X-linked inhibitor of apoptosis protein (XIAP) mediates cancer cell motility via Rho GDP dissociation inhibitor (RhoGDI)-dependent regulation of the cytoskeleton

SMAD7 Sustains XIAP Expression and Migration of Colorectal Carcinoma Cells

The reorganization of the cell cytoskeleton and changes in the content of cell adhesion molecules are crucial during the metastatic spread of tumor cells. Colorectal cancer (CRC) cells express high SMAD7, a protein involved in the control of CRC cell growth. In the present study, we evaluated whether SMAD7 regulates the cytoskeleton reorganization and dynamics in CRC. Knockdown of SMAD7 with a specific antisense oligonucleotide (AS) in HCT116 and DLD1, two human CRC cell lines, reduced the migration rate and the content of F-ACTIN filaments. A gene array, real-time PCR, and Western blotting of SMAD7 AS-treated cells showed a marked down-regulation of the X-linked inhibitor of apoptosis protein (XIAP), a member of the inhibitor of apoptosis family, which has been implicated in cancer cell migration. IL-6 and IL-22, two cytokines that activate STAT3, enhanced XIAP in cancer cells, and such induction was attenuated in SMAD7-deficient cells. Finally, in human CRC, SMAD7 mRNA correlated with XIAP expression. Our data show that SMAD7 positively regulates XIAP expression and migration of CRC cells, and suggest a mechanism by which SMAD7 controls the architecture components of the CRC cell cytoskeleton.

Anastasis enhances metastasis and chemoresistance of colorectal cancer cells through upregulating cIAP2/NFκB signaling

Chemotherapy is a common strategy to treat cancer. However, acquired resistance and metastasis are the major obstacles to successful treatment. Anastasis is a process by which cells survive executioner caspase activation when facing apoptotic stress. Here we demonstrate that colorectal cancer cells can undergo anastasis after transient exposure to chemotherapeutic drugs. Using a lineage tracing system to label and isolate cells that have experienced executioner caspase activation in response to drug treatment, we show that anastasis grants colorectal cancer cells enhanced migration, metastasis, and chemoresistance. Mechanistically, treatment with chemotherapeutic drugs induces upregulated expression of cIAP2 and activation of NFκB, which are required for cells to survive executioner caspase activation. The elevated cIAP2/NFκB signaling persists in anastatic cancer cells to promote migration and chemoresistance. Our study unveils that cIAP2/NFκB-dependent anastasis promotes acquired resistance and metastasis after chemotherapy.

Combined inhibition of XIAP and autophagy induces apoptosis and differentiation in acute myeloid leukaemia

Perturbations in autophagy, apoptosis and differentiation have greatly affected the progression and therapy of acute myeloid leukaemia (AML). The role of X-linked inhibitor of apoptosis (XIAP)-related autophagy remains unclear in AML therapeutics. Here, we found that XIAP was highly expressed and associated with poor overall survival in patients with AML. Furthermore, pharmacologic inhibition of XIAP using birinapant or XIAP knockdown via siRNA impaired the proliferation and clonogenic capacity by inducing autophagy and apoptosis in AML cells. Intriguingly, birinapant-induced cell death was aggravated in combination with ATG5 siRNA or an autophagy inhibitor spautin-1, suggesting that autophagy may be a pro-survival signalling. Spautin-1 further enhanced the ROS level and myeloid differentiation in THP-1 cells treated with birinapant. The mechanism analysis showed that XIAP interacted with MDM2 and p53, and XIAP inhibition notably downregulated p53, substantially increased the AMPKα1 phosphorylation and downregulated the mTOR phosphorylation. Combined treatment using birinapant and chloroquine significantly retarded AML progression in both a subcutaneous xenograft model injected with HEL cells and an orthotopic xenograft model injected intravenously with C1498 cells. Collectively, our data suggested that XIAP inhibition can induce autophagy, apoptosis and differentiation, and combined inhibition of XIAP and autophagy may be a promising therapeutic strategy for AML.

Induction of RAC1 protein translation and MKK7/JNK-dependent autophagy through dicer/miR-145/SOX2/miR-365a axis contributes to isorhapontigenin (ISO) inhibition of human bladder cancer invasion

Although our previous studies have identified that isorhapontigenin (ISO) is able to initiate autophagy in human bladder cancer (BC) cells by activating JNK/C-Jun/SESN2 axis and possesses an inhibitory effect on BC cell growth, association of autophagy directly with inhibition of BC invasion has never been explored. Also, upstream cascade responsible for ISO activating JNK remains unknown. Thus, we explored both important questions in the current study and discovered that ISO treatment initiated RAC1 protein translation, and its downstream kinase MKK7/JNK phosphorylation/activation, and in turn promoted autophagic responses in human BC cells. Inhibition of autophagy abolished ISO inhibition of BC invasion, revealing that autophagy inhibition was crucial for ISO inhibition of BC invasion. Consistently, knockout of RAC1 also attenuated induction of autophagy and inhibition of BC invasion by ISO treatment. Mechanistic studies showed that upregulation of RAC1 translation was due to ISO inhibition of miR-365a transcription, which reduced miR-365a binding to the 3'-UTR of RAC1 mRNA. Further study indicated that inhibition of miR-365a transcription was caused by downregulation of its transcription factor SOX2, while ISO-promoted Dicer protein translation increased miR-145 maturation, and consequently downregulating SOX2 expression. These findings not only provide a novel insight into the understanding association of autophagy induction with BC invasion inhibition by ISO, but also identify an upstream regulatory cascade, Dicer/miR145/SOX2/miR365a/RAC1, leading to MKK7/JNKs activation and autophagy induction.

Upregulation of XIAP promotes lung adenocarcinoma brain metastasis by modulating ceRNA network

Dysregulation of XIAP has been shown to affect the progression of a variety of cancers, including lung adenocarcinoma (LUAD). However, the function and mechanisms of XIAP in lung adenocarcinoma with brain metastasis (LUAD-BM) remains poorly understood. In this study, we analyzed the differential mRNA of 58 lung adenocarcinomas samples and 28 lung adenocarcinomas with brain metastases in GEO database. 191 differentially expressed mRNAs were significantly associated with immune response, the proliferation of the immune cell, cell-cell adhesion. Subsequent analyzed by lasso and SVM found that XIAP was significantly elevated in LUAD-BM and significantly associated with LUAD grade and metastasis. Then we constructed a molecular regulatory network of ncRNA-miRNA-mRNA ceRNA by Cystoscope based on the correlation obtained from Starbase. It was found that SBF2-AS1 or RUNDC3A-AS1, has-miR-338-3p and XIAP may have a regulatory relationship. Furthermore, we also initially found that XIAP was closely correlation with T cells, B cells, Mast cells, macrophages, and dendritic cells. In conclusion, we found that XIAP was significantly higher expressed in LUAD-BM compared with LUAD without brain metastasis, suggesting that XIAP may play an important role in the future prediction and clinical treatment of LUAD-BM.

Increased migration and motility in XIAP-null cells mediated by the C-RAF protein kinase

The product encoded by the X-linked inhibitor of apoptosis (XIAP) gene is a multi-functional protein which not only controls caspase-dependent cell death, but also participates in inflammatory signalling, copper homeostasis, response to hypoxia and control of cell migration. Deregulation of XIAP, either by elevated expression or inherited genetic deletion, is associated with several human disease states. Reconciling XIAP-dependent signalling pathways with its role in disease progression is essential to understand how XIAP promotes the progression of human pathologies. In this study we have created a panel of genetically modified XIAP-null cell lines using TALENs and CRISPR/Cas9 to investigate the functional outcome of XIAP deletion. Surprisingly, in our genetically modified cells XIAP deletion had no effect on programmed cell death, but instead the primary phenotype we observed was a profound increase in cell migration rates. Furthermore, we found that XIAP-dependent suppression of cell migration was dependent on XIAPdependent control of C-RAF levels, a protein kinase which controls cell signalling pathways that regulate the cytoskeleton. These results suggest that XIAP is not necessary for control of the apoptotic signalling cascade, however it does have a critical role in controlling cell migration and motility that cannot be compensated for in XIAP-knockout cells.

Electrostatic Forces Mediate the Specificity of RHO GTPase-GDI Interactions

Three decades of research have documented the spatiotemporal dynamics of RHO family GTPase membrane extraction regulated by guanine nucleotide dissociation inhibitors (GDIs), but the interplay of the kinetic mechanism and structural specificity of these interactions is as yet unresolved. To address this, we reconstituted the GDI-controlled spatial segregation of geranylgeranylated RHO protein RAC1 in vitro. Various biochemical and biophysical measurements provided unprecedented mechanistic details for GDI function with respect to RHO protein dynamics. We determined that membrane extraction of RHO GTPases by GDI occurs via a 3-step mechanism: (1) GDI non-specifically associates with the switch regions of the RHO GTPases; (2) an electrostatic switch determines the interaction specificity between the C-terminal polybasic region of RHO GTPases and two distinct negatively-charged clusters of GDI1; (3) a non-specific displacement of geranylgeranyl moiety from the membrane sequesters it into a hydrophobic cleft, effectively shielding it from the aqueous milieu. This study substantially extends the model for the mechanism of GDI-regulated RHO GTPase extraction from the membrane, and could have implications for clinical studies and drug development.

X-linked inhibitor of apoptosis protein (XIAP) inhibition in systemic sclerosis (SSc)

OBJECTIVE

X-linked inhibitor of apoptosis protein (XIAP) is a multifunctional protein with important functions in apoptosis, cellular differentiation and cytoskeletal organisation and is emerging as potential target for the treatment of various cancers. The aim of the current study was to investigate the role of XIAP in the pathogenesis of systemic sclerosis (SSc).

METHODS

The expression of XIAP in human skin samples of patients with SSc and chronic graft versus host disease (cGvHD) and healthy individuals was analysed by quantitative PCR, immunofluorescence (IF) and western blot. XIAP was inactivated by siRNA-mediated knockdown and pharmacological inhibition. The effects of XIAP inactivation were analysed in cultured fibroblasts and in the fibrosis models bleomycin-induced and topoisomerase-I-(topoI)-induced fibrosis and in Wnt10b-transgenic mice.

RESULTS

The expression of XIAP, but not of other inhibitor of apoptosis protein family members, was increased in fibroblasts in SSc and sclerodermatous cGvHD. Transforming growth factor beta (TGF-β) induced the expression of XIAP in a SMAD3-dependent manner. Inactivation of XIAP reduced WNT-induced fibroblast activation and collagen release. Inhibition of XIAP also ameliorated fibrosis induced by bleomycin, topoI and overexpression of Wnt10b in well-tolerated doses. The profibrotic effects of XIAP were mediated via WNT/β-catenin signalling. Inactivation of XIAP reduces binding of β-catenin to TCF to in a TLE-dependent manner to block WNT/β-catenin-dependent transcription.

CONCLUSIONS

Our data characterise XIAP as a novel link between two core pathways of fibrosis. XIAP is overexpressed in SSc and cGvHD in a TGF-β/SMAD3-dependent manner and in turn amplifies the profibrotic effects of WNT/β-catenin signalling on fibroblasts via transducin-like enhancer of split 3. Targeted inactivation of XIAP inhibits the aberrant activation of fibroblasts in murine models of SSc.

Silencing of METTL3 effectively hinders invasion and metastasis of prostate cancer cells

Background: Since primary prostate cancer (PCa) can advance to the life-threatening metastatic PCa, exploring the molecular mechanisms underlying PCa metastasis is crucial for developing the novel targeted preventive strategies for decreasing the mortality of PCa. RNA N6-methyladenosine (m6A) is an emerging regulatory mechanism for gene expression and its specific roles in PCa progression remains elusive. Methods: Western blotting, quantitative real-time PCR and immunohistochemical analyses were used to detect target gene expression in PCa cells in vitro and prostate tissues from patients. RNA immunoprecipitation was conducted to analyze the specific binding of mRNA to the target protein. Migration and invasion assays were used to assess the migratory capacities of cancer cells. The correlation between target gene expression and survival rate of PCa patients was analyzed based the TCGA database. Results: We found that total RNA N6-methyladenosine (m6A) modification levels were markedly upregulated in human PCa tissues due to increased expression of methyltransferase like 3 (METTL3). Further studies revealed that the migratory and invasive capacities of PCa cells were markedly suppressed upon METTL3 knockdown. Mechanistically, METTL3 mediates m6A modification of USP4 mRNA at A2696, and m6A reader protein YTHDF2 binds to and induces degradation of USP4 mRNA by recruiting RNA-binding protein HNRNPD to the mRNA. Decrease of USP4 fails to remove the ubiquitin group from ELAVL1 protein, resulting in a reduction of ELAVL1 protein. Lastly, downregulation of ELAVL1 in turn increases ARHGDIA expression, promoting migration and invasion of PCa cells. Conclusions: Our findings highlight the role of METTL3 in modulating invasion and metastasis of PCa cells, providing insight into promising therapeutic strategies for hindering PCa progressing to deadly metastases.

An Updated Review of Smac Mimetics, LCL161, Birinapant, and GDC-0152 in Cancer Treatment

Inhibitor of apoptosis proteins (IAPs) are suggested as therapeutic targets for cancer treatment. Smac/DIABLO is a natural IAP antagonist in cells; therefore, Smac mimetics have been developed for cancer treatment in the past decade. In this article, we review the anti-cancer potency and novel molecular targets of LCL161, birinapant, and GDC-0152. Preclinical studies demonstrated that Smac mimetics not only induce apoptosis but also arrest cell cycle, induce necroptosis, and induce immune storm in vitro and in vivo. The safety and tolerance of Smac mimetics are evaluated in phase 1 and phase 2 clinical trials. In addition, the combination of Smac mimetics and chemotherapeutic compounds was reported to improve anti-cancer effects. Interestingly, the novel anti-cancer molecular mechanism of action of Smac mimetics was reported in recent studies, suggesting that many unknown functions of Smac mimetics still need to be revealed. Exploring these currently unknown signaling pathways is important to provide hints for the modification and combination therapy of further compounds.

Rac1 Promotes Cell Motility by Controlling Cell Mechanics in Human Glioblastoma

The failure of existing therapies in treating human glioblastoma (GBM) mostly is due to the ability of GBM to infiltrate into healthy regions of the brain; however, the relationship between cell motility and cell mechanics is not well understood. Here, we used atomic force microscopy (AFM), live-cell imaging, and biochemical tools to study the connection between motility and mechanics in human GBM cells. It was found thatRac1 inactivation by genomic silencing and inhibition with EHT 1864 reduced cell motility, inhibited cell ruffles, and disrupted the dynamics of cytoskeleton organization and cell adhesion. These changes were correlated with abnormal localization of myosin IIa and a rapid suppression of the phosphorylation of Erk1/2. At the same time, AFM measurements of the GBM cells revealed a significant increase in cell elasticity and viscosity following Rac1 inhibition. These results indicate that mechanical properties profoundly affect cell motility and may play an important role in the infiltration of GBM. It is conceivable that the mechanical characters might be used as markers for further surgical and therapeutical interventions.

The Multiple Roles of the IAP Super-family in cancer

The Inhibitor of Apoptosis proteins (IAPs) are a family of proteins that are mainly known for their anti-apoptotic activity and ability to directly bind and inhibit caspases. Recent research has however revealed that they have extensive roles in governing numerous other cellular processes. IAPs are known to modulate ubiquitin (Ub)-dependent signaling pathways through their E3 ligase activity and influence activation of nuclear factor κB (NF-κB). In this review, we discuss the involvement of IAPs in individual hallmarks of cancer and the current status of therapies targeting these critical proteins.

X-linked inhibitor of apoptosis protein deficiency complicated with Crohn's disease-like enterocolitis and Takayasu arteritis: A case report

X-linked inhibitor of apoptosis protein (XIAP) deficiency results in monogenic inflammatory bowel disease. To date, no vasculitis associated with XIAP deficiency has been reported. A 10-year-old boy was diagnosed with Crohn's disease and he responded poorly to conventional treatment for Crohn's disease. He was dependent on corticosteroids and parenteral nutrition. To manage severe colitis, he underwent ileostomy followed by ileocolectomy for an ileo-sigmoid fistula. At the age of 15 years, he developed IgA vasculitis and at the age of 17 years, he developed refractory Takayasu arteritis (TAK), which was resistant to corticosteroid and immunosuppressive therapy. Whole-exome sequencing revealed a novel mutation of the splice acceptor site in XIAP (c.1057-1G > A) at the age of 19 years. Allogeneic hematopoietic stem cell transplantation was successful with subsequent withdrawal of intensive immunosuppressive therapy and clinical remission of both enterocolitis and TAK. This case suggests that patients with XIAP deficiency could develop intractable inflammatory disease involving the intestinal tract and blood vessels.

Novel XIAP mutation causing enhanced spontaneous apoptosis and disturbed NOD2 signalling in a patient with atypical adult-onset Crohn's disease

X-linked inhibitor of apoptosis (XIAP) is the most potent human inhibitor of apoptosis, and is also involved in NOD2-dependent NFκB and MAPK signalling cascade activation. The absence or defective function of XIAP leads to the development of a rare and severe primary immunodeficiency known as X-linked lymphoproliferative syndrome type 2 (XLP-2), which is characterized by a triad of clinical manifestations, including a high incidence of haemophagocytic lymphohistiocytosis (HLH), lymphoproliferation and inflammatory bowel disease (IBD), usually with very early onset. Here, we present a novel XIAP mutation identified in a patient with atypical adult-onset IBD complicated by relapsing HLH, splenomegaly and sarcoid-like disease. The c.266delA mutation in the XIAP gene creates a premature stop codon, and causes a severe reduction in XIAP protein expression. The mutation is also associated with impaired spontaneous and staurosporine- and PMA-induced apoptosis accompanied by significantly increased expression of pro-apoptotic genes. We also confirmed the negative impact of this particular XIAP mutation on NOD2-dependent NFκB and MAPK activation, while NOD2-independent activation was found to be unaffected. Moreover, we assume that the mutation has an impact on the overproduction of IL-12 and IFNγ, the shift towards the Th1 immune response and increased numbers of central memory and effector memory CD4+ and CD8+ T cells. All these changes contribute to immune dysregulation and the clinical manifestation of XLP-2.

Downregulation of miR-200c stabilizes XIAP mRNA and contributes to invasion and lung metastasis of bladder cancer

Our previous studies have demonstrated that XIAP promotes bladder cancer metastasis through upregulating RhoGDIβ/MMP-2 pathway. However, the molecular mechanisms leading to the XIAP upregulation was unclear. In current studies, we found that XIAP was overexpressed in human high grade BCs, high metastatic human BCs, and in mouse invasive BCs. Mechanistic studies indicated that XIAP overexpression in the highly metastatic T24T cells was due to increased mRNA stability of XIAP that was mediated by downregulated miR-200c. Moreover, the downregulated miR-200c was due to CREB inactivation, while miR-200c downregulation reduced its binding to the 3’-UTR region of XIAP mRNA. Collectively, our results demonstrate the molecular basis leading to XIAP overexpression and its crucial role in BC invasion.

XIAP Interaction with E2F1 and Sp1 via its BIR2 and BIR3 domains specific activated MMP2 to promote bladder cancer invasion

XIAP has generally been thought to function in bladder cancer. However, the potential function of structure-based function of XIAP in human BC invasion has not been well explored before. We show here that ectopic expression of the BIR domains of XIAP specifically resulted in MMP2 activation and cell invasion in XIAP-deleted BC cells, while Src was further defined as an XIAP downstream negative regulator for MMP2 activation and BC cell invasion. The inhibition of Src expression by the BIR domains was caused by attenuation of Src protein translation upon miR-203 upregulation; which was resulted from direct interaction of BIR2 and BIR3 with E2F1 and Sp1, respectively. The interaction of BIR2/BIR3 with E2F1/Sp1 unexpectedly occurred, which could be blocked by serum-induced XIAP translocation. Taken together, our studies, for the first time revealed that: (1) BIR2 and BIR3 domains of XIAP play their role in cancer cell invasion without affecting cell migration by specific activation of MMP2 in human BC cells; (2) by BIR2 interacting with E2F1 and BIR3 interacting with Sp1, XIAP initiates E2F1/Sp1 positive feedback loop-dependent transcription of miR-203, which in turn inhibits Src protein translation, further leading to MMP2-cleaved activation; (3) XIAP interaction with E2F1 and Sp1 is observed in the nucleus. Our findings provide novel insights into understanding the specific function of BIR2 and BIR3 of XIAP in BC invasion, which will be highly significant for the design/synthesis of new BIR2/BIR3-based compounds for invasive BC treatment.

X-linked inhibitor of apoptosis protein accelerates migration by inducing epithelial-mesenchymal transition through TGF-β signaling pathway in esophageal cancer cells

Background

The prognosis of esophageal cancer is still dismal because of its high probability of metastasis that is likely related to the cellular process of epithelial–mesenchymal transition (EMT). Recent studies have shown a novel role of X-linked inhibitor of apoptosis protein (XIAP) in regulating the migration process of cancer cells and, therefore, linking to progression and poor prognosis of cancer.

Methods

The expression of XIAP in esophageal squamous cell cancer (ESCC) tissues was determined by immunohistochemistry assay. Cell migration was analyzed by wound healing assay and Transwell assay. The expression of EMT markers (E-cadherin, N-cadherin and Vimentin) was revealed by immunofluorescence assay. Quantitative real‑time PCR analysis and Western blot analysis were used to detect the expression of XIAP and EMT markers as well as transforming growth factor-β (TGF-β) at mRNA and protein level, respectively.

Results

We found that the expression of XIAP closely correlated to the probability of lymphatic metastasis in patients and that ESCC patients with the high XIAP expression were associated with worse overall survival (OS). Univariate and multivariate analysis also revealed XIAP as an independent prognostic factor for overall survival in ESCC patients. In both EC9706 and TE13 cell lines, knockdown of XIAP decreased the migration of cancer cells by inhibiting EMT process through regulating the TGF-β signaling pathway, pinpointing a regulatory role of XIAP in migratory process upon TGF-β activation.

Conclusions

Taken together, our results suggest XIAP as a important prognostic and regulative factor in ESCC patients. XIAP may promote migration of esophageal cancer cells through the activation of TGF-β mediated EMT.

p85α Inactivates MMP-2 and Suppresses Bladder Cancer Invasion by Inhibiting MMP-14 Transcription and TIMP-2 Degradation

Recent studies show p85α up-regulates epidermal growth factor (EGF) receptor, thereby promoting malignant cell transformation and migration in normal mouse embryonic fibroblasts (MEFs). However, the potential role of p85α in human bladder cancer (BC) remains unknown. Here, we show that p85α is down-regulated in BC tumor tissues. Ectopic expression of p85α inhibited cell invasion, but not migration, whereas p85α knockdown promoted invasion in BC cells, revealing that p85α inhibits BC invasion. Overexpression of kinase-deficient p110 in T24 T(p85α) cells inhibited BC cell migration, but not invasion, suggesting that the inhibition of p85α on invasion is independent of PI3K activity. The effect of p85α on inhibiting BC invasion was mediated by the inactivation of MMP-2 concomitant with the up-regulation of TIMP-2 and down-regulation of MMP-14. Mechanistic studies revealed c-Jun inactivation was associated with p85α knockdown-induced MMP-14 expression, and down-regulated miR-190, leading to ATG7 mRNA degradation. This suppressed the autophagy-dependent removal of TIMP-2 in human BC cells. The present results identify a novel function of p85α and clarify the mechanisms underlying its inhibition of BC invasion, providing insight into the role of p85α in normal and cancer cells.

NFκB2 p52 stabilizes rhogdiβ mRNA by inhibiting AUF1 protein degradation via a miR-145/Sp1/USP8-dependent axis

Although overexpression of the non-canonical NFκB subunit p52 has been observed in several tumors, the function and mechanism of p52 in bladder cancer (BC) are less well understood. Here, we aimed at understanding the role and mechanism underlying p52 regulation of BC invasion. Human p52 was stably knockdown with shRNA targeting p52 in two bladder cancer cell lines (T24 and UMUC3). Two constitutively expressing constructs, p52 and p100, were stably transfected in to T24 or UMUC3, respectively. The stable transfectants were used to determine function and mechanisms responsible for p52 regulation of BC invasion. We demonstrate that p52 mediates human BC invasion. Knockdown of p52 impaired bladder cancer invasion by reduction of rhogdiβ mRNA stability and expression. Positively regulation of rhogdiβ mRNA stability was mediated by p52 promoting AUF1 protein degradation, consequently resulting in reduction of AUF1 binding to rhogdiβ mRNA. Further studies indicated that AUF1 protein degradation was mediated by upregulating USP8 transcription, which was modulated by its negative regulatory transcription factor Sp1. Moreover, we found that p52 upregulated miR-145, which directly bound to the 3'-UTR of sp1 mRNA, leading to downregulation of Sp1 protein translation. Our results reveal a comprehensive pathway that p52 acts as a positive regulator of BC invasion by initiating a novel miR-145/Sp1/USP8/AUF1/RhoGDIβ axis. These findings provide insight into the understanding of p52 in the pathology of human BC invasion and progression, which may be useful information in the development of preventive and therapeutic approaches for using p52 as a potential target.

The X-linked inhibitor of apoptosis protein (XIAP) is involved in melanoma invasion by regulating cell migration and survival

BACKGROUND

The X-linked inhibitor of apoptosis (XIAP) is a potent cellular inhibitor of apoptosis, based on its unique capability to bind and to inhibit caspases. However, XIAP is also involved in a number of additional cellular activities independent of its caspase inhibitory function. The aim of this study was to investigate whether modulation of XIAP expression affects apoptosis-independent functions of XIAP in melanoma cells, restores their sensitivity to apoptosis and/or affects their invasive and metastatic capacities.

METHODS

XIAP protein levels were analyzed by immunohistochemical staining of human tissues and by Western blotting of melanoma cell lysates. The effects of pharmacological inhibition or of XIAP down-regulation were investigated using ex-vivo and transwell invasion assays. The biological effects of XIAP down-regulation on melanoma cells were analyzed in vitro using BrdU/PI, nucleosome quantification, adhesion and migration assays. In addition, new XIAP binding partners were identified by co-immunoprecipitation followed by mass spectrometry.

RESULTS

Here we found that the expression of XIAP is increased in metastatic melanomas and in invasive melanoma-derived cell lines. We also found that the bivalent IAP antagonist birinapant significantly reduced the invasive capability of melanoma cells. This reduction could be reproduced by downregulating XIAP in melanoma cells. Furthermore, we found that the migration of melanoma cells and the formation of focal adhesions at cellular borders on fibronectin-coated surfaces were significantly reduced upon XIAP knockdown. This reduction may depend on an altered vimentin-XIAP association, since we identified vimentin as a new binding partner of XIAP. As a corollary of these molecular alterations, we found that XIAP down-regulation in melanoma cells led to a significant decrease in invasion of dermal skin equivalents.

CONCLUSION

From our data we conclude that XIAP acts as a multifunctional pro-metastatic protein in skin melanomas and, as a consequence, that XIAP may serve as a therapeutic target for these melanomas.

Negative regulation of angiogenesis by novel micro RNAs

Angiopoietin-1 (Ang-1) is a ligand of Tie-2 receptors that promotes survival, migration, and differentiation of endothelial cells (ECs). Recent studies have identified several microRNA (miRNA) families that either promote or inhibit angiogenesis. To date, the nature and functional importance of miRNAs in Ang-1-induced angiogenesis are unknown. Microarray screening of known miRNAs in human umbilical vein endothelial cells (HUVECs) revealed that the expressions of miR-103b, miR-330-5p, miR-557, miR-575, miR-1287-5p, and miR-1468-5p significantly decrease following exposure to Ang-1 for 24 h. Exposure to the angiogenesis factors angiopoietin-2 (Ang-2), vascular endothelial growth factor, fibroblast growth factor 2, and transforming growth factor β also inhibits miR-103b expression, but exerts varying effects on the other miRNAs. By overexpressing miR-103b, miR-330-5p, miR-557, miR-575, miR-1287-5p, and miR-1468-5p with selective mimics, we demonstrated that the pro-survival effects of Ang-1 are eliminated, Caspase-3 activity increases, and cell migration, proliferation, and capillary-like tube formation decreases. Conversely, transfection with selective miRNA inhibitors increases cell survival, inhibits Caspase-3 activity, and stimulates migration, proliferation and tube formation. miRNet miRNA-target gene network analyses revealed that miR-103, miR-330-5p, miR-557, miR-575, miR-1287-5p, and miR-1468-5p directly interact with 47, 95, 165, 108, 49, and 16 gene targets, respectively. Since many of these genes are positive regulators of angiogenic processes, we conclude that these miRNAs function as anti-angiogenic miRNAs and that their downregulation may be essential for Ang-1-induced angiogenesis to occur.

XIAP overexpression promotes bladder cancer invasion in vitro and lung metastasis in vivo via enhancing nucleolin-mediated Rho-GDIβ mRNA stability

Our recent studies demonstrate that X-linked inhibitor of apoptosis protein (XIAP) is essential for regulating colorectal cancer invasion. Here, we discovered that RhoGDIβ was a key XIAP downstream effector mediating bladder cancer (BC) invasion in vitro and in vivo. We found that both XIAP and RhoGDIβ expressions were consistently elevated in BCs of N-butyl-N-(4-hydroxybutyl)-nitrosamine (BBN)-treated mice in comparison to bladder tissues from vehicle-treated mice and human BCs in comparison to the paired adjacent normal bladder tissues. Knockdown of XIAP attenuated RhoGDIβ expression and reduced cancer cell invasion, whereas RhoGDIβ expression was attenuated in BBN-treated urothelium of RING-deletion knockin mice. Mechanistically, XIAP stabilized RhoGDIβ mRNA by its positively regulating nucleolin mRNA stability via Erks-dependent manner. Moreover, ectopic expression of GFP-RhoGDIβ in T24T(shXIAP) cells restored its lung metastasis in nude mice. Our results demonstrate that XIAP-regulated Erks/nucleolin/RhoGDIβ axis promoted BC invasion and lung metastasis.

Overcoming chemotherapy drug resistance by targeting inhibitors of apoptosis proteins (IAPs)

Inhibitors of apoptosis (IAPs) are a family of proteins that play a significant role in the control of programmed cell death (PCD). PCD is essential to maintain healthy cell turnover within tissue but also to fight disease or infection. Uninhibited, IAPs can suppress apoptosis and promote cell cycle progression. Therefore, it is unsurprising that cancer cells demonstrate significantly elevated expression levels of IAPs, resulting in improved cell survival, enhanced tumor growth and subsequent metastasis. Therapies to target IAPs in cancer has garnered substantial scientific interest and as resistance to anti-cancer agents becomes more prevalent, targeting IAPs has become an increasingly attractive strategy to re-sensitize cancer cells to chemotherapies, antibody based-therapies and TRAIL therapy. Antagonism strategies to modulate the actions of XIAP, cIAP1/2 and survivin are the central focus of current research and this review highlights advances within this field with particular emphasis upon the development and specificity of second mitochondria-derived activator of caspase (SMAC) mimetics (synthetic analogs of endogenously expressed inhibitors of IAPs SMAC/DIABLO). While we highlight the potential of SMAC mimetics as effective single agent or combinatory therapies to treat cancer we also discuss the likely clinical implications of resistance to SMAC mimetic therapy, occasionally observed in cancer cell lines.

Transcriptional and post-transcriptional upregulation of p27 mediates growth inhibition of isorhapontigenin (ISO) on human bladder cancer cells

There are few approved drugs available for the treatment of muscle-invasive bladder cancer (MIBC). Recently, we have demonstrated that isorhapontigenin (ISO), a new derivative isolated from the Chinese herb Gnetum cleistostachyum, effectively induces cell-cycle arrest at the G0/G1 phase and inhibits anchorage-independent cell growth through the miR-137/Sp1/cyclin D1 axis in human MIBC cells. Herein, we found that treatment of bladder cancer (BC) cells with ISO resulted in a significant upregulation of p27, which was also observed in ISO-treated mouse BCs that were induced by N-butyl-N-(4-hydroxybutyl) nitrosamine (BBN). Importantly, knockdown of p27 caused a decline in the ISO-induced G0-G1 growth arrest and reversed ISO suppression of anchorage-independent growth in BC cells. Mechanistic studies revealed that ISO promoted p27 expression at mRNA transcription level through increasing direct binding of forkhead box class O1 (FOXO1) to its promoter, while knockdown of FOXO1 attenuated ISO inhibition of BC cell growth. On the other hand, ISO upregulated the 3'-untranslated region (3'-UTR) activity of p27, which was accompanied by a reduction of miR-182 expression. In line with these observations, ectopic expression of miR-182 significantly blocked p27 3'-UTR activity, whereas mutation of the miR-182-binding site at p27 mRNA 3'-UTR effectively reversed this inhibition. Accordingly, ectopic expression of miR-182 also attenuated ISO upregulation of p27 expression and impaired ISO inhibition of BC cell growth. Our results not only provide novel insight into understanding of the underlying mechanism related to regulation of MIBC cell growth but also identify new roles and mechanisms underlying ISO inhibition of BC cell growth.

XIAP RING domain mediates miR-4295 expression and subsequently inhibiting p63α protein translation and promoting transformation of bladder epithelial cells

The X-linked inhibitor of apoptosis protein (XIAP) contains three N-terminal BIR domains that mediate anti-apoptosis and one C-terminal RING finger domain whose function(s) are not fully defined. Here we show that the RING domain of XIAP strongly inhibits the expression of p63α, a known tumor suppressor. XIAP knockdown in urothelial cells or RING deletion in knockin mice markedly upregulates p63α expression. This RING-mediated p63α downregulation is critical for the malignant transformation of normal urothelial cells following EGF treatment. We further show that the RING domain promotes Sp1-mediated transcription of miR-4295 which targets the 3′UTR of p63α mRNA and consequently inhibits p63α translation. Our results reveal a previously unknown function of the RING of XIAP in promoting miR-4295 transcription, thereby reducing p63α translation and enhancing urothelial transformation. Our data offer novel insights into the multifunctional effects of the XIAP RING domain on urothelial tumorigenesis and the potential for targeting this frequently overexpressed protein as a therapeutic alternative.

[Human RhoA is modified by SUMO2/3]

OBJECTIVE

To investigate whether human RhoA is modified by SUMO.

METHODS

Overlap extension PCR and double digestion technique were used to construct the eukaryotic expression vector pcDNA3-3flag-RhoA, which was identified by sequencing. The plasmid was transfected into HEK293T cells and its expression was detected by Western blotting. Immunofluorescence assay was used to detect whether RhoA is co-localized with SUMO. Co-Immunoprecipitation was used to detect whether RhoA is modified by SUMO.

RESULTS

The recombinant plasmid pcDNA3-3flag-RhoA was successfully constructed and verified. Western blotting showed that the recombinant plasmid pcDNA3-3flag-RhoA expressed abundant fusion protein in HEK293T cells. Immunofluorescence showed that RhoA was co-localized with SUMO2/3 but not with SUMO1. Co-immunoprecipitation verified that RhoA was modified by SUMO2/3 but not SUMO1.

CONCLUSIONS

Human RhoA is modified by SUMO2/3 and probably participates in the regulation of axon regrowth after nervous system injury.

The correlation between XIAP gene polymorphisms and esophageal squamous cell carcinoma susceptibility and prognosis in a Chinese population

OBJECTIVE

This study aims to explore the correlation between X-linked inhibitor of apoptosis protein (XIAP) gene polymorphisms (rs8371 and rs9856) with the susceptibility and prognosis of esophageal squamous cell carcinoma (ESCC), providing a potential treatment for ESCC.

METHOD

A total of 170 ESCC patients (case group) and 191 healthy people (control group) were enrolled in our study. Genotyping was conducted on the basis of the ligase detection reaction (LDR). The expressions of XIAP polymorphisms were detected. The patients were followed up every three months until death or the last follow-up day. The overall survival (OS) and progression free survival (PFS) were recorded by Kaplan-Meier survival curve, and the relationship between XIAP gene polymorphism and risk and prognosis of ESCC was assessed by Cox multivariate analysis.

RESULT

TT+CT genotype and T allele frequencies of XIAP rs8371 and rs9856 in the case group were significantly lower compared to those of the control group (all P<0.05), suggesting that TT+CT genotype of XIAP rs8371 and rs9856 was associated with ESCC susceptibility. XIAP rs8371 and rs9856 polymorphisms were associated with tumor node metastasis (TNM) staging, depth of invasion and lymph node metastasis. The OS and PFS of TT+CT genotype carriers of rs8371 were longer than those of CC genotype carriers. Smoking, alcohol, TNM staging, depth of invasion, and lymph node metastasis were significantly associated with the OS and PFS in ESCC patients. Higher TNM staging, depth of invasion, and presence of lymph node metastasis were independent risk factors, while XIAP rs8371 was an independent protective factor for the prognosis of ESCC patients.

CONCLUSION

The present study demonstrates that XIAP rs8371 and rs9856 are associated with susceptibility to ESCC, and rs8371 polymorphisms might serve as an indicator for improved clinical efficacy and prognosis of ESCC patients.

MicroRNA-212 inhibits the proliferation, migration and invasion of renal cell carcinoma by targeting X-linked inhibitor of apoptosis protein (XIAP)

MicroRNAs have been found to be critical regulator of cancer cell biology. MicroRNA-212 (miR-212) was identified to be a critical cancer-associated microRNA playing either oncogenic functions or tumor suppressive roles in different types of human cancers. In this study, we found that the level of miR-212 in renal cell carcinoma (RCC) tissues was significantly lower than that in adjacent non-tumor tissues. Decreased level of miR-212 was associated with advanced T stage and TNM stage of RCC. The expression of miR-212 was decreased in RCC cell lines as compared with the HK-2 cell line. Overexpression of miR-212 inhibited cell viability, proliferation, migration and invasion of CAKI-2 cells. Knockdown of miR-212 increased cell viability and proliferation, migration and invasion of ACHN cells. In vivo experiments showed that miR-212 inhibited the proliferation and promoted the apoptosis of ACHN cells in nude mice and thus inhibited the in vivo tumor growth of CAKI-2 cells. Furthermore, we confirmed that X-linked inhibitor of apoptosis protein (XIAP) was the downstream target of miR-212. The expression level of miR-212 was negatively correlated with XIAP expression in RCC tissues. Moreover, XIAP mediated the tumor suppressive roles of miR-212 in RCC. Finally, we demonstrated that the aberrant expression of miR-212 and XIAP was evidently correlated with poor prognosis of RCC patients. In all, miR-212 can act as a prognostic biomarker for RCC patients and inhibits the growth and metastasis of RCC cells by inhibiting XIAP.

NF-κB p65 Overexpression Promotes Bladder Cancer Cell Migration via FBW7-Mediated Degradation of RhoGDIα Protein

BACKGROUND

Since invasive bladder cancer (BC) is one of the most lethal urological malignant tumors worldwide, understanding the molecular mechanisms that trigger the migration, invasion, and metastasis of BC has great significance in reducing the mortality of this disease. Although RelA/p65, a member of the NF-kappa B transcription factor family, has been reported to be upregulated in human BCs, its regulation of BC motility and mechanisms have not been explored yet.

METHODS

NF-κBp65 expression was evaluated in N-butyl-N-(4-hydroxybutyl)-nitrosamine (BBN)-induced high invasive BCs by immunohistochemistry staining and in human BC cell lines demonstrated by Western Blot. The effects of NF-κBp65 knockdown on BC cell migration and invasion, as well as its regulated RhoGDIα and FBW7, were also evaluated in T24T cells by using loss- and gain-function approaches. Moreover, the interaction of FBW7 with RhoGDIα was determined with immunoprecipitation assay, while critical role of ubiquitination of RhoGDIα by FBW7 was also demonstrated in the studies.

RESULTS

p65 protein was remarkably upregulated in the BBN-induced high invasive BCs and in human BC cell lines. We also observed that p65 overexpression promoted BC cell migration by inhibiting RhoGDIα expression. The regulatory effect of p65 on RhoGDIα expression is mediated by its upregulation of FBW7, which specifically interacted with RhoGDIα and promoted RhoGDIα ubiquitination and degradation. Mechanistic studies revealed that p65 stabilizing the E3 ligase FBW7 protein was mediated by its attenuating pten mRNA transcription.

CONCLUSIONS

We demonstrate that p65 overexpression inhibits pten mRNA transcription, which stabilizes the protein expression of ubiquitin E3 ligase FBW7, in turn increasing the ubiquitination and degradation of RhoGDIα protein and finally promoting human BC migration. The novel identification of p65/PTEN/FBW7/RhoGDIα axis provides a significant insight into understanding the nature of BC migration, further offering a new theoretical support for cancer therapy.

Cellular inhibitor of apoptosis protein 2 promotes the epithelial-mesenchymal transition in triple-negative breast cancer cells through activation of the AKT signaling pathway

Triple-negative breast cancer (TNBC) represents approximately 10–17% of all breast cancers, and patients with TNBC show a poorer short-term prognosis than patients with other types of breast cancer. TNBCs also have a higher tendency for early distant metastasis and cancer recurrence due to induction of the epithelial-mesenchymal transition (EMT). Several recent reports have suggested that inhibitor of apoptosis (IAP) proteins function as regulators of the EMT. However, the roles of these proteins in TNBC are not clear. Accordingly, we investigated the roles of cIAP2 in TNBC. Among eight IAP genes, only cIAP2 was upregulated in TNBC cells compared with that in other breast cancer subtypes. Analysis of TMAs revealed that expression of cIAP2 was upregulated in TNBCs. In vitro studies showed that cIAP2 was highly expressed in TNBC cells compared with that in other types of breast cancer cells. Furthermore, silencing of cIAP2 in TNBC cells induced mesenchymal-epithelial transition (MET)-like processes and subsequently suppressed the migratory ability and invasion capacity of the cells by regulation of Snail through the AKT signaling pathway. In contrast, ectopic expression of cIAP2 in luminal-type breast cancer cells induced activation of the AKT signaling pathway. These results collectively indicated that cIAP2 regulated the EMT in TNBC via activation of the AKT signaling pathway, contributing to metastasis in TNBC. Our study proposes a novel mechanism through which cIAP2 regulates the EMT involving AKT signaling in TNBC cells. We suggest that cIAP2 may be an attractive candidate molecule for the development of targeted therapeutics in the future.

Prognostic value of Rho GDP dissociation inhibitors in patients with hepatocellular carcinoma following liver transplantation

Rho GDP dissociation inhibitors (GDIs) are pivotal regulators of Rho GTPases, which are essential for tumor progression, yet their role in hepatocellular carcinoma (HCC) remains poorly understood. The purpose of the present study was to assess the role of RhoGDIs in the invasiveness and migration of liver cancer, and to determine their clinical prognostic significances in HCC following liver transplantation (LT). In the present study, the expression of RhoGDIs was assessed using reverse transcription-quantitative polymerase chain reaction and confirmed by western-blot analysis and immunohistochemistry. Their prognostic values were also analyzed, and determined in patients treated with LT. In addition, the functions of RhoGDIs in liver cancer cell line were studied in vitro. As a result, the downregulation of RhoGDI1 and RhoGDI2 at mRNA and protein levels were detected in HCC when compared with that of adjacent noncancerous tissues (P<0.05). However, the level of RhoGDI3 was identified to be similar in tumor and para-carcinoma tissues. Additionally, Kaplan-Meier curves demonstrated that patients with lower expression of RhoGDI1 or RhoGDI2 exhibited significantly increased risk of tumor recurrence following LT (P=0.007 and P=0.006, respectively). Cox proportional hazards model analysis revealed that the decreased expression level of RhoGDI2 was an unfavorable independent prognostic factor (hazard ratio, 3.306; P=0.001). In vitro studies involving the silencing of RhoGDI1 or RhoGDI2 demonstrated a significant increase in the migratory and invasive ability of tumor cells upon the silencing of these genes. Results from the present study indicate that RhoGDI dysregulation is a frequent event in human HCC, and that it promotes cancer progression by stimulating cell migration and invasion. RhoGDI2 may be a prognostic biomarker for patients with HCC following LT, and act as a potential therapeutic target.

Ubiquitin-dependent regulation of Cdc42 by XIAP

Rho GTPases control fundamental cellular processes and Cdc42 is a well-studied member of the family that controls filopodia formation and cell migration. Although the regulation of Cdc42 activity by nucleotide binding is well documented, the mechanisms driving its proteostasis are not clear. Here, we demonstrate that the highly conserved, RING domain containing E3 ubiquitin ligase XIAP controls the protein stability of Cdc42. XIAP binds to Cdc42 and directly conjugates poly ubiquitin chains to the Lysine 166 of Cdc42 targeting it for proteasomal degradation. Depletion of XIAP led to an increased protein stability and activity of Cdc42 in normal and tumor cells. Consistently, loss of XIAP enhances filopodia formation in a Cdc42-dependent manner and this phenomenon phenocopies EGF stimulation. Further, XIAP depletion promotes lung colonization of tumor cells in mice in a Cdc42-dependent manner. These observations shed molecular insights into ubiquitin-dependent regulation of Cdc42 and that of actin cytoskeleton.

Role of Rho-specific guanine nucleotide dissociation inhibitor α regulation in cell migration

Cell migration is a vital process for many physiological and pathological events, and Rho GTPases have been confirmed as key factors in its regulation. The most studied negative regulator of Rho GTPases, Rho-specific guanine nucleotide dissociation inhibitor α (RhoGDIα), mediates cell migration through altering the overall expression and spatiotemporal activation of Rho GTPases. The RhoGDIα-Rho GTPases dissociation can be mediated by signal pathways targeting RhoGDIα directly. This review summarizes the research about the regulation of RhoGDIα during cell migration, which can be in a Rho GTPases association independent manner. Non-kinase proteins regulation, phosphorylation, SUMOylation and extracellular environmental factors are classified to discuss their direct signal regulations on RhoGDIα, which provide varied signal pathways for selective activation of Rho GTPases in cell migration.

XIAP BIR domain suppresses miR-200a expression and subsequently promotes EGFR protein translation and anchorage-independent growth of bladder cancer cell

BACKGROUND

The X-linked inhibitor of apoptosis protein (XIAP) is a well-known potent apoptosis suppressor and also participates in cancer cell biological behaviors, therefore attracting great attentions as a potential antineoplastic therapeutic target for past years. Anti-IAP therapy is reported to be closely related to epidermal growth factor receptor (EGFR) expression level. However, whether and how XIAP modulates EGFR expression remains largely unknown.

METHODS

Human XIAP was knockdown with short-hairpin RNA in two different bladder cancer cell lines, T24T and UMUC3. Two XIAP mutants, XIAP ∆BIR (deletion of N-terminal three BIR domains) and XIAP ∆RING (deletion of C-terminal RING domain and keeping the function of BIR domains), were generated to determine which domain is involved in regulating EGFR.

RESULTS

We found here that lacking of XIAP expression resulted in a remarkable suppression of EGFR expression, consequently leading to the deficiency of anchorage-independent cell growth. Further study demonstrated that BIR domain of XIAP was crucial for regulating the EGFR translation by suppressing the transcription and expression of miR-200a. Mechanistic studies indicated that BIR domain activated the protein phosphatase 2 (PP2A) activity by decreasing the phosphorylation of PP2A at Tyr307 in its catalytic subunit, PP2A-C. Such activated PP2A prevented the deviant phosphorylation and activation of MAPK kinases/MAPKs, their downstream effector c-Jun, and in turn inhibiting transcription of c-Jun-regulated the miR-200a.

CONCLUSIONS

Our study uncovered a novel function of BIR domain of XIAP in regulating the EGFR translation, providing significant insight into the understanding of the XIAP overexpression in the cancer development and progression, further offering a new theoretical support for using XIAP BIR domain and EGFR as targets for cancer therapy.

Regulating Rho GTPases and their regulators

Rho GTPases regulate cytoskeletal and cell adhesion dynamics and thereby coordinate a wide range of cellular processes, including cell migration, cell polarity and cell cycle progression. Most Rho GTPases cycle between a GTP-bound active conformation and a GDP-bound inactive conformation to regulate their ability to activate effector proteins and to elicit cellular responses. However, it has become apparent that Rho GTPases are regulated by post-translational modifications and the formation of specific protein complexes, in addition to GTP-GDP cycling. The canonical regulators of Rho GTPases - guanine nucleotide exchange factors, GTPase-activating proteins and guanine nucleotide dissociation inhibitors - are regulated similarly, creating a complex network of interactions to determine the precise spatiotemporal activation of Rho GTPases.

Isorhapontigenin (ISO) Inhibits Invasive Bladder Cancer Formation In Vivo and Human Bladder Cancer Invasion In Vitro by Targeting STAT1/FOXO1 Axis

Although our most recent studies have identified Isorhapontigenin (ISO), a novel derivative of stilbene that isolated from a Chinese herb Gnetum cleistostachyum, for its inhibition of human bladder cancer growth, nothing is known whether ISO possesses an inhibitory effect on bladder cancer invasion. Thus, we addressed this important question in current study and discovered that ISO treatment could inhibit mouse-invasive bladder cancer development following bladder carcinogen N-butyl-N-(4-hydroxybutyl) nitrosamine (BBN) exposure in vivo We also found that ISO suppressed human bladder cancer cell invasion accompanied by upregulation of the forkhead box class O 1 (FOXO1) mRNA transcription in vitro Accordingly, FOXO1 was profoundly downregulated in human bladder cancer tissues and was negatively correlated with bladder cancer invasion. Forced expression of FOXO1 specifically suppressed high-grade human bladder cancer cell invasion, whereas knockdown of FOXO1 promoted noninvasive bladder cancer cells becoming invasive bladder cancer cells. Moreover, knockout of FOXO1 significantly increased bladder cancer cell invasion and abolished the ISO inhibition of invasion in human bladder cancer cells. Further studies showed that the inhibition of Signal transducer and activator of transcription 1 (STAT1) phosphorylation at Tyr701 was crucial for ISO upregulation of FOXO1 transcription. Furthermore, this study revealed that metalloproteinase-2 (MMP-2) was a FOXO1 downstream effector, which was also supported by data obtained from mouse model of ISO inhibition BBN-induced mouse-invasive bladder cancer formation. These findings not only provide a novel insight into the understanding of mechanism of bladder cancer's propensity to invasion, but also identify a new role and mechanisms underlying the natural compound ISO that specifically suppresses such bladder cancer invasion through targeting the STAT1-FOXO1-MMP-2 axis. Cancer Prev Res; 9(7); 567-80. ©2016 AACR.

Rho GDIalpha Modulates Rabbit Trophoblast Stem Cell Survival and Migration

Trophoblast stem cells differentiate into different trophoblast cell populations that are indispensable for successful pregnancy through interactions with the maternal uterine decidua. Rho GTPases play an important role in the regulation of trophoblast stem cell (TSC) self-renewal and differentiation; however, the role of Rho GDP-dissociation inhibitors (Rho GDIs) remains unclear. Here we report that overexpression of Rho GDIalpha resulted in rapid apoptosis of TSCs, while its knockdown promoted proliferation. Moreover, Rho GDIalpha knockdown also enhanced TSC invasion. Collectively, these results establish a potential mechanism whereby TSCs can balance growth and apoptosis, and thus ensure normal fetal development.

Survivin promotes oxidative phosphorylation, subcellular mitochondrial repositioning, and tumor cell invasion

Survivin promotes cell division and suppresses apoptosis in many human cancers, and increased abundance correlates with metastasis and poor prognosis. We showed that a pool of survivin that localized to the mitochondria of certain tumor cell lines enhanced the stability of oxidative phosphorylation complex II, which promoted cellular respiration. Survivin also supported the subcellular trafficking of mitochondria to the cortical cytoskeleton of tumor cells, which was associated with increased membrane ruffling, increased focal adhesion complex turnover, and increased tumor cell migration and invasion in cultured cells, and enhanced metastatic dissemination in vivo. Therefore, we found that mitochondrial respiration enhanced by survivin contributes to cancer metabolism, and relocalized mitochondria may provide a "regional" energy source to fuel tumor cell invasion and metastasis.

High mobility group Box-1 inhibits cancer cell motility and metastasis by suppressing activation of transcription factor CREB and nWASP expression

The ability to metastasize is a hallmark of malignant tumors, and metastasis is the principal cause of death of cancer patients. The High Mobility Group Box-1 (HMGB1) is a multifunction protein that serves as both a chromatin protein and an extracellular signaling molecule. Our current study demonstrated a novel mechanism of HMGB1 in the regulation of cancer cell actin polymerization, cell skeleton formation, cancer cell motility and metastasis. We found that knockdown of HMGB1 in human lung cancer A549 cells significantly increased cell β-actin polymerization, cell skeleton formation, cancer cell migration and invasion in vitro, as well as metastasis in vivo. And this increase could be inhibited by treatment of HMGB1 knockdown cells with recombinant human HMGB1. Further studies discovered that HMGB1 suppressed phosphorylation, nuclear translocation, and activation of CREB, by inhibiting nuclear translocation of PKA catalytic subunit. This reduces nWASP mRNA transcription and expression, further impairing cancer cell motility. Our findings on the novel mechanism underlying the HMGB1 anti-metastatic effect on cancer provides significant insight into the understanding of the nature of HMGB1 in cancer invasion and metastasis, further serving as key information for utilization of HMGB1 and its regulated downstream components as new targets for cancer therapy.

A potential role of X-linked inhibitor of apoptosis protein in mitochondrial membrane permeabilization and its implication in cancer therapy

X-chromosome-linked inhibitor of apoptosis protein (XIAP) has an important regulatory role in programmed cell death by inhibiting the caspase cascade. Activation of XIAP-dependent signaling culminates into regulation of multiple cellular processes including apoptosis, innate immunity, epithelial-to-mesenchymal transition, cell migration, invasion, metastasis and differentiation. Although XIAP localizes to the cytosolic compartment, XIAP-mediated cellular signaling encompasses mitochondrial and post-mitochondrial levels. Recent findings demonstrate that XIAP also localizes to mitochondria and regulates mitochondria functions. XIAP acts upstream of mitochondrial cytochrome c release and modulates caspase-dependent apoptosis. The new function of XIAP has potential to enhance mitochondrial membrane permeabilization and other cellular functions controlling cytochrome c release. These findings could exploit the overexpression of XIAP in human tumors for therapeutic benefits.

Emerging roles of sumoylation in the regulation of actin, microtubules, intermediate filaments, and septins

Sumoylation is a powerful regulatory system that controls many of the critical processes in the cell, including DNA repair, transcriptional regulation, nuclear transport, and DNA replication. Recently, new functions for SUMO have begun to emerge. SUMO is covalently attached to components of each of the four major cytoskeletal networks, including microtubule-associated proteins, septins, and intermediate filaments, in addition to nuclear actin and actin-regulatory proteins. However, knowledge of the mechanisms by which this signal transduction system controls the cytoskeleton is still in its infancy. One story that is beginning to unfold is that SUMO may regulate the microtubule motor protein dynein by modification of its adaptor Lis1. In other instances, cytoskeletal elements can both bind to SUMO non-covalently and also be conjugated by it. The molecular mechanisms for many of these new functions are not yet clear, but are under active investigation. One emerging model links the function of MAP sumoylation to protein degradation through SUMO-targeted ubiquitin ligases, also known as STUbL enzymes. Other possible functions for cytoskeletal sumoylation are also discussed.

X-linked inhibitor of apoptosis protein (XIAP) lacking RING domain localizes to the nuclear and promotes cancer cell anchorage-independent growth by targeting the E2F1/Cyclin E axis

The inhibitor of apoptosis protein XIAP (X-linked inhibitor of apoptosis protein) is a well-documented protein that is located in cytoplasm acting as a potent regulator of cell apoptosis. Here, we showed that expressing XIAP with RING (Really Interesting New Gene) domain deletion (XIAP^ΔRING) in cancer cells promoted cancer cell anchorage-independent growth and G₁/S phase transition companied with increasing cyclin e transcription activity and protein expression. Further studies revealed that XIAP^ΔRING was mainly localized in nuclear with increased binding with E2F1, whereas XIAP with BIR (Baculoviral IAP Repeat) domains deletion (XIAP^ΔBIRs) was entirely presented in cytoplasma with losing its binding with E2F1, suggesting that RING domain was able to inhibit BIR domains nuclear localization, by which impaired BIRs binding with E2F1 in cellular nucleus in intact cells. These studies identified a new function of XIAP protein in cellular nucleus is to regulate E2F1 transcriptional activity by binding with E2F1 in cancer cells. Our current finding of an effect of XIAP^ΔRING expression on cancer cell anchorage-independent growth suggests that overexpression of this protein may contribute to genetic instability associated with cell cycle and checkpoint perturbations, in addition to its impact on cellular apoptosis.

IAPs and cell migration

Inhibitors of apoptosis (IAPs) constitute a family of cell signaling regulators controlling several fundamental biological processes such as innate immunity, inflammation, cell death, cell proliferation, and cell differentiation. Increasing evidence from in vivo and in vitro studies indicate a function for IAPs in the modulation of invasive and migratory properties of cells. Here, we present and discuss the mechanisms whereby IAPs can control cell migration.

A novel post-translational modification of nucleolin, SUMOylation at Lys-294, mediates arsenite-induced cell death by regulating gadd45α mRNA stability

Nucleolin is a ubiquitously expressed protein and participates in many important biological processes, such as cell cycle regulation and ribosomal biogenesis. The activity of nucleolin is regulated by intracellular localization and post-translational modifications, including phosphorylation, methylation, and ADP-ribosylation. Small ubiquitin-like modifier (SUMO) is a category of recently verified forms of post-translational modifications and exerts various effects on the target proteins. In the studies reported here, we discovered SUMOylational modification of human nucleolin protein at Lys-294, which facilitated the mRNA binding property of nucleolin by maintaining its nuclear localization. In response to arsenic exposure, nucleolin-SUMO was induced and promoted its binding with gadd45α mRNA, which increased gadd45α mRNA stability and protein expression, subsequently causing GADD45α-mediated cell death. On the other hand, ectopic expression of Mn-SOD attenuated the arsenite-generated superoxide radical level, abrogated nucleolin-SUMO, and in turn inhibited arsenite-induced apoptosis by reducing GADD45α expression. Collectively, our results for the first time demonstrate that nucleolin-SUMO at K294R plays a critical role in its nucleus sequestration and gadd45α mRNA binding activity. This novel biological function of nucleolin is distinct from its conventional role as a proto-oncogene. Therefore, our findings here not only reveal a new modification of nucleolin protein and its novel functional paradigm in mRNA metabolism but also expand our understanding of the dichotomous roles of nucleolin in terms of cancer development, which are dependent on multiple intracellular conditions and consequently the appropriate regulations of its modifications, including SUMOylation.

Survivin - The inconvenient IAP

Although technically a member of the Inhibitor of Apoptosis (IAP) gene family, survivin has consistently defied assumptions, refuted predictions and challenged paradigms. Despite its more than 5500 citations currently in Medline, the biology of survivin has remained fascinatingly complex, its exploitation in human disease, most notably cancer, tantalizing, and its regulation of cellular homeostasis unexpectedly far-reaching. An inconvenient outsider that resists schemes and dogmas, survivin continues to hold great promise to unlock fundamental circuitries of cellular functions in health and disease.

Hydrogen peroxide/ATR-Chk2 activation mediates p53 protein stabilization and anti-cancer activity of cheliensisin A in human cancer cells

Cheliensisine A (Chel A) as a novel styryl-lactone isolated from Goniothalamus cheliensis Hu has been indicated to be a chemotherapeutic agent in Leukemia HL-60 cells. However, its potential for cancer treatment and the underlying mechanisms are not deeply investigated to the best of our knowledge. Current studies showed that Chel A could trigger p53-mediated apoptosis, accompanied with dramatically inhibition of anchorage-independent growth of human colon cancer HCT116 cells. Further studies found that Chel A treatment resulted in p53 protein stabilization and accumulation via the induction of its phosphorylation at Ser20 and Ser15. Moreover, Chel A-induced p53 protein accumulation and activation required ATR/Chk2 axis, which is distinct from the mechanism that we have most recently identified the Chk1/p53-dependent apoptotic response by Chel A in normal mouse epidermal Cl41 cells. In addition, our results demonstrated that hydrogen peroxide generation induced by Chel A acted as a precursor for all these signaling events and downstream biological effects. Taken together, we have identified the Chel A as a new therapeutic agent, which highlights its potential for cancer therapeutic effect.

Small-molecule SMAC mimetics as new cancer therapeutics

Apoptosis is a tightly regulated cellular process and faulty regulation of apoptosis is a hallmark of human cancers. Targeting key apoptosis regulators with the goal to restore apoptosis in tumor cells has been pursued as a new cancer therapeutic strategy. XIAP, cIAP1, and cIAP2, members of inhibitor of apoptosis (IAP) proteins, are critical regulators of cell death and survival and are attractive targets for new cancer therapy. The SMAC/DIABLO protein is an endogenous antagonist of XIAP, cIAP1, and cIAP2. In the last decade, intense research efforts have resulted in the design and development of several small-molecule SMAC mimetics now in clinical trials for cancer treatment. In this review, we will discuss the roles of XIAP, cIAP1, and cIAP2 in regulation of cell death and survival, and the design and development of small-molecule SMAC mimetics as novel cancer treatments.

Non-nuclear function of sumoylated proteins

Post-translational modification by the SUMO moiety is now regarded as one of the key regulatory modifications in eukaryotic cells. Up to now, plenty of sumoylated proteins have been found to be involved in nuclear processes such as chromatin organization, transcription and DNA repair as well as in other cellular functions. Since the number of data concerning sumoylated proteins and their function outside the nucleus has grown rapidly, in this review we summarized the results describing the non-nuclear role of SUMO substrates. In particular, we focused on the role of sumoylation in the regulation of channel activity, receptor function, G-protein signaling, activity of enzymes, cytoskeletal organization, exocytosis, autophagy and mitochondrial dynamics.