F-BAR-containing adaptor CIP4 localizes to early endosomes and regulates Epidermal Growth Factor Receptor trafficking and downregulation

Risk scoring based on DNA methylation-driven related DEGs for colorectal cancer prognosis with systematic insights

Colorectal cancer is a common malignant tumor of the digestive tract. Despite advances in diagnostic techniques and medications. Its prognosis remains challenging. DNA methylation-driven related circulating tumor cells have attracted enormous interest in diagnosing owing to their non-invasive nature and early recognition properties. However, the mechanism through which risk biomarkers act remains elusive. Here, we designed a risk model based on differentially expressed genes, DNA methylation, robust, and survival-related factors in the framework of Cox regression. The model has satisfactory performance and is independently verified by an external and isolated dataset in terms of C-index value, ROC, and tROC. The model was applied to Colorectal cancer patients who were subsequently divided into high- and low-risk groups. Functional annotations, genomic alterations, tumor immune environment, and drug sensitivity were analyzed. We observed that up-regulated genes are associated with epithelial cell differentiation and MAPK signaling pathways. The down-regulated genes are related to IL-7 signaling and apoptosis-induced DNA fragmentation. Interestingly, the immune system was inhibited in high-risk groups. High-frequency mutation genes tend to co-occur. High-risk score patients are related to copy number amplification events. To address the challenges, we suggested eleven and twenty-one drugs that are sensitive to low- and high-risk patients. Finally, an artificial neural network was provided to evaluate the immunotherapeutic efficiency. Taken together, the findings demonstrated that our risk score model is robust and reliable for evaluating the prognosis with novel diagnostic and treatment targets. It also yields benefits for the treatment and provides unique insights into developing therapeutic strategies.

Low expression of CIP4 in predicting worse overall survival: A potential biomarker for laryngeal cancer

Previous reports indicate that Cdc42-interacting protein-4 (CIP4) has previously been reported to plays an important role in the progression of various cancers. However, its correlation with laryngeal cancer (LC) remains unreported. Data from TCGA and GEO databases were used to evaluate the role of CIP4 in LC. Based on GEO and TCGA datasets, we analyzed the differences in CIP4 expression between normal and tumor samples. The Wilcoxon signed-rank test was used to analyze the relationship between clinical features and CIP4. Cox regression and the Kaplan-Meier analyses were used to identify the clinical characteristics associated with the overall survival. Also, the GEPIA database was used to confirm the relationship between CIP4 and overall survival. Lastly, Gene Set Enrichment Analysis (GSEA) was performed based on the TCGA dataset. CIP4 expression in LC was significantly associated with gender and tumor stage (p-values<0.05). Similar to GEPIA validation, Kaplan-Meier survival analysis demonstrated that LC with CIP4-low exhibited a worse prognosis than that with CIP4-high. Univariate analysis revealed that CIP4-high significantly correlated with better overall survival (HR: 0.522, 95% CI: 0.293–0.830, P = 0.026). Besides, multivariate analysis revealed that CIP4 remained independently associated with the overall survival (HR: 0.61, 95% CI: 0.326–0.912, P = 0.012). GSEA showed that the p53, WNT signaling, TGF-β signaling pathways, etc. were enriched in a phenotype high CIP4 expression. In summary, the CIP4 gene is a potential prognostic molecular marker for patients diagnosed with laryngeal cancer. Moreover, the p53, WNT signaling, and TGF-β signaling pathways are potentially associated with CIP4 in LC.

Calcineurin Aβ-Specific Anchoring Confers Isoform-Specific Compartmentation and Function in Pathological Cardiac Myocyte Hypertrophy

BACKGROUND

The Ca²⁺/calmodulin-dependent phosphatase calcineurin is a key regulator of cardiac myocyte hypertrophy in disease. An unexplained paradox is how the β isoform of the calcineurin catalytic A-subunit (CaNAβ) is required for induction of pathological myocyte hypertrophy, despite calcineurin Aα expression in the same cells. It is unclear how the pleiotropic second messenger Ca²⁺ drives excitation-contraction coupling while not stimulating hypertrophy by calcineurin in the normal heart. Elucidation of the mechanisms conferring this selectivity in calcineurin signaling should reveal new strategies for targeting the phosphatase in disease.

METHODS

Primary adult rat ventricular myocytes were studied for morphology and intracellular signaling. New Förster resonance energy transfer reporters were used to assay Ca²⁺ and calcineurin activity in living cells. Conditional gene deletion and adeno-associated virus-mediated gene delivery in the mouse were used to study calcineurin signaling after transverse aortic constriction in vivo.

RESULTS

CIP4 (Cdc42-interacting protein 4)/TRIP10 (thyroid hormone receptor interactor 10) was identified as a new polyproline domain-dependent scaffold for CaNAβ2 by yeast 2-hybrid screen. Cardiac myocyte-specific CIP4 gene deletion in mice attenuated pressure overload-induced pathological cardiac remodeling and heart failure. Blockade of CaNAβ polyproline-dependent anchoring using a competing peptide inhibited concentric hypertrophy in cultured myocytes; disruption of anchoring in vivo using an adeno-associated virus gene therapy vector inhibited cardiac hypertrophy and improved systolic function after pressure overload. Live cell Förster resonance energy transfer biosensor imaging of cultured myocytes revealed that Ca²⁺ levels and calcineurin activity associated with the CIP4 compartment were increased by neurohormonal stimulation, but minimally by pacing. Conversely, Ca²⁺ levels and calcineurin activity detected by nonlocalized Förster resonance energy transfer sensors were induced by pacing and minimally by neurohormonal stimulation, providing functional evidence for differential intracellular compartmentation of Ca²⁺ and calcineurin signal transduction.

CONCLUSIONS

These results support a structural model for Ca²⁺ and CaNAβ compartmentation in cells based on an isoform-specific mechanism for calcineurin protein-protein interaction and localization. This mechanism provides an explanation for the specific role of CaNAβ in hypertrophy and its selective activation under conditions of pathologic stress. Disruption of CaNAβ polyproline-dependent anchoring constitutes a rational strategy for therapeutic targeting of CaNAβ-specific signaling responsible for pathological cardiac remodeling in cardiovascular disease deserving of further preclinical investigation.

Opposing functions of F-BAR proteins in neuronal membrane protrusion, tubule formation, and neurite outgrowth

Neurite formation is a fundamental antecedent to axon and dendrite formation, but the mechanisms that underlie this important process are poorly characterized. Here, we demonstrate that two F-BAR proteins, CIP4 and FBP17, have opposing functions in early cortical neuron development.

The F-BAR family of proteins play important roles in many cellular processes by regulating both membrane and actin dynamics. The CIP4 family of F-BAR proteins is widely recognized to function in endocytosis by elongating endocytosing vesicles. However, in primary cortical neurons, CIP4 concentrates at the tips of extending lamellipodia and filopodia and inhibits neurite outgrowth. Here, we report that the highly homologous CIP4 family member, FBP17, induces tubular structures in primary cortical neurons and results in precocious neurite formation. Through domain swapping and deletion experiments, we demonstrate that a novel polybasic region between the F-BAR and HR1 domains is required for membrane bending. Moreover, the presence of a poly-PxxP region in longer splice isoforms of CIP4 and FBP17 largely reverses the localization and function of these proteins. Thus, CIP4 and FBP17 function as an antagonistic pair to fine-tune membrane protrusion, endocytosis, and neurite formation during early neuronal development.

Folding Status Is Determinant over Traffic-Competence in Defining CFTR Interactors in the Endoplasmic Reticulum

The most common cystic fibrosis-causing mutation (F508del, present in ~85% of CF patients) leads to CFTR misfolding, which is recognized by the endoplasmic reticulum (ER) quality control (ERQC), resulting in ER retention and early degradation. It is known that CFTR exit from the ER is mediated by specific retention/sorting signals that include four arginine-framed tripeptide (AFT) retention motifs and a diacidic (DAD) exit code that controls the interaction with the COPII machinery. Here, we aim at obtaining a global view of the protein interactors that regulate CFTR exit from the ER. We used mass spectrometry-based interaction proteomics and bioinformatics analyses to identify and characterize proteins interacting with selected CFTR peptide motifs or full-length CFTR variants retained or bypassing these ERQC checkpoints. We conclude that these ERQC trafficking checkpoints rely on fundamental players in the secretory pathway, detecting key components of the protein folding machinery associated with the AFT recognition and of the trafficking machinery recognizing the diacidic code. Furthermore, a greater similarity in terms of interacting proteins is observed for variants sharing the same folding defect over those reaching the same cellular location, evidencing that folding status is dominant over ER escape in shaping the CFTR interactome.

BAR Domain Proteins Regulate Rho GTPase Signaling

The Bin-Amphiphysin-Rvs (BAR) domain is a membrane lipid binding domain present in a wide variety of proteins, often proteins with a role in Rho-regulated signaling pathways. BAR domains do not only confer binding to lipid bilayers, they also possess a membrane sculpturing ability and thereby directly control the topology of biomembranes. BAR domain-containing proteins participate in a plethora of physiological processes but the common denominator is their capacity to link membrane dynamics to actin dynamics and thereby integrate processes such as endocytosis, exocytosis, vesicle trafficking, cell morphogenesis and cell migration. The Rho family of small GTPases constitutes an important bridging theme for many BAR domain-containing proteins. This review article will focus predominantly on the role of BAR proteins as regulators or effectors of Rho GTPases and it will only briefly discuss the structural and biophysical function of the BAR domains.

Endocytosis and membrane receptor internalization: implication of F-BAR protein Carom

Endocytosis is a cellular process mostly responsible for membrane receptor internalization. Cell membrane receptors bind to their ligands and form a complex which can be internalized. We previously proposed that F-BAR protein initiates membrane curvature and mediates endocytosis via its binding partners. However, F-BAR protein partners involved in membrane receptor endocytosis and the regulatory mechanism remain unknown. In this study, we established database mining strategies to explore mechanisms underlying receptor-related endocytosis. We identified 34 endocytic membrane receptors and 10 regulating proteins in clathrin-dependent endocytosis (CDE), a major process of membrane receptor internalization. We found that F-BAR protein FCHSD2 (Carom) may facilitate endocytosis via 9 endocytic partners. Carom is highly expressed, along with highly expressed endocytic membrane receptors and partners, in endothelial cells and macrophages. We established 3 models of Carom-receptor complexes and their intracellular trafficking based on protein interaction and subcellular localization. We conclude that Carom may mediate receptor endocytosis and transport endocytic receptors to the cytoplasm for receptor signaling and lysosome/proteasome degradation, or to the nucleus for RNA processing, gene transcription and DNA repair.

CDC42-interacting protein 4 promotes metastasis of nasopharyngeal carcinoma by mediating invadopodia formation and activating EGFR signaling

Background

Nasopharyngeal carcinoma (NPC) is a common malignancy in Southern China and Southeast Asia. In this study, we investigated the functional and molecular mechanisms by which CDC42-interacting protein 4 (CIP4) influences NPC.

Methods

The expression levels of CIP4 were examined by Western blot, qRT-PCR or IHC. MTT assay was used to detect the proliferative rate of NPC cells. The invasive abilities were examined by matrigel and transwell assay. The metastatic abilities of NPC cells were revealed in BALB/c nude mice.

Results

We report that CIP4 is required for NPC cell motility and invasion. CIP4 promotes the activation of N-WASP that controls invadopodia formation and activates EGFR signaling, which induces downstream MMP2 (matrix metalloproteinase 2) upregulation. In addition, CIP4 could promote NPC metastasis by activating the EGFR pathway. In nude mouse models, distant metastasis was significantly inhibited in CIP4-silenced groups. High CIP4 expression is an independent adverse prognostic factor of overall survival (OS) and distant metastasis-free survival (DMFS).

Conclusion

We identify the critical role of CIP4 in metastasis of NPC which suggest that CIP4 may be a potential therapeutic target of NPC patients.

The HCV Replicase Complex and Viral RNA Synthesis

Replication of hepatitis C virus (HCV) is tightly linked to membrane alterations designated the membranous web, harboring the viral replicase complex. In this chapter we describe the morphology and 3D architecture of the HCV-induced replication organelles, mainly consisting of double membrane vesicles, which are generated by a concerted action of the nonstructural proteins NS3 to NS5B. Recent studies have furthermore identified a number of host cell proteins and lipids contributing to the biogenesis of the membranous web, which are discussed in this chapter. Viral RNA synthesis is tightly associated with these membrane alterations and mainly driven by the viral RNA dependent RNA polymerase NS5B. We summarize our current knowledge of the structure and function of NS5B, the role of cis-acting replication elements at the termini of the genome in regulating RNA synthesis and the contribution of additional viral and host factors to viral RNA synthesis, which is still ill defined.

CIP4 promotes metastasis in triple-negative breast cancer and is associated with poor patient prognosis

Signaling via epidermal growth factor receptor (EGFR) and Src kinase pathways promote triple-negative breast cancer (TNBC) cell invasion and tumor metastasis. Here, we address the role of Cdc42-interacting protein-4 (CIP4) in TNBC metastasis in vivo, and profile CIP4 expression in human breast cancer patients. In human TNBC cells, CIP4 knock-down (KD) led to less sustained activation of Erk kinase and impaired cell motility compared to control cells. This correlated with significant defects in 3D invasion of surrounding extracellular matrix by CIP4 KD TNBC cells when grown as spheroid colonies. In mammary orthotopic xenograft assays using both human TNBC cells (MDA-MB-231, HCC 1806) and rat MTLn3 cells, CIP4 silencing had no overt effect on tumor growth, but significantly reduced the incidence of lung metastases in each tumor model. In human invasive breast cancers, high CIP4 levels was significantly associated with high tumor stage, TNBC and HER2 subtypes, and risk of progression to metastatic disease. Together, these results implicate CIP4 in promoting metastasis in TNBCs.

BAR domain proteins regulate Rho GTPase signaling

BAR proteins comprise a heterogeneous group of multi-domain proteins with diverse biological functions. The common denominator is the Bin-Amphiphysin-Rvs (BAR) domain that not only confers targeting to lipid bilayers, but also provides scaffolding to mold lipid membranes into concave or convex surfaces. This function of BAR proteins is an important determinant in the dynamic reconstruction of membrane vesicles, as well as of the plasma membrane. Several BAR proteins function as linkers between cytoskeletal regulation and membrane dynamics. These links are provided by direct interactions between BAR proteins and actin-nucleation-promoting factors of the Wiskott-Aldrich syndrome protein family and the Diaphanous-related formins. The Rho GTPases are key factors for orchestration of this intricate interplay. This review describes how BAR proteins regulate the activity of Rho GTPases, as well as how Rho GTPases regulate the function of BAR proteins. This mutual collaboration is a central factor in the regulation of vital cellular processes, such as cell migration, cytokinesis, intracellular transport, endocytosis, and exocytosis.

F-BAR family proteins, emerging regulators for cell membrane dynamic changes-from structure to human diseases

Eukaryotic cell membrane dynamics change in curvature during physiological and pathological processes. In the past ten years, a novel protein family, Fes/CIP4 homology-Bin/Amphiphysin/Rvs (F-BAR) domain proteins, has been identified to be the most important coordinators in membrane curvature regulation. The F-BAR domain family is a member of the Bin/Amphiphysin/Rvs (BAR) domain superfamily that is associated with dynamic changes in cell membrane. However, the molecular basis in membrane structure regulation and the biological functions of F-BAR protein are unclear. The pathophysiological role of F-BAR protein is unknown. This review summarizes the current understanding of structure and function in the BAR domain superfamily, classifies F-BAR family proteins into nine subfamilies based on domain structure, and characterizes F-BAR protein structure, domain interaction, and functional relevance. In general, F-BAR protein binds to cell membrane via F-BAR domain association with membrane phospholipids and initiates membrane curvature and scission via Src homology-3 (SH3) domain interaction with its partner proteins. This process causes membrane dynamic changes and leads to seven important cellular biological functions, which include endocytosis, phagocytosis, filopodium, lamellipodium, cytokinesis, adhesion, and podosome formation, via distinct signaling pathways determined by specific domain-binding partners. These cellular functions play important roles in many physiological and pathophysiological processes. We further summarize F-BAR protein expression and mutation changes observed in various diseases and developmental disorders. Considering the structure feature and functional implication of F-BAR proteins, we anticipate that F-BAR proteins modulate physiological and pathophysiological processes via transferring extracellular materials, regulating cell trafficking and mobility, presenting antigens, mediating extracellular matrix degradation, and transmitting signaling for cell proliferation.

Novel Host Proteins and Signaling Pathways in Enteropathogenic E. coli Pathogenesis Identified by Global Phosphoproteome Analysis

Enteropathogenic Escherichia coli (EPEC) uses a type III secretion system (T3SS) to directly translocate effector proteins into host cells where they play a pivotal role in subverting host cell signaling needed for disease. However, our knowledge of how EPEC affects host protein phosphorylation is limited to a few individual protein studies. We employed a quantitative proteomics approach to globally map alterations in the host phosphoproteome during EPEC infection. By characterizing host phosphorylation events at various time points throughout infection, we examined how EPEC dynamically impacts the host phosphoproteome over time. This experimental setup also enabled identification of T3SS-dependent and -independent changes in host phosphorylation. Specifically, T3SS-regulated events affected various cellular processes that are known EPEC targets, including cytoskeletal organization, immune signaling, and intracellular trafficking. However, the involvement of phosphorylation in these events has thus far been poorly studied. We confirmed the MAPK family as an established key host player, showed its central role in signal transduction during EPEC infection, and extended the repertoire of known signaling hubs with previously unrecognized proteins, including TPD52, CIN85, EPHA2, and HSP27. We identified altered phosphorylation of known EPEC targets, such as cofilin, where the involvement of phosphorylation has so far been undefined, thus providing novel mechanistic insights into the roles of these proteins in EPEC infection. An overlap of regulated proteins, especially those that are cytoskeleton-associated, was observed when compared with the phosphoproteome of Shigella-infected cells. We determined the biological relevance of the phosphorylation of a novel protein in EPEC pathogenesis, septin-9 (SEPT9). Both siRNA knockdown and a phosphorylation-impaired SEPT9 mutant decreased bacterial adherence and EPEC-mediated cell death. In contrast, a phosphorylation-mimicking SEPT9 mutant rescued these effects. Collectively, this study provides the first global analysis of phosphorylation-mediated processes during infection with an extracellular, diarrheagenic bacterial pathogen.

A TOCA/CDC-42/PAR/WAVE functional module required for retrograde endocytic recycling

Endosome-to-Golgi transport is required for the function of many key membrane proteins and lipids, including signaling receptors, small-molecule transporters, and adhesion proteins. The retromer complex is well-known for its role in cargo sorting and vesicle budding from early endosomes, in most cases leading to cargo fusion with the trans-Golgi network (TGN). Transport from recycling endosomes to the TGN has also been reported, but much less is understood about the molecules that mediate this transport step. Here we provide evidence that the F-BAR domain proteins TOCA-1 and TOCA-2 (Transducer of Cdc42 dependent actin assembly), the small GTPase CDC-42 (Cell division control protein 42), associated polarity proteins PAR-6 (Partitioning defective 6) and PKC-3/atypical protein kinase C, and the WAVE actin nucleation complex mediate the transport of MIG-14/Wls and TGN-38/TGN38 cargo proteins from the recycling endosome to the TGN in Caenorhabditis elegans. Our results indicate that CDC-42, the TOCA proteins, and the WAVE component WVE-1 are enriched on RME-1-positive recycling endosomes in the intestine, unlike retromer components that act on early endosomes. Furthermore, we find that retrograde cargo TGN-38 is trapped in early endosomes after depletion of SNX-3 (a retromer component) but is mainly trapped in recycling endosomes after depletion of CDC-42, indicating that the CDC-42-associated complex functions after retromer in a distinct organelle. Thus, we identify a group of interacting proteins that mediate retrograde recycling, and link these proteins to a poorly understood trafficking step, recycling endosome-to-Golgi transport. We also provide evidence for the physiological importance of this pathway in WNT signaling.

The CD20 homologue MS4A4 directs trafficking of KIT toward clathrin-independent endocytosis pathways and thus regulates receptor signaling and recycling

MS4A4 traffics through endocytic recycling pathways and stabilizes surface KIT expression by regulating endocytosis and recycling. Silencing MS4A4 reduces KIT recruitment to lipid raft microdomains and PLCg1 signaling while promoting AKT signaling, cell migration, and proliferation. This study is the first to describe functions for human MS4A4.

MS4A family members differentially regulate the cell cycle, and aberrant, or loss of, expression of MS4A family proteins has been observed in colon and lung cancer. However, the precise functions of MS4A family proteins and their mechanistic interactions remain unsolved. Here we report that MS4A4 facilitates trafficking of the receptor tyrosine kinase KIT through endocytic recycling rather than degradation pathways by a mechanism that involves recruitment of KIT to caveolin-1–enriched microdomains. Silencing of MS4A4 in human mast cells altered ligand-induced KIT endocytosis pathways and reduced receptor recycling to the cell surface, thus promoting KIT signaling in the endosomes while reducing that in the plasma membrane, as exemplified by Akt and PLCγ1 phosphorylation, respectively. The altered endocytic trafficking of KIT also resulted in an increase in SCF-induced mast cell proliferation and migration, which may reflect altered signaling in these cells. Our data reveal a novel function for MS4A family proteins in regulating trafficking and signaling, which could have implications in both proliferative and immunological diseases.

Toca-1 is suppressed by p53 to limit breast cancer cell invasion and tumor metastasis

Introduction

Transducer of Cdc42-dependent actin assembly-1 (Toca-1) recruits actin regulatory proteins to invadopodia, and promotes breast tumor metastasis. Since metastatic breast tumors frequently harbor mutations in the tumor suppressor p53, we tested whether p53 regulates Toca-1 expression.

Methods

Normal mammary epithelial cells (HBL-100, MCF10A) and breast cancer cell lines expressing wild-type (WT) p53 (DU4475, MTLn3) were treated with camptothecin or Nutlin-3 to stabilize p53 to test effects on Toca-1 mRNA and protein levels. Chromatin immunoprecipitation (ChIP) assays were performed to identify p53 binding site in Toca-1 gene. Stable silencing of p53 and Toca-1 were performed in MTLn3 cells to test effects on invadopodia and cell invasion in vitro, and tumor metastasis in vivo.

Results

We observed that breast cancer cell lines with mutant p53 have high levels of Toca-1 compared to those with WT p53. Stabilization of WT p53 led to further reduction in Toca-1 mRNA and protein levels in normal breast epithelial cells and breast cancer cells. ChIP assays revealed p53 binding within intron 2 of toca1, and reduced histone acetylation within its promoter region upon p53 upregulation or activation. Stable silencing of WT p53 in MTLn3 cells led to increased extracellular matrix degradation and cell invasion compared to control cells. Interestingly, the combined silencing of p53 and Toca-1 led to a partial rescue of these effects of p53 silencing in vitro and reduced lung metastases in mice. In human breast tumors, Toca-1 levels were high in subtypes with frequent p53 mutations, and high Toca-1 transcript levels correlated with increased risk of relapse.

Conclusions

Based on these findings, we conclude that loss of p53 tumor suppressor function in breast cancers leads to upregulation of Toca-1, and results in enhanced risk of developing metastatic disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-014-0503-x) contains supplementary material, which is available to authorized users.

CIP4 promotes lung adenocarcinoma metastasis and is associated with poor prognosis

Aberrant Epidermal growth factor receptor (EGFR) signaling in non-small cell lung cancer (NSCLC) is linked to tumor progression, metastasis, and poor survival rates. Here, we report the role of Cdc42-interacting protein 4 (CIP4) in the regulation of NSCLC cell invasiveness and tumor metastasis. CIP4 was highly expressed in a panel of NSCLC cell lines and normal lung epithelial cell lines. Stable knock-down (KD) of CIP4 in lung adenocarcinoma H1299 cells, expressing wild-type EGFR, led to increased EGFR levels on the cell surface, and defects in sustained activation of Erk kinase in H1299 cells treated with EGF. CIP4 localized to leading edge projections in NSCLC cells, and CIP4 KD cells displayed defects in EGF-induced cell motility and invasion through extracellular matrix. This correlated with reduced expression and activity of matrix metalloproteinase-2 (MMP-2) in CIP4 KD cells compared to control. In xenograft assays, CIP4 silencing had no effect on tumor growth, but resulted in significant defects in spontaneous metastases to the lungs from these subcutaneous tumors. This correlated with reduced expression of the Erk target gene Zeb1, and the Zeb1 target gene MMP-2 in CIP4 KD tumors compared to control. CIP4 also enhanced rates of metastasis to the liver and lungs in an intrasplenic experimental metastasis model. In human NSCLC tumor sections, CIP4 expression was elevated ≥ 2-fold in 43% of adenocarcinomas and 32% of squamous carcinomas compared to adjacent normal lung tissues. Analysis of microarray data for NSCLC patients also revealed that high CIP4 transcript levels correlated with reduced overall survival. Together, these results identify CIP4 as a positive regulator of NSCLC metastasis, and a potential poor prognostic biomarker in lung adenocarcinoma.

Functional deregulation of KIT: link to mast cell proliferative diseases and other neoplasms

In this review, the authors discuss common gain-of-function mutations in the stem cell factor receptor KIT found in mast cell proliferation disorders and summarize the current understanding of the molecular mechanisms by which these transforming mutations may affect KIT structure and function leading to altered downstream signaling and cellular transformation. Drugs targeting KIT have shown mixed success in the treatment of mastocytosis and other hyperproliferative diseases. A brief overview of the most common KIT inhibitors currently used, the reasons for the varied clinical results of such inhibitors and a discussion of potential new strategies are provided.

CIP4 is required for the hypertrophic growth of neonatal cardiac myocytes

BACKGROUND

CIP4 is a scaffold protein that regulates membrane deformation and tubulation, organization of the actin cytoskeleton, endocytosis of growth factor receptors, and vesicle trafficking. Although expressed in the heart, CIP4 has not been studied with regards to its potential function in cardiac myocytes.

RESULTS

We now show using RNA interference that CIP4 expression in neonatal rat ventricular myocytes is required for the induction of non-mitotic, hypertrophic growth by the α-adrenergic agonist phenylephrine, the IL-6 cytokine leukemia inhibitor factor, and fetal bovine serum, as assayed using morphometry, immunocytochemistry for the hypertrophic marker atrial natriuretic factor and [3H]leucine incorporation for de novo protein synthesis. This requirement was consistent with the induction of CIP4 expression by hypertrophic stimulation. The inhibition of myocyte hypertrophy by CIP4 small interfering oligonucleotides (siRNA) was rescued by expression of a recombinant CIP4 protein, but not by a mutant lacking the N-terminal FCH domain responsible for CIP4 intracellular localization.

CONCLUSIONS

These results imply that CIP4 plays a significant role in the intracellular hypertrophic signal transduction network that controls the growth of cardiac myocytes in heart disease.

CIP4 controls CCL19-driven cell steering and chemotaxis in chronic lymphocytic leukemia

Solid tumor dissemination relies on the reprogramming of molecular pathways controlling chemotaxis. Whether the motility of nonsolid tumors such as leukemia depends on the deregulated expression of molecules decoding chemotactic signals remains an open question. We identify here the membrane remodeling F-BAR adapter protein Cdc42-interacting protein 4 (CIP4) as a key regulator of chemotaxis in chronic lymphocytic leukemia (CLL). CIP4 is expressed at abnormally high levels in CLL cells, where it is required for CCL19-induced chemotaxis. Upon CCL19 stimulation of CLL cells, CIP4 associates with GTP-bound Cdc42 and is recruited to the rear of the lamellipodium and along microspikes radiating through the lamellipodium. Consistent with its cellular distribution, CIP4 removal impairs both the assembly of the polarized lamellipodium and directional migration along a diffusible CCL19 gradient. Furthermore, CIP4 depletion results in decreased activation of WASP, but increased activation of PAK1 and p38 mitogen-activated protein kinase (MAPK). Notably, p38 MAPK inhibition results in impaired lamellipodium assembly and loss of directional migration. This suggests that CIP4 modulates both the WASP and p38 MAPK pathways to promote lamellipodium assembly and chemotaxis. Overall, our study reveals a critical role of CIP4 in mediating chemotaxis of CLL cells by controlling the dynamics of microspike-containing protrusions and cell steering.

The F-BAR protein PACSIN2 regulates epidermal growth factor receptor internalization

Signaling via growth factor receptors, including the epidermal growth factor (EGF) receptor, is key to various cellular processes, such as proliferation, cell survival, and cell migration. In a variety of human diseases such as cancer, aberrant expression and activation of growth factor receptors can lead to disturbed signaling. Intracellular trafficking is crucial for proper signaling of growth factor receptors. As a result, the level of cell surface expression of growth factor receptors is an important determinant for the outcome of downstream signaling. BAR domain-containing proteins represent an important family of proteins that regulate membrane dynamics. In this study, we identify a novel role for the F-BAR protein PACSIN2 in the regulation of EGF receptor signaling. We show that internalized EGF as well as the (activated) EGF receptor translocated to PACSIN2-positive endosomes. Furthermore, loss of PACSIN2 increased plasma membrane expression of the EGF receptor in resting cells and increased EGF-induced phosphorylation of the EGF receptor. As a consequence, EGF-induced activation of Erk and Akt as well as cell proliferation were enhanced in PACSIN2-depleted cells. In conclusion, this study identifies a novel role for the F-BAR-domain protein PACSIN2 in regulating EGF receptor surface levels and EGF-induced downstream signaling.

The F-BAR protein NOSTRIN participates in FGF signal transduction and vascular development

F-BAR proteins are multivalent adaptors that link plasma membrane and cytoskeleton and coordinate cellular processes such as membrane protrusion and migration. Yet, little is known about the function of F-BAR proteins in vivo. Here we report, that the F-BAR protein NOSTRIN is necessary for proper vascular development in zebrafish and postnatal retinal angiogenesis in mice. The loss of NOSTRIN impacts on the migration of endothelial tip cells and leads to a reduction of tip cell filopodia number and length. NOSTRIN forms a complex with the GTPase Rac1 and its exchange factor Sos1 and overexpression of NOSTRIN in cells induces Rac1 activation. Furthermore, NOSTRIN is required for fibroblast growth factor 2 dependent activation of Rac1 in primary endothelial cells and the angiogenic response to fibroblast growth factor 2 in the in vivo matrigel plug assay. We propose a novel regulatory circuit, in which NOSTRIN assembles a signalling complex containing FGFR1, Rac1 and Sos1 thereby facilitating the activation of Rac1 in endothelial cells during developmental angiogenesis.

The BAR Domain Superfamily Proteins from Subcellular Structures to Human Diseases

Eukaryotic cells have complicated membrane systems. The outermost plasma membrane contains various substructures, such as invaginations and protrusions, which are involved in endocytosis and cell migration. Moreover, the intracellular membrane compartments, such as autophagosomes and endosomes, are essential for cellular viability. The Bin-Amphiphysin-Rvs167 (BAR) domain superfamily proteins are important players in membrane remodeling through their structurally determined membrane binding surfaces. A variety of BAR domain superfamily proteins exist, and each family member appears to be involved in the formation of certain subcellular structures or intracellular membrane compartments. Most of the BAR domain superfamily proteins contain SH3 domains, which bind to the membrane scission molecule, dynamin, as well as the actin regulatory WASP/WAVE proteins and several signal transduction molecules, providing possible links between the membrane and the cytoskeleton or other machineries. In this review, we summarize the current information about each BAR superfamily protein with an SH3 domain(s). The involvement of BAR domain superfamily proteins in various diseases is also discussed.

The F-BAR protein CIP4 inhibits neurite formation by producing lamellipodial protrusions

Neurite formation is a seminal event in the early development of neurons. However, little is known about the mechanisms by which neurons form neurites. F-BAR proteins function in sensing and inducing membrane curvature. Cdc42-interacting protein 4 (CIP4), a member of the F-BAR family, regulates endocytosis in a variety of cell types. However, there is little data on how CIP4 functions in neurons. Here we show that CIP4 plays a novel role in neuronal development by inhibiting neurite formation. Remarkably, CIP4 exerts this effect not through endocytosis, but by producing lamellipodial protrusions. In primary cortical neurons CIP4 is concentrated specifically at the tips of extending lamellipodia and filopodia, instead of endosomes as in other cell types. Overexpression of CIP4 results in lamellipodial protrusions around the cell body, subsequently delaying neurite formation and enlarging growth cones. These effects depend on the F-BAR and SH3 domains of CIP4 and on its ability to multimerize. Conversely, cortical neurons from CIP4-null mice initiate neurites twice as fast as controls. This is the first study to demonstrate that an F-BAR protein functions differently in neuronal versus nonneuronal cells and induces lamellipodial protrusions instead of invaginations or filopodia-like structures.

Proline-serine-threonine phosphatase-interacting protein 2 (PSTPIP2), a host membrane-deforming protein, is critical for membranous web formation in hepatitis C virus replication

Hepatitis C virus (HCV) reorganizes intracellular membranes to establish sites of replication. How viral and cellular proteins target, bind, and rearrange specific membranes into the replication factory remains a mystery. We used a lentivirus-based RNA interference (RNAi) screening approach to identify the potential cellular factors that are involved in HCV replication. A protein with membrane-deforming activity, proline-serine-threonine phosphatase-interacting protein 2 (PSTPIP2), was identified as a potential factor. Knockdown of PSTPIP2 in HCV subgenomic replicon-harboring and HCV-infected cells was associated with the reduction of HCV protein and RNA expression. PSTPIP2 was localized predominantly in detergent-resistant membranes (DRMs), which contain the RNA replication complex. PSTPIP2 knockdown caused a significant reduction of the formation of HCV- and NS4B-induced membranous webs. A PSTPIP2 mutant defective in inducing membrane curvature failed to support HCV replication, confirming that the membrane-deforming ability of PSTPIP2 is essential for HCV replication. Taking these results together, we suggest that PSTPIP2 facilitates membrane alterations and is a key player in the formation of the membranous web, which is the site of the HCV replication complex.

Cdc42-interacting protein 4 is a Src substrate that regulates invadopodia and invasiveness of breast tumors by promoting MT1-MMP endocytosis

Invadopodia are actin-rich membrane protrusions that promote extracellular matrix degradation and invasiveness of tumor cells. Src protein-tyrosine kinase is a potent inducer of invadopodia and tumor metastases. Cdc42-interacting protein 4 (CIP4) adaptor protein interacts with actin regulatory proteins and regulates endocytosis. Here, we show that CIP4 is a Src substrate that localizes to invadopodia in MDA-MB-231 breast tumor cells expressing activated Src (MDA-SrcYF). To probe the function of CIP4 in invadopodia, we established stable CIP4 knockdown in MDA-SrcYF cell lines by RNA interference. Compared with control cells, CIP4 knockdown cells degrade more extracellular matrix (ECM), have increased numbers of mature invadopodia and are more invasive through matrigel. Similar results are observed with knockdown of CIP4 in EGF-treated MDA-MB-231 cells. This inhibitory role of CIP4 is explained by our finding that CIP4 limits surface expression of transmembrane type I matrix metalloprotease (MT1-MMP), by promoting MT1-MMP internalization. Ectopic expression of CIP4 reduces ECM digestion by MDA-SrcYF cells, and this activity is enhanced by mutation of the major Src phosphorylation site in CIP4 (Y471). Overall, our results identify CIP4 as a suppressor of Src-induced invadopodia and invasion in breast tumor cells by promoting endocytosis of MT1-MMP.

Functional characterization of Trip10 in cancer cell growth and survival

Background

The Cdc42-interacting protein-4, Trip10 (also known as CIP4), is a multi-domain adaptor protein involved in diverse cellular processes, which functions in a tissue-specific and cell lineage-specific manner. We previously found that Trip10 is highly expressed in estrogen receptor-expressing (ER⁺) breast cancer cells. Estrogen receptor depletion reduced Trip10 expression by progressively increasing DNA methylation. We hypothesized that Trip10 functions as a tumor suppressor and may be involved in the malignancy of ER-negative (ER^-) breast cancer. To test this hypothesis and evaluate whether Trip10 is epigenetically regulated by DNA methylation in other cancers, we evaluated DNA methylation of Trip10 in liver cancer, brain tumor, ovarian cancer, and breast cancer.

Methods

We applied methylation-specific polymerase chain reaction and bisulfite sequencing to determine the DNA methylation of Trip10 in various cancer cell lines and tumor specimens. We also overexpressed Trip10 to observe its effect on colony formation and in vivo tumorigenesis.

Results

We found that Trip10 is hypermethylated in brain tumor and breast cancer, but hypomethylated in liver cancer. Overexpressed Trip10 was associated with endogenous Cdc42 and huntingtin in IMR-32 brain tumor cells and CP70 ovarian cancer cells. However, overexpression of Trip10 promoted colony formation in IMR-32 cells and tumorigenesis in mice inoculated with IMR-32 cells, whereas overexpressed Trip10 substantially suppressed colony formation in CP70 cells and tumorigenesis in mice inoculated with CP70 cells.

Conclusions

Trip10 regulates cancer cell growth and death in a cancer type-specific manner. Differential DNA methylation of Trip10 can either promote cell survival or cell death in a cell type-dependent manner.

Integrin-mediated function of Rab GTPases in cancer progression

The RAS (rat sarcoma) superfamily of small GTPases is broadly subdivided into five groups: Ras, Rho, Rab, Ran, and Arf. Rab family proteins are important in regulating signal transduction and cellular processes such as differentiation, proliferation, vesicle transport, nuclear assembly, and cytoskeleton formation. However, some Rab proteins have been reported to be necessary for the adhesion and migration of cancer cells. Although Ras and Rho family members have been strongly implicated in cancer progression, knowledge of Rabs action in this regard is limited. Some reports have also linked Rab GTPases with cancer cell migration and invasiveness. This review discusses the implications of the involvement of Rabs in malignant transformation and cancer therapy through integrin-mediated signaling events, with particular emphasis on breast cancer.

Transducer of Cdc42-dependent actin assembly promotes epidermal growth factor-induced cell motility and invasiveness

Toca-1 (transducer of Cdc42-dependent actin assembly) interacts with the Cdc42·N-WASP and Abi1·Rac·WAVE F-actin branching pathways that function in lamellipodia formation and cell motility. However, the potential role of Toca-1 in these processes has not been reported. Here, we show that epidermal growth factor (EGF) induces Toca-1 localization to lamellipodia, where it co-localizes with F-actin and Arp2/3 complex in A431 epidermoid carcinoma cells. EGF also induces tyrosine phosphorylation of Toca-1 and interactions with N-WASP and Abi1. Stable knockdown of Toca-1 expression by RNA interference has no effect on cell growth, EGF receptor expression, or internalization. However, Toca-1 knockdown cells display defects in EGF-induced filopodia and lamellipodial protrusions compared with control cells. Further analyses reveal a role for Toca-1 in localization of Arp2/3 and Abi1 to lamellipodia. Toca-1 knockdown cells also display a significant defect in EGF-induced motility and invasiveness. Taken together, these results implicate Toca-1 in coordinating actin assembly within filopodia and lamellipodia to promote EGF-induced cell migration and invasion.

Cdc42-interacting protein 4 promotes breast cancer cell invasion and formation of invadopodia through activation of N-WASp

In the earliest stages of metastasis, breast cancer cells must reorganize the cytoskeleton to affect cell shape change and promote cell invasion and motility. These events require the cytoskeletal regulators Cdc42 and Rho, their effectors such as N-WASp/WAVE, and direct inducers of actin polymerization such as Arp2/3. Little consideration has been given to molecules that shape the cell membrane. The F-BAR proteins CIP4, TOCA-1, and FBP17 generate membrane curvature and act as scaffolding proteins for activated Cdc42 and N-WASp. We found that expression of CIP4, but not TOCA-1 or FBP17, was increased in invasive breast cancer cell lines in comparison with weakly or noninvasive breast cancer cell lines. Endogenous CIP4 localized to the leading edge of migrating cells and to invadopodia in cells invading gelatin. Because CIP4 serves as a scaffolding protein for Cdc42, Src, and N-WASp, we tested whether loss of CIP4 could result in decreased N-WASp function. Interaction between CIP4 and N-WASp was epidermal growth factor responsive, and CIP4 silencing by small interfering RNA caused decreased tyrosine phosphorylation of N-WASp at a Src-dependent activation site (Y256). CIP4 silencing also impaired the migration and invasion of MDA-MB-231 cells and was associated with decreased formation of invadopodia and gelatin degradation. This study presents a new role for CIP4 in the promotion of migration and invasion of MDA-MB-231 breast cancer cells and establishes the contribution of F-BAR proteins to cancer cell motility and invasion.

Cdc42 interacting protein 4 (CIP4) is essential for integrin-dependent T-cell trafficking

The F-BAR domain containing protein CIP4 (Cdc42 interacting protein 4) interacts with Cdc42 and WASP/N-WASP and is thought to participate in the assembly of filamentous actin. CIP4(-/-) mice had normal T- and B-lymphocyte development but impaired T cell-dependent antibody production, IgG antibody affinity maturation, and germinal center (GC) formation, despite an intact CD40L-CD40 axis. CIP4(-/-) mice also had impaired contact hypersensitivity (CHS) to haptens, and their T cells failed to adoptively transfer CHS. Ovalbumin-activated CD4(+) effector T cells from CIP4(-/-)/OT-II mice migrated poorly to antigen-challenged skin. Activated CIP4(-/-) T cells exhibited impaired adhesion and polarization on immobilized VCAM-1 and ICAM-1 and defective arrest and transmigration across murine endothelial cell monolayers under shear flow conditions. These results demonstrate an important role for CIP4 in integrin-dependent T cell-dependent antibody responses and GC formation and in integrin-mediated recruitment of effector T cells to cutaneous sites of antigen-driven immune reactions.

The proposed functions of membrane curvatures mediated by the BAR domain superfamily proteins

The plasma membrane, the outermost surface of eukaryotic cells, contains various substructures, such as protrusions or invaginations, which are associated with diverse functions, including endocytosis and cell migration. These structures of the plasma membrane can be considered as tubules or inverted tubules (protrusions) of the membrane. There are six modes of membrane curvature at the plasma membrane, which are classified by the positive or negative curvature and the location of the curvature (tip, neck or shaft of the tubules). The BAR domain superfamily proteins have structurally determined positive and negative curvatures of membrane contact at their BAR, F-BAR and I-BAR domains, which generate and maintain such curved membranes by binding to the membrane. Importantly, the SH3 domains of the BAR domain superfamily proteins bind to the actin regulatory WASP/WAVE proteins, and the BAR/F-BAR/I-BAR domain-SH3 unit could orient the actin filaments towards the membrane for each subcellular structure. These membrane tubulations are also considered to function in membrane fusion and fission.

Subcellular membrane curvature mediated by the BAR domain superfamily proteins

The Bin-Amphiphysin-Rvs167 (BAR) domain superfamily consists of proteins containing the BAR domain, the extended FCH (EFC)/FCH-BAR (F-BAR) domain, or the IRSp53-MIM homology domain (IMD)/inverse BAR (I-BAR) domain. These domains bind membranes through electrostatic interactions between the negative charges of the membranes and the positive charges on the structural surface of homo-dimeric BAR domain superfamily members. Some BAR superfamily members have membrane-penetrating insertion loops, which also contribute to the membrane binding by the proteins. The membrane-binding surface of each BAR domain superfamily member has its own unique curvature that governs or senses the curvature of the membrane for BAR-domain binding. The wide range of BAR-domain surface curvatures correlates with the various invaginations and protrusions of cells. Therefore, each BAR domain superfamily member may generate and recognize the curvature of the membrane of each subcellular structure, such as clathrin-coated pits or filopodia. The BAR domain superfamily proteins may regulate their own catalytic activity or that of their binding proteins, depending on the membrane curvature of their corresponding subcellular structures.

The direction of actin polymerization for vesicle fission suggested from membranes tubulated by the EFC/F-BAR domain protein FBP17

Actin polymerization mediated by the Arp2/3 complex is essential for membrane tubulation, vesicle formation and fission during clathrin-dependent endocytosis. However, the mechanism by which the polymerizing actin filaments participate in vesicle formation and fission has remained unclear. Our analyses revealed that actin polymerization occurs toward FBP17-induced membrane tubules, which are considered to be generated during endocytic vesicle formation. The tubulated membrane between the future endocytic vesicle and the plasma membrane is proposed to form an arc upon scission of the endocytic vesicle. Therefore, the actin polymerization toward the tubulated membrane may be gradually converted to those toward both the vesicles and the plasma membrane.