Emerging roles of Ruk/CIN85 in vesicle-mediated transport, adhesion, migration and malignancy

PIK3R1 fusion drives chemoresistance in ovarian cancer by activating ERK1/2 and inducing rod and ring-like structures

Gene fusions are common in high-grade serous ovarian cancer (HGSC). Such genetic lesions may promote tumorigenesis, but the pathogenic mechanisms are currently poorly understood. Here, we investigated the role of a PIK3R1-CCDC178 fusion identified from a patient with advanced HGSC. We show that the fusion induces HGSC cell migration by regulating ERK1/2 and increases resistance to platinum treatment. Platinum resistance was associated with rod and ring-like cellular structure formation. These structures contained, in addition to the fusion protein, CIN85, a key regulator of PI3K-AKT-mTOR signaling. Our data suggest that the fusion-driven structure formation induces a previously unrecognized cell survival and resistance mechanism, which depends on ERK1/2-activation.

Autoinhibition in the Signal Transducer CIN85 Modulates B Cell Activation

Signal transduction by the ligated B cell antigen receptor (BCR) depends on the preorganization of its intracellular components, such as the effector proteins SLP65 and CIN85 within phase-separated condensates. These liquid-like condensates are based on the interaction between three Src homology 3 (SH3) domains and the corresponding proline-rich recognition motifs (PRM) in CIN85 and SLP65, respectively. However, detailed information on the protein conformation and how it impacts the capability of SLP65/CIN85 condensates to orchestrate BCR signal transduction is still lacking. This study identifies a hitherto unknown intramolecular SH3:PRM interaction between the C-terminal SH3 domain (SH3C) of CIN85 and an adjacent PRM. We used high-resolution nuclear magnetic resonance (NMR) experiments to study the flexible linker region containing the PRM and determined the extent of the interaction in multidomain constructs of the protein. Moreover, we observed that the phosphorylation of a serine residue located in the immediate vicinity of the PRM regulates this intramolecular interaction. This allows for a dynamic modulation of CIN85's valency toward SLP65. B cell culture experiments further revealed that the PRM/SH3C interaction is crucial for maintaining the physiological level of SLP65/CIN85 condensate formation, activation-induced membrane recruitment of CIN85, and subsequent mobilization of Ca2+. Our findings therefore suggest that the intramolecular interaction with the adjacent disordered linker is effective in modulating CIN85's valency both in vitro and in vivo. This therefore constitutes a powerful way for the modulation of SLP65/CIN85 condensate formation and subsequent B cell signaling processes within the cell.

STS-1 and STS-2, Multi-Enzyme Proteins Equipped to Mediate Protein-Protein Interactions

STS-1 and STS-2 form a small family of proteins that are involved in the regulation of signal transduction by protein-tyrosine kinases. Both proteins are composed of a UBA domain, an esterase domain, an SH3 domain, and a PGM domain. They use their UBA and SH3 domains to modify or rearrange protein-protein interactions and their PGM domain to catalyze protein-tyrosine dephosphorylation. In this manuscript, we discuss the various proteins that have been found to interact with STS-1 or STS-2 and describe the experiments used to uncover their interactions.

Construction of the prognostic signature of alternative splicing revealed the prognostic predictor and immune microenvironment in head and neck squamous cell carcinoma

Background: Head and neck squamous cell carcinoma (HNSC) is a prevalent and heterogeneous malignancy with poor prognosis and high mortality rates. There is significant evidence of alternative splicing (AS) contributing to tumor development, suggesting its potential in predicting prognosis and therapeutic efficacy. This study aims to establish an AS-based prognostic signature in HNSC patients.

Methods: The expression profiles and clinical information of 486 HNSC patients were downloaded from the TCGA database, and the AS data were downloaded from the TCGA SpliceSeq database. The survival-associated AS events were identified by conducting a Cox regression analysis and utilized to develop a prognostic signature by fitting into a LASSO-regularized Cox regression model. Survival analysis, univariate and multivariate Cox regression analysis, and receiver operating characteristic (ROC) curve analysis were performed to evaluate the signature and an independent cohort was used for validation. The immune cell function and infiltration were analyzed by CIBERSORT and the ssGSEA algorithm.

Results: Univariate Cox regression analysis identified 2726 survival-associated AS events from 1714 genes. The correlation network reported DDX39B, PRPF39, and ARGLU1 as key splicing factors (SF) regulating these AS events. Eight survival-associated AS events were selected and validated by LASSO regression to develop a prognostic signature. It was confirmed that this signature could predict HNSC outcomes independent of other variables via multivariate Cox regression analysis. The risk score AUC was more than 0.75 for 3 years, highlighting the signature’s prediction capability. Immune infiltration analysis reported different immune cell distributions between the two risk groups. The immune cell content was higher in the high-risk group than in the low-risk group. The correlation analysis revealed a significant correlation between risk score, immune cell subsets, and immune checkpoint expression.

Conclusion: The prognostic signature developed from survival-associated AS events could predict the prognosis of HNSC patients and their clinical response to immunotherapy. However, this signature requires further research and validation in larger cohort studies.

B- and T-Cell Subset Abnormalities in Monogenic Common Variable Immunodeficiency

Common variable immunodeficiency (CVID) is a heterogeneous group of inborn errors of immunity characterized by reduced serum concentrations of different immunoglobulin isotypes. CVID is the most prevalent symptomatic antibody deficiency with a broad range of infectious and non-infectious clinical manifestations. Various genetic and immunological defects are known to be involved in the pathogenesis of CVID. Monogenic defects account for the pathogenesis of about 20-50% of CVID patients, while a variety of cases do not have a defined genetic background. Deficiencies in molecules of B cell receptor signaling or other pathways involving B-cell development, activation, and proliferation could be associated with monogenetic defects of CVID. Genetic defects damping different B cell developmental stages can alter B- and even other lymphocytes’ differentiation and might be involved in the clinical and immunologic presentations of the disorder. Reports concerning T and B cell abnormalities have been published in CVID patients, but such comprehensive data on monogenic CVID patients is few and no review article exists to describe the abrogation of lymphocyte subsets in these disorders. Hence, we aimed to review the role of altered B- and T-cell differentiation in the pathogenesis of CVID patients with monogenic defects.

Functions and Mechanisms of Pro-Lysyl Oxidase Processing in Cancers and Eye Pathologies with a Focus on Diabetic Retinopathy

Lysyl oxidases are multifunctional proteins derived from five lysyl oxidase paralogues (LOX) and lysyl oxidase-like 1 through lysyl oxidase-like 4 (LOXL1-LOXL4). All participate in the biosynthesis of and maturation of connective tissues by catalyzing the oxidative deamination of lysine residues in collagens and elastin, which ultimately results in the development of cross-links required to function. In addition, the five LOX genes have been linked to fibrosis and cancer when overexpressed, while tumor suppression by the propeptide derived from pro-LOX has been documented. Similarly, in diabetic retinopathy, LOX overexpression, activity, and elevated LOX propeptide have been documented. The proteolytic processing of pro-forms of the respective proteins is beginning to draw attention as the resultant peptides appear to exhibit their own biological activities. In this review we focus on the LOX paralogue, and what is known regarding its extracellular biosynthetic processing and the still incomplete knowledge regarding the activities and mechanisms of the released lysyl oxidase propeptide (LOX-PP). In addition, a summary of the roles of both LOX and LOX-PP in diabetic retinopathy, and brief mentions of the roles for LOX and closely related LOXL1 in glaucoma, and keratoconus, respectively, are included.

THE ACQUISITION OF RESISTANCE IN HUMAN NON-SMALL LUNG ADENOCARCINOMA MOR CELLS IS ASSOCIATED WITH UP-REGULATION OF ADAPTOR PROTEIN RUK/CIN85 AND EPITHELIAL-TO-MESENCHYMAL TRANSITION (EMT)

The aim of this study was to elucidate the regulatory role of Ruk/CIN85 in chemoresistance and EMT using human NSCLC MOR cells as a model. Methods. MOR (ECACC 84112312) cell line and drug-resistant cell line MOR/0.2R (ECACC 96042335) were cultured under standard conditions in DMEM medium. Knockdown of Ruk/CIN85 in MOR/0.2R cells was performed using shRNA lentiviral technology. Expression levels of Ruk/CIN85, vimentin and E-cadherin were estimated by RT-PCR. Results and Discussion. According to the results of qPCR, MOR/0.R cells showed an extremely higher level of Ruk/CIN85 mRNA expression, more than 10 times higher than the parental MOR cells. Preliminary data revealed that knockdown of Ruk/CIN85 in the MOR/0.2R cells led to significant decrease of their resistance to doxorubicin and development of epithelial phenotype. High content of RukCIN85 in doxorubicin-resistant (MOR/R) cells strongly correlate with their mesenchymal phenotype (high expression level of vimentin and low – E-cadherin), while its down-regulation is followed by restoration of expression values characteristic of parental MOR cells. Conclusions. In summary, high expression level of Ruk/CIN85 in doxorubicin-resistant MOR cells and the reversion of EMT-related transcriptome parameters and sensitivity to drug due to knockdown of adaptor protein in this subline suggests its involvement in regulation of EMT as well as cancer cells chemoresistance. Thus, the adaptor protein Ruk/CIN85 can be considered as a tissue-specific marker of carcinogenesis and perspective target for drug development.

MUC Glycoproteins: Potential Biomarkers and Molecular Targets for Cancer Therapy

MUC proteins have great significance as prognostic and diagnostic markers as well as a potential target for therapeutic interventions in most cancers of glandular epithelial origin. These are high molecular weight glycosylated proteins located in the epithelial lining of several tissues and ducts. Mucins belong to a heterogeneous group of large O-glycoproteins that can be either secreted or membrane-bound. Glycosylation, a post-translational modification affects the biophysical, functional and biochemical properties and provides structural complexity for these proteins. Aberrant expression and glycosylation of mucins contribute to tumour survival and proliferation in many cancers, which in turn activates numerous signalling pathways such as NF-kB, ERα, HIF, MAPK, p53, c-Src, Wnt and JAK-STAT, etc. This subsequently induces cancer cell growth, proliferation and metastasis. The present review mainly demonstrates the functional aspects of MUC glycoproteins along with its unique signalling mechanism and role of aberrant glycosylation in cancer progression and therapeutics. The importance of MUC proteins and its subtypes in a wide spectrum of cancers including but not limited to breast cancer, colorectal cancer, endometrial and cervical cancer, lung cancer, primary liver cancer, pancreatic cancer, prostate cancer and ovarian cancer has been exemplified with significance in targeting the same. Several patents associated with the MUC proteins in the field of cancer therapy are also emphasized in the current review.

High expression of CIN85 promotes proliferation and invasion of human esophageal squamous cell carcinoma

SH3 domain-containing kinase-binding protein 1 (CIN85), an 85 kDa protein known to be a member of the signal adaptor family, is abnormally expressed in several human malignancies and has been found to be involved in the growth, migration and invasion of these tumors. The objective of the present study was to clarify the clinical significance of CIN85 in human esophageal squamous cell carcinoma (ESCC), as well as its in vitro functions. CIN85 expression was evaluated in 129 cases of ESCC and its adjacent normal tissues using immunohistochemistry to explore its clinical relevance and prognostic value. The functions of CIN85 in the ESCC TE1 cell line were analyzed in vitro using the interfering short hairpin RNA silencing technique. MTS, wound healing, clone formation and Transwell assays were used to detect the proliferation, migration and invasion of ESCC cells. CIN85 expression was identified mainly in ESCCs and their adjacent normal tissues, and the high expression of CIN85 was significantly associated with advanced Tumor Node Metastasis stage and lymph node metastasis. CIN85 gene silencing significantly inhibited TE1 cell proliferation, migration and invasion. These results demonstrated that CIN85 was highly expressed in advanced stage ESCC and lymph node metastasis, and played a critical role in tumor proliferation and progression. Therefore, CIN85 may be a promising therapeutic target for human ESCC.

The Pro-Oncogenic Adaptor CIN85 Acts as an Inhibitory Binding Partner of Hypoxia-Inducible Factor Prolyl Hydroxylase 2

The EGFR adaptor protein, CIN85, has been shown to promote breast cancer malignancy and hypoxia-inducible factor (HIF) stability. However, the mechanisms underlying cancer promotion remain ill defined. Here we show that CIN85 is a novel binding partner of the main HIF-prolyl hydroxylase, PHD2, but not of PHD1 or PHD3. Mechanistically, the N-terminal SRC homology 3 domains of CIN85 interacted with the proline-arginine-rich region within the N-terminus of PHD2, thereby inhibiting PHD2 activity and HIF degradation. This activity is essential in vivo, as specific loss of the CIN85-PHD2 interaction in CRISPR/Cas9-edited cells affected growth and migration properties, as well as tumor growth in mice. Overall, we discovered a previously unrecognized tumor growth checkpoint that is regulated by CIN85-PHD2 and uncovered an essential survival function in tumor cells by linking growth factor adaptors with hypoxia signaling. SIGNIFICANCE: This study provides unprecedented evidence for an oxygen-independent mechanism of PHD2 regulation that has important implications in cancer cell survival. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/79/16/4042/F1.large.jpg.

Human Cytomegalovirus UL135 Interacts with Host Adaptor Proteins To Regulate Epidermal Growth Factor Receptor and Reactivation from Latency

Human cytomegalovirus, HCMV, is a betaherpesvirus that establishes a lifelong latent infection in its host that is marked by recurrent episodes of reactivation. The molecular mechanisms by which the virus and host regulate entry into and exit from latency remain poorly understood. We have previously reported that UL135 is critical for reactivation, functioning in part by overcoming suppressive effects of the latency determinant UL138 We have demonstrated a role for UL135 in diminishing cell surface levels and targeting epidermal growth factor receptor (EGFR) for turnover. The attenuation of EGFR signaling promotes HCMV reactivation in combination with cellular differentiation. In this study, we sought to define the mechanisms by which UL135 functions in regulating EGFR turnover and viral reactivation. Screens to identify proteins interacting with pUL135 identified two host adaptor proteins, CIN85 and Abi-1, with overlapping activities in regulating EGFR levels in the cell. We mapped the amino acids in pUL135 necessary for interaction with Abi-1 and CIN85 and generated recombinant viruses expressing variants of pUL135 that do not interact with CIN85 or Abi-1. These recombinant viruses replicate in fibroblasts but are defective for reactivation in an experimental model for latency using primary CD34+ hematopoietic progenitor cells (HPCs). These UL135 variants have altered trafficking of EGFR and are defective in targeting EGFR for turnover. These studies demonstrate a requirement for pUL135 interactions with Abi-1 and CIN85 for regulation of EGFR and mechanistically link the regulation of EGFR to reactivation.IMPORTANCE Human cytomegalovirus (HCMV) establishes a lifelong latent infection in the human host. While the infection is typically asymptomatic in healthy individuals, HCMV infection poses life-threatening disease risk in immunocompromised individuals and is the leading cause of birth defects. Understanding how HCMV controls the lifelong latent infection and reactivation of replication from latency is critical to developing strategies to control HCMV disease. Here, we identify the host factors targeted by a viral protein that is required for reactivation. We define the importance of this virus-host interaction in reactivation from latency, providing new insights into the molecular underpinnings of HCMV latency and reactivation.

Germline deletion of CIN85 in humans with X chromosome-linked antibody deficiency

Despite the numerous cellular functions attributed to the scaffolding protein CIN85, Keller et al. show that an inactivating germline deletion within the human CIN85 gene causes a remarkably specific defect in the activation of B lymphocytes, preventing proper immune responses.

Ubiquitously expressed Cbl-interacting protein of 85 kD (CIN85) is a multifunctional adapter molecule supposed to regulate numerous cellular processes that are critical for housekeeping as well as cell type–specific functions. However, limited information exists about the in vivo roles of CIN85, because only conditional mouse mutants with cell type–specific ablation of distinct CIN85 isoforms in brain and B lymphocytes have been generated so far. No information is available about the roles of CIN85 in humans. Here, we report on primary antibody deficiency in patients harboring a germline deletion within the CIN85 gene on the X chromosome. In the absence of CIN85, all immune cell compartments developed normally, but B lymphocytes showed intrinsic defects in distinct effector pathways of the B cell antigen receptor, most notably NF-κB activation and up-regulation of CD86 expression on the cell surface. These results reveal nonredundant functions of CIN85 for humoral immune responses.

Functional links between Disabled-2 Ser723 phosphorylation and thrombin signaling in human platelets

Essentials Disabled-2 (Dab2) phosphorylation status in thrombin signaling of human platelet was investigated. Ser723 was the major Dab2 phosphorylation site in human platelets stimulated by thrombin. Dab2 S723 phosphorylation (pS723) caused the dissociation of Dab2-CIN85 protein complex. Dab2-pS723 regulated ADP release and integrin αIIbβ3 activation in thrombin-treated platelets.

SUMMARY

Background Disabled-2 (Dab2) is a platelet protein that is functionally involved in thrombin signaling in mice. It is unknown whether or not Dab2 undergoes phosphorylation during human platelet activation. Objectives To investigate the phosphorylation status of Dab2 and its functional consequences in thrombin-stimulated human platelets. Methods Dab2 was immunoprecipitated from resting and thrombin-stimulated platelet lysates for differential isotopic labeling. After enrichment of the phosphopeptides, the phosphorylation sites were analyzed by mass spectrometry. The corresponding phospho-specific antibody was generated. The protein kinases responsible for and the functional significance of Dab2 phosphorylation were defined by the use of signaling pathway inhibitors/activators, protein kinase assays, and various molecular approaches. Results Dab2 was phosphorylated at Ser227, Ser394, Ser401 and Ser723 in thrombin-stimulated platelets, with Ser723 phosphorylation being the most significantly increased by thrombin. Dab2 was phosphorylated by protein kinase C at Ser723 in a Gαq -dependent manner. ADP released from the stimulated platelets further activated the Gβγ -dependent pathway to sustain Ser723 phosphorylation. The Cbl-interacting protein of 85 kDa (CIN85) bound to Dab2 at a motif adjacent to Ser723 in resting platelets. The consequence of Ser723 phosphorylation was the dissociation of CIN85 from the Dab2-CIN85 complex. These molecular events led to increases in fibrinogen binding and platelet aggregation in thrombin-stimulated platelets by regulating αIIb β3 activation and ADP release. Conclusions Dab2 Ser723 phosphorylation is a key molecular event in thrombin-stimulated inside-out signaling and platelet activation, contributing to a new function of Dab2 in thrombin signaling.

Intra- and Extra-Cellular Events Related to Altered Glycosylation of MUC1 Promote Chronic Inflammation, Tumor Progression, Invasion, and Metastasis

Altered glycosylation of mucin 1 (MUC1) on tumor cells compared to normal epithelial cells was previously identified as an important antigenic modification recognized by the immune system in the process of tumor immunosurveillance. This tumor form of MUC1 is considered a viable target for cancer immunotherapy. The importance of altered MUC1 glycosylation extends also to its role as a promoter of chronic inflammatory conditions that lead to malignant transformation and cancer progression. We review here what is known about the role of specific cancer-associated glycans on MUC1 in protein-protein interactions and intracellular signaling in cancer cells and in their adhesion to each other and the tumor stroma. The tumor form of MUC1 also creates a different landscape of inflammatory cells in the tumor microenvironment by controlling the recruitment of inflammatory cells, establishing specific interactions with dendritic cells (DCs) and macrophages, and facilitating tumor escape from the immune system. Through multiple types of short glycans simultaneously present in tumors, MUC1 acquires multiple oncogenic properties that control tumor development, progression, and metastasis at different steps of the process of carcinogenesis.

The adaptor protein CIN85 assembles intracellular signaling clusters for B cell activation

The adaptor molecule Cbl-interacting protein of 85 kD (CIN85) regulates signaling from a number of cell surface receptors, such as growth factor receptors and antigen receptors on lymphocytes. Because of its multidomain structure, CIN85 is thought to act as a classical adaptor protein that connects functionally distinct components of a given signaling pathway through diverse protein domains. However, we found that in B lymphocytes, CIN85 functions to oligomerize SLP-65, which is the central effector protein of the B cell receptor (BCR). Therefore, CIN85 trimerizes through a carboxyl-terminal, coiled-coil domain. The multiple Src homology 3 (SH3) domains of trimeric CIN85 molecules associated with multiple SLP-65 molecules, which recruited further CIN85 trimers, thereby perpetuating the oligomerization process. Formation of this oligomeric signaling complex in resting B cells rendered the cells poised for the efficient initiation of intracellular signaling upon BCR stimulation. Our data suggest that the functionality of signaling cascades does not rely solely on the qualitative linkage of their various components but requires a critical number of effectors to become concentrated in signaling complexes.

A Novel Interaction of the Catalytic Subunit of Protein Phosphatase 2A with the Adaptor Protein CIN85 Suppresses Phosphatase Activity and Facilitates Platelet Outside-in αIIbβ3 Integrin Signaling

The transduction of signals generated by protein kinases and phosphatases are critical for the ability of integrin αIIbβ3 to support stable platelet adhesion and thrombus formation. Unlike kinases, it remains unclear how serine/threonine phosphatases engage the signaling networks that are initiated following integrin ligation. Because protein-protein interactions form the backbone of signal transduction, we searched for proteins that interact with the catalytic subunit of protein phosphatase 2A (PP2Ac). In a yeast two-hybrid study, we identified a novel interaction between PP2Ac and an adaptor protein CIN85 (Cbl-interacting protein of 85 kDa). Truncation and alanine mutagenesis studies revealed that PP2Ac binds to the P3 block ((396)PAIPPKKPRP(405)) of the proline-rich region in CIN85. The interaction of purified PP2Ac with CIN85 suppressed phosphatase activity. Human embryonal kidney 293 αIIbβ3 cells overexpressing a CIN85 P3 mutant, which cannot support PP2Ac binding, displayed decreased adhesion to immobilized fibrinogen. Platelets contain the ∼85 kDa CIN85 protein along with the PP2Ac-CIN85 complex. A myristylated cell-permeable peptide derived from residues 395-407 of CIN85 protein (P3 peptide) disrupted the platelet PP2Ac-CIN85 complex and decreased αIIbβ3 signaling dependent functions such as platelet spreading on fibrinogen and thrombin-mediated fibrin clot retraction. In a phospho-profiling study P3 peptide treated platelets also displayed decreased phosphorylation of several signaling proteins including Src and GSK3β. Taken together, these data support a role for the novel PP2Ac-CIN85 complex in supporting integrin-dependent platelet function by dampening the phosphatase activity.

Pathobiological implications of mucin glycans in cancer: Sweet poison and novel targets

Mucins are large glycoproteins expressed on the epithelia that provide a protective barrier against harsh insults from toxins and pathogenic microbes. These glycoproteins are classified primarily as being secreted and membrane-bound; both forms are involved in pathophysiological functions including inflammation and cancer. The high molecular weight of mucins is attributed to their large polypeptide backbone that is extensively covered by glycan moieties that modulate the function of mucins and, hence, play an important role in physiological functions. Deregulation of glycosylation machinery during malignant transformation results in altered mucin glycosylation. This review describes the functional implications and pathobiological significance of altered mucin glycosylation in cancer. Further, this review delineates various factors such as glycosyltransferases and tumor microenvironment that contribute to dysregulation of mucin glycosylation during cancer. Finally, this review discusses the scope of mucin glycan epitopes as potential diagnostic and therapeutic targets.

CIN85 modulates TGFβ signaling by promoting the presentation of TGFβ receptors on the cell surface

Members of the transforming growth factor β (TGFβ) family initiate cellular responses by binding to TGFβ receptor type II (TβRII) and type I (TβRI) serine/threonine kinases, whereby Smad2 and Smad3 are phosphorylated and activated, promoting their association with Smad4. We report here that TβRI interacts with the SH3 domains of the adaptor protein CIN85 in response to TGFβ stimulation in a TRAF6-dependent manner. Small interfering RNA-mediated knockdown of CIN85 resulted in accumulation of TβRI in intracellular compartments and diminished TGFβ-stimulated Smad2 phosphorylation. Overexpression of CIN85 instead increased the amount of TβRI at the cell surface. This effect was inhibited by a dominant-negative mutant of Rab11, suggesting that CIN85 promoted recycling of TGFβ receptors. CIN85 enhanced TGFβ-stimulated Smad2 phosphorylation, transcriptional responses, and cell migration. CIN85 expression correlated with the degree of malignancy of prostate cancers. Collectively, our results reveal that CIN85 promotes recycling of TGFβ receptors and thereby positively regulates TGFβ signaling.

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.

Complex of MUC1, CIN85 and Cbl in Colon Cancer Progression and Metastasis

We previously reported that CIN85, an 85 KDa protein known to be involved in tumor cell migration and metastasis through its interaction with Cbl, associates with MUC1 in tumor cells. MUC1/CIN85 complex also regulates migration and invasion of tumor cells in vitro. Here, we examined specifically human colon carcinoma tissue microarrays (TMA) by immunohistochemistry for the expression of MUC1 and CIN85 and their potential role in cancer progression and metastasis. We detected a significant increase in expression of both MUC1 and CIN85 associated with advanced tumor stage and lymph node metastasis. We further investigated if Cbl could also be present in the MUC1/CIN85 complex. Co-immunoprecipitation assay showed that Cbl co-localized both with CIN85 and with MUC1 in a human colon cancer cell line. To begin to investigate the in vivo relevance of MUC1 overexpression and association with CIN85 and Cbl in cancer development and progression, we used human MUC1 transgenic mice that express MUC1 on the colonic epithelial cells, treated with azoxymethane to initiate and dextran sulfate sodium (AOM/DSS) to promote colorectal carcinogenesis. MUC1.Tg mice showed higher tumor incidence and decreased survival when compared with wild-type mice. Consistent with the in vitro data, the association of MUC1, CIN85 and Cbl was detected in colon tissues of AOM/DSS-treated MUC1 transgenic mice. MUC1/CIN85/Cbl complex appears to contribute to promotion and progression of colon cancer and thus increased expression of MUC1, CIN85 and Cbl in early stage colon cancer might be predictive of poor prognosis.

MS/MS-based strategies for proteomic profiling of invasive cell structures

Acquired capacity of cancer cells to penetrate through the extracellular matrix of surrounding tissues is a prerequisite for tumour metastatic spread - the main source of cancer-associated mortality. Through combined efforts of many research groups, we are beginning to understand that the ability of cells to invade through the extracellular matrix is a multi-faceted phenomenon supported by variety of specialised protrusive cellular structures, primarily pseudopodia, invadopodia and podosomes. Additionally, secreted extracellular vesicles are being increasingly recognised as important mediators of invasive cell phenotypes and therefore may be considered bona fide invasive cell structures. Dissection of the molecular makings underlying biogenesis and function of all of these structures is crucial to identify novel targets for specific anti-metastatic therapies. Rapid advances and growing accessibility of MS/MS-based protein identification made this family of techniques a suitable and appropriate choice for proteomic profiling of invasive cell structures. In this review, we provide a summary of current progress in the characterisation of protein composition and topology of protein interaction networks of pseudopodia, invadopodia, podosomes and extracellular vesicles, as well as outline challenges and perspectives of the field.

SEPT9 negatively regulates ubiquitin-dependent downregulation of EGFR

Septins constitute a family of GTP-binding proteins that are involved in a variety of biological processes. Several isoforms have been implicated in disease, but the molecular mechanisms underlying pathogenesis are poorly understood. Here, we show that depletion of SEPT9 decreases surface levels of epidermal growth factor receptors (EGFRs) by enhancing receptor degradation. We identify a consensus motif within the SEPT9 N-terminal domain that supports its association with the adaptor protein CIN85 (also known as SH3KBP1). We further show CIN85-SEPT9 to be localized exclusively to the plasma membrane, where SEPT9 is recruited to EGF-engaged receptors in a CIN85-dependent manner. Finally, we demonstrate that SEPT9 negatively regulates EGFR degradation by preventing the association of the ubiquitin ligase Cbl with CIN85, resulting in reduced EGFR ubiquitylation. Taken together, these data provide a mechanistic explanation of how SEPT9, though acting exclusively at the plasma membrane, impairs the sorting of EGFRs into the degradative pathway.

Altered glycosylation of MUC1 influences its association with CIN85: the role of this novel complex in cancer cell invasion and migration

MUC1 is a transmembrane glycoprotein abnormally expressed in human adenocarcinomas. The extracellular domain of MUC1 contains a variable number of tandem repeats (VNTR) region that is extensively O-glycosylated in normal epithelia and underglycosylated in tumor cells. This change in posttranslational modification of MUC1 leads to changes in its normal functions including, we hypothesized, its interaction with other molecules. We identified CIN85, an adaptor protein involved in multiple cellular processes including signal transduction, cytoskeletal remodeling and cancer cell invasion, as one of several proteins that associate with MUC1 in tumor cells. CIN85 associates with both the cytosolic tail and the extracellular VNTR of MUC1. Co-immunoprecipitation and confocal immunofluorescence confirmed that MUC1 and CIN85 co-localize primarily at the plasma membrane but the complex can be found also in the cytosol and on the cytoskeleton. MUC1 and CIN85 are both over-expressed in early as well as advanced clinical stages of breast cancer and co-localize on invadopodia-like structures implicated in cell invasion. siRNA-mediated silencing of CIN85 and/or MUC1 revealed that MUC1 enhances CIN85-dependent breast cancer cell migration and invasion in vitro. However, ectopic expression of MUC1 enhances the motility induced by CIN85. When tested in vivo in a tumor metastasis model of B16 melanoma, mice injected with CIN85-depleted melanoma cells exhibited few or no lung metastasis and, similarly to the in vitro results, overexpression of MUC1 recovered the shCIN85-reduced metastatic process. Our findings implicate this newly identified CIN85/MUC1 complex associated with invadopodia-related molecules in promoting the invasive and metastatic potential of breast cancer.

Inhibition of CIN85-mediated invasion by a novel SH3 domain binding motif in the lysyl oxidase propeptide

The lysyl oxidase gene inhibits Ras signaling in transformed fibroblasts and breast cancer cells. Its activity was mapped to the 162 amino acid propeptide domain (LOX-PP) of the lysyl oxidase precursor protein. LOX-PP inhibited the Her-2/Ras signaling axis in breast cancer cells, and reduced the Her-2-driven breast tumor burden in a xenograft model. Since its mechanism of action is largely unknown, co-affinity-purification/mass spectrometry was performed and the “Cbl-interacting protein of 85-kDa” (CIN85) identified as an associating protein. CIN85 is an SH3-containing adapter protein that is overexpressed in invasive breast cancers. The CIN85 SH3 domains interact with c-Cbl, an E3 ubiquitin ligase, via an unconventional PxxxPR ligand sequence, with the highest affinity displayed by the SH3-B domain. Interaction with CIN85 recruits c-Cbl to the AMAP1 complex where its ubiquitination activity is necessary for cancer cells to develop an invasive phenotype and to degrade the matrix. Direct interaction of LOX-PP with CIN85 was confirmed using co-immunoprecipitation analysis of lysates from breast cancer cells and of purified expressed proteins. CIN85 interaction with c-Cbl was reduced by LOX-PP. Domain specific CIN85 regions and deletion mutants of LOX-PP were prepared and used to map the sites of interaction to the SH3-B domain of CIN85 and to an epitope encompassing amino acids 111 to 116 of LOX-PP. Specific LOX-PP point mutant proteins P111A and R116A failed to interact with CIN85 or to compete for CIN85 binding with c-Cbl. Structural modeling identified a new atypical PxpxxRh SH3-binding motif in this region of LOX-PP. The LOX-PP interaction with CIN85 was shown to reduce the invasive phenotype of breast cancer cells, including their ability to degrade the surrounding extracellular matrix and for Matrigel outgrowth. Thus, LOX-PP interacts with CIN85 via a novel SH3-binding motif and this association reduces CIN85-promoted invasion by breast cancer cells.

Spatiotemporal control of Cindr at ring canals during incomplete cytokinesis in the Drosophila male germline

During male and female gametogenesis in species ranging from insects to mammals, germ cell cyst formation by incomplete cytokinesis involves the stabilization of cleavage furrows and the formation of stable intercellular bridges called ring canals. Accurate regulation of incomplete cytokinesis is required for both female and male fertility in Drosophila melanogaster. Nevertheless, the molecular mechanisms controlling complete versus incomplete cytokinesis are largely unknown. Here, we show that the scaffold protein Cindr is a novel component of both mitotic and meiotic ring canals during Drosophila spermatogenesis. Strikingly, unlike other male germline ring canal components, including Anillin and Pavarotti, Cindr and contractile ring F-actin dissociate from mitotic ring canals and translocate to the fusome upon completion of the mitotic germ cell divisions. We provide evidence that the loss of Cindr from mitotic ring canals is coordinated by signals that mediate the transition from germ cell mitosis to differentiation. Interestingly, Cindr loss from ring canals coincides with completion of the mitotic germ cell divisions in both Drosophila females and males, thus marking a common step of gametogenesis. We also show that Cindr co-localizes with Anillin at mitotic and meiotic ring canals and is recruited to the contractile ring by Anillin during male germ cell meiotic cytokinesis. Taken together, our analyses reveal a key step of incomplete cytokinesis at the endpoint of the mitotic germ cell divisions in D. melanogaster.

Adaptor protein complex of FRS2β and CIN85/CD2AP provides a novel mechanism for ErbB2/HER2 protein downregulation

Overexpression of the ErbB2/HER2 receptor tyrosine kinase contributes to tumorigenesis. However, mechanisms regulating ErbB2 protein levels remain largely unclear. Here, we identified novel mechanisms of ErbB2 downregulation. ErbB2 constitutively binds to an adaptor protein FRS2β. We found that FRS2β bound to CD2AP and CIN85, which induces endosomal trafficking that targets lysosomes. FRS2β colocalized with CIN85 in the cytoplasm. Expression of wild type FRS2β but not its CIN85 non-binding mutant, downregulated the ErbB2 protein and inhibited anchorage-independent cell growth. Moreover, the E3 ubiquitin-protein ligase Cbl was contained within a complex of FRS2β and CIN85. Knockdown of both CIN85 and CD2AP or of Cbl, or treatment with lysosomal degradation inhibitors diminished FRS2β downregulation of ErbB2. In addition, knockdown of endogenous FRS2β caused upregulation of ErbB2 in primary neural cells. Finally, immunohistochemical analysis showed that human breast cancer tissues that overexpress ErbB2 expressed low levels of FRS2β. Thus, an FRS2β-CIN85/CD2AP-Cbl axis for downregulation of ErbB2 may regulate ErbB2 protein levels in physiological and pathological settings. Molecular targeting drugs that can increase or stabilize the ErbB2-FRS2β-CIN85/CD2AP-Cbl axis may have promise for the control of ErbB2-overexpressing tumors.

Membrane trafficking in podocyte health and disease

Podocytes are highly specialized epithelial cells localized in the kidney glomerulus. The distinct cell signaling events and unique cytoskeletal architecture tailor podocytes to withstand changes in hydrostatic pressure during glomerular filtration. Alteration of glomerular filtration leads to kidney disease and frequently manifests with proteinuria. It has been increasingly recognized that cell signaling and cytoskeletal dynamics are coupled more tightly to membrane trafficking than previously thought. Membrane trafficking coordinates the cross-talk between protein networks and signaling cascades in a spatially and temporally organized fashion and may be viewed as a communication highway between the cell exterior and interior. Membrane trafficking involves transport of cargo from the plasma membrane to the cell interior (i.e., endocytosis) followed by cargo trafficking to lysosomes for degradation or to the plasma membrane for recycling. Yet, recent studies indicate that the conventional classification does not fully reflect the complex and versatile nature of membrane trafficking. While the increasing complexity of elaborate protein scaffolds and signaling cascades is being recognized in podocytes, the role of membrane trafficking is less well understood. This review will focus on the role of membrane trafficking in podocyte health and disease.

Dab1 stabilizes its interaction with Cin85 by suppressing Cin85 phosphorylation at serine 587

Crk and CrkL adaptors play essential neuronal positioning roles downstream of Reelin-induced Dab1 tyrosine phosphorylation. Recently we identified Cin85 to be a CrkL-SH3 binding partner from embryonic murine brain while others found Cin85 binds directly to Dab1. Here using mass spectrometry, biochemical and mutational analyses we show that Dab1 suppresses Cin85 phosphorylation at Ser587. Furthermore a Cin85 Ser587 phosphomimetic disrupts the Dab1-Cin85 complex without affecting the Cin85-CapZ complex. These data provide an early glimpse into how Cin85 phosphorylation might alter the composition of its scaffolding partners to regulate its diverse roles including vesicular trafficking, receptor endocytosis and actin remodeling.

Increased levels of the HER1 adaptor protein Rukl/CIN85 contribute to breast cancer malignancy

The adaptor protein regulator for ubiquitous kinase/c-Cbl-interacting protein of 85kDa (Ruk/CIN85) was found to modulate HER1/EGFR signaling and processes like cell adhesion and apoptosis. Although these features imply a role in carcinogenesis, it is so far unknown how and by which molecular mechanisms Ruk/CIN85 could affect a certain tumor phenotype. By analyzing samples from breast cancer patients, we found high levels of Ruk(l)/CIN85 especially in lymph node metastases from patients with invasive breast adenocarcinomas, suggesting that Ruk(l)/CIN85 contributes to malignancy. Expression of Ruk(l)/CIN85 in weakly invasive breast adenocarcinoma cells deficient of Ruk(l)/CIN85 indeed converted them into more malignant cells. In particular, Ruk(l)/CIN85 reduced the growth rate, decreased cell adhesion, enhanced anchorage-independent growth, increased motility in both transwell migration and wound healing assays as well as affected the response to epidermal growth factor. Thereby, Ruk(l)/CIN85 led to a more rapid and prolonged epidermal growth factor-dependent activation of Src, Akt and ERK1/2 and treatment with the Src inhibitor PP2 and the PI3K inhibitor LY294002 abolished the Ruk(l)/CIN85-dependent changes in cell motility. Together, this study indicates that high levels of Ruk(l)/CIN85 contribute to the conversion of breast adenocarcinoma cells into a more malignant phenotype via modulation of the Src/Akt pathway.

CD2AP regulates SUMOylation of CIN85 in podocytes

Podocytes are highly differentiated and polarized epithelial cells located on the visceral side of the glomerulus. They form an indispensable component of the glomerular filter, the slit diaphragm, formed by several transmembrane proteins and adaptor molecules. Disruption of the slit diaphragm can lead to massive proteinuria and nephrotic syndrome in mice and humans. CD2AP is an adaptor protein that is important for the maintenance of the slit diaphragm. Together with its paralogue, CIN85, CD2AP belongs to a family of adaptor proteins that are primarily described as being involved in endocytosis and downregulation of receptor tyrosine kinase activity. We have shown that full-length CIN85 is upregulated in podocytes in the absence of CD2AP, whereas in wild-type cells, full-length CIN85 is not detectable. In this study, we show that full-length CIN85 is postranslationally modified by SUMOylation in wild-type podocytes. We can demonstrate that CIN85 is SUMOylated by SUMO-1, -2, and -3 and that SUMOylation is enhanced in the presence of CD2AP. Conversion of lysine 598 to arginine completely abolishes SUMOylation and leads to increased binding of CIN85 to nephrin. Our results indicate a novel role for CD2AP in regulating posttranslational modification of CIN85.

The B-cell antigen receptor signals through a preformed transducer module of SLP65 and CIN85

Spleen tyrosine kinase Syk and its substrate SLP65 (also called BLNK) are proximal signal transducer elements of the B-cell antigen receptor (BCR). Yet, our understanding of signal initiation and processing is limited owing to the incomplete list of SLP65 interaction partners and our ignorance of their association kinetics. We have now determined and quantified the in vivo interactomes of SLP65 in resting and stimulated B cells by mass spectrometry. SLP65 orchestrated a complex signal network of about 30 proteins that was predominantly based on dynamic interactions. However, a stimulation-independent and constant association of SLP65 with the Cbl-interacting protein of 85 kDa (CIN85) was requisite for SLP65 phosphorylation and its inducible plasma membrane translocation. In the absence of a steady SLP65/CIN85 complex, BCR-induced Ca(2+) and NF-κB responses were abrogated. Finally, live cell imaging and co-immunoprecipitation experiments further confirmed that both SLP65 and CIN85 are key components of the BCR-associated primary transducer module required for the onset and progression phases of BCR signal transduction.

CIN85 regulates ubiquitination and degradative endosomal sorting of the EGF receptor

CIN85 has been demonstrated to interact with a number of proteins involved in endocytosis and intracellular sorting. However, the exact functional role of CIN85 in endocytosis remains unclear. We have investigated whether CIN85 plays a role in EGF-induced EGF receptor (EGFR) internalization, as previously suggested, or whether CIN85 is rather involved in endosomal sorting of the EGFR. When over-expressing a dominant negative interfering CIN85 mutant consisting of three SH3 domains only, we found that internalization of EGF was inhibited. However, when knocking down CIN85 by RNAi, the EGF-EGFR uptake appeared similar to in control cells. Furthermore, in CIN85 depleted cells, EGF-induced ubiquitination of the EGFR was decreased, and degradation of EGF-EGFR complexes was delayed. Our data further demonstrated that depletion of CIN85 increased the recycling of EGF, suggesting that CIN85 plays a role in endosomal sorting of the ubiquitinated EGFR. Our data also demonstrated that CIN85 was constitutively associated with Hrs, and this strengthens the hypothesis of a functional role of CIN85 in endosomal EGFR sorting.

CIN85 modulates the down-regulation of Fc gammaRIIa expression and function by c-Cbl in a PKC-dependent manner in human neutrophils

We previously described a non-classical mechanism that arrests FcγRIIa signaling in human neutrophils once engaged by immune complexes or opsonized pathogens. The engagement of FcγRIIa leads to its ubiquitination by the ubiquitin ligase c-Cbl and degradation by the proteasome. Herein, we further examined some of the events regulating this novel pathway. The adaptor protein CIN85 was described in other systems to be involved in the regulation of the c-Cbl-dependent pathway. We found that CIN85 is expressed in human neutrophils and that it translocates like c-Cbl from the cytosol to the plasma membrane following receptor cross-linking. CIN85 was also recruited to the same subset of high density detergent-resistant membrane fractions in which stimulated FcγRIIa partitioned with c-Cbl. The integrity of these microdomains is essential to the FcγRIIa degradation process because the cholesterol-depleting agent methyl-β-cyclodextrin inhibits this event. Silencing the expression of CIN85 by siRNA in dibutyryl cyclic AMP-differentiated PLB 985 cells prevented FcγRIIa degradation and increased IgG-mediated phagocytosis. Confocal microscopy revealed that the presence of CIN85 is essential to the proper sorting of FcγRIIa during endocytosis. We also provide direct evidence that CIN85 is a substrate of serine/threonine kinase PKCs. Classical PKCs positively regulate FcγRIIa ubiquitination and degradation because these events were inhibited by Gö6976, a classical PKC inhibitor. We conclude that the ubiquitination and degradation of stimulated FcγRIIa mediated by c-Cbl are positively regulated by the adaptor protein CIN85 in a PKC-dependent manner and that these events contribute to the termination of FcγRIIa signaling.

A Dyn2-CIN85 complex mediates degradative traffic of the EGFR by regulation of late endosomal budding

The epidermal growth factor receptor (EGFR) is over-expressed in a variety of human cancers. Downstream signalling of this receptor is tightly regulated both spatially and temporally by controlling its internalization and subsequent degradation. Internalization of the EGFR requires dynamin 2 (Dyn2), a large GTPase that deforms lipid bilayers, leading to vesicle scission. The adaptor protein CIN85 (cbl-interacting protein of 85 kDa), which has been proposed to indirectly link the EGFR to the endocytic machinery at the plasma membrane, is also thought to be involved in receptor internalization. Here, we report a novel and direct interaction between Dyn2 and CIN85 that is induced by EGFR stimulation and, most surprisingly, occurs late in the endocytic process. Importantly, disruption of the CIN85-Dyn2 interaction results in accumulation of internalized EGFR in late endosomes that become aberrantly elongated into distended tubules. Consistent with the accumulation of this receptor is a sustention of downstream signalling cascades. These findings provide novel insights into a previously unknown protein complex that can regulate EGFR traffic at very late stages of the endocytic pathway.