Survivin withdrawal by nuclear export failure as a physiological switch to commit cells to apoptosis

The conservation of IAP-like proteins in fungi, and their potential role in fungal programmed cell death

Programmed cell death (PCD) is a tightly regulated process which is required for survival and proper development of all cellular life. Despite this ubiquity, the precise molecular underpinnings of PCD have been primarily characterized in animals. Attempts to expand our understanding of this process in fungi have proven difficult as core regulators of animal PCD are apparently absent in fungal genomes, with the notable exception of a class of proteins referred to as inhibitors of apoptosis proteins (IAPs). These proteins are characterized by the conservation of a distinct Baculovirus IAP Repeat (BIR) domain and animal IAPs are known to regulate a number of processes, including cellular death, development, organogenesis, immune system maturation, host-pathogen interactions and more. IAP homologs are broadly conserved throughout the fungal kingdom, but our understanding of both their mechanism and role in fungal development/virulence is still unclear. In this review, we provide a broad and comparative overview of IAP function across taxa, with a particular focus on fungal processes regulated by IAPs. Furthermore, their putative modes of action in the absence of canonical interactors will be discussed.

Localization matters: nuclear-trapped Survivin sensitizes glioblastoma cells to temozolomide by elevating cellular senescence and impairing homologous recombination

To clarify whether differential compartmentalization of Survivin impacts temozolomide (TMZ)-triggered end points, we established a well-defined glioblastoma cell model in vitro (LN229 and A172) and in vivo, distinguishing between its nuclear and cytoplasmic localization. Expression of nuclear export sequence (NES)-mutated Survivin (SurvNESmut-GFP) led to impaired colony formation upon TMZ. This was not due to enhanced cell death but rather due to increased senescence. Nuclear-trapped Survivin reduced homologous recombination (HR)-mediated double-strand break (DSB) repair, as evaluated by γH2AX foci formation and qPCR-based HR assay leading to pronounced induction of chromosome aberrations. Opposite, clones, expressing free-shuttling cytoplasmic but not nuclear-trapped Survivin, could repair TMZ-induced DSBs and evaded senescence. Mass spectrometry-based interactomics revealed, however, no direct interaction of Survivin with any of the repair factors. The improved TMZ-triggered HR activity in Surv-GFP was associated with enhanced mRNA and stabilized RAD51 protein expression, opposite to diminished RAD51 expression in SurvNESmut cells. Notably, cytoplasmic Survivin could significantly compensate for the viability under RAD51 knockdown. Differential Survivin localization also resulted in distinctive TMZ-triggered transcriptional pathways, associated with senescence and chromosome instability as shown by global transcriptome analysis. Orthotopic LN229 xenografts, expressing SurvNESmut exhibited diminished growth and increased DNA damage upon TMZ, as manifested by PCNA and γH2AX foci expression, respectively, in brain tissue sections. Consequently, those mice lived longer. Although tumors of high-grade glioma patients expressed majorly nuclear Survivin, they exhibited rarely NES mutations which did not correlate with survival. Based on our in vitro and xenograft data, Survivin nuclear trapping would facilitate glioma response to TMZ.

miR-34a-Mediated Survivin Inhibition Improves the Antitumor Activity of Selinexor in Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is an aggressive disease with limited therapeutic options. Here, we pursued a combinatorial therapeutic approach to enhance the activity of selinexor, the first-in-class XPO1 inhibitor, by miR-34a ectopic expression in human TNBC experimental models. Anti-proliferative activity induced by selinexor and miR-34a expression, singly and in combination, was evaluated by MTS assay and cell counting. The effect of treatments on survivin and apoptosis-related proteins was assessed by western blotting and ELISA. The antitumor and toxic effects of individual and combined treatments were evaluated on TNBC orthotopic xenografts in SCID mice. Selinexor consistently showed anti-proliferative activity, although to a variable extent, in the different TNBC cell lines and caused the impairment of survivin expression and intracellular distribution, accompanied by apoptosis induction. Consistent with in vitro data, the XPO1 inhibitor variably affected the growth of TNBC orthotopic xenografts. miR-34a cooperated with selinexor to reduce survivin expression and improved its anti-proliferative activity in TNBC cells. Most importantly, miR-34a expression markedly enhanced selinexor antitumor activity in the less sensitive TNBC xenograft model, in absence of toxicity. Our data form a solid foundation for promoting the use of a miR-34a-based approach to improve the therapeutic efficacy of selinexor in TNBC patients.

On the asymmetric partitioning of nucleocytoplasmic transport - recent insights and open questions

Macromolecular cargoes are asymmetrically partitioned in the nucleus or cytoplasm by nucleocytoplasmic transport (NCT). At the center of this activity lies the nuclear pore complex (NPC), through which soluble factors circulate to orchestrate NCT. These include cargo-carrying importin and exportin receptors from the β-karyopherin (Kapβ) family and the small GTPase Ran, which switches between guanosine triphosphate (GTP)- and guanosine diphosphate (GDP)-bound forms to regulate cargo delivery and compartmentalization. Ongoing efforts have shed considerable light on how these soluble factors traverse the NPC permeability barrier to sustain NCT. However, this does not explain how importins and exportins are partitioned in the cytoplasm and nucleus, respectively, nor how a steep RanGTP-RanGDP gradient is maintained across the nuclear envelope. In this Review, we peel away the multiple layers of control that regulate NCT and juxtapose unresolved features against known aspects of NPC function. Finally, we discuss how NPCs might function synergistically with Kapβs, cargoes and Ran to establish the asymmetry of NCT.

Selinexor versus doxorubicin in dedifferentiated liposarcoma PDXs: evidence of greater activity and apoptotic response dependent on p53 nuclear accumulation and survivin down-regulation

BACKGROUND

Dedifferentiated liposarcoma (DDLPS), a tumor that lacks effective treatment strategies and is associated with poor outcomes, expresses amplified MDM2 in the presence of wild-type p53. MDM2 ubiquitination of p53 facilitates its XPO1-mediated nuclear export, thus limiting p53 tumor suppressor functions. Consequently, nuclear export is a rational target in DDLPS. We directly compared the antitumor activity of the first-in class XPO1 inhibitor selinexor and doxorubicin, the standard front-line therapy in sarcomas, in DDLPS patient-derived xenografts (PDXs) and primary cell lines.

METHODS

Drug activity was assessed in three PDXs (and two corresponding cell lines) established from the dedifferentiated component of primary untreated retroperitoneal DDLPS with myogenic (N = 2) and rhabdomyoblastic (N = 1) differentiation from patients who underwent surgery. These models were marked by amplification of MDM2, CDK4 and HMGA2 genes.

RESULTS

Selinexor was moderately active in the three PDXs but achieved greater tumor response compared to doxorubicin (maximum tumor volume inhibition: 46-80 % vs. 37-60 %). The PDX harboring rhabdomyoblastic dedifferentiation showed the highest sensitivity to both agents. PDX response to selinexor and doxorubicin was not associated with the extent of MDM2 and CDK4 gene amplification. Interestingly, the most chemosensitive PDX model showed the lowest extent of HMGA2 amplification. Selinexor was also more efficient than doxorubicinin in inducing an apoptotic response in PDXs and cell lines. Consistently, an increased nuclear accumulation of p53 was seen in all selinexor-treated models. In addition, a time-dependent decrease of survivin expression, with an almost complete abrogation of the cytoplasmic anti-apoptotic pool of this protein, was observed as a consequence of the decreased acetylation/activation of STAT3 and the increased ubiquitination of nuclear survivin.

CONCLUSIONS

Selinexor showed a moderate antitumor activity in three DDLPS PDXs, which was, however, consistently higher than doxorubicin across all different models regardless the extent of MDM2 amplification and the histological differentiation. The depletion of survivin protein seems to significantly contribute to the induction of apoptosis through which selinexor exerts its antitumor activity.

Role of the Transcription Factor Yin Yang 1 and Its Selectively Identified Target Survivin in High-Grade B-Cells Non-Hodgkin Lymphomas: Potential Diagnostic and Therapeutic Targets

B-cell non-Hodgkin lymphomas (B-NHLs) are often characterized by the development of resistance to chemotherapeutic drugs and/or relapse. During drug-induced apoptosis, Yin Yang 1 (YY1) transcription factor might modulate the expression of apoptotic regulators genes. The present study was aimed to: (1) examine the potential oncogenic role of YY1 in reversing drug resistance in B-NHLs; and (2) identify YY1 transcriptional target(s) that regulate the apoptotic pathway in B-NHLs. Predictive analyses coupled with database-deposited data suggested that YY1 binds the promoter of the BIRC5/survivin anti-apoptotic gene. Gene Expression Omnibus (GEO) analyses of several B-NHL repositories revealed a conserved positive correlation between YY1 and survivin, both highly expressed, especially in aggressive B-NHLs. Further validation experiments performed in Raji Burkitt’s lymphomas cells, demonstrated that YY1 silencing was associated with survivin downregulation and sensitized the cells to apoptosis. Overall, our results revealed that: (1) YY1 and survivin are positively correlated and overexpressed in B-NHLs, especially in BLs; (2) YY1 strongly binds to the survivin promoter, hence survivin may be suggested as YY1 transcriptional target; (3) YY1 silencing sensitizes Raji cells to drug-induced apoptosis via downregulation of survivin; (4) both YY1 and survivin are potential diagnostic markers and therapeutic targets for the treatment of resistant/relapsed B-NHLs.

Dominant-negative ATF5 rapidly depletes survivin in tumor cells

Survivin (BIRC5, product of the BIRC5 gene) is highly expressed in many tumor types and has been widely identified as a potential target for cancer therapy. However, effective anti-survivin drugs remain to be developed. Here we report that both vector-delivered and cell-penetrating dominant-negative (dn) forms of the transcription factor ATF5 that promote selective death of cancer cells in vitro and in vivo cause survivin depletion in tumor cell lines of varying origins. dn-ATF5 decreases levels of both survivin mRNA and protein. The depletion of survivin protein appears to be driven at least in part by enhanced proteasomal turnover and depletion of the deubiquitinase USP9X. Survivin loss is rapid and precedes the onset of cell death triggered by dn-ATF5. Although survivin downregulation is sufficient to drive tumor cell death, survivin over-expression does not rescue cancer cells from dn-ATF5-promoted apoptosis. This indicates that dn-ATF5 kills malignant cells by multiple mechanisms that include, but are not limited to, survivin depletion. Cell-penetrating forms of dn-ATF5 are currently being developed for potential therapeutic use and the present findings suggest that they may pose an advantage over treatments that target only survivin.

Crm1 knockdown by specific small interfering RNA reduces cell proliferation and induces apoptosis in head and neck cancer cell lines

Head and neck squamous cell carcinoma (HNSCC) is the most common and most aggressive type of head and neck cancer. Current approaches for the treatment of HNSCC are not sufficient to increase the patient survival or to reduce the high recurrence rate. Consequently, there is a need to explore the molecular characteristics of this cancer in order to discover potential therapeutic target molecules. The overexpression of chromosome region maintenance 1 (Crm1), responsible for the transport of different classes of macromolecules from the nuclear membrane to the cytoplasm, in various cancer cells has made it an attractive target molecule in cancer research. It has been reported that transcription factors, which are the target cargo proteins of Crm1, have critical roles in regulating intracellular processes via their expression levels and functions, which in turn are regulated by the cell cycle and signaling proteins. Previous findings show that head and neck cancer cells overexpress Crm1 and that these cells become highly dependent on Crm1 function. The results of this study show that after decreasing Crm1 expression levels in HNSCC cells through either treatment with specific Crm1 RNA interference (siRNA) or the selective Crm1 inhibitor leptomycin B (LMB), cell viability, proliferation, migration, and wound-healing abilities decreased, suppressing tumorigenic properties through the induction of apoptosis. Crm1 is a powerful diagnostic biomarker because of its central role in cancerogenesis, and it has a high potential for the development of targeted Crm1 molecules or synthetic agents, such as LMB, as well as for the improvement of the clinical features in head and neck cancer.

ROS modifiers and NOX4 affect the expression of the survivin-associated radio-adaptive response

The survivin-associated radio-adaptive response can be induced following exposure to ionizing radiation in the dose range from 5 to 100 mGy, and its magnitude of expression is dependent upon the TP53 mutational status of cells and ROS signaling. The purpose of the study was to investigate the potential role of ROS in the development of the survivin-associated adaptive response. Utilizing human colon carcinoma HCT116 TP53 wild type (WT) and HCT116 isogenic TP53 null mutant (Mut) cell cultures, the roles of inter- and intracellular ROS signaling on expression of the adaptive response as evidenced by changes in intracellular translocation of survivin measured by ELISA, and cell survival determined by a standard colony forming assay were investigated using ROS modifying agents that include emodin, N-acetyl-L-cysteine (NAC), fulvene-5, honokiol, metformin and rotenone. The role of NADPH oxidase 4 (NOX4) in the survivin-associated adaptive response was investigated by transfecting HCT116 cells, both WT and Mut, with two different NOX4 siRNA oligomers and Western blotting. A dose of 5 mGy or a 15 min exposure to 50 µM of the ROS producing drug emodin were equally effective in inducing a pro-survival adaptive response in TP53 WT and a radio-sensitization adaptive response in TP53 Mut HCT116 cells. Each response was associated with a corresponding translocation of survivin into the cytoplasm or nucleus, respectively. Exposure to 10 mM NAC completely inhibited both responses. Exposure to 10 µM honokiol induced responses similar to those observed following NAC exposure in TP53 WT and Mut cells. The mitochondrial complex 1 inhibitor rotenone was effective in reducing both cytoplasmic and nuclear survivin levels, but was ineffective in altering the expression of the adaptive response in either TP53 WT or Mut cells. In contrast, both metformin and fulvene-5, inhibitors of NOX4, facilitated the reversal of TP53 WT and Mut adaptive responses from pro-survival to radio-sensitization and vice versa, respectively. These changes were accompanied by corresponding reversals in the translocation of survivin to the nuclei of TP53 WT and to the cytoplasm of TP53 Mut cells. The potential role of NOX4 in the expression of the survivin-associated adaptive response was investigated by transfecting HCT116 cells with NOX4 siRNA oligomers to inhibit NOX4 expression. Under these conditions NOX4 expression was inhibited by about 50%, resulting in a reversal in the expression of the TP53 WT and Mut survivin-associated adaptive responses as was observed following metformin and fulvene-5 treatment. Exposure to 5 mGy resulted in enhanced NOX4 expression by about 40% in both TP53 WT and Mut cells, in contrast to only a 1-2% increase following a 2 Gy only exposure. Utilizing mixed cultures of HCT116 TP53 WT and isogenic null Mut cells, as few as 10% TP53 Mut cells were sufficient to control the expression of the remaining 90% WT cells and resulted in an overall radio-sensitization response accompanied by the nuclear translocation of survivin characteristic of homogeneous TP53 Mut populations.

CRM1/XPO1 expression in pancreatic adenocarcinoma correlates with survivin expression and the proliferative activity

CRM1/XPO1 (CRM1) is a nuclear export chaperone that mediates the export of proteins essential to growth regulation and tumor suppression. Its overexpression in tumors was found to be associated with poor prognosis. Selective inhibitors of nuclear export are in phase I and II clinical trials for several tumor types. Our aim was to investigate CRM1 expression in pancreatic adenocarcinoma (PAC) and its relationship to survivin expression and the proliferative activity. Sections of tissue microarray containing 76 formalin fixed and paraffin embedded PAC were stained by immunohistochemistry (IHC) for CRM1, survivin, and Cyclin A. Expression levels of CRM1 and survivin and the proliferative activity, the S-phase fraction (SPF) in tumor cells, were determined using a quantitative digital image analysis solution (OTMIAS). Sixty-six of the 76 (86%) PAC showed positive staining for CRM1, and 10 (14%) were completely negative. The mean CRM1 expression levels ranged from 0.3 to 53 units and the median from 0.3 to 45 units. There was significant positive correlation between the mean and median expression levels of CRM1 in tumor cells and the mean and median levels of survivin (p<0.001). Moreover, there was positive correlation between the mean and median CRM1 levels in tumor cells and the SPF (p=0.013). Our results show that CRM1 is expressed in a significant proportion of PAC, and increased CRM1 levels correlates with increased survivin levels and increased proliferative activity.

CRM1, a novel independent prognostic factor overexpressed in invasive breast carcinoma of poor prognosis

Breast cancer (BC) is the most commonly diagnosed cancer in females globally and is more aggressive at later stages. Chromosome region maintenance 1 (CRM1) is involved in the nuclear export of proteins and RNAs and has been associated with a number of malignancies. However, the clinicopathological significance of its expression in BC remains to be elucidated therefore this was investigated in the present study. CRM1 expression in 280 breast cancer tissues and 60 normal tissues was retrospectively analyzed using immunohistochemistry (IHC) and western blotting. IHC investigation demonstrated that CRM1 expression was significantly increased in BC compared with the normal breast epithelium (P<0.0001). Overexpression of CRM1 was markedly associated with poor prognostic characteristics, including larger tumor size (P=0.024), positive lymph node metastasis (P=0.032), invasive histological type (P=0.004) and distant metastasis (P=0.026). Significant associations were also observed between increased CRM1 expression and the progesterone receptor (P=0.028) and Ki67 (P=0.019). Kaplan-Meier survival analysis demonstrated that patients with high CRM1 expression exhibited a reduced disease-free survival and overall survival compared with those with low CRM1 expression (P=0.013). In the multivariate analysis, CRM1 expression (P=0.011), tumor size (P=0.001) and lymph node metastasis (P<0.001) were independent prognostic markers of BC. In conclusion, CRM1 serves an important role in BC and may serve as a predictive and prognostic factor for a poor outcome in patients with BC.

Targeting mitotic pathways for endocrine-related cancer therapeutics

A colossal amount of basic research over the past few decades has provided unprecedented insights into the highly complex process of cell division. There is an ever-expanding catalog of proteins that orchestrate, participate and coordinate in the exquisite processes of spindle formation, chromosome dynamics and the formation and regulation of kinetochore microtubule attachments. Use of classical microtubule poisons has still been widely and often successfully used to combat a variety of cancers, but their non-selective interference in other crucial physiologic processes necessitate the identification of novel druggable components specific to the cell cycle/division pathway. Considering cell cycle deregulation, unscheduled proliferation, genomic instability and chromosomal instability as a hallmark of tumor cells, there lies an enormous untapped terrain that needs to be unearthed before a drug can pave its way from bench to bedside. This review attempts to systematically summarize the advances made in this context so far with an emphasis on endocrine-related cancers and the avenues for future progress to target mitotic mechanisms in an effort to combat these dreadful cancers.

TP53 Mutational Status and ROS Effect the Expression of the Survivin-Associated Radio-Adaptive Response

A survivin-associated radio-adaptive response, characterized by increased radiation resistance or sensitization, was induced by exposure to 5 mGy of ionizing radiation and was correlated to the TP53 mutational status of exposed cells. Ten human cancer lines were investigated: colorectal carcinomas HCT116 and RKO [TP53 wild-type (WT)] and their respective TP53 null isogenic lines; breast adenocarcinomas MCF7 (TP53 WT) and MDA-MB-231 (TP53 Mut); lung carcinomas A549 (TP53 WT) and NCI-H1975 (TP53 Mut); and pancreatic carcinomas Hs766T (TP53 WT) and Panc-1 (TP53 Mut). Radiation induced (5 mGy) changes in the subsequent responses to 2 Gy in a multi-dose paradigm. Effects on radiation sensitivity were associated with changes in survivin's intracellular translocation to the cytoplasm (TP53 WT) or nucleus (TP53 Mut). Survival responses were determined using a colony forming assay. Intracellular localization of survivin was determined by ELISA and correlated with survival response. Two 2 Gy doses had minimal effects on the intracellular translocation of survivin. When preceded 15 min earlier by a 5 mGy exposure, survivin translocated to the cytoplasm in all of the TP53 WT cell lines, and to the nuclei in the TP53 null and Mut cells. All TP53 WT cells were protected (P < 0.001) by 5 mGy exposures, while Mut cells were sensitized (P < 0.001). HCT116 and RKO TP53 WT cells were admixed with their respective isogenic TP53 null counterparts in different proportions: 75% to 25%, 50% to 50% and 25% to 75%, respectively. All mixed confluent cultures expressed enhanced radio-sensitization (P ≤ 0.047) characteristic of TP53 Mut cells, which could be inhibited by their exposure to the antioxidant N-acetyl-l-cysteine (NAC) indicating a role for intercellular signaling by reactive oxygen species (ROS). ROS signaling in propagating the survivin-mediated response is involved in both intra- and intercellular communication processes.

Glioblastoma cellular cross-talk converges on NF-κB to attenuate EGFR inhibitor sensitivity

Zanca et al. show that heterogeneous expression of the wild-type EGFR receptor and its constitutively active mutant form, EGFRvIII, limits sensitivity to EGFR-directed therapies through an interclonal communication mechanism mediated by IL-6 cytokine secreted from EGFRvIII-positive tumor cells.

In glioblastoma (GBM), heterogeneous expression of amplified and mutated epidermal growth factor receptor (EGFR) presents a substantial challenge for the effective use of EGFR-directed therapeutics. Here we demonstrate that heterogeneous expression of the wild-type receptor and its constitutively active mutant form, EGFRvIII, limits sensitivity to these therapies through an interclonal communication mechanism mediated by interleukin-6 (IL-6) cytokine secreted from EGFRvIII-positive tumor cells. IL-6 activates a NF-κB signaling axis in a paracrine and autocrine manner, leading to bromodomain protein 4 (BRD4)-dependent expression of the prosurvival protein survivin (BIRC5) and attenuation of sensitivity to EGFR tyrosine kinase inhibitors (TKIs). NF-κB and survivin are coordinately up-regulated in GBM patient tumors, and functional inhibition of either protein or BRD4 in in vitro and in vivo models restores sensitivity to EGFR TKIs. These results provide a rationale for improving anti-EGFR therapeutic efficacy through pharmacological uncoupling of a convergence point of NF-κB-mediated survival that is leveraged by an interclonal circuitry mechanism established by intratumoral mutational heterogeneity.

Very low doses of ionizing radiation and redox associated modifiers affect survivin-associated changes in radiation sensitivity

Exposure of cells to a dose of ionizing radiation as low as 5mGy can induce changes in radiation sensitivity expressed by cells exposed to subsequent higher doses at later times. This is referred to as an adaptive effect. We describe a unique survivin-associated adaptive response in which increased radiation resistance or sensitization of cells can be induced by exposure to 5mGy or to the reactive oxygen species (ROS) generating drug Emodin (1,3,8-trihydroxy-6-methylanthraquinone), a naturally occurring anthraquinone. The purpose of this study was to determine the role of ROS generating processes in affecting both the intracellular localization of the inhibitor of apoptosis protein survivin and its subsequent effect on radiation response in the presence or absence of the anti-oxidant N-acetyl-L-cysteine (NAC). Experiments were performed using two well characterized murine sarcomas: SA-NH p53 wild-type (WT) and FSa p53 mutant (Mut), grown either in culture or as solid tumors in the right hind legs of C3H mice. Doses of 5mGy or 50μM Emodin were used to induce changes in the response of these tumor cells to higher radiation exposures using a multi-dosing paradigm. Effects on radiation sensitivity were determined for SA-NH and FSa cells as a function of survivin translocation either to the cytoplasm or nucleus in the presence or absence of 10mM NAC treatment. In vitro survival assays (2Gy per fraction, two once daily fractions) and tumor growth delay (TGD) (5Gy per fraction, five once daily fractions) studies were performed. Intracellular localization of survivin was determined by enzyme-linked immunosorbent assay (ELISA) and correlated to survival response and treatment conditions. 2Gy alone had no effect on intracellular translocation of survivin. When preceded 15min earlier by 5mGy or Emodin exposures, survivin became elevated in the cytoplasm of p53 WT SA-NH as compared to the nuclei of p53 Mut FSa cells. SA-NH cells transfected with p53 small interfering RNA (siRNA), in contrast, responded similarly to p53 Mut FSa cells by becoming more radiation sensitive if exposed to 5mGy prior to each 2Gy irradiation. In contrast to their respective responses to five once daily 5Gy fractions, SA-NH tumors were protected by 5mGy exposures administered 15min prior to each daily 5Gy dose as evidenced by a more rapid growth (1.9 day decrease in TGD, P=0.032), while FSa tumors were sensitized, growing at a much slower rate (4.5 day increase in TGD, P<0.001). Exposure of SA-NH and FSa tumor cells to 10mM NAC inhibited the ability of 5mGy and Emodin to induce intracellular translocation of survivin and the corresponding altered adaptive survival response. The survivin-associated adaptive response can be induced following a multi-dosing scheme in which very low radiation doses are followed shortly thereafter by higher doses consistent with a standard image guided radiotherapy protocol that is currently widely used in the treatment of cancer. While induced by exposure to ROS generating stresses, the ultimate expression of changes in radiation response is dependent upon the bi-functionality of the tumor associated protein survivin and its intracellular translocation.

RanBP3 Regulates Melanoma Cell Proliferation via Selective Control of Nuclear Export

Chromosome region maintenance 1-mediated nucleocytoplasmic transport has been shown as a potential anticancer target in various malignancies. However, the role of the most characterized chromosome region maintenance 1 cofactor ran binding protein 3 (RanBP3) in cancer cell biology has never been investigated. Utilizing a loss-of-function experimental setting in a vast collection of genetically varied melanoma cell lines, we observed the requirement of RanBP3 in melanoma cell proliferation and survival. Mechanistically, we suggest the reinstatement of transforming growth factor-β (TGF-β)-Smad2/3-p21(Cip1) tumor-suppressor axis as part of the RanBP3 silencing-associated antiproliferative program. Employing extensive nuclear export sequence analyses and immunofluorescence-based protein localization studies, we further present evidence suggesting the requirement of RanBP3 function for the nuclear exit of the weak nuclear export sequence-harboring extracellular signal-regulated kinase protein, although it is dispensable for general CRM1-mediated nuclear export of strong nuclear export sequence-harboring cargoes. Rendering mechanistic support to RanBP3 silencing-mediated apoptosis, consequent to extracellular signal-regulated kinase nuclear entrapment, we observed increased levels of cytoplasmically restricted nonphosphorylated/active proapoptotic Bcl-2-antagonist of cell death (BAD) protein. Last, we present evidence suggesting the frequently activated mitogen-activated protein kinase signaling in melanoma as a potential founding basis for a deregulated post-translational control of RanBP3 activity. Collectively, the presented data suggest RanBP3 as a potential target for therapeutic intervention in human melanoma.

Chromosome region maintenance 1 expression and its association with clinical pathological features in primary carcinoma of the liver

Liver cancer is the third leading cause of cancer-associated mortality worldwide. Recurrence and metastasis are the major factors affecting the prognosis; thus, investigation of the underlying molecular mechanisms of invasion and metastasis, and detection of novel drug target may improve the mortality rate of liver cancer patients. Chromosome region maintenance 1 (CRM1) recognizes specific leucine-rich nuclear export signal sequences, and its overexpression is associated with tumor-suppressor gene inactivation, proliferation, invasion and resistance to chemotherapy. The aim of the present study was to examine the association of CRM1 expression with the clinical and pathological features of primary liver cancer. In total, 152 cases diagnosed with liver cancer were included. CRM1 expression was detected in cancer tissues and adjacent normal tissues by immunohistochemical assay. No statistically significant difference was found between the CRM1 expression levels in tumor and adjacent normal tissues (P=0.106). However, CRM1 expression in adjacent normal tissues was higher compared with that in tumor tissues in the negative hepatitis B envelope antigen (HBeAg; P=0.029) and low differentiation (P=0.004) groups. In tumor tissues, CRM1 expression was significantly correlated with differentiation (P=0.045), whereas in adjacent normal tissues, CRM1 expression was significantly correlated with the tumor diameter (P=0.004). Therefore, it can be concluded that CRM1 is highly expressed in both tumor and adjacent normal tissues. Furthermore, CRM1 expression is associated with the tumor differentiation degree and diameter. Lower differentiation and larger tumor diameter resulted in higher CRM1 expression in adjacent normal tissues, and higher tendency for invasion and metastasis. In addition, the risk of invasion and metastasis remains in chronic hepatitis B patients with negative HBeAg.

XPO1 Inhibition Enhances Radiation Response in Preclinical Models of Rectal Cancer

PURPOSE

Combination of radiation with radiosensitizing chemotherapeutic agents improves outcomes for locally advanced rectal cancer. Current treatment includes 5-fluorouracil-based chemoradiation prior to surgical resection; however pathologic complete response varies from 15% to 20%, prompting the need to identify new radiosensitizers. Exportin 1 (XPO1, also known as chromosome region 1, CRM1) mediates the nuclear export of critical proteins required for rectal cancer proliferation and treatment resistance. We hypothesize that inhibition of XPO1 may radiosensitize cancer cells by altering the function of these critical proteins resulting in decreased radiation resistance and enhanced antitumoral effects.

EXPERIMENTAL DESIGN

To test our hypothesis, we used the selective XPO1 inhibitor, selinexor, to inhibit nuclear export in combination with radiation fractions similar to that given in clinical practice for rectal cancer: hypofractionated short-course radiation dosage of 5 Gy per fraction or the conventional long-course radiation dosage of 1 Gy fractions. Single and combination treatments were tested in colorectal cancer cell lines and xenograft tumor models.

RESULTS

Combination treatment of radiotherapy and selinexor resulted in an increase of apoptosis and decrease of proliferation compared with single treatment, which correlated with reduced tumor size. We found that the combination promoted nuclear survivin accumulation and subsequent depletion, resulting in increased apoptosis and enhanced radiation antitumoral effects.

CONCLUSIONS

Our findings suggest a novel therapeutic option for improving radiation sensitivity in the setting of rectal cancer and provide the scientific rationale to evaluate this combination strategy for clinical trials.

HSET overexpression fuels tumor progression via centrosome clustering-independent mechanisms in breast cancer patients

Human breast tumors harbor supernumerary centrosomes in almost 80% of tumor cells. Although amplified centrosomes compromise cell viability via multipolar spindles resulting in death-inducing aneuploidy, cancer cells tend to cluster extra centrosomes during mitosis. As a result cancer cells display bipolar spindle phenotypes to maintain a tolerable level of aneuploidy, an edge to their survival. HSET/KifC1, a kinesin-like minus-end directed microtubule motor has recently found fame as a crucial centrosome clustering molecule. Here we show that HSET promotes tumor progression via mechanisms independent of centrosome clustering. We found that HSET is overexpressed in breast carcinomas wherein nuclear HSET accumulation correlated with histological grade and predicted poor progression-free and overall survival. In addition, deregulated HSET protein expression was associated with gene amplification and/or translocation. Our data provide compelling evidence that HSET overexpression is pro-proliferative, promotes clonogenic-survival and enhances cell-cycle kinetics through G2 and M-phases. Importantly, HSET co-immunoprecipitates with survivin, and its overexpression protects survivin from proteasome-mediated degradation, resulting in its increased steady-state levels. We provide the first evidence of centrosome clustering-independent activities of HSET that fuel tumor progression and firmly establish that HSET can serve both as a potential prognostic biomarker and as a valuable cancer-selective therapeutic target.

Anti-tumor activity of selective inhibitors of XPO1/CRM1-mediated nuclear export in diffuse malignant peritoneal mesothelioma: the role of survivin

Survivin, which is highly expressed and promotes cell survival in diffuse malignant peritoneal mesothelioma (DMPM), exclusively relies on exportin 1 (XPO1/CRM1) to be shuttled into the cytoplasm and perform its anti-apoptotic function. Here, we explored the efficacy of Selective Inhibitors of Nuclear Export (SINE), KPT-251, KPT-276 and the orally available, clinical stage KPT-330 (selinexor), in DMPM preclinical models. Exposure to SINE induced dose-dependent inhibition of cell growth, cell cycle arrest at G1-phase and caspase-dependent apoptosis, which were consequent to a decrease of XPO1/CRM1 protein levels and the concomitant nuclear accumulation of its cargo proteins p53 and CDKN1a. Cell exposure to SINE led to a time-dependent reduction of cytoplasmic survivin levels. In addition, after an initial accumulation, the nuclear protein abundance progressively decreased, as a consequence of an enhanced ubiquitination and proteasome-dependent degradation. SINE and the survivin inhibitor YM155 synergistically cooperated in reducing DMPM cell proliferation. Most importantly, orally administered SINE caused a significant anti-tumor effect in subcutaneous and orthotopic DMPM xenografts without appreciable toxicity. Overall, we have demonstrated a marked efficacy of SINE in DMPM preclinical models that may relay on the interference with survivin intracellular distribution and function. Our study suggests SINE-mediated XPO1/CRM1 inhibition as a novel therapeutic option for DMPM.

Epigallocatechin-3-gallate enhances the therapeutic effects of leptomycin B on human lung cancer a549 cells

Our previous studies have shown Leptomycin B (LMB) is a promising antilung cancer drug. Epigallocatechin-3-gallate (EGCG) has antitumor properties but a debatable clinical application. The objective of this study is to evaluate the combination therapeutic effect of LMB and EGCG and its molecular mechanisms in human lung cancer A549 cells. Increased cytotoxicity was observed in LMB+EGCG-treated cells compared to LMB-treated cells. Elevated ROS was maximized 2 h after treatment, and LMB+EGCG-treated cells had higher ROS levels compared to LMB. N-Acetyl-L-cysteine (NAC) studies confirmed the oxidative role of LMB and/or EGCG treatment. In comparison to the control, CYP3A4, SOD, GPX1, and p21 mRNA expression levels were increased 7.1-, 2.0-, 4.6-, and 13.1-fold in LMB-treated cells, respectively, while survivin was decreased 42.6-fold. Additionally, these increases of CYP3A4, SOD, and GPX1 were significantly reduced, while p21 was significantly increased in LMB+EGCG-treated cells compared to LMB-treated cells. The qRT-PCR results for p21 and survivin were further confirmed by Western blot. Our study first shows that LMB produces ROS and is possibly metabolized by CYP3A4, GPX1, and SOD in A549 cells, and combination treatment of LMB and EGCG augments LMB-induced cytotoxicity through enhanced ROS production and the modulation of drug metabolism and p21/survivin pathways.

CRM1 as a new therapeutic target for non-Hodgkin lymphoma

The chromosomal region maintenance 1 (CRM1) may serve as a novel target for cancer treatment. Here, we investigated the anti non-Hodgkin lymphoma (NHL) activity of two novel CRM1 inhibitors (KPT-185 and KPT-276) in vitro and in vivo. KPT-185 displayed potent antiproliferative properties and induced cell-cycle arrest and apoptosis in several NHL cell lines and patients' tumor cells. The antitumor activity mainly consisted of inducing caspase cleavage and downregulating the expression of antiapoptotic proteins such as CRM1, nuclear factor-κB, and survivin. Furthermore, oral administration of KPT-276 significantly suppressed tumor growth in mice with Jeko-1 xenograft without any major toxic effects.

XPO1/CRM1-selective inhibitors of nuclear export (SINE) reduce tumor spreading and improve overall survival in preclinical models of prostate cancer (PCa)

BACKGROUND

Exportin 1 (XPO1), also called chromosome region maintenance 1 (CRM1), is the sole exportin mediating transport of many multiple tumor suppressor proteins out of the nucleus.

AIM AND METHODS

To verify the hypothesis that XPO1 inhibition affects prostate cancer (PCa) metastatic potential, orally available, potent and selective, SINE compounds, Selinexor (KPT- 330) and KPT-251, were tested in preclinical models known to generate bone lesions and systemic tumor spread.

RESULTS

In vitro, Selinexor reduced both secretion of proteases and ability to migrate and invade of PCa cells. SINEs impaired secretion of pro-angiogenic and pro-osteolytic cytokines and reduced osteoclastogenesis in RAW264.7 cells. In the intra-prostatic growth model, Selinexor reduced DU145 tumor growth by 41% and 61% at the doses of 4 mg/Kg qd/5 days and 10 mg/Kg q2dx3 weeks, respectively, as well as the incidence of macroscopic visceral metastases. In a systemic metastasis model, following intracardiac injection of PCb2 cells, 80% (8/10) of controls, 10% (1/10) Selinexor- and 20% (2/10) KPT-251-treated animals developed radiographic evidence of lytic bone lesions. Similarly, after intra-tibial injection, the lytic areas were higher in controls than in Selinexor and KPT-251 groups. Analogously, the serum levels of osteoclast markers (mTRAP and type I collagen fragment, CTX), were significantly higher in controls than in Selinexor- and KPT-251-treated animals. Importantly, overall survival and disease-free survival were significantly higher in Selinexor- and KPT-251-treated animals when compared to controls.

CONCLUSIONS

Selective blockade of XPO1-dependent nuclear export represents a completely novel approach for the treatment of advanced and metastatic PCa.

Torc1/Torc2 inhibitor, Palomid 529, enhances radiation response modulating CRM1-mediated survivin function and delaying DNA repair in prostate cancer models

BACKGROUND

P529, a Torc1/Torc2 inhibitor, has demonstrated its potential as a radiosensitizer. However the molecular mechanisms underlying this phenomenon still need to be elucidated. Aim of this study is to dissect molecular mechanisms regulating the radiosensitizing properties of P529 in a wide panel of prostate cancer models.

METHODS

Six tumor cell lines and xenograft models were used for in vitro and in vivo studies. Clonogenic survival, apoptotic, autophagic, and senescence assays were used to examine the effects of ionizing radiation (IR) alone and in combination with P529. CRM1, survivin, GSK-3β, and DNA-DSBs expression and modulation, upon P529 and RT, were monitored by western blot. In vivo treatment response upon P529, irradiation or combination of P529 with IR was monitored by tumor volume, time to progression (TTP), and immunohistochemical analysis.

RESULTS

P529 treatment induced significantly more apoptosis and DNA double-strand break (DSB) when combined with radiotherapy resulting in cellular radiosensitization and growth delay of irradiated tumor xenografts. Upon P529 treatment Rad51, DNA-PKcs, and Ku70 protein expression was downregulated, indicating delayed DNA double-strand damage repair. The radiosensitizing properties of P529 were partially linked to GSK-3β, cyclin-D1, and c-myc modulation with associated inhibition of CRM1-mediated nuclear export of survivin. Importantly, autophagy and tumor senescence were involved in the enhanced P529 radioresponse.

CONCLUSIONS

Impaired DNA double-strand damage repair, inhibition of CRM1-mediated nuclear export of survivin, modulation of cyclin-D1 and c-myc with associated pro-apoptotic and autophagic and senescent events explain the radiosensitizing properties of P529 in preclinical models of prostate cancer.

XPO1 (CRM1) inhibition represses STAT3 activation to drive a survivin-dependent oncogenic switch in triple-negative breast cancer

Inhibition of XPO1 (CRM1)-mediated nuclear export of multiple tumor suppressor proteins has been proposed as a novel cancer therapeutic strategy to turn off oncogenic signals and enhance tumor suppression. Survivin is a multifunctional protein with oncogenic properties when expressed in the cytoplasm that requires the XPO1-RanGTP complex for its nuclear export. We investigated the antitumor mechanisms of the drug-like selective inhibitors of nuclear export (SINE) XPO1 antagonists KPT-185, KPT-251 KPT-276, and KPT-330 in estrogen receptor-positive and triple-negative breast cancer (TNBC) cell lines and xenograft models of human breast tumors. KPT compounds significantly inhibited breast cancer cell growth and induced tumor cell death, both in vitro and in vivo. These drugs initially promoted survivin accumulation within tumor cell nuclei. However, their major in vitro effect was to decrease survivin cytoplasmic protein levels, correlating with the onset of apoptosis. XPO1 inhibition repressed Survivin transcription by inhibiting CREB-binding protein-mediated STAT3 acetylation, and blocking STAT3 binding to the Survivin promoter. In addition, caspase-3 was activated to cleave survivin, rendering it unavailable to bind X-linked inhibitor of apoptosis protein and block the caspase cascade. Collectively, these data demonstrate that XPO1 inhibition by SINE compounds represses STAT3 transactivation to block the selective oncogenic properties of survivin and supports their clinical use in TNBC.

Expression of nuclear survivin in normal skin and squamous cell carcinoma: a possible role in tumour invasion

Background:

Survivin is detected in few adult normal cells and it is highly expressed in cancer. Nuclear survivin facilitates cell cycle entry, whereas the mitochondrial pool protects cells from apoptosis. Survivin is overexpressed in keratinocyte stem cells (KSCs) and protects them from apoptosis.

Methods:

As KSCs are at the origin of squamous cell carcinoma (SCC), we evaluated survivin expression in normal and cancerous skin in vivo by immunohistochemistry and western blotting. HaCaT cells overexpressing survivin and wound-healing assay are used. Analysis of variance and Student's T-tests are used for statistical analysis.

Results:

Survivin is localised in both the cytoplasm and nucleus of normal adult and young keratinocytes. Nuclear survivin is detected in one every 10 of 11 basal keratinocytes. When present in suprabasal cells, nuclear survivin is coexpressed with K10 but not with K15 or p75-neurotrophin receptor (p75NTR), a transit amplifying cell marker. Nuclear, but not cytoplasmic, survivin expression markedly increases in actinic keratosis and in SCC in situ, as compared with normal epidermis, and it is highest in poorly differentiated SCC. In SCC tumours, nuclear survivin-positive cells are mainly K10/p75NTR-negative and K15-positive. In poorly differentiated tumours, survivin mostly localises in the deep infiltrating areas. When overexpressed in keratinocytes, survivin increases cell migration.

Conclusion:

High survivin expression and the subcellular localisation of survivin correlate with keratinocyte differentiation and are associated with undifferentiated and more invasive SCC phenotype.

Survivin - biology and potential as a therapeutic target in oncology

Survivin is a member of the inhibitor-of-apoptosis proteins (IAPs) family; its overexpression has been widely demonstrated to occur in various types of cancer. Overexpression of survivin also correlates with tumor progression and induces anticancer drug resistance. Interestingly, recent studies reveal that survivin exhibits multiple pro-mitotic and anti-apoptotic functions; the differential functions of survivin seem to be caused by differential subcellular localization, phosphorylation, and acetylation of this molecule. In this review, the complex expression regulations and post-translational modifications of survivin are discussed. This review also discusses how recent discoveries improve our understanding of survivin biology and also create opportunities for developing differential-functioned survivin-targeted therapy. Databases such as PubMed, Scopus® (Elsevier, New York, NY, USA), and SciFinder® (CAS, Columbus, OH, USA) were used to search for literature in the preparation of this review.

Function of survivin in trophoblastic cells of the placenta

BACKGROUND

Preeclampsia is one of the leading causes of maternal and perinatal mortality and morbidity worldwide and its pathogenesis is not totally understood. As a member of the chromosomal passenger complex and an inhibitor of apoptosis, survivin is a well-characterized oncoprotein. Its roles in trophoblastic cells remain to be defined.

METHODS

The placental samples from 16 preeclampsia patients and 16 well-matched controls were included in this study. Real-time PCR, immunohistochemistry and Western blot analysis were carried out with placental tissues. Primary trophoblastic cells from term placentas were isolated for Western blot analysis. Cell proliferation, cell cycle analysis and immunofluorescence staining were performed in trophoblastic cell lines BeWo, JAR and HTR-8/SVneo.

RESULTS

The survivin gene is reduced but the protein amount is hardly changed in preeclamptic placentas, compared to control placentas. Upon stress, survivin in trophoblastic cells is phosphorylated on its residue serine 20 by protein kinase A and becomes stabilized, accompanied by increased heat shock protein 90. Depletion of survivin induces chromosome misalignment, abnormal centrosome integrity, and reduced localization and activity of Aurora B at the centromeres/kinetochores in trophoblastic metaphase cells.

CONCLUSIONS

Our data indicate that survivin plays pivotal roles in cell survival and proliferation of trophoblastic cells. Further investigations are required to define the function of survivin in each cell type of the placenta in the context of proliferation, differentiation, apoptosis, angiogenesis, migration and invasion.

Potential effects of CRM1 inhibition in mantle cell lymphoma

Mantle cell lymphoma (MCL) is an aggressive histotype of B-cell non-Hodgkin lymphoma. The disease has no known cure, which prompts the urgent need for novel therapeutic agents. Chromosomal region maintenance 1 (CRM1) may play a role in human neoplasia and serve as a novel target of cancer treatment. This study summarizes MCL pathogenesis and determines the involvement of CRM1 in the regulation of several vital signaling pathways contributing to MCL pathogenesis, including the pathways of cell cycle progression, DNA damage response, phosphoinositide kinase-3, nuclear factor-κB activation, and chromosomal stability. A preclinical study is also presented to compare the CRM1 status in MCL cell lines and primary MCL cells with normal B cells, as well as the therapeutic efficiency of CRM1 inhibition in MCL in vitro and in vivo, which make these agents potential targets of novel MCL treatments.

The process of apoptosis in a holocrine gland as shown by the avian uropygial gland

This study was designed to elucidate the presence of apoptosis and the localization of apoptosis-related Bax and survivin proteins and proliferating cell nuclear antigen (PCNA) within the chicken uropygial gland, a specialized holocrine secretory gland. In day-old chicks, survivin and Bax immunoreactivities were observed in the cell cytoplasm of the germinative and secretory layers of the luminal epithelium and tubules. During this period, the TUNEL reaction, an indication of apoptosis, was only sporadically positive in the tubules. From the 7th day to the 150th day of posthatching, survivin was detected in the cytoplasm of cells in the germinative layer and in the nuclei of some cells in the secretory layers of the gland. The germinative layer cells showed weak homogeneous cytoplasmic staining for Bax, whereas the cells of the secretory and intermediate layers of luminal epithelium and tubules exhibited granular cytoplasmic staining. After day 7, TUNEL-positive cells were observed in the secretory and degenerative layers of the luminal epithelium and central tubules. After day 12, some TUNEL-positive cells were also seen in the peripheral tubules. At all posthatch ages, the cytoplasm and nucleus of the germinative layers of luminal epithelium and tubules reacted with PCNA, whereas only a small number of cell nuclei in the secretory layers were immunopositive. These results support the theory that specific PCNA/Bax/survivin expression patterns could reflect particular cell differentiation states in the uropygial gland and that holocrine secretion in the gland is realized mainly by way of apoptosis.

Survivin selective inhibitor YM155 induce apoptosis in SK-NEP-1 Wilms tumor cells

Background

Survivin, a member of the family of inhibitor of apoptosis proteins, functions as a key regulator of mitosis and programmed cell death. YM155, a novel molecular targeted agent, suppresses survivin, which is overexpressed in many tumor types. The aim of this study was to determine the antitumor activity of YM155 in SK-NEP-1 cells.

Methods

SK-NEP-1 cell growth in vitro and in vivo was assessed by MTT and nude mice experiments. Annexin V/propidium iodide staining followed by flow cytometric analysis was used to detect apoptosis in cell culture. Then gene expression profile of tumor cells treated with YM155 was analyzed with real-time PCR arrays. We then analyzed the expression data with MEV (Multi Experiment View) cluster software. Datasets representing genes with altered expression profile derived from cluster analyses were imported into the Ingenuity Pathway Analysis tool.

Results

YM155 treatment resulted in inhibition of cell proliferation of SK-NEP-1cells in a dose-dependent manner. Annexin V assay, cell cycle, and activation of caspase-3 demonstrates that YM155 induced apoptosis in SK-NEP-1 cells. YM155 significantly inhibited growth of SK-NEP-1 xenografts (YM155 5 mg/kg: 1.45 ± 0.77 cm³; YM155 10 mg/kg: 0.95 ± 0.55 cm³) compared to DMSO group (DMSO: 3.70 ± 2.4 cm³) or PBS group cells (PBS: 3.78 ± 2.20 cm³, ANOVA P < 0.01). YM155 treatment decreased weight of tumors (YM155 5 mg/kg: 1.05 ± 0.24 g; YM155 10 mg/kg: 0.72 ± 0.17 g) compared to DMSO group (DMSO: 2.06 ± 0.38 g) or PBS group cells (PBS: 2.36 ± 0.43 g, ANOVA P < 0.01). Real-time PCR array analysis showed between Test group and control group there are 32 genes significantly up-regulated and 54 genes were significantly down-regulated after YM155 treatment. Ingenuity pathway analysis (IPA) showed cell death was the highest rated network with 65 focus molecules and the significance score of 44. The IPA analysis also groups the differentially expressed genes into biological mechanisms that are related to cell death, cellular function maintenance, cell morphology, carbohydrate metabolism and cellular growth and proliferation. Death receptor signaling (3.87E-19), TNFR1 signaling, induction of apoptosis by HIV1, apoptosis signaling and molecular mechanisms of cancer came out to be the top four most significant pathways. IPA analysis also showed top molecules up-regulated were BBC3, BIRC3, BIRC8, BNIP1, CASP7, CASP9, CD5, CDKN1A, CEBPG and COL4A3, top molecules down-regulated were ZNF443, UTP11L, TP73, TNFSF10, TNFRSF1B, TNFRSF25, TIAF1, STK17A, SST and SPP1, upstream regulator were NR3C1, TP53, dexamethasone , TNF and Akt.

Conclusions

The present study demonstrates that YM155 treatment resulted in apoptosis and inhibition of cell proliferation of SK-NEP-1cells. YM155 had significant role and little side effect in the treatment of SK-NEP-1 xenograft tumors. Real-time PCR array analysis firstly showed expression profile of genes dyes-regulated after YM155 treatment. IPA analysis also represents new molecule mechanism of YM155 treatment, such as NR3C1 and dexamethasone may be new target of YM155. And our results may provide new clues of molecular mechanism of apoptosis induced by YM155.

Functional characterization of novel mutations affecting survivin (BIRC5)-mediated therapy resistance in head and neck cancer patients

Survivin (BIRC5) is an acknowledged cancer therapy-resistance factor and overexpressed in head and neck squamous cell carcinomas (HNSCC). Driven by its nuclear export signal (NES), Survivin shuttles between the nucleus and the cytoplasm, and is detectable in both cellular compartments in tumor biopsies. Although predominantly nuclear Survivin is considered a favorable prognostic disease marker for HNSCC patients, the underlying molecular mechanisms are not resolved. Hence, we performed immunohistochemical and mutational analyses using laser capture microdissection on HNSCC biopsies from patients displaying high levels of nuclear Survivin. We found somatic BIRC5 mutations, c.278T>C (p.Phe93Ser), c.292C>T (p.Leu98Phe), and c.288A>G (silent), in tumor cells, but not in corresponding normal tissues. Comprehensive functional characterization of the Survivin mutants by ectopic expression and microinjection experiments revealed that p.Phe93Ser, but not p.Leu98Phe inactivated Survivin's NES, resulted in a predominantly nuclear protein, and attenuated Survivin's dual cytoprotective activity against chemoradiation-induced apoptosis. Notably, in xenotransplantation studies, HNSCC cells containing the p.Phe93Ser mutation responded significantly better to cisplatin-based chemotherapy. Collectively, our results underline the disease relevance of Survivin's nucleocytoplasmic transport, and provide first evidence that genetic inactivation of Survivin's NES may account for predominantly nuclear Survivin and increased therapy response in cancer patients.

Inhibition of CRM1-mediated nucleocytoplasmic transport: triggering human melanoma cell apoptosis by perturbing multiple cellular pathways

Development of multiple drug resistance mechanisms in melanomas necessitates the identification of new drug targets, which when inhibited could impact multiple cellular pathways, thus circumventing potential resistance. By performing complementary DNA microarray analysis, we identified four key components of the nucleocytoplasmic transport machinery-CRM1, RAN (RAN-GTPase), RANGAP1, and RANBP1-to be overexpressed in human melanoma metastases. Chromosome region maintenance 1 (CRM1) inhibition induced a marked depletion of prosurvival/cytoplasmic extracellular signal-regulated kinase 1/2 (Erk1/2) and p90 ribosomal S6 kinase1 and elicited persistent Erk-signaling hyperactivation. Consistently, CRM1 inhibition inflicted extensive apoptosis in melanoma cells while sparing nontransformed melanocytes and primary lung fibroblasts. Apoptosis required both the intrinsic and extrinsic apoptotic pathways and was associated with a nuclear entrapment and downregulation of the antiapoptotic CRM1 target protein, Survivin. Apoptosis was preceded by a G1 cell-cycle arrest, and even though CRM1 inhibition mediated marked p53 and p21 induction in wild-type p53 melanoma cells, the latter's silencing or inactivation failed to alleviate apoptosis. Notably, CRM1 inhibition induced cell line-specific, G1 to S progression-retarding changes in the expression of multiple cell-cycle regulatory proteins, thus potentially explaining p53 dispensability. We propose CRM1 as a potential therapeutic target in human melanoma, whose inhibition induces loss of prosurvival/cytoplasmic Erk1/2, mediates persistent Erk hyperactivation, and initiates a multitude of cell context-dependent molecular events to trigger G1 arrest followed by massive apoptosis.

Survivin expression is associated with lens epithelial cell proliferation and fiber cell differentiation

PURPOSE

Survivin (Birc5) is the smallest member of the inhibitor of apoptosis (IAP) protein family, which regulates the cell cycle/apoptosis balance. The purpose of this study was to examine Survivin expression in the embryonic chick lens, in chick lens epithelial cell cultures, and in the postnatal mouse lens.

METHODS

Survivin expression was examined using a combination of quantitative real-time polymerase chain reaction, western blotting, and immunocytochemistry. To correlate Survivin expression with the timing of proliferation, we determined the profile of cell proliferation in the developing lens using the cell cycle marker proliferating cell nuclear antigen (PCNA) in quantitative western blotting and immunocytochemistry studies. We also examined the expression of PCNA and the extent of denucleation using terminal deoxynucleotidyl transferase (TdT)-mediated biotin-dUTP nick-end labeling (TUNEL) of lentoids (lens fiber-like cells) during chick lens epithelial cell differentiation in vitro.

RESULTS

At embryonic day (ED) 4, Survivin immunostaining was present in two pools in lens epithelial cells and fiber cells: cytoplasmic and nuclear. The nuclear staining became more pronounced as the lens epithelial cells differentiated into lens fiber cells. At ED12, Survivin staining was observed in lens fiber cell nuclei containing marginalized chromatin, indicative of early denucleation events. Using western blotting, Survivin expression peaked at ED6, diminishing thereafter. This profile of expression correlated with the events in chick lens epithelial cell cultures: i) increased Survivin expression was associated with an increase in PCNA staining up to day 6 of culture and ii) downregulation of Survivin expression at day 8 of culture was coincident with a dramatic decrease in PCNA staining and an increase in TdT-mediated biotin-dUTP nick-end labeling in lentoids. In early postnatal mouse lenses, Survivin and PCNA were highly expressed and decreased thereafter during postnatal lens maturation.

CONCLUSIONS

Survivin is expressed during chick and mouse lens development and in chick lens epithelial cell cultures. High levels of Survivin expression correlated with high rates of proliferation of lens epithelial cells at early stages of development. Downregulation of Survivin expression with development and its progressive localization to the nuclei of lens fiber cells was coincident with a decrease in cell proliferation and increased denucleation in differentiating lens fiber cells. These studies suggest an important role for Survivin as a dual regulator of lens epithelial cell proliferation and lens fiber cell differentiation.

Novel transglutaminase 1 mutations in patients affected by lamellar ichthyosis

Lamellar Ichthyosis (LI) is a form of congenital ichthyosis that is caused by mutations in the TGM1 gene that encodes for the transglutaminase 1 (TG1) enzyme. Functional inactivation of TG1 could be due to mutations, deletion or insertions. In this study, we have screened 16 patients affected by LI and found six new mutations: two transition/transversion (R37G, V112A), two nonsense mutations and two putative splice site both leading to a premature stop codon. The mutations are localized in exons 2 (N-terminal domain), 5, 11 (central catalytic domain), and none is located in the two beta-barrel C-terminal domains. In conclusion, this study expands the current knowledge on TGM1 mutation spectrum, increasing the characterization of mutations would provide more accurate prenatal genetic counselling for parents at-risk individuals.

Mitosis-targeted anti-cancer therapies: where they stand

The strategy of clinically targeting cancerous cells at their most vulnerable state during mitosis has instigated numerous studies into the mitotic cell death (MCD) pathway. As the hallmark of cancer revolves around cell-cycle deregulation, it is not surprising that antimitotic therapies are effective against the abnormal proliferation of transformed cells. Moreover, these antimitotic drugs are also highly selective and sensitive. Despite the robust rate of discovery and the development of mitosis-selective inhibitors, the unpredictable complexities of the human body's response to these drugs still herald the biggest challenge towards clinical success. Undoubtedly, the need to bridge the gap between promising preclinical trials and effective translational bedside treatment prompts further investigations towards mapping out the mechanistic pathways of MCD, understanding how these drugs work as medicine in the body and more comprehensive target validations. In this review, current antimitotic agents are summarized with particular emphasis on the evaluation of their clinical efficacy as well as their limitations. In addition, we discuss the basis behind the lack of activity of these inhibitors in human trials and the potential and future directions of mitotic anticancer strategies.

The CRM1 nuclear export protein in normal development and disease

CRM1 (Chromosomal Maintenance 1, also known as Exportin 1) is the major mammalian export protein that facilitates the transport of large macromolecules including RNA and protein across the nuclear membrane to the cytoplasm. The gene encoding CRM1 was originally identified in yeast as required to maintain higher order chromosome structure. In mammalian cells, CRM1 was found to bind several nuclear pore proteins hence its role in nuclear-cytosolic transport was discovered. In addition to nuclear-cytosolic transport, CRM1 also plays a role in centrosome duplication and spindle assembly, especially in response to DNA damage. The crystal structure of CRM1 suggests a complex protein that binds the Ran protein bound to GTP, allowing for a conformational change that facilitates binding to different cargo proteins through a nuclear export signal (NES). Included in the cadre of cargo are multiple tumor suppressor and oncoproteins as p53, BRCA1, Survivin, NPM, and APC, which function in the nucleus to regulate transcription or aid in chromosomal assembly and movement. An imbalance in the cytosolic level of these proteins has been observed in cancer cells, resulting in either inactivation (tumor suppressor) or an excess of anti-apoptotic activity (oncoprotein). Thus, the concept of inhibiting CRM1 has been explored as a potential therapeutic intervention. Indeed, inhibition of CRM1 by a variety of small molecules that interfere with cargo-NES binding results in cancer cell death. Whether all of these proteins together are responsible for this phenotype or whether specific proteins are required for this effect is unclear at this time.

Histone deacetylase 6 (HDAC6) deacetylates survivin for its nuclear export in breast cancer

Survivin is an oncogenic protein that is highly expressed in breast cancer and has a dual function that is dependent on its subcellular localization. In the cytosol, survivin blocks programmed cell death by inactivating caspase proteins; however, in the nucleus it facilitates cell division by regulating chromosomal movement and cytokinesis. In prior work, we showed that survivin is acetylated by CREB-binding protein (CBP), which restricts its localization to the nuclear compartment and thereby inhibits its anti-apoptotic function. Here, we identify histone deacetylase 6 (HDAC6) as responsible for abrogating CBP-mediated survivin acetylation in the estrogen receptor (ER)-positive breast cancer cell line, MCF-7. HDAC6 directly binds survivin, an interaction that is enhanced by CBP. In quiescent breast cancer cells in culture and in malignant tissue sections from ER+ breast tumors, HDAC6 localizes to a perinuclear region of the cell, undergoing transport to the nucleus following CBP activation where it then deacetylates survivin. Genetically modified mouse embryonic fibroblasts that lack mhdac6 localize survivin predominantly to the nuclear compartment, whereas wild-type mouse embryonic fibroblasts localize survivin to distinct cytoplasmic structures. Together, these data imply that HDAC6 deacetylates survivin to regulate its nuclear export, a feature that may provide a novel target for patients with ER+ breast cancer.

Hormesis, cell death and aging

Frequently, low doses of toxins and other stressors not only are harmless but also activate an adaptive stress response that raise the resistance of the organism against high doses of the same agent. This phenomenon, which is known as "hormesis", is best represented by ischemic preconditioning, the situation in which short ischemic episodes protect the brain and the heart against prolonged shortage of oxygen and nutrients. Many molecules that cause cell death also elicit autophagy, a cytoprotective mechanism relying on the digestion of potentially harmful intracellular structures, notably mitochondria. When high doses of these agents are employed, cells undergo mitochondrial outer membrane permeabilization and die. In contrast, low doses of such cytotoxic agents can activate hormesis in several paradigms, and this may explain the lifespan-prolonging potential of autophagy inducers including resveratrol and caloric restriction.

Cell death pathology: the war against cancer

Programmed cell death was a fundamental discovery, awarded with the Nobel price in 2002 to Sulston, Brenner and Horvitz. Since then it has been clear that alteration of apoptotic pathways is a common feature of tumors, enabling cancer cells to survive chemotherapeutic interventions. Thus, apoptosis is an attractive target in cancer therapy, with the aim to revert the cancer-related alterations of the cell death machinery. Here, we overview the fundamental apoptotic pathways and summarize the attempts to target apoptosis to restore cell death in cancer cells with a special focus on the p53-family and autophagy.

Cell death in disease: from 2010 onwards

The strong interest in cell death, and the shift in emphasis from basic mechanisms to translational aspects fostered the launch last year of the new sister journal of Cell Death and Differentiation, named Cell Death and Disease, to reflect its stronger focus towards clinical applications. Here, we review that first year of activity, which reflects an enthusiastic response by the scientific community. On the basis of this, we now launch two novel initiatives, the start of a new section dedicated to cancer metabolism and the opening of a new editorial office in Shanghai.

Survivin monomer plays an essential role in apoptosis regulation

Survivin was initially described as an inhibitor of apoptosis and attracted growing attention as one of the most tumor-specific genes in the human genome and a promising target for cancer therapy. Lately, it has been shown that survivin is a multifunctional protein that takes part in several crucial cell processes. At first, it was supposed that survivin functions only as a homodimer, but now data indicate that many processes require monomeric survivin. Moreover, recent studies reveal a special mechanism regulating the balance between monomeric and dimeric forms of the protein. In this paper we studied the mutant form of survivin that was unable to dimerize and investigated its role in apoptosis. We showed that survivin monomer interacts with Smac/DIABLO and X-linked inhibitor of apoptosis protein (XIAP) both in vitro and in vivo. Due to this feature, it protects cells from caspase-dependent apoptosis even more efficiently than the wild-type survivin. We also identified that mutant monomeric survivin prevents apoptosis-inducing factor release from the mitochondrial intermembrane space, protecting human fibrosarcoma HT1080 cells from caspase-independent apoptosis. On the other hand, our results indicate that only wild-type survivin, but not the monomer mutant form, enhances tubulin stability in cells. These findings suggest that survivin partly performs its functions as a monomer and partly as a dimer. The mechanism of dimer-monomer balance regulation may also work as a "switcher" between survivin functions and thereby explain remarkable functional diversities of this protein.