p53-independent tumor suppression by cell-cycle arrest via CREB/ATF transcription factor OASIS

CREB/ATF transcription factor OASIS/CREB3L1 is upregulated in long-term-cultured astrocytes undergoing cell-cycle arrest due to loss of DNA integrity by repeated replication. However, the roles of OASIS in the cell cycle remain unexplored. We find that OASIS arrests the cell cycle at G₂/M phase after DNA damage via direct induction of p21. Cell-cycle arrest by OASIS is dominant in astrocytes and osteoblasts, but not in fibroblasts, which are dependent on p53. In a brain injury model, Oasis^-/- reactive astrocytes surrounding the lesion core show sustained growth and inhibition of cell-cycle arrest, resulting in prolonged gliosis. We find that some glioma patients exhibit low expression of OASIS due to high methylation of its promoter. Specific removal of this hypermethylation in glioblastomas transplanted into nude mice by epigenomic engineering suppresses the tumorigenesis. These findings suggest OASIS as a critical cell-cycle inhibitor with potential to act as a tumor suppressor.

The survival and proliferation of osteosarcoma cells are dependent on the mitochondrial BIG3-PHB2 complex formation

Previous studies reported the critical role of the brefeldin A-inhibited guanine nucleotide exchange protein 3-prohibitin 2 (BIG3-PHB2) complex in modulating estrogen signaling activation in breast cancer cells, yet its pathophysiological roles in osteosarcoma (OS) cells remain elusive. Here, we report a novel function of BIG3-PHB2 in OS malignancy. BIG3-PHB2 complexes were localized mainly in mitochondria in OS cells, unlike in estrogen-dependent breast cancer cells. Depletion of endogenous BIG3 expression by small interfering RNA (siRNA) treatment led to significant inhibition of OS cell growth. Disruption of BIG3-PHB2 complex formation by treatment with specific peptide inhibitor also resulted in significant dose-dependent suppression of OS cell growth, migration, and invasion resulting from G2/M-phase arrest and in PARP cleavage, ultimately leading to PARP-1/apoptosis-inducing factor (AIF) pathway activation-dependent apoptosis in OS cells. Subsequent proteomic and bioinformatic pathway analyses revealed that disruption of the BIG3-PHB2 complex might lead to downregulation of inner mitochondrial membrane protein complex activity. Our findings indicate that the mitochondrial BIG3-PHB2 complex might regulate PARP-1/AIF pathway-dependent apoptosis during OS cell proliferation and progression and that disruption of this complex may be a promising therapeutic strategy for OS.

The GALNT6‑LGALS3BP axis promotes breast cancer cell growth

Polypeptide N‑acetylgalactosaminyltransferase 6 (GALNT6), which is involved in the initiation of O‑glycosylation, has been reported to play crucial roles in mammary carcinogenesis through binding to several substrates; however, its biological roles in mediating growth‑promoting effects remain unknown. The present study demonstrated a crucial pathophysiological role of GALNT6 through its O‑glycosylation of lectin galactoside‑binding soluble 3 binding protein (LGALS3BP), a secreted growth‑promoting glycoprotein, in breast cancer growth. The Cancer Genome Atlas data analysis revealed that high expression levels of GALNT6 were significantly associated with poor prognosis of breast cancer. GALNT6 O‑glycosylated LGALS3BP in breast cancer cells, whereas knockdown of GALNT6 by siRNA led to the inhibition of both the O‑glycosylation and secretion of LGALS3BP, resulting in the suppression of breast cancer cell growth. Notably, LGALS3BP is potentially O‑glycosylated at three sites (T556, T571 and S582) by GALNT6, thereby promoting autocrine cell growth, whereas the expression of LGALS3BP with three Ala substitutions (T556A, T571A and S582A) in cells drastically reduced GALNT6‑dependent LGALS3BP O‑glycosylation and secretion, resulting in suppression of autocrine growth‑promoting effect. The findings of the present study suggest that the GALNT6‑LGALS3BP axis is crucial for breast cancer cell proliferation and may be a therapeutic target and biomarker for mammary tumors.

Biophysical characterization of the breast cancer-related BIG3-PHB2 interaction: Effect of non-conserved loop region of BIG3 on the structure and the interaction

Brefeldin A-inhibited guanine nucleotide-exchange protein 3 (BIG3) interacts with and inhibits the tumor suppressor function of prohibitin-2 (PHB2), and recent in vivo studies have demonstrated that the BIG3-PHB2 interaction is a promising target for breast cancer therapy. However, little biophysical characterization on BIG3 and its interaction with PHB2 has been reported. Here we compared the calculated 8-class secondary structure of the N-terminal domains of BIG family proteins and identified a loop region unique to BIG3. Our biophysical characterization demonstrated that this loop region significantly affects the colloidal and thermodynamic stability of BIG3 and the thermodynamic and kinetic profile of its interaction with PHB2. These results establish a model for the BIG3-PHB2 interaction and an entry for drug discovery for breast cancer.

Abstract 3813: PHB2 inactivation by AKAP-BIG3 is required for progression of HER2-overexpressing breast cancer

Overexpression of the human epidermal growth factor receptor 2 (HER2) in breast cancer is linked to aggressive tumor behavior and a poorer prognosis. Anti-HER2 monoclonal antibody, trastuzumab extends the overall survival of patients with HER2-overexpressing breast cancer, but resistance to trastuzumab and/or other HER2-targeted therapies remains a serious clinical problem. Our previous studies demonstrated that Brefeldin A-Inhibited Guanine nucleotide-exchange protein 3 (BIG3), which is exclusively overexpressed in the majority of breast cancers, functions as a cancer specific A-kinase anchoring protein that binds protein kinase A (PKA) and protein phosphatase 1 (PP1Cα), thereby inactivating prohibitin2 (PHB2) suppressive activity through its dephosphorylation on Ser39. We further developed dominant-negative stapling peptide (stERAP), which is designed to specifically disrupt binding of BIG3-PHB2 complex and improve duration of their anti-tumor effects. Here we newly report that stERAP has significant suppressive effects on the HER2 signaling network by activating the tumor suppressive ability of PHB2. stERAP resulted in intrinsic PHB2 release from BIG3, followed by rapid phosphorylation on Ser39, Thr42 and Thr169 via PKCα, TTK and MK5, respectively. Importantly, PHB2 released from BIG3 by stERAP treatment translocated into nucleus, followed by acting as a transcriptional co-repressor by recruiting HDAC1 and NcoR through its Ser39-phosphorylation. More importantly, we observed that serine/threonine phosphorylations of PHB2 are necessary for disruption of HER2-HER3 hetero-dimerization and NF-κB signalling activation which are associated with acquired resistance to trastuzumab. We demonstrated that weekly treatment of stERAP completely suppressed the proliferation of trastuzumab-resistant HER2-positive breast cancer cells in vitro and in vivo. We are currently examining the association of both BIG3 overexpression and PHB2 dephosphorylation with poor prognosis of patients with HER2-positive breast cancers by immunohistochemical staining, and will report these results at this meeting. We demonstrated for the first time that PHB2 inactivation by the AKAP-BIG3 (BIG3/PKA/PP1Cα tri-complex) is required for oncogenic HER2 signalling activation in breast cancer cells, and stERAP may be a promising anti-cancer drug for trastuzumab-resistant breast cancer.

Citation Format: Tetsuro Yoshimaru, Yosuke Matsushita, Mitsunori Sasa, Yasuo Miyoshi, Toyomasa Katagiri. PHB2 inactivation by AKAP-BIG3 is required for progression of HER2-overexpressing breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3813.

Abstract 5313: Frequent downregulation of SALL3 by genetic and epigenetic alterations is involved in progression and chemoresistance of triple negative breast cancers

Triple negative breast cancer (TNBC) is an aggressive subtype of breast cancer and worse disease-specific outcomes compared with other subtypes. Because of the lack of estrogen and progesterone receptors and HER2 gene amplification, cytotoxic agents remain the mainstay of treatment for TNBC patients. Although TNBC is enriched for germline and somatic BRCA mutation, a phenotype termed BRCAness, PARP inhibitors as monotherapy failed to improve the outcome of TNBC patients. Therefore, we aimed to uncover molecular characterization in TNBC cases by whole-exome sequencing analysis of genomic DNAs from 36 Japanese patients with TNBC compared with their corresponding normal. We identified 36 genes that were recurrently mutated (>10% of cases) in TNBC cases, including TP53 and PIK3CA as described in the previous next generation sequencing analysis of TNBC cases. Remarkably, we identified a number of epigenetic-related genes involved in histone modification and DNA methylation, which were mutated in 20 out of 36 (55.6%) cases. Among them, we focused on spalt like transcription factor 3 (SALL3) gene which shows recurrent somatic mutations, and are most frequently downregulated in TNBC cases. Ectopic overexpression of the wildtype SALL3, but not the somatically mutated SALL3 into BT549 breast cancer cells, which expresses low level of SALL3 gene, caused the significant suppression of cell growth. Importantly, promoter regions of SALL3 gene was frequently hypermethylated and transcriptionally silenced in only TNBC cases, but not in other types of breast cancer by TCGA data analysis. Moreover, the expression of SALL3 was restored after treatments of 5-aza-2’-deoxycitidine in TNBC cell line, HCC1937. Notably, siRNA-mediated knockdown of SALL3 expression in BT20 cells enhanced chemoresistance against paclitaxel and docetaxel, respectively. Moreover, low expression of SALL3 was associated with significantly shorter relapse free survival. Notably, because SALL3 retains eight C2H2-type zinc finger domains which are extremely conserved in mammalian transcription factors, we hypothesized that SALL3 transcriptionally regulates genes which are involved in progression and chemoresistance of TNBC. We identified the several candidates of SALL3-taget genes by gene expression and chromatin immunoprecipitation analyses. Our findings provide the evidence of a pathophysiological role for SALL3 as a tumor suppressor which is possibly associated with progression and chemoresistance of TNBC.

Citation Format: Yosuke Matsushita, Masato Komatsu, Kazuma Kiyotani, Tetsuro Yoshimaru, Hiromu Suzuki, Yasuo Miyoshi, Mitsunori Sasa, Toyomasa Katagiri. Frequent downregulation of SALL3 by genetic and epigenetic alterations is involved in progression and chemoresistance of triple negative breast cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5313.

Abstract 1837: Overcoming trastuzumab resistance in HER2-overexpressing breast cancer by utilizing PHB2, a tumor suppressor of multiple resistance pathways

Overexpression of the human epidermal growth factor receptor 2 (HER2) is associated with aggressive tumor behavior and poor prognosis in breast cancer. Although anti-HER2 monoclonal antibody, trastuzumab shows considerable efficacy and extends the overall survival of patients with HER2 overexpressing breast cancer, about half of individuals with HER2-overexpressing breast cancer do not respond to trastuzumab-based therapies due to multiple resistance mechanisms. Therefore, acquired and de novo resistance to trastuzumab remains an important issue in the clinical treatment of HER2-overexpressing breast cancer. Our previous studies demonstrated that Brefeldin A-Inhibited Guanine nucleotide-exchange protein 3 (BIG3), which is exclusively overexpressed in the majority of breast cancers, functions as an A-kinase anchoring protein that binds protein kinase A (PKA) and protein phosphatase 1 (PP1Cα), thereby inactivating prohibitin2 (PHB2) suppressive activity through its dephosphorylation on Ser39. We further developed the stapled dominant-negative peptide (stERAP; stapled ERAP), which is designed to specifically inhibit the BIG3-PHB2 interaction and improve duration of their anti-tumor effects. Here we newly report that stERAP has significant suppressive effects on the HER2 signaling network by activating the tumor suppressive ability of PHB2. Intrinsic PHB2 released from BIG3 by stERAP was rapidly serine- and threonine-phosphorylated via PKCα and/or TTK, which are essential for its tumor suppressive activity, and effectively disrupted the HER2-HER3 interaction associated with acquired resistance to trastuzumab, resulting in significant reduction of proliferation of HER2-overexpressing breast cancer cells (IC50 = 54 nM in SK-BR-3 cells). We also confirm that stERAP inhibited HER2 phosphorylation on Thr488, HER2-HER3 interaction, and NF-κB pathway, which are associated with trastuzumab-resistance, respectively, resulting in significant suppression of growth of trastuzumab-resistant breast cancer cells. More importantly, stERAP treatment led to the enhancement of trastuzumab-sensitivity, resulting in a synergistic growth suppression of HER2-overexpressing and trastuzumab-resistant breast cancer cells, respectively. Our findings strongly suggest that stERAP is a novel promising anti-cancer drug to suppress the growth of trastuzumab-resistant breast cancer in clinical use.

Citation Format: Tetsuro Yoshimaru, Yosuke Matsushita, Mitsunori Sasa, Yasuo Miyoshi, Toyomasa Katagiri. Overcoming trastuzumab resistance in HER2-overexpressing breast cancer by utilizing PHB2, a tumor suppressor of multiple resistance pathways [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1837.

Abstract 5315: Frequent downregulation of SALL3 by recurrent genetic and epigenetic alterations is involved in triple-negative breast cancers

Triple negative breast cancers (TNBC), defined by the lack of estrogen and progesterone receptors and HER2 gene amplification, is a heterogeneous and clinically aggressive disease due to the lack of beneficial therapeutic targets. Even though one of the most major risk for the development of TNBC is carrying a deleterious germline and somatic mutations of BRCA1 are not frequently found in sporadic cases of TNBC. Therefore, we aimed to search genomic alterations in TNBC cases by whole-exome sequencing analysis of genomic DNAs from 36 Japanese patients with TNBC compared with their corresponding normal. We identified 36 genes that were recurrently mutated (>10% of cases) in TNBC cases, including TP53 and PIK3CA as described in the previous next generation sequencing analysis of TNBC cases. Remarkably, we identified a number of epigenetic-related genes involved in histone modification and DNA methylation, which were mutated in 20 out of 36 (55.6%) cases. Among them, we focused on spalt like transcription factor 3 (SALL3) gene which shows recurrent somatic mutations, and are most frequently downregulated in TNBC cases. Nonsense-mutation of SALL3 (E169X) completely abolish its binding to DNAMT3A. Ectopic overexpression of the wildtype SALL3, but not the somatically mutated SALL3 into BT549 breast cancer cells, which expresses low level of SALL3 gene, caused the significant suppression of cell growth. Importantly, SALL3 gene was frequently hypermethylated and transcriptionally silenced in only TNBC cases, but not in other types of breast cancer using TCGA data sets. Moreover, the expression of SALL3 was restored after treatments of 5-aza-2'-deoxycitidine (5-aza-dC) in TNBC cell line, HCC1937. Notably, siRNA-mediated knockdown of SALL3 expression in BT20 cells enhanced chemoresistance against paclitaxel and docetaxel, respectively. Moreover, low expression of SALL3 was associated with significantly shorter relapse free survival. Our findings provide the evidence of a pathophysiological role for SALL3 as a tumor suppressor which is possibly associated with carcinogenesis for TNBC.

Citation Format: Yosuke Matsushita, Masato Komatsu, Kazuma Kiyotani, Tetsuro Yoshimaru, Hiromu Suzuki, Yasuo Miyoshi, Mitsunori Sasa, Toyomasa Katagiri. Frequent downregulation of SALL3 by recurrent genetic and epigenetic alterations is involved in triple-negative breast cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5315.

Abstract 94: DDX31 cooperates with mutant p53 and EGFR to promote the multistep progression of invasive bladder cancer

Bladder cancer is the most common malignancy of the urinary tract worldwide. Approximately 70% of cases are diagnosed as non-muscle-invasive bladder cancer (NMIBC), while the remaining 30% of cases are classified as muscle-invasive bladder cancer (MIBC). Evidence based on molecular biology has highlighted that the aggressiveness of MIBC advances through a multistep mechanism due to many genomic alterations. Notably, alterations of TP53 and EGFR pathways frequently occur in bladder cancers and are associated with poor prognosis, respectively. However, the connection between the overexpression of EGFR and the p53 mutation in multistep carcinogenesis and the progression of MIBC remains unknown. Here we report the distinct critical roles of DEAD box polypeptide 31 (DDX31) in the multistep progression of muscle invasive bladder cancer (MIBC) through its sequential interaction with mutant p53 (mutp53) and EGFR. In early MIBC cells, nuclear DDX31 acts as a transcriptional co-activator that binds to mutp53/SP1 and enhances mutp53 transcriptional activation, thereby upregulating the EPB41L4B gene, which plays a critical role in metastatic behavior and promotes the invasion and migration of MIBC. Notably, in advanced MIBC, cytoplasmic DDX31, which is transported from the nucleus, functions as an adaptor scaffold protein that forms a complex with EGFR via its interaction with phosho-nucleolin (NCL), leading to constitutive activation of EGFR-Akt signaling. Significantly, high expression of both cytoplasmic DDX31 and p53 proteins is correlated with a poor prognosis in MIBC patients. More importantly, blocking the DDX31-NCL interaction via a dominant-negative peptide led to downregulation of EGFR-Akt signaling, resulting in a significant anti-tumoral effect of bladder cancer in vivo. Our findings reveal that DDX31 cooperates with mutp53 and EGFR to promote the multistep progression of MIBC and that inhibition of DDX31-NCL formation may lead to potential treatment strategies for advanced MIBC.

Citation Format: Toyomasa Katagiri, Kei Daizumoto, Tetsuro Yoshimaru, Yosuke Matsushita, Tomoya Fukawa, Masaya Ono, Hiro-omi Kanayama. DDX31 cooperates with mutant p53 and EGFR to promote the multistep progression of invasive bladder cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 94.

Frequent downregulation of LRRC26 by epigenetic alterations is involved in the malignant progression of triple-negative breast cancer

Triple-negative breast cancer (TNBC), defined as breast cancer lacking estrogen- and progesterone‑receptor expression and human epidermal growth factor receptor 2 (HER2) amplification, is a heterogeneous disease. RNA-sequencing analysis of 15 TNBC specimens and The Cancer Genome Atlas-TNBC dataset analysis identified the frequent downregulation of leucine-rich repeat-containing 26 (LRRC26), which negatively regulates nuclear factor-κB (NF-κB) signaling, in TNBC tissues. Quantitative polymerase chain reaction and bisulfite pyrosequencing analyses revealed that LRRC26 was frequently silenced in TNBC tissues and cell lines as a result of promoter methylation. LRRC26 expression was restored by 5-aza-2'-deoxycytidine (5'-aza-dC) treatment in HCC1937 TNBC cells, which lack LRRC26 expression. Notably, small interfering RNA-mediated knockdown of LRRC26 expression significantly enhanced the anchorage-independent growth, invasion and migration of HCC70 cells, whereas ectopic overexpression of LRRC26 in BT20 cells suppressed their invasion and migration. Conversely, neither knockdown nor overexpression of LRRC26 had an effect on cell viability in the absence of tumor necrosis factor-α (TNF-α) stimulation. Meanwhile, overexpression of LRRC26 caused the reduction of TNF-α-mediated NF-κB luciferase reporter activity, whereas depleting LRRC26 expression resulted in the upregulation of TNF-α-mediated NF-κB downstream genes [interleukin-6 (IL-6), IL-8 and C-X-C motif chemokine ligand-1]. Taken together, these findings demonstrate that LRRC26 is frequently downregulated in TNBC due to DNA methylation and that it suppresses the TNF-α-independent anchorage-independent growth, invasion and migration of TNBC cells. Loss of LRRC26 function may be a critical event in the aggressiveness of TNBC cells through a TNF-α/NF-κB-independent mechanism.

A DDX31/Mutant-p53/EGFR Axis Promotes Multistep Progression of Muscle-Invasive Bladder Cancer

The p53 and EGFR pathways are frequently altered in bladder cancer, yet their contributions to its progression remain elusive. Here we report that DEAD box polypeptide 31 (DDX31) plays a critical role in the multistep progression of muscle-invasive bladder cancer (MIBC) through its sequential interactions with mutant p53 (mutp53) and EGFR. In early MIBC cells, nuclear DDX31-bound mutp53/SP1 enhanced mutp53 transcriptional activation, leading to migration and invasion of MIBC. Cytoplasmic DDX31 also bound EGFR and phospho-nucleolin in advanced MIBC, leading to EGFR-Akt signaling activation. High expression of both cytoplasmic DDX31 and p53 proteins correlated with poor prognosis in patients with MIBC, and blocking the DDX31/NCL interaction resulted in downregulation of EGFR/Akt signaling, eliciting an in vivo antitumor effect against bladder cancer. These findings reveal that DDX31 cooperates with mutp53 and EGFR to promote progression of MIBC, and inhibition of DDX31/NCL formation may lead to potential treatment strategies for advanced MIBC.Significance: DDX31 cooperates with mutp53 and EGFR to promote progression of muscle invasive bladder cancer. Cancer Res; 78(9); 2233-47. ©2018 AACR.

Abstract 3613: Development of chemically modified peptide inhibitor ERAP targeting BIG3-PHB2 complex on hormone-resistant breast tumor

Approximately 70% of breast cancer cells express estrogen receptor alpha (ERα), and depend on estrogen (E2) for proliferative and metastatic activity. The current endocrine therapies for breast cancer are mainly based on targeting ERα signaling using selective ERα modulators, ERα downregulators, and aromatase inhibitor. However, up to 50% of patients with ERα-positive tumors either initially do not respond or become resistant to these drugs. The precise molecular mechanisms for the endocrine resistance contributes to be an active area of research. Therefore, identifying the factors and pathways responsible for resistance and defining ways to overcome it lead to develop novel molecular-target therapies to endocrine resistance. Recent findings support that the Brefeldin A-inhibited guanine nucleotide-exchange protein 3-prohibitin 2 (BIG3-PHB2) complex plays a crucial role in E2/ERα signaling modulation in these cells. Moreover, specific inhibition of the BIG3-PHB2 interaction using ERα activity-regulator synthetic peptide (ERAP: 165-177 amino acids) derive from a helical BIG3 sequence, a dominant-negative peptide inhibitor leads to the significant anti-tumor effect. However, duration of its effect is very short for clinical use. Here, we report the development of the chemically modified ERAP using stapling methods (stapled ERAP) to improve duration of its antitumor effects. The stapled ERAP specifically inhibited the BIG3-PHB2 interaction, thereby exhibiting the long-lasting suppressive activity and their intracellular localization without membrane-permeable polyarginine sequence supposedly through the formation of stable α-helix structure induced by the stapling. Importantly, a combination of stapled ERAP and tamoxifen caused a synergistic inhibitory effect in breast cancer cell growth. Tumor bearing mice treated with every 7 days with stapled ERAP treatment effectively prevented the BIG3-PHB2 interaction as well as daily treatment, leading to the complete regression of E2-dependent tumor in vivo. Our findings suggest that the stapled ERAP may be a promising anti-tumor drug to suppress the growth of luminal-type breast cancer in clinical use.

Citation Format: Toyomasa Katagiri, Tetsuro Yoshimaru. Development of chemically modified peptide inhibitor ERAP targeting BIG3-PHB2 complex on hormone-resistant breast tumor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3613. doi:10.1158/1538-7445.AM2017-3613

A-kinase anchoring protein BIG3 coordinates oestrogen signalling in breast cancer cells

Approximately 70% of breast cancer cells express oestrogen receptor alpha (ERα). Previous studies have shown that the Brefeldin A-inhibited guanine nucleotide-exchange protein 3–prohibitin 2 (BIG3-PHB2) complex has a crucial role in these cells. However, it remains unclear how BIG3 regulates the suppressive activity of PHB2. Here we demonstrate that BIG3 functions as an A-kinase anchoring protein that binds protein kinase A (PKA) and the α isoform of the catalytic subunit of protein phosphatase 1 (PP1Cα), thereby dephosphorylating and inactivating PHB2. E2-induced PKA-mediated phosphorylation of BIG3-S305 and -S1208 serves to enhance PP1Cα activity, resulting in E2/ERα signalling activation via PHB2 inactivation due to PHB2-S39 dephosphorylation. Furthermore, an analysis of independent cohorts of ERα-positive breast cancers patients reveal that both BIG3 overexpression and PHB2-S39 dephosphorylation are strongly associated with poor prognosis. This is the first demonstration of the mechanism of E2/ERα signalling activation via the BIG3–PKA–PP1Cα tri-complex in breast cancer cells.

BIG3 is highly expressed in breast cancers and its interaction with PHB2 results in constitutive activation of E2/ERa signalling. Here the authors unveil the mechanistic details of this regulation showing that BIG3 binds PKA and regulates PP1Ca activity in an oestrogen-dependent manner.

Protein kinase A inhibition facilitates the antitumor activity of xanthohumol, a valosin-containing protein inhibitor

Xanthohumol (XN), a simple prenylated chalcone, can be isolated from hops and has the potential to be a cancer chemopreventive agent against several human tumor cell lines. We previously identified valosin‐containing protein (VCP) as a target of XN; VCP can also play crucial roles in cancer progression and prognosis. Therefore, we investigated the molecular mechanisms governing the contribution of VCP to the antitumor activity of XN. Several human tumor cell lines were treated with XN to investigate which human tumor cell lines are sensitive to XN. Several cell lines exhibited high sensitivity to XN both in vitro and in vivo. shRNA screening and bioinformatics analysis identified that the inhibition of the adenylate cyclase (AC) pathway synergistically facilitated apoptosis induced by VCP inhibition. These results suggest that there is crosstalk between the AC pathway and VCP function, and targeting both VCP and the AC pathway is a potential chemotherapeutic strategy for a subset of tumor cells.

BIG3 Inhibits the Estrogen-Dependent Nuclear Translocation of PHB2 via Multiple Karyopherin-Alpha Proteins in Breast Cancer Cells

We recently reported that brefeldin A-inhibited guanine nucleotide-exchange protein 3 (BIG3) binds Prohibitin 2 (PHB2) in cytoplasm, thereby causing a loss of function of the PHB2 tumor suppressor in the nuclei of breast cancer cells. However, little is known regarding the mechanism by which BIG3 inhibits the nuclear translocation of PHB2 into breast cancer cells. Here, we report that BIG3 blocks the estrogen (E2)-dependent nuclear import of PHB2 via the karyopherin alpha (KPNA) family in breast cancer cells. We found that overexpressed PHB2 interacted with KPNA1, KPNA5, and KPNA6, thereby leading to the E2-dependent translocation of PHB2 into the nuclei of breast cancer cells. More importantly, knockdown of each endogenous KPNA by siRNA caused a significant inhibition of E2-dependent translocation of PHB2 in BIG3-depleted breast cancer cells, thereby enhancing activation of estrogen receptor alpha (ERα). These data indicated that BIG3 may block the KPNAs (KPNA1, KPNA5, and KPNA6) binding region(s) of PHB2, thereby leading to inhibition of KPNAs-mediated PHB2 nuclear translocation in the presence of E2 in breast cancer cells. Understanding this regulation of PHB2 nuclear import may provide therapeutic strategies for controlling E2/ERα signals in breast cancer cells.

Therapeutic advances in BIG3-PHB2 inhibition targeting the crosstalk between estrogen and growth factors in breast cancer

Our previous studies demonstrated that specific inhibition of the BIG3-PHB2 complex, which is a critical modulator in estrogen (E2) signaling, using ERAP, a dominant negative peptide inhibitor, leads to suppression of E2-dependent estrogen receptor (ER) alpha activation through the reactivation of the tumor suppressive activity of PHB2. Here, we report that ERAP has significant suppressive effects against synergistic activation caused by the crosstalk between E2 and growth factors associated with intrinsic or acquired resistance to anti-estrogen tamoxifen in breast cancer cells. Intrinsic PHB2 released from BIG3 by ERAP effectively disrupted each interaction of membrane-associated ERα and insulin-like growth factor 1 receptor beta (IGF-1Rβ), EGFR, PI3K or human epidermal growth factor 2 (HER2) in the presence of E2 and the growth factors IGF or EGF, followed by inhibited the activation of IGF-1Rβ, EGFR or HER2, and reduced Akt, MAPK and ERα phosphorylation levels, resulting in significant suppression of proliferation of ERα-positive breast cancer cells in vitro and in vivo. More importantly, combined treatment with ERAP and tamoxifen led to a synergistic suppression of signaling that was activated by crosstalk between E2 and growth factors or HER2 amplification. Taken together, our findings suggest that the specific inhibition of BIG3-PHB2 is a novel potential therapeutic approach for the treatment of tamoxifen-resistant breast cancers activated by the crosstalk between E2 and growth factor signaling, especially in premenopausal women.

Xanthohumol suppresses oestrogen-signalling in breast cancer through the inhibition of BIG3-PHB2 interactions

Xanthohumol (XN) is a natural anticancer compound that inhibits the proliferation of oestrogen receptor-α (ERα)-positive breast cancer cells. However, the precise mechanism of the antitumour effects of XN on oestrogen (E2)-dependent cell growth, and especially its direct target molecule(s), remain(s) largely unknown. Here, we focus on whether XN directly binds to the tumour suppressor protein prohibitin 2 (PHB2), forming a novel natural antitumour compound targeting the BIG3-PHB2 complex and acting as a pivotal modulator of E2/ERα signalling in breast cancer cells. XN treatment effectively prevented the BIG3-PHB2 interaction, thereby releasing PHB2 to directly bind to both nuclear- and cytoplasmic ERα. This event led to the complete suppression of the E2-signalling pathways and ERα-positive breast cancer cell growth both in vitro and in vivo, but did not suppress the growth of normal mammary epithelial cells. Our findings suggest that XN may be a promising natural compound to suppress the growth of luminal-type breast cancer.

Early growth response 4 is involved in cell proliferation of small cell lung cancer through transcriptional activation of its downstream genes

Small cell lung cancer (SCLC) is aggressive, with rapid growth and frequent bone metastasis; however, its detailed molecular mechanism remains poorly understood. Here, we report the critical role of early growth factor 4 (EGR4), a DNA-binding, zinc-finger transcription factor, in cell proliferation of SCLC. EGR4 overexpression in HEK293T cells conferred significant upregulation of specific splice variants of the parathyroid hormone-related protein (PTHrP) gene, resulting in enhancement of the secretion of PTHrP protein, a known mediator of osteolytic bone metastasis. More importantly, depletion of EGR4 expression by siRNA significantly suppressed growth of the SCLC cell lines, SBC-5, SBC-3 and NCI-H1048. On the other hand, introduction of EGR4 into NIH3T3 cells significantly enhanced cell growth. We identified four EGR4 target genes, SAMD5, RAB15, SYNPO and DLX5, which were the most significantly downregulated genes upon depletion of EGR4 expression in all of the SCLC cells examined, and demonstrated the direct recruitment of EGR4 to their promoters by ChIP and luciferase reporter analysis. Notably, knockdown of the expression of these genes by siRNA remarkably suppressed the growth of all the SCLC cells. Taken together, our findings suggest that EGR4 likely regulates the bone metastasis and proliferation of SCLC cells via transcriptional regulation of several target genes, and may therefore be a promising target for the development of anticancer drugs for SCLC patients.

Brefeldin A-inhibited guanine nucleotide-exchange protein 3 (BIG3) is predicted to interact with its partner through an ARM-type α-helical structure

Background

Brefeldin A-inhibited guanine nucleotide-exchange protein 3 (BIG3) has been identified recently as a novel regulator of estrogen signalling in breast cancer cells. Despite being a potential target for new breast cancer treatment, its amino acid sequence suggests no association with any well-characterized protein family and provides little clues as to its molecular function. In this paper, we predicted the structure, function and interactions of BIG3 using a range of bioinformatic tools.

Results

Homology search results showed that BIG3 had distinct features from its paralogues, BIG1 and BIG2, with a unique region between the two shared domains, Sec7 and DUF1981. Although BIG3 contains Sec7 domain, the lack of the conserved motif and the critical glutamate residue suggested no potential guaninyl-exchange factor (GEF) activity. Fold recognition tools predicted BIG3 to adopt an α-helical repeat structure similar to that of the armadillo (ARM) family. Using state-of-the-art methods, we predicted interaction sites between BIG3 and its partner PHB2.

Conclusions

The combined results of the structure and interaction prediction led to a novel hypothesis that one of the predicted helices of BIG3 might play an important role in binding to PHB2 and thereby preventing its translocation to the nucleus. This hypothesis has been subsequently verified experimentally.

Targeting BIG3-PHB2 interaction to overcome tamoxifen resistance in breast cancer cells

The acquisition of endocrine resistance is a common obstacle in endocrine therapy of patients with oestrogen receptor-α (ERα)-positive breast tumours. We previously demonstrated that the BIG3–PHB2 complex has a crucial role in the modulation of oestrogen/ERα signalling in breast cancer cells. Here we report a cell-permeable peptide inhibitor, called ERAP, that regulates multiple ERα-signalling pathways associated with tamoxifen resistance in breast cancer cells by inhibiting the interaction between BIG3 and PHB2. Intrinsic PHB2 released from BIG3 by ERAP directly binds to both nuclear- and membrane-associated ERα, which leads to the inhibition of multiple ERα-signalling pathways, including genomic and non-genomic ERα activation and ERα phosphorylation, and the growth of ERα-positive breast cancer cells both in vitro and in vivo. More importantly, ERAP treatment suppresses tamoxifen resistance and enhances tamoxifen responsiveness in ERα-positive breast cancer cells. These findings suggest inhibiting the interaction between BIG3 and PHB2 may be a new therapeutic strategy for the treatment of luminal-type breast cancer.

Oestrogen receptor-α (ERα) signalling has a role in breast cancer drug resistance. Here, the authors report a synthetic peptide that disrupts the interaction between the signalling molecules BIG3 and PHB2, and thereby suppresses tamoxifen resistance.

Involvement of B3GALNT2 overexpression in the cell growth of breast cancer

A number of glycosyltransferases have been identified and biologically characterized in cancer cells, yet their exact pathophysiological functions are largely unknown. Here, we report the critical role of β1,3-N-acetylgalactosaminyltransferase II (B3GALNT2), which transfers N-acetylgalactosamine (GalNAc) in a β1,3 linkage to N-acetylglucosamine, in the growth of breast cancer cells. Comprehensive transcriptomics, quantitative PCR and northern blot analyses indicated this molecule to be exclusively upregulated in the majority of breast cancers. Knockdown of B3GALNT2 expression by small interfering RNA attenuated cell growth and induced apoptosis in breast cancer cells. Overexpression of B3GALNT2 in HEK293T cells prompted secretion of the gene product into the culture medium, suggesting that B3GALNT2 is potentially a secreted protein. Furthermore, we demonstrated that B3GALNT2 is N-glycosylated on both Asn-116 and Asn-174 and that this modification is necessary for its secretion in breast cancer cells. Our findings suggest that this molecule represents a promising candidate for the development of a novel therapeutic targeting drug and a potential diagnostic tumor marker for patients with breast cancer, especially TNBC.

Abstract C18: Antitumor activity of xanthohumol, an inhibitor of valosin-containing protein

Autophagy is a bulk, nonspecific protein degradation pathway that is involved in the pathogenesis of cancer and neurodegenerative disease. Here, we observed that xanthohumol (XN), a prenylated chalcone present in hops (Humulus lupus L.) and beer, modulates autophagy. By using XN-immobilized beads, valosin-containing protein (VCP) was identified as a XN-binding protein. VCP has been reported to be an essential protein for autophagosome maturation. Using an in vitro pull down assay, we showed that XN bound directly to the N domain, which is known to mediate co-factor and substrate binding to VCP. These data indicated that XN inhibited the function of VCP, thereby allowing the impairment of autophagosome maturation, and resulting in the accumulation of microtubule-associated protein 1 light chain 3-II (LC3-II).On the other hand, it has been reported that the expression level of VCP is correlated with progression of cancer, and VCP-overexpressing cell lines showed the resistance to apoptosis. Therefore, in this study, we examined the antitumor effects of XN on several types of human tumor cells. First we tested the sensitivity to XN in 15 human tumor cell lines. Each cell was treated with XN for 48 hrs, and XN-induced apoptosis was quantitatively analyzed by flow cytometry. As a result, XN potently induced apoptosis in 6 cell lines (SW480, SW620, HCT116, A2058, A375 and SW48 cells) as judged from subG1 population, and another 9 tumor cell lines were resistant to XN. Next, we examined whether VCP is involved in XN-induced apoptosis. Although, these 15 cell lines showed similar expression levels of VCP, another VCP inhibitor, Eeyarestatin I, also induced apoptosis in XN-sensitive tumor cells (SW480 cells and HCT116 cells) but not in VCP-insensitive tumor cells (A431 cells and EC17 cells). These findings suggest that the several human tumor cell lines require VCP function for their survival, and VCP would be a potential chemotherapeutic target molecule for subset of tumor cells.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C18.

Citation Format: Yuki Shikata, Shuhei Kanagaki, Yukiko Sasazawa, Etsu Tashiro, Tetsuro Yoshimaru, Masato Komatsu, Toyomasa Katagiri, Masaya Imoto. Antitumor activity of xanthohumol, an inhibitor of valosin-containing protein. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C18.

Molecular features of triple negative breast cancer cells by genome-wide gene expression profiling analysis

Triple negative breast cancer (TNBC) has a poor outcome due to the lack of beneficial therapeutic targets. To clarify the molecular mechanisms involved in the carcinogenesis of TNBC and to identify target molecules for novel anticancer drugs, we analyzed the gene expression profiles of 30 TNBCs as well as 13 normal epithelial ductal cells that were purified by laser-microbeam microdissection. We identified 301 and 321 transcripts that were significantly upregulated and downregulated in TNBC, respectively. In particular, gene expression profile analyses of normal human vital organs allowed us to identify 104 cancer-specific genes, including those involved in breast carcinogenesis such as NEK2, PBK and MELK. Moreover, gene annotation enrichment analysis revealed prominent gene subsets involved in the cell cycle, especially mitosis. Therefore, we focused on cell cycle regulators, asp (abnormal spindle) homolog, microcephaly-associated (Drosophila) (ASPM) and centromere protein K (CENPK) as novel therapeutic targets for TNBC. Small-interfering RNA-mediated knockdown of their expression significantly attenuated TNBC cell viability due to G1 and G2/M cell cycle arrest. Our data will provide a better understanding of the carcinogenesis of TNBC and could contribute to the development of molecular targets as a treatment for TNBC patients.

Identification of genes potentially involved in bone metastasis by genome-wide gene expression profile analysis of non-small cell lung cancer in mice

Lung cancer is commonly associated with multi-organ metastasis, and the bone is a frequent metastatic site for lung cancer. However, the molecular mechanism of organ-specific metastasis remains poorly understood. To elucidate this issue, we analyzed in this study genome-wide gene expression profiles of 15 metastatic lesions from three organs (bone, lung and liver) in a mouse model with multi-organ metastasis properties of human non-small cell lung cancer cells (ACC-LC319/bone2), using a combination of laser-microbeam microdissection and DNA microarrays. We identified 299 genes that could potentially be involved in the organ-selective nature of lung cancer metastasis. Among them, 77 were bone-specifically expressed elements, including genes involved in cell adhesion, cytoskeleton/cell motility, extracellular matrix remodeling and cell-cell signaling as well as genes already known to be involved in the bone metastasis of breast cancers. Quantitative RT-PCR confirmed the specific upregulation of eight genes in bone metastasis tumors, suggesting that these genes may be involved in bone metastasis. Our findings should be helpful for a better understanding of the molecular aspects of the metastatic process in different organs, and could lead to molecular target-based anticancer drugs and prevention of metastasis, especially bone metastasis.

Discrete generations of intracellular hydrogen peroxide and superoxide in antigen-stimulated mast cells: reciprocal regulation of store-operated Ca2+ channel activity

Mast cells and T cells produce reactive oxygen species (ROS) after stimulation with the high-affinity IgE receptor (Fc epsilon RI) and T cell receptor. A growing body of evidence suggests the existence of ROS-regulated intracellular and/or plasma membrane Ca(2+) channels in these cells but their molecular entities remain to be identified. Here, we report that store-operated Ca(2+) channel (SOC) activity is regulated by superoxide (O(2)(*-)) and hydrogen peroxide (H(2)O(2)) in mast cells. MnTBaP (Mn(III)tetrakis(4-benzoic acid)porphyrin) and ebselen (2-phenyl-1,2-benziso-selenazol-3(2H)-one) selectively blocked the generation of O(2)(*-) and H(2)O(2), respectively, in antigen-stimulated cells. The H(2)O(2) generation was dependent on the Src family kinase (SFK) and phosphatidylinositol-3-kinase (PI3K) activities but independent of extracellular Ca(2+), and the Fc epsilon RI beta-chain immunoreceptor tyrosine-based activation motif played an essential role. On the other hand, O(2)(*-) generation was strictly dependent on extracellular Ca(2+), but negatively regulated by the SFK and PI3K activities. Inhibition of O(2)(*-) generation resulted in increased H(2)O(2) generation and reduced SOC activity, although it had a minimal effect on endoplasmic reticulum Ca(2+) store depletion. On the contrary, inhibition of H(2)O(2) generation resulted in increased intracellular O(2)(*-) generation and augmented SOC activity. The findings suggest that O(2)(*-) and H(2)O(2), which are generated by separate signaling pathways/sources, reciprocally regulate SOC activity in mast cells. Such generations of multiple oxidant species and their distinct roles in the regulation of SOC activity may facilitate the fine tuning of Ca(2+) signaling in mast cells.

Ca2+-dependent mast cell death induced by Ag (I) via cardiolipin oxidation and ATP depletion

In genetically susceptible humans and/or experimental animals, ions of heavy metals, Hg (II), Au (III), and Ag (I) have been shown to strongly induce autoimmunity, in which mast cells have been implicated to play a role. Here, we demonstrate that Ag (I) application results in mast cell death through a unique Ca(2+)- and mitochondria-dependent pathway. As cellular susceptibilities to Ag (I) cytotoxicity varied considerably, we analyzed the cell death pathway in the low and high responding cells. In the low responding cells, long application (e.g., 20 h) of Ag (I) at concentrations (>or=30 microM) induced cell death, which was accompanied by mitochondrial membrane depolarization, cyt c release, and caspase-3/7 activation but was not prevented by selective inhibitors of caspase-3/7 and the mitochondrial permeability transition. The cell death was preceded by elevations in the cytoplasmic and mitochondrial Ca(2+) levels, and Ca(2+) responses and cell death were prevented by thiol reagents, including DTT, N-acetylcysteine, and reduced glutathione monoethyl ester. In the high responding cells, Ag (I) evoked considerable cell death by necrosis within 1 h, without inducing caspase activation, and this cell death was reduced significantly by depleting extracellular but not intracellular Ca(2+). Moreover, Ag (I) strongly induced Ca(2+)-dependent CL oxidation and intracellular ATP depletion, both of which were blocked by thiol reagents. These results suggest that Ag (I) activates thiol-dependent Ca(2+) channels, thereby promoting Ca(2+)-dependent CL oxidation, cyt c release, and ATP depletion. This necrotic cell death may play roles in Ag-induced inflammation and autoimmune disorders.

Aspirin and salicylates modulate IgE-mediated leukotriene secretion in mast cells through a dihydropyridine receptor-mediated Ca(2+) influx

Aspirin is a well-known nonsteroidal anti-inflammatory drug (NSAID) that may potentiate some acute allergies and causes adverse immunological reactions collectively referred to as aspirin intolerance. Aspirin intolerance is accompanied by increased leukotriene (LT) synthesis, and high levels of serum IgE are a risk factor for NSAID sensitivity. Here we demonstrate that aspirin modulates LTC(4) secretion in mast cells. Therapeutic levels of aspirin and salicylates (<or=0.3 mM, i.e., the concentrations observed in vivo in the use of antipyretic analgesic) increased IgE-mediated LTC(4) secretion. Aspirin-induced stimulation was accompanied by increased Ser-505 phosphorylation of cytosolic phospholipase A(2), which occurred independently of extracellular signal-regulated protein kinase-1/2 and p38 mitogen-activated protein kinase pathways. Aspirin also increased IgE-mediated Ca(2+) influx, whereas aspirin at concentrations of >or=0.3 mM dose-dependently reduced Ca(2+) store emptying and Ca(2+) release-activated Ca(2+) channel activation. Instead, aspirin facilitated a dihydropyridine receptor-mediated Ca(2+) influx, resulting in increased LTC(4) secretion. This novel action of aspirin may play roles in exacerbation of immediate allergy and aspirin intolerance.

L-type Ca2+ channels in mast cells: activation by membrane depolarization and distinct roles in regulating mediator release from store-operated Ca2+ channels

Store-operated Ca(2+) channels (SOCs) are considered to be the principal route of Ca(2+) influx in non-excitable cells. We have previously shown that in mast cells IgE+antigen (Ag) induces a dihydropyridine (DHP)-sensitive Ca(2+) influx independently of Ca(2+) store depletion. Since the DHP receptor is the alpha subunit of L-type Ca(2+) channels (LTCCs), we examined the possible role of LTCCs in mast cell activation. Mast cells exhibited substantial expression of the alpha(1C) (Ca(V)1.2) subunit mRNA and protein on their cell surface. IgE+Ag-induced Ca(2+) influx was substantially reduced by the LTCC inhibitor nifedipine, and enhanced by the LTCC activator (S)-BayK8644, whereas these agents had minimal effects on thapsigargin (TG)-induced Ca(2+) influx. These LTCC-modulating agents regulated IgE+Ag-induced cell activation but not TG-induced cell activation. Inhibition of SOCs by 2-aminoethoxydiphenyl borate reduced both degranulation and production of cytokines, including interleukin-13 and tumor necrosis factor-alpha, whereas LTCC modulation reciprocally regulated degranulation and cytokine production. IgE+Ag, but not TG, induced substantial plasma membrane depolarization, which stimulated a DHP-sensitive Ca(2+) response. Moreover, IgE+Ag-, but not TG-induced mitochondrial Ca(2+) increase was regulated by LTCC modulators. Finally, gene silencing analyses using small interfering RNA revealed that the alpha(1C) (Ca(V)1.2) LTCC mediated the pharmacological effects of the LTCC-modulating agents. These results demonstrate that mast cells express LTCCs, which becomes activated by membrane depolarization to regulate cytosolic and mitochondrial Ca(2+), thereby controlling mast cell activation in a distinct manner from SOCs.

Positive and negative regulation of high affinity IgE receptor signaling by Src homology region 2 domain-containing phosphatase 1

Src homology region 2 domain-containing phosphatase 1 (SHP-1), a cytoplasmic protein tyrosine phosphatase, plays an important role for the regulation of signaling from various hematopoietic cell receptors. Although SHP-1 is shown to be a negative signal modulator in mast cells, its precise molecular mechanisms are not well defined. To elucidate how SHP-1 regulates mast cell signaling, we established bone marrow-derived mast cells from SHP-1-deficient motheaten and wild-type mice and analyzed downstream signals induced by cross-linking of high affinity IgE receptor, Fc epsilonRI. Upon Fc epsilonRI ligation, motheaten-derived bone marrow-derived mast cells showed enhanced tyrosine phosphorylation of Src homology region 2 domain-containing leukocyte protein of 76 kDa (SLP-76) and linker for activation of T cells, activation of mitogen-activated protein kinases and gene transcription and production of cytokine. Because the activity of Syk, responsible for the phosphorylation of SLP-76 and linker for activation of T cells, is comparable irrespective of SHP-1, both molecules might be substrates of SHP-1 in mast cells. Interestingly, the absence of SHP-1 expression disrupted the association between SLP-76 and phospholipase Cgamma, which resulted in the decreased phospholipase Cgamma phosphorylation, calcium mobilization, and degranulation. Collectively, these results suggest that SHP-1 regulates Fc epsilonRI-induced downstream signaling events both negatively and positively by functioning as a protein tyrosine phosphatase and as an adaptor protein contributing to the formation of signaling complex, respectively.

Extracellular superoxide released from mitochondria mediates mast cell death by advanced glycation end products

Advanced glycation end products (AGEs) accumulate during aging and to higher extents under pathological conditions such as diabetes. Since we previously showed that mast cells expressed the AGE-binding protein, receptor for AGEs (RAGE) on their cell surface, we examined whether AGE affected mast cell survival. Herein, we demonstrate that mast cells undergo apoptosis in response to AGE. Glycated albumin (GA), an AGE, but not stimulation with the high-affinity IgE receptor (FcepsilonRI), can induce mast cell death, as measured by annexin V/propidium iodide double-staining. GA (> or =0.1 mg/ml) exhibited this pro-apoptotic activity in a concentration-dependent manner. GA and FcepsilonRI stimulation increased the cytosolic Ca(2+) levels to a similar extent, whereas GA, but not FcepsilonRI stimulation, caused mitochondrial Ca(2+) overload and membrane potential collapse, resulting in mitochondrial integrity disruption, cytochrome c release and caspase-3/7 activation. In addition, GA, but not FcepsilonRI stimulation, induced extracellular release of superoxide from mitochondria, and this release played a key role in the disruption of Ca(2+) homeostasis. Knockdown of RAGE expression using small interfering RNA abolished GA-induced apoptosis, mitochondrial Ca(2+) overload, and superoxide release, demonstrating that RAGE mediates the GA-induced mitochondrial death pathway. AGE-induced mast cell apoptosis may contribute to the immunocompromised and inflammatory conditions.

Na-Tosyl-Phe chloromethyl ketone prevents granule movement and mast cell synergistic degranulation elicited by costimulation of antigen and adenosine

Adenosine has been shown to enhance mast cell degranulation when added together with an antigen. Such augmentation of mast cell activation is relevant to exacerbation of allergic asthma symptoms. Na-Tosyl-Phe chloromethyl ketone (TPCK) is a chymotrypsine-like chymase inhibitor, which has anti-inflammatory properties. In this study, we investigated the effects of TPCK on mast cell synergistic degranulation induced by antigen and adenosine. Here, we report that TPCK almost completely suppressed enhanced degranulation by inhibiting granule movement. Consistent with this, intraperitoneal administration of TPCK resulted in significant amelioration of passive cutaneous anaphylaxis in mice. Furthermore, we demonstrated that TPCK completely inhibited Thr308 phosphorylation of protein kinase B in mast cells stimulated with antigen and adenosine. These results provide a novel action of TPCK for the prevention of mast cell degranulation induced by antigen and adenosine.

Galectin-3 but not galectin-1 induces mast cell death by oxidative stress and mitochondrial permeability transition

Galectin-1 and galectin-3 are the most ubiquitously expressed members of the galectin family and more importantly, these two molecules are shown to have opposite effects on pro-inflammatory responses and/or apoptosis depending on the cell type. Herein, we demonstrate for the first time that galectin-3 induces mast cell apoptosis. Mast cells expressed substantial levels of galectin-3 and galectin-1 and to a lesser extent the receptor for advanced glycation end products (RAGE) on their surfaces. Treatment of cells with galectin-3 at concentrations of > or =100 nM for 18-44 h resulted in cell death by apoptosis. Galectin-3-induced apoptosis was completely prevented by lactose, neutralizing antibody to RAGE, and the caspase-3 inhibitor z-DEVD-fmk. Galectin-3-induced apoptosis was also completely abolished by dithiothreitol and superoxide dismutase, but not inhibited by catalase. Moreover, galectin-3 but not galectin-1 induced the release of superoxide, which was blocked by lactose, anti-RAGE, and dithiothreitol. Finally, galectin-3-induced apoptosis was blocked by bongkrekic acid, an antagonist of the mitochondrial permeability transition pore (PTP), while atractyloside, an agonist of the PTP, greatly facilitated galectin-1-induced apoptosis. These data suggest that galectin-3 induces oxidative stress, PTP opening, and the caspase-dependent death pathway by binding to putative surface receptors including RAGE via the carbohydrate recognition domain.

Reactive oxygen species produced up- or downstream of calcium influx regulate proinflammatory mediator release from mast cells: role of NADPH oxidase and mitochondria

Earlier studies have demonstrated that mast cells produce reactive oxygen species (ROS), which play a role in regulating Ca(2+) influx, while in other cell types ROS are produced in a Ca(2+)-dependent manner. We sought to determine whether ROS are produced downstream of the extracellular Ca(2+) entry in mast cells. Thapsigargin (TG), a receptor-independent agonist, could evoke a robust burst of intracellular ROS. However, this response was distinct from the antigen-induced burst of ROS with respect to time course and dependence on Ca(2+) and phosphatidylinositol-3-kinase (PI3K). The antigen-induced ROS generation occurred immediately, while the TG-induced ROS generation occurred with a significant lag time (~2 min). Antigen but not TG caused extracellular release of superoxide (O(2)(*-))/hydrogen peroxide (H(2)O(2)), which was blocked by diphenyleneiodonium, apocynin, and wortmannin. A capacitative Ca(2+) entry resulted in the generation of O(2)(*-) in the mitochondria in a PI3K-independent manner. Blockade of ROS generation inhibited TG-induced mediator release. Finally, when used together, antigen and TG evoked the release of leukotriene C(4), tumor necrosis factor-alpha, and interleukin-13 as well as ROS generation synergistically. These results suggest that ROS produced upstream of Ca(2+) influx by NADPH oxidase and downstream of Ca(2+) influx by the mitochondria regulate the proinflammatory response of mast cells.

Silver activates mast cells through reactive oxygen species production and a thiol-sensitive store-independent Ca2+ influx

In genetically susceptible human and/or experimental animals, heavy metals such as mercury, gold, and silver have been shown to highly induce adverse immunological reactions such as allergy and autoimmunity, in which mast cell degranulation is implicated as playing a role. We previously reported that silver activates mast cells and induces Ca2+ influx without stimulating intracellular signaling events required for activation of store-operated Ca2+ channels (SOCs). The purpose of the present study was to elucidate the possible involvement of reactive oxygen species (ROS) in the biological effects of silver. Analysis using oxidant-sensitive fluorescent probes such as dichlorodihydrofluorescein and scopoletin, as well as MCLA-amplified chemiluminescence, showed that silver induced intracellular production and/or extracellular release of ROS. Silver induced mast cell degranulation in a Ca2+ -dependent manner. Unlike IgE antigen, silver-induced Ca2+ influx was not affected by depletion of internal Ca2+ stores. Instead, the metal-induced Ca2+ influx was abolished and reversed by the cell-impermeant thiol-reducing agent dithiothreitol, indicating the regulation by oxidation of vicinal thiols on the cell surface. Consistent with this view, Ca2+ influx was blocked by the glutathione peroxidase mimetic ebselen (2-phenyl-1,2-benzisoselenazol-3(2H)-one) and the superoxide dismutase mimetic manganese(III) tetrakis 4-(benzoic acid)porphyrin, but not by exogenously added catalase or superoxide dismutase. These findings indicate that silver evokes the release of ROS and oxidation of thiols critical for the activation of a Ca2+ channel other than SOC. Such a novel ROS-dependent pathway might play a role in mast cell degranulation in metal-induced allergic and autoimmune reactions.

Mitochondrial Ca2+ flux is a critical determinant of the Ca2+ dependence of mast cell degranulation

An increase in intracellular Ca2+ ([Ca2+]i) is necessary for mast cell exocytosis, but there is controversy over the requirement for Ca2+ in the extracellular medium. Here, we demonstrate that mitochondrial function is a critical determinant of Ca2+ dependence. In the presence of extracellular Ca2+, mitochondrial metabolic inhibitors, including rotenone, antimycin A, and the protonophore carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP), significantly reduced degranulation induced by immunoglobulin E (IgE) antigen or by thapsigargin, as measured by beta-hexosaminidase release. In the absence of extracellular Ca2+; however, antimycin A and FCCP, but not rotenone, enhanced, rather than reduced, degranulation to a maximum of 76% of that observed in the presence of extracellular Ca2+. This enhancement of extracellular, Ca2+-independent degranulation was concomitant with a rapid collapse of the mitochondrial transmembrane potential. Mitochondrial depolarization did not enhance degranulation induced by thapsigargin, irrespective of the presence or absence of extracellular Ca2+. IgE antigen was more effective than thapsigargin as an inducer of [Ca2+]i release, and mitochondrial depolarization augmented IgE-mediated but not thapsigargin-induced Ca2+ store release and mitochondrial Ca2+ ([Ca2+]m) release. Finally, atractyloside and bongkrekic acid [an agonist and an antagonist, respectively, of the mitochondrial permeability transition pore (mPTP)], respectively, augmented and reduced IgE-mediated Ca2+ store release, [Ca2+]m release, and/or degranulation, whereas they had no effects on thapsigargin-induced Ca2+ store release. These data suggest that the mPTP is involved in the regulation of Ca2+ signaling, thereby affecting the mode of mast cell degranulation. This finding may shed light on a new role for mitochondria in the regulation of mast cell activation.

Fungal metabolite gliotoxin blocks mast cell activation by a calcium- and superoxide-dependent mechanism: implications for immunosuppressive activities

Fungal secondary metabolites such as gliotoxin, an epipolythiodioxopiperazine toxin produced by pathogenic fungi like Candida and Aspergillus, possess immunosuppressive activities and have been thought to contribute to pathology of fungal infections in animals and humans. Since recent studies show that mast cell plays a crucial role in the front of host defense, we examined whether fungal secondary metabolites affected mast cell activation. We found that gliotoxin had suppressive effects on FcepsilonRI-dependent or -independent mast cell activation, including degranulation, leukotriene C4 secretion, and TNF-alpha and IL-13 production. Gliotoxin also suppressed intracellular Ca2+ rise through store-operated Ca2+ channels with a minimal effect on depletion of internal Ca2+ stores. Finally, gliotoxin induced intracellular production of superoxide possibly through a thiol redox cycling, which appeared to mediate suppressive effects on mast cell activation. These findings suggest that suppression of mast cell activation might contribute to the establishment of infections with gliotoxin-producing fungi.

Role of oxidants in mast cell activation

Reactive oxygen species (ROS), such as superoxide, hydrogen peroxide (H2O2), and hydroxyl radical, have for a long time been considered as accidental by-products of respiratory energy production in mitochondria and as being useless and rather deleterious to biological systems. Contrary to such a classical view, accumulating evidence indicates that upon stimulation of divergent receptor systems, ROS are intentionally produced and even required for appropriate signal transduction and biological responses. Work by our group and that of others have shown that stimulation of mast cells through the high-affinity IgE receptor (FcepsilonRI) induces the production of ROS such as superoxide and H2O2 possibly by the phagocyte NADPH oxidase homologue and that these endogenously produced oxidants have important functions in regulation of various mast cell responses, including degranulation, leukotriene secretion, and cytokine production. Subsequent studies have defined particular biochemical pathways that can be targeted by ROS and/or cellular redox balance. More recent research reveals that ROS may also play an important role in mast cell activation by divergent allergy-relevant environmental substances, for instance heavy metals and polycyclic aromatic hydrocarbons. This review summarizes current knowledge on the role of endogenous oxidants in mast cell activation.

Dapsone suppresses human neutrophil superoxide production and elastase release in a calcium-dependent manner

BACKGROUND

Dapsone (4,4'-diaminodiphenyl sulphone) is a powerful therapeutic tool in many skin diseases including neutrophilic dermatoses. The drug has an outstanding therapeutic efficacy against many skin diseases characterized by neutrophil-rich infiltrates; however, mechanisms of its action are poorly understood.

OBJECTIVES

We investigated the effects of dapsone on respiratory and secretory functions of human neutrophils triggered by the chemotactic peptide N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP), the physiological agonist C5a, and phorbol myristate acetate (PMA).

METHODS

Human neutrophils were isolated from venous blood obtained from healthy donors. We detected extracellular production of superoxide (O(2) (-)) by cytochrome C reduction assay, and intracellular production of O(2) (-) by flow cytometry. Neutrophil elastase release was measured by the cleavage of the specific elastase substrate N-methoxysuccinyl-Ala-Ala-Pro-Val-p-nitroanilide. Measurement of cytosolic free calcium concentration was performed using the calcium-reactive fluorescence probe, Fluo-3.

RESULTS

Dapsone suppressed intra- and extracellular production of O(2) (-) and elastase release triggered by fMLP and C5a, but not by PMA. Both fMLP and C5a signalled the above pathways by inducing calcium influx, but PMA functions bypassed calcium influx. Dapsone was capable of antagonizing the induction of calcium influx.

CONCLUSIONS

These findings suggest that one mechanism of the anti-inflammatory action of dapsone is inhibition of calcium-dependent functions of neutrophils including release of tissue-damaging oxidants and proteases in the affected skin.

Role of the FcepsilonRI beta-chain ITAM as a signal regulator for mast cell activation with monomeric IgE

The beta-chain of the high-affinity receptor for IgE (FcepsilonRI) plays a crucial role for amplification of the intracellular signaling in mast cells upon FcepsilonRI cross-linking by IgE*antigen complexes (IgE*Ag). Some monomeric IgE as well as IgE*Ag stimulate FcepsilonRI-signaling pathways, leading to cell activation, whereas the biological functions of the beta-chain in the monomeric IgE-mediated mast cell signaling and responses are largely unknown. In the present study, FcepsilonRI is reconstituted with either wild-type beta-chain or mutated beta-chain immunoreceptor tyrosine-based activation motif (ITAM) employing retrovirus-mediated gene transfer into the FcepsilonRI beta-chain-/- mast cells. We demonstrated that the transfectants with mutated beta-chain ITAM stimulated with monomeric IgE sufficiently produce inflammatory cytokines, although degranulation, intracellular Ca(2+) mobilization and leukotriene C(4) synthesis are significantly reduced. Furthermore, analyses of molecular mechanisms of the signaling revealed that the expression of cytokine genes and activation of extracellular signal-regulated kinase 1/2 and protein kinase C were significantly delayed in the beta-chain ITAM mutant cells stimulated with monomeric IgE, suggesting that the beta-chain ITAM regulates kinetics of gene transcriptions and signaling pathways for cytokine production. These findings for the first time revealed the unique functions of the beta-chain ITAM in both chemical mediator release and cytokine production of mast cells upon monomeric IgE stimulation.

Fc epsilon RI signaling of mast cells activates intracellular production of hydrogen peroxide: role in the regulation of calcium signals

Earlier studies, including our own, revealed that activation of mast cells is accompanied by production of reactive oxygen species (ROS) that help to mediate the release of the inflammatory mediators, including histamine and eicosanoids. However, little is known about the mechanisms of ROS production, including the species of oxidants produced. In this study we show that in both the RBL-2H3 mast cell line and bone marrow-derived mast cells, FcepsilonRI cross-linking stimulates intracellular oxidative burst, including hydrogen peroxide (H(2)O(2)) production, as defined with the oxidant-sensitive dyes dichlorofluorescein and scopoletin and the selective scavenger ebselen (2-phenyl-1,2-benzisoselenazol-3(2H)-one). The oxidative burst was observed immediately after stimulation and was most likely due to an NAD(P)H oxidase. Experiments using selective pharmacological inhibitors demonstrated that activation of tyrosine kinases and phosphatidylinositol-3-kinase is required for induction of the oxidative burst. Blockade of the oxidative burst by diphenyleneiodonium impaired the release of preformed granular mediators, such as histamine and beta-hexosaminidase, and the secretion of newly synthesized leukotriene C(4), whereas selective scavenging H(2)O(2) by ebselen impaired leukotriene C(4) secretion, but not degranulation. Sustained elevation of cytosolic calcium through store-operated calcium entry was totally abolished when ROS production was blocked. In contrast, selective depletion of H(2)O(2) caused a considerable decrease and delay of the calcium response. Finally, tyrosine phosphorylation of phospholipase Cgamma and the linker for activation of T cells, an event required for calcium influx, was suppressed by diphenyleneiodonium and ebselen. These studies demonstrate that activation of the intracellular oxidative burst is an important regulatory mechanism of mast cell responses.

Silver Activates Calcium Signals in Rat Basophilic Leukemia-2H3 Mast Cells by a Mechanism That Differs from the FcεRI-Activated Response

We previously showed that silver stimulates degranulation and leukotriene (LT) C(4) production in rat basophilic leukemia mast cells and now show that silver induces these events by a mechanism that differs from the FcepsilonRI-mediated response. In common with FcepsilonRI cross-linking, silver induced tyrosine phosphorylation of extracellular signal-regulated kinases and furthermore, PD98059, a specific inhibitor of extracellular signal-regulated kinase kinase dose-dependently inhibited the silver-induced LTC(4) production. In contrast to FcepsilonRI cross-linking, silver had no effect on the production of IL-4 and TNF-alpha, indicating that different mechanisms are involved in the activation by these two stimuli. In line with this, silver had no or only marginal effect on the tyrosine phosphorylation of FcepsilonRIbeta, Lyn, Syk, and linker for activation of T cells, the early and crucial events in FcepsilonRI signaling. Silver induced calcium signals that were involved in the metal-induced degranulation, but not LTC(4) production. Unlike Ag, the silver-induced calcium signals were resistant to the depletion of thapsigargin-sensitive calcium stores and the inhibition of tyrosine kinases and phospholipase Cgamma. These findings indicate that silver activates mast cells by bypassing the early signaling events required for the induction of calcium influx. Our data strongly suggest the existence of an alternative pathway bypassing the early signaling events in mast cell activation and indicate that silver may be useful for analyses of such alternative mechanisms.

Blockade of superoxide generation prevents high-affinity immunoglobulin E receptor-mediated release of allergic mediators by rat mast cell line and human basophils

BACKGROUND

Previous studies have shown that rat peritoneal mast cells and mast cell model rat basophilic leukaemia (RBL-2H3) cells generate intracellular reactive oxygen species (ROS) in response to antigen challenge. However, the physiological significance of the burst of ROS is poorly understood.

OBJECTIVE

The present study was undertaken to investigate the role of superoxide anion in mediator release in rat and human cell systems.

METHODS

RBL-2H3 cells were directly stimulated with anti-rat FcepsilonRI alpha-subunit monoclonal antibody (mAb). For the analysis of human cell system, leucocytes were isolated by dextran sedimentation from healthy volunteers or from patients, and challenged either with anti-human FcepsilonRI mAb or with the relevant antigens. Superoxide generation was determined by chemiluminescence-based methods. The releases of histamine and leukotrienes (LT)s were determined by enzyme-linked immunosorben assay (ELISA).

RESULTS

Cross-linking of FcepsilonRI on RBL-2H3 cells or on human leucocytes from healthy donors by the anti-FcepsilonRI mAb resulted in a rapid generation of superoxide anion, as determined by chemiluminescence using superoxide-specific probes. Similarly, leucocytes from patients generated superoxide anion in response to the challenge with the relevant allergen but not with the irrelevant allergen. Furthermore, diphenyleneiodonium (DPI), a well-known inhibitor of flavoenzymes suppressed the superoxide generation and the release of histamine and LTC4 induced by the anti-FcepsilonRI mAb or by allergen in parallel.

CONCLUSION

These results indicate that both RBL-2H3 cells and human basophils generate superoxide anion upon FcepsilonRI cross-linking either by antibody or by allergen challenge and that blockade of the generation prevents the release of allergic mediators. The findings strongly support the role of superoxide generation in the activation of mast cells and basophils under both physiological and pathological conditions. The findings suggest that drugs regulating the superoxide generation have potential therapeutic use for allergic disorders.

Exposure of RBL-2H3 mast cells to Ag(+) induces cell degranulation and mediator release

There is a growing need to understand the impact of environmental sulfhydryl group-reactive heavy metals on the immune system. Here we show that Ag(+) induces mast cell degranulation, as does the aggregation of the high affinity immunoglobulin E receptor (FcepsilonRI). Micromolar quantities of Ag(+) specifically induced degranulation of mast cell model rat basophilic leukemia (RBL-2H3) cells without showing cytotoxicity. The Ag(+)-mediated degranulation could be observed as rapidly as 5 min after the addition of the ions. Ag(+) also induced a rapid change in tyrosine phosphorylation of multiple cellular proteins including the focal adhesion kinase but not Syk kinase. The Syk-selective inhibitor piceatannol and the Src family-selective tyrosine kinase inhibitor PP1 dose-dependently inhibited FcepsilonRI-mediated degranulation, whereas neither compound inhibited the Ag(+)-mediated degranulation. Furthermore, likewise FcepsilonRI aggregation, Ag(+) also induced leukotriene secretion. These results show that Ag(+) activates RBL-2H3 mast cells through a tyrosine phosphorylation-linked mechanism, which is distinct from that involved in FcepsilonRI-mediated activation.

Diphenyleneiodonium prevents reactive oxygen species generation, tyrosine phosphorylation, and histamine release in RBL-2H3 mast cells

Mast cells play a central role in immediate allergic reactions mediated by immunoglobulin E. It has recently been reported that mast cells generate intracellular reactive oxygen species (ROS) in response to stimulation with divergent physiologically relevant stimulants. However, the physiological role of ROS is poorly understood. Here we demonstrate that mast cell model rat basophilic leukemia (RBL-2H3) cells generate ROS in response to antigen and the calcium-ionophore A23187 via activation of diphenyleneiodonuim (DPI)-sensitive enzyme and that blockade of ROS generation by DPI suppresses histamine release induced by either stimulant. Increased tyrosine phosphorylation of pp125(FAK) and a 77-kDa protein coprecipitating specifically with the kinase occurred in parallel with the secretion, and blockade of ROS generation by DPI also suppressed the tyrosine phosphorylation of both proteins. These findings suggest that ROS generated by a flavoenzyme-dependent mechanism may be involved in histamine release through the pp125(FAK) pathway.

Epigallocatechin gallate inhibits histamine release from rat basophilic leukemia (RBL-2H3) cells: role of tyrosine phosphorylation pathway

Some tea polyphenolic compounds including (-)-epigallocatechin gallate (EGCG) have been shown to inhibit histamine release from mast cells through poorly understood mechanisms. By using a mast cell model rat basophilic leukemia (RBL-2H3) cells we explored the mechanism of the inhibition. EGCG inhibited histamine release from RBL-2H3 cells in response to antigen or the calcium-ionophore A23187, while (-)-epicatechin (EC) had little effect. Increased tyrosine phosphorylation of several proteins including approximately 120 kDa proteins occurred in parallel with the secretion induced by either stimulation. EGCG also inhibited tyrosine phosphorylation of the approximately 120-kDa proteins induced by either stimulation, whereas EC did not. The tyrosine kinase-specific inhibitor piceatannol inhibited the secretion and tyrosine phosphorylation of these proteins induced by either stimulation also. Further analysis showed that the focal adhesion kinase pp125(FAK) was one of the approximately 120-kDa proteins. These findings suggest that EGCG prevents histamine release from mast cells mainly by inhibiting tyrosine phosphorylation of proteins including pp125(FAK).