Abelson interactor protein-1 positively regulates breast cancer cell proliferation, migration, and invasion

Adaptor protein Abelson interactor 1 in homeostasis and disease

Dysregulation of Abelson interactor 1 (ABI1) is associated with various states of disease including developmental defects, pathogen infections, and cancer. ABI1 is an adaptor protein predominantly known to regulate actin cytoskeleton organization processes such as those involved in cell adhesion, migration, and shape determination. Linked to cytoskeleton via vasodilator-stimulated phosphoprotein (VASP), Wiskott-Aldrich syndrome protein family (WAVE), and neural-Wiskott-Aldrich syndrome protein (N-WASP)-associated protein complexes, ABI1 coordinates regulation of various cytoplasmic protein signaling complexes dysregulated in disease states. The roles of ABI1 beyond actin cytoskeleton regulation are much less understood. This comprehensive, protein-centric review describes molecular roles of ABI1 as an adaptor molecule in the context of its dysregulation and associated disease outcomes to better understand disease state-specific protein signaling and affected interconnected biological processes.

Pan-cancer transcriptomic data of ABI1 transcript variants and molecular constitutive elements identifies novel cancer metastatic and prognostic biomarkers

BACKGROUND

Abelson interactor 1 (ABI1) is associated with the metastasis and prognosis of many malignancies. The association between ABI1 transcript spliced variants, their molecular constitutive exons and exon-exon junctions (EEJs) in 14 cancer types and clinical outcomes remains unsolved.

OBJECTIVE

To identify novel cancer metastatic and prognostic biomarkers from ABI1 total mRNA, TSVs, and molecular constitutive elements.

METHODS

Using data from TCGA and TSVdb database, the standard median of ABI1 total mRNA, TSV, exon, and EEJ expression was used as a cut-off value. Kaplan-Meier analysis, Chi-squared test (X2) and Kendall's tau statistic were used to identify novel metastatic and prognostic biomarkers, and Cox regression analysis was performed to screen and identify independent prognostic factors.

RESULTS

A total of 35 ABI1-related factors were found to be closely related to the prognosis of eight candidate cancer types. A total of 14 ABI1 TSVs and molecular constitutive elements were identified as novel metastatic and prognostic biomarkers in four cancer types. A total of 13 ABI1 molecular constitutive elements were identified as independent prognostic biomarkers in six cancer types.

CONCLUSIONS

In this study, we identified 14 ABI1-related novel metastatic and prognostic markers and 21 independent prognostic factors in total 8 candidate cancer types.

Comprehensive pan-cancer investigation: unraveling the oncogenic, prognostic, and immunological significance of Abelson interactor family member 3 gene in human malignancies

Background: Abelson interactor Family Member 3 (ABI3) encodes protein that not only suppresses the ectopic metastasis of tumor cells but also hinders their migration. Although ABI3 had been found to modulate the advancement of diverse neoplasms, there is no comprehensive pan-cancer analysis of its effects. Methods: The transcriptomics data of neoplasm and normal tissues were retrieved from the Genomic Data Commons (GDC) data portal, and UCSC XENA database. To gather protein information for ABI3, Human Protein Atlas (HPA) and GeneMANIA websites were utilized. Additionally, Tumor Immune Single-cell Hub (TISCH) database was consulted to determine the primary cell types expressing ABI3 in cancer microenvironments. Univariate Cox regression approach was leveraged to evaluate ABI3's prognostic role across cancers. The Cbioportal and Gene Set Cancer Analysis (GSCA) website were leveraged to scrutinize the genomic landscape information across cancers. TIMER2.0 was leveraged to probe the immune cell infiltrations associated with ABI3 across cancers. The associations of ABI3 with immune-related genes were analyzed through Spearman correlation method. Gene Set Enrichment Analysis (GSEA) and Gene Set Variation Analysis (GSVA) were utilized to search associated biological pathways. The CellMiner database and molecular docking were implemented to identify potential interactions between the ABI3 protein and specific anticarcinogen. Findings: ABI3 expression and its ability to predict prognosis varied distinct tumor, with particularly high expression observed in Tprolif cells and monocytes/macrophages. Copy number variation (CNV) and methylation negatively correlated with ABI3 expression in the majority of malignancies. Corresponding mutation survival analysis indicated that the mutation status of ABI3 was strongly connected to the prognosis of LGG patients. ABI3 expression was linked to immunotherapeutic biomarkers and response in cancers. ESTIMATE and immune infiltrations analyses presented ABI3 association with immunosuppression. ABI3 was significantly correlated with immunoregulators and immune-related pathways. Lastly, prospective ABI3-targeted drugs were filtered and docked to ABI3 protein. Interpretation: Our study reveals that ABI3 acts as a robust tumor biomarker. Its functions are vital that could inhibit ectopic metastasis of tumor cells and modulate cellular adhesion and migration. The discoveries presented here may have noteworthy consequences for the creation of fresh anticancer suppressors, especially those targeting BRCA.

A Novel and Validated 8-Pyroptosis-Related Genes Based Risk Prediction Model for Diffuse Large B Cell Lymphoma

BACKGROUND

Diffuse large B-cell lymphoma (DLBCL), the most common type of Non-Hodgkin's Lymphoma (NHL), has a lethal nature. Thus, the establishment of a novel model to predict the prognosis of DLBCL and guide its therapy is an urgency. Meanwhile, pyroptosis is engaged in the progression of DLBCL with further investigations required to reveal the underlying mechanism.

METHODS

LASSO regression was conducted to establish a risk model based on those PRGs. External datasets, RT-qPCR and IHC images from The Human Protein Alta (HPA) database were utilized to validate the model. ssGSEA was utilized to estimate the score of immune components in DLBCL.

RESULTS

A model based on 8 PRGs was established to generate a risk score. Validation of the model confirmed its robust performance. The risk score was associated with advanced clinical stages and shorter overall survivals. Two novel second-line chemotherapies were found to be potential treatments for high-risk patients. The risk score was also found to be correlated with immune components in DLBCL.

CONCLUSION

This novel model can be utilized in clinical practices to predict the prognosis of DLBCL and guide the treatment of patients at high risk, providing an overview of immune regulatory program via pyroptosis in DLBCL.

Targeting the WASF3 complex to suppress metastasis

Wiskott-Aldrich syndrome protein family members (WASF) regulate the dynamics of the actin cytoskeleton, which plays an instrumental role in cancer metastasis and invasion. WASF1/2/3 forms a hetero-pentameric complex with CYFIP1/2, NCKAP1/1 L, Abi1/2/3 and BRK1 called the WASF Regulatory Complex (WRC), which cooperatively regulates actin nucleation by WASF1/2/3. Activation of the WRC enables actin networking and provides the mechanical force required for the formation of lamellipodia and invadopodia. Although the WRC drives cell motility essential for several routine physiological functions, its aberrant deployment is observed in cancer metastasis and invasion. WASF3 expression is correlated with metastatic potential in several cancers and inversely correlates with overall progression-free survival. Therefore, disruption of the WRC may serve as a novel strategy for targeting metastasis. Given the complexity involved in the formation of the WRC which is largely comprised of large protein-protein interfaces, there are currently no inhibitors for WASF3. However, several constrained peptide mimics of the various protein-protein interaction interfaces within the WRC were found to successfully disrupt WASF3-mediated migration and invasion. This review explores the role of the WASF3 WRC in driving metastasis and how it may be selectively targeted for suppression of metastasis.

A new strategy for the rapid identification and validation of direct toxicity targets of psoralen-induced hepatotoxicity

The interaction between small-molecule compounds of traditional Chinese medicine and their direct targets is the molecular initiation event, which is the key factor for toxicity efficacy. Psoralen, an active component of Fructus Psoraleae, is toxic to the liver and has various pharmacological properties. Although the mechanism of psoralen-induced hepatotoxicity has been studied, the direct target of psoralen remains unclear. Thus, the aim of this study was to discover direct targets of psoralen. To this end, we initially used proteomics based on drug affinity responsive target stability (DARTS) technology to identify the direct targets of psoralen. Next, we used surface plasmon resonance (SPR) analysis and verified the affinity effect of the 'component-target protein'. This method combines molecular docking technology to explore binding sites between small molecules and proteins. SPR and molecular docking confirmed that psoralen and tyrosine-protein kinase ABL1 could be stably combined. Based on the above experimental results, ABL1 is a potential direct target of psoralen-induced hepatotoxicity. Finally, the targets Nrf2 and mTOR, which are closely related to the hepatotoxicity caused by psoralen, were predicted by integrating proteomics and network pharmacology. The direct target ABL1 is located upstream of Nrf2 and mTOR, Nrf2 can influence the expression of mTOR by affecting the level of reactive oxygen species. Immunofluorescence experiments and western blot results showed that psoralen could affect ROS levels and downstream Nrf2 and mTOR protein changes, whereas the ABL1 inhibitor imatinib and ABL1 agonist DPH could enhance or inhibit this effect. In summary, we speculated that when psoralen causes hepatotoxicity, it acts on the direct target ABL1, resulting in a decrease in Nrf2 expression, an increase in ROS levels and a reduction in mTOR expression, which may cause cell death. We developed a new strategy for predicting and validating the direct targets of psoralen. This strategy identified the toxic target, ABL1, and the potential toxic mechanism of psoralen.

ABL1 Is a Prognostic Marker and Associated with Immune Infiltration in Hepatocellular Carcinoma

Background

The role of ABL1 in hepatocellular carcinoma (HCC) is still unclear. Therefore, this study aims to explore the potential role of ABL1 in the progression of HCC using bioinformatics methods.

Methods

We analyzed the expression, prognostic potential, and immune cell effect of ABL1 in HCC by using a variety of datasets.

Results

ABL1 is highly expressed in HCC and associated with unfavorable overall survival (OS) and disease-free survival (DFS). Functional network analysis revealed that ABL1 plays an important role in mitochondrial activity, ATP metabolism, protein translation and metabolism, various neurological diseases, nonalcoholic fatty liver disease, and notch signaling pathway. In addition, we found that ABL1 expression was closely correlated with B cells, CD8 + T cells, CD4 + T cells, macrophages, neutrophils, and dendritic cells. Furthermore, ABL1 expression was positively associated with the expression levels of immune checkpoint genes, such as PD-1L, TIM3, TIGIT, and CTLA4.

Conclusion

ABL1 is associated with immune infiltration and prognosis of HCC.

The roles and prognostic significance of ABI1-TSV-11 expression in patients with left-sided colorectal cancer

Abnormally expressed and/or phosphorylated Abelson interactor 1 (ABI1) participates in the metastasis and progression of colorectal cancer (CRC). ABI1 presents as at least 12 transcript variants (TSVs) by mRNA alternative splicing, but it is unknown which of them is involved in CRC metastasis and prognosis. Here, we firstly identified ABI1-TSV-11 as a key TSV affecting the metastasis and prognosis of left-sided colorectal cancer (LsCC) and its elevated expression is related to lymph node metastasis and shorter overall survival (OS) in LsCC by analyzing data from The Cancer Genome Atlas and TSVdb. Secondly, ABI1-TSV-11 overexpression promoted LoVo and SW480 cells adhesion and migration in vitro, and accelerated LoVo and SW480 cells lung metastasis in vivo. Finally, mechanism investigations revealed that ABI1-isoform-11 interacted with epidermal growth factor receptor pathway substrate 8 (ESP8) and regulated actin dynamics to affect LoVo and SW480 cells biological behaviors. Taken together, our data demonstrated that ABI1-TSV-11 plays an oncogenic role in LsCC, it is an independent risk factor of prognosis and may be a potential molecular marker and therapeutic target in LsCC.

Abelson interactor 1 splice isoform-L plays an anti-oncogenic role in colorectal carcinoma through interactions with WAVE2 and full-length Abelson interactor 1

BACKGROUND

Expression of the full-length isoform of Abelson interactor 1 (ABI1), ABI1-p65, is increased in colorectal carcinoma (CRC) and is thought to be involved in one or more steps leading to tumor progression or metastasis. The ABI1 splice isoform-L (ABI1-SiL) has conserved WAVE2-binding and SH3 domains, lacks the homeo-domain homologous region, and is missing the majority of PxxP- and Pro-rich domains found in full-length ABI1-p65. Thus, ABI1-SiL domain structure suggests that the protein may regulate CRC cell morphology, adhesion, migration, and metastasis via interactions with the WAVE2 complex pathway.

AIM

To investigate the potential role and underlying mechanisms associated with ABI1-SiL-mediated regulation of CRC.

METHODS

ABI1-SiL mRNA expression in CC tissue and cell lines was measured using both qualitative reverse transcriptase-polymerase chain reaction (RT-PCR) and real-time quantitative RT-PCR. A stably ABI1-SiL overexpressing SW480 cell model was constructed using Lipofectamine 2000, and cells selected with G418. Image J software, CCK8, and transwell assays were used to investigate SW480 cell surface area, proliferation, migration, and invasion. Immunoprecipitation, Western blot, and co-localization assays were performed to explore intermolecular interactions between ABI1-SiL, WAVE2, and ABI1-p65 proteins.

RESULTS

ABI1-SiL was expressed in normal colon tissue and was significantly decreased in CRC cell lines and tissues. Overexpression of ABI1-SiL in SW480 cells significantly increased the cell surface area and inhibited the adhesive and migration properties of the cells, but did not alter their invasive capacity. Similar to ABI1-p65, ABI1-SiL still binds WAVE2, and the ABI1-p65 isoform in SW480 cells. Furthermore, co-localization assays confirmed these intermolecular interactions.

CONCLUSION

These results support a model in which ABI1-SiL plays an anti-oncogenic role by competitively binding to WAVE2 and directly interacting with phosphorylated and non-phosphorylated ABI1-p65, functioning as a dominant-negative form of ABI1-p65.

PTEN suppresses epithelial-mesenchymal transition and cancer stem cell activity by downregulating Abi1

The epithelial–mesenchymal transition (EMT) is an embryonic program frequently reactivated during cancer progression and is implicated in cancer invasion and metastasis. Cancer cells can also acquire stem cell properties to self-renew and give rise to new tumors through the EMT. Inactivation of the tumor suppressor PTEN has been shown to induce the EMT, but the underlying molecular mechanisms are less understood. In this study, we reconstituted PTEN-deficient breast cancer cells with wild-type and mutant PTEN, demonstrating that restoration of PTEN expression converted cancer cells with mesenchymal traits to an epithelial phenotype and inhibited cancer stem cell (CSC) activity. The protein rather than the lipid phosphatase activity of PTEN accounts for the reversal of the EMT. PTEN dephosphorylates and downregulates Abi1 in breast cancer cells. Gain- and loss-of-function analysis indicates that upregulation of Abi1 mediates PTEN loss-induced EMT and CSC activity. These results suggest that PTEN may suppress breast cancer invasion and metastasis via dephosphorylating and downregulating Abi1.

Integrin-associated molecules and signalling cross talking in osteoclast cytoskeleton regulation

In the ageing skeleton, the balance of bone reconstruction could commonly be broken by the increasing of bone resorption and decreasing of bone formation. Consequently, the bone resorption gradually occupies a dominant status. During this imbalance process, osteoclast is unique cell linage act the bone resorptive biological activity, which is a highly differentiated ultimate cell derived from monocyte/macrophage. The erosive function of osteoclasts is that they have to adhere the bone matrix and migrate along it, in which adhesive cytoskeleton recombination of osteoclast is essential. In that, the podosome is a membrane binding microdomain organelle, based on dynamic actin, which forms a cytoskeleton superstructure connected with the plasma membrane. Otherwise, as the main adhesive protein, integrin regulates the formation of podosome and cytoskeleton, which collaborates with the various molecules including: c-Cbl, p130^Cas , c-Src and Pyk2, through several signalling cascades cross talking, including: M-CSF and RANKL. In our current study, we discuss the role of integrin and associated molecules in osteoclastogenesis cytoskeletal, especially podosomes, regulation and relevant signalling cascades cross talking.

Role for polo-like kinase 4 in mediation of cytokinesis

The mitotic protein polo-like kinase 4 (PLK4) plays a critical role in centrosome duplication for cell division. By using immunofluorescence, we confirm that PLK4 is localized to centrosomes. In addition, we find that phospho-PLK4 (pPLK4) is cleaved and distributed to kinetochores (metaphase and anaphase), spindle midzone/cleavage furrow (anaphase and telophase), and midbody (cytokinesis) during cell division in immortalized epithelial cells as well as breast, ovarian, and colorectal cancer cells. The distribution of pPLK4 midzone/cleavage furrow and midbody positions pPLK4 to play a functional role in cytokinesis. Indeed, we found that inhibition of PLK4 kinase activity with a small-molecule inhibitor, CFI-400945, prevents translocation to the spindle midzone/cleavage furrow and prevents cellular abscission, leading to the generation of cells with polyploidy, increased numbers of duplicated centrosomes, and vulnerability to anaphase or mitotic catastrophe. The regulatory role of PLK4 in cytokinesis makes it a potential target for therapeutic intervention in appropriately selected cancers.

[Regulator proteins of actin dynamics as possible targets of antineoplastic therapies]

BACKGROUND

The ability of tumor cells to leave the primary tumor is prerequisite for metastatic spread. In previous studies, we identified regulator proteins of actin reorganization with essential functions in both synaptogenesis and tumor cell migration.

OBJECTIVE

The aim of the studies summarized in this article is to identify signaling pathways associated with actin-related proteins that might represent potential molecular targets for antiinvasive and/or antineoplastic therapies.

MATERIALS AND METHODS

We used immunohistochemical analyses of protein expression as well as in vitro techniques (cell culture, fluorescence microscopy, RNAi-based knockdown of protein expression, protein biochemistry and in vivo animal experiment substitutes).

RESULTS

We show that phosphorylation of Abelson interactor 1 (Abi1) is essential for the adhesion and invasion of colorectal carcinoma cells and might be targeted by the tyrosine kinase inhibitor STI571/Glivec®. HnRNP K, a protein interaction partner of Abi1, is upregulated in malignant melanoma in response to ionizing radiation; this upregulation is impaired upon application of the MEK inhibitor PD98059, enhancing radiosensivity of melanoma. Edelfosin, an alkyl-lipid blocker of the Abi1 interaction partner SK3, inhibits invasion of urothelial carcinoma cells.

CONCLUSION

The studies summarized in this overview confirm a central role for the investigated proteins in tumor cell invasion and resistance to antineoplastic therapies and identify possible molecular targets for novel therapeutic compounds.

Oncogenic function and prognostic significance of Abelson interactor 1 in hepatocellular carcinoma

Aberrant expression of Abelson interactor 1 (ABI1) has been reported in multiple cancers. However, its clinical significance and potential biological roles in hepatocellular carcinoma (HCC) have not been fully elucidated. In this study, we found that ABI1 was obviously upregulated in HCC tissues compared with non-tumor tissues. Moreover, high ABI1 expression was significantly correlated with tumor size (P=0.041), tumor number (P<0.001), tumor encapsulation (P<0.001) and BCLC stage (P=0.010). Importantly, Kaplan-Meier survival analysis showed that increased ABI1 expression predicted shorter overall survival time (P<0.001) and a higher tendency of tumor recurrence (P=0.001) in HCC patients. Multivariate Cox regression analysis further confirmed high ABI1 expression was an independent predictor for both overall survival (HR=1.795, P=0.025) and early recurrence (HR=1.893, P=0.012) after surgical resection. Furthermore, in vitro studies indicated that overexpression of ABI1 induced an increase in cell proliferation, migration and invasion of HCC cells, whereas knockdown of ABI1 did the opposite. Xenograft mouse models verified the promoting effects of ABI1 on HCC growth and lung metastasis in vivo. Collectively, our findings indicated that ABI1 contributes to the development and progression of HCC as an oncogene and may serve as a valuable prognostic marker for HCC patients.

Human Endometrial Exosomes Contain Hormone-Specific Cargo Modulating Trophoblast Adhesive Capacity: Insights into Endometrial-Embryo Interactions

Embryo implantation into receptive endometrium requires synergistic endometrial-blastocyst interactions within the uterine cavity and is essential for establishing pregnancy. We demonstrate that exosomes (40-150 nm nanovesicles) released from endometrial epithelial cells are an important component of these interactions. We defined the proteome of purified endometrial epithelial-derived exosomes (Exos) influenced by menstrual cycle hormones estrogen (E; proliferative phase) and estrogen plus progesterone (EP; receptive phase) and examined their potential to modify trophoblast function. E-/EP-Exos were uniquely enriched with 254 and 126 proteins, respectively, with 35% newly identified proteins not previously reported in exosome databases. Importantly, EP-Exos protein cargo was related to fundamental changes in implantation: adhesion, migration, invasion, and extracellular matrix remodeling. These findings from hormonally treated ECC1 endometrial cancer cells were validated in human primary uterine epithelial cell-derived exosomes. Functionally, exosomes were internalized by human trophoblast cells and enhanced their adhesive capacity, a response mediated partially through active focal adhesion kinase (FAK) signaling. Thus, exosomes contribute to the endometrial-embryo interactions within the human uterine microenvironment essential for successful implantation.

Upregulation of Abelson interactor protein 1 predicts tumor progression and poor outcome in epithelial ovarian cancer

Abelson interactor protein 1 (Abi1) is a key regulator of actin reorganization and lamellipodia formation. Because of its role in cell migration, Abi1 has been implicated in tumor progression. In the present study, we investigated the role of Abi1 in epithelial ovarian cancer (EOC) by analyzing its expression and correlation with clinicopathological and survival data. We evaluated the expression of Abi1 in 223 paraffin-embedded EOC specimens by immunohistochemistry and 46 frozen EOC samples by Western blot and real-time reverse transcription polymerase chain reaction analysis. Results showed that Abi1 protein and mRNA expression was significantly higher in EOC tissue compared with noncancerous tumors and normal ovaries (P < .05). Moreover, high level of Abi1 expression was significantly correlated with advanced stage, high grade, elevated Ca-125 level, and suboptimal surgical debulking (P < .05). By Western blot analysis, Abi1 was expressed in highly invasive cells compared with weakly invasive cells (P < .05). Immunofluorescence was performed to demonstrate Abi1 expression in SKOV3 cells. Additionally, upregulation of Abi1 significantly correlated with shorter survival (P < .05). Most importantly, multivariate analysis showed that Abi1 overexpression is an independent prognostic factor, complementary to clinical stage and residual tumor size. In conclusion, our findings suggest that Abi1 acts as a tumor-promoting gene in EOC progression, which may lead to unfavorable prognosis. Abi1 may serve as a potential effective prognostic marker for EOC.

Action of hexachlorobenzene on tumor growth and metastasis in different experimental models

Hexachlorobenzene (HCB) is a widespread organochlorine pesticide, considered a possible human carcinogen. It is a dioxin-like compound and a weak ligand of the aryl hydrocarbon receptor (AhR). We have found that HCB activates c-Src/HER1/STAT5b and HER1/ERK1/2 signaling pathways and cell migration, in an AhR-dependent manner in MDA-MB-231 breast cancer cells. The aim of this study was to investigate in vitro the effect of HCB (0.005, 0.05, 0.5, 5μM) on cell invasion and metalloproteases (MMPs) 2 and 9 activation in MDA-MB-231 cells. Furthermore, we examined in vivo the effect of HCB (0.3, 3, 30mg/kg b.w.) on tumor growth, MMP2 and MMP9 expression, and metastasis using MDA-MB-231 xenografts and two syngeneic mouse breast cancer models (spontaneous metastasis using C4-HI and lung experimental metastasis using LM3). Our results show that HCB (5μM) enhances MMP2 expression, as well as cell invasion, through AhR, c-Src/HER1 pathway and MMPs. Moreover, HCB increases MMP9 expression, secretion and activity through a HER1 and AhR-dependent mechanism, in MDA-MB-231 cells. HCB (0.3 and 3mg/kg b.w.) enhances subcutaneous tumor growth in MDA-MB-231 and C4-HI in vivo models. In vivo, using MDA-MB-231 model, the pesticide (0.3, 3 and 30mg/kg b.w.) activated c-Src, HER1, STAT5b, and ERK1/2 signaling pathways and increased MMP2 and MMP9 protein levels. Furthermore, we observed that HCB stimulated lung metastasis regardless the tumor hormone-receptor status. Our findings suggest that HCB may be a risk factor for human breast cancer progression.

Phosphoregulation of the WAVE regulatory complex and signal integration

The WAVE2 regulatory complex (WRC) induces actin polymerization by activating the actin nucleator Arp2/3. Polymerizing actin pushes against the cell membrane and induces dramatic edge protrusions. In order to properly control such changes in cell morphology and function, cells have evolved multiple methods to tightly regulate WRC and Arp2/3 activity in space and time. Of these mechanisms, phosphorylation plays a fundamental role in transmitting extracellular and intracellular signals to the WRC and the actin cytoskeleton. This review discusses the phosphorylation-based regulatory inputs into the WRC. Signaling pathways that respond to growth factors, chemokines, hormones, and extracellular matrix converge upon the WAVE and ABI components of the WRC. The Abl, Src, ERK, and PKA kinases promote complex activation through a WRC conformation change that permits interaction with the Arp2/3 complex and through WRC translocation to the cell edge. The neuron-specific CDK5 and constitutively active CK2 kinases inhibit WRC activation. These regulatory signals are integrated in space and time as they coalesce upon the WRC. The combination of WRC phosphorylation events and WRC activity is controlled by stimulus, cell type, and cell cycle-specific pathway activation and via pathway cross-inhibition and cross-activation.

Crk and ABI1: binary molecular switches that regulate abl tyrosine kinase and signaling to the cytoskeleton

The nonreceptor tyrosine kinases Abl and Arg are among the most well-characterized tyrosine kinases in the human genome. The activation of Abl by N-terminal fusions with Bcr (Bcr-Abl) or Gag (v-Abl) is responsible for chronic myeloid leukemia or Ph+ acute lymphoblastic leukemia and mouse leukemia virus, respectively. In addition, aberrant Abl and Arg activation downstream of several oncogenic growth factor receptors contributes to the development and progression of a variety of human cancers, often associated with poor clinical outcome, drug resistance, and tumor invasion and metastasis. Abl activation can occur by a variety of mechanisms that include domain interactions involving structural remodeling of autoinhibited conformations as well as direct phosphorylation by upstream kinases and phosphatases. Constitutive activation of Abl plays a significant role in regulating the actin cytoskeleton by modulating cell adhesion, motility, and invadopodia. This review addresses the role of Abl and Arg in tumor progression with particular emphasis on the roles of Crk and Abi1 adapter proteins as distinct molecular switches for Abl transactivation. These insights, combined with new insights into the structure of these kinases, provide the rationale to envision that Crk and Abi1 fine-tune Abl regulation to control signaling to the cytoskeleton.

KIF14 negatively regulates Rap1a-Radil signaling during breast cancer progression

The kinesin KIF14 associates with the PDZ domain of Radil and negatively regulates Rap1-mediated inside-out integrin activation by tethering Radil on microtubules.

The small GTPase Rap1 regulates inside-out integrin activation and thereby influences cell adhesion, migration, and polarity. Several Rap1 effectors have been described to mediate the cellular effects of Rap1 in a context-dependent manner. Radil is emerging as an important Rap effector implicated in cell spreading and migration, but the molecular mechanisms underlying its functions are unclear. We report here that the kinesin KIF14 associates with the PDZ domain of Radil and negatively regulates Rap1-mediated inside-out integrin activation by tethering Radil on microtubules. The depletion of KIF14 led to increased cell spreading, altered focal adhesion dynamics, and inhibition of cell migration and invasion. We also show that Radil is important for breast cancer cell proliferation and for metastasis in mice. Our findings provide evidence that the concurrent up-regulation of Rap1 activity and increased KIF14 levels in several cancers is needed to reach optimal levels of Rap1–Radil signaling, integrin activation, and cell–matrix adhesiveness required for tumor progression.

Scar/WAVE3 contributes to motility and plasticity of lamellipodial dynamics but not invasion in three dimensions

The Scar (suppressor of cAMP receptor)/WAVE [WASP (Wiskott-Aldrich syndrome protein) verprolin homologous] complex plays a major role in the motility of cells by activating the Arp2/3 complex, which initiates actin branching and drives protrusions. Mammals have three Scar/WAVE isoforms, which show some tissue-specific expression, but their functions have not been differentiated. In the present study we show that depletion of Scar/WAVE3 in the mammalian breast cancer cells MDA-MB-231 results in larger and less dynamic lamellipodia. Scar/WAVE3-depleted cells move more slowly but more persistently on a two-dimensional matrix and they typically only show one lamellipod. However, Scar/WAVE3 appears to have no role in driving invasiveness in a three-dimensional Matrigel™ invasion assay or a three-dimensional collagen invasion assay, suggesting that lamellipodial persistence as seen in two-dimensions is not crucial in three-dimensional environments.

Validation of the Cancer BioChip System as a 3D siRNA screening tool for breast cancer targets

Genomic studies have revealed that breast cancer consists of a complex biological process with patient-specific genetic variations, revealing the need for individualized cancer diagnostic testing and selection of patient-specific optimal therapies. One of the bottlenecks in translation of genomic breakthroughs to the clinic is the lack of functional genomic assays that have high clinical translatability. Anchorage-independent three-dimensional (3D) growth assays are considered to be the gold-standard for chemosensitivity testing, and leads identified with these assays have high probability of clinical success. The Cancer BioChip System (CBCS) allows for the simultaneous, quantitative, and real time evaluation of multitudes of anchorage-independent breast cancer cell growth inhibitors. We employed a Test Cancer BioChip that contains silencing RNAs (siRNAs) targeting cancer-related genes to identify 3D-specific effectors of breast cancer cell growth. We compared the effect of these siRNAs on colony growth of the hormone receptor positive (MCF7) and Human Epidermal Growth Factor Receptor 2/c- Erythroblastic Leukemia Viral Oncogene Homolog 2 (HER2/c-erb-b2) positive (SK-BR-3) cells on the Test Cancer BioChip. Our results confirmed cell-specific inhibition of MCF7 and SK-BR-3 colony formation by estrogen receptor α (ESR1) and (ERBB2) siRNA, respectively. Both cell lines were also suppressed by Phosphoinositide-3-kinase Catalytic, alpha Polypeptide (PIK3CA) siRNA. Interestingly, we have observed responses to siRNA that are unique to this 3D setting. For example, ß-actin (ACTB) siRNA suppressed colony growth in both cell types while Cathepsin L2 (CTSL2) siRNA caused opposite effects. These results further validate the importance of the CBCS as a tool for the identification of clinically relevant breast cancer targets.

Expression of Abelson interactor 1 (Abi1) correlates with inflammation, KRAS mutation and adenomatous change during colonic carcinogenesis

Background

Abelson interactor 1 (Abi1) is an important regulator of actin dynamics during cytoskeletal reorganization. In this study, our aim was to investigate the expression of Abi1 in colonic mucosa with and without inflammation, colonic polyps, colorectal carcinomas (CRC) and metastases as well as in CRC cell lines with respect to BRAF/KRAS mutation status and to find out whether introduction of KRAS mutation or stimulation with TNFalpha enhances Abi1 protein expression in CRC cells.

Methodology/Principal Findings

We immunohistochemically analyzed Abi1 protein expression in 126 tissue specimens from 95 patients and in 5 colorectal carcinoma cell lines with different mutation status by western immunoblotting. We found that Abi1 expression correlated positively with KRAS, but not BRAF mutation status in the examined tissue samples. Furthermore, Abi1 is overexpressed in inflammatory mucosa, sessile serrated polyps and adenomas, tubular adenomas, invasive CRC and CRC metastasis when compared to healthy mucosa and BRAF-mutated as well as KRAS wild-type hyperplastic polyps. Abi1 expression in carcinoma was independent of microsatellite stability of the tumor. Abi1 protein expression correlated with KRAS mutation in the analyzed CRC cell lines, and upregulation of Abi1 could be induced by TNFalpha treatment as well as transfection of wild-type CRC cells with mutant KRAS. The overexpression of Abi1 could be abolished by treatment with the PI3K-inhibitor Wortmannin after KRAS transfection.

Conclusions/Significance

Our results support a role for Abi1 as a downstream target of inflammatory response and adenomatous change as well as oncogenic KRAS mutation via PI3K, but not BRAF activation. Furthermore, they highlight a possible role for Abi1 as a marker for early KRAS mutation in hyperplastic polyps. Since the protein is a key player in actin dynamics, our data encourages further studies concerning the exact role of Abi1 in actin reorganization upon enhanced KRAS/PI3K signalling during colonic tumorigenesis.

Abi1, a critical molecule coordinating actin cytoskeleton reorganization with PI-3 kinase and growth signaling

Coordination of actin cytoskeletal reorganization with growth and proliferation signals is a key cellular process that is not fully understood. PI-3 kinase is one of the central nodes for distributing growth and proliferation signals downstream from growth factor receptors to the nucleus. Although PI-3 kinase function has been associated with actin cytoskeleton remodeling, satisfactory explanations of the mechanisms mediating this regulation have been elusive. Here we propose that interaction of the Abi1 protein with the p85 regulatory subunit of PI-3 kinase represents the link between growth receptor signaling and actin cytoskeleton remodeling. This function of Abi1, which involves WAVE complex, was initially observed in macropinocytosis, and may explain the coincident dysregulation of PI-3 kinase and actin cytoskeleton in cancer.

Activation of c-Src/HER1/STAT5b and HER1/ERK1/2 signaling pathways and cell migration by hexachlorobenzene in MDA-MB-231 human breast cancer cell line

Hexachlorobenzene (HCB) is a widespread environmental pollutant. It is a dioxin-like compound and a weak ligand of the aryl hydrocarbon receptor (AhR) protein. HCB is a tumor cocarcinogen in rat mammary gland and an inducer of cell proliferation and c-Src kinase activity in MCF-7 breast cancer cells. This study was carried out to investigate HCB action on c-Src and the human epidermal growth factor receptor (HER1) activities and their downstream signaling pathways, Akt, extracellular-signal-regulated kinase (ERK1/2), and signal transducers and activators of transcription (STAT) 5b, as well as on cell migration in a human breast cancer cell line, MDA-MB-231. We also investigated whether the AhR is involved in HCB-induced effects. We have demonstrated that HCB (0.05μM) produces an early increase of Y416-c-Src, Y845-HER1, Y699-STAT5b, and ERK1/2 phosphorylation. Moreover, our results have shown that the pesticide (15 min) activates these pathways in a dose-dependent manner (0.005, 0.05, 0.5, and 5μM). In contrast, HCB does not alter T308-Akt activation. Pretreatment with a specific inhibitor for c-Src (4-amino-5-(4-chlorophenyl)-7-(t-butyl) pyrazolo[3,4-d]pyrimidine [PP2]) prevents Y845-HER1 and Y699-STAT5b phosphorylation. AG1478, a specific HER1 inhibitor, abrogates HCB-induced STAT5b and ERK1/2 activation, whereas 4,7-orthophenanthroline and α-naphthoflavone, two AhR antagonists, prevent HCB-induced STAT5b and ERK1/2 phosphorylation. HCB enhances cell migration evaluated by scratch motility and transwell assays. Pretreatment with PP2, AG1478, and 4,7-orthophenanthroline suppresses HCB-induced cell migration. These results demonstrate that HCB stimulates c-Src/HER1/STAT5b and HER1/ERK1/2 signaling pathways in MDA-MB-231. c-Src, HER1, and AhR are involved in HCB-induced increase in cell migration. The present study makes a significant contribution to the molecular mechanism of action of HCB in mammary carcinogenesis.

Integrity of SOS1/EPS8/ABI1 tri-complex determines ovarian cancer metastasis

Ovarian cancer is mainly confined in peritoneal cavity and its metastasis is often associated with the formation of malignant ascites. As lysophosphatidic acid (LPA) is present at high levels in ascites of ovarian cancer patients and potently stimulates cell migration, we reason that LPA-stimulated cell migration may play an important role in ovarian cancer metastasis. Here, we show that only ovarian cancer cell lines with LPA migratory response undergo peritoneal metastatic colonization. LPA-stimulated cell migration is required for metastatic colonization because knockdown of LPA receptor subtype 1 (LPAR(1)) abolishes this event. However, the difference in metastatic potentials is not caused by the absence of LPAR(1) because both metastatic and nonmetastatic lines express similar levels of LPAR(1). Instead, we find that LPA can activate Rac only in metastatic cells and that metastatic colonization of ovarian cancer cells necessitates Rac activity. These results thus suggest that LPA-induced Rac activation is a prerequisite for ovarian cancer metastasis. In metastatic cells, Rac activation is facilitated by SOS1/EPS8/ABI1 tri-complex and the integrity of this tri-complex is essential for LPA-stimulated cell migration and metastatic colonization. We show that at least 1 member of SOS1/EPS8/ABI1 tri-complex is absent in nonmetastatic ovarian cancer cells and reexpressing the missing one conferred them with metastatic capability. Importantly, coexpression of SOS1, EPS8, and ABI1, but not of any individual member of SOS1/EPS8/ABI1 tri-complex, correlates with advanced stages and shorter survival of ovarian cancer patients. Our study implicates that the integrity of SOS1/EPS8/ABI1 tri-complex is a determinant of ovarian cancer metastasis.

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

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

Expression of Abl interactor 1 and its prognostic significance in breast cancer: a tissue-array-based investigation

Abl interactor 1 (Abi1) is an adaptor protein involved in cell migration. Previous in vitro work suggested that Abi1 is a regulator of breast cancer proliferation, migration, and invasion. In the present study, we explore the expression of Abi1 and its downstream effector phospho-Akt (p-Akt) in a series of breast cancers and correlate their expression with clinicopathological and survival data. Using tissue microarrays, 988 patients with invasive breast carcinoma were evaluated by immunohistochemistry. Statistical correlation was performed to determine associations between Abi1 and p-Akt expression and standard breast clinicopathological factors. The prognostic value of Abi1 and p-Akt for disease-free (DFS) and overall survival (OS) was also evaluated. Abi1 expression was demonstrated in 33.7% (314/933) of invasive carcinomas, while p-Akt was expressed in 46.7% (441/944). There was a significant association between Abi1 and p-Akt expression (P=0.001). Abi1 expression showed significant positive correlation with older age at diagnosis and the Ki67 index. Most importantly, it was demonstrated to be an independent predictor of both DFS and OS (HR = 1.6 and 1.5, P<0.001, respectively). There was no association between p-Akt expression and survival. To the best of our knowledge, this is the first study evaluating Abi1 expression in a large group of breast cancers. Our analysis demonstrated that tumors expressing high levels of Abi1 are significantly associated with early recurrence and worse survival on multivariate analysis. This suggests that Abi1 expression has potential as a molecular marker to refine outcome prediction in breast cancer patients.

Brick1 is an essential regulator of actin cytoskeleton required for embryonic development and cell transformation

Brick1 (Brk1) is the less-studied component of the Wave/Scar pathway involved in the branched nucleation of actin fibers. The clinical relevance of Brk1 is emphasized by correlative data showing that Von Hippel-Lindau (VHL) patients that also lose the BRK1 gene are protected against the development of tumors. This contrasts with recent evidence suggesting that the Wave complex may function as an invasion suppressor in epithelial cancers. Here, we show that the downregulation of Brk1 results in abnormal actin stress fiber formation and vinculin distribution and loss of Arp2/3 and Wave proteins at the cellular protrusions. Brk1 is required for cell proliferation and cell transformation by oncogenes. In addition, Brk1 downregulation results in defective directional migration and invasive growth in renal cell carcinoma cells as well as in other tumor cell types. Finally, genetic ablation of Brk1 results in dramatic defects in embryo compaction and development, suggesting an essential role for this protein in actin dynamics. Thus, genetic loss or inhibition of BRK1 is likely to be protective against tumor development due to proliferation and motility defects in affected cells.

Downregulation of ABI1 expression affects the progression and prognosis of human gastric carcinoma

Abelson interactor protein-1 (ABI1) is a promising candidate tumor suppressor, and plays critical roles both in the pathogenesis of BCR-Abl-induced leukemia and in the spread of several solid tumors. The expression of ABI1 and its role in cancer progression and prognosis are largely unknown in the majority of solid tumors, including gastric cancer. In this study, we analyzed the correlation between ABI1 expression and the clinicopathological characteristics, tumor progression, and prognosis of patients with gastric carcinoma. Tissue specimens were from 103 gastric cancer patients who underwent gastrectomy in our hospital between January 2000 and December 2007. Among them 59 tumor tissue samples were matched with normal tissue samples. The expression of ABI1 protein was measured using immunohistochemical staining of paraffin-embedded tissue specimens. Meanwhile, quantitative real-time RT-PCR and Western blotting were used to identify the expression of ABI1 in human gastric normal mucosal cell line (GES-1) and gastric cancer cell lines (N87, AGS). We performed a statistical analysis of the potential correlation between ABI1 expression and the patients' clinicopathological characteristics, 5-year survival, and median survival time. The immunohistochemical staining results of 59 patients showed that ABI1 was expressed in 28.8% (17/59) of gastric cancer tissues, compared to 91.5% (54/59) of normal samples. ABI1 expression in 103 patients was strongly correlated with tumor differentiation, clinical stage, and lymph node status (P < 0.01). The 5-year survival rate was 15.3% in the ABI1-negative group and 63.7% in the ABI1-positive group. Median survival time in the ABI1-negative and ABI1-positive groups was 25.0 months (95% CI: 19.7-30.3) and 74.0 months (95% CI: 54.6-93.3), respectively. There was a significant difference between the two groups (chi(2) = 10.888, P = 0.001). Furthermore, we found that ABI1 expressed lowly in poor differentiated AGS, whereas highly in GES-1 and well-differentiated N87. Downregulation of ABI1 expression in human gastric carcinoma may play a critical role in tumor progression and in determining patient prognosis. ABI1 may be a useful diagnostic or prognostic molecular biomarker, and might be a potential target for therapeutic intervention.

Involvement of the PI3K/Akt signaling pathway in platelet-derived growth factor-induced migration of human lens epithelial cells

PURPOSE

Posterior capsular opacification (PCO) is caused partially by the migration of lens epithelial cells. To date, the mechanism of the migration is largely unknown. The purpose of this study was to investigate the effect of platelet-derived growth factor (PDGF)-triggered signaling pathways and its downstream effectors in the migration of lens epithelial cells.

METHODS

In vitro scratch-wound healing and transwell migration assays were used to measure the migration of lens epithelial cells. The activation of PDGFR beta, phosphatidylinositol 3-kinas (PI3K)/protein kinase B (Akt) and mitogen activation protein kinase (MAPK) pathways, the impact of PDGF stimulation on the expression of cell protrusion molecules, and the stabilization of beta-catenin were measured by western blotting. The translocation of beta-catenin was detected using indirect immunofluorescence.

RESULTS

PDGF was found to enhance cell migration, which depended on the PI3K/Akt pathway. The activation of the PI3K/Akt pathway by the PDGF/PDGFR beta axis induced the up regulation of cell protrusion molecules and stabilization and translocation of beta-catenin, contributing to enhanced cell migration.

CONCLUSION

Data from this study directly linked the central PI3K/Akt pathway to lens epithelial cell migration and pointed to new avenues for therapeutic intervention in PCO.

Platelet-derived growth factor-D contributes to aggressiveness of breast cancer cells by up-regulating Notch and NF-κB signaling pathways

Platelet-derived growth factor-D (PDGF-D) has been linked with several human malignancies; however, its role in breast cancer progression is not known. We found that PDGF-D expressing breast cancer cell lines MDA-MB-231 and SUM-149 are more invasive compared to cell lines with little or no expression of PDGF-D such as MDA-MB-468 and MCF-7 cells. Over-expression of PDGF-D in PDGF-D low expressing MDA-MB-468 and MCF-7 cells by cDNA transfection showed increased cell proliferation while silencing the expression of PDGF-D by siRNA in PDGF-D high expressing MDA-MB-231 and SUM-149 cells showed decreased cell proliferation and increased apoptosis. Moreover, PDGF-D over-expression was positively correlated with the expression of Notch-1 and Jagged-1, and the expression of mesenchymal markers (Vimentin and ZEB-2) with concomitant decreased expression of epithelial marker E-cadherin. Since NF-κB activation plays a crucial role in Notch signaling as well as in epithelial-mesenchymal transition and tumor aggressiveness, we determined the DNA binding activity of NF-κB and our findings are consistent showing that PDGF-D over-expression led to increased DNA binding activity of NF-κB while it was found to be decreased by inactivation of PDGF-D. These results were also consistent with the expression and activity of MMP-9 and VEGF, as well as invasive characteristics. Further, forced expression of Notch-1/Jagged-1 by cDNA transfection de-repressed the effects of PDGF-D silencing on NF-κB activity and invasion. From these results, we conclude that PDGF-D plays an important role in breast tumor aggressiveness and this process is mechanistically linked with the activation of Notch and NF-κB signaling.

Interactome mapping of the phosphatidylinositol 3-kinase-mammalian target of rapamycin pathway identifies deformed epidermal autoregulatory factor-1 as a new glycogen synthase kinase-3 interactor

The phosphatidylinositol 3-kinase-mammalian target of rapamycin (PI3K-mTOR) pathway plays pivotal roles in cell survival, growth, and proliferation downstream of growth factors. Its perturbations are associated with cancer progression, type 2 diabetes, and neurological disorders. To better understand the mechanisms of action and regulation of this pathway, we initiated a large scale yeast two-hybrid screen for 33 components of the PI3K-mTOR pathway. Identification of 67 new interactions was followed by validation by co-affinity purification and exhaustive literature curation of existing information. We provide a nearly complete, functionally annotated interactome of 802 interactions for the PI3K-mTOR pathway. Our screen revealed a predominant place for glycogen synthase kinase-3 (GSK3) A and B and the AMP-activated protein kinase. In particular, we identified the deformed epidermal autoregulatory factor-1 (DEAF1) transcription factor as an interactor and in vitro substrate of GSK3A and GSK3B. Moreover, GSK3 inhibitors increased DEAF1 transcriptional activity on the 5-HT1A serotonin receptor promoter. We propose that DEAF1 may represent a therapeutic target of lithium and other GSK3 inhibitors used in bipolar disease and depression.

Abl interactor 1 regulates Src-Id1-matrix metalloproteinase 9 axis and is required for invadopodia formation, extracellular matrix degradation and tumor growth of human breast cancer cells

Abl interactor 1 (Abi1) is a key regulator of actin polymerization/depolymerization. The involvement of Abi1 in the development of abnormal cytoskeletal functions of cancer cells has recently been reported. It remains unclear, however, how Abi1 exerts its effects in tumor cells and whether it contributes to tumor progression in vivo. We report here a novel function for Abi1 in the regulation of invadopodia formation and Src-inhibitor of differentiation protein 1 (Id1)-matrix metalloproteinase (MMP)-9 pathway in MDA-MB-231 human breast cancer cells. Abi1 is found in the invadopodia of MDA-MB-231 cells. Epigenetic silencing of the Abi1 gene by short hairpin RNA in MDA-MB-231 cells impaired the formation of invadopodia and resulted in downregulation of the Src activation and Id1/MMP-9 expression. The decreased invadopodia formation and MMP-9 expression correlate with a reduction in the ability of these cells to degrade extracellular matrix. Remarkably, the knockdown of Abi1 expression inhibited tumor cell proliferation and migration in vitro and slowed tumor growth in vivo. Taken together, these results indicate that the Abi1 signaling plays a critical role in breast cancer progression and suggest that this pathway may serve as a therapeutic target for the treatment of human breast cancer.

Abi plays an opposing role to Abl in Drosophila axonogenesis and synaptogenesis

Abl tyrosine kinase (Abl) regulates axon guidance by modulating actin dynamics. Abelson interacting protein (Abi), originally identified as a kinase substrate of Abl, also plays a key role in actin dynamics, yet its role with respect to Abl in the developing nervous system remains unclear. Here we show that mutations in abi disrupt axonal patterning in the developing Drosophila central nervous system (CNS). However, reducing abi gene dosage by half substantially rescues Abl mutant phenotypes in pupal lethality, axonal guidance defects and locomotion deficits. Moreover, we show that mutations in Abl increase synaptic growth and spontaneous synaptic transmission frequency at the neuromuscular junction. Double heterozygosity for abi and enabled (ena) also suppresses the synaptic overgrowth phenotypes of Abl mutants, suggesting that Abi acts cooperatively with Ena to antagonize Abl function in synaptogenesis. Intriguingly, overexpressing Abi or Ena alone in cultured cells dramatically redistributed peripheral F-actin to the cytoplasm, with aggregates colocalizing with Abi and/or Ena, and resulted in a reduction in neurite extension. However, co-expressing Abl with Abi or Ena redistributed cytoplasmic F-actin back to the cell periphery and restored bipolar cell morphology. These data suggest that abi and Abl have an antagonistic interaction in Drosophila axonogenesis and synaptogenesis, which possibly occurs through the modulation of F-actin reorganization.