induced during involution express high levels of SEMA7A. Overexpression of SEMA7A promoted the presence of myeloid-derived podoplanin (PDPN)-expressing cells in the tumor microenvironment and during involution. SEMA7A drove the expression of PDPN in macrophages, which led to integrin- and PDPN-dependent motility and adherence to lymphatic endothelial cells to promote lymphangiogenesis. In support of this mechanism, mammary tissue from SEMA7A-knockout mice exhibited decreased myeloid-derived PDPN-expressing cells, PDPN-expressing endothelial cells, and lymphatic vessel density. Furthermore, coexpression of SEMA7A, PDPN, and macrophage marker CD68 predicted for decreased distant metastasis-free survival in a cohort of over 600 cases of breast cancer as well as in ovarian, lung, and gastric cancers. Together, our results indicate that SEMA7A may orchestrate macrophage-mediated lymphatic vessel remodeling, which in turn drives metastasis in breast cancer.Signficance: SEMA7A, which is expressed on mammary cells during glandular involution, alters macrophage biology and lymphangiogenesis to drive breast cancer metastasis. Cancer Res; 78(22); 6473-85. ©2018 AACR.

Semaphorins and Their Receptors: From Axonal Guidance to Atherosclerosis

Semaphorins are a large family of secreted, transmembrane, or GPI-anchored proteins initially identified as axon guidance cues signaling through their receptors, neuropilins, and plexins. Emerging evidence suggests that beyond the guidance, they also function in a broad spectrum of pathophysiological conditions, including atherosclerosis, a vascular inflammatory disease. Particular semaphorin members have been demonstrated to participate in atherosclerosis via eliciting endothelial dysfunction, leukocyte infiltration, monocyte-macrophage retention, platelet hyperreactivity, and neovascularization. In this review, we focus on the role of those semaphorin family members in the development of atherosclerosis and highlight the mechanistic relevance of semaphorins to atherogenesis.

Plexin C1 Marks Liver Cancer Cells with Epithelial Phenotype and Is Overexpressed in Hepatocellular Carcinoma

BACKGROUND AND AIMS

Hepatocellular carcinoma is an aggressive malignancy of the liver and is ranked as the sixth most common cancer worldwide. There is still room for novel markers to improve the diagnosis and monitoring of HCC. Our observations in cancer databases that PLXNC1 is upregulated in HCC led us to investigate the expression profile of Plexin C1 mRNA and protein in HCC cell lines and tissues.

METHODS

A recombinant protein encompassing part of the extracellular domain of Plexin C1 was used as an antigen for monoclonal antibody development. Transcript and protein levels of Plexin C1 in HCC cell lines were determined by RT-qPCR and Western blotting, respectively. In vivo evaluation of Plexin C1 expression in HCC tissues was accomplished by immunohistochemistry studies in tissue microarrays.

RESULTS

A monoclonal antibody, clone PE4, specific to Plexin C1, was generated. In silico and in vitro analyses revealed a Plexin C1-based clustering of well-differentiated HCC cell lines. Staining of HCC and nontumoral liver tissues with PE4 showed a membrane-localized overexpression of Plexin C1 in tumors (p=0.0118). In addition, this expression was correlated with the histological grades of HCC cases.

CONCLUSIONS

Plexin C1 distinguishes HCC cells of epithelial characteristics from those with the mesenchymal phenotype. Compared to the nontumoral liver, HCC tissues significantly overexpress Plexin C1. The newly generated PE4 antibody can be evaluated in larger HCC cohorts and might be exploited for the examination of Plexin C1 expression pattern in other epithelial malignancies.

Exploiting the impact of the secretome of MSCs isolated from different tissue sources on neuronal differentiation and axonal growth

Cell transplantation using Mesenchymal stem cell (MSC) secretome have recently been presented as a possible free-based therapy for CNS related disorders. MSC secretome is rich in several bio-factors that act synergically towards the repair of damaged tissues, thus making it an ideal candidate for regenerative applications. Great effort is currently being made to map the molecules that compose the MSC secretome. Previous proteomic characterization of the secretome (in the form of conditioned media - CM) of MSCs derived from adipose tissue (ASC), bone-marrow (BMSC) and umbilical cord (HUCPVC) was performed by our group, where proteins relevant for neuroprotection, neurogenic, neurodifferentiation, axon guidance and growth functions were identified. Moreover, we have found significant differences among the expression of several molecules, which may indicate that their therapeutic outcome might be distinct. Having this in mind, in the present study, the neuroregulatory potential of ASC, BMSC and HUCPVC CM in promoting neurodifferentiation and axonal outgrowth was tested in vitro, using human telencephalon neuroprogenitor cells and dorsal root ganglion explants, respectively. The CM from the three MSC populations induced neuronal differentiation from human neural progenitor cells, as well as neurite outgrowth from dorsal root ganglion explants. Moreover, all the MSC populations promoted the same extent of neurodifferentiation, while ASC CM demonstrated higher potential in promoting axonal growth.

Precise role of dermal fibroblasts on melanocyte pigmentation

Dermal fibroblasts are traditionally recognized as synthesizing, remodeling and depositing collagen and extracellular matrix, the structural framework for tissues, helping to bring thickness and firmness to the skin. However, the role of fibroblasts on skin pigmentation arouses concern recently. More is known about the interactions between epidermal melanocytes and keratinocytes. This review highlights the importance of fibroblast-derived melanogenic paracrine mediators in the regulation of melanocyte activities. Fibroblasts act on melanocytes directly and indirectly through neighboring cells by secreting a large number of cytokines (SCF), proteins (DKK1, sFRP, Sema7a, CCN, FAP-α) and growth factors (KGF, HGF, bFGF, NT-3, NRG-1, TGF-β) which bind to receptors and modulate intracellular signaling cascades (MAPK/ERK, cAMP/PKA, Wnt/β-catenin, PI3K/Akt) related to melanocyte functions. These factors influence the growth, the pigmentation of melanocytes via the expression of melanin-producing enzymes and melanosome transfer, as well as their dendricity, mobility and adhesive properties. Thus, fibroblasts are implicated in both skin physiological and pathological pigmentation. In order to investigate their contribution, various in vitro models have been developed, based on cellular senescence. UV exposure, a major factor implicated in pigmentary disorders, may affect the secretory crosstalk between dermal and epithelial cells. Therefore, identification of the interactions between fibroblasts and melanocytes could provide novel insights not only for the development of melanogenic agents in the clinical and cosmetic fields, but also for a better understanding of the melanocyte biology and melanogenesis regulation.

Semaphorin 7A as a potential immune regulator and promising therapeutic target in rheumatoid arthritis

Background

Semaphorin 7A (Sema7A) is expressed by several different classes of lymphoid and myeloid cells and is a potent immunomodulator. We examined the role of Sema7A in modulating cellular immune responses and to provide experimental data validating the therapeutic potential of Sema7A in rheumatoid arthritis (RA).

Methods

Soluble Sema7A (sSema7A) levels in the serum and synovial fluid from patients with RA or osteoarthritis, as well as cytokine secretions, were analyzed with an enzyme-linked immunosorbent assay. The cell surface levels and transcripts of Sema7A were evaluated in T cells and monocytes from patients with RA. The effect of Sema7A on the functions of primary T cells isolated from the peripheral blood of healthy donors was observed. Detection of the activation of the signal mediator focal adhesion kinase was performed by Western blotting. Shedding of sSema7A was evaluated in monocytes. The introduction of anti-Sema7A antibody to mice with collagen-induced arthritis (CIA) was observed in vivo.

Results

Upregulation of sSema7A levels in both the serum and synovial fluid of patients with RA was correlated with disease activity markers. sSema7A markedly increased Th1/Th17 cytokine secretion and induced evident upregulation of T-bet and retinoic acid receptor-related orphan nuclear receptor γt levels in T cells. Cell surface Sema7A was cleaved by a disintegrin and metalloprotease 17 (ADAM17) in monocytes. Interleukin-6 and tumor necrosis factor-α stimulated ADAM17 secretion in synovial macrophages. Blocking of β1-integrin abrogated the Sema7A-mediated cytokine secretion. Treatment with an anti-Sema7A antibody significantly attenuated CIA.

Conclusions

These findings indicate that Sema7A as a potent activator of T cells and monocytes in the immune response contributes to the inflammation and progression of RA, suggesting its therapeutic potential in the treatment of RA.

Endogenous Semaphorin-7A Impedes Human Lung Fibroblast Differentiation

Semaphorin-7A is a glycosylphosphatidylinositol-anchored protein, initially characterized as an axon guidance protein. Semaphorin-7A also contributes to immune cell regulation and may be an essential pro-fibrotic factor when expressed by non-fibroblast cell types (exogenous). In mouse models, semaphorin-7A was shown to be important for TGF-ß1-induced pulmonary fibrosis characterized by myofibroblast accumulation and extracellular matrix deposition, but the cell-specific role of semaphorin-7A was not examined in fibroblasts. The purpose of this study is to determine semaphorin-7A expression by fibroblasts and to investigate the function of endogenously expressed semaphorin-7A in primary human lung fibroblasts (HLF).

Herein, we show that non-fibrotic HLF expressed high levels of cell surface semaphorin-7A with little dependence on the percentage of serum or recombinant TGF-ß1. Semaphorin-7A siRNA strongly decreased semaphorin-7A mRNA expression and reduced cell surface semaphorin-7A. Reduction of semaphorin-7A induced increased proliferation and migration of non-fibrotic HLF. Also, independent of the presence of TGF-ß1, the decline of semaphorin-7A by siRNA was associated with increased α-smooth muscle actin production and gene expression of periostin, fibronectin, laminin, and serum response factor (SRF), indicating differentiation into a myofibroblast. Conversely, overexpression of semaphorin-7A in the NIH3T3 fibroblast cell line reduced the production of pro-fibrotic markers. The inverse association between semaphorin-7A and pro-fibrotic fibroblast markers was further analyzed using HLF from idiopathic pulmonary fibrosis (IPF) (n = 6) and non-fibrotic (n = 7) lungs. Using these 13 fibroblast lines, we observed that semaphorin-7A and periostin expression were inversely correlated. In conclusion, our study indicates that endogenous semaphorin-7A in HLF plays a role in maintaining fibroblast homeostasis by preventing up-regulation of pro-fibrotic genes. Therefore, endogenous and exogenous semaphorin-7A may have opposite effects on the fibroblast phenotype.

Plexin C1 deficiency permits synaptotagmin 7-mediated macrophage migration and enhances mammalian lung fibrosis

Pulmonary fibrosis is a progressive and often fatal condition that is believed to be partially orchestrated by macrophages. Mechanisms that control migration of these cells into and within the lung remain undefined. We evaluated the contributions of the semaphorin receptor, plexin C1 (PLXNC1), and the exocytic calcium sensor, synaptotagmin 7 (Syt7), in these processes. We evaluated the role of PLXNC1 in macrophage migration by using Boyden chambers and scratch tests, characterized its contribution to experimentally induced lung fibrosis in mice, and defined the mechanism for our observations. Our findings reveal that relative to control participants, patients with idiopathic pulmonary fibrosis demonstrate excessive monocyte migration and underexpression of PLXNC1 in the lungs and circulation, a finding that is recapitulated in the setting of scleroderma-related interstitial lung disease. Relative to wild type, PLXNC1^-/- mouse macrophages are excessively migratory, and PLXNC1^-/- mice show exacerbated collagen accumulation in response to either inhaled bleomycin or inducible lung targeted TGF-β1 overexpression. These findings are ameliorated by replacement of PLXNC1 on bone marrow-derived cells or by genetic deletion of Syt7. These data demonstrate the previously unrecognized observation that PLXNC1 deficiency permits Syt7-mediated macrophage migration and enhances mammalian lung fibrosis.-Peng, X., Moore, M., Mathur, A., Zhou, Y., Sun, H., Gan, Y., Herazo-Maya, J. D., Kaminski, N., Hu, X., Pan, H., Ryu, C., Osafo-Addo, A., Homer, R. J., Feghali-Bostwick, C., Fares, W. H., Gulati, M., Hu, B., Lee, C.-G., Elias, J. A., Herzog, E. L. Plexin C1 deficiency permits synaptotagmin 7-mediated macrophage migration and enhances mammalian lung fibrosis.

Semaphorin 7a exerts pleiotropic effects to promote breast tumor progression

Understanding what drives breast tumor progression is of utmost importance for blocking tumor metastasis; we have identified that semaphorin 7a is a potent driver of ductal carcinoma in situ (DCIS) progression. Semaphorin 7a is a GPI membrane anchored protein that promotes attachment and spreading in multiple cell types. Here we show that increased expression of SEMA7A occurs in a large percentage of breast cancers and is associated with decreased overall and distant metastasis free survival. In both in vitro and in vivo models, shRNA mediated silencing of SEMA7A reveals roles for semaphorin 7a in the promotion of DCIS growth, motility, and invasion as well as lymphangiogenesis in the tumor microenvironment. Our studies also uncover a relationship between COX-2 and semaphorin 7a expression and suggest that semaphorin 7a promotes tumor cell invasion on collagen and lymphangiogenesis via activation of β₁-integrin receptor. Our results suggest that semaphorin 7a, may be novel target for blocking breast tumor progression.

Fine-tuned SRF activity controls asymmetrical neuronal outgrowth: implications for cortical migration, neural tissue lamination and circuit assembly

The stimulus-regulated transcription factor Serum Response Factor (SRF) plays an important role in diverse neurodevelopmental processes related to structural plasticity and motile functions, although its precise mechanism of action has not yet been established. To further define the role of SRF in neural development and distinguish between cell-autonomous and non cell-autonomous effects, we bidirectionally manipulated SRF activity through gene transduction assays that allow the visualization of individual neurons and their comparison with neighboring control cells. In vitro assays showed that SRF promotes survival and filopodia formation and is required for normal asymmetric neurite outgrowth, indicating that its activation favors dendrite enlargement versus branching. In turn, in vivo experiments demonstrated that SRF-dependent regulation of neuronal morphology has important consequences in the developing cortex and retina, affecting neuronal migration, dendritic and axonal arborization and cell positioning in these laminated tissues. Overall, our results show that the controlled and timely activation of SRF is essential for the coordinated growth of neuronal processes, suggesting that this event regulates the switch between neuronal growth and branching during developmental processes.

Evidence for glycosylation as a regulator of the pigmentary system: key roles of sialyl(α2-6)gal/GalNAc-terminated glycans in melanin synthesis and transfer

The major regulators of melanogenesis are glycoproteins, however no role for glycosylation in the pathway has yet been described. We stained skin biopsies and melanocyte-keratinocyte co-cultures with a panel of 20 lectins as oligosaccharide markers. Notably, the Elderberry Bark Lectin (EBL/SNA) stained melanocytes in both systems. EBL binds the sequence Neu5Ac(α(2-6)Gal/GalNAc)- at the termini of some oligosaccharide antennae. We used inhibitors of synthesis and/or binding of this sequence to assess effects on pigmentation. METHODS. Cell culture, lectin histochemistry, siRNA transfection, and assays for dopa oxidase and melanin were carried out by standard techniques. RESULTS. 6′-sialyllactose, a short homolog of the sequence in question, anti-sialyltransferase 6 (ST6) siRNA, and cytidine, a sialyltransferase (ST) inhibitor, each inhibited EBL binding, melanogenesis and melanosome transfer. Unexpectedly, 3′-sialyllactose and siRNA for ST3, chosen as a negative controls, also inhibited these processes. Though strong inhibitors of melanization, none of the agents affected tyrosinase/dopa oxidase activity, indicating previously unrecognized post-tyrosinase regulation of melanization. CONCLUSIONS. We report for the first time that Neu5Ac (α(2-6)Gal/GalNAc)- and possibly Neu5Ac(α(2–3)Gal/GalNAc)-terminated oligosaccharides play multiple roles in melanin synthesis and transfer.

Shaping the Reproductive System: Role of Semaphorins in Gonadotropin-Releasing Hormone Development and Function

The semaphorin proteins, which contribute to the morphogenesis and homeostasis of a wide range of systems, are among the best-studied families of guidance cues. Much recent research has focused on the role of semaphorins in the development and adult activity of hormone systems and, reciprocally, how circulating reproductive hormones regulate their expression and function. Specifically, several reports have focused on the molecular mechanisms underlying the effects of semaphorins on the migration, survival and structural and functional plasticity of neurons that secrete gonadotropin-releasing hormone (GnRH), essential for the acquisition and maintenance of reproductive competence in mammals. Alterations in the development of this neuroendocrine system lead to anomalous or absent GnRH secretion, resulting in heterogeneous reproductive disorders such as congenital hypogonadotropic hypogonadism (CHH) or other conditions characterized by infertility or subfertility. This review summarizes current knowledge of the role of semaphorins and their receptors on the development, differentiation and plasticity of the GnRH system. In addition, the involvement of genetic deficits in semaphorin signaling in some forms of CHH in humans is discussed.

Role of chitinase 3-like-1 and semaphorin 7a in pulmonary melanoma metastasis

The prototypic chitinase-like protein Chi3l1 is induced in cancers and portends a poor prognosis, but whether it contributes to cancer progression is unknown. To address this gap in knowledge, we investigated the production of Chi3l1 in melanoma lung metastases. We found that Chi3l1 was induced during pulmonary melanoma metastasis and that this induction was regulated by the semaphorin Sema7a, interacting in stimulatory or inhibitory ways with its β1 integrin or Plexin C1 receptors, respectively. In mouse strains with genetic deletions of Chi3l1 or Sema7a, there was a significant reduction in pulmonary metastasis. Notably, antiserum raised against Chi3l1 or Sema7a phenocopied the reduction produced by genetic deletions. Melanoma lung metastasis was also decreased in the absence of IL13Rα2, a recently identified receptor for Chi3l1, consistent with a key role for Chi3l1 in melanoma spread. We confirmed roles for Sema7a and Chi3l1 in pulmonary metastasis of EMT6 breast cancer cells. Taken together, our studies establish a novel pathway through which Sem7a and its receptors regulate Chi3l1, revealing a host axis involving IL13Rα2 that plays a critical role in generating a pulmonary microenvironment that is critical to license metastasis.

Skin as a living coloring book: how epithelial cells create patterns of pigmentation

The pigmentation of mammalian skin and hair develops through the interaction of two basic cell types - pigment donors and recipients. The pigment donors are melanocytes, which produce and distribute melanin through specialized structures. The pigment recipients are epithelial cells, which acquire melanin and put it to use, collectively yielding the pigmentation visible to the eye. This review will focus on the pigment recipients, the historically less understood cell type. These end-users of pigment are now known to exert a specialized control over the patterning of pigmentation, as they identify themselves as melanocyte targets, recruit pigment donors, and stimulate the transfer of melanin. As such, this review will discuss the evidence that the skin is like a coloring book: the pigment recipients create a 'picture,' a blueprint for pigmentation, which is colorless initially but outlines where pigment should be placed. Melanocytes then melanize the recipients and 'color in' the picture.

Semaphorin7A: branching beyond axonal guidance and into immunity

Semaphorins are a family of proteins that were originally described for their role in axonal guidance. Studies now show that semaphorins encompass many physiological functions outside of the nervous system, including immune responses. Semaphorin7A (SEMA7A) belongs to the "immune" semaphorin group and has been shown to play a crucial role in regulating immune responses. In this review, we discuss the structure and function of SEMA7A as well as its role in innate and adaptive immunity [corrected].We further describe SEMA7A's involvement in inflammatory disease and its emergent role in cancer.

The role of axon guidance factor semaphorin 6B in the invasion and metastasis of gastric cancer

OBJECTIVE

To investigate the role of semaphorin 6B in gastric cancer invasion and metastasis.

METHODS

Immunohistochemistry for semaphorin 6B was performed on gastric cancer tumour tissue samples in this retrospective study. Levels of semaphorin 6B protein and mRNA were determined in gastric cancer cell lines by Western blotting and quantitative reverse transcription-polymerase chain reaction, respectively. The human gastric cancer cell line SGC-7901 was transfected with small interfering RNA targeting semaphorin 6B; effects on cell adhesion, migration and invasion were determined by cell adhesion assay, transwell chamber migration assay and wound healing assay, respectively.

RESULTS

Tumour tissue samples from 220 patients were analysed. In vivo, semaphorin 6B immunopositivity correlated with tumour differentiation, lymph node metastasis and distant metastasis but not patient age, sex or tumour stage. Semaphorin 6B gene silencing significantly suppressed adhesion, migration and invasion of gastric cancer cells in vitro.

CONCLUSIONS

Semaphorin 6B is related to tumour differentiation and metastasis in vivo, and tumour cell migration, adhesion and invasion in vitro. Semaphorin 6B may represent a reliable biomarker for diagnosis, evaluation and gene-targeted therapy of gastric cancer.

Semaphorin signaling in the development and function of the gonadotropin hormone-releasing hormone system

The semaphorin proteins are among the best-studied families of guidance cues, contributing to morphogenesis and homeostasis in a wide range of tissue types. The major semaphorin receptors are plexins and neuropilins, however other receptors and co-receptors are capable to mediate signaling by semaphorins. These guidance proteins were originally identified as growth cone "collapsing factors" or as inhibitory signals, crucial for nervous system development. Since those seminal discoveries, the list of functions of semaphorins has rapidly grown. Over the past few years, a growing body of data indicates that semaphorins are involved in the regulation of the immune and vascular systems, in tumor growth/cancer cell metastasis and in neural circuit formation. Recently there has been increasing emphasis on research to determine the potential influence of semaphorins on the development and homeostasis of hormone systems and how circulating reproductive hormones regulate their expression and functions. Here, we focus on the emerging role of semaphorins in the development, differentiation and plasticity of unique neurons that secrete gonadotropin-releasing hormone (GnRH), which are essential for the acquisition and maintenance of reproductive competence in all vertebrates. Genetic evidence is also provided showing that insufficient semaphorin signaling contributes to some forms of reproductive disorders in humans, characterized by the reduction or failure of sexual competence. Finally, we will review some studies with the goal of highlighting how the expression of semaphorins and their receptors might be regulated by gonadal hormones in physiological and pathological conditions.

Identifying novel Plasmodium falciparum erythrocyte invasion receptors using systematic extracellular protein interaction screens

The invasion of host erythrocytes by the parasite Plasmodium falciparum initiates the blood stage of infection responsible for the symptoms of malaria. Invasion involves extracellular protein interactions between host erythrocyte receptors and ligands on the merozoite, the invasive form of the parasite. Despite significant research effort, many merozoite surface ligands have no known erythrocyte binding partner, most likely due to the intractable biochemical nature of membrane-tethered receptor proteins and their interactions. The few receptor–ligand pairs that have been described have largely relied on sourcing erythrocytes from patients with rare blood groups, a serendipitous approach that is unsatisfactory for systematically identifying novel receptors. We have recently developed a scalable assay called AVEXIS (for AVidity-based EXtracellular Interaction Screen), designed to circumvent the technical difficulties associated with the identification of extracellular protein interactions, and applied it to identify erythrocyte receptors for orphan P. falciparum merozoite ligands. Using this approach, we have recently identified Basigin (CD147) and Semaphorin-7A (CD108) as receptors for RH5 and MTRAP respectively. In this essay, we review techniques used to identify Plasmodium receptors and discuss how they could beapplied in the future to identify novel receptors both for Plasmodium parasites but also other pathogens.

Vitiligo road map

Vitiligo is a depigmenting disorder stemming from melanocyte loss or dysfunction. It has a complex, multifaceted etiology. We constructed a "vitiligo road map," consisting of basic science, clinical, and treatment components, in order to better portray our current understanding of vitiligo pathogenesis and reflect upon novel biomarkers and therapeutic targets for future research. The melanocyte map elaborates on the molecular processes and intracellular signaling pathways initiated by various external autocrine/paracrine factors in representing normal melanocyte homeostatic functions modulating its viability, proliferation, differentiation, dendricity, migration, and melanogenic processes. This vitiligo map identifies known inducers/triggers of vitiligo onset and progression that cultivate a microenvironment for melanocyte disappearance, real or functional. This map describes the molecular mechanisms of currently utilized clinical and experimental treatments of vitiligo that facilitate repigmentation.

Semaphorin7A and its receptors: pleiotropic regulators of immune cell function, bone homeostasis, and neural development

Semaphorins form a large, evolutionary conserved family of cellular guidance signals. The semaphorin family contains several secreted and transmembrane proteins, but only one GPI-anchored member, Semaphorin7A (Sema7A). Although originally identified in immune cells, as CDw108, Sema7A displays widespread expression outside the immune system. It is therefore not surprising that accumulating evidence supports roles for this protein in a wide variety of biological processes in different organ systems and in disease. Well-characterized biological effects of Sema7A include those during bone and immune cell regulation, neuron migration and neurite growth. These effects are mediated by two receptors, plexinC1 and integrins. However, most of what is known today about Sema7A signaling concerns Sema7A-integrin interactions. Here, we review our current knowledge of Sema7A function and signaling in different organ systems, highlighting commonalities between the cellular effects and signaling pathways activated by Sema7A in different cell types. Furthermore, we discuss a potential role for Sema7A in disease and provide directions for further research.

Semaphorins in the development, homeostasis and disease of hormone systems

Semaphorin proteins are among the best-studied families of guidance cues. Initially characterized as repulsive neuronal guidance cues, during the last decade, significant progress has been made in defining their involvement in the regulation of dynamic changes in the cellular cytoskeleton during embryonic and postnatal neuronal development, under both physiological and pathological conditions. However, semaphorins are not restricted to the nervous system but widely expressed in other tissues, where they play key roles in angiogenesis and organogenesis. In recent years, there has been an increasing emphasis on the potential influence of semaphorins on the development and homeostasis of hormone systems, and conversely, how circulating reproductive hormones regulate semaphorin expression. In this review, we summarize recent studies analyzing the contribution of semaphorin signaling to the morphogenesis, differentiation and plasticity of fundamental neuroendocrine and endocrine systems that regulate key physiological processes, such as reproduction, bone formation and the control of energy homeostasis.

The neural guidance receptor Plexin C1 delays melanoma progression

Plexin C1 is a type I transmembrane receptor with intrinsic R-Ras GTPase activity, which regulates cytoskeletal remodeling and adhesion in normal human melanocytes. Melanocytes are pigment-producing cells of the epidermis, precursors for melanoma, and express high levels of Plexin C1, which is lost in melanoma in vitro and in vivo. To determine if Plexin C1 is a tumor suppressor for melanoma, we introduced Plexin C1 into a primary human melanoma cell line, and phenotypes including migration, apoptosis, proliferation and tumor growth in mice were analyzed. Complimentary studies in which Plexin C1 was silenced in human melanocytes were performed. Plexin C1 significantly inhibited migration and proliferation in melanoma, whereas in melanocytes, loss of Plexin C1 increased migration and proliferation. In mouse xenografts, Plexin C1 delayed tumor growth of melanoma at early time points, but tumors eventually escaped the suppressive effects of Plexin C1, due to Plexin C1-dependent activation of the pro-survival protein Akt. R-Ras activation stimulates melanoma migration. Plexin C1 lowered R-Ras activity in melanoma and melanocytes, consistent with inhibitory effects of Plexin C1 on migration of melanocytes and melanoma. To determine if R-Ras is expressed in melanocytic lesions in vivo, staining of tissue microarrays of nevi and melanoma were performed. R-Ras expression was highly limited in melanocytic lesions, being essentially confined to primary melanoma, and almost completely absent in nevi and metastatic melanoma. These data suggest that loss of Plexin C1 in melanoma may promote early steps in melanoma progression through suppression of migration and proliferation, but pro-survival effects of Plexin C1 ultimately abrogate the tumor suppressive effects of Plexin C1. In primary melanoma, loss of Plexin C1 may function in early steps of melanoma progression by releasing inhibition of R-Ras activation, and stimulating migration.

Semaphorin-7A is an erythrocyte receptor for P. falciparum merozoite-specific TRAP homolog, MTRAP

The motility and invasion of Plasmodium parasites is believed to require a cytoplasmic actin-myosin motor associated with a cell surface ligand belonging to the TRAP (thrombospondin-related anonymous protein) family. Current models of invasion usually invoke the existence of specific receptors for the TRAP-family ligands on the surface of the host cell; however, the identities of these receptors remain largely unknown. Here, we identify the GPI-linked protein Semaphorin-7A (CD108) as an erythrocyte receptor for the P. falciparum merozoite-specific TRAP homolog (MTRAP) by using a systematic screening approach designed to detect extracellular protein interactions. The specificity of the interaction was demonstrated by showing that binding was saturable and by quantifying the equilibrium and kinetic biophysical binding parameters using surface plasmon resonance. We found that two MTRAP monomers interact via their tandem TSR domains with the Sema domains of a Semaphorin-7A homodimer. Known naturally-occurring polymorphisms in Semaphorin-7A did not quantitatively affect MTRAP binding nor did the presence of glycans on the receptor. Attempts to block the interaction during in vitro erythrocyte invasion assays using recombinant proteins and antibodies showed no significant inhibitory effect, suggesting the inaccessibility of the complex to proteinaceous blocking agents. These findings now provide important experimental evidence to support the model that parasite TRAP-family ligands interact with specific host receptors during cellular invasion.

Apicomplexan parasites are one of the most significant groups of pathogens infecting humans and include Plasmodium falciparum, the parasite responsible for malaria. These parasites critically depend on their human host and must invade our cells to multiply; therefore, understanding this invasion process - with the eventual aim of therapeutically preventing it - has been a focus for scientific investigation. A key component of the invasion machinery is a family of proteins (the “TRAP” family) which traverse the membrane surrounding the parasite: the part remaining within the parasite connects to a molecular motor that powers invasion, whilst the surface-exposed region is thought to interact with proteins on the surface of the target host cell. One major question that remains unanswered is the identity of the host receptors for the TRAPs. In our paper, we use a method specifically designed to detect interactions that occur in the extracellular space between host and pathogen proteins to reveal a host receptor called Semaphorin-7A for the TRAP-family member used by the blood stage of the malarial parasite – a protein called MTRAP. The characterization of this host-parasite interaction may therefore lead to novel therapies based upon preventing parasite invasion.

Plexin structures are coming: opportunities for multilevel investigations of semaphorin guidance receptors, their cell signaling mechanisms, and functions

Plexin transmembrane receptors and their semaphorin ligands, as well as their co-receptors (Neuropilin, Integrin, VEGFR2, ErbB2, and Met kinase) are emerging as key regulatory proteins in a wide variety of developmental, regenerative, but also pathological processes. The diverse arenas of plexin function are surveyed, including roles in the nervous, cardiovascular, bone and skeletal, and immune systems. Such different settings require considerable specificity among the plexin and semaphorin family members which in turn are accompanied by a variety of cell signaling networks. Underlying the latter are the mechanistic details of the interactions and catalytic events at the molecular level. Very recently, dramatic progress has been made in solving the structures of plexins and of their complexes with associated proteins. This molecular level information is now suggesting detailed mechanisms for the function of both the extracellular as well as the intracellular plexin regions. Specifically, several groups have solved structures for extracellular domains for plexin-A2, -B1, and -C1, many in complex with semaphorin ligands. On the intracellular side, the role of small Rho GTPases has been of particular interest. These directly associate with plexin and stimulate a GTPase activating (GAP) function in the plexin catalytic domain to downregulate Ras GTPases. Structures for the Rho GTPase binding domains have been presented for several plexins, some with Rnd1 bound. The entire intracellular domain structure of plexin-A1, -A3, and -B1 have also been solved alone and in complex with Rac1. However, key aspects of the interplay between GTPases and plexins remain far from clear. The structural information is helping the plexin field to focus on key questions at the protein structural, cellular, as well as organism level that collaboratoria of investigations are likely to answer.

Semaphorin signals tweaking the tumor microenvironment

Solid tumors not only comprise malignant cells but also other nonmalignant cell types, forming a unique microenvironment that can strongly influence the behavior of tumor cells. Recent advances in the understanding of cancer biology have highlighted the functional role of semaphorins. In fact, semaphorins form a family of molecular signals known to guide and control cell migration during embryo development and in adults. Tumor cells express semaphorins as well as their receptors, plexins and neuropilins. It has been shown that semaphorin signaling can regulate tumor cell behavior. Moreover, semaphorins are important regulators of tumor angiogenesis. Conversely, very little is known about the functional relevance of semaphorin signals for tumor-infiltrating stromal cells, such as leukocytes. In this chapter, we review the current knowledge on the functional role of semaphorins in cancer progression, and we focus on the emerging role of semaphorins in mediating the cross talk between tumor cells and different tumor stromal cells.

Role of semaphorin 7a signaling in transforming growth factor β1-induced lung fibrosis and scleroderma-related interstitial lung disease

OBJECTIVE

Semaphorin 7a regulates transforming growth factor β1 (TGFβ1)-induced fibrosis. This study was undertaken to test the hypothesis that semaphorin 7a exerts its profibrotic effects in part by promoting the tissue accumulation of CD45+ fibrocytes.

METHODS

A murine model of pulmonary fibrosis in which an inducible, bioactive form of the human TGFβ1 gene is overexpressed in the lung was used. Fibrosis and fibrocytes were evaluated in TGFβ1-transgenic mice in which the semaphorin 7a locus had been disrupted. The effect of replacement or deletion of semaphorin 7a on bone marrow-derived cells was ascertained using bone marrow transplantation. The role of the semaphorin 7a receptor β1 integrin was assessed using neutralizing antibodies. The applicability of these findings to TGFβ1-driven fibrosis in humans was examined in patients with scleroderma-related interstitial lung disease (ILD).

RESULTS

The appearance of fibrocytes in the lungs of TGFβ1-transgenic mice required semaphorin 7a. Replacement of semaphorin 7a on bone marrow-derived cells restored lung fibrosis and fibrocytes. Immunoneutralization of β1 integrin reduced pulmonary fibrocytes and fibrosis. Peripheral blood mononuclear cells (PBMCs) from patients with scleroderma-related ILD showed increased levels of messenger RNA for semaphorin 7a and its receptors, with semaphorin 7a located on collagen-producing fibrocytes and CD19+ lymphocytes. Peripheral blood fibrocyte outgrowth was enhanced in these patients. Stimulation of normal human PBMCs with recombinant semaphorin 7a enhanced fibrocyte differentiation; these effects were attenuated by β1 integrin neutralization.

CONCLUSION

Our findings indicate that interventions that reduce semaphorin 7a expression or prevent the semaphorin 7a-β1 integrin interaction may ameliorate TGFβ1-driven or fibrocyte-associated autoimmune fibroses.