Palmitoylation of cytoskeleton associated protein 4 by DHHC2 regulates antiproliferative factor-mediated signaling

Unraveling the potential contribution of DHHC2 in cancer biology via untargeted metabolomics

DHHC-mediated protein-S-palmitoylation is recognized as a distinct and reversible lipid modification, playing a pivotal role in the progression and prevention of multiple diseases, including cancer and neurodegenerative disorders. Over the past decade, growing evidence indicated the crucial role of DHHC2 in preventing tumorigenesis by palmitoylation of various protein substrates. However, a comprehensive understanding of the specific impact of DHHC2 on cancer cell metabolic regulation remains unclear. To investigate the metabolic changes by DHHC2, we conducted untargeted metabolomic profiling on the HEK-293T cell line with DHHC2-Knockdown (DHHC2-KD), DHHC2-Overexpression (DHHC2-OE) and empty vector control (Ctrl) conditions via LC-MS/MS-based analysis. Our dataset revealed the identification of a total of 73 metabolites encompassing all the conditions, with only 22 showing significant differences in univariate analysis. Furthermore, we performed pathway analysis with metabolites having VIP ≥ 0.7, P value ≤ 0.05, and fold change (FC) > 2 in DHHC2-OE (upregulated) and FC < 0.5 in DHHC2-OE or FC > 2 in DHHC2-KD condition (downregulated). We unveiled significant expression of the pyrimidine metabolism, urea cycle, and aspartate metabolism due to the abundance of onco-metabolites such as glutamine, uridine, and glutamic acid in the DHHC2-KD condition. However, DHHC2 overexpression resulted in a higher expression of metabolites previously reported to be associated with anti-cancer activity, such as betaine and 5'-methylthioadenosine (5'-MTA). Overall, this study sheds light on the changes mediated by DHHC2 in a cancer cell metabolome and suggests avenues for further investigation into other DHHC isoforms and their metabolic aspects.

Recapitulating the potential contribution of protein S-palmitoylation in cancer

Protein S-palmitoylation is a reversible form of protein lipidation in which the formation of a thioester bond occurs between a cysteine (Cys) residue of a protein and a 16-carbon fatty acid chain. This modification is catalyzed by a family of palmitoyl acyl transferases, the DHHC enzymes, so called because of their Asp-His-His-Cys (DHHC) catalytic motif. Deregulation of DHHC enzymes has been linked to various diseases, including cancer and infections. Cancer, a major cause of global mortality, is characterized by features like uncontrolled cell growth, resistance to cell death, angiogenesis, invasion, and metastasis. Several of these processes are controlled by DHHC-mediated S-palmitoylation of oncogenes or tumor suppressors, including growth factor receptors (e.g., EGFR), kinases (e.g., AKT), and transcription factors (e.g., β-catenin). Dynamic regulation of S-palmitoylation is also governed by protein depalmitoylases. These enzymes balance the cycling of palmitoylation and regulate cellular signaling, cell growth, and its organization. Given the significance of S-palmitoylation in cancer, the DHHCs and protein depalmitoylases are promising targets for cancer therapy. Here we summarize the catalytic mechanisms of DHHC enzymes and depalmitoylases, their role in cancer progression and prevention, as well as the crosstalk of palmitoylation with other post-translational modifications. Additionally, we discuss the methods to detect S-palmitoylation, the limitations of available DHHC-targeting inhibitors, and ongoing research efforts to address these obstacles.

Thyroid hormone T3 induces Fyn modification and modulates palmitoyltransferase gene expression through αvβ3 integrin receptor in PC12 cells during hypoxia

Thyroid hormones (THs) are essential in neuronal and glial cell development and differentiation, synaptogenesis, and myelin sheath formation. In addition to nuclear receptors, TH acts through αvβ3-integrin on the plasma membrane, influencing transcriptional regulation of signaling proteins that, in turn, affect adhesion and survival of nerve cells in various neurologic disorders. TH exhibits protective properties during brain hypoxia; however, precise intracellular mechanisms responsible for the preventive effects of TH remain unclear. In this study, we investigated the impact of TH on integrin αvβ3-dependent downstream systems in normoxic and hypoxic conditions of pheochromocytoma PC12 cells. Our findings reveal that triiodothyronine (T3), acting through αvβ3-integrin, induces activation of the JAK2/STAT5 pathway and suppression of the SHP2 in hypoxic PC12 cells. This activation correlates with the downregulation of the expression palmitoyltransferase-ZDHHC2 and ZDHHC9 genes, leading to a subsequent decrease in palmitoylation and phosphorylation of Fyn tyrosine kinase. We propose that these changes may occur due to STAT5-dependent epigenetic silencing of the palmitoyltransferase gene, which in turn reduces palmitoylation/phosphorylation of Fyn with a subsequent increase in the survival of cells. In summary, our study provides the first evidence demonstrating the involvement of integrin-dependent JAK/STAT pathway, SHP2 suppression, and altered post-translational modification of Fyn in protective effects of T3 during hypoxia.

Diverse Roles of Protein Palmitoylation in Cancer Progression, Immunity, Stemness, and Beyond

Protein S-palmitoylation, a type of post-translational modification, refers to the reversible process of attachment of a fatty acyl chain-a 16-carbon palmitate acid-to the specific cysteine residues on target proteins. By adding the lipid chain to proteins, it increases the hydrophobicity of proteins and modulates protein stability, interaction with effector proteins, subcellular localization, and membrane trafficking. Palmitoylation is catalyzed by a group of zinc finger DHHC-containing proteins (ZDHHCs), whereas depalmitoylation is catalyzed by a family of acyl-protein thioesterases. Increasing numbers of oncoproteins and tumor suppressors have been identified to be palmitoylated, and palmitoylation is essential for their functions. Understanding how palmitoylation influences the function of individual proteins, the physiological roles of palmitoylation, and how dysregulated palmitoylation leads to pathological consequences are important drivers of current research in this research field. Further, due to the critical roles in modifying functions of oncoproteins and tumor suppressors, targeting palmitoylation has been used as a candidate therapeutic strategy for cancer treatment. Here, based on recent literatures, we discuss the progress of investigating roles of palmitoylation in regulating cancer progression, immune responses against cancer, and cancer stem cell properties.

A network map of cytoskeleton-associated protein 4 (CKAP4) mediated signaling pathway in cancer

Cytoskeleton-associated protein 4 (CKAP4) is a non-glycosylated type II transmembrane protein that serves as a cell surface-activated receptor. It is expressed primarily in the plasma membranes of bladder epithelial cells, type II alveolar pneumocytes, and vascular smooth muscle cells. CKAP4 is involved in various biological activities including cell proliferation, cell migration, keratinocyte differentiation, glycogenesis, fibrosis, thymic development, cardiogenesis, neuronal apoptosis, and cancer. CKAP4 has been described as a pro-tumor molecule that regulates the progression of various cancers, including lung cancer, breast cancer, esophageal squamous cell carcinoma, hepatocellular carcinoma, cervical cancer, oral cancer, bladder cancer, cholangiocarcinoma, pancreatic cancer, myeloma, renal cell carcinoma, melanoma, squamous cell carcinoma, colorectal cancer, and osteosarcoma. CKAP4 and its isoform bind to DKK1 or DKK3 (Dickkopf proteins) or antiproliferative factor (APF) and regulates several downstream signaling cascades. The CKAP4 complex plays a crucial role in regulating the signaling pathways including PI3K/AKT and MAPK1/3. Recently, CKAP4 has been recognized as a potential target for cancer therapy. Due to its biomedical importance, we integrated a network map of CKAP4. The available literature on CKAP4 signaling was manually curated according to the NetPath annotation criteria. The consolidated pathway map comprises 41 activation/inhibition events, 21 catalysis events, 35 molecular associations, 134 gene regulation events, 83 types of protein expression, and six protein translocation events. CKAP4 signaling pathway map data is freely accessible through the WikiPathways Database ( https://www.wikipathways.org/index.php/Pathway:WP5322 ). Generation of CKAP4 signaling pathway map.

Control of mitochondria-associated endoplasmic reticulum membranes by protein S-palmitoylation: Novel therapeutic targets for neurodegenerative diseases

Mitochondria-associated endoplasmic reticulum membranes (MAMs) are dynamic coupling structures between mitochondria and the endoplasmic reticulum (ER). As a new subcellular structure, MAMs combine the two critical organelle functions. Mitochondria and the ER could regulate each other via MAMs. MAMs are involved in calcium (Ca²⁺) homeostasis, autophagy, ER stress, lipid metabolism, etc. Researchers have found that MAMs are closely related to metabolic syndrome and neurodegenerative diseases (NDs). The formation of MAMs and their functions depend on specific proteins. Numerous protein enrichments, such as the IP3R-Grp75-VDAC complex, constitute MAMs. The changes in these proteins govern the interaction between mitochondria and the ER; they also affect the biological functions of MAMs. S-palmitoylation is a reversible protein post-translational modification (PTM) that mainly occurs on protein cysteine residues. More and more studies have shown that the S-palmitoylation of proteins is closely related to their membrane localization. Here, we first briefly describe the composition and function of MAMs, reviewing the component and biological roles of MAMs mediated by S-palmitoylation, elaborating on S-palmitoylated proteins in Ca²⁺ flux, lipid rafts, and so on. We try to provide new insight into the molecular basis of MAMs-related diseases, mainly NDs. Finally, we propose potential drug compounds targeting S-palmitoylation.

Expression of cytoskeleton-associated protein 4 is associated with poor prognosis and metastasis in nasopharyngeal carcinoma

Cytoskeleton-associated protein 4 (CKAP4) acts as a key transmembrane protein that connects the endoplasmic reticulum (ER) to microtubule dynamics. Researchers have not examined the roles of CKAP4 in nasopharyngeal carcinoma (NPC). The study aimed at evaluating the prognostic value and metastasis-regulating effect of CKAP4 in NPC. CKAP4 protein could be observed in 86.36% of 557 NPC specimens but not in normal nasopharyngeal epithelial tissue. According to immunoblot assays, NPC cell lines presented high CKAP4 expression relative to NP69 immortalized nasopharyngeal epithelial cells. Moreover, CKAP4 was highly expressed at the NPC tumor front and in matched liver, lung, and lymph node metastasis samples. Furthermore, high CKAP4 expression reported poor overall survival (OS) and presented a positive relevance to tumor (T) classification, recurrence, and metastasis. According to multivariate analysis, CKAP4 could independently and negatively predict patients' prognosis. Stable knockdown of CKAP4 expression in NPC cells inhibited cell migration, invasion and metastasis in vitro and in vivo. Moreover, CKAP4 promoted epithelial-mesenchymal transition (EMT) in NPC cells. CKAP4 knockdown was followed by the downregulation of the interstitial marker vimentin, and upregulation of the epithelial marker E-cadherin. In NPC tissues, high CKAP4 expression exhibited a positive relevance to vimentin expression and a negative relevance to E-cadherin expression. In conclusion, CKAP4 is an independent predictor of NPC, and CKAP4 might contribute NPC progression and metastasis, which may be involved in EMT with vimentin and E-cadherin.

Flotillin-1 palmitoylation turnover by APT-1 and ZDHHC-19 promotes cervical cancer progression by suppressing IGF-1 receptor desensitization and proteostasis

We have shown that insulin-like growth factor-1 (IGF-1) induces palmitoylation turnover of Flotillin-1 (Flot-1) in the plasma membrane (PM) for cell proliferation, after IGF-1 receptor (IGF-1R) signaling activation. However, the enzymes responsible for the turnover have not been identified. Herein, we show that acyl protein thioesterases-1 (APT-1) catalyzes Flot-1 depalmitoylation, and zinc finger DHHC domain-containing protein palmitoyltransferase-19 (ZDHHC-19) repalmitoylation of the depalmitoylated Flot-1 for the turnover in cervical cancer cells. The turnover prevented desensitization of IGF-1R via endocytosis and lysosomal degradation, thereby exerting excessive IGF-1R activation in cervical cancer cells. FLOT1, LYPLA1 and ZDHHC19 were highly expressed, and epithelial-to-mesenchymal transition (EMT)-inducing TIAM1 and GREM1 coordinately upregulated in malignant cervical cancer tissues. And blocking the turnover suppressed the EMT, migration, and invasion of cervical cancer cells. Our study identifies the specific enzymes regulating Flot-1 palmitoylation turnover, and reveals a novel regulatory mechanism of IGF-1-mediated cervical cancer progression.

Post-Translational Modifications by Lipid Metabolites during the DNA Damage Response and Their Role in Cancer

Genomic DNA damage occurs as an inevitable consequence of exposure to harmful exogenous and endogenous agents. Therefore, the effective sensing and repair of DNA damage are essential for maintaining genomic stability and cellular homeostasis. Inappropriate responses to DNA damage can lead to genomic instability and, ultimately, cancer. Protein post-translational modifications (PTMs) are a key regulator of the DNA damage response (DDR), and recent progress in mass spectrometry analysis methods has revealed that a wide range of metabolites can serve as donors for PTMs. In this review, we will summarize how the DDR is regulated by lipid metabolite-associated PTMs, including acetylation, S-succinylation, N-myristoylation, palmitoylation, and crotonylation, and the implications for tumorigenesis. We will also discuss potential novel targets for anti-cancer drug development.

Protein palmitoylation in cancer: molecular functions and therapeutic potential

Protein S-palmitoylation (hereinafter referred to as protein palmitoylation) is a reversible lipid posttranslational modification catalyzed by the zinc finger DHHC-type containing (ZDHHC) protein family. The reverse reaction, depalmitoylation, is catalyzed by palmitoyl-protein thioesterases (PPTs), including acyl-protein thioesterases (APT1/2), palmitoyl protein thioesterases (PPT1/2), or alpha/beta hydrolase domain-containing protein 17A/B/C (ABHD17A/B/C). Proteins encoded by several oncogenes and tumor suppressors are modified by palmitoylation, which enhances the hydrophobicity of specific protein subdomains, and can confer changes in protein stability, membrane localization, protein-protein interaction, and signal transduction. The importance for protein palmitoylation in tumorigenesis has just started to be elucidated in the past decade; palmitoylation appears to affect key aspects of cancer, including cancer cell proliferation and survival, cell invasion and metastasis, and antitumor immunity. Here we review the current literature on protein palmitoylation in the various cancer types, and discuss the potential of targeting of palmitoylation enzymes or palmitoylated proteins for tumor treatment.

Palmitoylation of Voltage-Gated Ion Channels

Protein lipidation is one of the most common forms of posttranslational modification. This alteration couples different lipids, such as fatty acids, phospho- and glycolipids and sterols, to cellular proteins. Lipidation regulates different aspects of the protein’s physiology, including structure, stability and affinity for cellular membranes and protein–protein interactions. In this scenario, palmitoylation is the addition of long saturated fatty acid chains to amino acid residues of the proteins. The enzymes responsible for this modification are acyltransferases and thioesterases, which control the protein’s behavior by performing a series of acylation and deacylation cycles. These enzymes target a broad repertoire of substrates, including ion channels. Thus, protein palmitoylation exhibits a pleiotropic role by differential modulation of the trafficking, spatial organization and electrophysiological properties of ion channels. Considering voltage-gated ion channels (VGICs), dysregulation of lipidation of both the channels and the associated ancillary subunits correlates with the development of various diseases, such as cancer or mental disorders. Therefore, a major role for protein palmitoylation is currently emerging, affecting not only the dynamism and differential regulation of a moiety of cellular proteins but also linking to human health. Therefore, palmitoylation of VGIC, as well as related enzymes, constitutes a novel pharmacological tool for drug development to target related pathologies.

Cytoskeleton-Associated Protein 4, a Promising Biomarker for Tumor Diagnosis and Therapy

Cytoskeleton-associated protein 4 (CKAP4) is located in the rough endoplasmic reticulum (ER) and plays an important role in stabilizing the structure of ER. Meanwhile, CKAP4 is also found to act as an activated receptor at the cell surface. The multifunction of CKAP4 was gradually discovered with growing research evidence. In addition to the involvement in various physiological events including cell proliferation, cell migration, and stabilizing the structure of ER, CKAP4 has been implicated in tumorigenesis. However, the role of CKAP4 is still controversial in tumor biology, which may be related to different signal transduction pathways mediated by binding to different ligands in various microenvironments. Interestingly, CKAP4 has been recently recognized as a serological marker of several tumors and CKAP4 is expected to be a tumor therapeutic target. Therefore, deciphering the gene status, expression regulation, functions of CKAP4 in different diseases may shed new light on CKAP4-based cancer diagnosis and therapeutic strategy. This review discusses the publications that describe CKAP4 in various diseases, especially on tumor promotion and suppression, and provides a detailed discussion on the discrepancy.

Palmitoylated CKAP4 regulates mitochondrial functions through an interaction with VDAC2 at ER-mitochondria contact sites

Cytoskeleton-associated protein 4 (CKAP4) is a palmitoylated type II transmembrane protein localized to the endoplasmic reticulum (ER). Here, we found that knockout (KO) of CKAP4 in HeLaS3 cells induces the alteration of mitochondrial structures and increases the number of ER-mitochondria contact sites. To understand the involvement of CKAP4 in mitochondrial functions, the binding proteins of CKAP4 were explored, enabling identification of the mitochondrial porin voltage-dependent anion-selective channel protein 2 (VDAC2), which is localized to the outer mitochondrial membrane. Palmitoylation at Cys100 of CKAP4 was required for the binding between CKAP4 and VDAC2. In CKAP4 KO cells, the binding of inositol trisphosphate receptor (IP3R) and VDAC2 was enhanced, the intramitochondrial Ca2+ concentration increased and the mitochondrial membrane potential decreased. In addition, CKAP4 KO decreased the oxidative consumption rate, in vitro cancer cell proliferation under low-glucose conditions and in vivo xenograft tumor formation. The phenotypes were not rescued by expression of a palmitoylation-deficient CKAP4 mutant. These results suggest that CKAP4 plays a role in maintaining mitochondrial functions through the binding to VDAC2 at ER-mitochondria contact sites and that palmitoylation is required for this novel function of CKAP4.This article has an associated First Person interview with the first author of the paper.

In vivo Screen Identifies Zdhhc2 as a Critical Regulator of Germinal Center B Cell Differentiation

Germinal center (GC) B cell differentiation is critical for the production of affinity-matured pathogen-specific antibodies, the dysregulation of which may lead to humoral immunodeficiency or autoimmunity. The development of an in vivo screening system for factors regulating GC B cell differentiation has been a challenge. Here we describe a small-scale in vivo screening system with NP-specific B1-8^hi cells and a retroviral shRNA library targeting 78 candidate genes to search for B cell-intrinsic factors that specifically regulate GC B cell differentiation. Zdhhc2, a gene encoding palmitoyltransferase ZDHHC2 and highly expressed in GC B cells, is identified as a strong positive regulator of GC B cell differentiation. B1-8^hi cells transduced with Zdhhc2-shRNA are severely compromised in differentiating into GC B cells. A further analysis of in vitro differentiated B cells transduced with Zdhhc2-shRNA shows that Zdhhc2 is critical for the proliferation and the survival of B cells stimulated by CD40L, BAFF, and IL-21 and consequently impacts on their differentiation into GC B cells and post-GC B cells. These studies not only identify Zdhhc2 as a novel regulator of GC B cell differentiation but also represent a proof of concept of in vivo screen for regulators of GC B cell differentiation.

Self-Association of Purified Reconstituted ER Luminal Spacer Climp63

Membranes of the endoplasmic reticulum (ER) are shaped into cisternal sheets and cylindrical tubules. How ER sheets are generated and maintained is not clear. ER membrane protein Climp63 is enriched in sheets and routinely used as a marker of this structure. The luminal domain (LD) of Climp63 is predicted to be highly helical, and it may form bridges between parallel membranes, regulating the abundance and width of ER sheets. Here, we purified the LD and full-length (FL) Climp63 to analyze their homotypic interactions. The N-terminal tagged LD formed low-order oligomers in solution, but was extremely aggregation-prone when the GST tag was removed. Purified FL Climp63 formed detectable but moderate interactions with both the FL protein and the LD. When Climp63 was reconstituted into proteoliposomes with its LD facing out, the homotypic interactions were retained and could be competed by soluble LD, though vesicle clustering was not observed. These results demonstrate a direct self-association of Climp63, supporting its role as an ER luminal spacer.

Activation of JNK and p38 MAPK Mediated by ZDHHC17 Drives Glioblastoma Multiforme Development and Malignant Progression

Rationale: Glioblastoma multiforme (GBM) almost invariably gain invasive phenotype with limited therapeutic strategy and ill-defined mechanism. By studying the aberrant expression landscape of gliomas, we find significant up-regulation of p-MAPK level in GBM and a potent independent prognostic marker for overall survival. DHHC family was generally expressed in glioma and closely related to the activation of MAPK signaling pathway, but its role and clinical significance in GBM development and malignant progression are yet to be determined.

Method: Bioinformatics analysis, western blotting and immunohistochemistry (IHC) were performed to detect the expression of ZDHHC17 in GBM. The biological function of ZDHHC17 was demonstrated by a series of in vitro and in vivo experiments. Pharmacological treatment, flow cytometry, Transwell migration assay, Co- Immunoprecipitation and GST pulldown were carried out to demonstrate the potential mechanisms of ZDHHC17.

Results: ZDHHC17 is up-regulated and coordinated with MAPK activation in GBM. Mechanistically, ZDHHC17 interacts with MAP2K4 and p38/JNK to build a signaling module for MAPK activation and malignant progression. Notably, the ZDHHC17-MAP2K4-JNK/p38 signaling module contributes to GBM development and malignant progression by promoting GBM cell tumorigenicity and glioma stem cell (GSC) self-renewal. Moreover, we identify a small molecule, genistein, as a specific inhibitor to disrupt ZDHHC17-MAP2K4 complex formation for GBM cell proliferation and GSC self-renewal. Moreover, genistein, identified herein as a lead candidate for ZDHHC17-MAP2K4 inhibition, demonstrated potential therapeutic effect in patients with ZDHHC17-expressing GBM.

Conclusions: Our study identified disruption of a previously unrecognized signaling module as a target strategy for GBM treatment, and provided direct evidence of the efficacy of its inhibition in glioma using a specific inhibitor.

Dynamic palmitoylation controls the microdomain localization of the DKK1 receptors CKAP4 and LRP6

Dickkopf1 (DKK1) was originally identified as an antagonist of Wnt signaling that binds to and induces the clathrin-mediated endocytosis of the Wnt coreceptors low-density lipoprotein receptor-related proteins 5 and 6 (LRP5/6). DKK1 also binds to cytoskeleton-associated protein 4 (CKAP4), which was originally identified as an endoplasmic reticulum (ER) protein but also functions at the plasma membrane as a receptor for various ligands. The DKK1-CKAP4 pathway is activated in several human cancers and promotes cell proliferation by activating signaling through the kinases PI3K and AKT. We found that both CKAP4 and LRP6 primarily localized to detergent-resistant membrane (DRM) fractions of the plasma membrane in a palmitoylation-dependent manner and that palmitoylation of CKAP4 was required for it to promote cell proliferation. DKK1 induced the depalmitoylation of both CKAP4 and LRP6 by acylprotein thioesterases (APTs), resulting in their translocation to the non-DRM fractions. Moreover, DKK1-dependent depalmitoylation of both receptors required activation of the PI3K-AKT pathway. DKK1 simultaneously bound CKAP4 and LRP6, resulting in the formation of a ternary complex. LRP5/6 knockdown decreased DKK1-dependent AKT activation and cancer cell proliferation through CKAP4, whereas CKAP4 knockdown did not affect DKK1-dependent inhibition of Wnt signaling through LRP5/6. These results indicate that the palmitoylation states of CKAP4 and LRP6 play important roles in their signaling and that LRP5/6 enhance DKK1-CKAP4 signaling.

Protein palmitoylation and cancer

Protein S-palmitoylation is a reversible post-translational modification that alters the localization, stability, and function of hundreds of proteins in the cell. S-palmitoylation is essential for the function of both oncogenes (e.g., NRAS and EGFR) and tumor suppressors (e.g., SCRIB, melanocortin 1 receptor). In mammalian cells, the thioesterification of palmitate to internal cysteine residues is catalyzed by 23 Asp-His-His-Cys (DHHC)-family palmitoyl S-acyltransferases while the removal of palmitate is catalyzed by serine hydrolases, including acyl-protein thioesterases (APTs). These enzymes modulate the function of important oncogenes and tumor suppressors and often display altered expression patterns in cancer. Targeting S-palmitoylation or the enzymes responsible for palmitoylation dynamics may therefore represent a candidate therapeutic strategy for certain cancers.

Cytoskeleton-Associated Protein 4 Is a Novel Serodiagnostic Marker for Lung Cancer

Our aim was to develop a serodiagnostic marker for lung cancer. Monoclonal antibodies were generated, and one antibody designated as KU-Lu-1, recognizing cytoskeleton-associated protein 4 (CKAP4), was studied further. To evaluate the utility of KU-Lu-1 antibody as a serodiagnostic marker for lung cancer, reverse-phase protein array analysis was performed with sera of 271 lung cancer patients and 100 healthy controls. CKAP4 was detected in lung cancer cells and tissues, and its secretion into the culture supernatant was also confirmed. The serum CKAP4 levels of lung cancer patients were significantly higher than those of healthy controls (P < 0.0001), and the area under the curve of receiver-operating characteristic curve analysis was 0.890, with 81.1% sensitivity and 86.0% specificity. Furthermore, the serum CKAP4 levels were also higher in patients with stage I adenocarcinoma or squamous cell carcinoma than in healthy controls (P < 0.0001). Serum CKAP4 levels may differentiate lung cancer patients from healthy controls, and they may be detected early even in stage I non-small cell lung cancer. Serum CKAP4 levels were also significantly higher in lung cancer patients than in healthy controls in the validation set (P < 0.0001). The present results provide evidence that CKAP4 may be a novel early serodiagnostic marker for lung cancer.

First case of AML with rare chromosome translocations: a case report of twins

BACKGROUND

Leukemia is different from solid tumor by harboring genetic rearrangements that predict prognosis and guide treatment strategy. PML-RARA, RUNX1-RUNX1T1, and KMT2A-rearrangement are common genetic rearrangements that drive the development of acute myeloid leukemia (AML). By contrast, rare genetic rearrangements may also contribute to leukemogenesis but are less summarized.

CASE PRESENTATION

Here we reported rare fusion genes ZNF717-ZNF37A, ZNF273-DGKA, and ZDHHC2-TTTY15 in a 47-year-old AML-M4 patient with FLT3 internal tandem duplication (ITD) discovered by whole genome sequencing (WGS) using the patient's healthy sibling as a sequencing control.

CONCLUSION

This is, to our knowledge, the first case of AML with fusion gene ZNF717-ZNF37A, ZNF273-DGKA, and ZDHHC2-TTTY15.

Protein Lipidation: Occurrence, Mechanisms, Biological Functions, and Enabling Technologies

Protein lipidation, including cysteine prenylation, N-terminal glycine myristoylation, cysteine palmitoylation, and serine and lysine fatty acylation, occurs in many proteins in eukaryotic cells and regulates numerous biological pathways, such as membrane trafficking, protein secretion, signal transduction, and apoptosis. We provide a comprehensive review of protein lipidation, including descriptions of proteins known to be modified and the functions of the modifications, the enzymes that control them, and the tools and technologies developed to study them. We also highlight key questions about protein lipidation that remain to be answered, the challenges associated with answering such questions, and possible solutions to overcome these challenges.

Antiproliferative factor (APF) binds specifically to sites within the cytoskeleton-associated protein 4 (CKAP4) extracellular domain

Background

Antiproliferative factor (APF) is a sialoglycopeptide elevated in the urine of patients with interstitial cystitis—a chronic, painful bladder disease. APF inhibits the proliferation of normal bladder epithelial cells and cancer cells in vitro, presumably by binding to its cellular receptor, cytoskeleton associated-protein 4 (CKAP4); however, the biophysical interaction of APF with CKAP4 has not been characterized previously. In this study, we used surface plasmon resonance (SPR) to explore the binding kinetics of the interaction of APF and as-APF (a desialylated APF analogue with full activity) to CKAP4.

Results

We immobilized non-glycosylated APF (TVPAAVVVA) to the Fc1 channel as the control and as-APF to Fc2 channel as the ligand in order to measure the binding of CKAP4 recombinant proteins encompassing only the extracellular domain (Aa 127–602) or the extracellular domain plus the transmembrane domain (Aa 106–602). Positive binding was detected to both CKAP4_126–602 and CKAP4_106–602, suggesting that as-APF can bind specifically to CKAP4 and that the potential binding site(s) are located within the extracellular domain. To identify the primary APF binding site(s) within the CKAP4 extracellular domain, deletion mutants were designed according to structural predictions, and the purified recombinant proteins were immobilized on a CM5 chip through amine-coupling to measure as-APF binding activity. Importantly, both CKAP4_127–360 and CKAP4_361–524 exhibited a fast association rate (k_on) and a slow dissociation rate (k_off), thus generating high binding affinity and suggesting that both regions contribute relatively equally to overall as-APF binding. Therefore, two or more as-APF binding sites may exist within the Aa 127–524 region of the CKAP4 extracellular domain.

Conclusions

We determined that the CKAP4_127–360 and CKAP4_361–524 mutants exhibit improved binding activity to as-APF as compared to the full-length extracellular domain, making it possible to detect low concentrations of as-APF in urine, thereby establishing a foundation for a non-invasive diagnostic assay for IC. Further, these data have revealed novel APF binding site(s) suggesting that targeting this region of CKAP4 to inhibit APF binding may be a useful strategy for treating IC-related bladder pathology.

The Dickkopf1-cytoskeleton-associated protein 4 axis creates a novel signalling pathway and may represent a molecular target for cancer therapy

Dickkopf 1 (DKK1) is a secreted protein and antagonizes oncogenic Wnt signalling by binding to the Wnt co-receptor, low-density lipoprotein receptor-related protein 6. DKK1 has also been suggested to regulate its own signalling, associated with tumour aggressiveness. However, the underlying mechanism by which DKK1 promotes cancer cell proliferation has remained to be clarified for a long time. The cytoskeleton-associated protein 4 (CKAP4), originally identified as an endoplasmic reticulum membrane protein, was recently found to act as a novel DKK1 receptor. DKK1 stimulates cancer cell proliferation when CKAP4 is expressed on the cell surface membrane. Although there are no tyrosine residues in the intracellular region of CKAP4, CKAP4 forms a complex with PI3K upon the binding of DKK1, leading to the activation of Akt. Both DKK1 and CKAP4 are frequently expressed in pancreatic and lung tumours, and their simultaneous expression is negatively correlated with prognosis. Knockdown of CKAP4 in cancer cells and treatment of mice with the anti-CKAP4 antibody inhibit Akt activity in cancer cells and suppress xenograft tumour formation, suggesting that CKAP4 may represent a therapeutic target for cancers expressing both DKK1 and CKAP4. This review will provide details of the novel DKK1-CKAP4 signalling axis that promotes cancer proliferation and discuss the possibility of targeting this pathway in future cancer drug development.

LINKED ARTICLES

This article is part of a themed section on WNT Signalling: Mechanisms and Therapeutic Opportunities. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.24/issuetoc.

Protein lipid modifications--More than just a greasy ballast

Covalent lipid modifications of proteins are crucial for regulation of cellular plasticity, since they affect the chemical and physical properties and therefore protein activity, localization, and stability. Most recently, lipid modifications on proteins are increasingly attracting important regulatory entities in diverse signaling events and diseases. In all cases, the lipid moiety of modified proteins is essential to allow water-soluble proteins to strongly interact with membranes or to induce structural changes in proteins that are critical for elemental processes such as respiration, transport, signal transduction, and motility. Until now, roughly about ten lipid modifications on different amino acid residues are described at the UniProtKB database and even well-known modifications are underrepresented. Thus, it is of fundamental importance to develop a better understanding of this emerging and so far under-investigated type of protein modification. Therefore, this review aims to give a comprehensive and detailed overview about enzymatic and nonenzymatic lipidation events, will report their role in cellular biology, discuss their relevancy for diseases, and describe so far available bioanalytical strategies to analyze this highly challenging type of modification.

Abnormal Akt signalling in bladder epithelial cell explants from patients with interstitial cystitis/bladder pain syndrome can be induced by antiproliferative factor treatment of normal bladder cells

OBJECTIVES

To determine whether protein kinase B (Akt) signalling and secretion of specific downstream effector proteins are abnormal in specific cell fractions of bladder epithelial cells from patients with interstitial cystitis/bladder pain syndrome (IC/BPS), as explanted bladder epithelial cells from patients with IC/BPS produce a frizzled 8-related glycopeptide antiproliferative factor (APF) that inhibits normal bladder epithelial cell proliferation and expression of several proteins known to be regulated by Akt signalling. A related secondary objective was to determine whether treatment of normal bladder epithelial cells with active synthetic asialo-antiproliferative factor (as-APF) induces similar changes in Akt signalling and specific downstream effector proteins/mRNAs.

PATIENTS AND METHODS

Cell proteins were extracted into four subcellular fractions from primary bladder epithelial explants of six patients who fulfilled modified National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) criteria for IC/BPS and six age- and gender-matched controls. Total and/or phosphorylated cellular Akt, glycogen synthase kinase 3β (GSK3β), and β-catenin; total cellular JunB; and secreted matrix metalloproteinase 2 (MMP2) and heparin-binding epidermal growth factor-like growth factor (HB-EGF) levels were determined by Western blot. MMP2, JunB, p53, uroplakin 3 (UPK3), and β-actin mRNAs were quantified by quantitative reverse transcriptase-polymerase chain reaction. Akt activity was determined by nonradioactive assay.

RESULTS

IC/BPS cells had lower Akt activity, along with lower Akt ser473- and GSK3β ser9-phosphorylation and higher β-catenin ser33,37/thr41-phosphorylation in specific fractions as compared with matched control cells. IC/BPS explants also had evidence of additional downstream abnormalities compared with control cells, including lower nuclear JunB; lower secreted MMP2 and HB-EGF; plus lower MMP2, JunB, and UPK3 mRNAs but higher p53 mRNA relative to β-actin. Each of these IC/BPS cell abnormalities was also induced in normal cells by as-APF.

CONCLUSION

These findings indicate that IC/BPS cells have abnormal Akt activity with downstream protein expression abnormalities including decreased MMP2 and HB-EGF secretion. They also support the hypothesis that APF plays a role in the pathogenesis of IC/BPS via its effects on cell Akt signalling and HB-EGF production.

How many lives does CLIMP-63 have?

In 1995, in the Biochemical Society Transactions, Mundy published the first review on CLIMP-63 (cytoskeleton-linking membrane protein 63) or CKPA4 (cytoskeleton-associated protein 4), initially just p63 [1]. Here we review the following 20 years of research on this still mysterious protein. CLIMP-63 is a type II transmembrane protein, the cytosolic domain of which has the capacity to bind microtubules whereas the luminal domain can form homo-oligomeric complexes, not only with neighbouring molecules but also, in trans, with CLIMP-63 molecules on the other side of the endoplasmic reticulum (ER) lumen, thus promoting the formation of ER sheets. CLIMP-63 however also appears to have a life at the cell surface where it acts as a ligand-activated receptor. The still rudimentary information of how CLIMP-63 fulfills these different roles, what these are exactly and how post-translational modifications control them, will be discussed.

Increased Susceptibility to Skin Carcinogenesis Associated with a Spontaneous Mouse Mutation in the Palmitoyl Transferase Zdhhc13 Gene

Here we describe a spontaneous mutation in the Zdhhc13 (zinc finger, DHHC domain containing 13) gene (also called Hip14l), one of 24 genes encoding palmitoyl acyltransferase (PAT) enzymes in the mouse. This mutation (Zdhhc13luc) was identified as a nonsense base substitution, which results in a premature stop codon that generates a truncated form of the ZDHHC13 protein, representing a potential loss-of-function allele. Homozygous Zdhhc13luc/Zdhhc13luc mice developed generalized hypotrichosis, associated with abnormal hair cycle, epidermal and sebaceous gland hyperplasia, hyperkeratosis, and increased epidermal thickness. Increased keratinocyte proliferation and accelerated transit from basal to more differentiated layers were observed in mutant compared with wild-type (WT) epidermis in untreated skin and after short-term 12-O-tetradecanoyl-phorbol-13-acetate treatment and acute UVB exposure. Interestingly, this epidermal phenotype was associated with constitutive activation of NF-κB (RelA) and increased neutrophil recruitment and elastase activity. Furthermore, tumor multiplicity and malignant progression of papillomas after chemical skin carcinogenesis were significantly higher in mutant mice than WT littermates. To our knowledge, this is the first report of a protective role for PAT in skin carcinogenesis.

Protein S-palmitoylation and cancer

Protein S-palmitoylation is a reversible posttranslational modification of proteins with fatty acids, an enzymatic process driven by a recently discovered family of protein acyltransferases (PATs) that are defined by a conserved catalytic domain characterized by a DHHC sequence motif. Protein S-palmitoylation has a prominent role in regulating protein location, trafficking and function. Recent studies of DHHC PATs and their functional effects have demonstrated that their dysregulation is associated with human diseases, including schizophrenia, X-linked mental retardation, and Huntington's Disease. A growing number of reports indicate an important role for DHHC proteins and their substrates in tumorigenesis. Whereas DHHC PATs comprise a family of 23 enzymes in humans, a smaller number of enzymes that remove palmitate have been identified and characterized as potential therapeutic targets. Here we review current knowledge of the enzymes that mediate reversible palmitoylation and their cancer-associated substrates and discuss potential therapeutic applications.

A critical role for ZDHHC2 in metastasis and recurrence in human hepatocellular carcinoma

It has been demonstrated that loss of heterozygosity (LOH) was frequently observed on chromosomes 8p22-p23 in hepatocellular carcinoma (HCC) and was associated with metastasis and prognosis of HCC. However, putative genes functioning on this chromosomal region remain unknown. In this study, we evaluated LOH status of four genes on 8p22-p23 (MCPH1, TUSC3, KIAA1456, and ZDHHC2). LOH on ZDHHC2 was associated with early metastatic recurrence of HCC following liver transplantation and was correlated with tumor size and portal vein tumor thrombi. Furthermore, our results indicate that ZDHHC2 expression was frequently decreased in HCC. Overexpression of ZDHHC2 could inhibit proliferation, migration, and invasion of HCC cell line Bel-7402 in vitro. These results suggest an important role for ZDHHC2 as a tumor suppressor in metastasis and recurrence of HCC.

Identification of ZDHHC14 as a novel human tumour suppressor gene

Genomic changes affecting tumour suppressor genes are fundamental to cancer. We applied SNP array analysis to a panel of testicular germ cell tumours to search for novel tumour suppressor genes and identified a frequent small deletion on 6q25.3 affecting just one gene, ZDHHC14. The expression of ZDHHC14, a putative protein palmitoyltransferase with unknown cellular function, was decreased at both RNA and protein levels in testicular germ cell tumours. ZDHHC14 expression was also significantly decreased in a panel of prostate cancer samples and cell lines. In addition to our findings of genetic and protein expression changes in clinical samples, inducible overexpression of ZDHHC14 led to reduced cell viability and increased apoptosis through the classic caspase-dependent apoptotic pathway and heterozygous knockout of ZDHHC14 increased [CORRECTED] cell colony formation ability. Finally, we confirmed our in vitro findings of the tumour suppressor role of ZDHHC14 in a mouse xenograft model, showing that overexpression of ZDHHC14 inhibits tumourigenesis. Thus, we have identified a novel tumour suppressor gene that is commonly down-regulated in testicular germ cell tumours and prostate cancer, as well as given insight into the cellular functional role of ZDHHC14, a potential protein palmitoyltransferase that may play a key protective role in cancer.

A synthetic form of frizzled 8-associated antiproliferative factor enhances p53 stability through USP2a and MDM2

Frizzled 8-associated Antiproliferative Factor (APF) is a sialoglycopeptide urinary biomarker of interstitial cystitis/painful bladder syndrome (IC/PBS), a chronic condition of unknown etiology with variable symptoms that generally include pelvic and/or perineal pain, urinary frequency, and urgency. We previously reported that native human APF suppresses the proliferation of normal bladder epithelial cells through a mechanism that involves increased levels of p53. The goal of this study was to delineate the regulatory mechanism whereby p53 expression is regulated by APF. Two APF-responsive cell lines (T24 bladder carcinoma cells and the immortalized human bladder epithelial cell line, TRT-HU1) were treated with asialo-APF (as-APF), a chemically synthesized form of APF. Biochemical analysis revealed that as-APF increased p53 levels in two ways: by decreasing ubiquitin specific protease 2a (USP2a) expression leading to enhanced ubiquitination of murine double minute 2 E3 ubiquitin ligase (MDM2), and by suppressing association of p53 with MDM2, thus impairing p53 ubiquitination. Biological responses to as-APF were suppressed by increased expression of wild type, but not mutant USP2a, which enhanced cell growth via upregulation of a cell cycle mediator, cyclin D1, at both transcription and protein levels. Consistent with this, gene silencing of USP2a with siRNA arrested cell proliferation. Our findings suggest that APF upregulates cellular p53 levels via functional attenuation of the USP2a-MDM2 pathway, resulting in p53 accumulation and growth arrest. These data also imply that targeting USP2a, MDM2, p53 and/or complex formation by these molecules may be relevant in the development of novel therapeutic approaches to IC/PBS.

Cytoskeleton-Associated Protein 4: Functions Beyond the Endoplasmic Reticulum in Physiology and Disease

Cytoskeleton-associated protein 4 (CKAP4; also known as p63, CLIMP-63, or ERGIC-63) is a 63 kDa, reversibly palmitoylated and phosphorylated, type II transmembrane (TM) protein, originally identified as a resident of the endoplasmic reticulum (ER)/Golgi intermediate compartment (ERGIC). When localized to the ER, a major function of CKAP4 is to anchor rough ER to microtubules, organizing the overall structure of ER with respect to the microtubule network. There is also steadily accumulating evidence for diverse roles for CKAP4 localized outside the ER, including data demonstrating functionality of cell surface forms of CKAP4 in various cell types and of CKAP4 in the nucleus. We will review the recent studies that provide evidence for the existence of CKAP4 in multiple cellular compartments (i.e., ER, plasma membrane, and the nucleus) and discuss CKAP4’s role in the regulation of various physiological and pathological processes, such as interstitial cystitis, drug-induced cytotoxicity, pericullar proteolytic activity, and lung lipid homeostasis.

Antiproliferative factor regulates connective tissue growth factor (CTGF/CCN2) expression in T24 bladder carcinoma cells

Connective tissue growth factor (CTGF/CNN2) is a novel APF target gene. A novel mechanism is described by which the APF cellular receptor, cytoskeleton-associated protein 4 (CKAP4), mediates APF-induced CTGF transcription.

Antiproliferative factor (APF) is a sialoglycopeptide elevated in the urine of patients with interstitial cystitis (IC)—a chronic, painful bladder disease of unknown etiology. APF inhibits the proliferation of normal bladder epithelial and T24 bladder carcinoma cells in vitro by binding to cytoskeleton-associated protein 4 (CKAP4) and altering the transcription of genes involved in proliferation, cellular adhesion, and tumorigenesis; however, specific molecular mechanisms and effector genes that control APF's antiproliferative effects are unknown. In this study, we found that there was a 7.5-fold up-regulation of connective tissue growth factor (CTGF/CCN2) expression in T24 bladder carcinoma cells treated with APF. Western blot revealed a dose-dependent increase in CCN2 protein levels, with secretion into the culture medium after APF treatment. CCN2 overexpression enhanced APF's antiproliferative activity, whereas CCN2 knockdown diminished APF-induced p53 expression. Using a luciferase reporter construct, we found that APF treatment resulted in fivefold activation of the CCN2 proximal promoter and, of importance, that small interfering RNA–mediated knockdown of CKAP4 inhibited CCN2 upregulation. In addition, we demonstrate that CKAP4 translocates to the nucleus and binds to the CCN2 proximal promoter in an APF-dependent manner, providing evidence that CCN2 regulation by APF involves CKAP4 nuclear translocation and binding to the CCN2 promoter.

Antiproliferative factor-induced changes in phosphorylation and palmitoylation of cytoskeleton-associated protein-4 regulate its nuclear translocation and DNA binding

Cytoskeleton-associated protein 4 (CKAP4) is a reversibly palmitoylated and phosphorylated transmembrane protein that functions as a high-affinity receptor for antiproliferative factor (APF)—a sialoglycopeptide secreted from bladder epithelial cells of patients with interstitial cystitis (IC). Palmitoylation of CKAP4 by the palmitoyl acyltransferase, DHHC2, is required for its cell surface localization and subsequent APF signal transduction; however, the mechanism for APF signal transduction by CKAP4 is unknown. In this paper, we demonstrate that APF treatment induces serine phosphorylation of residues S3, S17, and S19 of CKAP4 and nuclear translocation of CKAP4. Additionally, we demonstrate that CKAP4 binds gDNA in a phosphorylation-dependent manner in response to APF treatment, and that a phosphomimicking, constitutively nonpalmitoylated form of CKAP4 localizes to the nucleus, binds DNA, and mimics the inhibitory effects of APF on cellular proliferation. These results reveal a novel role for CKAP4 as a downstream effecter for APF signal transduction.

Antiproliferative factor signaling and interstitial cystitis/painful bladder syndrome

A unique glycopeptide, antiproliferative factor (APF), has been suggested as a urinary biomarker and potential mediator of long-term bladder disorder Interstitial Cystitis/Painful Bladder Syndrome. There is no known cause for this disease. Several mechanistic approaches have been employed to address the underlying mechanism whereby APF regulates cellular responses in the bladder epithelium. A summary of recent literature is provided, and is focused on signal transduction pathways and networks that are responsive to APF.

Human DHHC proteins: a spotlight on the hidden player of palmitoylation

Palmitoylation is one of the most common posttranslational lipid modifications of proteins and we now know quite a lot about it. However, the state of knowledge about the enzymes that catalyze this process is clearly insufficient. This review is focused on 23 human DHHC genes and their products - protein palmitoyltransferases. Here we describe mainly the structure and function of these proteins, but also, to a lesser degree, what the substrates of the enzymes are and whether they are related to various diseases. The main aim of this review was to catalogue existing information concerning the human DHHC family of genes/proteins, making them and their functions easier to understand.

The effect of a novel frizzled 8-related antiproliferative factor on in vitro carcinoma and melanoma cell proliferation and invasion

Antiproliferative factor (APF) is a potent frizzled protein 8-related sialoglycopeptide inhibitor of bladder epithelial cell proliferation that mediates its activity by binding to cytoskeletal associated protein 4 in the cell membrane. Synthetic asialylated APF (as-APF) (Galβ1-3GalNAcα-O-TVPAAVVVA) was previously shown to inhibit both normal bladder epithelial as well as T24 bladder carcinoma cell proliferation and heparin-binding epidermal growth factor-like growth factor (HB-EGF) production at low nanomolar concentrations, and an L: -pipecolic acid derivative (Galβ1-3GalNAcα-O-TV-pipecolic acid-AAVVVA) was also shown to inhibit normal bladder epithelial cell proliferation. To better determine their spectrum of activity, we measured the effects of these APF derivatives on the proliferation of cells derived from additional urologic carcinomas (bladder and kidney), non-urologic carcinomas (ovary, lung, colon, pancreas, and breast), and melanomas using a (3)H-thymidine incorporation assay. We also measured the effects of as-APF on cell HB-EGF and matrix metalloproteinase (MMP2) secretion plus cell invasion, using qRT-PCR, Western blot and an in vitro invasion assay. L: -pipecolic acid as-APF and/or as-APF significantly inhibited proliferation of each cell line in a dose-dependent manner with IC(50)'s in the nanomolar range, regardless of tissue origin, cell type (carcinoma vs. melanoma), or p53 or ras mutation status. as-APF also inhibited HB-EGF and MMP2 production plus in vitro invasion of tested bladder, kidney, breast, lung, and melanoma tumor cell lines, in a dose-dependent manner (IC(50) = 1-100 nM). Synthetic APF derivatives are potent inhibitors of urologic and non-urologic carcinoma plus melanoma cell proliferation, MMP2 production, and invasion, and may be useful for development as adjunctive antitumor therapy(ies).

Normalization of proliferation and tight junction formation in bladder epithelial cells from patients with interstitial cystitis/painful bladder syndrome by d-proline and d-pipecolic acid derivatives of antiproliferative factor

Interstitial cystitis/painful bladder syndrome is a chronic bladder disorder with epithelial thinning or ulceration, pain, urinary frequency and urgency, for which there is no reliably effective therapy. We previously reported that interstitial cystitis/painful bladder syndrome bladder epithelial cells make a glycopeptide antiproliferative factor or 'APF' (Neu5Acα2-3Galβ1-3GalNAcα-O-TVPAAVVVA) that induces abnormalities in normal cells similar to those in interstitial cystitis/painful bladder syndrome cells in vitro, including decreased proliferation, decreased tight junction formation, and increased paracellular permeability. We screened inactive APF derivatives for their ability to block antiproliferative activity of asialylated-APF ('as-APF') in normal bladder cells and determined the ability of as-APF-blocking derivatives to normalize tight junction protein expression, paracellular permeability, and/or proliferation of interstitial cystitis/painful bladder syndrome cells. Only two of these derivatives [Galβ1-3GalNAcα-O-TV-(d-pipecolic acid)-AAVVVA and Galβ1-3GalNAcα-O-TV-(d-proline)-AAVVVA] blocked as-APF antiproliferative activity in normal cells (p < 0.001 for both). Both of these antagonists also 1) significantly increased mRNA expression of ZO-1, occludin, and claudins 1, 4, 8, and 12 in interstitial cystitis/painful bladder syndrome cells by qRT-PCR; 2) normalized interstitial cystitis/painful bladder syndrome epithelial cell tight junction protein expression and tight junction formation by confocal immunofluorescence microscopy; and 3) decreased paracellular permeability of (14) C-mannitol and (3) H-inulin between confluent interstitial cystitis/painful bladder syndrome epithelial cells on Transwell plates, suggesting that these potent APF antagonists may be useful for the development as interstitial cystitis/painful bladder syndrome therapies.

The palmitoyl transferase DHHC2 targets a dynamic membrane cycling pathway: regulation by a C-terminal domain

Intracellular palmitoylation dynamics are regulated by a large family of DHHC (Asp-His-His-Cys) palmitoyl transferases. The majority of DHHC proteins associate with endoplasmic reticulum (ER) or Golgi membranes, but an interesting exception is DHHC2, which localizes to dendritic vesicles of unknown origin in neurons, where it regulates dynamic palmitoylation of PSD95. Dendritic targeting of newly synthesized PSD95 is likely preceded by palmitoylation on Golgi membranes by DHHC3 and/or DHHC15. The precise intracellular distribution of DHHC2 is presently unclear, and there is very little known in general about how DHHC proteins achieve their respective localizations. In this study, membrane targeting of DHHC2 in live and fixed neuroendocrine cells was investigated and mutational analysis employed to define regions of DHHC2 that regulate targeting. We report that DHHC2 associates with the plasma membrane, Rab11-positive recycling endosomes, and vesicular structures. Plasma membrane integration of DHHC2 was confirmed by labeling of an extrafacial HA epitope in nonpermeabilized cells. Antibody-uptake experiments suggested that DHHC2 traffics between the plasma membrane and intracellular membranes. This dynamic localization was confirmed using fluorescence recovery after photo-bleaching analysis, which revealed constitutive refilling of the recycling endosome (RE) pool of DHHC2. The cytoplasmic C-terminus of DHHC2 regulates membrane targeting and a mutant lacking this domain was associated with the ER. Although DHHC2 is closely related to DHHC15, these proteins populate distinct membrane compartments. Construction of chimeric DHHC2/DHHC15 proteins revealed that this difference in localization is a consequence of divergent sequences within their C-terminal tails. This study is the first to highlight dynamic cycling of a mammalian DHHC protein between clearly defined membrane compartments, and to identify domains that specify membrane targeting of this protein family.

Quantitative proteomics identifies a beta-catenin network as an element of the signaling response to Frizzled-8 protein-related antiproliferative factor

Antiproliferative factor (APF), a Frizzled-8 protein-related sialoglycopeptide involved in the pathogenesis of interstitial cystitis, potently inhibits proliferation of normal urothelial cells as well as certain cancer cells. To elucidate the molecular mechanisms of the growth-inhibitory effect of APF, we performed stable isotope labeling by amino acids in cell culture analysis of T24 bladder cancer cells treated with and without APF. Among over 2000 proteins identified, 54 were significantly up-regulated and 48 were down-regulated by APF treatment. Bioinformatic analysis revealed that a protein network involved in cell adhesion was substantially altered by APF and that β-catenin was a prominent node in this network. Functional assays demonstrated that APF down-regulated β-catenin, at least in part, via proteasomal and lysosomal degradation. Moreover, silencing of β-catenin mimicked the antiproliferative effect of APF whereas ectopic expression of nondegradable β-catenin rescued growth inhibition in response to APF, confirming that β-catenin is a key mediator of APF signaling. Notably, the key role of β-catenin in APF signaling is not restricted to T24 cells, but was also observed in an hTERT-immortalized human bladder epithelial cell line, TRT-HU1. In addition, the network model suggested that β-catenin is linked to cyclooxygenase-2 (COX-2), implying a potential connection between APF and inflammation. Functional assays verified that APF increased the production of prostaglandin E(2) and that down-modulation of β-catenin elevated COX-2 expression, whereas forced expression of nondegradable β-catenin inhibited APF-induced up-regulation of COX-2. Furthermore, we confirmed that β-catenin was down-regulated whereas COX-2 was up-regulated in epithelial cells explanted from IC bladder biopsies compared with control tissues. In summary, our quantitative proteomics study describes the first provisional APF-regulated protein network, within which β-catenin is a key node, and provides new insight that targeting the β-catenin signaling pathway may be a rational approach toward treating interstitial cystitis.

Small molecule inhibition of cytoskeletal dynamics in melanoma tumors results in altered transcriptional expression patterns of key genes involved in tumor initiation and progression

BACKGROUND

Rho kinase signaling plays an important role in the oncogenic process largely through its regulation of F-actin dynamics, and inhibition of this pathway results in reduction in tumor volume and metastasis across a number of tumor types. While the cytoskeletal-regulatory role of Rho kinase has been a topic of in-depth study, the mechanisms linking Rho kinase to altered gene expression are largely unknown.

MATERIALS AND METHODS

Global gene expression analysis was performed on melanoma tumors treated with sham or the small molecule inhibitor Y27632.

RESULTS

Inhibition of Rho kinase activity in melanoma tumors results in a statistically significant change in gene transcription of 94 genes, many of which are critically involved in tumor initiation and progression.

CONCLUSION

In addition to regulating tumorigenesis through modulation of the phosphoproteome, Rho kinase signaling also contributes to the regulation of the tumor transcriptome.

Gi/o signaling and the palmitoyltransferase DHHC2 regulate palmitate cycling and shuttling of RGS7 family-binding protein

R7BP (RGS7 family-binding protein) has been proposed to function in neurons as a palmitoylation-regulated protein that shuttles heterodimeric, G(i/o)α-specific GTPase-activating protein (GAP) complexes composed of Gβ5 and RGS7 (R7) isoforms between the plasma membrane and nucleus. To test this hypothesis we studied R7BP palmitoylation and localization in neuronal cells. We report that R7BP undergoes dynamic, signal-regulated palmitate turnover; the palmitoyltransferase DHHC2 mediates de novo and turnover palmitoylation of R7BP; DHHC2 silencing redistributes R7BP from the plasma membrane to the nucleus; and G(i/o) signaling inhibits R7BP depalmitoylation whereas G(i/o) inactivation induces nuclear accumulation of R7BP. In concert with previous evidence, our findings suggest that agonist-induced changes in palmitoylation state facilitate GAP action by (i) promoting Giα depalmitoylation to create optimal GAP substrates, and (ii) inhibiting R7BP depalmitoylation to stabilize membrane association of R7-Gβ5 GAP complexes. Regulated palmitate turnover may also enable R7BP-bound GAPs to shuttle between sites of low and high G(i/o) activity or the plasma membrane and nucleus, potentially providing spatio-temporal control of signaling by G(i/o)-coupled receptors.

Antiproliferative factor decreases Akt phosphorylation and alters gene expression via CKAP4 in T24 bladder carcinoma cells

Background

Urinary bladder cancer is a common malignancy worldwide, and outcomes for patients with advanced bladder cancer remain poor. Antiproliferative factor (APF) is a potent glycopeptide inhibitor of epithelial cell proliferation that was discovered in the urine of patients with interstitial cystitis, a disorder with bladder epithelial thinning and ulceration. APF mediates its antiproliferative activity in primary normal bladder epithelial cells via cytoskeletal associated protein 4 (CKAP4). Because synthetic asialo-APF (as-APF) has also been shown to inhibit T24 bladder cancer cell proliferation at nanomolar concentrations in vitro, and because the peptide segment of APF is 100% homologous to part of frizzled 8, we determined whether CKAP4 mediates as-APF inhibition of proliferation and/or downstream Wnt/frizzled signaling events in T24 cells.

Methods

T24 cells were transfected with double-stranded siRNAs against CKAP4 and treated with synthetic as-APF or inactive control peptide; cells that did not undergo electroporation and cells transfected with non-target (scrambled) double-stranded siRNA served as negative controls. Cell proliferation was determined by ³H-thymidine incorporation. Expression of Akt, glycogen synthase kinase 3β (GSK3β), β-catenin, p53, and matrix metalloproteinase 2 (MMP2) mRNA was determined by quantitative reverse transcriptase polymerase chain reaction (qRT-PCR). Akt, GSK-3β, MMP2, β-catenin, and p53 protein expression, plus Akt, GSK-3β, and β-catenin phosphorylation, were determined by Western blot.

Results

T24 cell proliferation, MMP2 expression, Akt ser473 and thr308 phosphorylation, GSK3β tyr216 phosphorylation, and β-catenin ser45/thr41 phosphorylation were all decreased by APF, whereas p53 expression, and β-catenin ser33,37/thr41 phosphorylation, were increased by APF treatment in non-electroporated and non-target siRNA-transfected cells. Neither mRNA nor total protein expression of Akt, GSK3β, or β-catenin changed in response to APF in these cells. In addition, the changes in cell proliferation, MMP2/p53 mRNA and protein expression, and Akt/GSK3β/β-catenin phosphorylation in response to APF treatment were all specifically abrogated following CKAP4 siRNA knockdown.

Conclusions

Synthetic as-APF inhibits cell proliferation in T24 bladder carcinoma cells via the CKAP4 receptor. The mechanism for this inhibition involves regulating phosphorylation of specific cell signaling molecules (Akt, GSK3β, and β-catenin) plus mRNA and protein expression of p53 and MMP2.

CLIMP-63 is a gentamicin-binding protein that is involved in drug-induced cytotoxicity

Aminoglycoside-induced nephrotoxicity and ototoxicity is a major clinical problem. To understand how aminoglycosides, including gentamicin, induce cytotoxicity in the kidney proximal tubule and the inner ear, we identified gentamicin-binding proteins (GBPs) from mouse kidney cells by pulling down GBPs with gentamicin–agarose conjugates and mass spectrometric analysis. Among several GBPs specific to kidney proximal tubule cells, cytoskeleton-linking membrane protein of 63 kDa (CLIMP-63) was the only protein localized in the endoplasmic reticulum, and was co-localized with gentamicin-Texas Red (GTTR) conjugate after cells were treated with GTTR for 1 h. In western blots, kidney proximal tubule cells and cochlear cells, but not kidney distal tubule cells, exhibited a dithiothreitol (DTT)-resistant dimer band of CLIMP-63. Gentamicin treatment increased the presence of DTT-resistant CLIMP-63 dimers in both kidney proximal (KPT11) and distal (KDT3) tubule cells. Transfection of wild-type and mutant CLIMP-63 into 293T cells showed that the gentamicin-dependent dimerization requires CLIMP-63 palmitoylation. CLIMP-63 siRNA transfection enhanced cellular resistance to gentamicin-induced toxicity, which involves apoptosis, in KPT11 cells. Thus, the dimerization of CLIMP-63 is likely an early step in aminoglycoside-induced cytotoxicity in the kidney and cochlea. Gentamicin also enhanced the binding between CLIMP-63 and 14-3-3 proteins, and we also identified that 14-3-3 proteins are involved in gentamicin-induced cytotoxicity, likely by binding to CLIMP-63.

Structure-Activity Studies on Antiproliferative Factor (APF) Glycooctapeptide Derivatives

Antiproliferative factor (APF), a sialylated glycopeptide secreted by explanted bladder epithelial cells from interstitial cystitis/painful bladder syndrome (IC/PBS) patients, and its unsialylated analogue (as-APF) significantly decrease proliferation of bladder epithelial cells and/or certain carcinoma cell lines in vitro. We recently reported a structure-activity relationship profile for the peptide portion of as-APF and revealed that truncation of the C-terminal alanine did not significantly affect antiproliferative activity. To better understand the structural basis for the maintenance of activity of this truncated eight amino acid as-APF (as-APF8), we synthesized several amino acid-substituted derivatives and studied their ability to inhibit bladder epithelial cell proliferation in vitro as well as their solution conformations by CD and NMR spectroscopy. While single amino acid changes to as-APF8 often strongly reduced activity, full potency was retained when the trivaline tail was replaced with three alanines. The Ala(6-8) derivative 9 is the simplest, fully potent APF analogue synthesized to date.