The actin filament-associated protein AFAP-110 is an adaptor protein that modulates changes in actin filament integrity

AFAP1L1 promotes gastric cancer progression by interacting with VAV2 to facilitate CDC42-mediated activation of ITGA5 signaling pathway

BACKGROUND

The actin filament-associated protein (AFAP) family genes include AFAP1/AFAP-110, AFAP1L1 and AFAP1L2/XB130. Increasing evidence indicates these three AFAP family members participate in tumor progression, but their clinical significance and molecular mechanisms in gastric cancer (GC) remain unclear.

METHODS

We first analyzed expression of AFAP family genes using public datasets and verified the results. The clinical significance of AFAP family genes in GC patients was also analyzed. In vitro and in vivo experiments were applied to explore the function of AFAP1L1. Enrichment analysis was used to explore potential molecular mechanisms. We then performed additional experiments, such as cell adhesion assay, co-immunoprecipitation and so on to confirm the downstream molecular mechanisms of AFAP1L1.

RESULTS

Public data analyses and our verification both showed AFAP1L1 was the only AFAP family members that was significantly upregulated in GC compared with normal gastric tissues. Besides, only AFAP1L1 could predict poor prognosis and act as an independent risk factor for GC patients. In addition, AFAP1L1 promotes GC cells proliferation, migration, invasion in vitro and tumor growth, metastasis in vivo by inducing epithelial-to-mesenchymal transition (EMT). In terms of mechanism, AFAP1L1 interacts with VAV guanine nucleotide exchange factor 2 (VAV2) to activate Rho family GTPases CDC42, which finally promotes expression of integrin subunit alpha 5 (ITGA5) and activation of integrin signaling pathway.

CONCLUSION

AFAP1L1 promotes GC progression by inducing EMT through VAV2-mediated activation of CDC42 and ITGA5 signaling pathway, indicating AFAP1L1 may be a promising prognostic biomarker and therapeutic target for GC patients.

Long Non-Coding RNAs ASB16-AS1 and AFAP1-AS1: Diagnostic, Prognostic Impact and Survival Analysis in Colorectal Cancer

Background

We aimed to evaluate the diagnostic roles of AFAP1-AS1 and ASB16-AS1 in colorectal cancer and highlight their roles in predicting colorectal cancer patients’ prognosis.

Methods

In this case–control study, 146 participants were involved. Group I included 47 patients with CRC. Group II composed of 49 patients with benign lesions in the colon, and Group III included 50 apparently normal subjects of coincided age and gender as controls. All participants were subjected to clinical and endoscopic evaluations, CA19-9, CEA, and quantification of relative expression of lncRNAs ASB16-AS1 and AFAP1-AS1.

Results

CRC patients had significantly elevated expression levels of both lncRNAs in tissue and plasma samples versus benign and control groups (p < 0.001). Despite the higher sensitivity of tissue samples results, the relative expression of both lncRNAs in plasma samples was very encouraging in the discrimination between patients with CRC versus control and benign groups. Furthermore, both lncRNAs could discriminate patients with early-stage CRC (stage I&II) from being colonic lesion and control groups with better sensitivity and specificity presented by ASB16-AS1 in tissue and plasma than results detailed by AFAP1-AS1. High expression levels of ASB16-AS1 in tissue and plasma and tissue lncRNA AFAP1-AS1 are significantly correlated with decreased overall survival (p < 0.001) and reduced progression-free (p < 0.001) compared to low expression in CRC patients.

Conclusion

We propose the utilization of lncRNA ASB16-AS1 and lncRNA AFAP1-AS1 as biomarkers in diagnosis and prognosis estimation for CRC patients. Moreover, their value in early CRC patients may affect the assortment of target therapy and treatment protocols.

Bioinformatic Prioritization and Functional Annotation of GWAS-Based Candidate Genes for Primary Open-Angle Glaucoma

Background: Primary open-angle glaucoma (POAG) is the most prevalent glaucoma subtype, but its exact etiology is still unknown. In this study, we aimed to prioritize the most likely ‘causal’ genes and identify functional characteristics and underlying biological pathways of POAG candidate genes. Methods: We used the results of a large POAG genome-wide association analysis study from GERA and UK Biobank cohorts. First, we performed systematic gene-prioritization analyses based on: (i) nearest genes; (ii) nonsynonymous single-nucleotide polymorphisms; (iii) co-regulation analysis; (iv) transcriptome-wide association studies; and (v) epigenomic data. Next, we performed functional enrichment analyses to find overrepresented functional pathways and tissues. Results: We identified 142 prioritized genes, of which 64 were novel for POAG. BICC1, AFAP1, and ABCA1 were the most highly prioritized genes based on four or more lines of evidence. The most significant pathways were related to extracellular matrix turnover, transforming growth factor-β, blood vessel development, and retinoic acid receptor signaling. Ocular tissues such as sclera and trabecular meshwork showed enrichment in prioritized gene expression (>1.5 fold). We found pleiotropy of POAG with intraocular pressure and optic-disc parameters, as well as genetic correlation with hypertension and diabetes-related eye disease. Conclusions: Our findings contribute to a better understanding of the molecular mechanisms underlying glaucoma pathogenesis and have prioritized many novel candidate genes for functional follow-up studies.

A Review on the Role of AFAP1-AS1 in the Pathoetiology of Cancer

AFAP1-AS1 is a long non-coding RNA which partakes in the pathoetiology of several cancers. The sense protein coding gene from this locus partakes in the regulation of cytophagy, cell motility, invasive characteristics of cells and metastatic ability. In addition to acting in concert with AFAP1, AFAP1-AS1 can sequester a number of cancer-related miRNAs, thus affecting activity of signaling pathways involved in cancer progression. Most of animal studies have confirmed that AFAP1-AS1 silencing can reduce tumor volume and invasive behavior of tumor cells in the xenograft models. Moreover, statistical analyses in the human subjects have shown strong correlation between expression levels of this lncRNA and clinical outcomes. In the present work, we review the impact of AFAP1-AS1 in the carcinogenesis.

LncRNA AFAP1-AS1 Modulates the Proliferation and Invasion of Gastric Cancer Cells by Regulating AFAP1 via miR-205-5p

Purpose

The present study investigated the expression and function of the long noncoding RNA (lncRNA) actin filament associated protein 1 antisense RNA1 (AFAP1-AS1) related to gastric cancer (GC), based on previous results from a microarray analysis.

Methods

Real-time quantitative polymerase chain reaction (qPCR) was used to verify the expression of AFAP1-AS1 in 97 fresh GC tissues and paired non-GC tissues, as well as in six different GC cell lines (BGC-823, SGC-7901, MGC-803, AGS, MKN-45, and MKN-28). The expression levels were subsequently correlated with the clinicopathological features of patients. siRNA against AFAP1-AS1 was transfected into GC cell lines, and cell proliferation, migration, and invasion were detected before and after silencing of AFAP1-AS1 expression. Luciferase reporter gene analysis was used to confirm the target gene of microRNA-205-5p (miR-205-5p) in 293T cells. The potential mechanism was subsequently investigated.

Results

qPCR results showed that AFAP1-AS1 was significantly overexpressed in GC tumor tissues and also GC cell lines, comparing to their paired non-GC tissues. Furthermore, statistical analysis revealed that the overexpression of AFAP1-AS1 was significantly correlated with tumor size (p=0.018) and grade of differentiation (p=0.042). Subsequently, artificially decreasing the expression of AFAP1-AS1 with its specific siRNA dramatically inhibited the proliferation, migration and invasion of GC cell lines (SGC-7901 and BGC-823 cells). Mechanical analysis suggested that AFAP1-AS1 is involved in regulation of its maternal gene, AFAP1, at both mRNA level and protein level. Luciferase reporter gene assay indicated that lncRNA AFAP1-AS1, as a ceRNA, is able to sponge miR-205-5p. Moreover, miR-205-5p has been well demonstrated to participate in the regulation of AFAP1 expression and the phenotypes of GC cells, including proliferation, migration and invasion.

Conclusion

AFAP1-AS1, as a novel biomarker of GC, promotes the proliferation migration and invasion of GC cells and function as ceRNA to target AFAP1 by sponging miR-205-5p.

Actin-Binding Proteins as Potential Biomarkers for Chronic Inflammation-Induced Cancer Diagnosis and Therapy

Actin-binding proteins (ABPs), by interacting with actin, regulate the polymerization, depolymerization, bundling, and cross-linking of actin filaments, directly or indirectly, thereby mediating the maintenance of cell morphology, cell movement, and many other biological functions. Consequently, these functions of ABPs help regulate cancer cell invasion and metastasis when cancer occurs. In recent years, a variety of ABPs have been found to be abnormally expressed in various cancers, indicating that the detection and interventions of unusual ABP expression to alter this are available for the treatment of cancer. The early stages of most cancer development involve long-term chronic inflammation or repeated stimulation. This is the case for breast cancer, gastric cancer, lung cancer, prostate cancer, liver cancer, esophageal cancer, pancreatic cancer, melanoma, and colorectal cancer. This article discusses the relationship between chronic inflammation and the above-mentioned cancers, emphatically introduces relevant research on the abnormal expression of ABPs in chronic inflammatory diseases, and reviews research on the expression of different ABPs in the above-mentioned cancers. Furthermore, there is a close relationship between ABP-induced inflammation and cancer. In simple terms, abnormal expression of ABPs contributes to the chronic inflammation developing into cancer. Finally, we provide our viewpoint regarding these unusual ABPs serving as potential biomarkers for chronic inflammation-induced cancer diagnosis and therapy, and interventions to reverse the abnormal expression of ABPs represent a potential approach to preventing or treating the corresponding cancers.

Spatial proximity of proteins surrounding zyxin under force-bearing conditions

Sensing physical forces is a critical first step in mechano-transduction of cells. Zyxin, a LIM domain-containing protein, is recruited to force-bearing actin filaments and is thought to repair and strengthen them. Yet, the precise force-induced protein interactions surrounding zyxin remain unclear. Using BioID analysis, we identified proximal proteins surrounding zyxin under normal and force-bearing conditions by label-free mass spectrometry analysis. Under force-bearing conditions, increased biotinylation of α-actinin 1, α-actinin 4, and AFAP1 were detected, and these proteins accumulated along force-bearing actin fibers independently from zyxin, albeit at a lower intensity than zyxin. VASP also accumulated along force-bearing actin fibers in a zyxin-dependent manner, but the biotinylation of VASP remained constant regardless of force, supporting the model of a free zyxin-VASP complex in the cytoplasm being corecruited to tensed actin fibers. In addition, ARHGAP42, a RhoA GAP, was also identified as a proximal protein of zyxin and colocalized with zyxin along contractile actin bundles. The overexpression of ARHGAP42 reduced the rate of small wound closure, a zyxin-dependent process. These results demonstrate that the application of proximal biotinylation can resolve the proximity and composition of protein complexes as a function of force, which had not been possible with traditional biochemical analysis.

Src kinase: Key effector in mechanosignalling

Cells have developed a unique set of molecular mechanisms that allows them to probe mechanical properties of the surrounding environment. These systems are based on deformable primary mechanosensors coupled to tension transmitting proteins and enzymes generating biochemical signals. This modular setup enables to transform a mechanical load into more versatile biochemical information. Src kinase appears to be one of the central components of the mechanotransduction network mediating force-induced signalling across multiple cellular contexts. In tight cooperation with primary sensors and the cytoskeleton, Src functions as an effector molecule necessary for transformation of mechanical stimuli into biochemical outputs executing cellular response and adaptation to mechanical cues.

Emerging roles of long noncoding RNAs in cholangiocarcinoma: Advances and challenges

Cholangiocarcinoma (CCA), a cancer with a relatively low incidence rate, is usually associated with poor prognosis. Current modalities for the diagnosis and treatment of CCA patients are still far from satisfactory. In recent years, numerous long noncoding RNAs (lncRNAs) have been identified as crucial players in the development of various cancers, including CCA. Abnormally expressed lncRNAs in CCA, regulated by some upstream molecules, significantly influence the biological behavior of tumor cells and are involved in tumor development through various mechanisms, including interactions with functional proteins, participation in competing for endogenous RNA (ceRNA) regulatory networks, activation of cancer‐related signaling pathways and epigenetic modification of gene expression. Furthermore, several lncRNAs are closely associated with the clinicopathological features of CCA patients, and are promising biomarkers for diagnosing and prognostication of CCA. Some of these lncRNAs play an important role in chemotherapy drug resistance. In addition, lncRNAs have also been shown to be involved in the inflammation microenvironment of CCA and malignant outcome of CCA risk factors, such as cholestatic liver diseases. In view of the difficulty of diagnosing CCA, more attention should be paid to detectable lncRNAs in the serum or bile. This review summarizes the recent knowledge on lncRNAs in CCA and provides a new outlook on the molecular mechanisms of CCA development from the perspective of lncRNAs. Moreover, we also discussed the limitations of the current studies and differential expression of lncRNAs in different types of CCA.

Bidirectional interaction of lncRNA AFAP1-AS1 and CRKL accelerates the proliferative and metastatic abilities of hepatocarcinoma cells

Actin filament-associated protein 1 antisense RNA 1 (AFAP1-AS1), a long non-coding RNA transcribed from the antisense strand of protein coding gene AFAP1, has attracted attention in cancer research. Despite, its biological function and regulatory mechanism in hepatocellular carcinoma still unknown. The present study revealed AFAP1-AS1 mediated hepatocarcinoma progression through targeting CRKL. The bidirectional interaction of AFAP1-AS1 and oncogenic protein CRKL, and the deregulation of AFAP1-AS1 effects on Ras, MEK and c-Jun activities were investigated in depth. AFAP1-AS1 was upregulated in surgical tumorous tissues from hepatocarcinoma patients compared with the paired paracancerous non-tumor liver tissues, and in hepatocarcinoma Huh7, HCCLM3 and HepG2 cell lines compared with LO2, a normal liver cell line. AFAP1-AS1 knockdown noticeably suppressed the proliferative, migratory and invasive properties, and the epithelial-mesenchymal transition (EMT) process of HepG2 and HCCLM3 through upregulating E-cadherin and downregulating N-cadherin and vimentin. CRKL knockdown reduced AFAP1-AS1 expression levels in HepG2 and HCCLM3 cells. AFAP1-AS1 suppression impaired CRKL expression in HepG2 and HCCLM3. AFAP1-AS1 level change was positively correlated with the expression level changes of Ras, MEK and c-Jun in mediating the invasiveness of hepatocarcinoma cells. Current work demonstrated AFAP1-AS1 to be an applicable progression indicator of hepatocarcinoma. AFAP1-AS1 probably promotes the proliferation, EMT progression and metastasis of hepatocarcinoma cells via CRKL mediated Ras/MEK/c-Jun and cadherin/vimentin signaling pathways. AFAP1-AS1-CRKL bidirectional feedback signaling is worthy of further study on the monitoring, diagnosis and treatment of cancers.

Dynamic actin remodeling in response to lysophosphatidic acid

Lysophosphatidic acid (LPA) is a multifunctional regulator of actin cytoskeleton that exerts a dramatic impact on the actin cytoskeleton to build a platform for diverse cellular processes including growth cone guidance, neurite retraction and cell motility. It has been implicated in the formation and dissociation of complexes between actin and actin binding proteins, supporting its role in actin remodeling. Several studies point towards its ability to facilitate formation of special cellular structures including focal adhesions and actin stress fibres by phosphoregulation of several actin associated proteins and their multiple regulatory kinases and phosphatases. In addition, multiple levels of crosstalk among the signaling cascades activated by LPA, affect actin cytoskeleton-mediated cell migration and chemotaxis which in turn play a crucial role in cancer metastasis. In the current review, we have attempted to highlight the role of LPA as an actin modulator which functions by controlling activities of specific cellular proteins that underlie mechanisms employed in cytoskeletal and pathophysiological events within the cell. Further studies on the actin affecting/remodeling activity of LPA in different cell types will no doubt throw up many surprises essential to gain a full understanding of its contribution in physiological processes as well as in diseases.Communicated by Ramaswamy H. Sarma.

AFAP1 and its naturally occurring antisense RNA are downregulated in gastric cancer samples

Actin filament-associated protein 1 (AFAP1) encodes a protein which is an SRC proto-oncogene, non-receptor tyrosine kinase binding partner. This protein alters actin filament integrity in reaction to cellular signals. A long non-coding RNA, namely AFAP1-antisense RNA 1 (AS1), is transcribed from the antisense strand of this gene and potentially regulates its expression. In the present study, the expression levels of these two genes were evaluated in 30 gastric cancer samples and adjacent non-cancerous tissues (ANCTs) to identify their importance in this type of human malignancy. These two genes were significantly downregulated in gastric tumor samples compared with ANCTs (expression ratio 0.26 and 0.36, P=0.001 and P=0.04 for AFAP1 and AFAP1-AS1, respectively). Relative expressions of these two genes were associated with the location of primary tumor, in that AFAP1 and AFAP1-AS1 were significantly downregulated in all cardia tumor types compared with their paired ANCTs (P=0.04 and P=0.001, respectively). There were indications of a significant association between the expression levels of AFAP1 and peritoneal invasion and smoking history (P=0.05). Additionally, a lower expression level of AFAP1 was detected in younger patients and in high grade tumor types compared with olders and low grade tumors respectively (P=0.01 and P=0.04, respectively) and significantly higher expression levels of AFAP1-AS1 in patients with lymphatic/vascular invasion compared with those without lymphatic/vascular invasion (P=0.01). Furthermore, significant pairwise correlations were identified between the transcript levels of these genes in tumoral tissues and ANCTs (P values<0.05). The diagnostic power of AFAP1 and AFAP1-AS1 in gastric cancer was calculated as area under the curve (AUC) 0.75 and 0.67, respectively. The combination of the transcript levels of these two genes significantly enhanced the diagnostic power compared with diagnostic power of each gene (AUC, 0.76; P<0.001). The present study demonstrates the dysregulation of AFAP1 and AFAP1-AS1 in gastric cancer tissues in association with the clinicopathological data of patients and demonstrates the potential of these genes as diagnostic biomarkers.

Long noncoding RNAs in head and neck cancer

Head and neck cancers (HNCs) include a series of malignant tumors arising in epithelial tissues, typically oral cancer, laryngeal cancer, nasopharynx cancer and thyroid cancer. HNCs are important contributors to cancer incidence and mortality, leading to approximately 225,100 new patients and 77,500 deaths in China every year. Determination of the mechanisms of HNC carcinogenesis and progression is an urgent priority in HNC treatment. Long noncoding RNAs (lncRNAs) are noncoding RNAs longer than 200 bps. lncRNAs have been reported to participate in a broad scope of biological processes, and lncRNA dysregulation leads to diverse human diseases, including cancer. In this review, we focus on lncRNAs that are dysregulated in HNCs, summarize the latest findings regarding the function and molecular mechanisms of lncRNAs in HNC carcinogenesis and progression, and discuss the clinical application of lncRNAs in HNC diagnosis, prognosis and therapy.

Meta-analysis of the prognostic value of long non-coding RNA AFAP1-AS1 for cancer patients in China

LncRNA actin filament-associated protein 1 antisense RNA 1 (AFAP1-AS1) is often dysregulated in cancer. We performed this meta-analysis to clarify the usefulness of AFAP1-AS1 as a prognostic marker in malignant tumors. The PubMed, Medline, OVID, Cochrane Library, and Web of Science databases were searched from inception to Augest 7, 2017. Sixteen studies with a total of 1,386 patients were included in the study. The pooled hazard ratio (HR) suggested high AFAP1-AS1 expression correlated with poor overall survival (OS) (HR = 1.98, 95% confidence interval (CI): 1.71–2.28), disease-free survival (DFS) (HR = 1.54, 95% CI: 1.22–1.95), and progression-free survival (PFS) (HR = 2.17, 95% CI:1.64–2.88) in cancer patients, without obvious heterogeneity. High AFAP1-AS1 expression also correlated with larger tumor size (odds ratio (OR) = 2.04, 95% CI: 1.54–2.72), advanced tumor stage (OR=2.35, 95% CI: 1.70–3.26), poor histological grade (OR =1.39, 95% CI: 1.02–1.90), lymph node metastasis (OR = 2.71, 95% CI: 1.98–3.72) and distant metastasis (OR = 2.96, 95% CI: 2.03–4.32). Thus high AFAP1-AS1 expression is predictive of poor OS, DFS, PFS, lymph node metastasis, distant metastasis, histological grade, larger tumor size and tumor stage, which suggests high AFAP1-AS1 expression may serve as a novel biomarker of poor prognosis in cancer.

LncRNA AFAP1-AS1 promotes growth and metastasis of cholangiocarcinoma cells

We investigated the role of actin filament associated protein 1 antisense RNA1 (AFAP1-AS1) lncRNA in promoting cholangiocarcinoma (CCA). qRT-PCR analysis of patient samples showed that AFAP1-AS1 expression was higher in CCA tumors than matched adjacent non-tumor tissue. AFAP1-AS1 levels were also higher in CCA cell lines (HuCCT1 and TFK-1) than a normal biliary epithelium cell line (HIBEpic). AFAP1-AS1 knockdown in CCA cell lines using shAFAP1-AS1 reduced cell proliferation and colony formation in CCK-8 and colony formation assays, respectively. Cell cycle analysis demonstrated that AFAP1-AS1 knockdown resulted in G0/G1 cell cycle arrest and inhibition of S-G2/M transition compared to the controls. CCA cells transfected with shAFAP1-AS1 also exhibited reduced metastasis and invasiveness in Transwell and wound healing assays. This was further confirmed in xenograft experiments with nude mice using CCA cells transfected with shAFAP1-AS1 or control shRNA. AFAP1-AS1 knockdown cells produced smaller tumors, demonstrating that AFAP1-AS1 promotes tumor growth in vivo. AFAP1-AS1 knockdown also increased expression of actin filament associated protein 1 (AFAP1) and reduced cell stress filament integrity, as determined from western blot and immunofluorescence assays, respectively. These findings indicate that AFAP1-AS1 exerts oncogenic effects in CCA. We postulate that AFAP1-AS1 is a potentially useful diagnostic and prognostic biomarker and therapeutic target for CCA.

Significance of kinase activity in the dynamic invadosome

Invadosomes are actin rich protrusive structures that facilitate invasive migration in multiple cell types. Comprised of invadopodia and podosomes, these highly dynamic structures adhere to and degrade the extracellular matrix, and are also thought to play a role in mechanosensing. Many extracellular signals have been implicated in invadosome stimulation, activating complex signalling cascades to drive the formation, activity and turnover of invadosomes. While the structural components of invadosomes have been well studied, the regulation of invadosome dynamics is still poorly understood. Protein kinases are essential to this regulation, affecting all stages of invadosome dynamics and allowing tight spatiotemporal control of their activity. Invadosome organisation and function have been linked to pathophysiological states such as cancer invasion and metastasis; therapeutic targeting of invadosome regulatory components is thus warranted. In this review, we discuss the involvement of kinase signalling in every stage of the invadosome life cycle and evaluate its significance.

Long noncoding RNA AFAP1-AS1, a potential novel biomarker to predict the clinical outcome of cancer patients: a meta-analysis

A number of studies have demonstrated that the expression level of actin filament-associated protein 1 antisense RNA 1 (AFAP1-AS1) was upregulated in various cancers. High expression of AFAP1-AS1 is associated with an increased risk of metastasis and a poor prognosis in cancer patients. The electronic search was conducted in PubMed, EMBASE, Cochrane Library, China National Knowledge Infrastructure, and Wanfang database. We collected relevant articles to explore the association between the expression levels of AFAP1-AS1 and lymph node metastasis, distant metastasis, overall survival, relapse-free survival, and progression-free survival. A total of 1,017 patients from eight studies were finally included. The results showed that cancer patients with high AFAP1-AS1 expression suffered an increased risk of developing lymph node metastasis (odds ratio =3.19, 95% confidence interval [CI]: 2.11-4.83, P<0.00001) and distant metastasis (odds ratio =3.05, 95% CI: 1.84-5.04, P<0.0001). Moreover, we found that patients with high AFAP1-AS1 expression also had a poorer overall survival (hazard ratio [HR]: 1.98, 95% CI: 1.57-2.38, P=0.000), a worse progression-free survival (HR: 1.73, 95% CI: 1.11-2.35, P=0.000), and a shorter recurrence-free survival (HR: 1.96, 95% CI: 1.02-2.90, P=0.000) than those with low AFAP1-AS1 expression. High expression of AFAP1-AS1 was associated with poor clinical outcome. AFAP1-AS1 might serve as a potential novel biomarker for indicating the clinical outcomes in human cancers.

Preparation and Characterization of a Polyclonal Antibody against Human Actin Filament-Associated Protein-120 kD

Actin filament-associated protein-120kD (AFAP-120) is an alternatively spliced isoform of actin filament-associated protein-110kD (AFAP-110) and contains an additional neuronal insert (NINS) fragment in addition to identical domains to the AFAP-110. Unlike AFAP-110 widely expressed in tissues, AFAP-120 is specifically expressed in the nervous system and plays a role in organizing dynamic actin structures during neuronal differentiation. However, anti-AFAP-120 antibody is still commercially unavailable, and this may hinder the function research for AFAP-120. In this study, we simultaneously used the ABCpred online server and the BepiPred 1.0 server to predict B-cell epitopes in the exclusive NINS sequence of human AFAP-120 protein, and found that a 16aa-peptide sequence was the consensus epitope predicted by both tools. This peptide was chemically synthesized and used as an immunogen to develop polyclonal antibody against AFAP-120 (anti-AFAP-120). The sensitivity and specificity of anti-AFAP-120 were analyzed with immunoblotting, immunoprecipitation, and immunofluorescence assays. Our results indicated that anti-AFAP-120 could react with over-expressed and endogenous human AFAP-120 protein under denatured condition, but not with human AFAP-110 protein. Moreover, native human AFAP-120 protein could also be recognized by the anti-AFAP-120 antibody. These results suggested that the prepared anit-AFAP-120 antibody would be a useful tool for studying the biochemical and biological functions of AFAP-120.

XB130: A novel adaptor protein in cancer signal transduction

Adaptor proteins are functional proteins that contain two or more protein-binding modules to link signaling proteins together, which affect cell growth and shape and have no enzymatic activity. The actin filament-associated protein (AFAP) family is an important member of the adaptor proteins, including AFAP1, AFAP1L1 and AFAP1L2/XB130. AFAP1 and AFAP1L1 share certain common characteristics and function as an actin-binding protein and a cSrc-activating protein. XB130 exhibits certain unique features in structure and function. The mRNA of XB130 is expressed in human spleen, thyroid, kidney, brain, lung, pancreas, liver, colon and stomach, and the most prominent disease associated with XB130 is cancer. XB130 has a controversial effect on cancer. Studies have shown that XB130 can promote cancer progression and downregulation of XB130-reduced growth of tumors derived from certain cell lines. A higher mRNA level of XB130 was shown to be associated with a better survival in non-small cell lung cancer. Previous studies have shown that XB130 can regulate cell growth, migration and invasion and possibly has the effect through the cAMP-cSrc-phosphoinositide 3-kinase/Akt pathway. Except for cancer, XB130 is also associated with other pathological or physiological procedures, such as airway repair and regeneration.

Phosphatidylinositol 3-Kinase-Associated Protein (PI3KAP)/XB130 Crosslinks Actin Filaments through Its Actin Binding and Multimerization Properties In Vitro and Enhances Endocytosis in HEK293 Cells

Actin-crosslinking proteins control actin filament networks and bundles and contribute to various cellular functions including regulation of cell migration, cell morphology, and endocytosis. Phosphatidylinositol 3-kinase-associated protein (PI3KAP)/XB130 has been reported to be localized to actin filaments (F-actin) and required for cell migration in thyroid carcinoma cells. Here, we show a role for PI3KAP/XB130 as an actin-crosslinking protein. First, we found that the carboxyl terminal region of PI3KAP/XB130 containing amino acid residues 830-840 was required and sufficient for localization to F-actin in NIH3T3 cells, and this region is directly bound to F-actin in vitro. Moreover, actin-crosslinking assay revealed that recombinant PI3KAP/XB130 crosslinked F-actin. In general, actin-crosslinking proteins often multimerize to assemble multiple actin-binding sites. We then investigated whether PI3KAP/XB130 could form a multimer. Blue native-PAGE analysis showed that recombinant PI3KAP/XB130 was detected at 250-1200 kDa although the molecular mass was approximately 125 kDa, suggesting that PI3KAP/XB130 formed multimers. Furthermore, we found that the amino terminal 40 amino acids were required for this multimerization by co-immunoprecipitation assay in HEK293T cells. Deletion mutants of PI3KAP/XB130 lacking the actin-binding region or the multimerizing region did not crosslink actin filaments, indicating that actin binding and multimerization of PI3KAP/XB130 were necessary to crosslink F-actin. Finally, we examined roles of PI3KAP/XB130 on endocytosis, an actin-related biological process. Overexpression of PI3KAP/XB130 enhanced dextran uptake in HEK 293 cells. However, most of the cells transfected with the deletion mutant lacking the actin-binding region incorporated dextran to a similar extent as control cells. Taken together, these results demonstrate that PI3KAP/XB130 crosslinks F-actin through both its actin-binding region and multimerizing region and plays an important role in endocytosis.

Comparative Microarray Analysis of Proliferating and Differentiating Murine ENS Progenitor Cells

Postnatal neural progenitor cells of the enteric nervous system are a potential source for future cell replacement therapies of developmental dysplasia like Hirschsprung's disease. However, little is known about the molecular mechanisms driving the homeostasis and differentiation of this cell pool. In this work, we conducted Affymetrix GeneChip experiments to identify differences in gene regulation between proliferation and early differentiation of enteric neural progenitors from neonatal mice. We detected a total of 1333 regulated genes that were linked to different groups of cellular mechanisms involved in cell cycle, apoptosis, neural proliferation, and differentiation. As expected, we found an augmented inhibition in the gene expression of cell cycle progression as well as an enhanced mRNA expression of neuronal and glial differentiation markers. We further found a marked inactivation of the canonical Wnt pathway after the induction of cellular differentiation. Taken together, these data demonstrate the various molecular mechanisms taking place during the proliferation and early differentiation of enteric neural progenitor cells.

AFAP1 Is a Novel Downstream Mediator of TGF-β1 for CCN2 Induction in Osteoblasts

Background

CCN2 acts as an anabolic growth factor to regulate osteoblast differentiation and function. CCN2 is induced by TGF-β1 and acts as a mediator of TGF-β1 induced matrix production in osteoblasts and Src is required for CCN2 induction by TGF-β1; however, the molecular mechanisms that control CCN2 induction in osteoblasts are poorly understood. AFAP1 binds activated forms of Src and can direct the activation of Src in certain cell types, however a role for AFAP1 downstream of TGF-β1 or in osteoblats is undefined. In this study, we investigated the role of AFAP1 for CCN2 induction by TGF-β1 in primary osteoblasts.

Results

We demonstrated that AFAP1 expression in osteoblasts occurs in a biphasic pattern with maximal expression levels occurring during osteoblast proliferation (~day 3), reduced expression during matrix production/maturation (~day 14–21), an a further increase in expression during mineralization (~day 21). AFAP1 expression is induced by TGF-β1 treatment in osteoblasts during days 7, 14 and 21. In osteoblasts, AFAP1 binds to Src and is required for Src activation by TGF-β1 and CCN2 promoter activity and protein induction by TGF-β1 treatment was impaired using AFAP1 siRNA, indicating the requirement of AFAP1 for CCN2 induction by TGF-β1. We also demonstrated that TGF-β1 induction of extracellular matrix protein collagen XIIa occurs in an AFAP1 dependent fashion.

Conclusions

This study demonstrates that AFAP1 is an essential downstream signaling component of TGF-β1 for Src activation, CCN2 induction and collagen XIIa in osteoblasts.

The up-regulation of long non-coding RNA AFAP1-AS1 is associated with the poor prognosis of NSCLC patients

Long non-coding RNA (lncRNA) is actively transcribed from human genome and has been considered to participate in many processes of various cancers. The purpose of this study was to investigate the expression of LncRNA AFAP1-AS1 and its prognostic value in NSCLC. LncRNA AFAP1-AS1 expression was detected by qRT-PCR which demonstrated that the expression was significantly increased in tumor tissues compared with the adjacent non-cancerous tissues and healthy tissues. The clinical stage, smoking history, infiltration degree, lymph node metastasis and distant metastasis were all proved to impact the expression of LncRNA AFAP1-AS1 (P<0.05). Kaplan-Meier analysis was performed to evaluate the overall survival of NSCLC patients with different expression level of LncRNA AFAP1-AS1, and results showed that patients with high LncRNA AFAP1-AS1 expression lived shorter than those with low LncRNA AFAP1-AS1 expression (Log rank test, P<0.001). Besides, the prognostic value of LncRNA AFAP1-AS1 as well as the clinical features was assessed by Cox regression analysis. The outcome revealed that LncRNA AFAP1-AS1 was closely related to the prognosis of NSCLC. Taken together, LncRNA AFAP1-AS1 was up-regulated in NSCLC tissues and it could be an independent prognostic indicator for NSCLC patients.

Upregulated long non-coding RNA AFAP1-AS1 expression is associated with progression and poor prognosis of nasopharyngeal carcinoma

Altered expression of long noncoding RNAs (lncRNAs) associated with human carcinogenesis. We performed a cDNA microarray analysis of lncRNA expression in 12 cases of nasopharyngeal carcinoma (NPC) and 4 non-tumor nasopharyngeal epitheliums. One lncRNA, actin filament associated protein 1 antisense RNA1 (AFAP1-AS1), was identified and selected for further study. AFAP1-AS1 expression was upregulated in NPC and associated with NPC metastasis and poor prognosis. In vitro experiments demonstrated that AFAP1-AS1 knockdown significantly inhibited the NPC cell migration and invasive capability. AFAP1-AS1 knockdown also increased AFAP1 protein expression. Proteomic and bioinformatics analyses suggested that AFAP1-AS1 affected the expression of several small GTPase family members and molecules in the actin cytokeratin signaling pathway. AFAP1-AS1 promoted cancer cell metastasis via regulation of actin filament integrity. AFAP1-AS1 might be a potential novel marker that can predict cancer patient prognosis and as a potential therapeutic target for NPC.

AFAP1-AS1, a long noncoding RNA upregulated in lung cancer and promotes invasion and metastasis

Long noncoding RNAs (lncRNAs) have emerged as a major regulator of cancer. Significant fraction of lncRNAs is represented on widely used microarray platforms; however, many of which have no known function. To discover novel lung cancer-related lncRNAs, we analyzed the lncRNA expression patterns in five sets of previously published lung cancer gene expression profile data that were represented on Affymetrix HG-U133 Plus 2.0 array, and identified dysregulated lncRNAs in lung cancer. One lncRNA, actin filament associated protein 1 antisense RNA1 (AFAP1-AS1), was the most significantly upregulated in lung cancer and associated with poor prognosis. In vitro experiments demonstrated that AFAP1-AS1 knockdown significantly inhibited the cell invasive and migration capability in lung cancer cells. AFAP1-AS1 knockdown also increased the expression of its antisense protein coding gene, actin filament associated protein 1 (AFAP1), and affected the expression levels of several small GTPase family members and molecules in the actin cytokeratin signaling pathway, which suggested that AFAP1-AS1 promoted cancer cell metastasis via regulation of actin filament integrity. Our findings extend the number of noncoding RNAs functionally implicated in lung cancer progression and highlight the role of AFAP1-AS1 as potential prognostic biomarker and therapeutic target of lung cancer.

Actin filament-associated protein 1 is required for cSrc activity and secretory activation in the lactating mammary gland

Actin filament-associated protein 1 (AFAP1) is an adaptor protein of cSrc that binds to filamentous actin and regulates the activity of this tyrosine kinase to affect changes to the organization of the actin cytoskeleton. In breast and prostate cancer cells, AFAP1 has been shown to regulate cellular responses requiring actin cytoskeletal changes such as adhesion, invadopodia formation and invasion. However, a normal physiologic role for AFAP1 has remained elusive. In this study, we generated an AFAP1 knockout mouse model that establishes a novel physiologic role for AFAP1 in lactation. Specifically, these animals displayed a defect in lactation that resulted in an inability to nurse efficiently. Histologically, the mammary glands of the lactating knockout mice were distinguished by the accumulation of large cytoplasmic lipid droplets in the alveolar epithelial cells. There was a reduction in lipid synthesis and the expression of lipogenic genes without a corresponding reduction in the production of β-casein, a milk protein. Furthermore, these defects were associated with histologic and biochemical signs of precocious involution. This study also demonstrated that AFAP1 responds to prolactin, a lactogenic hormone, by forming a complex with cSrc and becoming tyrosine phosphorylated. Taken together, these observations pointed to a defect in secretory activation. Certain characteristics of this phenotype mirrored the defect in secretory activation in the cSrc knockout mouse, but most importantly, the activity of cSrc in the mammary gland was reduced during early lactation in the AFAP1-null mouse and the localization of active cSrc at the apical surface of luminal epithelial cells during lactation was selectively lost in the absence of AFAP1. These data define, for the first time, the requirement of AFAP1 for the spatial and temporal regulation of cSrc activity in the normal breast, specifically for milk production.

XB130-A Novel Adaptor Protein: Gene, Function, and Roles in Tumorigenesis

Several adaptor proteins have previously been shown to play an important role in the promotion of tumourigenesis. XB130 (AFAP1L2) is an adaptor protein involved in many cellular functions, such as cell survival, cell proliferation, migration, and gene and miRNA expression. XB130's functional domains and motifs enable its interaction with a multitude of proteins involved in several different signaling pathways. As a tyrosine kinase substrate, tyrosine phosphorylated XB130 associates with the p85 α regulatory subunit of phosphoinositol-3-kinase (PI3K) and subsequently affects Akt activity and its downstream signalling. Tumourigenesis studies show that downregulation of XB130 expression by RNAi inhibits tumor growth in mouse xenograft models. Furthermore, XB130 affects tumor oncogenicity by regulating the expression of specific tumour suppressing miRNAs. The expression level and pattern of XB130 has been studied in various human tumors, such as thyroid, esophageal, and gastric cancers, as well as, soft tissue tumors. Studies show the significant effects of XB130 in tumourigenesis and suggest its potential as a diagnostic biomarker and therapeutic target for cancer treatments.

AFAP1L1, a novel associating partner with vinculin, modulates cellular morphology and motility, and promotes the progression of colorectal cancers

We have previously identified actin filament-associated protein 1-like 1 (AFAP1L1) as a metastasis-predicting marker for spindle cell sarcomas by gene expression profiling, and demonstrated that AFAP1L1 is involved in the cell invasion process by in vitro analyses. However, its precise molecular function has not been fully elucidated, and it remains unknown whether AFAP1L1 could be a prognostic marker and/or therapeutic target of other malignancies. In this study, we found a marked elevation of AFAP1L1 gene expression in colorectal cancer (CRC) tissues as compared to the adjacent normal mucosa. Multivariate analysis revealed that AFAP1L1 was an independent and significant factor for the recurrence of rectal cancers. Moreover, the addition of the AFAP1L1 expression level to the lymph node metastasis status provided more predictive information regarding postoperative recurrence in rectal cancers. AFAP1L1-transduced CRC cells exhibited a rounded shape, increased cell motility on planar substrates, and resistance to anoikis in vitro. AFAP1L1 localized to the ringed structure of the invadopodia, together with vinculin, and AFAP1L1 was identified as a novel associating partner of vinculin by immunoprecipitation assay. AFAP1L1-transduced cells showed accelerated tumor growth in vivo, presumably reflecting the anoikis resistance of these AFAP1L1-expressing cells. Furthermore, the local administration of a siRNA against AFAP1L1 significantly suppressed the in vivo tumor growth of xenografts, suggesting that AFAP1L1 might be a candidate therapeutic target for CRCs. These results suggest that AFAP1L1 plays a role in the progression of CRCs by modulating cell shape and motility and by inhibiting anoikis, presumably through interactions with vinculin-including protein complexes.

SRChing for the substrates of Src

By the mid 1980's, it was clear that the transforming activity of oncogenic Src was linked to the activity of its tyrosine kinase domain and attention turned to identifying substrates, the putative next level of control in the pathway to transformation. Among the first to recognize the potential of phosphotyrosine-specific antibodies, Parsons and colleagues launched a risky shotgun-based approach that led ultimately to the cDNA cloning and functional characterization of many of today's best-known Src substrates (for example, p85-Cortactin, p110-AFAP1, p130Cas, p125FAK and p120-catenin). Two decades and over 6000 citations later, the original goals of the project may be seen as secondary to the enormous impact of these protein substrates in many areas of biology. At the request of the editors, this review is not restricted to the current status of the substrates, but reflects also on the anatomy of the project itself and some of the challenges and decisions encountered along the way.

Hypomethylation of noncoding DNA regions and overexpression of the long noncoding RNA, AFAP1-AS1, in Barrett's esophagus and esophageal adenocarcinoma

BACKGROUND & AIMS

Alterations in methylation of protein-coding genes are associated with Barrett's esophagus (BE) and esophageal adenocarcinoma (EAC). Dysregulation of noncoding RNAs occurs during carcinogenesis but has never been studied in BE or EAC. We applied high-resolution methylome analysis to identify changes at genomic regions that encode noncoding RNAs in BE and EAC.

METHODS

We analyzed methylation of 1.8 million CpG sites using massively parallel sequencing-based HELP tagging in matched EAC, BE, and normal esophageal tissues. We also analyzed human EAC (OE33, SKGT4, and FLO-1) and normal (HEEpic) esophageal cells.

RESULTS

BE and EAC exhibited genome-wide hypomethylation, significantly affecting intragenic and repetitive genomic elements as well as noncoding regions. These methylation changes targeted small and long noncoding regions, discriminating normal from matched BE or EAC tissues. One long noncoding RNA, AFAP1-AS1, was extremely hypomethylated and overexpressed in BE and EAC tissues and EAC cells. Its silencing by small interfering RNA inhibited proliferation and colony-forming ability, induced apoptosis, and reduced EAC cell migration and invasion without altering the expression of its protein-coding counterpart, AFAP1.

CONCLUSIONS

BE and EAC exhibit reduced methylation that includes noncoding regions. Methylation of the long noncoding RNA AFAP1-AS1 is reduced in BE and EAC, and its expression inhibits cancer-related biologic functions of EAC cells.

Junctional adhesion molecules 2 and 3 may potentially be involved in progression of gastric adenocarcinoma tumors

Tight junctions (TJs) of epithelia are responsible for integrity of polarized epithelial cells. It is now well established that the deregulation of their functions and expressions contribute to initiation and progression of cancer through activation of cytoskeleton machinery. The aim of this study was to examine the expression level of two genes encoding tight junction-associated proteins of Jam2 and Jam3 in gastric adenocarcinoma and compare with normal gastric tissues dissected from same patients. Significant difference of expression level for these genes was observed between tumor and adjacent normal tissues. Also, we analyzed the expression level of actin filament-associated protein gene that appears to be a downstream factor of JAM2 and JAM3. The expression level of this gene was significantly higher in tumor tissues. Some correlations between the expression level of these genes with each other and with pathological features were observed. These data brought new evidences for the role of these three genes in progression of gastric adenocarcinoma.

Phosphatidylinositol 3-kinase-binding protein, PI3KAP/XB130, is required for cAMP-induced amplification of IGF mitogenic activity in FRTL-5 thyroid cells

We previously demonstrated that long-term pretreatment of rat FRTL-5 thyroid cells with TSH or cAMP-generating reagents potentiated IGF-I-dependent DNA synthesis. Under these conditions, cAMP treatment increased tyrosine phosphorylation of a 125-kDa protein (p125) and its association with a p85 regulatory subunit of phosphatidylinositol 3-kinase (p85 PI3K), which were suggested to mediate potentiation of DNA synthesis. This study was undertaken to identify p125 and to elucidate its roles in potentiation of DNA synthesis induced by IGF-I. Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) analysis revealed p125 to be a rat ortholog of human XB130, which we named PI3K-associated protein (PI3KAP). cAMP treatment elevated PI3KAP/XB130 mRNA and protein levels as well as tyrosine phosphorylation and interaction with p85 PI3K leading to increased PI3K activities associated with PI3KAP/XB130, supporting the role of PI3KAP/XB130 in DNA synthesis potentiation. Importantly, PI3KAP/XB130 knockdown attenuated cAMP-dependent potentiation of IGF-I-induced DNA synthesis. Furthermore, c-Src was associated with PI3KAP/XB130 and was activated in response to cAMP. Addition of Src family kinase inhibitors, PP1 or PP2, during cAMP treatment abolished tyrosine phosphorylation of PI3KAP/XB130 and its interaction with p85 PI3K. Finally, introduction of PI3KAP/XB130 into NIH3T3 fibroblasts lacking endogenous PI3KAP/XB130 enhanced IGF-I-induced DNA synthesis; however, a mutant Y72F incapable of binding to p85 PI3K did not show this response. Together, these data indicate that cAMP-dependent induction of PI3KAP/XB130, which is associated with PI3K, is required for enhancement of IGF mitogenic activities.

The actin-binding domain of actin filament-associated protein (AFAP) is involved in the regulation of cytoskeletal structure

Actin filament-associated protein (AFAP) plays a critical role in the regulation of actin filament integrity, formation and maintenance of the actin network, function of focal contacts, and cell migration. Here, we show that endogenous AFAP was present not only in the cytoskeletal but also in the cytosolic fraction. Depolymerization of actin filaments with cytochalasin D or latrunculin A increased AFAP in the cytosolic fraction. AFAP harbors an actin-binding domain (ABD) in its C-terminus. AFAPΔABD, an AFAP mutant with selective ABD deletion, was mainly in the cytosolic fraction when overexpressed in the cells, which was associated with a disorganized cytoskeleton with reduced stress fibers, accumulation of F-actin on cellular membrane, and formation of actin-rich small dots. Cortactin, a well-known podosome marker, was colocalized with AFAPΔABD in these small dots at the ventral surface of the cell, indicating that these small dots fulfill certain criteria of podosomes. However, these podosome-like small dots did not digest gelatin matrix. This may be due to the reduced interaction between AFAPΔABD and c-Src. When AFAPΔABD-transfected cells were stimulated with phorbol ester, they formed podosome-like structures with larger sizes, less numerous and longer life span, in comparison with wild-type AFAP-transfected cells. These results indicate that the association of AFAP with F-actin through ABD is crucial for AFAP to regulate cytoskeletal structures. The AFAPΔABD, as cytosolic proteins, may be more accessible to the cellular membrane, podosome-like structures, and thus be more interactive for the regulation of cellular functions.

AFAP1L1 is a novel adaptor protein of the AFAP family that interacts with cortactin and localizes to invadosomes

The actin-filament associated protein (AFAP) family of adaptor proteins consists of three members: AFAP1, AFAP1L1, and AFAP1L2/XB130 with AFAP1 being the best described as a cSrc binding partner and actin cross-linking protein. A homology search of AFAP1 recently identified AFAP1L1 which has a similar sequence, domain structure and cellular localization; however, based upon sequence variations, AFAP1L1 is hypothesized to have unique functions that are distinct from AFAP1. While AFAP1 has the ability to bind to the SH3 domain of the nonreceptor tyrosine kinase cSrc via an N-terminal SH3 binding motif, it was unable to bind cortactin. However, the SH3 binding motif of AFAP1L1 was more efficient at interacting with the SH3 domain of cortactin and not cSrc. AFAP1L1 was shown by fluorescence microscopy to decorate actin filaments and move to punctate actin structures and colocalize with cortactin, consistent with localization to invadosomes. Upon overexpression in A7r5 cells, AFAP1L1 had the ability to induce podosome formation and move to podosomes without stimulation. Immunohistochemical analysis of AFAP1L1 in human tissues shows differential expression when contrasted with AFAP1 with localization of AFAP1L1 to unique sites in muscle and the dentate nucleus of the brain where AFAP1 was not detectable. We hypothesize AFAP1L1 may play a similar role to AFAP1 in affecting changes in actin filaments and bridging interactions with binding partners, but we hypothesize that AFAP1L1 may forge unique protein interactions in which AFAP1 is less efficient, and these interactions may allow AFAP1L1 to affect invadosome formation.

Actin filament associated protein mediates c-Src related SRE/AP-1 transcriptional activation

AFAP is an adaptor protein involved in cytoskeletal organization and intracellular signaling. AFAP binds and activates c-Src; however, the downstream signals of this interaction remain unknown. Here we show that co-expression of AFAP and c-Src induce transcriptional activation of SRE and AP-1 in a c-Src activity dependent fashion. Structural-functional studies suggest that the proline-rich motif in the N-terminus of AFAP is critical for c-Src activation, and subsequent SRE/AP-1 transactivation and the actin-binding domain in the AFAP C-terminus is negatively involved in the regulation of AFAP/c-Src mediated SRE/AP-1 transactivation. Selective deletion of this domain enhances transactivation of SRE. We conclude that in addition to its role in the regulation of cytoskeletal structures, AFAP may also be involved in the c-Src related transcriptional activities.

Cooperative expression of junctional adhesion molecule-C and -B supports growth and invasion of glioma

Brain invasion is a biological hallmark of glioma that contributes to its aggressiveness and limits the potential of surgery and irradiation. Deregulated expression of adhesion molecules on glioma cells is thought to contribute to this process. Junctional adhesion molecules (JAMs) include several IgSF members involved in leukocyte trafficking, angiogenesis, and cell polarity. They are expressed mainly by endothelial cells, white blood cells, and platelets. Here, we report JAM-C expression by human gliomas, but not by their normal cellular counterpart. This expression correlates with the expression of genes involved in cytoskeleton remodeling and cell migration. These genes, identified by a transcriptomic approach, include poliovirus receptor and cystein-rich 61, both known to promote glioma invasion, as well as actin filament associated protein, a c-Src binding partner. Gliomas also aberrantly express JAM-B, a high affinity JAM-C ligand. Their interaction activates the c-Src proto-oncogene, a central upstream molecule in the pathways regulating cell migration and invasion. In the tumor microenvironment, this co-expression may thus promote glioma invasion through paracrine stimuli from both tumor cells and endothelial cells. Accordingly, JAM-C/B blocking antibodies impair in vivo glioma growth and invasion, highlighting the potential of JAM-C and JAM-B as new targets for the treatment of human gliomas.

AFAP120 regulates actin organization during neuronal differentiation

During development, dynamic changes in the actin cytoskeleton determine both cell motility and morphological differentiation. In most mature tissues, cells are generally minimally motile and have morphologies specialized to their functions. In metastatic cancer, cells generally lose their specialized morphology and become motile. Therefore, proteins that regulate the transition between the motile and morphologically differentiated states can play important roles in determining cancer outcomes. AFAP120 is a neuronal-specific protein that binds Src kinase and protein kinase C (PKC) and cross-links actin filaments. Here we report that expression and tyrosine phosphorylation of AFAP120 are developmentally regulated in the cerebellum. In cerebellar cultures, PKC activation induces Src kinase-dependent phosphorylation of AFAP120, indicating that AFAP120 may be a downstream effector of Src. In neuroblastoma cells induced to differentiate by treatment with a PKC activator, tyrosine phosphorylation of AFAP120 appears to regulate the formation of the lamellar actin structures and subsequent neurite initiation. Together, these results indicate that AFAP120 plays a role in organizing dynamic actin structures during neuronal differentiation and suggest that AFAP120 may help regulate the transition from motile precursor to morphologically differentiated neurons.

The actin cross-linking protein AFAP120 regulates axon elongation in a tyrosine phosphorylation-dependent manner

Growth cone guidance and axon elongation require the dynamic coordinated regulation of the actin cytoskeleton. As the growth cone moves, actin-dependent forces generate tension that enables protrusive activity in the periphery and drives growth cone translocation. This dynamic remodeling of the actin cytoskeleton in response to membrane tension requires activation of Src kinase. Although it has been proposed that these actin-dependent forces vary with the extent of actin cross-linking, the identity of the cross-linking protein(s) remains unknown. AFAP120 is a nervous system specific actin cross-linking protein that is regulated by Src kinase phosphorylation. Here, we report that AFAP120 is expressed and tyrosine phosphorylated in differentiating cerebellar granule cells, where it is enriched in the axon and growth cone. Over-expression of AFAP120 enhances neurite elongation in a tyrosine phosphorylation-dependent manner. These findings suggest that AFAP120 may coordinate Src signaling with the dynamic changes in the actin cytoskeleton that drive growth cone motility and axon elongation.

Phosphorylation of AFAP-110 affects podosome lifespan in A7r5 cells

AFAP-110 is an actin-binding and -crosslinking protein that is enriched in Src and phorbol ester (PE)-induced podosomes. In vascular smooth muscle cells endogenous AFAP-110 localized to actin stress fibers and, in response to treatment with phorbol-12,13-dibutyrate (PDBu), to actin-rich podosomes. Since PEs can activate PKCalpha, AFAP-110 is a substrate of PKCalpha and PKCalpha-AFAP-110 interactions direct podosome formation, we sought to identify a PE-induced phosphorylation site in AFAP-110 and determine whether phosphorylation is linked to the formation of podosomes. Mutational analysis revealed Ser277 of AFAP-110 to be phosphorylated in PE-treated cells. The use of a newly generated, phospho-specific antibody directed against phosphorylated Ser277 revealed that PKCalpha activation is associated with PE-induced AFAP-110 phosphorylation. In PDBu-treated A7r5 rat vascular smooth muscle cells, immunolabeling using the phospho-specific antibody showed that phospho-AFAP-110 is primarily associated with actin in podosomes. Although mutation of Ser at position 277 to Ala (AFAP-110(S277A)) did not alter the ability of AFAP-110 to localize to podosomes, overexpression of AFAP-110(S277A) in treated and untreated A7r5 cells resulted in an increased number of cells that display podosomes. Video microscopy demonstrated that AFAP-110(S277A) expression correlates with an increased number of long-lived podosomes. Therefore, we hypothesize that AFAP-110 phosphorylation and/or dephosphorylation is involved in the regulation of podosome stability and lifespan.

AFAP-110 is required for actin stress fiber formation and cell adhesion in MDA-MB-231 breast cancer cells

Regulation of actin organization and dynamics is a highly complex process that involves a number of actin-binding proteins, including capping, branching, severing, sequestering, and cross-linking proteins. The actin-binding and cross-linking protein AFAP-110 is expressed in normal myoepithelial cells. Screening of different breast epithelial cell lines revealed high expression levels of AFAP-110 in the human breast cancer cell lines MDA-MB-231 and MDA-MB-435. Knockdown of AFAP-110 expression in MDA-MB-231 cells does not result in any changes in cell proliferation but did result in a loss of actin stress fiber cross-linking and decreased adhesion to fibronectin. An inducible knockdown approach confirms that MDA-MB-231 breast cancer cells require AFAP-110 expression for stress fiber formation and adhesion. Thus, AFAP-110 may provide cytoskeletal tension through stress fiber formation, which is required for focal adhesion formation. Indeed, we could not detect any focal contacts or focal adhesions in AFAP-110 knockdown cells after adhesion to fibronectin. Although expression levels of crucial focal adhesion components were not influenced by AFAP-110 expression levels, treatment of AFAP-110 knockdown cells with LPA did not result in induction of actin stress fibers and focal adhesions. In summary, AFAP-110 plays an important role in MDA-MB-231 breast cancer cell adhesion possibly by regulating stress filament cross-linking which would promote focal adhesion formation.

AFAP-110 is overexpressed in prostate cancer and contributes to tumorigenic growth by regulating focal contacts

The actin filament-associated protein AFAP-110 is an actin cross-linking protein first identified as a substrate of the viral oncogene v-Src. AFAP-110 regulates actin cytoskeleton integrity but also functions as an adaptor protein that affects crosstalk between Src and PKC. Here we investigated the roles of AFAP-110 in the tumorigenic process of prostate carcinoma. Using immunohistochemistry of human tissue arrays, we found that AFAP-110 was absent or expressed at very low levels in normal prostatic epithelium and benign prostatic hyperplasia but significantly increased in prostate carcinomas. The level of AFAP-110 in carcinomas correlated with the Gleason scores. Downregulation of AFAP-110 in PC3 prostate cancer cells inhibited cell proliferation in vitro and tumorigenicity and growth in orthotopic nude mouse models. Furthermore, downmodulation of AFAP-110 resulted in decreased cell-matrix adhesion and cell migration, defective focal adhesions, and reduced integrin beta1 expression. Reintroduction of avian AFAP-110 or a mutant disabling its interaction with Src restored these properties. However, expression of an AFAP-110 lacking the PKC-interacting domain failed to restore properties of parental cells. Thus, increased expression of AFAP-110 is associated with progressive stages of prostate cancer and is critical for tumorigenic growth, in part by regulating focal contacts in a PKC-dependent mechanism.

PI3K activation is required for PMA-directed activation of cSrc by AFAP-110

Activation of PKCalpha will induce the cSrc binding partner AFAP-110 to colocalize with and activate cSrc. The ability of AFAP-110 to colocalize with cSrc is contingent on the integrity of the amino-terminal pleckstrin homology (PH1) domain, while the ability to activate cSrc is dependent on the integrity of its SH3 binding motif, which engages the cSrc SH3 domain. The outcome of AFAP-110-directed cSrc activation is a change in actin filament integrity and the formation of podosomes. Here, we address what cellular signals promote AFAP-110 to colocalize with and activate cSrc, in response to PKCalpha activation or PMA treatment. Because PH domain integrity in AFAP-110 is required for colocalization, and PH domains are known to interact with both protein and lipid binding partners, we sought to determine whether phosphatidylinositol 3-kinase (PI3K) activation played a role in PMA-induced colocalization between AFAP-110 and cSrc. We show that PMA treatment is able to direct activation of PI3K. Treatment of mouse embryo fibroblast with PI3K inhibitors blocked PMA-directed colocalization between AFAP-110 and cSrc and subsequent cSrc activation. PMA also was unable to induce colocalization or cSrc activation in cells that lacked the p85alpha and -beta regulatory subunits of PI3K. This signaling pathway was required for migration in a wound healing assay. Cells that were null for cSrc or the p85 regulatory subunits or expressed a dominant-negative AFAP-110 also displayed a reduction in migration. Thus PI3K activity is required for PMA-induced colocalization between AFAP-110 and cSrc and subsequent cSrc activation, and this signaling pathway promotes cell migration.

Structural and functional diversity of adaptor proteins involved in tyrosine kinase signalling

Adaptors are proteins of multi-modular structure without enzymatic activity. Their capacity to organise large, temporary protein complexes by linking proteins together in a regulated and selective fashion makes them of outstanding importance in the establishment and maintenance of specificity and efficiency in all known signal transduction pathways. This review focuses on the structural and functional characterisation of adaptors involved in tyrosine kinase (TK) signalling. TK-linked adaptors can be distinguished by their domain composition and binding specificities. However, such structural classifications have proven inadequate as indicators of functional roles. A better way to understand the logic of signalling networks might be to look at functional aspects of adaptor proteins such as signalling specificity, negative versus positive contribution to signal propagation, or their position in the signalling hierarchy. All of these functions are dynamic, suggesting that adaptors have important regulatory roles rather than acting only as stable linkers in signal transduction.

Lyn kinase activity is the predominant cellular SRC kinase activity in glioblastoma tumor cells

Cellular Src activity modulates cell migration, proliferation, and differentiation, and recent reports suggest that individual members of the Src family may play specific roles in these processes. As we have found that Lyn, but not Fyn, activity promotes migration of glioblastoma cells in response to the cooperative signal generated by platelet-derived growth factor receptor beta and integrin alpha(v)beta3, we compared the activity and expression of Lyn and Fyn in glioblastoma (grade IV) tumor biopsy samples with that in anaplastic astrocytoma (grade III) tumors, nonneoplastic brain, and normal autopsy brain samples. Lyn kinase activity was significantly elevated in glioblastoma tumor samples. Notably, the Lyn kinase activity accounted for >90% of pan-Src kinase activity in glioblastoma samples but only approximately 30% of pan-Src kinase activity in the other groups. The levels of phosphorylation of the autophosphorylation site were consistent with significantly higher Lyn activity in glioblastoma tumor tissue than nonneoplastic brain. Although the normalized levels of Lyn protein and the relative levels of Lyn message were significantly higher in glioblastoma samples than nonneoplastic brain, the normalized levels of Lyn protein did not correlate with Lyn activity in the glioblastoma samples. There was no significant difference in the normalized levels of c-Src and Fyn protein and message in the glioblastoma and nonneoplastic brain. Immunostaining revealed that Lyn is located primarily in the glioblastoma cells in the tumor biopsies. These data indicate that Lyn kinase activity is significantly elevated in glioblastoma tumors and suggest that it is the Lyn activity that promotes the malignant phenotype in these tumors.

Role for the pleckstrin homology domain-containing protein CKIP-1 in AP-1 regulation and apoptosis

The oncogenic transcription factor c-Jun plays an important role in cell proliferation, transformation and differentiation. All identified c-Jun-interacting proteins are localized to the nucleus or cytoplasm and function in their intact forms. Here we show that the pleckstrin homology domain-containing protein CKIP-1 (casein kinase 2-interacting protein-1) functions as a plasma membrane-bound AP-1 regulator. During apoptosis, CKIP-1 is cleaved by caspase-3 and translocated to the cytoplasm and then to the nucleus. C-terminal fragments of cleaved CKIP-1 strongly repress AP-1 activity. Importantly, CKIP-1 overexpression promotes apoptosis by forming a positive feedback loop between CKIP-1 and caspase-3. RNA interference of CKIP-1 or overexpression of c-Jun attenuates the sensitivity to apoptosis, indicating a novel role of CKIP-1 in apoptosis. CKIP-1 is the first case of a c-Jun-interacting protein that regulates AP-1 activity via caspase-3-dependent cleavage and translocation.

Analysis of the role of the leucine zipper motif in regulating the ability of AFAP-110 to alter actin filament integrity

AFAP-110 has an intrinsic ability to alter actin filament integrity as an actin filament crosslinking protein. This capability is regulated by a carboxy terminal leucine zipper (Lzip) motif. The Lzip motif facilitates self-association stabilizing the AFAP-110 multimers. Deletion of the Lzip motif (AFAP-110(Deltalzip)) reduces the stability of the AFAP-110 multimer and concomitantly increases its ability to crosslink actin filaments, in vitro, and to activate cSrc and alter actin filament integrity, in vivo. We sought to determine how the Lzip motif regulates AFAP-110 function. Substitution of the c-Fos Lzip motif in place of the AFAP-110 Lzip motif (AFAP-110(fos)) was predicted to preserve the alpha-helical structure while changing the sequence. To alter the structure of the alpha-helix, a leucine to proline mutation was generated in the AFAP-110 alpha-helical Lzip motif (AFAP-110(581P)), which largely preserved the sequence. The helix mutants, AFAP-110(Deltalzip), AFAP-110(fos), and AFAP-110(581P), demonstrated reduced multimer stability with an increased capacity to crosslink actin filaments, in vitro, relative to AFAP-110. An analysis of opposing binding sites indicated that the carboxy terminus/Lzip motif can contact sequences within the amino terminal pleckstrin homology (PH1) domain indicating an auto-inhibitory mechanism for regulating multimer stability and actin filament crosslinking. In vivo, only AFAP-110(Deltalzip) and AFAP-110(581P) were to activate cSrc and to alter cellular actin filament integrity. These data indicate that the intrinsic ability of AFAP-110 to crosslink actin filaments is dependent upon both the sequence and structure of the Lzip motif, while the ability of the Lzip motif to regulate AFAP-110-directed activation of cSrc and changes in actin filament integrity in vivo is dependent upon the structure or presence of the Lzip motif. We hypothesize that the intrinsic ability of AFAP-110 to crosslink actin filaments or activate cSrc are distinct functions.

Pleckstrin homology domain of G protein-coupled receptor kinase-2 binds to PKC and affects the activity of PKC kinase

AIM: To study the detail mechanism of interaction between PKC and GRK₂ and the effect of GRK₂ on activity of PKC.

METHODS: The cDNA of pleckstrin homology (PH) domain located in GRK₂ residue 548 to 660 was amplified by PCR with the mRNA of human GRK₂ (β1-adrenergic receptor kinase) as template isolated from human fresh placenta, the expression vector pGEX-PH inserted with the aboved cDNA sequence for GRK₂ PH domain protein and the expression vectors for GST (glutathion-s-transferase) -GRK₂ PH domain fusion protein, BTK (Bruton’s tyrosine kinase) PH domain and GST protein were constructed. The expression of GRK₂ in culture mammalian cells (6 cell lines: PC-3, MDCK, SGC7901, Jurkat cell etc.) was determined by SDS-PAGE and Co-immunoprecipitation. The binding of GRK₂ PH domain, GST-GRK₂ PH domain fusion protein and BTK PH domain to PKC in vitro were detected by SDS-PAGE and Western blot, upon prolonged stimulation of epinephrine, the binding of GRK₂ to PKC was also detected by western blot and Co-immunoprecipitation.

RESULTS: The binding of GRK₂ PH domain to PKC in vitro was confirmed by western blot, as were the binding upon prolonged stimulation of epinephrine and the binding of BTK PH domain to PKC. In the present study, GRK₂ PH domain was associated with PKC and down-regulated PKC activity, but Btk PH domain up-regulated PKC activity as compared with GRK₂ PH domain.

CONCLUSION: GRK₂ can bind with PKC and down-regulated PKC activity.