Abi enhances Abl-mediated CDC2 phosphorylation and inactivation

Inhibition of ABI2 ubiquitination-dependent degradation suppresses TNBC cell growth via down-regulating PI3K/Akt signaling pathway

Triple negative breast cancer (TNBC) is a type of cancer that lacks receptor expression and has complex molecular mechanisms. Recent evidence shows that the ubiquitin-protease system is closely related to TNBC. In this study, we obtain a key ubiquitination regulatory substrate-ABI2 protein by bioinformatics methods, which is also closely related to the survival and prognosis of TNBC. Further, through a series of experiments, we demonstrated that ABI2 expressed at a low level in TNBC tumors, and it has the ability to control cell cycle and inhibit TNBC cell migration, invasion and proliferation. Molecular mechanism studies proved E3 ligase CBLC could increase the ubiquitination degradation of ABI2 protein. Meanwhile, RNA-seq and IP experiments indicated that ABI2, acting as a crucial factor of tumor suppression, can significantly inhibit PI3K/Akt signaling pathway via the interaction with Rho GTPase RAC1. Finally, based on TNBC drug target ABI2, we screened and found that FDA-approved drug Colistimethate sodium(CS) has significant potential in suppressing the proliferation of TNBC cells and inducing cell apoptosis, making it a promising candidate for impeding the progression of TNBC.

Orchestration of synaptic functions by WAVE regulatory complex-mediated actin reorganization

The WAVE regulatory complex (WRC), composed of five components-Cyfip1/Sra1, WAVE/Scar, Abi, Nap1/Nckap1, and Brk1/HSPC300-is essential for proper actin cytoskeletal dynamics and remodeling in eukaryotic cells, likely by matching various patterned signals to Arp2/3-mediated actin nucleation. Accumulating evidence from recent studies has revealed diverse functions of the WRC in neurons, demonstrating its crucial role in dictating the assembly of molecular complexes for the patterning of various trans-synaptic signals. In this review, we discuss recent exciting findings on the physiological role of the WRC in regulating synaptic properties and highlight the involvement of WRC dysfunction in various brain disorders.

Exosomes: Insights from Retinoblastoma and Other Eye Cancers

Exosomes, considered as cell debris or garbage bags, have been later characterized as nanometer-sized extracellular double-membrane lipid bilayer bio-vesicles secreted by the fusion of vesicular bodies with the plasma membrane. The constituents and the rate of exosomes formation differ in different pathophysiological conditions. Exosomes are also observed and studied in different parts of the eye, like the retina, cornea, aqueous, and vitreous humor. Tear fluid consists of exosomes that are shown to regulate various cellular processes. The role of exosomes in eye cancers, especially retinoblastoma (RB), is not well explored, although few studies point towards their presence. Retinoblastoma is an intraocular tumor that constitutes 3% of cases of cancer in children. Diagnosis of RB may require invasive procedures, which might lead to the spread of the disease to other parts. Due to this reason, better ways of diagnosis are being explored. Studies on the exosomes in RB tumors and serum might help designing better diagnostic approaches for RB. In this article, we reviewed studies on exosomes in the eye, with a special emphasis on RB. We also reviewed miRNAs expressed in RB tumor, serum, and cell lines and analyzed the targets of these miRNAs from the proteins identified in the RB tumor exosomes. hsa-miR-494 and hsa-miR-9, upregulated and downregulated, respectively in RB, have the maximum number of targets. Although oppositely regulated, they share the same targets in the proteins identified in RB tumor exosomes. Overall this review provides the up-to-date progress in the area of eye exosome research, with an emphasis on RB.

Proteomic Profiling of Retinoblastoma-Derived Exosomes Reveals Potential Biomarkers of Vitreous Seeding

Retinoblastoma (RB) is the most common tumor of the eye in early childhood. Although recent advances in conservative treatment have greatly improved the visual outcome, local tumor control remains difficult in the presence of massive vitreous seeding. Traditional biopsy has long been considered unsafe in RB, due to the risk of extraocular spread. Thus, the identification of new biomarkers is crucial to design safer diagnostic and more effective therapeutic approaches. Exosomes, membrane-derived nanovesicles that are secreted abundantly by aggressive tumor cells and that can be isolated from several biological fluids, represent an interesting alternative for the detection of tumor-associated biomarkers. In this study, we defined the protein signature of exosomes released by RB tumors (RBT) and vitreous seeding (RBVS) primary cell lines by high resolution mass spectrometry. A total of 5666 proteins were identified. Among these, 5223 and 3637 were expressed in exosomes RBT and one RBVS group, respectively. Gene enrichment analysis of exclusively and differentially expressed proteins and network analysis identified in RBVS exosomes upregulated proteins specifically related to invasion and metastasis, such as proteins involved in extracellular matrix (ECM) remodeling and interaction, resistance to anoikis and the metabolism/catabolism of glucose and amino acids.

Thin is required for cell death in the Drosophila abdominal muscles by targeting DIAP1

In holometabolous insects, developmentally controlled programmed cell death (PCD) is a conserved process that destroys a subset of larval tissues for the eventual creation of new adult structures. This process of histolysis is relatively well studied in salivary gland and midgut tissues, while knowledge concerning larval muscle destruction is limited. Here, we have examined the histolysis of a group of Drosophila larval abdominal muscles called the dorsal external oblique muscles (DEOMs). Previous studies have defined apoptosis as the primary mediator of DEOM breakdown, whose timing is controlled by ecdysone signaling. However, very little is known about other factors that contribute to DEOM destruction. In this paper, we examine the role of thin (tn), which encodes for the Drosophila homolog of mammalian TRIM32, in the regulation of DEOM histolysis. We find that loss of Tn blocks DEOM degradation independent of ecdysone signaling. Instead, tn genetically functions in a pathway with the death-associated inhibitor of apoptosis (DIAP1), Dronc, and death-associated APAF1-related killer (Dark) to regulate apoptosis. Importantly, blocking Tn results in the absence of active Caspase-3 immunostaining, upregulation of DIAP1 protein levels, and inhibition of Dronc activation. DIAP1 and Dronc mRNA levels are not altered in tn mutants, showing that Tn acts post-transcriptionally on DIAP1 to regulate apoptosis. Herein, we also find that the RING domain of Tn is required for DEOM histolysis as loss of this domain results in higher DIAP1 levels. Together, our results suggest that the direct control of DIAP1 levels, likely through the E3 ubiquitin ligase activity of Tn, provides a mechanism to regulate caspase activity and to facilitate muscle cell death.

Ecdysone-responsive microRNA-252-5p controls the cell cycle by targeting Abi in Drosophila

The steroid hormone ecdysone has a central role in the developmental transitions of insects through its control of responsive protein-coding and microRNA (miRNA) gene expression. However, the complete regulatory network controlling the expression of these genes remains to be elucidated. In this study, we performed cross-linking immunoprecipitation coupled with deep sequencing of endogenous Argonaute 1 (Ago1) protein, the core effector of the miRNA pathway, in Drosophila S2 cells. We found that regulatory interactions between miRNAs and their cognate targets were substantially altered by Ago1 in response to ecdysone signaling. Additionally, during the larva-to-adult metamorphosis, miR-252-5p was up-regulated via the canonical ecdysone-signaling pathway. Moreover, we provide evidence that miR-252-5p targets Abelson interacting protein ( Abi) to decrease the protein levels of cyclins A and B, controlling the cell cycle. Overall, our data suggest a potential role for the ecdysone/miR-252-5p/Abi regulatory axis partly in cell-cycle control during metamorphosis in Drosophila.-Lim, D.-H., Lee, S., Han, J. Y., Choi, M.-S., Hong, J.-S., Seong, Y., Kwon, Y.-S., Lee, Y. S. Ecdysone-responsive microR-252-5p controls the cell cycle by targeting Abi in Drosophila.

TRIM32 ubiquitin E3 ligase, one enzyme for several pathologies: From muscular dystrophy to tumours

TRIM32 is a member of the TRIpartite Motif family characterised by the presence of an N-terminal three-domain-module that includes a RING domain, which confers E3 ubiquitin ligase activity, one or two B-box domains and a Coiled-Coil region that mediates oligomerisation. Several TRIM32 substrates were identified including muscular proteins and proteins involved in cell cycle regulation and cell motility. As ubiquitination is a versatile post-translational modification that can affect target turnover, sub-cellular localisation or activity, it is likely that diverse substrates may be differentially affected by TRIM32-mediated ubiquitination, reflecting its multi-faceted roles in muscle physiology, cancer and immunity. With particular relevance for muscle physiology, mutations in TRIM32 are associated with autosomal recessive Limb-Girdle Muscular Dystrophy 2H, a muscle-wasting disease with variable clinical spectrum ranging from almost asymptomatic to wheelchair-bound patients. In this review, we will focus on the ability of TRIM32 to mark specific substrates for proteasomal degradation discussing how the TRIM32-proteasome axis may (i) be important for muscle homeostasis and for the pathogenesis of muscular dystrophy; and (ii) define either an oncogenic or tumour suppressive role for TRIM32 in the context of different types of cancer.

The NESH/Abi-3-based WAVE2 complex is functionally distinct from the Abi-1-based WAVE2 complex

BACKGROUND

Abl interactor (Abi) family proteins play significant roles in actin cytoskeleton organization through participation in the WAVE complex. Mammals possess three Abi proteins: Abi-1, Abi-2, and NESH/Abi-3. Abi-1 and Abi-2 were originally identified as Abl tyrosine kinase-binding proteins. It has been disclosed that Abi-1 acts as a bridge between c-Abl and WAVE2, and c-Abl-mediated WAVE2 phosphorylation promotes actin remodeling. We showed previously that NESH/Abi-3 is present in the WAVE2 complex, but neither binds to c-Abl nor promotes c-Abl-mediated phosphorylation of WAVE2.

RESULTS

In this study, we characterized NESH/Abi-3 in more detail, and compared its properties with those of Abi-1 and Abi-2. NESH/Abi-3 was ectopically expressed in NIH3T3 cells, in which Abi-1, but not NESH/Abi-3, is expressed. The expression of NESH/Abi-3 caused degradation of endogenous Abi-1, which led to the formation of a NESH/Abi-3-based WAVE2 complex. When these cells were plated on fibronectin-coated dishes, the translocation of WAVE2 to the plasma membrane was significantly reduced and the formation of peripheral lamellipodial structures was disturbed, suggesting that the NESH/Abi-3-based WAVE2 complex was unable to help produce lamellipodial protrusions. Next, Abi-1, Abi-2, or NESH/Abi-3 was expressed in v-src-transformed NIH3T3 cells. Only in NESH/Abi-3-expressed cells did treatment with an Abl kinase inhibitor, imatinib mesylate, or siRNA-mediated knockdown of c-Abl promote the formation of invadopodia, which are ventral membrane protrusions with extracellular matrix degradation activity. Structural studies showed that a linker region between the proline-rich regions and the Src homology 3 (SH3) domain of Abi-1 is crucial for its interaction with c-Abl and c-Abl-mediated phosphorylation of WAVE2.

CONCLUSIONS

The NESH/Abi-3-based WAVE2 complex is functionally distinct from the Abi-1-based one, and NESH/Abi-3 may be involved in the formation of ventral protrusions under certain conditions.

Synergistic effects of proteasome inhibitor carfilzomib in combination with tyrosine kinase inhibitors in imatinib-sensitive and -resistant chronic myeloid leukemia models

The tyrosine kinase inhibitor (TKI) imatinib has transformed the treatment and outlook of chronic myeloid leukemia (CML); however, the development of drug resistance and the persistence of TKI-resistant stem cells remain obstacles to eradicating the disease. Inhibition of proteasome activity with bortezomib has been shown to effectively induce apoptosis in TKI-resistant cells. In this study, we show that exposure to the next generation proteasome inhibitor carfilzomib is associated with a decrease in ERK signaling and increased expression of Abelson interactor proteins 1 and 2 (ABI-1/2). We also investigate the effect of carfilzomib in models of imatinib-sensitive and -resistant CML and demonstrate a potent reduction in proliferation and induction of apoptosis in a variety of models of imatinib-resistant CML, including primitive CML stem cells. Carfilzomib acts synergistically with the TKIs imatinib and nilotinib, even in imatinib-resistant cell lines. In addition, we found that the presence of immunoproteasome subunits is associated with an increased sensitivity to carfilzomib. The present findings provide a rational basis to examine the potential of carfilzomib in combination with TKIs as a potential therapy for CML, particularly in imatinib-resistant disease.

c-ABL tyrosine kinase modulates p53-dependent p21 induction and ensuing cell fate decision in response to DNA damage

The c-ABL non-receptor tyrosine kinase and the p53 tumor suppressor protein are pivotal modulators of cellular responses to DNA damage. However, a comprehensive understanding of the role of c-ABL kinase in p53-dependent transcription of p21(CIP1/WAF1) and ensuing cell fate decision is still obscure. Here, we demonstrate that c-ABL tyrosine kinase regulates p53-dependent induction of p21. As a result, it modulates cell fate decision by p53 in response to DNA damage differently according to the extent of DNA damage. When human cancer cells were treated with DNA damaging agent, adriamycin (0.08 μg/ml), p21 was induced following p53 induction. Owing largely to p21, a substantial fraction of cells treated with adriamycin were blocked at the G2 phase of the cell cycle and most cells eventually became senescent. When these cells were simultaneously treated with a c-ABL kinase inhibitor, STI571, or a c-ABL-specific siRNA along with adriamycin, the p53-dependent p21 induction was dramatically diminished, even though p53 is substantially induced. Accordingly, G2-arrest, and cellular senescence largely dependent on p21 were substantially abrogated. On the contrary, when cells were treated with a relatively high dose of adriamycin (0.4 μg/ml) cells became apoptotic, and the simultaneous presence of a c-ABL kinase inhibitor STI571 augmented the extent of apoptosis. We speculate this is due to abrogation of p53-dependent p21 induction, which leads to elimination of anti-apoptotic function of p21. In summary, c-ABL appears to promote senescence or inhibit apoptosis, depending on the extent of DNA damage. These findings suggest that the combined use of ABL kinase inhibitor and DNA damaging drug in chemotherapy against tumors retaining wild type p53 should be carefully designed.

Functional mechanisms and roles of adaptor proteins in abl-regulated cytoskeletal actin dynamics

Abl is a nonreceptor tyrosine kinase and plays an essential role in the modeling and remodeling of F-actin by transducing extracellular signals. Abl and its paralog, Arg, are unique among the tyrosine kinase family in that they contain an unusual extended C-terminal half consisting of multiple functional domains. This structural characteristic may underlie the role of Abl as a mediator of upstream signals to downstream signaling machineries involved in actin dynamics. Indeed, a group of SH3-containing accessory proteins, or adaptor proteins, have been identified that bind to a proline-rich domain of the C-terminal portion of Abl and modulate its kinase activity, substrate recognition, and intracellular localization. Moreover, the existence of signaling cascade and biological outcomes unique to each adaptor protein has been demonstrated. In this paper, we summarize functional roles and mechanisms of adaptor proteins in Abl-regulated actin dynamics, mainly focusing on a family of adaptor proteins, Abi. The mechanism of Abl's activation and downstream signaling mediated by Abi is described in comparison with those by another adaptor protein, Crk.

Abl-1-bridged tyrosine phosphorylation of VASP by Abelson kinase impairs association of VASP to focal adhesions and regulates leukaemic cell adhesion

Mena [mammalian Ena (Enabled)]/VASP (vasodilator-stimulated phosphoprotein) proteins are the homologues of Drosophila Ena. In Drosophila, Ena is a substrate of the tyrosine kinase DAbl (Drosophila Abl). However, the link between Abl and the Mena/VASP family is not fully understood in mammals. We previously reported that Abi-1 (Abl interactor 1) promotes phosphorylation of Mena and BCAP (B-cell adaptor for phosphoinositide 3-kinase) by bridging the interaction between c-Abl and the substrate. In the present study we have identified VASP, another member of the Mena/VASP family, as an Abi-1-bridged substrate of Abl. VASP is phosphorylated by Abl when Abi-1 is co-expressed. We also found that VASP interacted with Abi-1 both in vitro and in vivo. VASP was tyrosine-phosphorylated in Bcr-Abl-positive leukaemic cells in an Abi-1-dependent manner. Co-expression of c-Abl and Abi-1 or the phosphomimetic Y39D mutation in VASP resulted in less accumulation of VASP at focal adhesions. VASP Y39D had a reduced affinity to the proline-rich region of zyxin. Interestingly, overexpression of both phosphomimetic and unphosphorylated forms of VASP, but not wild-type VASP, impaired adhesion of K562 cells to fibronectin. These results suggest that the phosphorylation and dephosphorylation cycle of VASP by the Abi-1-bridged mechanism regulates association of VASP with focal adhesions, which may regulate adhesion of Bcr-Abl-transformed leukaemic cells.

CDK1-mediated phosphorylation of Abi1 attenuates Bcr-Abl-induced F-actin assembly and tyrosine phosphorylation of WAVE complex during mitosis

Coordinated actin remodeling is crucial for cell entry into mitosis. The WAVE regulatory complex is a key regulator of actin assembly, yet how the WAVE signaling is regulated to coordinate actin assembly with mitotic entry is not clear. Here, we have uncovered a novel mechanism that regulates the WAVE complex at the onset of mitosis. We found that the Bcr-Abl-stimulated F-actin assembly is abrogated during mitosis. This mitotic inhibition of F-actin assembly is accompanied by an attenuation of Bcr-Abl-induced tyrosine phosphorylation of the WAVE complex. We identified serine 216 of Abi1 as a target of CDK1/cyclin B kinase that is phosphorylated in cells at the onset of mitosis. The Abi1 phosphorylated on serine 216 displayed greatly reduced tyrosine phosphorylation in the hematopoietic cells transformed by Bcr-Abl. Moreover, a phosphomimetic mutation of serine 216 to aspartic acid in Abi1 was sufficient to attenuate Bcr-Abl-induced tyrosine phosphorylation of the WAVE complex and F-actin assembly. Ectopic expression of Abi1 with serine 216 mutations interfered with cell cycle progression. Together, these data show that CDK1-mediated phosphorylation of serine 216 in Abi1 serves as a regulatory mechanism that may contribute to coordinated actin cytoskeleton remodeling during mitosis.

Tracking of specific integrant clones in dogs treated with foamy virus vectors

Vector integration can lead to proto-oncogene activation and malignancies during hematopoietic stem cell gene therapy. We previously used foamy virus vectors to deliver the CD18 gene under the control of an internal murine stem cell virus promoter and successfully treated dogs with canine leukocyte adhesion deficiency. Here we have tracked the copy numbers of 11 specific proviruses found in these animals for 36-42 months after transplantation, including examples within or near proto-oncogenes, tumor suppressor genes, and genes unrelated to cancer. We found no evidence for clonal expansion of any of the clones, including those with proviruses in the MECOM gene (MDS1-EVI1 complex). These results suggest that although foamy virus vectors may integrate near proto-oncogenes, this does not necessarily lead to clonal expansion and malignancies. Additionally, we show that copy number estimates of these specific proviruses based on linker-mediated PCR results are different from those obtained by quantitative PCR, but can provide a qualitative assessment of provirus levels.

The actin-cytoskeleton pathway and its potential role in inflammatory bowel disease-associated human colorectal cancer

INTRODUCTION

To improve our understanding of the various clinical phenotypes in inflammatory bowel disease (IBD)-associated colorectal cancer (CRC) and provide potential targets for early diagnosis and future therapy, we sought to identify new candidate genes and molecular pathways involved in the pathogenesis and progression of this disorder. Recent evidence has implicated the actin-cytoskeleton pathway in the development of metastatic sporadic CRC through cytoskeletal proteins such as fascin-1. We hereby propose that similar genetic polymorphisms and mutations among regulatory genes of the actin-cytoskeleton pathway may also be associated with increased dysplasia, carcinogenesis, and susceptibility for invasion and metastasis in IBD-associated CRC, as compared with sporadic CRC.

MATERIALS AND METHODS

To test this hypothesis, we identified three patients with IBD-associated CRC. We subsequently retrieved normal, dysplastic, and cancerous tissue from within the same surgical colonic specimen. Messenger RNA was subsequently isolated from fresh frozen tissue, and oligonucleotide arrays were carried out to identify genes that were differentially expressed between the three various tissue types (normal, dysplasia, and cancer). By utilizing the same specimen to obtain each of the three various tissue types, we excluded intersubject variability during the analysis. Finally, we performed bioinformatic interaction pathway analysis using the "Ingenuity Pathway Analysis" software.

RESULTS

Computerized pathway analysis revealed that the actin-cytoskeleton pathway was significantly dysregulated in the progression of normal cells, via dysplasia, to IBD-associated CRC (p < 0.05). Significantly up-regulated genes identified in the analysis included the fibroblast growth factor, Abelson interactor gene-2, profilin-2, and radixin genes. Conversely, the diaphanous homolog gene appeared to be significantly down-regulated.

CONCLUSION

Via the dysregulation of these five genes within the actin-cytoskeleton pathway, we propose that this molecular pathway provides a potential mechanism for the malignant transformation and progression of normal tissue, via dysplasia, to IBD-associated CRC.

ABL tyrosine kinases: evolution of function, regulation, and specificity

ABL-family proteins comprise one of the best conserved branches of the tyrosine kinases. Each ABL protein contains an SH3-SH2-TK (Src homology 3-Src homology 2-tyrosine kinase) domain cassette, which confers autoregulated kinase activity and is common among nonreceptor tyrosine kinases. This cassette is coupled to an actin-binding and -bundling domain, which makes ABL proteins capable of connecting phosphoregulation with actin-filament reorganization. Two vertebrate paralogs, ABL1 and ABL2, have evolved to perform specialized functions. ABL1 includes nuclear localization signals and a DNA binding domain through which it mediates DNA damage-repair functions, whereas ABL2 has additional binding capacity for actin and for microtubules to enhance its cytoskeletal remodeling functions. Several types of posttranslational modifications control ABL catalytic activity, subcellular localization, and stability, with consequences for both cytoplasmic and nuclear ABL functions. Binding partners provide additional regulation of ABL catalytic activity, substrate specificity, and downstream signaling. Information on ABL regulatory mechanisms is being mined to provide new therapeutic strategies against hematopoietic malignancies caused by BCR-ABL1 and related leukemogenic proteins.

Cell cycle genes and ovarian cancer susceptibility: a tagSNP analysis

Background:

Dysregulation of the cell cycle is a hallmark of many cancers including ovarian cancer, a leading cause of gynaecologic cancer mortality worldwide.

Methods:

We examined single nucleotide polymorphisms (SNPs) (n=288) from 39 cell cycle regulation genes, including cyclins, cyclin-dependent kinases (CDKs) and CDK inhibitors, in a two-stage study. White, non-Hispanic cases (n=829) and ovarian cancer-free controls (n=941) were genotyped using an Illumina assay.

Results:

Eleven variants in nine genes (ABL1, CCNB2, CDKN1A, CCND3, E2F2, CDK2, E2F3, CDC2, and CDK7) were associated with risk of ovarian cancer in at least one genetic model. Seven SNPs were then assessed in four additional studies with 1689 cases and 3398 controls. Association between risk of ovarian cancer and ABL1 rs2855192 found in the original population [odds ratio, OR_{BB vs AA} 2.81 (1.29–6.09), P=0.01] was also observed in a replication population, and the association remained suggestive in the combined analysis [OR_{BB vs AA} 1.59 (1.08–2.34), P=0.02]. No other SNP associations remained suggestive in the replication populations.

Conclusion:

ABL1 has been implicated in multiple processes including cell division, cell adhesion and cellular stress response. These results suggest that characterization of the function of genetic variation in this gene in other ovarian cancer populations is warranted.

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.

Tripartite motif protein 32 facilitates cell growth and migration via degradation of Abl-interactor 2

Tripartite motif protein 32 (TRIM32) mRNA has been reported to be highly expressed in human head and neck squamous cell carcinoma, but the involvement of TRIM32 in carcinogenesis has not been fully elucidated. In this study, we found by using yeast two-hybrid screening that TRIM32 binds to Abl-interactor 2 (Abi2), which is known as a tumor suppressor and a cell migration inhibitor, and we showed that TRIM32 mediates the ubiquitination of Abi2. Overexpression of TRIM32 promoted degradation of Abi2, resulting in enhancement of cell growth, transforming activity, and cell motility, whereas a dominant-negative mutant of TRIM32 lacking the RING domain inhibited the degradation of Abi2. In addition, we found that TRIM32 suppresses apoptosis induced by cis-diamminedichloroplatinum (II) in HEp2 cell lines. These findings suggest that TRIM32 is a novel oncogene that promotes tumor growth, metastasis, and resistance to anticancer drugs.

Abi1 gene silencing by short hairpin RNA impairs Bcr-Abl-induced cell adhesion and migration in vitro and leukemogenesis in vivo

Abl interactor (Abi) 1 was first identified as the downstream target of Abl tyrosine kinases and was found to be dysregulated in leukemic cells expressing oncogenic Bcr-Abl and v-Abl. Although the accumulating evidence supports a role of Abi1 in actin cytoskeleton remodeling and growth factor/receptor signaling, it is not clear how it contributes to Bcr-Abl-induced leukemogenesis. We show here that Abi1 gene silencing by short hairpin RNA attenuated the Bcr-Abl-induced abnormal actin remodeling, membrane-type 1 metalloproteinase clustering and inhibited cell adhesion and migration on fibronectin-coated surfaces. Although the knock down of Abi1 expression did not affect growth factor-independent growth of Bcr-Abl-transformed Ba/F3 cells in vitro, it impeded competitive expansion of these cells in non obese diabetic (NOD)/ severe combined immuno-deficiency (SCID) mice. Remarkably, the knock down of Abi1 expression in Bcr-Abl-transformed Ba/F3 cells impaired the leukemogenic potential of these cells in NOD/SCID mice. Abi1 contributes to Bcr-Abl-induced leukemogenesis in part through Src family kinases, as the knock down of Abi1 expression attenuates Bcr-Abl-stimulated activation of Lyn. Together, these data provide for the first time the direct evidence that supports a critical role of Abi1 pathway in the pathogenesis of Bcr-Abl-induced leukemia.

Abi induces ectopic sensory organ formation by stimulating EGFR signaling

One of the central regulators coupling tyrosine phosphorylation with cytoskeletal dynamics is the Abelson interactor (Abi). Its activity regulates WASP-/WAVE mediated F-actin formation and in addition modulates the activity of the Abelson tyrosine kinase (Abl). We have recently shown that the Drosophila Abi is capable of promoting bristle development in a wasp dependent fashion. Here, we report that Drosophila Abi induces sensory organ development by modulating EGFR signaling. Expression of a membrane-tethered activated Abi protein (Abi(Myr)) leads to an increase in MAPK activity. Additionally, suppression of EGFR activity inhibits the induction of extra-sensory organs by Abi(Myr), whereas co-expression of activated Abi(Myr) and EGFR dramatically enhances the neurogenic phenotype. In agreement with this observation Abi is able to associate with the EGFR in a common complex. Furthermore, Abi binds the Abl tyrosine kinase. A block of Abl kinase-activity reduces Abi protein stability and strongly abrogates ectopic sensory organ formation induced by Abi(Myr). Concomitantly, we noted changes in tyrosine phosphorylation supporting previous reports that Abi protein stability is linked to tyrosine phosphorylation mediated by Abl.

The Involvement of Abl and PTP61F in the Regulation of Abi Protein Localization and Stability and Lamella Formation in Drosophila S2 Cells

Most aspects of cellular events are regulated by a series of protein phosphorylation and dephosphorylation processes. Abi (Abl interactor protein) functions as a substrate adaptor protein for Abl and a core member of the WAVE complex, relaying signals from Rac to Arp2/3 complex and regulating actin dynamics. It is known that the recruitment of Abi into the lamella promotes polymerization of actin, although how it does this is unclear. In this study, we found PTP61F, a Drosophila homolog of mammalian PTP1B, can reverse the Abl phosphorylation of Abi and colocalizes with Abi in Drosophila S2 cells. Abi can be translocalized from the cytosol to the cell membrane by either increasing Abl or reducing endogenous PTP61F. This reciprocal regulation of Abi phosphorylation is also involved in modulating Abi protein level, which is thought to affect the stability of the WAVE complex. Using mass spectrometry, we identified several important tyrosine phosphorylation sites in Abi. We compared the translocalization and protein half-life of wild type (wt) and phosphomutant Abi and their abilities to restore the lamellipodia structure of the Abi-reduced cells. We found the phosphomutant to have reduced ability to translocalize and to have a protein half-life shorter than that of wt Abi. We also found that although the wt Abi could fully restore the lamellipodia structure, the phosphomutant could not. Together, these findings suggest that the reciprocal regulation of Abi phosphorylation by Abl and PTP61F may regulate the localization and stability of Abi and may regulate the formation of lamella.

Partner proteins that interact with Clonorchis sinensis WD40-repeat protein

WD40-repeat proteins have four to eight repeat units, which have Gly-His (GH) and Trp-Asp (WD) at both termini and fold into a beta-propeller. In particular, the WD40-repeat protein of Clonorchis sinensis (CsWD1) has seven WD-repeat units and is expressed stage-specifically in metacercariae. By yeast two-hybrid screening, putative interacting protein cDNAs were cloned from a C. sinensis metacercaria cDNA library and purified further by higher stringency screening and lacZ colony-lift assay. After assessing their nucleotide and polypeptide sequences, 21 putative partner protein cDNAs were selected and assembled into 14 clones. Using YRG2 strain yeast, 12 putative partner protein clones were confirmed to interact with CsWD1 protein. These 12 proteins were grouped into functional categories, i.e., signal proteins, transporters, proteases, and muscle proteins. These results suggest that CsWD1 protein is associated with intracellular protein translocation and cell cycle control in C. sinensis metacercaria.

NESH (Abi-3) is present in the Abi/WAVE complex but does not promote c-Abl-mediated phosphorylation

Abl interactor (Abi) was identified as an Abl tyrosine kinase-binding protein and subsequently shown to be a component of the macromolecular Abi/WAVE complex, which is a key regulator of Rac-dependent actin polymerization. Previous studies showed that Abi-1 promotes c-Abl-mediated phosphorylation of Mammalian Enabled (Mena) and WAVE2. In addition to Abi-1, mammals possess Abi-2 and NESH (Abi-3). In this study, we compared the three Abi proteins in terms of the promotion of c-Abl-mediated phosphorylation and the formation of Abi/WAVE complex. Although Abi-2, like Abi-1, promoted the c-Abl-mediated phosphorylation of Mena and WAVE2, NESH (Abi-3) had no such effect. This difference was likely due to their binding abilities as to c-Abl. Immunoprecipitation revealed that NESH (Abi-3) is present in the Abi/WAVE complex. Our results suggest that NESH (Abi-3), like Abi-1 and Abi-2, is a component of the Abi/WAVE complex, but likely plays a different role in the regulation of c-Abl.

Abl deregulates Cdk5 kinase activity and subcellular localization in Drosophila neurodegeneration

Although Abl functions in mature neurons, work to date has not addressed Abl's role on Cdk5 in neurodegeneration. We found that beta-amyloid (Abeta42) initiated Abl kinase activity and that blockade of Abl kinase rescued both Drosophila and mammalian neuronal cells from cell death. We also found activated Abl kinase to be necessary for the binding, activation, and translocalization of Cdk5 in Drosophila neuronal cells. Conversion of p35 into p25 was not observed in Abeta42-triggered Drosophila neurodegeneration, suggesting that Cdk5 activation and protein translocalization can be p25-independent. Our genetic studies also showed that abl mutations repressed Abeta42-induced Cdk5 activity and neurodegeneration in Drosophila eyes. Although Abeta42 induced conversion of p35 to p25 in mammalian cells, it did not sufficiently induce Cdk5 activation when c-Abl kinase activity was suppressed. Therefore, we propose that Abl and p35/p25 cooperate in promoting Cdk5-pY15, which deregulates Cdk5 activity and subcellular localization in Abeta42-triggered neurodegeneration.

The expression of Abl interactor 2 in leiomyoma and myometrium and regulation by GnRH analogue and transforming growth factor-β

BACKGROUND

Abelson (Abl) interactor 2 (Abi-2) has been considered as a key regulator of cell/tissue structural organization and is differentially expressed in leiomyomas. The objective of this study was to evaluate the expression of Abi-2 in leiomyoma/myometrium during the menstrual cycle and following GnRH analogue (GnRHa) therapy, as well as regulation by transforming growth factor (TGF)-beta1 in leiomyoma and myometrial smooth muscle cells (LSMC and MSMC).

METHODS

We used real-time PCR, Western blotting and immunohistochemistry to determine the expression of Abi-2 in paired leiomyoma and myometrium (n = 27) from proliferative (n = 8) and secretory (n = 12) phases of the menstrual cycle and from patients who received GnRHa therapy (n = 7). Time-dependent action of TGF-beta1 (2.5 ng/ml) and GnRHa (0.1 microM) on Abi-2 expression was determined in LSMC and MSMC.

RESULTS

Leiomyomas express elevated levels of Abi-2 as compared with myometrium from the proliferative but not the secretory phase of the menstrual cycle, with a significant reduction following GnRHa therapy (P < 0.05). Western blotting showed a similar trend in Abi-2 protein expression in leiomyoma/myometrial tissue extracts, which was immunolocalized in LSMC and MSMC, connective tissue fibroblasts and arterial walls. The expression of Abi-2 in LSMC and MSMC was increased by TGF-beta1 (2.5 ng/ml) and was inhibited by GnRHa (0.1 microM) in a time- and cell-dependent manner, and pretreatment with Smad3 SiRNA and U0126, an MEK-1/2 inhibitor, respectively, reversed their actions.

CONCLUSION

Based on the menstrual cycle-dependent expression, the influence of GnRHa therapy, and regulation by TGF-beta in LSMC/MSMC, we conclude that Abi-2 may have a key regulatory function in leiomyomas cellular/tissue structural organization during growth and regression.

Distinct translation regulation by two alternative 5'UTRs of a stress-responsive protein--dPrx I

Translation efficiency is often regulated in part by 5'-untranslated region (5'UTR). Sequence analysis of an evolutionarily conserved stress-responsive protein, Drosophila Peroxiredoxin I (dPrx I), found the transcript to have two alternative 5'UTRs that lead to an identical coding sequence: namely Ia and Ib. Although both isoforms coexisted in Drosophila cells, the Ia isoform appeared to be dominant. Furthermore, reporter assay found that Ia enhanced translation in steady-state cells while Ib increased translation in cells under oxidative stress. Together, our data suggest that the two alternative 5'UTRs of dPrx I may be involved in a translational regulatory mechanism that responds to cellular oxidative stress.