Mammalian sprouty proteins inhibit cell growth and differentiation by preventing ras activation

Paclitaxel Aggravating Radiation-Induced Pulmonary Fibrosis Is Associated with the Down-Regulation of the Negative Regulatory Function of Spry2

Paclitaxel (PTX) is capable of aggravating radiation-induced pulmonary fibrosis (RIPF), but the mechanism is unknown. Spry2 is a negative regulator of receptor tyrosine kinase-related Ras/Raf/extracellular signal regulated kinase (ERK) pathway. This experiment was aimed at exploring whether the aggravation of RIPF by PTX is related to Spry2. The RIPF model was established with C57BL/6 mice by thoracic irradiation, and PTX was administered concurrently. Western blot was used to detect the expression level of ERK signaling molecules and the distribution of Spry2 in the plasma membrane/cytoplasm. Co-immunoprecipitation (co-IP) and immunofluorescence were used to observe the colocalization of Spry2 with the plasma membrane and tubulin. The results showed that PTX-concurrent radiotherapy could aggravate fibrotic lesions in RIPF, downregulate the content of membrane Spry2, and upregulate the levels of p-c-Raf and p-ERK in lung tissue. It was found that knockdown of Spry2 in fibroblast abolished the upregulation of p-c-Raf and p-ERK by PTX. Both co-IP results and immunofluorescence staining showed that PTX increased the binding of Spry2 to tubulin, and microtubule depolymerizing agents could abolish PTX's inhibition of Spry2 membrane distribution and inhibit PTX's upregulation of Raf/ERK signaling. Both nintedanib and ERK inhibitor were effective in relieving PTX-exacerbated RIPF. Taken together, the mechanism of PTX's aggravating RIPF was related to its ability to enhance Spry2's binding to tubulin, thus attenuating Spry2's negative regulation on Raf/ERK pathway. SIGNIFICANCE STATEMENT: This study revealed that paclitaxel (PTX) concurrent radiation therapy exacerbates radiation-induced pulmonary fibrosis during the treatment of thoracic tumors, which is associated with PTX restraining Spry2 and upregulating the Raf/extracellular signal regulated kinase signaling pathway, and provided drug targets for mitigating this complication.

Signal Transduction Regulators in Axonal Regeneration

Intracellular signal transduction in response to growth factor receptor activation is a fundamental process during the regeneration of the nervous system. In this context, intracellular inhibitors of neuronal growth factor signaling have become of great interest in the recent years. Among them are the prominent signal transduction regulators Sprouty (SPRY) and phosphatase and tensin homolog deleted on chromosome 10 (PTEN), which interfere with major signaling pathways such as extracellular signal-regulated kinase (ERK) or phosphoinositide 3-kinase (PI3K)/Akt in neurons and glial cells. Furthermore, SPRY and PTEN are themselves tightly regulated by ubiquitin ligases such as c-casitas b-lineage lymphoma (c-CBL) or neural precursor cell expressed developmentally down-regulated protein 4 (NEDD4) and by different microRNAs (miRs) including miR-21 and miR-222. SPRY, PTEN and their intracellular regulators play an important role in the developing and the lesioned adult central and peripheral nervous system. This review will focus on the effects of SPRY and PTEN as well as their regulators in various experimental models of axonal regeneration in vitro and in vivo. Targeting these signal transduction regulators in the nervous system holds great promise for the treatment of neurological injuries in the future.

Epigenetic DNA Modifications Upregulate SPRY2 in Human Colorectal Cancers

Conventional wisdom is that Sprouty2 (SPRY2), a suppressor of Receptor Tyrosine Kinase (RTK) signaling, functions as a tumor suppressor and is downregulated in many solid tumors. We reported, for the first time, that increased expression of SPRY2 augments cancer phenotype and Epithelial-Mesenchymal-Transition (EMT) in colorectal cancer (CRC). In this report, we assessed epigenetic DNA modifications that regulate SPRY2 expression in CRC. A total of 4 loci within SPRY2 were evaluated for 5mC using Combined Bisulfite Restriction Analysis (COBRA). Previously sequenced 5hmC nano-hmC seal data within SPRY2 promoter and gene body were evaluated in CRC. Combined bioinformatics analyses of SPRY2 CRC transcripts by RNA-seq/microarray and 450K methyl-array data archived in The Cancer Genome Atlas (TCGA) and GEO database were performed. SPRY2 protein in CRC tumors and cells was measured by Western blotting. Increased SPRY2 mRNA was observed across several CRC datasets and increased protein expression was observed among CRC patient samples. For the first time, SPRY2 hypomethylation was identified in adenocarcinomas in the promoter and gene body. We also revealed, for the first time, increases of 5hmC deposition in the promoter region of SPRY2 in CRC. SPRY2 promoter hypomethylation and increased 5hmC may play an influential role in upregulating SPRY2 in CRC.

Identification of SPRY4 as a Novel Candidate Susceptibility Gene for Familial Nonmedullary Thyroid Cancer

Background: The molecular basis of familial nonmedullary thyroid cancer (FNMTC) is still poorly understood, representing a limitation for molecular diagnosis and clinical management. In this study, we aimed to identify new susceptibility genes for FNMTC through whole-exome sequencing (WES) analysis of leukocyte DNA of patients from a highly informative FNMTC family. Methods: We selected six affected family members to conduct WES analysis. Bioinformatic analyses were undertaken to filter and select the genetic variants shared by the affected members, which were subsequently validated by Sanger sequencing. To select the most likely pathogenic variants, several studies were performed, including family segregation analysis, in silico impact characterization, and gene expression (messenger RNA and protein) depiction in databases. For the most promising variant identified, we performed in vitro studies to validate its pathogenicity. Results: Several potentially pathogenic variants were identified in different candidate genes. After filtering with appropriate criteria, the variant c.701C>T, p.Thr234Met in the SPRY4 gene was prioritized for in vitro functional characterization. This SPRY4 variant led to an increase in cell viability and colony formation, indicating that it confers a proliferative advantage and potentiates clonogenic capacity. Phosphokinase array and Western blot analyses suggested that the effects of the SPRY4 variant were mediated through the mitogen-activated protein kinase/extracellular signal-regulated kinase pathway, which was further supported by a higher responsiveness of thyroid cancer cells with the SPRY4 variant to a MEK inhibitor. Conclusions: WES analysis in one family identified SPRY4 as a likely novel candidate susceptibility gene for FNMTC, allowing a better understanding of the cellular and molecular mechanisms underlying thyroid cancer development.

Sprouty4 negatively regulates ERK/MAPK signaling and the transition from in situ to invasive breast ductal carcinoma

Breast ductal carcinoma in situ (DCIS) is a non-obligate precursor of invasive ductal carcinoma (IDC). It is still unclear which DCIS will become invasive and which will remain indolent. Patients often receive surgery and radiotherapy, but this early intervention has not produced substantial decreases in late-stage disease. Sprouty proteins are important regulators of ERK/MAPK signaling and have been studied in various cancers. We hypothesized that Sprouty4 is an endogenous inhibitor of ERK/MAPK signaling and that its loss/reduced expression is a mechanism by which DCIS lesions progress toward IDC, including triple-negative disease. Using immunohistochemistry, we found reduced Sprouty4 expression in IDC patient samples compared to DCIS, and that ERK/MAPK phosphorylation had an inverse relationship to Sprouty4 expression. These observations were reproduced using a 3D culture model of disease progression. Knockdown of Sprouty4 in MCF10.DCIS cells increased ERK/MAPK phosphorylation as well as their invasive capability, while overexpression of Sprouty4 in MCF10.CA1d IDC cells reduced ERK/MAPK phosphorylation, invasion, and the aggressive phenotype exhibited by these cells. Immunofluorescence experiments revealed reorganization of the actin cytoskeleton and relocation of E-cadherin back to the cell surface, consistent with the restoration of adherens junctions. To determine whether these effects were due to changes in ERK/MAPK signaling, MEK1/2 was pharmacologically inhibited in IDC cells. Nanomolar concentrations of MEK162/binimetinib restored an epithelial-like phenotype and reduced pericellular proteolysis, similar to Sprouty4 overexpression. From these data we conclude that Sprouty4 acts to control ERK/MAPK signaling in DCIS, thus limiting the progression of these premalignant breast lesions.

Circulating microRNA profile unveils mechanisms of action of acitretin for psoriasis vulgaris

Psoriasis vulgaris is a common chronic and recurrent inflammatory skin disease. In clinical practice, acitretin is the first-line treatment drug for psoriasis vulgaris. MicroRNAs (miRNAs) play a vital role in the initiation and development of psoriasis vulgaris. However few studies focused on the mechanisms of acitretin in the treatment of psoriasis vulgaris from the perspective of miRNAs. Here, the expression profiles of circulating miRNAs in the plasma of 12 patients with psoriasis vulgaris before and after acitretin treatment were sequenced. Three miRNAs (miR-146a-5p, miR-122-5p and miR-21-5p) were identified using expression pattern analysis, and the levels were significantly decreased after acitretin treatment (P< 0.001). Receiver operating characteristic (ROC) analyses indicated that the three miRNAs have the potential to be utilized as molecular markers to evaluate the therapeutic effect of acitretin, and the values of the area under the curve (AUC) were 0.825, 0.831, and 0.796, respectively. In addition, we predicted target genes of the three miRNAs and performed signaling pathway enrichment analyses. The results demonstrated that the target genes were mainly involved in the MAPK, JAK-STAT, and NF-κB signaling pathways, which were further validated through in vitro experiments. In conclusion, acitretin can suppress miRNA-mediated MAPK, JAK-STAT, and NF-κB signaling pathways by decreasing miRNAs expression, thereby inhibiting the proliferation and inflammatory response of keratinocytes.

Predicting tumor response to drugs based on gene-expression biomarkers of sensitivity learned from cancer cell lines

Background

Human cancer cell line profiling and drug sensitivity studies provide valuable information about the therapeutic potential of drugs and their possible mechanisms of action. The goal of those studies is to translate the findings from in vitro studies of cancer cell lines into in vivo therapeutic relevance and, eventually, patients’ care. Tremendous progress has been made.

Results

In this work, we built predictive models for 453 drugs using data on gene expression and drug sensitivity (IC₅₀) from cancer cell lines. We identified many known drug-gene interactions and uncovered several potentially novel drug-gene associations. Importantly, we further applied these predictive models to ~ 17,000 bulk RNA-seq samples from The Cancer Genome Atlas (TCGA) and the Genotype-Tissue Expression (GTEx) database to predict drug sensitivity for both normal and tumor tissues. We created a web site for users to visualize and download our predicted data (https://manticore.niehs.nih.gov/cancerRxTissue). Using trametinib as an example, we showed that our approach can faithfully recapitulate the known tumor specificity of the drug.

Conclusions

We demonstrated that our approach can predict drugs that 1) are tumor-type specific; 2) elicit higher sensitivity from tumor compared to corresponding normal tissue; 3) elicit differential sensitivity across breast cancer subtypes. If validated, our prediction could have relevance for preclinical drug testing and in phase I clinical design.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07581-7.

Sprouty2 positively regulates T cell function and airway inflammation through regulation of CSK and LCK kinases

The function of Sprouty2 (Spry2) in T cells is unknown. Using 2 different (inducible and T cell-targeted) knockout mouse strains, we found that Spry2 positively regulated extracellular signal-regulated kinase 1/2 (ERK1/2) signaling by modulating the activity of LCK. Spry2-/- CD4+ T cells were unable to activate LCK, proliferate, differentiate into T helper cells, or produce cytokines. Spry2 deficiency abrogated type 2 inflammation and airway hyperreactivity in a murine model of asthma. Spry2 expression was higher in blood and airway CD4+ T cells from patients with asthma, and Spry2 knockdown impaired human T cell proliferation and cytokine production. Spry2 deficiency up-regulated the lipid raft protein caveolin-1, enhanced its interaction with CSK, and increased CSK interaction with LCK, culminating in augmented inhibitory phosphorylation of LCK. Knockdown of CSK or dislodgment of caveolin-1-bound CSK restored ERK1/2 activation in Spry2-/- T cells, suggesting an essential role for Spry2 in LCK activation and T cell function.

The MEK/ERK Network as a Therapeutic Target in Human Cancer

The RAS-RAF-MEK-ERK pathway is the most well-studied of the MAPK cascades and is critical for cell proliferation, differentiation, and survival. Abnormalities in regulation resulting from mutations in components of this pathway, particularly in upstream proteins, RAS and RAF, are responsible for a significant fraction of human cancers and nearly all cutaneous melanomas. Activation of receptor tyrosine kinases by growth factors and various extracellular signals leads to the sequential activation of RAS, RAF, MEK, and finally ERK, which activates numerous transcription factors and facilitates oncogenesis in the case of aberrant pathway activation. While extensive studies have worked to elucidate the activation mechanisms and structural components of upstream MAPK components, comparatively less attention has been directed toward the kinases, MEK and ERK, due to the infrequency of oncogenic-activating mutations in these kinases. However, acquired drug resistance has become a major issue in the treatment of RAS- and RAF-mutated cancers. Targeting the terminal kinases in the MAPK cascade has shown promise for overcoming many of these resistance mechanisms and improving treatment options for patients with MAPK-aberrant cancers. Here, we will describe the role of MEK and ERK in MAPK signaling and summarize the current understanding of their interaction and activation mechanisms. We will also discuss existing approaches for targeting MEK and ERK, and the benefits of alternative strategies. Areas requiring further exploration will be highlighted to guide future research endeavors and aid in the development of alternative therapeutic strategies to combat surmounting drug resistance in treating MAPK-mediated cancers. VISUAL OVERVIEW: http://mcr.aacrjournals.org/content/molcanres/19/3/361/F1.large.jpg.

Sprouty2 limits intestinal tuft and goblet cell numbers through GSK3β-mediated restriction of epithelial IL-33

Dynamic regulation of intestinal cell differentiation is crucial for both homeostasis and the response to injury or inflammation. Sprouty2, an intracellular signaling regulator, controls pathways including PI3K and MAPKs that are implicated in differentiation and are dysregulated in inflammatory bowel disease. Here, we ask whether Sprouty2 controls secretory cell differentiation and the response to colitis. We report that colonic epithelial Sprouty2 deletion leads to expanded tuft and goblet cell populations. Sprouty2 loss induces PI3K/Akt signaling, leading to GSK3β inhibition and epithelial interleukin (IL)-33 expression. In vivo, this results in increased stromal IL-13+ cells. IL-13 in turn induces tuft and goblet cell expansion in vitro and in vivo. Sprouty2 is downregulated by acute inflammation; this appears to be a protective response, as VillinCre;Sprouty2^F/F mice are resistant to DSS colitis. In contrast, Sprouty2 is elevated in chronic colitis and in colons of inflammatory bowel disease patients, suggesting that this protective epithelial-stromal signaling mechanism is lost in disease.

Dynamic regulation of colonic secretory cell numbers is a critical component of the response to intestinal injury and inflammation. Here, the authors show that loss of the intracellular signalling regulator Sprouty2 in the intestinal epithelial cells is a protective response to injury that leads to increased secretory cell numbers, thus limiting colitis severity.

Overexpression of sprouty 1 protein in human oral squamous cell carcinogenesis

Abstract Background/purpose

Sprouty (SPRY) has four isoforms, SPRY1–4, and its deficiency produces haphazard ‘sprouting’ of tracheal tubules. This study investigated SPRY1 protein expression in human oral potentially malignant disorders (OPMDs) and oral squamous cell carcinomas (OSCCs).

Materials and methods

90 OSCCs, 10 OPMDs with malignant transformation (MT), 17 OPMDs without MT, and six normal oral mucosa (NOM) tissue samples were subjected to immunohistochemical staining. Three human oral cancer cell lines (OCCLs), an oral precancer cell line (DOK), and a primary culture of normal oral keratinocytes (HOK) were used for western blotting.

Results

Significantly increased expression of SPRY1 protein from NOM and OPMD without MT to OSCC was observed. The protein expressions of SPRY1 in OCCLs were significantly enhanced as compared with DOK and HOK. Increased phosphor/total-ERK expression was observed in OCCLs as compared with HOK. A significantly increased SPRY1 protein level was noted in OPMDs with MT as compared with those without MT, in addition to a significant increase in DOK in comparison with HOK.

Conclusion

Our results indicated that overexpression of SPRY1 protein is potentially associated with human oral squamous cell carcinogenesis.

Controlling TIME: How MNK Kinases Function to Shape Tumor Immunity

A number of studies have clearly established the oncogenic role for MAPK-interacting protein kinases (MNK) in human malignancies. Modulation of MNK activity affects translation of mRNAs involved in cancer development, progression, and resistance to therapies. As a result, there are ongoing efforts to develop and evaluate MNK inhibitors for cancer treatment. However, it is important to recognize that MNK activity also plays an important role in regulating the innate and adaptive immune systems. A better understanding of the role of MNK kinases and MNK-mediated signals in regulating the immune system could help mitigate undesired side effects while maximizing therapeutic efficacy of MNK inhibitors. Here, we provide a systematic review on the function of MNK kinases and their substrates in immune cells.

Peritoneal fibrosis and epigenetic modulation

Peritoneal dialysis (PD) is an effective treatment for patients with end-stage renal disease. However, peritoneal fibrosis (PF) is a common complication that ultimately leads to ultrafiltration failure and discontinuation of PD after long-term PD therapy. There is currently no effective therapy to prevent or delay this pathologic process. Recent studies have reported epigenetic modifications involved in PF, and accumulating evidence suggests that epigenetic therapies may have the potential to prevent and treat PF clinically. The major epigenetic modifications in PF include DNA methylation, histone modification, and noncoding RNAs. The mechanisms of epigenetic regulation in PF are complex, predominantly involving modification of signaling molecules, transcriptional factors, and genes. This review will describe the mechanisms of epigenetic modulation in PF and discuss the possibility of targeting them to prevent and treat this complication.

The pVHL neglected functions, a tale of hypoxia-dependent and -independent regulations in cancer

The von Hippel–Lindau protein (pVHL) is a tumour suppressor mainly known for its role as master regulator of hypoxia-inducible factor (HIF) activity. Functional inactivation of pVHL is causative of the von Hippel–Lindau disease, an inherited predisposition to develop different cancers. Due to its impact on human health, pVHL has been widely studied in the last few decades. However, investigations mostly focus on its role in degrading HIFs, whereas alternative pVHL protein–protein interactions and functions are insistently surfacing in the literature. In this review, we analyse these almost neglected functions by dissecting specific conditions in which pVHL is proposed to have differential roles in promoting cancer. We reviewed its role in regulating phosphorylation as a number of works suggest pVHL to act as an inhibitor by either degrading or promoting downregulation of specific kinases. Further, we summarize hypoxia-dependent and -independent pVHL interactions with multiple protein partners and discuss their implications in tumorigenesis.

Loss of Spry1 reduces growth of BRAFV600-mutant cutaneous melanoma and improves response to targeted therapy

Mitogen-activated protein kinase (MAPK) pathway activation is a central step in BRAF^V600-mutant cutaneous melanoma (CM) pathogenesis. In the last years, Spry1 has been frequently described as an upstream regulator of MAPK signaling pathway. However, its specific role in BRAF^V600-mutant CM is still poorly defined. Here, we report that Spry1 knockdown (Spry1^KO) in three BRAF^V600-mutant CM cell lines markedly induced cell cycle arrest and apoptosis, repressed cell proliferation in vitro, and impaired tumor growth in vivo. Furthermore, our findings indicated that Spry1^KO reduced the expression of several markers of epithelial–mesenchymal transition, such as MMP-2 both in vitro and in vivo. These effects were associated with a sustained and deleterious phosphorylation of ERK1/2. In addition, p38 activation along with an increase in basal ROS levels were found in Spry1^KO clones compared to parental CM cell lines, suggesting that BRAF^V600-mutant CM may restrain the activity of Spry1 to avoid oncogenic stress and to enable tumor growth. Consistent with this hypothesis, treatment with the BRAF inhibitor (BRAFi) vemurafenib down-regulated Spry1 levels in parental CM cell lines, indicating that Spry1 expression is sustained by the MAPK/ERK signaling pathway in a positive feedback loop that safeguards cells from the potentially toxic effects of ERK1/2 hyperactivation. Disruption of this feedback loop rendered Spry1^KO cells more susceptible to apoptosis and markedly improved response to BRAFi both in vitro and in vivo, as a consequence of the detrimental effect of ERK1/2 hyperactivation observed upon Spry1 abrogation. Therefore, targeting Spry1 might offer a treatment strategy for BRAF^V600-mutant CM by inducing the toxic effects of ERK-mediated signaling.

SPRY4 regulates trophoblast proliferation and apoptosis via regulating IFN-γ-induced STAT1 expression and activation in recurrent miscarriage

PROBLEM

The dysregulation of trophoblast functions is one of the leading causes of recurrent miscarriage (RM), which frustrates 1%-5% of couples of childbearing ages. Sprouty 4 (SPRY4) is considered as a tumour suppressor and exerts a negative role in cell viability. However, its role in regulating trophoblast behaviors at the maternal-fetal interface remains largely unknown.

METHOD OF STUDY

First-trimester villous samples were collected from RM patients and healthy controls (HCs) to determine the SPRY4 expression in human placenta during early pregnancy. The HTR8/SVneo cell line was introduced to clarify trophoblast cell functions via transfecting with specific short interfering RNA against SPRY4 or SPRY4-overexpressing lentivirus in vitro. In addition, gene expression microarray analysis was performed to explore the downstream molecules and pathways.

RESULTS

Our results revealed that SPRY4 expression was significantly increased in the first-trimester cytotrophoblasts of RM patients compared with HCs. Furthermore, SPRY4 overexpression inhibited trophoblast proliferation and accelerated apoptosis in vitro, while SPRY4 knockdown reversed these effects. Mechanistically, IFN-γ -induced STAT1 expression and activation were involved in the regulation of trophoblast proliferation and apoptosis by SPRY4, and IFN-γ promoted SPRY4 expression and STAT1 phosphorylation through PI3K/AKT pathway. Additionally, both STAT1 and phosphorylated STAT (p-STAT) levels were also upregulated in trophoblasts from RM patients and positively correlated with SPRY4 expression.

CONCLUSION

Our findings indicate that SPRY4 may act as a negative regulator of trophoblast functions through upregulating IFN-γ/PI3K/AKT-induced STAT1 activation. High levels of SPRY4 and STAT1 may contribute to RM development and progression, and blocking of either target could be a novel therapeutic strategy for RM patients.

Dominant-negative antagonists of the Ras-ERK pathway: DA-Raf and its related proteins generated by alternative splicing of Raf

The Ras-ERK pathway regulates a variety of cellular and physiological responses, including cell proliferation, differentiation, morphogenesis during animal development, and homeostasis in adults. Deregulated activation of this pathway leads to cellular transformation and tumorigenesis as well as RASopathies. Several negative regulators of this pathway have been documented. Each of these proteins acts at particular points of the pathway, and they exert specific cellular and physiological functions. Among them, DA-Raf1 (DA-Raf), which is a splicing isoform of A-Raf and contains the Ras-binding domain but lacks the kinase domain, antagonizes the Ras-ERK pathway in a dominant-negative manner. DA-Raf induces apoptosis, skeletal myocyte differentiation, lung alveolarization, and fulfills tumor suppressor functions by interfering with the Ras-ERK pathway. After the findings of DA-Raf, several kinase-domain-truncated splicing variants of Raf proteins have also been reported. The family of these truncated proteins represents the concept that alternative splicing can generate antagonistic proteins to their full-length counterparts.

Quantitative Phosphoproteomics Reveals System-Wide Phosphorylation Network Altered by Spry in Mouse Mammary Stromal Fibroblasts

Understanding the fundamental role of the stroma in normal development and cancer progression has been an emerging focus in recent years. The receptor tyrosine kinase (RTK) signaling pathway has been reported playing critical roles in regulating the normal and cancer microenvironment, but the underlying mechanism is still not very clear. By applying the quantitative phosphoproteomic analysis of Sprouty proteins (SPRYs), generic modulators of RTK signaling and deleted mouse mammary fibroblasts, we quantified a total of 11,215 unique phosphorylation sites. By contrast, 554 phosphorylation sites on 425 proteins had SPRY-responsive perturbations. Of these, 554 phosphosites, 362 sites on 277 proteins, were significantly increased, whereas 192 sites on 167 proteins were decreased. Among the regulated proteins, we identified 31 kinases, 7 phosphatases, and one phosphatase inhibitor that were not systematically characterized before. Furthermore, we reconstructed a phosphorylation network centered on RTK signaling regulated by SPRY. Collectively, this study uncovered a system-wide phosphorylation network regulated by SPRY, providing an additional insight into the complicated RTK signaling pathways involved in the mammary gland microenvironment.

CRISPR-Cas9-mediated knockout of SPRY2 in human hepatocytes leads to increased glucose uptake and lipid droplet accumulation

BACKGROUND

The prevalence of obesity and its comorbidities, including type 2 diabetes mellitus (T2DM), is dramatically increasing throughout the world; however, the underlying aetiology is incompletely understood. Genome-wide association studies (GWAS) have identified hundreds of genec susceptibility loci for obesity and T2DM, although the causal genes and mechanisms are largely unknown. SPRY2 is a candidate gene identified in GWAS of body fat percentage and T2DM, and has recently been linked to insulin production in pancreatic β-cells. In the present study, we aimed to further understand SPRY2 via functional characterisation in HepG2 cells, an in vitro model of human hepatocytes widely used to investigate T2DM and insulin resistance.

METHODS

CRISPR-Cas9 genome editing was used to target SPRY2 in HepG2 cells, and the functional consequences of SPRY2 knockout (KO) and overexpression subsequently assessed using glucose uptake and lipid droplet assays, measurement of protein kinase phosphorylation and RNA sequencing.

RESULTS

The major functional consequence of SPRY2 KO was a significant increase in glucose uptake, along with elevated lipid droplet accumulation. These changes were attenuated, but not reversed, in cells overexpressing SPRY2. Phosphorylation of protein kinases across key signalling pathways (including Akt and mitogen activated protein kinases) was not altered after SPRY2 KO. Transcriptome profiling in SPRY2 KO and mock (control) cells revealed a number of differentially expressed genes related to cholesterol biosynthesis, cell cycle regulation and cellular signalling pathways. Phospholipase A2 group IIA (PLA2G2A) mRNA level was subsequently validated as significantly upregulated following SPRY2 KO, highlighting this as a potential mediator downstream of SPRY2.

CONCLUSION

These findings suggest a role for SPRY2 in glucose and lipid metabolism in hepatocytes and contribute to clarifying the function of this gene in the context of metabolic diseases.

Sprouty2 enhances the tumorigenic potential of glioblastoma cells

Background

Sprouty2 (SPRY2), a feedback regulator of receptor tyrosine kinase (RTK) signaling, has been shown to be associated with drug resistance and cell proliferation in glioblastoma (GBM), but the underlying mechanisms are still poorly defined.

Methods

SPRY2 expression and survival patterns of patients with gliomas were analyzed using publicly available databases. Effects of RNA interference targeting SPRY2 on cellular proliferation in established GBM or patient-derived GBM stemlike cells were examined. Loss- or gain-of-function of SPRY2 to regulate the tumorigenic capacity was assessed in both intracranial and subcutaneous xenografts.

Results

SPRY2 was found to be upregulated in GBM, which correlated with reduced survival in GBM patients. SPRY2 knockdown significantly impaired proliferation of GBM cells but not of normal astrocytes. Silencing of SPRY2 increased epidermal growth factor-induced extracellular signal-regulated kinase (ERK) and Akt activation causing premature onset of DNA replication, increased DNA damage, and impaired proliferation, suggesting that SPRY2 suppresses DNA replication stress. Abrogating SPRY2 function strongly inhibited intracranial tumor growth and led to significantly prolonged survival of U87 xenograft-bearing mice. In contrast, SPRY2 overexpression promoted tumor propagation of low-tumorigenic U251 cells.

Conclusions

The present study highlights an antitumoral effect of SPRY2 inhibition that is based on excessive activation of ERK signaling and DNA damage response, resulting in reduced cell proliferation and increased cytotoxicity, proposing SPRY2 as a promising pharmacological target in GBM patients.

Reduced Expression of Sprouty1 Contributes to the Aberrant Proliferation and Impaired Apoptosis of Acute Myeloid Leukemia Cells

In most of the acute myeloid leukemia patients there is an aberrant tyrosine kinase activity. The prototype of Sprouty proteins was originally identified in Drosophila melanogaster as antagonists of Breathless, the mammalian ortholog of fibroblast growth factor receptor. Usually, SPRY family members are inhibitors of RAS signaling induced by tyrosine kinases receptors and they are implicated in negative feedback processes regulating several intracellular pathways. The present study aims to investigate the role of a member of the Sprouty family, Sprouty1, as a regulator of cell proliferation and growth in patients affected by acute myeloid leukemia. Sprouty1 mRNA and protein were both significantly down-regulated in acute myeloid leukemia cells compared to the normal counterpart, but they were restored when remission is achieved after chemotherapy. Ectopic expression of Sprouty1 revealed that it plays a key role in the proliferation and apoptotic defect that represent a landmark of the leukemic cells. Our study identified Sprouty1 as negative regulator involved in the aberrant signals of adult acute myeloid leukemia. Furthermore, we found a correlation between Sprouty1 and FoxO3a delocalization in acute myeloid leukemia (AML) patients at diagnosis, suggesting a multistep regulation of RAS signaling in human cancers.

Epigenetic programming underpins B cell dysfunction in human SLE

Systemic lupus erythematosus (SLE) is characterized by the expansion of extrafollicular pathogenic B cells derived from newly activated naïve cells. Although these cells express distinct markers, their epigenetic architecture and how it contributes to SLE remains poorly understood. To address this, we determined the DNA methylomes, chromatin accessibility and transcriptomes from five human B cell subsets, including a newly defined effector B cell subset from SLE and healthy subjects. Our data define a differentiation hierarchy between the subsets and elucidate the epigenetic and transcriptional differences between effector and memory B cells. Importantly, an SLE molecular signature was already established in resting naïve cells and was dominated by accessible chromatin enriched in AP-1 and EGR transcription factor motifs. Together, these factors acted in synergy with T-BET to shape the epigenome of expanded SLE effector B cell subsets. Thus, our data define the molecular foundation of pathogenic B cell dysfunction in SLE.

[Exploring the association between SPRY gene family and non-syndromic oral clefts among Chinese populations using data of a next-generation sequencing study]

OBJECTIVE

To explore the association between SPRY gene family and the risk of non-syndromic oral clefts among Chinese populations, in respect of single nucleotide polymorphisms (SNPs) association and parent-of-origin effects.

METHODS

Based on case-parent design, this study used the data of SPRY gene family in a next generation sequencing study of 183 non-syndromic cleft lip with or without cleft palate (NSCL/P) case-parent trios (549 participants) recruited from 2016 to 2018, to analyze the effects of SNP association and parent-of-origin. The sequencing study adopted a two-stage design. In the first stage, whole exome sequencing was conducted among 24 NSCL/P trios with family history to explore potential signals. Then in the second stage, another 159 NSCL/P trios were used as validation samples to verify the signals found in the first stage. The data of general information, disease features and parental environmental exposures for participants were collected through questionnaires. Blood samples were collected from each participant for DNA extraction and sequencing. Transmission disequilibrium tests (TDT) were conducted to test for the association between SNPs and NSCL/P, while Z score tests were applied to analyze parent-of-origin effects. The analyses were performed using Plink (v1.07). TRIO package in R (v3.5.1). Besides, famSKAT analyses were conducted in the first stage to combine the effect of SNPs located on the same gene, using famSKAT package in R(V3.5.1). Bonferroni method was adopted to correct multiple tests in the second stage.

RESULTS

Twenty-two SNPs in SPRY gene family were included for analyses after the quality control process in the first stage. Based on the variants annotation, functional prediction and statistical analysis, rs1298215244 (SPRY1) and rs504122 (SPRY2) were included in the second verification stage. TDTs in the verification stage revealed that rs1298215244: T>C, rs504122: G>C and rs504122: G>T were associated with the risk of NSCL/P after Bonferroni corrections, where rs504122: G>T was a rare variation. Although the test for parent-of-origin effect of rs1298215244: T>C reached nominal significance level, no SNP showed significant association with NSCL/P through parent-of-origin effect after Bonferroni corrections.

CONCLUSION

This study found that SNPs (including both common and rare variants) among the SPRY gene family were associated with the risk of NSCL/P among Chinese populations. This study failed to detect parent-of-origin effects among the SPRY gene family.

Spatial signal repression as an additional role of Sprouty2 protein variants

Sprouty2 (Spry2) is a prominent member of a protein family with crucial functions in the modulation of signal transduction. One of its main actions is the repression of mitogen-activated protein kinase (MAPK) pathway in response to growth factor-induced signalling. A common single nucleotide polymorphism within the Spry2 gene creates two protein variants where a proline adjacent to the serine rich domain is converted to an additional serine. Both protein variants perform similar functions although their efficiency in fulfilling these tasks varies. In this report, we used biochemical fractionation methods as well as confocal microscopy to analyse quantitative and qualitative differences in the distribution of Spry2 variants. We found that Spry2 proteins localize not solely to the plasma membrane, but also to other membrane engulfed compartments like for example the Golgi apparatus. In these less dense organelles, predominantly slower migrating forms reside indicating that posttranslational modification contributes to the distribution profile of Spry2. However there is no significant difference in the distribution of the two variants. Additionally, we found that Spry2 could be found exclusively in membrane fractions irrespective of the mitogen availability and the phosphorylation status. Considering the interference of extracellular signal-regulated kinase (ERK) activation in the cytoplasm, both Spry2 variants inhibited the levels of phosphorylated ERK (pERK) significantly to a similar extent. In contrast, the induction profiles of pERK levels were completely different in the nuclei. Again, both Spry2 variants diminished the levels of pERK. While the proline variant lowered the activation throughout the observation period, the serine variant failed to interfere with immediate accumulation of nuclear pERK levels, but the signal duration was shortened. Since the extent of the pERK inhibition in the nuclei was drastically more pronounced than in the cytoplasm, we conclude that Spry2 - in addition to its known functions as a repressor of general ERK phosphorylation - functions as a spatial repressor of nucleic ERK activation. Accordingly, a dominant negative version of Spry2 was only able to enhance the pERK levels of serum-deprived cells in the cytosol, while in the nucleus the intensity of the pERK signal in response to serum addition was significantly increased.

Regulators of the RAS-ERK pathway as therapeutic targets in thyroid cancer

Thyroid cancer is mostly an ERK-driven carcinoma, as up to 70% of thyroid carcinomas are caused by mutations that activate the RAS/ERK mitogenic signaling pathway. The incidence of thyroid cancer has been steadily increasing for the last four decades; yet, there is still no effective treatment for advanced thyroid carcinomas. Current research efforts are focused on impairing ERK signaling with small-molecule inhibitors, mainly at the level of BRAF and MEK. However, despite initial promising results in animal models, the clinical success of these inhibitors has been limited by the emergence of tumor resistance and relapse. The RAS/ERK pathway is an extremely complex signaling cascade with multiple points of control, offering many potential therapeutic targets: from the modulatory proteins regulating the activation state of RAS proteins to the scaffolding proteins of the pathway that provide spatial specificity to the signals, and finally, the negative feedbacks and phosphatases responsible for inactivating the pathway. The aim of this review is to give an overview of the biology of RAS/ERK regulators in human cancer highlighting relevant information on thyroid cancer and future areas of research.

Spred2 Regulates High Fat Diet-Induced Adipose Tissue Inflammation, and Metabolic Abnormalities in Mice

Chronic low-grade inflammation in visceral adipose tissues triggers the development of obesity-related insulin resistance, leading to the metabolic syndrome, a serious health condition with higher risk of cardiovascular disease, diabetes, and stroke. In the present study, we investigated whether Sprouty-related EVH1-domain-containing protein 2 (Spred2), a negative regulator of the Ras/Raf/ERK/MAPK pathway, plays a role in the development of high fat diet (HFD)-induced obesity, adipose tissue inflammation, metabolic abnormalities, and insulin resistance. Spred2 knockout (KO) mice, fed with HFD, exhibited an augmented body weight gain, which was associated with enhanced adipocyte hypertrophy in mesenteric white adipose tissue (mWAT) and deteriorated dyslipidemia, compared with wild-type (WT) controls. The number of infiltrating macrophages with a M1 phenotype, and the crown-like structures, composed of macrophages surrounding dead or dying adipocytes, were more abundant in Spred2 KO-mWAT compared to in WT-mWAT. Exacerbated adipose tissue inflammation in Spred2 KO mice led to aggravated insulin resistance and fatty liver disease. To analyze the mechanism(s) that caused adipose tissue inflammation, cytokine response in mWAT was investigated. Stromal vascular fraction that contained macrophages from Spred2 KO-mWAT showed elevated levels of tumor necrosis factor α (TNFα) and monocyte chemoattractant protein-1 (MCP-1/CCL2) compared with those from WT-mWAT. Upon stimulation with palmitate acid (PA), bone marrow-derived macrophages (BMDMs) derived from Spred2 KO mice secreted higher levels of TNFα and MCP-1 than those from WT mice with enhanced ERK activation. U0126, a MEK inhibitor, reduced the PA-induced cytokine response. Taken together, these results suggested that Spred2, in macrophages, negatively regulates high fat diet-induced obesity, adipose tissue inflammation, metabolic abnormalities, and insulin resistance by inhibiting the ERK/MAPK pathway. Thus, Spred2 represents a potential therapeutic tool for the prevention of insulin resistance and resultant metabolic syndrome.

Sprouty1 regulates neuritogenesis and survival of cortical neurons

In multicellular organisms, receptor tyrosine kinases (RTKs) control a variety of cellular processes, including cell proliferation, differentiation, migration, and survival. Sprouty (SPRY) proteins represent an important class of ligand-inducible inhibitors of RTK-dependent signaling pathways. Here, we investigated the role of SPRY1 in cells of the central nervous system (CNS). Expression of SPRY1 was substantially higher in neural stem cells than in cortical neurons and was increased during neuronal differentiation of cortical neurons. We found that SPRY1 was a direct target gene of the CNS-specific microRNA, miR-124 and miR-132. In primary cultures of cortical neurons, the neurotrophic factors brain-derived neurotrophic factor (BDNF) and Basic fibroblast growth factor (FGF2) downregulated SPRY1 expression to positively regulate their own functions. In immature cortical neurons and mouse N₂ A cells, we found that overexpression of SPRY1 inhibited neurite development, whereas knockdown of SPRY1 expression promoted neurite development. In mature neurons, overexpression of SPRY1 inhibited the prosurvival effects of both BDNF and FGF2 on glutamate-mediated neuronal cell death. SPRY1 was also upregulated upon glutamate treatment in mature neurons and partially contributed to the cytotoxic effect of glutamate. Together, our results indicate that SPRY1 contributes to the regulation of CNS functions by influencing both neuronal differentiation under normal physiological processes and neuronal survival under pathological conditions.

Gene Expression Signatures Point to a Male Sex-Specific Lung Mesenchymal Cell PDGF Receptor Signaling Defect in Infants Developing Bronchopulmonary Dysplasia

Male sex is a risk factor for development of bronchopulmonary dysplasia (BPD), a common chronic lung disease following preterm birth. We previously found that tracheal aspirate mesenchymal stromal cells (MSCs) from premature infants developing BPD show reduced expression of PDGFRα, which is required for normal lung development. We hypothesized that MSCs from male infants developing BPD exhibit a pathologic gene expression profile deficient in PDGFR and its downstream effectors, thereby favoring delayed lung development. In a discovery cohort of 6 male and 7 female premature infants, we analyzed the tracheal aspirate MSCs transcriptome. A unique gene signature distinguished MSCs from male infants developing BPD from all other MSCs. Genes involved in lung development, PDGF signaling and extracellular matrix remodeling were differentially expressed. We sought to confirm these findings in a second cohort of 13 male and 12 female premature infants. mRNA expression of PDGFRA, FGF7, WNT2, SPRY1, MMP3 and FOXF2 were significantly lower in MSCs from male infants developing BPD. In female infants developing BPD, tracheal aspirate levels of proinflammatory CCL2 and profibrotic Galectin-1 were higher compared to male infants developing BPD and female not developing BPD. Our findings support a notion for sex-specific differences in the mechanisms of BPD development.

Disproportionately high levels of HGF induce the degradation of the c-met receptor through the proteasomal degradation pathway

Hepatocyte growth factor (HGF) receptor is a member of the receptor tyrosine kinases (RTKs) and has been reported to perform diverse functions in various cell types during both the developmental and adult stages. Among different roles, HGF is best known for its angiogenic effects of inducing the migration of endothelial cells. Because angiogenesis is one of the prerequisite steps for tumor metastasis, HGF-dependent cell migration has to be tightly controlled. However, the underlying mechanisms regulating the optimum level of HGF/c-met signaling have been poorly understood. In this study, we tested whether the migration of endothelial cells is regulated by a negative feedback mechanism under disproportionately large amounts of HGF. Data from endothelial cell migration assays showed that HGF activity increased as its concentration increased, but declined beyond a certain point. Under limiting conditions, amounts of phosphorylated Erk and Akt surged, reaching a plateau in which the enhanced level was more or less maintained. The c-met receptor was degraded when unnecessarily large amounts of HGF were present. Under these conditions, HGF could no longer activate downstream signaling pathways even if cells were re-treated with optimal amounts of HGF. Excessive doses of HGF increased the phosphorylation of tyrosine residue 1003 involved in the ubiquitination of c-met, and phosphorylated c-met was diverted toward the proteasomal degradation pathway. Taken together, HGF/c-met signaling is tightly regulated by a negative feedback loop through an ubiquitin-proteasomal degradation pathway.

Spred negatively regulates lens growth by modulating epithelial cell proliferation and fiber differentiation

Spred, like Sprouty (Spry) and also Sef proteins, have been identified as important regulators of receptor tyrosine kinase (RTK)-mediated MAPK/ERK-signaling in various developmental systems, controlling cellular processes such as proliferation, migration and differentiation. Spreds are widely expressed during early embryogenesis, and in the eye lens, become more localised in the lens epithelium with later development, overlapping with other antagonists including Spry. Given the synexpression of Spreds and Spry in lens, in order to gain a better understanding of their specific roles in regulating growth factor mediated-signaling and cell behavior, we established and characterised lines of transgenic mice overexpressing Spred1 or Spred2, specifically in the lens. This overexpression of Spreds resulted in a small lens phenotype during ocular morphogenesis, retarding its growth by compromising epithelial cell proliferation and fiber differentiation. These in situ findings were shown to be dependent on the ability of Spreds to suppress MAPK-signaling, in particular FGF-induced ERK1/2-signaling in lens cells. This was validated in vitro using lens epithelial explants, that highlighted the overlapping role of Spreds with Spry2, but not Spry1. This study provides insights into the putative function of Spreds and Spry in situ, some overlapping and some distinct, and their importance in regulating lens cell proliferation and fiber differentiation contributing to lens and eye growth.

Gene-Gene Interactions among SPRYs for Nonsyndromic Cleft Lip/Palate

Nonsyndromic cleft lip with or without cleft palate (NSCL/P) is a common birth defect with a complex genetic architecture. Gene-gene interactions have been increasingly regarded as contributing to the etiology of NSCL/P. A recent genome-wide association study revealed that a novel single-nucleotide polymorphism at SPRY1 in 4q28.1 showed a significant association with NSCL/P. In the current study, we explored the role of 3 SPRY genes in the etiology of NSCL/P by detecting gene-gene interactions: SPRY1, SPRY2, and SPRY4-with SPRY3 excluded due to its special location on the X chromosome. We selected markers in 3 SPRY genes to test for gene-gene interactions using 1,908 case-parent trios recruited from an international consortium established for a genome-wide association study of nonsyndromic oral clefts. As the trios came from populations with different ancestries, subgroup analyses were conducted among Europeans and Asians. Cordell's method based on conditional logistic regression models was applied to test for potential gene-gene interactions via the statistical package TRIO in R software. Gene-gene interaction analyses yielded 10 pairs of SNPs in Europeans and 6 pairs in Asians that achieved significance after Bonferroni correction. The significant interactions were confirmed in the 10,000-permutation tests (empirical P = 0.003 for the most significant interaction). The study identified gene-gene interactions among SPRY genes among 1,908 NSCL/P trios, which revealed the importance of potential gene-gene interactions for understanding the genetic architecture of NSCL/P. The evidence of gene-gene interactions in this study also provided clues for future biological studies to further investigate the mechanism of how SPRY genes participate in the development of NSCL/P.

Sprouty2-a Novel Therapeutic Target in the Nervous System?

Clinical trials applying growth factors to alleviate symptoms of patients with neurological disorders have largely been unsuccessful in the past. As an alternative approach, growth factor receptors or components of their signal transduction machinery may be targeted directly. In recent years, the search for intracellular signaling integrator downstream of receptor tyrosine kinases provided valuable novel substrates. Among them are the Sprouty proteins which mainly act as inhibitors of growth factor-dependent neuronal and glial signaling pathways. In this review, we summarize the role of Sprouties in the lesioned central and peripheral nervous system with particular reference to Sprouty2 that is upregulated in various experimental models of neuronal degeneration and regeneration. Increased synthesis under pathological conditions makes Sprouty2 an attractive pharmacological target to enhance intracellular signaling activities, notably the ERK pathway, in affected neurons or activated astrocytes. Interestingly, high Sprouty2 levels are also found in malignant glioma cells. We recently demonstrated that abrogating Sprouty2 function strongly inhibits intracranial tumor growth and leads to significantly prolonged survival of glioblastoma bearing mice by induction of ERK-dependent DNA replication stress. On the contrary, knockdown of Sprouty proteins increases proliferation of activated astrocytes and, consequently, reduces secondary brain damage in neuronal lesion models such as kainic acid-induced epilepsy or endothelin-induced ischemia. Furthermore, downregulation of Sprouty2 improves nerve regeneration in the lesioned peripheral nervous system. Taken together, targeting Sprouties as intracellular inhibitors of the ERK pathway holds great promise for the treatment of various neurological disorders including gliomas. Since the protein lacks enzymatic activities, it will be difficult to develop chemical compounds capable to directly and specifically modulate Sprouty functions. However, interfering with Sprouty expression by gene therapy or siRNA treatment provides a realistic approach to evaluate the therapeutic potential of indirectly stimulating ERK activities in neurological disease.

Lack of Sprouty 1 and 2 enhances survival of effector CD8+ T cells and yields more protective memory cells

Identifying novel pathways that promote robust function and longevity of cytotoxic T cells has promising potential for immunotherapeutic strategies to combat cancer and chronic infections. We show that sprouty 1 and 2 (Spry1/2) molecules regulate the survival and function of memory CD8⁺ T cells. Spry1/2 double-knockout (DKO) ovalbumin (OVA)-specific CD8⁺ T cells (OT-I cells) mounted more vigorous autoimmune diabetes than WT OT-I cells when transferred to mice expressing OVA in their pancreatic β-islets. To determine the consequence of Spry1/2 deletion on effector and memory CD8⁺ T cell development and function, we used systemic infection with lymphocytic choriomeningitis virus (LCMV) Armstrong. Spry1/2 DKO LCMV gp33-specific P14 CD8⁺ T cells survive contraction better than WT cells and generate significantly more polyfunctional memory T cells. The larger number of Spry1/2 DKO memory T cells displayed enhanced infiltration into infected tissue, demonstrating that absence of Spry1/2 can result in increased recall capacity. Upon adoptive transfer into naive hosts, Spry1/2 DKO memory T cells controlled Listeria monocytogenes infection better than WT cells. The enhanced formation of more functional Spry1/2 DKO memory T cells was associated with significantly reduced mTORC1 activity and glucose uptake. Reduced p-AKT, p-FoxO1/3a, and T-bet expression was also consistent with enhanced survival and memory accrual. Collectively, loss of Spry1/2 enhances the survival of effector CD8⁺ T cells and results in the formation of more protective memory cells. Deleting Spry1/2 in antigen-specific CD8⁺ T cells may have therapeutic potential for enhancing the survival and functionality of effector and memory CD8⁺ T cells in vivo.

A Sprouty4 reporter to monitor FGF/ERK signaling activity in ESCs and mice

The FGF/ERK signaling pathway is highly conserved throughout evolution and plays fundamental roles during embryonic development and in adult organisms. While a plethora of expression data exists for ligands, receptors and pathway regulators, we know little about the spatial organization or dynamics of signaling in individual cells within populations. To this end we developed a transcriptional readout of FGF/ERK activity by targeting a histone H2B-linked Venus fluorophore to the endogenous locus of Spry4, an early pathway target, and generated Spry4^H2B-Venus embryonic stem cells (ESCs) and a derivative mouse line. The Spry4^H2B-Venus reporter was heterogeneously expressed within ESC cultures and responded to FGF/ERK signaling manipulation. In vivo, the Spry4^H2B-Venus reporter recapitulated the expression pattern of Spry4 and localized to sites of known FGF/ERK activity including the inner cell mass of the pre-implantation embryo and the limb buds, somites and isthmus of the post-implantation embryo. Additionally, we observed highly localized reporter expression within adult organs. Genetic and chemical disruption of FGF/ERK signaling, in vivo in pre- and post-implantation embryos, abrogated Venus expression establishing the reporter as an accurate signaling readout. This tool will provide new insights into the dynamics of the FGF/ERK signaling pathway during mammalian development.

Negative regulation of lens fiber cell differentiation by RTK antagonists Spry and Spred

Sprouty (Spry) and Spred proteins have been identified as closely related negative regulators of the receptor tyrosine kinase (RTK)-mediated MAPK pathway, inhibiting cellular proliferation, migration and differentiation in many systems. As the different members of this antagonist family are strongly expressed in the lens epithelium in overlapping patterns, in this study we used lens epithelial explants to examine the impact of these different antagonists on the morphologic and molecular changes associated with fibroblast growth factor (FGF)-induced lens fiber differentiation. Cells in lens epithelial explants were transfected using different approaches to overexpress the different Spry (Spry1, Spry2) and Spred (Spred1, Spred2, Spred3) members, and we compared their ability to undergo FGF-induced fiber differentiation. In cells overexpressing any of the antagonists, the propensity for FGF-induced cell elongation was significantly reduced, indicative of a block to lens fiber differentiation. Of these antagonists, Spry1 and Spred2 appeared to be the most potent among their respective family members, demonstrating the greatest block in FGF-induced fiber differentiation based on the percentage of cells that failed to elongate. Consistent with the reported activity of Spry and Spred, we show that overexpression of Spry2 was able to suppress FGF-induced ERK1/2 phosphorylation in lens cells, as well as the ERK1/2-dependent fiber-specific marker Prox1, but not the accumulation of β-crystallins. Taken together, Spry and Spred proteins that are predominantly expressed in the lens epithelium in situ, appear to have overlapping effects on negatively regulating ERK1/2-signaling associated with FGF-induced lens epithelial cell elongation leading to fiber differentiation. This highlights the important regulatory role for these RTK antagonists in establishing and maintaining the distinct architecture and polarity of the lens.

New insights into RAS biology reinvigorate interest in mathematical modeling of RAS signaling

RAS is the most frequently mutated gene across human cancers, but developing inhibitors of mutant RAS has proven to be challenging. Given the difficulties of targeting RAS directly, drugs that impact the other components of pathways where mutant RAS operates may potentially be effective. However, the system-level features, including different localizations of RAS isoforms, competition between downstream effectors, and interlocking feedback and feed-forward loops, must be understood to fully grasp the opportunities and limitations of inhibiting specific targets. Mathematical modeling can help us discern the system-level impacts of these features in normal and cancer cells. New technologies enable the acquisition of experimental data that will facilitate development of realistic models of oncogenic RAS behavior. In light of the wealth of empirical data accumulated over decades of study and the advancement of experimental methods for gathering new data, modelers now have the opportunity to advance progress toward realization of targeted treatment for mutant RAS-driven cancers.

Overexpression of sprouty2 in human oral squamous cell carcinogenesis

OBJECTIVE

This study investigated SPRY2 expression in human oral potentially malignant disorders (OPMDs) and oral squamous cell carcinomas (OSCCs).

METHODS

75 OSCCs, 23 OPMDs with malignant transformation (MT), 17 OPMDs without MT, and eight normal oral mucosa (NOM) tissues were used for immunohistochemical staining; three OSCC tissues with normal tissue counterparts were used for western blotting. Three human oral cancer cell lines (OCCLs), an oral precancer cell line (DOK), and a NOM primary culture (NOMPC) were used for western blotting; OCCLs and NOMPC were employed for real-time quantitative reverse transcription-polymerase chain reaction. OCCLs were evaluated in terms of proliferation, migration, invasion and BRAF V600E point mutation assays.

RESULTS

Significantly increased SPRY2 protein expression was observed in OSCCs as compared with NOM, and SPRY2 expression also differed between OSCC patients with and without lymph-node metastasis. SPRY2 protein and mRNA expressions were significantly enhanced as compared with NOMPC. Increased phospho-ERK expression was observed in OCCLs as compared with NOMPC. Significant decreases in the proliferation rate, degrees of migration and invasion were noted in OCCLs with SPRY2 siRNA transfection as compared with those without SPRY2 siRNA transfection. No BRAF V600E point mutation was observed for OCCLs as compared with NOMPC. A significantly increased SPRY2 protein level was noted in OPMDs with MT as compared to those without MT, and was also found in OPMDs with MT in comparison with NOM, as well as in DOK in comparison with NOMPC.

CONCLUSIONS

Our results indicated that SPRY2 overexpression is associated with human oral squamous-cell carcinogenesis.

Muscle Stem Cells and Aging

Satellite cells (SCs) are a population of muscle-resident stem cells that are essential for efficient tissue repair. SCs reside in a relatively quiescent state during normal tissue turnover, but are activated in response to injury through the microenvironment and cell-intrinsic signals. During aging, SC dysfunction is a major contributor to the decline in regenerative potential of muscle tissue. Recent studies have demonstrated that both cell-intrinsic and cell-extrinsic factors are deregulated during aging. Interventions that reverse age-associated changes in SCs or the niche have shown to partially rejuvenate the regenerative capacity of aged muscle SCs. In this review, we discuss recent advances in SC biology as it pertains to the deleterious effects of aging. A better understanding of how age-dependent changes in the SC and its environment niche impact muscle regeneration could lead to interventions to ameliorate the effects of aging in humans.

Negative Regulation of Receptor Tyrosine Kinase (RTK) Signaling: A Developing Field

Trophic factors control cellular physiology by activating specific receptor tyrosine kinases (RTKs). While the over activation of RTK signaling pathways is associated with cell growth and cancer, recent findings support the concept that impaired down-regulation or deactivation of RTKs may also be a mechanism involved in tumor formation. Under this perspective, the molecular determinants of RTK signaling inhibition may act as tumor-suppressor genes and have a potential role as tumor markers to monitor and predict disease progression. Here, we review the current understanding of the physiological mechanisms that attenuate RTK signaling and discuss evidence that implicates deregulation of these events in cancer.

The receptor protein tyrosine phosphatase PTPRB negatively regulates FGF2-dependent branching morphogenesis

PTPRB is a transmembrane protein tyrosine phosphatase known to regulate blood vessel remodelling and angiogenesis. Here, we demonstrate that PTPRB negatively regulates branching morphogenesis in the mouse mammary epithelium. We show that Ptprb is highly expressed in adult mammary stem cells and also, although at lower levels, in oestrogen receptor-positive luminal cells. During mammary development, Ptprb expression is downregulated during puberty, a period of extensive ductal outgrowth and branching. In vivo shRNA knockdown of Ptprb in the cleared mammary fat pad transplant assay resulted in smaller epithelial outgrowths with an increased branching density and also increased branching in an in vitro organoid assay. Organoid branching was dependent on stimulation by FGF2, and Ptprb knockdown in mammary epithelial cells resulted in a higher level of fibroblast growth factor receptor (FGFR) activation and ERK1/2 phosphorylation, both at baseline and following FGF2 stimulation. Therefore, PTPRB regulates branching morphogenesis in the mammary epithelium by modulating the response of the FGFR signalling pathway to FGF stimulation. Considering the importance of branching morphogenesis in multiple taxa, our findings have general importance outside mammary developmental biology.

IL-22-induced miR-122-5p promotes keratinocyte proliferation by targeting Sprouty2

Psoriasis is a common inflammatory skin disease, but the exact pathogenesis is largely unknown. Interleukin-22 (IL-22) has demonstrated its vital role in T-cell-mediated immune response by interacting with keratinocytes in the pathogenesis of psoriasis. Here, we showed the differentially expressed miRNAs and their potential targets in HaCaT cells stimulated by IL-22 using miRNA and mRNA microarrays. We revealed a total of 20 significantly changed (more than twofold) miRNAs in HaCaT cells and validated the results with quantitative reverse transcriptase PCR (qRT-PCR). We demonstrated that miR-122-5p was up-regulated both in HaCaT cells stimulated by IL-22 and in psoriatic lesions. Then, we aimed to investigate the biological roles and potential mechanism of miR-122-5p in keratinocytes. As a result, CCK-8 assay indicated that overexpression of miR-122-5p in keratinocytes promoted proliferation and conversely inhibition of endogenous miR-122-5p suppressed proliferation. According to the microarray analysis, we assumed that Sprouty2 (Spry2), a negative regulator of extracellular signal regulated kinase/mitogen-activated protein kinase signalling pathway, was a direct target gene of miR-122-5p. We found that the staining of Spry2 in cytoplasm was mainly localized in both basal and suprabasal layers of epidermis and showed a markedly decreased expression in psoriasis than in normal control by immunohistochemistry. Luciferase reporter and Western blot assays in HaCaT cells demonstrated that Spry2 was a direct target gene of miR-122-5p. In conclusion, IL-22-induced miR-122-5p promotes keratinocyte proliferation possibly by downregulating the expression of Spry2 thus playing important roles in the pathogenesis of psoriasis.

MiR-122 promotes renal cancer cell proliferation by targeting Sprouty2

MicroRNAs are short non-coding RNAs, which have been implicated in several biological processes. Aberrant expression of the microRNA miR-122 has frequently been reported in malignant cancers. However, the mechanism underlying the effects of miR-122 in renal cell carcinoma remains unknown. The aim of this study was to determine the biological function of miR-122 in renal cell carcinoma and to identify a novel molecular target regulated by miR-122. We measured the expression levels of Sprouty2 in six renal cell carcinoma tissue samples and adjacent non-tumor tissues by western blot analysis. We then used reverse transcription polymerase chain reaction to measure miR-122 levels in 40 primary renal cell carcinoma and adjacent non-malignant tissue samples. The effects of miR-122 down-regulation or Sprouty2 knockdown were evaluated via Cell Counting Kit-8 assay, flow cytometry, and western blot analysis. The relationship between miR-122 and Sprouty2 was determined using dual-luciferase reporter assays. Sprouty2 was down-regulated in renal cell carcinoma tissue samples compared with adjacent normal tissue. In contrast, miR-122 was up-regulated in primary renal cell carcinoma tissue samples compared with adjacent normal tissue samples. Down-regulation of miR-122 substantially weakened the proliferative ability of renal cell carcinoma cell lines in vitro. In contrast, Sprouty2 knockdown promoted the in vitro proliferation of renal cell carcinoma cell lines. The spry2 gene could therefore be a direct target of miR-122. In conclusion, miR-122 could act as a tumor promoter and potentially target Sprouty2. MiR-122 promotes renal cell carcinoma cell proliferation, migration, and invasion and could be a molecular target in novel therapies for renal cell carcinoma.

Hypoxia inducible factors regulate the transcription of the sprouty2 gene and expression of the sprouty2 protein

Receptor Tyrosine Kinase (RTK) signaling plays a major role in tumorigenesis and normal development. Sprouty2 (Spry2) attenuates RTK signaling and inhibits processes such as angiogenesis, cell proliferation, migration and survival, which are all upregulated in tumors. Indeed in cancers of the liver, lung, prostate and breast, Spry2 protein levels are markedly decreased correlating with poor patient prognosis and shorter survival. Thus, it is important to understand how expression of Spry2 is regulated. While prior studies have focused on the post-translation regulation of Spry2, very few studies have focused on the transcriptional regulation of SPRY2 gene. Here, we demonstrate that in the human hepatoma cell line, Hep3B, the transcription of SPRY2 is inhibited by the transcription regulating hypoxia inducible factors (HIFs). HIFs are composed of an oxygen regulated alpha subunit (HIF1α or HIF2α) and a beta subunit (HIF1β). Intriguingly, silencing of HIF1α and HIF2α elevates SPRY2 mRNA and protein levels suggesting HIFs reduce the transcription of the SPRY2 promoter. In silico analysis identified ten hypoxia response elements (HREs) in the proximal promoter and first intron of SPRY2. Using chromatin immunoprecipitation (ChIP), we show that HIF1α/2α bind near the putative HREs in the proximal promoter and intron of SPRY2. Our studies demonstrated that not only is the SPRY2 promoter methylated, but silencing HIF1α/2α reduced the methylation. ChIP assays also showed DNA methyltransferase1 (DNMT1) binding to the proximal promoter and first intron of SPRY2 and silencing HIF1α/2α decreased this association. Additionally, silencing of DNMT1 mimicked the HIF1α/2α silencing-mediated increase in SPRY2 mRNA and protein. While simultaneous silencing of HIF1α/2α and DNMT1 increased SPRY2 mRNA a little more, the increase was not additive suggesting a common mechanism by which DNMT1 and HIF1α/2α regulate SPRY2 transcription. Together these data suggest that the transcription of SPRY2 is inhibited by HIFs, in part, via DNMT1- mediated methylation.

Neurotrophin Promotes Neurite Outgrowth by Inhibiting Rif GTPase Activation Downstream of MAPKs and PI3K Signaling

Members of the well-known semaphorin family of proteins can induce both repulsive and attractive signaling in neural network formation and their cytoskeletal effects are mediated in part by small guanosine 5'-triphosphatase (GTPases). The aim of this study was to investigate the cellular role of Rif GTPase in the neurotrophin-induced neurite outgrowth. By using PC12 cells which are known to cease dividing and begin to show neurite outgrowth responding to nerve growth factor (NGF), we found that semaphorin 6A was as effective as nerve growth factor at stimulating neurite outgrowth in PC12 cells, and that its neurotrophic effect was transmitted through signaling by mitogen-activated protein kinases (MAPKs) and phosphatidylinositol-3-kinase (PI3K). We further found that neurotrophin-induced neurite formation in PC12 cells could be partially mediated by inhibition of Rif GTPase activity downstream of MAPKs and PI3K signaling. In conclusion, we newly identified Rif as a regulator of the cytoskeletal rearrangement mediated by semaphorins.

Reverse Pathway Genetic Approach Identifies Epistasis in Autism Spectrum Disorders

Although gene-gene interaction, or epistasis, plays a large role in complex traits in model organisms, genome-wide by genome-wide searches for two-way interaction have limited power in human studies. We thus used knowledge of a biological pathway in order to identify a contribution of epistasis to autism spectrum disorders (ASDs) in humans, a reverse-pathway genetic approach. Based on previous observation of increased ASD symptoms in Mendelian disorders of the Ras/MAPK pathway (RASopathies), we showed that common SNPs in RASopathy genes show enrichment for association signal in GWAS (P = 0.02). We then screened genome-wide for interactors with RASopathy gene SNPs and showed strong enrichment in ASD-affected individuals (P < 2.2 x 10-16), with a number of pairwise interactions meeting genome-wide criteria for significance. Finally, we utilized quantitative measures of ASD symptoms in RASopathy-affected individuals to perform modifier mapping via GWAS. One top region overlapped between these independent approaches, and we showed dysregulation of a gene in this region, GPR141, in a RASopathy neural cell line. We thus used orthogonal approaches to provide strong evidence for a contribution of epistasis to ASDs, confirm a role for the Ras/MAPK pathway in idiopathic ASDs, and to identify a convergent candidate gene that may interact with the Ras/MAPK pathway.

How Genetics Has Helped Piece Together the MAPK Signaling Pathway

Cells respond to changes in their environment, to developmental cues, and to pathogen aggression through the action of a complex network of proteins. These networks can be decomposed into a multitude of signaling pathways that relay signals from the microenvironment to the cellular components involved in eliciting a specific response. Perturbations in these signaling processes are at the root of multiple pathologies, the most notable of these being cancer. The study of receptor tyrosine kinase (RTK) signaling led to the first description of a mechanism whereby an extracellular signal is transmitted to the nucleus to induce a transcriptional response. Genetic studies conducted in drosophila and nematodes have provided key elements to this puzzle. Here, we briefly discuss the somewhat lesser known contribution of these multicellular organisms to our understanding of what has come to be known as the prototype of signaling pathways. We also discuss the ostensibly much larger network of regulators that has emerged from recent functional genomic investigations of RTK/RAS/ERK signaling.

Anacardic acid inhibits gelatinases through the regulation of Spry2, MMP-14, EMMPRIN and RECK

Earlier studies from our laboratory have identified Anacardic acid (AA) as a potent inhibitor of gelatinases (MMP-2 and 9), which are over-expressed in a wide variety of cancers (Omanakuttan et al., 2012). Disruption of the finely tuned matrix metalloproteinase (MMP) activator/inhibitor balance plays a decisive role in determining the fate of the cell. The present study demonstrates for the first time, that in addition to regulating the expression as well as activity of gelatinases, AA also inhibits the expression of its endogenous activators like MMP-14 and Extracellular Matrix MetalloProteinase Inducer (EMMPRIN) and induces the expression of its endogenous inhibitor, REversion-inducing Cysteine-rich protein with Kazal motifs (RECK). In addition to modulating gelatinases, AA also inhibits the expression of various components of the Epidermal Growth Factor (EGF) pathway like EGF, Protein Kinase B (Akt) and Mitogen-activated protein kinases (MAPK). Furthermore, AA also activates the expression of Sprouty 2 (Spry2), a negative regulator of EGF pathway, and silencing Spry2 results in up-regulation of expression of gelatinases as well as MMP-14. The present study thus elucidates a novel mechanism of action of AA and provides a strong basis for utilizing this molecule as a template for cancer therapeutics.

Novel Function of Sprouty4 as a Regulator of Stemness and Differentiation of Embryonic Stem Cells

Sprouty (Spry) genes encode inhibitors of the receptor tyrosine kinase signaling cascade, which plays important roles in stem cells. However, the role of Spry4 in the stemness of embryonic stem cells has not been fully elucidated. Here, we used mouse embryonic stem cells (mESCs) as a model system to investigate the role of Spry4 in the stem cells. Suppression of Spry4 expression results in the decreases of cell proliferation, EB formation and stemness marker expression, suggesting that Spry4 activity is associated with stemness of mESCs. Teratoma assay showed that the cartilage maturation was facilitated in Spry4 knocked down mESCs. Our results suggest that Spry4 is an important regulator of the stemness and differentiation of mESCs.