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Triple-negative breast cancer (TNBC) is an aggressive breast cancer subtype characterized by a lack of therapeutic targets. The paucity of effective treatment options motivated a number of studies to tackle this problem. Immunosuppressive cells infiltrated into the tumor microenvironment (TME) of TNBC are currently considered as candidates for new therapeutic targets. Myeloid-derived suppressor cells (MDSCs) have been reported to populate in the TME of TNBC, but their roles in the clinical and biological features of TNBC have not been clarified. This study identified that interleukin-34 (IL-34) released by TNBC cells is a crucial immunomodulator to regulate MDSCs accumulation in the TME. We provide evidence that IL-34 induces a differentiation of myeloid stem cells into monocytic MDSCs (M-MDSCs) that recruits regulatory T (Treg) cells, while suppressing a differentiation into polymorphonuclear MDSCs (PMN-MDSCs). As a result, the increase in M-MDSCs contributes to the creation of an immunosuppressive TME, and the decrease in PMN-MDSCs suppresses angiogenesis, leading to an acquisition of resistance to chemotherapy. Accordingly, blockade of M-MDSC differentiation with an estrogen receptor inhibitor or anti-IL-34 monoclonal antibody suppressed M-MDSCs accumulation causing retardation of tumor growth and restores chemosensitivity of the tumor by promoting PMN-MDSCs accumulation. This study demonstrates previously poorly understood mechanisms of MDSCs-mediated chemoresistance in the TME of TNBC, which is originated from the existence of IL-34, suggesting a new rationale for TNBC treatment.

The IL-6 amplifier, which describes the simultaneous activation of STAT3 and NF-kB, in synovial fibroblasts causes the infiltration of immune cells into the joints of F759 mice. The result is a disease that resembles human rheumatoid arthritis. However, the kinetics and regulatory mechanisms of how augmented transcriptional activation by STAT3 and NF-kB leads to F759 arthritis is unknown. We here show that the STAT3-NF-κB complex is present in the cytoplasm and nucleus and accumulates around NFkB binding sites of the IL-6 promoter region and established a computer model that shows IL-6 and IL-17 signaling promotes the formation of the STAT3-NF-κB complex followed by its binding on promoter regions of NF-kB target genes to accelerate inflammatory responses, including the production of IL-6, epiregulin, and CCL2, phenotypes consistent with in vitro experiments. The binding also promoted cell growth in the synovium and the recruitment of Th17 cells and macrophages in the joints. Anti-IL-6 blocking antibody treatment inhibited inflammatory responses even at the late phase, but anti-IL-17 and anti-TNFα antibodies did not. However, anti-IL-17 antibody at the early phase showed inhibitory effects, suggesting that the IL-6 amplifier is dependent on IL-6 and IL-17 stimulation at the early phase, but only on IL-6 at the late phase. These findings demonstrate the molecular mechanism of F759 arthritis can be recapitulated in silico and identify a possible therapeutic strategy for IL-6 amplifier-dependent chronic inflammatory diseases.

The acquisition of mesenchymal traits leads to immune evasion in various cancers, but the underlying molecular mechanisms remain unclear. In this study, we found that the expression levels of AT-rich interaction domain-containing protein 5a (Arid5a), an RNA-binding protein, were substantially increased in mesenchymal tumor subtypes. The deletion of Arid5a in tumor cell lines enhanced antitumor immunity in immunocompetent mice, but not in immunodeficient mice, suggesting a role for Arid5a in immune evasion. Furthermore, an Arid5a-deficient tumor microenvironment was shown to have robust antitumor immunity, as manifested by suppressed infiltration of granulocytic myeloid-derived suppressor cells and regulatory T cells. In addition, infiltrated T cells were more cytotoxic and less exhausted. Mechanistically, Arid5a stabilized Ido1 and Ccl2 mRNAs and augmented their expression, resulting in enhanced tryptophan catabolism and an immunosuppressive tumor microenvironment. Thus, our findings demonstrate the role of Arid5a beyond inflammatory diseases and suggest Arid5a as a promising target for the treatment of immunotolerant malignant tumors.See related Spotlight by Van den Eynde, p. 854.

Supplementary Figures 1-8 and Tables 1-3

Aim: The tumor microenvironment (TME) of pancreatic ductal adenocarcinoma (PDAC) is highly immune suppressive with modest T-cell infiltration, and only rarely responds to immune checkpoint inhibition (ICI) therapy. Our aim was to clarify the molecular basis underlying the immune suppressive properties of PDAC.Background: Mutations in both KRAS and TP53 genes are characteristic of PDAC. A major target of KRAS/TP53 double mutations is the ARF6-AMAP1 pathway, which promotes the fibrosis, acidosis, invasion, and immune evasion of cancer cells. KPC cells are a genetically well-defined mouse cell model of human PDAC bearing Kras/Trp53 mutations, and express Arf6 and Amap1 at high levels.Findings: Intact KPC cells predominantly expressed immune suppressive chemokines, such as Cxcl12 and Cxcl5, but when Amap1 was silenced, immune surveillance chemokines, such as Cxcl10 and Ccl5 became predominant. A similar, albeit fragmented, chemokine switching was observed in human PDAC cells, and this mechanism appeared to be used in the normal pancreas of humans and mice. The silencing of Amap1 in KPC cells significantly changed the types and numbers of tumor infiltrating lymphocytes to be less favorable for immune evasion.Conclusions: Many PDAC cells appear to have a hitherto unidentified mechanism of malignancy, by which they can change the types of chemokines that they produce to be favorable for immune evasion. The ARF6-AMAP1 pathway is integral to this chemokine switching. Hence, this malignancy appears to be the result of KRAS/TP53 double mutations, which are not common in other types of cancer unless they are in the advanced stages. Our results are consistent with our previous findings that blockade of the ARF6- AMAP1 pathway significantly improves the efficacy of ICI therapy.

The acquisition of mesenchymal traits leads to immune evasion in various cancers, but the underlying molecular mechanisms remain unclear. In this study, we found that the expression levels of AT-rich interaction domain-containing protein 5a (Arid5a), an RNA-binding protein, were substantially increased in mesenchymal tumor subtypes. The deletion of Arid5a in tumor cell lines enhanced antitumor immunity in immunocompetent mice, but not in immunodeficient mice, suggesting a role for Arid5a in immune evasion. Furthermore, an Arid5a-deficient tumor microenvironment was shown to have robust antitumor immunity, as manifested by suppressed infiltration of granulocytic myeloid-derived suppressor cells and regulatory T cells. In addition, infiltrated T cells were more cytotoxic and less exhausted. Mechanistically, Arid5a stabilized Ido1 and Ccl2 mRNAs and augmented their expression, resulting in enhanced tryptophan catabolism and an immunosuppressive tumor microenvironment. Thus, our findings demonstrate the role of Arid5a beyond inflammatory diseases and suggest Arid5a as a promising target for the treatment of immunotolerant malignant tumors. See related Spotlight by Van den Eynde, p. 854.

Background Not merely the onset of immune evasion, but other factors, such as acidosis and fibrosis, are also major barriers in cancer therapeutics. Dense fibrosis is a hallmark of pancreatic ductal carcinoma (PDAC), in which hyperactivation of focal adhesion kinase (FAK) in tumor cells was shown to be crucial. Double mutations of KRAS/ TP53 are characteristic to PDAC. We previously showed that high protein expression of ARF6 and its downstream effector AMAP1, as well as processes involved in the ARF6 activation by cell surface tyrosine kinase receptors, are major targets of the KRAS/TP53 mutations to promote PDAC invasion, metastasis, and immune evasion. This notion was recaptured by KPC mouse model of human PDAC (LSL-Kras(G12D/+); LSL-Trp53(R172H/+)); Pdx-1-Cre). Mechanistically, the ARF6-AMAP1 pathway is primarily involved in cellular dynamics of PD-L1, β1-integrins, and E-cadherin; and hence modulates cell-adhesion properties when ARF6 is activated. Here, with an aim to understand whether the ARF6-AMAP1 pathway is critically involved in the elevated levels of PD-L1 and fibrosis of PDAC, we analyzed relationship between AMAP1 and these malignant phenotypes. Moreover, because the ARF6 pathway may closely be related to focal adhesion dynamics and hence to FAK, we also investigated whether AMAP1 employs FAK in fibrosis. Methods Clinical specimens, as well as KPC cells/tumors and their shAMAP1 or shFAK derivatives were analyzed. Results Elevated levels of PD-L1 and fibrosis correlated with poor outcome of our patient cohort, to be consistent with previous reports; in which high AMAP1 expression statistically correlated with the elevated PD-L1 and fibrosis. To be consistent, silencing of AMAP1 (shAMAP1) in KPC cells resulted in reduced PD-L1 expression and fibrosis in their tumors. On the other hand, shAMAP1 only slightly affected FAK activation in KPC cells, and phosphorylated FAK did not correlate with enhanced fibrosis or with poor outcome of our patients. Conclusions Together with our previous data, our results collectively indicated that the ARF6-AMAP1 pathway, empowered by the KRAS/TP53 mutations, is closely associated with elevated PD-L1 expression and fibrosis of human PDACs, to be recaptured in the KPC mouse model. The ARF6 pathway may promote fibrosis independent of FAK.

Signal-transducing adaptor family member-2 (STAP-2) is an adaptor protein that regulates various intracellular signals. We previously demonstrated that STAP-2 binds to epidermal growth factor receptor (EGFR) and facilitates its stability and activation of EGFR signaling in prostate cancer cells. Inhibition of this interaction may be a promising direction for cancer treatment. Here, we found that 2D5 peptide, a STAP-2-derived peptide, blocked STAP-2-EGFR interactions and suppressed EGFR-mediated proliferation in several cancer cell lines. 2D5 peptide inhibited tumor growth of human prostate cancer cell line DU145 and human lung cancer cell line A549 in murine xenograft models. Additionally, we determined that EGFR signaling and its stability were decreased by 2D5 peptide treatment during EGF stimulation. In conclusion, our study shows that 2D5 peptide is a novel anticancer peptide that inhibits STAP-2-mediated activation of EGFR signaling and suppresses prostate and lung cancer progression.

Although KRAS and TP53 mutations are major drivers of pancreatic ductal adenocarcinoma (PDAC), the incurable nature of this cancer still remains largely elusive. ARF6 and its effector AMAP1 are often overexpressed in different cancers and regulate the intracellular dynamics of integrins and E-cadherin, thus promoting tumor invasion and metastasis when ARF6 is activated. Here we show that the ARF6-AMAP1 pathway is a major target by which KRAS and TP53 cooperatively promote malignancy. KRAS was identified to promote eIF4A-dependent ARF6 mRNA translation, which contains a quadruplex structure at its 5'-untranslated region, by inducing TEAD3 and ETV4 to suppress PDCD4; and also eIF4E-dependent AMAP1 mRNA translation, which contains a 5'-terminal oligopyrimidine-like sequence, via up-regulating mTORC1. TP53 facilitated ARF6 activation by platelet-derived growth factor (PDGF), via its known function to promote the expression of PDGF receptor beta (PDGFR beta) and enzymes of the mevalonate pathway (MVP). The ARF6-AMAP1 pathway was moreover essential for PDGF-driven recycling of PD-L1, in which KRAS, TP53, elF4A/4E-dependent translation, mTOR, and MVP were all integral. We moreover demonstrated that the mouse PDAC model KPC cells, bearing KRAS/TP53 mutations, express ARF6 and AMAP1 at high levels and that the ARF6-based pathway is closely associated with immune evasion of KPC cells. Expression of ARF6 pathway components statistically correlated with poor patient outcomes. Thus, the cooperation among elF4A/4E-dependent mRNA translation and MVP has emerged as a link by which pancreatic driver mutations may promote tumor cell motility, PD-L1 dynamics, and immune evasion, via empowering the ARF6-based pathway and its activation by external ligands.

Significance Pancreatic ductal carcinomas (PDACs) have been extensively studied regarding their genomic alterations, microenvironmental intercommunication, and metabolic reprogramming. However, identification of the protein machinery of tumor cells that eventually drives malignancy as a result of driver mutations, and their associated events, is highly anticipated toward the development of precision medicine. The lack of such information regarding PDACs has hindered the elucidation of mechanisms driving malignancies, leaving them incurable. Here we demonstrated that the 2 well-known pancreatic driver mutations cooperatively activate a specific signaling pathway that promotes tumor invasion and immune evasion properties. Our results provide insights into the molecular basis by which malignancies often develop in parallel with oncogenesis and PDAC cell growth, as well as druggable targets for immunotherapies., Although KRAS and TP53 mutations are major drivers of pancreatic ductal adenocarcinoma (PDAC), the incurable nature of this cancer still remains largely elusive. ARF6 and its effector AMAP1 are often overexpressed in different cancers and regulate the intracellular dynamics of integrins and E-cadherin, thus promoting tumor invasion and metastasis when ARF6 is activated. Here we show that the ARF6–AMAP1 pathway is a major target by which KRAS and TP53 cooperatively promote malignancy. KRAS was identified to promote eIF4A-dependent ARF6 mRNA translation, which contains a quadruplex structure at its 5′-untranslated region, by inducing TEAD3 and ETV4 to suppress PDCD4; and also eIF4E-dependent AMAP1 mRNA translation, which contains a 5′-terminal oligopyrimidine-like sequence, via up-regulating mTORC1. TP53 facilitated ARF6 activation by platelet-derived growth factor (PDGF), via its known function to promote the expression of PDGF receptor β (PDGFRβ) and enzymes of the mevalonate pathway (MVP). The ARF6–AMAP1 pathway was moreover essential for PDGF-driven recycling of PD-L1, in which KRAS, TP53, eIF4A/4E-dependent translation, mTOR, and MVP were all integral. We moreover demonstrated that the mouse PDAC model KPC cells, bearing KRAS/TP53 mutations, express ARF6 and AMAP1 at high levels and that the ARF6-based pathway is closely associated with immune evasion of KPC cells. Expression of ARF6 pathway components statistically correlated with poor patient outcomes. Thus, the cooperation among eIF4A/4E-dependent mRNA translation and MVP has emerged as a link by which pancreatic driver mutations may promote tumor cell motility, PD-L1 dynamics, and immune evasion, via empowering the ARF6-based pathway and its activation by external ligands.

Endothelin (ET)-1 is involved in the vascular system, cell proliferation and apoptosis. ET receptors consist of ET type A receptor (ETA R) and ET type B receptor (ETB R). ETA R and ETB R generally exhibit opposite responses, although many exceptions exist. In the present study, we attempted to identify ETA R- or ETB R-specific binding proteins to understand the differences in ETA R- and ETB R-mediated responses after ET-1 stimulation. The 78-kDa glucose-regulated protein (GRP78) showed a stronger binding affinity towards ETB R than towards ETA R. Moreover, GRP78 overexpression promoted ETB R-mediated ERK activation and GRP78 silencing suppressed ETB R-mediated ERK activation. Furthermore, ETB R can localize GRP78 to the cell periphery. These results suggest that the interaction of ETB R with GRP78 affects ERK activation and GRP78 localization.

The mevalonate pathway (MVP) is a metabolic pathway associated with tumor invasiveness and is known to prenylate proteins, but which prenylated proteins are critical for MVP-driven cancers is unknown. Hashimoto et al. show that MVP-driven cancers require activation of the GTPase Arf6 for invasion and that the MVP substrate Rab11 is required for Arf6 activation., Drug resistance, metastasis, and a mesenchymal transcriptional program are central features of aggressive breast tumors. The GTPase Arf6, often overexpressed in tumors, is critical to promote epithelial–mesenchymal transition and invasiveness. The metabolic mevalonate pathway (MVP) is associated with tumor invasiveness and known to prenylate proteins, but which prenylated proteins are critical for MVP-driven cancers is unknown. We show here that MVP requires the Arf6-dependent mesenchymal program. The MVP enzyme geranylgeranyl transferase II (GGT-II) and its substrate Rab11b are critical for Arf6 trafficking to the plasma membrane, where it is activated by receptor tyrosine kinases. Consistently, mutant p53, which is known to support tumorigenesis via MVP, promotes Arf6 activation via GGT-II and Rab11b. Inhibition of MVP and GGT-II blocked invasion and metastasis and reduced cancer cell resistance against chemotherapy agents, but only in cells overexpressing Arf6 and components of the mesenchymal program. Overexpression of Arf6 and mesenchymal proteins as well as enhanced MVP activity correlated with poor patient survival. These results provide insights into the molecular basis of MVP-driven malignancy.

Background The small GTPase Arf6 and its downstream effector AMAP1 (also called ASAP1/DDEF1) constitute a signaling pathway promoting cell invasion, in which AMAP1 interacts with several different proteins, including PRKD2, EPB41L5, paxillin, and cortactin. Components of this pathway are often overexpressed in human breast cancer cells, to be correlated with poor prognosis of the patients, whereas overexpression of the Arf6 pathway did not correlate with the four main molecular classes of human breast tumors. In this pathway, receptor tyrosine kinases, including EGFR and Her2, activate Arf6 via GEP100. MMTV-PyMT mice and MMTV-Neu mice are well-established models of human breast cancer, and exhibit the early dissemination and the lung metastasis, by utilizing protein tyrosine phosphorylation for oncogenesis. PyMT-tumors and Neu-tumors are known to have overlapping gene expression profiles, which primarily correspond to the luminal B-type of human mammary tumors, although they differ in the time necessary for tumor onset and metastasis. Given the common usage of protein tyrosine phosphorylation, as well as the frequent use of these animal models for studying breast cancer at the molecular level, we here investigated whether mammary tumors in these mouse models utilize the Arf6-based pathway for invasion. Methods Expression levels of Arf6, AMAP1, and GEP100 were analyzed in PyMT-tumors and Neu-tumors by western blotting. Expression of Arf6 and AMAP1 was also analyzed by immunohistochemistry. The involvement of AMAP1 in invasion, and the possible correlation of its high expression levels with cancer mesenchymal properties were also investigated. Results We found that PyMT-tumors, but not Neu-tumors, frequently overexpress AMAP1 and use it for invasion, whereas both types of tumors expressed Arf6 and GEP100 at different levels. High levels of the AMAP1 expression among PyMT-tumor cells were frequently correlated with loss of the epithelial marker CK8 and also with expression of the mesenchymal marker vimentin both at the primary sites and at sites of the lung metastases. Conclusions PyMT-tumors appear to frequently utilize the Arf6-based invasive machinery, whereas Neu-tumors do not. Our results suggest that MMTV-PyMT mice, rather than MMTV-Neu mice, are useful to study the Arf6-based mammary tumor malignancies, as a representative model of human breast cancer. Electronic supplementary material The online version of this article (10.1186/s12964-017-0212-z) contains supplementary material, which is available to authorized users.

The erythrocyte protein band 4.1-like5 (EPB4.1L5) regulates E-cadherin in cancer invasion and metastasis inducing epithelial-to-mesenchymal transition. This study aimed to investigate the biological significance of EPB4.1L5 in upper urinary tract urothelial carcinoma (UTUC).Retrospective analysis of the clinical records of 165 patients with UTUC (Ta-4N0M0) subjected to radical nephroureterectomy and immunohistochemical examination of EPB4.1L5 expression in those tissues.The median follow-up period was 62.2 months (interquartile range = 77.0). The score of EPB4.1L5 significantly correlated with tumor grade, pathological T stage, and lymphovascular invasion (all P0.001). The 5-year Kaplan-Meier recurrence-free survival and cancer-specific survival rates were 54.1% and 59.5% in patients with high EPB4.1L5 expression, compared with 81.6% and 87.2%, (all P0.001) in their counterparts. Multivariate analyses revealed that high expression of EPB4.1L5 was one of the independent prognostic factors for tumor recurrence (P = 0.022, HR = 2.40) and cancer-specific survival (P = 0.015, HR = 2.94).High EPB4.1L5 expression was related to worse clinical outcome in patients with UTUC. These results indicated that EPB4.1L5 could provide prognostic information in patients with UTUC regarding epithelial-to-mesenchymal transition.

Background TP53 mutations in cancer cells often evoke cell invasiveness, whereas fibroblasts show invasiveness in the presence of intact TP53. AMAP1 (also called DDEF1 or ASAP1) is a downstream effector of ARF6 and is essential for the ARF6-driven cell-invasive phenotype. We found that AMAP1 levels are under the control of p53 (TP53 gene product) in epithelial cells but not in fibroblasts, and here addressed that molecular basis of the epithelial-specific function of p53 in suppressing invasiveness via targeting AMAP1. Methods Using MDA-MB-231 cells expressing wild-type and p53 mutants, we identified miRNAs in which their expression is controlled by normal-p53. Among them, we identified miRNAs that target AMAP1 mRNA, and analyzed their expression levels and epigenetic statuses in epithelial cells and nonepithelial cells. Results We found that normal-p53 suppresses AMAP1 mRNA in cancer cells and normal epithelial cells, and that more than 30 miRNAs are induced by normal-p53. Among them, miR-96 and miR-182 were found to target the 3′-untranslated region of AMAP1 mRNA. Fibroblasts did not express these miRNAs at detectable levels. The ENCODE dataset demonstrated that the promoter region of the miR-183-96-182 cistron is enriched with H3K27 acetylation in epithelial cells, whereas this locus is enriched with H3K27 trimethylation in fibroblasts and other non-epithelial cells. miRNAs, such as miR-423, which are under the control of p53 but not associated with AMAP1 mRNA, demonstrated similar histone modifications at their gene loci in epithelial cells and fibroblasts, and were expressed in these cells. Conclusion Histone modifications of certain miRNA loci, such as the miR-183-96-182 cistron, are different between epithelial cells and non-epithelial cells. Such epithelial-specific miRNA regulation appears to provide the molecular basis for the epithelial-specific function of p53 in suppressing ARF6-driven invasiveness. Electronic supplementary material The online version of this article (10.1186/s12964-018-0302-6) contains supplementary material, which is available to authorized users.

Background Squamous cell carcinoma of the tongue (tongue SCC) is a major subtype of head and neck squamous cell carcinoma (HNSCC), which is an intractable cancer under current therapeutics. ARF6 and its effector AMAP1 are often overexpressed in different types of cancers, such as breast cancer and renal cancer, and in these cancers, AMAP1 binds to EPB41L5 to promote invasion, metastasis, and drug resistance. EPB41L5 is a mesenchymal-specific protein, normally induced during epithelial-mesenchymal transition (EMT) to promote focal adhesion dynamics. Similarly to breast cancer and renal cancer, the acquisition of mesenchymal phenotypes is the key process that drives the malignancy of HNSCC. We previously showed that the overexpression of AMAP1 in tongue SCC is statistically correlated with the poor outcome of patients. In this study, we examined whether tongue SCC also expresses EPB41L5 at high levels. Results Immunohistochemical staining of clinical specimens of tongue SCC demonstrated that high expression levels of EPB41L5 statistically correlate with poor disease-free survival and poor overall survival rates of patients. The tongue SCC cell line SCC-9, which overexpress Arf6 and AMAP1, also expressed EPB41L5 at high levels to promote invasiveness, whereas the weakly invasive SCC-25 cells did not express EPB41L5 at notable levels. Among the different EMT-associated transcriptional factors, ZEB1 was previously found to be most crucial in inducing EPB41L5 in breast cancer and renal cancer. In contrast, expression levels of ZEB1 did not correlate with the expression levels of EPB41L5 in tongue SCC, whereas KLF8 and FOXO3 levels showed positive correlations with EPB41L5 levels. Moreover, silencing of EPB41L5 only marginally improved the drug resistance of SCC-9 cells, even when coupled with ionizing radiation. Conclusion Our results indicate that activation of the cancer mesenchymal program in tongue SCC, which leads to EPB41L5 expression, closely correlates with the poor prognosis of patients. However, ZEB1 was not the major inducer of EPB41L5 in tongue SCC, unlike in breast cancer and renal cancer. Thus, processes that trigger the mesenchymal program of tongue SCC, which drives their malignancies, seem to be substantially different from those of other cancers.

Onset of the cancer mesenchymal program is closely associated with cancer malignancy and drug resistance. Among the different epithelial–mesenchymal transition (EMT)-associated transcriptional factors, ZEB1 has a key role in inducing the mesenchymal phenotypes and stem cell-like properties of different breast cancer cells. ARF6 and its effector AMAP1 are frequently overexpressed in breast cancer cells, and promote invasion, metastasis and drug resistance. EPB41L5 is induced during EMT, and mediates the disruption of E-cadherin-based cell–cell adhesion and the promotion of focal adhesion dynamics. Here we show that EPB41L5 is an integral component of the ARF6-based pathway, which is induced by ZEB1. We found that EPB41L5 is expressed at high levels in malignant breast cancer cells and binds to AMAP1. ZEB1 induced EPB41L5 both in cancer cells and normal cells. This relationship was recaptured with The Cancer Genome Atlas RNASeq data set, and correlated with the poor outcome of the patients. In contrast, diversified events, such as tumor growth factor β1 stimulation, expression of SNAI1 and TP53 mutation, can each cause the induction of ZEB1 and EPB41L5, depending on the cellular context. Our results demonstrated that the ZEB1-EPB41L5 axis is at the core of the cancer mesenchymal program that drives ARF6-based invasion, metastasis and drug resistance of significant populations of primary breast cancers, and is tightly correlated with the poor outcomes of patients.

EGF signaling activates Rab5c and promotes the intracellular association of AMAP1 and PRKD2 to enhance β1 integrin recycling and promote the invasiveness of breast cancer cells., Epidermal growth factor receptor (EGFR) signaling is one of the crucial factors in breast cancer malignancy. Breast cancer cells often overexpress Arf6 and its effector, AMAP1/ASAP1/DDEF1; in these cells, EGFR signaling may activate the Arf6 pathway to induce invasion and metastasis. Active recycling of some integrins is crucial for invasion and metastasis. Here, we show that the Arf6–AMAP1 pathway links to the machinery that recycles β1 integrins, such as α3β1, to promote cell invasion upon EGFR stimulation. We found that AMAP1 had the ability to bind directly to PRKD2 and hence to make a complex with the cytoplasmic tail of the β1 subunit. Moreover, GTP-Rab5c also bound to AMAP1, and activation of Rab5c by EGFR signaling was necessary to promote the intracellular association of AMAP1 and PRKD2. Our results suggest a novel mechanism by which EGFR signaling promotes the invasiveness of some breast cancer cells via integrin recycling.

Epidermal growth factor (EGF) receptor (EGFR) signalling is implicated in tumour invasion and metastasis1,2. However, whether there are EGFR signalling pathways specifically used for tumour invasion still remains elusive. Overexpression of Arf6 and its effector, AMAP1, correlates with and is crucial for the invasive phenotypes of different breast cancer cells3,4,5,6. Here we identify the mechanism by which Arf6 is activated to induce tumour invasion. We found that GEP100/BRAG2, a guanine nucleotide exchanging factor (GEF) for Arf6, is responsible for the invasive activity of MDA-MB-231 breast cancer cells, whereas the other ArfGEFs are not. GEP100, through its pleckstrin homology domain, bound directly to Tyr1068/1086-phosphorylated EGFR to activate Arf6. Overexpression of GEP100, together with Arf6, caused non-invasive MCF7 cells7 to become invasive, which was dependent on EGF stimulation. Moreover, GEP100 knockdown blocked tumour metastasis. GEP100 was expressed in 70% of primary breast ductal carcinomas, and was preferentially co-expressed with EGFR in the malignant cases. Our results indicate that GEP100 links EGFR signalling to Arf6 activation to induce invasive activities of some breast cancer cells, and hence may contribute to their metastasis and malignancy.

In neutrophils, superoxide anion production generally accompanies chemotaxis and functions in killing invading pathogens. The GIT2 GTPase-activating protein binds to the guanine nucleotide-exchange factor alphaPIX. Here we show that GIT2 was necessary for directional chemotaxis and for the suppression of superoxide production in G protein-coupled receptor-stimulated neutrophils. GIT2 was also necessary for the orientation of superoxide production toward chemoattractant sources. GIT2 suppressed the activity of ADP ribosylation factor 1 and was a component of the Gbetagamma subunit-mediated direction-sensing machinery 'downstream' of G protein-coupled receptor signaling. This study establishes a function for GIT2 in linking chemotaxis and superoxide production in neutrophils and shows that loss of GIT2 in vivo leads to an immunodeficient state.

In most human breast cancer cell lines, there is a direct correlation between their in vivo invasive phenotypes and in vitro invasion activities. Here, we found that ADP-ribosylation factor 6 (Arf6) is localized at the invadopodia of the cultured breast cancer cells MDA-MB-231, and its suppression by a small-interfering RNA duplex effectively blocks the invasive activities of the cells, such as invadopodia formation, localized matrix degradation and Matrigel transmigration but not the cell-adhesion activity. We also found that the GTP hydrolysis-defective mutant Arf6(Q67L) and the GTP-binding defective mutant Arf6(T27N) both blocked these invasive activities but not cell adhesion, suggesting the necessity of continued activation and cycling of the Arf6 GTPase cycle in invasion. Among the different human breast cancer cell lines that we examined, cell lines with high invasive activities expressed higher amounts of Arf6 protein than those in weakly invasive and noninvasive cell lines, although no notable correlation was found between Arf6 mRNA expression levels and invasive activities. Moreover, Matrigel-transmigration activity of all of these invasive cells was blocked effectively by an Arf6 small-interfering RNA duplex. Hence, Arf6 appears to be an integral component of breast cancer invasive activities, and we propose that Arf6 and the intracellular machinery regulating Arf6 during invasion should be considered as therapeutic targets for the prevention of breast cancer invasion.

Two signaling pathways known to be essential for progression from immature to mature B cells are BAFF receptor (BAFF-R) and the B cell receptor (BCR). Here, we first show that phospholipase C (PLC)-gamma2 is required for a BAFF-R-mediated survival signal. Then, we have examined the question of whether the reduced number of mature B cells in PLC-gamma2-/- mice is caused by a defect in either BCR or BAFF-R signaling. We find that a PLC-gamma2 SH2 mutant, which inhibits coupling between BCR and PLC-gamma2, fails to restore B cell maturation, despite supporting BAFF-dependent survival. Therefore, our data suggest that the BAFF-R-mediated survival signal, provided by PLC-gamma2, is not sufficient to promote B cell maturation, and that, in addition, activation of PLC-gamma2 by BCR is required for B cell development.

NF-κB is a major transcriptional factor regulating many cellular functions including inflammation; therefore, its appropriate control is of high importance. The detailed mechanism of its activation has been well characterized, but that of negative regulation is poorly understood. In this study, we showed AMAP1, an Arf-GTPase activating protein, as a negative feedback regulator for NF-κB by binding with IKKβ, an essential kinase in NF-κB signaling. Proteomics analysis identified AMAP1 as a binding protein with IKKβ. Overexpression of AMAP1 suppressed NF-κB activity by interfering the binding of IKKβ and NEMO, and deletion of AMAP1 augmented NF-κB activity. The activation of NF-κB induced translocation of AMAP1 to cytoplasm from cell membrane and nucleus, which resulted in augmented interaction of AMAP1 and IKKβ. These results demonstrated a novel role of AMAP1 as a negative feedback regulator of NF-κB, and presented it as a possible target for anti-inflammatory treatments.

While Arf-family small GTPases (Arf-GTPases) consist of 5 members in humans, 31 human genes have been identified that encode proteins bearing the GTPase-activating protein (GAP) domain for Arf-GTPases. Interestingly, Arf1, the first identified Arf, was shown to substantially lack intrinsic GTPase activity, which other Ras-superfamily members of small GTPases generally bear. Likewise, ArfGAP domains primarily consist of zinc-finger structures, and do not resemble GAP domains for other small GTPases. Arfs primarily function in intracellular vesicle/membrane trafficking. A general model shows that Arfs play roles in membrane budding, in which GTP-Arfs recruit coatomer proteins to generate and maintain membrane curvature to initiate the budding. Coatomers are thought to be separated from Arf-mediated vesicles before they reach the target membrane, while this separation may or may not be coupled with the GTP hydrolysis activity. We have shown that several ArfGAPs, such as AMAP1 and AMAP2, have the ability to bind stably to GTP-Arf6, without immediate GTP hydrolysis. They each contain a BAR domain and hence may act as coatomers for Arf-mediated vesicles. These ArfGAPs moreover act to recruit their binding proteins to sites of Arf6 activation, which are not coatomer components. These findings have amended the classical, general model of the functions of ArfGAPs, as well as Arf-GTPases. In this review, we will describe the recent information revealed about ArfGAPs, with the aim to decipher and discuss their fundamental roles.

Cross-linking of the B cell Ag receptor (BCR) induces the tyrosine phosphorylation of multiple cellular substrates, including phospholipase C (PLC)-γ2, which is involved in the activation of the phosphatidylinositol pathway. To assess the importance of PLC-γ2 in murine lymphopoiesis, the PLC-γ2 gene was inducibly ablated by using IFN-regulated Cre recombinase. Mice with a neonatally induced loss of PLC-γ2 function displayed reduced numbers of mature conventional B cells and peritoneal B1 cells and defective responses in vitro to BCR stimulation and in vivo to immunization with thymus-independent type II Ags. In contrast, T cell development and TCR-mediated proliferation were normal. Taken together, PLC-γ2 is a critical component of BCR signaling pathways and is required to promote B cell development.

The serine/threonine kinase HPK1 is a member of the germinal center kinase (GCK) family that has been implicated in the regulation of MAP kinase pathways. Here, we demonstrate the involvement of HPK1 in antigen receptor signaling. Engagement of the TCR or the BCR resulted in a marked induction of HPK1 catalytic activity. Subsequent analysis revealed that Src and Syk/ZAP-70 tyrosine kinases and the adaptor proteins LAT, SLP-76, BLNK, Grb2, and Grap are involved in HPK1 activation. Overexpression of HPK1 inhibited TCR activation of AP-1 and ERK2, whereas the kinase-inactive mutant of HPK1 potentiated these responses. Neither form of HPK1 affected PMA or v-Ras activation of AP-1 and ERK2. Thus, HPK1 is a negative regulator of the TCR-induced AP-1 response pathway.

A major problem of current cancer research and therapy is prediction of tumor recurrence after initial treatment, rather than the simple biological characterization of the malignancy and proliferative properties of tumors. Breast conservation therapy (BCT) is a well-approved, standard treatment for patients with early stages of breast cancer, which consists of lumpectomy and whole-breast irradiation. In spite of extensive studies, only 'age' and 'Ki-67 positivity' have been identified to be well correlated with local recurrence after BCT. An Arf6 pathway, activated by GEP100 under receptor tyrosine kinases (RTKs) and employs AMAP1 as its effector, is crucial for invasion and metastasis of some breast cancer cells. This pathway activates beta 1 integrins and perturbs E-cadherin-based adhesions, hence appears to be integral for epithelial-mesenchymal transdifferentiation (EMT). We here show that expression of the Arf6 pathway components statistically correlates with rapid local recurrence after BCT. We retrospectively analyzed four hundred seventy-nine patients who received BCT in Hokkaido University Hospital, and found 20 patients had local recurrence. We then analyzed pathological samples of patients who experienced local recurrence by use of Kaplan-Meier analysis, Stepwise regression analysis and the t-test, coupled with immunostaining, and found that co-overexpression of GEP100 and AMAP1 correlates with rapidity of the local recurrence. Their margin-status, node-positivity, and estrogen receptor (ER)-or progesterone receptor (PgR)positivity did not correlated with the rapidity. This study is the first to show that expression of a certain set of proteins correlates with the rapidity of local recurrence. Our results are useful not only for prediction, but highlight the possibility of developing novel strategies to block local recurrence. We also discuss why mRNAs encoding these proteins have not been identified to correlate with local recurrence by previous conventional gene expression profiling analyses.

The mevalonate pathway results in the prenylation of small GTPases, which are pivotal for oncogenesis and cancer malignancies. However, inhibitors of this pathway, such as statins, have not necessarily produced favorable results in clinical trials. We recently identified properties of statin responders, together with the underlying molecular mechanisms and simple biomarkers to predict these responders.

Acquisition of mesenchymal properties by cancer cells is critical for their malignant behaviour, but regulators of the mesenchymal molecular machinery and how it is activated remain elusive. Here we show that clear cell renal cell carcinomas (ccRCCs) frequently utilize the Arf6-based mesenchymal pathway to promote invasion and metastasis, similar to breast cancers. In breast cancer cells, ligand-activated receptor tyrosine kinases employ GEP100 to activate Arf6, which then recruits AMAP1; and AMAP1 then binds to the mesenchymal-specific protein EPB41L5, which promotes epithelial–mesenchymal transition and focal adhesion dynamics. In renal cancer cells, lysophosphatidic acid (LPA) activates Arf6 via its G-protein-coupled receptors, in which GTP-Gα12 binds to EFA6. The Arf6-based pathway may also contribute to drug resistance. Our results identify a specific mesenchymal molecular machinery of primary ccRCCs, which is triggered by a product of autotaxin and it is associated with poor outcome of patients., Acquisition of mesenchymal properties by cancer cells is a critical event for the development of malignancy. Here, the authors show that in renal cancer cells, lysosphosphatidic acid does not utilize the RhoA pathway but specifically activates the Arf6 mesenchymal pathway via its GPCRs and EFA6 to promote invasion, metastasis and drug resistance.

Review on ASAP1 (ArfGAP with SH3 domain, ankyrin repeat and PH domain 1), with data on DNA, on the protein encoded, and where the gene is implicated.

Overexpression of Her2/ErbB2/Neu in cancer is often correlated with recurrent distant metastasis, although the mechanism still remains largely elusive. We have previously shown that EGFR, when tyrosine-phosphorylated, binds to GEP100/BRAG2 to activate Arf6, which induces cancer invasion and metastasis. We now show that overexpressed Her2 in lung adenocarcinoma cells also employs GEP100. Like EGFR-GEP100 binding, this association is primarily mediated by the pleckstrin homology (PH) domain of GEP100 and Tyr1139/Tyr1196 of Her2. Tyr1139/Tyr1196 are autonomously phosphorylated, when Her2 is overexpressed. Accordingly, invasive activities mediated by the Her2-GEP100 pathway are not dependent on external factors. Blocking Her2-GEP100 binding, as well as its signaling pathway all inhibit cancer invasive activities. Moreover, our clinical study indicates that co-overexpression of Her2 with GEP100 in primary lung adenocarcinomas of patients is correlated with the presence of their node-metastasis with a statistical significance. Since the GEP100 PH domain interacts with both Her2 and EGFR, targeting this domain may provide novel cancer therapeutics.

Tumors are tissue-specific diseases, and their mechanisms of invasion and metastasis are highly diverse. In breast cancer, biomarkers that specifically correlate with the invasive phenotypes have not been clearly identified. A small GTPase Arf6 primarily regulates recycling of plasma membrane components. We have shown that Arf6 and its effector AMAP1 (DDEF1, DEF1, ASAP1 and centaurin beta4) are abnormally overexpressed in some breast cancers and used for their invasion and metastasis. Overexpression of these proteins is independent of the transcriptional upregulation of their genes, and occurs only in highly malignant breast cancer cells. We recently identified GEP100 (BRAG2) to be responsible for the Arf6 activation to induce invasion and metastasis, by directly binding to ligand-activated epidermal growth factor receptor (EGFR). A series of our studies revealed that for activation of the invasion pathway of EGFR, it is prerequisite that Arf6 and AMAP1 both are highly overexpressed, and that EGFR is activated by ligands. Pathological analyses indicate that a significant large population of human ductal cancers may utilize the EGFR-GEP100-Arf6-AMAP1 pathway for their malignancy. Microenvironments have been highly implicated in the malignancy of mammary tumors. Our results reveal an aspect of the precise molecular mechanisms of some breast cancers, in which full invasiveness is not acquired just by intracellular alterations of cancer cells, but extracellular factors from microenvironments may also be necessary. Possible translation of our knowledge to cancer therapeutics will also be discussed.

Arf6 and its effector AMAP1 are overexpressed in malignant breast cancer cells, and are involved in their invasion and metastasis. We recently revealed that GEP100, a guanine nucleotide exchanging factor, is responsible for the activation of Arf6 which induces invasion and metastasis. GEP100 associated directly with ligand-activated epidermal growth factor receptor (EGFR) to be activated. Disruption of E-cadherin-mediated cell-cell adhesion is one of the major steps involved in acquisition of invasive phenotypes of most carcinomas. The EGFR-GEP100-Arf6 pathway not only activated matrix invasion activity but also perturbed E-cadherin function. GEP100 was found to be expressed in more than 80% of invasive ductal carcinomas. However, 60% of ductal carcinomas in situ were also positive for GEP100, in which GEP100 was preferentially coexpressed with EGFR in their malignant cases. Microenvionments have been highly implicated in the development of tumor malignancy. Our results reveal an aspect of the precise molecular mechanism of cancer invasion and metastasis, in which full invasiveness is not acquired just by alterations of cancer cells themselves, but their microenvironments may also play pivotal roles.

Invasive potentials of carcinomas greatly contribute to their metastasis, which is a major threat in most cancers. We have recently shown that Arf6 plays a pivotal role in breast cancer invasive activities and identified AMAP1 as an effector of GTP-Arf6 in invasion. Expression of AMAP1 correlates well with invasive phenotypes of primary tumors of the human breast. We also have shown that AMAP1 functions by forming a trimeric protein complex with cortactin and paxillin. In this complex, AMAP1 binds to the src homology 3 (SH3) domain of cortactin via its proline-rich peptide, SKKRPPPPPPGHKRT. SH3 domains are known to bind generally to the proline-rich ligands with a one-to-one stoichiometry. We found that AMAP1/cortactin binding is very atypical in its stoichiometry and interface structure, in which one AMAP1 proline-rich peptide binds to two cortactin SH3 domains simultaneously. We made a cell-permeable peptide derived from the AMAP1 peptide, and we show that this peptide specifically blocks AMAP1/cortactin binding, but not other canonical SH3/proline bindings, and effectively inhibits breast cancer invasion and metastasis. Moreover, this peptide was found to block invasion of other types of cancers, such as glioblastomas and lung carcinomas. We also found that a small-molecule compound, UCS15A, which was previously judged as a weak inhibitor against canonical SH3/proline bindings, effectively inhibits AMAP1/cortactin binding and breast cancer invasion and metastasis. Together with fine structural analysis, we propose that the AMAP1/cortactin complex, which is not detected in normal mammary epithelial cells, is an excellent drug target for cancer therapeutics.

The GTPase-activating protein (GAP) domain for Arfs primarily consists of a zinc-finger structure, which is not present in known GAPs for the other Ras-superfamily GTPases. More than 20 genes have been found to encode proteins bearing the ArfGAP domain in the human genome: a number that is much larger than that of the Arf isoforms. Several Arf isoforms, such as Arf1 and Arf6, indeed have been shown to each employ multiple different ArfGAPs for their regulation and function. We have found that two ArfGAPs, namely AMAP1 and AMAP2, exhibit a novel biochemical property of directly and selectively binding to GTP-Arf6 without immediate GAPing activity, while they were previously shown to exhibit efficient catalytic GAPing activities to Arf isoforms except Arf6 in vitro. Such property of AMAPs appears to be important for AMAPs-mediated recruitment of auxiliary molecules, including paxillin, cortactin, amphiphysin, and intersectin, to sites of Arf6 activation. AMAPs thus appear to act as "effectors" rather than simple GAPs in some aspects of Arf6 function. This article presents methods and protocols developed for the functional characterization of AMAPs in Arf6 function. These methods may be applied to other types of ArfGAPs to further clarify the cellular functions of ArfGAPs as well as Arfs.

Identification of the molecular machinery employed in cancer invasion, but not in normal adult cells, will greatly contribute to cancer therapeutics. Here we found that an ArfGAP, AMAP1/PAG2, is expressed at high levels in highly invasive breast cancer cells, but at very low levels in noninvasive breast cancer cells and normal mammary epithelial cells. siRNA-mediated silencing of AMAP1 effectively blocked the invasive activities. AMAP1 expression in human breast primary tumors also indicated its potential correlation with malignancy. Paxillin and cortactin have been shown to colocalize at invadopodia and play a pivotal role in breast cancer invasion. We found that AMAP1 is also localized at invadopodia, and acts to bridge paxillin and cortactin. This AMAP1-mediated trimeric protein complex was detected only in invasive cancer cells, and blocking this complex formation effectively inhibited their invasive activities in vitro and metastasis in mice. Our results indicate that AMAP1 is a component involved in invasive activities of different breast cancers, and provide new information regarding the possible therapeutic targets for prevention of breast cancer invasion and metastasis.

The GTPase-activating protein (GAP) domain for Arfs primarily consists of a zinc-finger structure, which is not present in known GAPs for the other Ras-superfamily GTPases. More than 20 genes have been found to encode proteins bearing the ArfGAP domain in the human genome: a number that is much larger than that of the Arf isoforms. Several Arf isoforms, such as Arf1 and Arf6, indeed have been shown to each employ multiple different ArfGAPs for their regulation and function. We have found that two ArfGAPs, namely AMAP1 and AMAP2, exhibit a novel biochemical property of directly and selectively binding to GTP-Arf6 without immediate GAPing activity, while they were previously shown to exhibit efficient catalytic GAPing activities to Arf isoforms except Arf6 in vitro. Such property of AMAPs appears to be important for AMAPs-mediated recruitment of auxiliary molecules, including paxillin, cortactin, amphiphysin, and intersectin, to sites of Arf6 activation. AMAPs thus appear to act as "effectors" rather than simple GAPs in some aspects of Arf6 function. This article presents methods and protocols developed for the functional characterization of AMAPs in Arf6 function. These methods may be applied to other types of ArfGAPs to further clarify the cellular functions of ArfGAPs as well as Arfs.