iASPP inhibits p53-independent apoptosis by inhibiting transcriptional activity of p63/p73 on promoters of proapoptotic genes

iASPP regulates neurite development by interacting with Spectrin proteins

Introduction

Since its discovery in 1999, a substantial body of research has shown that iASPP is highly expressed in various kinds of tumors, interacts with p53, and promotes cancer cell survival by antagonizing the apoptotic activity of p53. However, its role in neurodevelopment is still unknown.

Methods

We studied the role of iASPP in neuronal differentiation through different neuronal differentiation cellular models, combined with immunohistochemistry, RNA interference and gene overexpression, and studied the molecular mechanism involved in the regulation of neuronal development by iASPP through coimmunoprecipitation coupled with mass spectrometry (CoIP-MS) and coimmunoprecipitation (CoIP).

Results

In this study, we found that the expression of iASPP gradually decreased during neuronal development. iASPP silencing promotes neuronal differentiation, while its overexpression inhibited neurite differentiation in a variety of neuronal differentiation cellular models. iASPP associated with the cytoskeleton-related protein Sptan1 and dephosphorylated the serine residues in the last spectrin repeat domain of Sptan1 by recruiting PP1. The non-phosphorylated and phosphomimetic mutant form of Sptbn1 inhibited and promoted neuronal cell development respectively.

Conclusion

Overall, we demonstrate that iASPP suppressed neurite development by inhibiting phosphorylation of Sptbn1.

Distinct interactors define the p63 transcriptional signature in epithelial development or cancer

The TP63 is an indispensable transcription factor for development and homeostasis of epithelia and its derived glandular tissue. It is also involved in female germline cell quality control, muscle and thymus development. It is expressed as multiple isoforms transcribed by two independent promoters, in addition to alternative splicing occurring at the mRNA 3′-UTR. Expression of the TP63 gene, specifically the amino-deleted p63 isoform, ΔNp63, is required to regulate numerous biological activities, including lineage specification, self-renewal capacity of epithelial stem cells, proliferation/expansion of basal keratinocytes, differentiation of stratified epithelia. In cancer, ΔNp63 is implicated in squamous cancers pathogenesis of different origin including skin, head and neck and lung and in sustaining self-renewal of cancer stem cells. How this transcription factor can control such a diverse set of biological pathways is central to the understanding of the molecular mechanisms through which p63 acquires oncogenic activity, profoundly changing its down-stream transcriptional signature. Here, we highlight how different proteins interacting with p63 allow it to regulate the transcription of several central genes. The interacting proteins include transcription factors/regulators, epigenetic modifiers, and post-transcriptional modifiers. Moreover, as p63 depends on its interactome, we discuss the hypothesis to target the protein interactors to directly affect p63 oncogenic activities and p63-related diseases.

iASPP is essential for HIF-1α stabilization to promote angiogenesis and glycolysis via attenuating VHL-mediated protein degradation

Hypoxia-inducible factor-1α (HIF-1α) plays central roles in the hypoxia response. It is highly expressed in multiple cancers, but not always correlated with hypoxia. Mutation of the von Hippel-Lindau (VHL) gene, which encodes an E3 ligase, contributes to the constructive activation of HIF-1α in specific tumor types, as exemplified by renal cell carcinoma; but how VHL wild-type tumors acquire this ability is not completely understood. Here, we found that the oncogene iASPP (inhibitor of apoptosis-simulating protein of p53) plays essential roles in such a context. Genetic inhibition of iASPP reduced tumor growth, accompanied by impaired angiogenesis, increased areas of tumor necrosis, and reduced glycolysis that was HIF-1α-dependent. These abilities of iASPP were validated by in vitro assays. Mechanistically, iASPP directly binds VHL at its β domain, a region also involved in HIF-1α binding, therefore blocking VHL's binding and the subsequent degradation of HIF-1α protein under normoxia. iASPP levels correlate with HIF-1α protein and vascular endothelial growth factor (VEGF) and the glucose transporter protein type 1(GLUT1), representative HIF-1α target genes, in human colon cancer tissues. Furthermore, inhibition of iASPP expression synergizes with low toxic dose of the HIF-1α inhibitor YC-1 to inhibit HIF-1α expression and tumor growth. Our findings suggest that iASPP contributes to HIF-1α activation in cancers, and that iASPP-mediated HIF-1α stabilization has potential as a therapeutic approach against cancer.

Upregulation of iASPP ameliorates hypoxia/reoxygenation-induced apoptosis and oxidative stress in cardiomyocytes by upregulating Nrf2 signaling

The inhibitor of apoptosis-stimulating protein of p53 (iASPP) acts as a key modulator of cellular protection against oxidative stress. In the present work, we assessed the role of iASPP in the regulation of cardiomyocyte injury induced by hypoxia/reoxygenation (H/R). We found that H/R-exposed cardiomyocytes expressed decreased levels of iASPP. The upregulation of iASPP repressed H/R-induced injury by decreasing levels of apoptosis and reactive oxygen species production. The upregulation of iASPP increased nuclear factor (erythroid-derived 2)-like 2 (Nrf2) nuclear translocation and enhanced Nrf2 activation. The overexpression of Kelch-like ECH-associated protein 1 reversed iASPP-mediated promotion of Nrf2 activation. Nrf2 inhibition abrogated iASPP-mediated cardioprotective effects in H/R-exposed cardiomyocytes. Our work demonstrates that the upregulation of iASPP ameliorates H/R-induced apoptosis and oxidative stress in cardiomyocytes via potentiating Nrf2 signaling via modulation of Keap1.

p53-Related Transcription Targets of TAp73 in Cancer Cells-Bona Fide or Distorted Reality?

Identification of p73 as a structural homolog of p53 fueled early studies aimed at determining if it was capable of performing p53-like functions. This led to a conundrum as p73 was discovered to be hardly mutated in cancers, and yet, TAp73, the full-length form, was found capable of performing p53-like functions, including transactivation of many p53 target genes in cancer cell lines. Generation of mice lacking p73/TAp73 revealed a plethora of developmental defects, with very limited spontaneous tumors arising only at a later stage. Concurrently, novel TAp73 target genes involved in cellular growth promotion that are not regulated by p53 were identified, mooting the possibility that TAp73 may have diametrically opposite functions to p53 in tumorigenesis. We have therefore comprehensively evaluated the TAp73 target genes identified and validated in human cancer cell lines, to examine their contextual relevance. Data from focused studies aimed at appraising if p53 targets are also regulated by TAp73—often by TAp73 overexpression in cell lines with non-functional p53—were affirmative. However, genome-wide and phenotype-based studies led to the identification of TAp73-regulated genes involved in cellular survival and thus, tumor promotion. Our analyses therefore suggest that TAp73 may not necessarily be p53’s natural substitute in enforcing tumor suppression. It has likely evolved to perform unique functions in regulating developmental processes and promoting cellular growth through entirely different sets of target genes that are not common to, and cannot be substituted by p53. The p53-related targets initially reported to be regulated by TAp73 may therefore represent an experimental possibility rather than the reality.

miR-129 targets CDK1 and iASPP to modulate Burkitt lymphoma cell proliferation in a TAp63-dependent manner

Burkitt lymphoma is one of the most common lymphatic system cancers with poor outcome in adult patients. p53-induced apoptosis is a critical signaling for preventing tumor development. Cyclin B/cyclin-dependent kinase 1 (CDK1) phosphorylates inhibitor of apoptosis stimulating protein of P53 (iASPP) to promote iASPP nucleus localization and its inhibitory effect on p53. However, p53 is frequently mutated in Burkitt lymphoma, which gains novel oncogenic properties. Recently, the p53 family member, p63, became an attractive gene for the therapeutic strategies for patients with cancer. Therefore, we investigated the role of iASPP in the transactivation domain p63 (TAp63)-dependent cell proliferation inhibition in Burkitt lymphoma. We verified that the oncogenic effect of iASPP on Burkitt lymphoma is TAp63 dependent rather than p53 and confirmed that the interaction between CDK1 and iASPP enhanced the inhibitory effect of iASPP on p53 and TAp63. An online tool predicated that miR-129 might bind to 3'-untranslated region of iASPP and CDK1. We revealed that miR-129 acted as a tumor suppressor by inhibiting cancer cell proliferation and inhibiting CDK1 and iASPP via direct binding. An miR-129 inhibitor increased nucleus iASPP and decreased nucleus p53 and TAp63 levels, which could be reversed by the CDK1 knockdown, indicating that miR-129 might target CDK1 to inhibit iASPP phosphorylation, thus hindering iASPP nucleus localization and its inhibitory effect on p53 and TAp63 protein levels. Taken together, miR-129 could targetedly inhibit the expression of CDK1 and iASPP. CDK1 knockdown inhibits iASPP S84/S113 phosphorylation, thus blocking iASPP nucleus localization, suppressing the inhibitory effect of iASPP on p53 and TAp63, and restoring TAp63-induced proliferation inhibition in Burkitt lymphoma cells.

Mild Therapeutic Hypothermia Protects the Brain from Ischemia/Reperfusion Injury through Upregulation of iASPP

Mild therapeutic hypothermia, a robust neuroprotectant, reduces neuronal apoptosis, but the precise mechanism is not well understood. Our previous study showed that a novel inhibitor of an apoptosis-stimulating protein of p53 (iASPP) might be involved in neuronal death after stroke. The aim of this study was to confirm the role of iASPP after stroke treated with mild therapeutic hypothermia. To address this, we mimicked ischemia/reperfusion injury in vitro by using oxygen-glucose deprivation/reperfusion (OGD/R) in primary rat neurons. In our in vivo approach, we induced middle cerebral artery occlusion (MCAO) for 60 min in C57/B6 mice. From the beginning of ischemia, focal mild hypothermia was applied for two hours. To evaluate the role of iASPP, small interfering RNA (siRNA) was injected intracerebroventricularly. Our results showed that mild therapeutic hypothermia increased the expression of iASPP and decreased the expression of its targets, Puma and Bax, and an apoptosis marker, cleaved caspase-3, in primary neurons under OGD/R. Increased iASPP expression and decreased ASPP1/2 expression were observed under hypothermia treatment in MCAO mice. iASPP siRNA (iASPPi) or hypothermia plus iASPPi application increased infarct volume, apoptosis and aggravated the neurological deficits in MCAO mice. Furthermore, iASPPi downregulated iASPP expression, and upregulated the expression of proapoptotic effectors, Puma, Bax and cleaved caspase-3, in mice after stroke treated with mild therapeutic hypothermia. In conclusion, mild therapeutic hypothermia protects against ischemia/reperfusion brain injury in mice by upregulating iASPP and thus attenuating apoptosis. iASPP may be a potential target in the therapy of stroke.

Role of Kruppel-like factor 4 in regulating inhibitor of apoptosis-stimulating protein of p53 in the progression of gastric cancer

Gastric cancer (GC) remains one of the leading causes of cancer-associated mortality. The overexpression of inhibitor of apoptosis-stimulating protein of p53 (iASPP) has been detected in GC tissues but the function of iASPP in the viability of GC cells and its underlying molecular mechanism remains unknown. Kruppel-like factor 4 (KLF4) is a tumor suppressor gene in GC and it may interact with p53. iASPP is an evolutionarily conserved inhibitor of p53, whereas KLF4 may be negatively associated with iASPP in GC. However, whether KLF4 has regulatory effects on iASPP remains to be investigated. The objective of the present study was to examine the function of iASPP and KLF4 in the proliferation of GC cells and to determine whether KLF4 has regulatory effects on iASPP. It was demonstrated that iASPP was upregulated and KLF4 was downregulated in GC cell lines. Downregulation of iASPP inhibited the proliferation and colony formation ability, and promoted the apoptosis of GC cells. Additionally, upregulation of KLF4 inhibited the proliferation and colony formation ability, and promoted apoptosis of GC cells. Furthermore, upregulation of KLF4 inhibited the expression of iASPP. Upregulation of iASPP following overexpression of KLF4 reversed the KLF4-mediated effects in GC cells. In vivo upregulation of KLF4 or downregulation of iASPP inhibited the growth of tumors, whereas upregulation of iASPP promoted the growth of tumors. In conclusion, iASPP may act as an oncogene that promotes the proliferation of GC cells. The results demonstrated that KLF4 was a negative regulatory factor of iASPP and that overexpression of iASPP inhibited the effects of KLF4. Thus, downregulation of KLF4 in GC may lead to overexpression of iASPP and promote the development of cancer.

MicroRNA-150 inhibits the proliferation and metastasis potential of colorectal cancer cells by targeting iASPP

In the present study, the function of miR-150 and its downstream target iASPP in the growth and metastasis of colorectal cancer (CRC) cells was investigated. The expression of miR-150 and iASPP was first investigated in clinical CRC samples. Subsequently, the effects of miR-150 overexpression and iASPP inhibition on cell viability, cell cycle distribution, apoptosis, migration and invasion were detected with CCK-8, flow cytometry, scratch and Transwell assays. The interaction between miR-150 and iASPP was confirmed using a dual-luciferase assay. Subsequently, the key role of iASPP in the anti-CRC function of miR-150 was assessed by inducing the expression of the gene in miR-150 overexpressed SW480 cells. In clinical samples, the level of miR-150 was downregulated, while iASPP was induced. Enforced expression of miR-150 decreased the viability, induced G1 cell cycle arrest and apoptosis, and inhibited the migration and invasion of SW480 cells. Knockdown of iASPP exerted a similar effect on SW480 cells to that of the overexpression of miR-150. Dual-luciferase assay demonstrated that miR-150 directly bound to iASPP and inhibited its transcription. The function of miR-150 depended on the inhibition of iASPP; induced expression of iASPP in miR-150-knockdown SW480 and HCT116 cells restored cell viability, migration and invasion while inhibiting G1 cell cycle arrest and apoptosis. Increased expression of miR-150 suppressed viability, proliferation, migration and invasion of SW480 cells. Furthermore, iASPP was a direct target of miR-150 and played a key role in its anti-CRC function. miR-150 may be a promising predictor of prognosis in CRC patients.

The miR-124-p63 feedback loop modulates colorectal cancer growth

Among the diverse co-regulatory relationships between transcription factors (TFs) and microRNAs (miRNAs), feedback loops have received the most extensive research attention. The co-regulation of TFs and miRNAs plays an important role in colorectal cancer (CRC) growth. Here, we show that miR-124 can regulate two isoforms of p63, TAp63 and ΔNp63, via iASPP, while p63 modulates signal transducers and activators of transcription 1 (STAT1) expression by targeting miR-155. Moreover, STAT1 acts as a regulator of CRC growth by targeting miR-124. Taken together, these results reveal a feedback loop between miRNAs and TFs. This feedback loop comprises miR-124, iASPP, STAT1, miR-155, TAp63 and ΔNp63, which are essential for CRC growth. Moreover, this feedback loop is perturbed in human colon carcinomas, which suggests that the manipulation of this microRNA-TF feedback loop has therapeutic potential for CRC.

2-anilino-4-amino-5-aroylthiazole-type compound AS7128 inhibits lung cancer growth through decreased iASPP and p53 interaction

Lung cancer is the leading cause of cancer-related death worldwide. Thus, developing novel therapeutic agents has become critical for lung cancer treatment. In this study, compound AS7128 was selected from a 2-million entry chemical library screening and identified as a candidate drug against non-small cell lung cancer in vitro and in vivo. Further investigation indicated that AS7128 could induce cell apoptosis and cell cycle arrest, especially in the mitosis stage. In addition, we also found that iASPP, an oncogenic protein that functionally inhibits p53, might be associated with AS7128 through mass identification. Further exploration indicated that AS7128 treatment could restore the transactivation ability of p53 and, thus, increase the expressions of its downstream target genes, which are related to cell cycle arrest and apoptosis. This occurs through disruption of the interactions between p53 and iASPP in cells. Taken together, AS7128 could bind to iASPP, disrupt the interaction between iASPP and p53, and result in cell cycle arrest and apoptosis. These findings may provide new insight for using iASPP as a therapeutic target for non-small cell lung cancer treatment.

A novel HSP90 inhibitor with reduced hepatotoxicity synergizes with radiotherapy to induce apoptosis, abrogate clonogenic survival, and improve tumor control in models of colorectal cancer

The chaperone heat shock protein 90 (HSP90) crucially supports the maturation, folding, and stability of a variety of client proteins which are of pivotal importance for the survival and proliferation of cancer cells. Consequently, targeting of HSP90 has emerged as an attractive strategy of anti-cancer therapy, and it appears to be particularly effective in the context of molecular sensitization towards radiotherapy as has been proven in preclinical models of different cancer entities. However, so far the clinical translation has largely been hampered by suboptimal pharmacological properties and serious hepatotoxicity of first- and second-generation HSP90 inhibitors. Here, we report on NW457, a novel radicicol-derived member of the pochoxime family with reduced hepatotoxicity, how it inhibits the DNA damage response and how it synergizes with ionizing irradiation to induce apoptosis, abrogate clonogenic survival, and improve tumor control in models of colorectal cancer in vitro and in vivo.

Sertad1 antagonizes iASPP function by hindering its entrance into nuclei to interact with P53 in leukemic cells

Background

As the important suppressor of P53, iASPP is found to be overexpressed in leukemia, and functions as oncogene that inhibited apoptosis of leukemia cells. Sertad1 is identified as one of the proteins that can bind with iASPP in our previous study by two-hybrid screen.

Methods

Co-immunoprecipitation and immunofluorescence were perfomed to identified the interaction between iASPP and Sertad1 protein. Westernblot and Real-time quantitative PCR were used to determine the expression and activation of proteins. Cell proliferation assays, cell cycle and cell apoptosis were examined by flow cytometric analysis.

Results

iASPP combined with Sertad1 in leukemic cell lines and the interaction occurred in the cytoplasm near nuclear membrane. iASPP could interact with Sertad1 through its Cyclin-A, PHD-bromo, C terminal domain, except for S domain. Overexpression of iASPP in leukemic cells resulted in the increased cell proliferation and resistance to apoptosis induced by chemotherapy drugs. While overexpression of iASPP and Sertad1 at the same time could slow down the cell proliferation, lead the cells more vulnerable to the chemotherapy drugs, the resistance to chemotherapeutic drug in iASPP^hi leukemic cells was accompanied by Puma protein expression. Excess Sertad1 protein could tether iASPP protein in the cytoplasm, further reduced the binding between iASPP and P53 in the nucleus.

Conclusions

Sertad1 could antagonize iASPP function by hindering its entrance into nuclei to interact with P53 in leukemic cells when iASPP was in the stage of overproduction.

Electronic supplementary material

The online version of this article (10.1186/s12885-017-3787-2) contains supplementary material, which is available to authorized users.

The lncRNA XIST interacts with miR-140/miR-124/iASPP axis to promote pancreatic carcinoma growth

Long non-coding RNA (lncRNA) X-inactive specific transcript (XIST) is involved in the development and progression of many tumors. In this study, XIST was specifically upregulated in pancreatic carcinoma tissues and cell lines; a higher XIST expression was correlated to poorer clinicopathologic features. After XIST knockdown, the proliferation of PC cell lines was suppressed and cell cycle stagnated in G1 phase; XIST knockdown also reduced the protein levels of inhibitor of apoptosis-stimulating protein of p53 (iASPP) and Cyclin-dependent kinase 1 (CDK1), increased the protein level of P21, a potent CDK inhibitor. In PC cell lines, XIST and miR-140/miR-124, two tumor-associated miRNAs, could inversely regulate each other, respectively; miR-140/miR-124 could bind to XIST and the 3’UTR of PPP1R13L, respectively. XIST and miR-140/miR-124 exerted opposite effects on iASPP, CDK1, P21 and P27 proteins; whereas the effects of LV-sh-XIST on the indicated protein levels could be partially reversed by miR-140 and/or miR-124 inhibitor. In PC tissues, miR-140 and miR-124 expression was down-regulated, iASPP and CDK1 mRNA expression was up-regulated. XIST positively correlated with iASPP and CDK1, inversely correlated with miR-140 and miR-124, respectively. Taken together, our data indicated that XIST might be an oncogenic lncRNA that promoted proliferation of PC cell line through inhibiting miR-140/miR-124 expression and promoting cell cycle-related factor expression, and could be regarded as a therapeutic target in human pancreatic carcinoma.

iASPP, a microRNA‑124 target, is aberrantly expressed in astrocytoma and regulates malignant glioma cell migration and viability

MicroRNAs (miRNAs) regulate biogenesis and disease development by targeting numerous mRNAs. miRNA (miR)‑124 and its direct target, inhibitor of apoptosis‑stimulating protein of p53 (iASPP), may be involved in tumor development and progression. The aim of the present study was to explore the role of miR‑124‑targeted iASPP in glioma. The results demonstrated that miR‑124 was aberrantly expressed in astrocytic glioma tissue and in the human glioblastoma cell lines U87 and U251. The expression of miR‑124 was lower in astrocytic gliomas compared with normal brain (NB) tissues, with a more reduced expression in higher‑grade tumors. In addition, several miR‑124 loci (including miR‑124‑1, miR‑124‑2 and miR‑124‑3) were revealed to be more highly methylated in U87 cells compared with methylation levels in U251 cells and NB cells. Furthermore, the expression of iASPP was higher in high‑grade astrocytic gliomas compared with low‑grade astrocytic gliomas. miR‑124 overexpression effectively inhibited U87 and U251 cell migration. In addition, miR‑124 regulated cell viability and arrested the cell cycle at the G0/G1 phase in these two cell lines. miR‑124 also reduced the expression levels of the cell cycle related genes iASPP, cyclin‑dependent kinase (CDK)4, CDK6 and cyclin D1. Results from the present study indicated that expression of the miR‑124 target gene iASPP may contribute to glioma development and progression.

iASPP facilitates tumor growth by promoting mTOR-dependent autophagy in human non-small-cell lung cancer

Autophagy serves a critical function in the pathogenesis, response to therapy and clinical outcome in cancers. Although a recent report showed a role of iASPP in suppressing autophagy, its potential activity as a regulator of autophagy has not been investigated in lung cancer. Here we investigated the potential function and molecular mechanism of iASPP in mediating autophagy in human non-small-cell lung cancer. Our data suggested that forced expression of iASPP triggered autophagic flux, while inhibition of iASPP suppressed autophagy at the autophagsome formation stage in vitro. Furthermore, in vivo overexpression of iASPP in SCID/NOD mice promoted tumorigenesis and autophagy, with an increase in the conversion from LC3-I to LC3-II. The effects of iASPP were mediated through activation of mTOR pathway. Finally, cytoplasmic iASPP expression was upregulated in lung cancer patients, and was identified as an independent poor prognostic factor for lung cancer-specific death in patient samples. Taken together, our data showed that iASPP could promote tumor growth by increasing autophagic flux, and iASPP could serve as a poor prognostic factor and a potential therapeutic target in lung cancer.

Sequence variation in PPP1R13L results in a novel form of cardio-cutaneous syndrome

Dilated cardiomyopathy (DCM) is a life-threatening disorder whose genetic basis is heterogeneous and mostly unknown. Five Arab Christian infants, aged 4-30 months from four families, were diagnosed with DCM associated with mild skin, teeth, and hair abnormalities. All passed away before age 3. A homozygous sequence variation creating a premature stop codon at PPP1R13L encoding the iASPP protein was identified in three infants and in the mother of the other two. Patients' fibroblasts and PPP1R13L-knocked down human fibroblasts presented higher expression levels of pro-inflammatory cytokine genes in response to lipopolysaccharide, as well as Ppp1r13l-knocked down murine cardiomyocytes and hearts of Ppp1r13l-deficient mice. The hypersensitivity to lipopolysaccharide was NF-κB-dependent, and its inducible binding activity to promoters of pro-inflammatory cytokine genes was elevated in patients' fibroblasts. RNA sequencing of Ppp1r13l-knocked down murine cardiomyocytes and of hearts derived from different stages of DCM development in Ppp1r13l-deficient mice revealed the crucial role of iASPP in dampening cardiac inflammatory response. Our results determined PPP1R13L as the gene underlying a novel autosomal-recessive cardio-cutaneous syndrome in humans and strongly suggest that the fatal DCM during infancy is a consequence of failure to regulate transcriptional pathways necessary for tuning cardiac threshold response to common inflammatory stressors.

iASPP overexpression is associated with clinical outcome in spinal chordoma and influences cellular proliferation, invasion, and sensitivity to cisplatin in vitro

The oncogenetic function of inhibitory member of the apoptosis stimulating protein of p53 family (iASPP) in chordoma is unclear and remains to elucidate. The expression of iASPP in chordoma tissues and cells, its correlation to clinicopathological parameters and the effect on the patients’ prognosis were evaluated. Cellular proliferation, invasion and cisplatin-response were observed after the iASPP knockdown or overexpression in vitro. Co-Immunoprecipitation assay was used to explore the interaction between iASPP and p53. The regulation of miRNA-124 on the expression and apoptotic function of iASPP was explored after transiently transfecting cells with miRNA-124 mimics or inhibitor. Results indicated that iASPP overexpressed in chordoma tissues and cells. Its overexpression was associated with tumor invasion and local recurrence, and was predictive of patients’ poor prognosis. Cells with iASPP-silence showed a decreased ability of proliferation and invasion, but an increasing sensitivity to cisplatin. Besides, iASPP could combine with p53 in either endogenous or exogenous detection. Post-transcriptionally, miRNA-124 negatively regulated the expression of iASPP, which further led to the changes of apoptosis-related proteins. Thus, iASPP overexpression is associated with the clinical outcome in spinal chordoma and influences cellular proliferation, invasion, and the sensitivity to cisplatin.

Inhibitory member of the apoptosis-stimulating protein of p53 is overexpressed in bladder cancer and correlated to its progression

Several lines of direct evidence show that inhibitory member of the apoptosis-stimulating protein of p53 (iASPP) has an important function in cancer progression. However, its expression pattern and relationship with clinical pathologic characteristics in bladder cancer (BC) have not been completely elucidated. In this study, firstly, samples from 3 patients with invasive BC were detected by liquid chromatography tandem mass spectrometry to confirm overexpression of iASPP in BC, then samples from patients with noninvasive and invasive BC were detected by real-time polymerase chain reaction, Western blot, and tissue microarry immunohistochemistry. The relationship between iASPP expression and various clinicopathological features was investigated. The results showed m-RNA and protein of iASPP were overexpressed in BC and the rate of iASPP-positive cells was positively correlated with Union for International Cancer Control-Tumor, Node, Metastases stage, histologic grade, lymph node metastasis and poor overall survive. The data demonstrate that iASPP is overexpressed in BC and promotes the malignancy of BC. iASPP maybe serve as a potential therapeutic target for BC.

Overexpression of iASPP-SV in glioma is associated with poor prognosis by promoting cell viability and antagonizing apoptosis

Inhibitor of apoptosis-stimulating protein of p53 (iASPP), encoded by PPP1R13L gene, is often overexpressed in human cancers. From the PPP1R13L gene, at least two isoforms, iASPP-L and iASPP-SV, are produced through alternative splicing. However, the role of these isoforms in glioma is still elusive. In this study, we examined the expression of iASPP-SV in astrocytic glioma tissues with different grades and normal human cerebral tissues. The result showed a higher messenger RNA (mRNA) expression level of iASPP-SV in astrocytic glioma patients with World Health Organization (WHO) grade II to IV in comparison to the normal controls. Additionally, mRNA expression level of iASPP-SV was gradually increased with the raise of the grade in glioma. High mRNA expression level of iASPP-SV was significantly associated with malignant WHO grades (P < 0.001). The protein expression level of iASPP-SV was consistent with the mRNA expression level. The Kaplan-Meier analysis revealed that high iASPP-SV mRNA expression significantly affected overall survival and progression-free survival (both P < 0.001). Furthermore, multivariate analysis indicated that the mRNA expression of iASPP-SV was an independent prognostic marker in glioma (P < 0.001). To further explore the role of iASPP-SV in glioma, U87 cells were transfected with iASPP-SV by lentivirus and then treated with temozolomide (TMZ). Overexpression of iASPP-SV promoted the cell viability and downregulated the expression of pro-apoptosis genes (Bax, Puma, p21, and Noxa) to inhibit apoptosis induced by TMZ. Our study provides the first evidence that high iASPP-SV expression may be a novel prognostic factor and therapeutic target for glioma.

Reactivating p53 functions by suppressing its novel inhibitor iASPP: a potential therapeutic opportunity in p53 wild-type tumors

Although mutational inactivation of p53 is found in 50% of all human tumors, a subset of tumors display defective p53 function, but retain wild-type (WT) p53. Here, direct and indirect mechanisms leading to the loss of WT p53 activities are discussed. We summarize the oncogenic roles of iASPP, an inhibitor of WT p53, in promoting proliferation, invasion, drug or radiation-resistance and metastasis. From the therapeutic view, we highlight promising perspectives of microRNA-124, peptide and small molecules that reduce or block iASPP for the treatment of cancer. High iASPP expression enhances proliferation, aggressive behavior, the resistance to radiation/chemotherapy and correlates with poor prognosis in a range of human tumors. Overexpression of iASPP accelerates tumorigenesis and invasion through p53-dependent and p53-independent mechanisms. MicroRNA-124 directly targets iASPP and represses the growth and invasiveness of cancer cells. The disruption of iASPP-p53 interaction by a p53-derived peptide A34 restores p53 function in cancer cells. The inhibition of iASPP phosphorylation with small molecules induces p53-dependent apoptosis and growth suppression. The mechanisms underlying aberrant expression of iASPP in human tumors should be further investigated. Reactivating WT p53 functions by targeting its novel inhibitor iASPP holds promise for potential therapeutic interventions in the treatment of WT p53-containing tumors.

Highly homologous proteins exert opposite biological activities by using different interaction interfaces

We present a possible molecular basis for the opposite activity of two homologues proteins that bind similar ligands and show that this is achieved by fine-tuning of the interaction interface. The highly homologous ASPP proteins have opposite roles in regulating apoptosis: ASPP2 induces apoptosis while iASPP inhibits it. The ASPP proteins are regulated by an autoinhibitory interaction between their Ank-SH3 and Pro domains. We performed a detailed biophysical and molecular study of the Pro - Ank-SH3 interaction in iASPP and compared it to the interaction in ASPP2. We found that iASPP Pro is disordered and that the interaction sites are entirely different: iASPP Ank-SH3 binds iASPP Pro via its fourth Ank repeat and RT loop while ASPP2 Ank-SH3 binds ASPP2 Pro via its first Ank repeat and the n-src loop. It is possible that by using different moieties in the same interface, the proteins can have distinct and specific interactions resulting in differential regulation and ultimately different biological activities.

A Screen for Extracellular Signal-Regulated Kinase-Primed Glycogen Synthase Kinase 3 Substrates Identifies the p53 Inhibitor iASPP

The Kaposi's sarcoma-associated herpesvirus (KSHV) LANA protein is essential for the replication and maintenance of virus genomes in latently KSHV-infected cells. LANA also drives dysregulated cell growth through a multiplicity of mechanisms that include altering the activity of the cellular kinases extracellular signal-regulated kinase (ERK) and glycogen synthase kinase 3 (GSK-3). To investigate the potential impact of these changes in enzyme activity, we used protein microarrays to identify cell proteins that were phosphorylated by the combination of ERK and GSK-3. The assays identified 58 potential ERK-primed GSK-3 substrates, of which 23 had evidence for in vivo phosphorylation in mass spectrometry databases. Two of these, SMAD4 and iASPP, were selected for further analysis and were confirmed as ERK-primed GSK-3 substrates. Cotransfection experiments revealed that iASPP, but not SMAD4, was targeted for degradation in the presence of GSK-3. iASPP interferes with apoptosis induced by p53 family members. To determine the importance of iASPP to KSHV-infected-cell growth, primary effusion lymphoma (PEL) cells were treated with an iASPP inhibitor in the presence or absence of the MDM2 inhibitor Nutlin-3. Drug inhibition of iASPP activity induced apoptosis in BC3 and BCBL1 PEL cells but did not induce poly(ADP-ribose) polymerase (PARP) cleavage in virus-negative BJAB cells. The effect of iASPP inhibition was additive with that of Nutlin-3. Interfering with iASPP function is therefore another mechanism that can sensitize KSHV-positive PEL cells to cell death.

IMPORTANCE

KSHV is associated with several malignancies, including primary effusion lymphoma (PEL). The KSHV-encoded LANA protein is multifunctional and promotes both cell growth and resistance to cell death. LANA is known to activate ERK and limit the activity of another kinase, GSK-3. To discover ways in which LANA manipulation of these two kinases might impact PEL cell survival, we screened a human protein microarray for ERK-primed GSK-3 substrates. One of the proteins identified, iASPP, showed reduced levels in the presence of GSK-3. Further, blocking iASPP activity increased cell death, particularly in p53 wild-type BC3 PEL cells.

Downregulation of inhibitor of apoptosis‑stimulating protein of p53 inhibits proliferation and promotes apoptosis of gastric cancer cells

Gastric cancer (GC) remains one of the leading causes of cancer-associated mortality. Inhibitor of apoptosis-stimulating protein of p53 (iASPP) is a member of the inhibitory apoptosis-stimulating protein p53 family. The overexpression of iASPP has been detected in several types of tumor in humans. However, the role of iASPP in GC remains to be elucidated. The objectives of the present study were to detect the expression of iASPP in GC and examine the potential role of iASPP in GC cell lines. Using reverse transcription-quantitative polymerase chain reaction and western blot analyses, it was identified that the expression of iASPP in GC tissues and GC cell lines was higher compared with that in adjacent normal tissues and in a normal gastric mucosa cell line (GES-1). To examine the role of iASPP in GC cells, the expression of iASPP was inhibited using a small interfering (si)RNA against iASPP and it was observed that iASPP expression was significantly downregulated. Using MTT assays, colony-formation assays and flow cytometry, it was identified that the inhibition of iASPP was able to significantly inhibit the proliferation and colony forming ability and promote apoptosis in GC cells. To examine the role of iASPP in GC cells in vivo, GC cells, which were infected with iASPP-siRNA or control-siRNA were subcutaneously injected into nude mice. It was identified that downregulation of iASPP significantly inhibited tumor growth in vivo. Thus, iASPP may be a potential molecular target in GC therapy.

A pro-apoptotic function of iASPP by stabilizing p300 and CBP through inhibition of BRMS1 E3 ubiquitin ligase activity

The p53 family and its cofactors are potent inducers of apoptosis and form a barrier to cancer. Here, we investigated the impact of the supposedly inhibitory member of the apoptosis-stimulating protein of p53, iASPP, on the activity of the p53 homolog TAp73, and its cofactors p300 and CBP. We found that iASPP interacted with and stabilized the histone acetyltransferase p300 and its homolog CBP upon cisplatin treatment. Vice versa, iASPP depletion by shRNA resulted in decreased amounts of p300 and CBP, impaired binding of p300 and TAp73 to target site promoters, reduced induction of pro-apoptotic TAp73 target genes, and impaired apoptosis. Mechanistically, we observed that the p300-regulatory E3 ubiquitin ligase BRMS1 could rescue the degradation of p300 and CBP in cisplatin-treated, iASPP-depleted cells. This argues that iASPP stabilizes p300 and CBP by interfering with their BRMS1-mediated ubiquitination, thereby contributing to apoptotic susceptibility. In line, iASPP overexpression partially abolished the interaction of BRMS1 and CBP upon DNA damage. Reduced levels of iASPP mRNA and protein as well as CBP protein were observed in human melanoma compared with normal skin tissue and benign melanocytic nevi. In line with our findings, iASPP overexpression or knockdown of BRMS1 each augmented p300/CBP levels in melanoma cell lines, thereby enhancing apoptosis upon DNA damage. Taken together, destabilization of p300/CBP by downregulation of iASPP expression levels appears to represent a molecular mechanism that contributes to chemoresistance in melanoma cells.

JNK-NQO1 axis drives TAp73-mediated tumor suppression upon oxidative and proteasomal stress

Hyperproliferating cancer cells produce energy mainly from aerobic glycolysis, which results in elevated ROS levels. Thus aggressive tumors often possess enhanced anti-oxidant capacity that impedes many current anti-cancer therapies. Additionally, in ROS-compromised cancer cells ubiquitin proteasome system (UPS) is often deregulated for timely removal of oxidized proteins, thus enabling cell survival. Taken that UPS maintains the turnover of factors controlling cell cycle and apoptosis--such as p53 or p73, it represents a promising target for pharmaceutical intervention. Enhancing oxidative insult in already ROS-compromised cancer cells appears as an attractive anti-tumor scenario. TAp73 is a bona fide tumor suppressor that drives the chemosensitivity of some cancers to cisplatin or γ-radiation. It is an important drug target in tumors where p53 is lost or mutated. Here we discovered a novel synergistic mechanism leading to potent p73 activation and cancer cell death by oxidative stress and inhibition of 20S proteasomes. Using a small-molecule inhibitor of 20S proteasome and ROS-inducer--withaferin A (WA), we found that WA-induced ROS activates JNK kinase and stabilizes phase II anti-oxidant response effector NF-E2-related transcription factor (NRF2). This results in activation of Nrf2 target--NQO1 (NADPH quinone oxidoreductase), and TAp73 protein stabilization. The observed effect was ablated by the ROS scavenger--NAC. Concurrently, stress-activated JNK phosphorylates TAp73 at multiple serine and threonine residues, which is crucial to ablate TAp73/MDM2 complex and to promote TAp73 transcriptional function and induction of robust apoptosis. Taken together our data demonstrate that ROS insult in combination with the inhibition of 20S proteasome and TAp73 activation endows synthetic lethality in cancer cells. Thus, our results may enable the establishment of a novel pharmacological strategy to exploit the enhanced sensitivity of tumors to elevated ROS and proteasomal stress to kill advanced tumors by pharmacological activation of TAp73 using molecules like WA.

In vitro effect of iASPP on cell growth of oral tongue squamous cell carcinoma

iASPP is an inhibitory member of the apoptosis-stimulating proteins of P53 (ASPP) family. iASPP is over expressed in several malignant tumors and potentially affects cancer progression. However, the expression and potential role of iASPP in oral tongue squamous cell carcinoma (OTSCC) have not been addressed. In our study, we detected iASPP expression in OTSCC by immunohistochemistry. iASPP expression is up-regulated in OTSCC tissues. Moreover, in clinical pathology specimens, we found that increased iASPP expression correlates with poor differentiation and lymph node metastasis. Using multicellular tumor spheroids (MTS) and flow cytometry, we demonstrated that iASPP down-regulation arrests OTSCC cells at the G0/G1 phase, induces OTSCC cell apoptosis and inhibits OTSCC cell proliferation. These results indicate that iASPP plays a significant role in the progression of OTSCC and may serve as a biomarker or therapeutic target for OTSCC patients.

Cytoplasmic iASPP expression as a novel prognostic indicator in oral cavity squamous cell carcinoma

BACKGROUND

Inhibitor of apoptosis-stimulating protein of p53 (iASPP) is a key inhibitor of tumor suppressor p53 that is overexpressed in several human cancers; however, its role in oral cavity squamous cell carcinomas (OSCC) remains unknown. The present study investigated the prognostic role of iASPP in patients with OSCC.

METHODS

This study included 186 OSCC patients who underwent curative surgery at our institution between 2000 and 2011. Cytoplasmic and nuclear iASPP expression were examined separately by immunohistochemistry, and dichotomized to low and high. Clinicopathological variables associated with locoregional control (LRC), disease-free survival (DFS), and overall survival (OS) were identified by univariate and multivariate analyses.

RESULTS

Patients were followed-up for a median period of 74 months (range 16-166 months), and 5-year LRC, DFS, and OS was 73.6, 70.2, and 75.3 %, respectively. High iASPP immunostaining reactivity was detected in the cytoplasm and nucleus in 132 (71.0 %) and 93 (50.0 %) patients, respectively. In univariate analysis, pathologic nodal metastasis, advanced overall stage III-IV, lymphovascular invasion, and cytoplasmic iASPP were significantly associated with poor LRC, DFS, and OS (p < 0.05). High-grade and positive resection margins were significant factors associated with poor DFS and OS (p < 0.02). In multivariate analysis, N classification, lymphovascular invasion, and cytoplasmic iASPP expression remained independent variables for LRC, DFS, and OS (p < 0.05).

CONCLUSION

High iASPP expression in the tumor cell cytoplasm is associated with poor outcomes of OSCC patients in terms of recurrence and survival, suggesting a role for iASPP as a novel biomarker and therapeutic target for OSCC.

HOXB1 restored expression promotes apoptosis and differentiation in the HL60 leukemic cell line

BACKGROUND

Homeobox (HOX) genes deregulation has been largely implicated in the development of human leukemia. Among the HOXB cluster, HOXB1 was silent in a number of analyzed acute myeloid leukemia (AML) primary cells and cell lines, whereas it was expressed in normal terminally differentiated peripheral blood cells.

METHODS

We evaluated the biological effects and the transcriptome changes determined by the retroviral transduction of HOXB1 in the human promyelocytic cell line HL60.

RESULTS

Our results suggest that the enforced expression of HOXB1 reduces cell growth proliferation, inducing apoptosis and cell differentiation along the monocytic and granulocytic lineages. Accordingly, gene expression analysis showed the HOXB1-dependent down-regulation of some tumor promoting genes, paralleled by the up-regulation of apoptosis- and differentiation-related genes, thus supporting a tumor suppressor role for HOXB1 in AML. Finally, we indicated HOXB1 promoter hypermethylation as a mechanism responsible for HOXB1 silencing.

CONCLUSIONS

We propose HOXB1 as an additional member of the HOX family with tumour suppressor properties suggesting a HOXB1/ATRA combination as a possible future therapeutic strategy in AML.

The TP73 complex network: ready for clinical translation in cancer?

TP73 is a member of the TP53 family, whose deregulated expression has been reported in a wide variety of cancers and linked to patients' outcome. The fact that TP73 encodes a complex number of isoforms (TAp73 and ΔTAp73) with opposing functions and the cross-talk with other members of the family (TP53 and TP63) make it difficult to determine its clinical relevance. Here, we review the molecular mechanisms driving TAp73 and ΔTAp73 expression and how these variants inhibit or promote carcinogenesis. We also highlight the intricate interplay between TP53 family members. In addition, we comment on current pharmacological approaches targeting the TP73 pathway and those affecting the TAp73/ΔTAp73 ratio. Finally, we discuss the current data available in the literature that provide evidence on the role of TP73 variants in predicting prognosis. To date, most of the studies that evaluate the status levels of TP73 isoforms have been based on limited-size series. Despite this limitation, these publications highlight the correlation between high levels of the oncogenic forms and failure to respond to chemotherapy and/or shorter survival. Finally, we emphasize the need for studies to evaluate the significance of combining the deregulation of various members of the TP53 family in order to define patient outcome or their responsiveness to specific therapies.

MicroRNA-124-mediated regulation of inhibitory member of apoptosis-stimulating protein of p53 family in experimental stroke

BACKGROUND AND PURPOSE

p53-mediated neuronal death is a central pathway of stroke pathophysiology, but its mechanistic details remain unclear. Here, we identified a novel microRNA mechanism that downregulation of inhibitory member of the apoptosis-stimulating proteins of p53 family (iASPP) by the brain-specific microRNA-124 (miR-124) promotes neuronal death after cerebral ischemia.

METHODS

In a mouse model of focal permanent cerebral ischemia, the expression of iASPP and miR-124 was quantified by reverse transcription quantitative real-time polymerase chain reaction, immunofluorescence staining, and Western blot. Luciferase reporter assay was used to validate whether miR-124 can directly bind to the 3'-untranslated region of iASPP mRNA. To evaluate the role of miR-124, miR-124 mimic and its inhibitor were transfected into Neuro-2a cells and C57 mice.

RESULTS

There was no change in the iASPP mRNA level in cerebral ischemia. However, iASPP protein was remarkably decreased, with a concurrent elevation in miR-124 level. Furthermore, miR-124 can bind to the 3'-untranslated region of iASPP in 293T cells and downregulate its protein levels in Neuro-2a cells. In vivo, infusion of miR-124 decreased brain levels of iASPP, whereas inhibition of miR-124 enhanced iASPP levels and significantly reduced infarction in mouse focal cerebral ischemia.

CONCLUSIONS

These data demonstrate that p53-mediated neuronal cell death after stroke can be nontranscriptionally regulated by a novel mechanism involving suppression of endogenous cell death inhibitors by miR-124. Further dissection of microRNA regulatory mechanisms may lead to new therapeutic opportunities for preventing neuronal death after stroke.

Downregulation of miR-124 promotes the growth and invasiveness of glioblastoma cells involving upregulation of PPP1R13L

microRNA-124 (miR-124) plays an important role in regulating growth, invasiveness, stem-like traits, differentiation and apoptosis of glioblastoma cells. PPP1R3L, an inhibitory member of the apoptosis-stimulating protein of p53 family (IASPP), is also able to affect growth, cell cycle progression, metastasis and apoptosis of various types of cancer. To investigate the regulation of PPP1R13L expression by miR-124 and their effects on proliferation, cell cycle transition and invasion in glioblastoma cells, U251 and U373 glioblastoma cells were transfected with miR-124 mimics, its negative control (NC) or an inhibitor. We found that miR-124 was downregulated in glioblastoma tissues, and inversely regulated PPP1R13L expression in U251 and U373 glioblastoma cells. PPP1R13L was found to be a direct target of miR-124 in glioblastoma cells. Overexpression of miR-124 inhibited proliferation, G1/S transition and invasiveness in glioblastoma cells. miR-124 downregulation-mediated malignant progression of glioblastoma was partly attributed to increased PPP1R13L expression. Consequently, our findings provide a molecular basis for the role of miR-124/PPP1R13L in the progression of human glioblastoma and suggest a novel target for the treatment of glioblastoma.