ΔNp63α activates CD82 metastasis suppressor to inhibit cancer cell invasion

Hypoxia-activated XBP1s recruits HDAC2-EZH2 to engage epigenetic suppression of ΔNp63α expression and promote breast cancer metastasis independent of HIF1α

Hypoxia is a hallmark of cancer development. However, the molecular mechanisms by which hypoxia promotes tumor metastasis are not fully understood. In this study, we demonstrate that hypoxia promotes breast cancer metastasis through suppression of ΔNp63α in a HIF1α-independent manner. We show that hypoxia-activated XBP1s forms a stable repressor protein complex with HDAC2 and EZH2 to suppress ΔNp63α transcription. Notably, H3K27ac is predominantly occupied on the ΔNp63 promoter under normoxia, while H3K27me3 on the promoter under hypoxia. We show that XBP1s binds to the ΔNp63 promoter to recruit HDAC2 and EZH2 in facilitating the switch of H3K27ac to H3K27me3. Pharmacological inhibition or the knockdown of either HDAC2 or EZH2 leads to increased H3K27ac, accompanied by the reduced H3K27me3 and restoration of ΔNp63α expression suppressed by hypoxia, resulting in inhibition of cell migration. Furthermore, the pharmacological inhibition of IRE1α, but not HIF1α, upregulates ΔNp63α expression in vitro and inhibits tumor metastasis in vivo. Clinical analyses reveal that reduced p63 expression is correlated with the elevated expression of XBP1, HDAC2, or EZH2, and is associated with poor overall survival in human breast cancer patients. Together, these results indicate that hypoxia-activated XBP1s modulates the epigenetic program in suppression of ΔNp63α to promote breast cancer metastasis independent of HIF1α and provides a molecular basis for targeting the XBP1s/HDAC2/EZH2-ΔNp63α axis as a putative strategy in the treatment of breast cancer metastasis.

∆Np63α inhibits Rac1 activation and cancer cell invasion through suppression of PREX1

ΔNp63α, a member of the p53 family of transcription factors, plays a critical role in maintaining the proliferative potential of stem cells in the stratified epithelium. Although ΔNp63α is considered an oncogene and is frequently overexpressed in squamous cell carcinoma, loss of ΔNp63α expression is associated with increased tumor cell invasion and metastasis. We recently identified a ΔNp63α/miR-320a/PKCγ signaling axis that regulates cancer cell invasion by inhibiting phosphorylation of the small GTPase Rac1, a master switch of cell motility that positively regulates cell invasion in multiple human cancers. In this study, we identified a novel mechanism by which ΔNp63α negatively regulates Rac1 activity, by inhibiting the expression of the Rac-specific Guanine Exchange Factor PREX1. ΔNp63α knockdown in multiple squamous cell carcinoma cell lines leads to increased Rac1 activation, which is abrogated by treatment with the Rac1 inhibitor NSC23766. Furthermore, ΔNp63α negatively regulates PREX1 transcript and protein levels. Using a Rac-GEF activation assay, we also showed that ΔNp63α reduces the levels of active PREX1. The inhibition of the PREX1-Rac1 signaling axis by ΔNp63α leads to impaired cell invasion, thus establishing the functional relevance of this link. Our results elucidated a novel molecular mechanism by which ΔNp63α negatively affects cancer cell invasion and identifies the ΔNp63α/Rac1 axis as a potential target for metastasis.

ΔNp63 Regulates Radioresistance in Human Head and Neck Squamous Carcinoma Cells

Radiation therapy is commonly used to treat head and neck squamous cell carcinoma (HNSCC); however, recurrence results from the development of radioresistant cancer cells. Therefore, it is necessary to identify the underlying mechanisms of radioresistance in HNSCC. Previously, we showed that the inhibition of karyopherin-β1 (KPNB1), a factor in the nuclear transport system, enhances radiation-induced cytotoxicity, specifically in HNSCC cells, and decreases the localization of SCC-specific transcription factor ΔNp63. This suggests that ΔNp63 may be a KPNB1-carrying nucleoprotein that regulates radioresistance in HNSCC. Here, we determined whether ΔNp63 is involved in the radioresistance of HNSCC cells. Cell survival was measured by a colony formation assay. Apoptosis was assessed by annexin V staining and cleaved caspase-3 expression. The results indicate that ΔNp63 knockdown decreased the survival of irradiated HNSCC cells, increased radiation-induced annexin V+ cells, and cleaved caspase-3 expression. These results show that ΔNp63 is involved in the radioresistance of HNSCC cells. We further investigated which specific karyopherin-α (KPNA) molecules, partners of KPNB1 for nuclear transport, are involved in nuclear ΔNp63 expression. The analysis of nuclear ΔNp63 protein expression suggests that KPNA1 is involved in nuclear ΔNp63 expression. Taken together, our results suggest that ΔNp63 is a KPNB1-carrying nucleoprotein that regulates radioresistance in HNSCC.

Toward Colorectal Cancer Biomarkers: The Role of Genetic Variation, Wnt Pathway, and Long Noncoding RNAs

Colorectal cancer (CRC) is the third leading cause of death worldwide, comprising nearly 8% of cancer-related deaths per year. In South Korea, for example, CRC is the second most common cancer in men, and third in women. This study reports on the association of CRC with genetic variations in long noncoding RNAs, activators, and inhibitors of a cell proliferation pathway. Five normal colon mucosa tissue samples and their matched five-stage IV CRC samples were evaluated (dataset Gene Expression Omnibus accession: GSE50760). We identified more than 5000 differentially expressed genes (DEGs). The Wnt pathway had the greatest portion of DEGs, including activators, inhibitors, and associated long noncoding RNAs (lncRNAs), suggesting the importance of Wnt pathway in CRC. The following genes were aberrantly expressed: WIF1, SFRP4, CD82, WNT2, WNT3, WNT5A, HOTAIR, CRNDE, and UCA1. Notably, HOTAIR is known to silence WIF1, and WIF1 inhibits the Wnt ligands to negatively regulate the pathway. The lncRNA CRNDE positively regulates WNT5A, while UCA1 positively regulates WNT2 and WNT3. We note that HOTAIR was unable to silence WIF1. CRNDE and UCA1 were found to be upregulated, which may explain the high expression of the WIF1 targets. Furthermore, 10 single-nucleotide polymorphisms (SNPs) were identified in five of the candidate genes above. A possible novel SNP in CD82, chr11:44619242T > C, was predicted to introduce a ZBTB7A binding site. These SNPs are hypothesized to contribute to aberrant and discrepant regulation of the Wnt pathway in a context of CRC pathogenesis. These findings collectively inform future research on diagnostics and therapeutics innovation in CRC.

Role of a metastatic suppressor gene KAI1/CD82 in the diagnosis and prognosis of breast cancer

Globally, breast cancer is the most common type of cancer in females and is one of the leading causes of cancer death in women. The advancement in the targeted therapies and the slight understanding of the molecular cascades of the disease have led to small improvement in the rate of survival of breast cancer patients. However, metastasis and resistance to the current drugs still remain as challenges in the management of breast cancer patients. Metastasis, potentially, leads to failure of the available treatment, and thereby, makes the research on metastatic suppressors a high priority. Tumor metastasis suppressors are several genes and their protein products that have the capability of arresting the metastatic process without affecting the tumor formation. The metastasis suppressors KAI1 (also known as CD82) has been found to inhibit tumor metastasis in various types of solid cancers, including breast cancer. KAI1 was identified as a metastasis suppressor that inhibits the process of metastasis by regulating several mechanisms, including cell motility and invasion, induction of cell senescence, cell–cell adhesion and apoptosis. KAI1 is a member of tetraspanin membrane protein family. It interacts with other tetraspanins, chemokines and integrins to control diverse signaling pathways, which are crucial for protein trafficking and intracellular communication. It follows that better understanding of the molecular events of such genes is needed to develop prognostic biomarkers, and to identify specific therapies for breast cancer patients. This review aims to discuss the role of KAI1/CD82 as a prognosticator in breast cancer.

Noncanonical TGF-β signaling leads to FBXO3-mediated degradation of ΔNp63α promoting breast cancer metastasis and poor clinical prognosis

Transforming growth factor-β (TGF-β) signaling plays a critical role in promoting epithelial-to-mesenchymal transition (EMT), cell migration, invasion, and tumor metastasis. ΔNp63α, the major isoform of p63 protein expressed in epithelial cells, is a key transcriptional regulator of cell adhesion program and functions as a critical metastasis suppressor. It has been documented that the expression of ΔNp63α is tightly controlled by oncogenic signaling and is frequently reduced in advanced cancers. However, whether TGF-β signaling regulates ΔNp63α expression in promoting metastasis is largely unclear. In this study, we demonstrate that activation of TGF-β signaling leads to stabilization of E3 ubiquitin ligase FBXO3, which, in turn, targets ΔNp63α for proteasomal degradation in a Smad-independent but Erk-dependent manner. Knockdown of FBXO3 or restoration of ΔNp63α expression effectively rescues TGF-β-induced EMT, cell motility, and tumor metastasis in vitro and in vivo. Furthermore, clinical analyses reveal a significant correlation among TGF-β receptor I (TβRI), FBXO3, and p63 protein expression and that high expression of TβRI/FBXO3 and low expression of p63 are associated with poor recurrence-free survival (RFS). Together, these results demonstrate that FBXO3 facilitates ΔNp63α degradation to empower TGF-β signaling in promoting tumor metastasis and that the TβRI-FBXO3-ΔNp63α axis is critically important in breast cancer development and clinical prognosis. This study suggests that FBXO3 may be a potential therapeutic target for advanced breast cancer treatment.

ERK3 is transcriptionally upregulated by ∆Np63α and mediates the role of ∆Np63α in suppressing cell migration in non-melanoma skin cancers

BACKGROUND

p63, a member of the p53 gene family, is an important regulator for epithelial tissue growth and development. ∆Np63α is the main isoform of p63 and highly expressed in Non-melanoma skin cancer (NMSC). Extracellular signal-regulated kinase 3 (ERK3) is an atypical mitogen-activated protein kinase (MAPK) whose biochemical features and cellular regulation are distinct from those of conventional MAPKs such as ERK1/2. While ERK3 has been shown to be upregulated in lung cancers and head and neck cancers, in which it promotes cancer cell migration and invasion, little is known about the implication of ERK3 in NMSCs.

METHODS

Fluorescent immunohistochemistry was performed to evaluate the expression levels of ΔNp63α and ERK3 in normal and NMSC specimens. Dunnett's test was performed to compare mean fluorescence intensity (MFI, indicator of expression levels) of p63 or ERK3 between normal cutaneous samples and NMSC samples. A mixed effects (ANOVA) test was used to determine the correlation between ΔNp63α and ERK3 expression levels (MFI). The regulation of ERK3 by ΔNp63α was studied by qRT-PCR, Western blot and luciferase assay. The effect of ERK3 regulation by ΔNp63α on cell migration was measured by performing trans-well migration assay.

RESULTS

The expression level of ∆Np63α is upregulated in NMSCs compared to normal tissue. ERK3 level is significantly upregulated in AK and SCC in comparison to normal tissue and there is a strong positive correlation between ∆Np63α and ERK3 expression in normal skin and skin specimens of patients with AK, SCC or BCC. Further, we found that ∆Np63α positively regulates ERK3 transcript and protein levels in A431 and HaCaT skin cells, underlying the upregulation of ERK3 expression and its positive correlation with ∆Np63α in NMSCs. Moreover, similar to the effect of ∆Np63α depletion, silencing ERK3 greatly enhanced A431 cell migration. Restoration of ERK3 expression under the condition of silencing ∆Np63α counteracted the increase in cell migration induced by the depletion of ∆Np63α. Mechanistically, ERK3 inhibits the phosphorylation of Rac1 G-protein and the formation of filopodia of A431 skin SCC cells.

CONCLUSIONS

ERK3 is positively regulated by ∆Np63α and mediates the role of ∆Np63α in suppressing cell migration in NMSC.

Targeting of ΔNp63α by miR-522 promotes the migration of breast epithelial cells

The TP63 gene, which encodes the p63 protein, is involved in multiple biological processes, including embryonic development and tumorigenesis. ΔNp63α, the predominant isoform of p63 in epithelial cells, acts as an oncogene in early-stage tumors, but paradoxically acts as a potent antimetastatic factor in advanced cancers. Here, we report that ΔNp63α is a direct target of hsa-miR-522 (miR-522). Induced expression of miR-522 reduced the levels of ΔNp63α, predisposing breast epithelial cells to a loss of epithelial and acquisition of mesenchymal morphology, resulting in accelerated collective and single-cell migration. Restoration of ΔNp63α repressed miR-522-induced migration. Interestingly, overexpression of miR-522 did not affect breast epithelial cell proliferation, suggesting that miR-522 acts specifically through ΔNp63α in this context. Furthermore, expression of miR-522-3p and p63 was negatively correlated in human cancer samples. Thus, miR-522 might be a causative factor for breast tumorigenesis and cancer metastasis. In summary, our results reveal a novel miR-522/p63 axis in cell migration and thus suggest a potential strategy for therapeutic treatment of cancer metastasis.

p53-R273H promotes cancer cell migration via upregulation of neuraminidase-1

Accumulating evidence indicates that hotspot p53 mutants have gain-of-function in promoting cell migration and tumor metastasis. However, the molecular mechanisms are not completely understood. Here, we show that a hotspot mutation, p53-R273H, promotes non-small cell lung cancer (NSCLC) cell migration and upregulates the mRNA and protein expression of neuraminidase-1 (NEU1), a sialidase involved in cell proliferation, cell migration and tumorigenesis. Silencing of NEU1 leads to upregulation of integrin β4 which significantly inhibits NSCLC cell migration induced by p53-R273H. Mechanistically, p53-R273H promotes NEU1 transcription via activation of AKT signaling. Importantly, NEU1 expression is upregulated in human NSCLC samples harboring mutant p53 and is associated with poor clinical outcome. Overall, this study highlights an important role of NEU1 in p53-R273H-induced NSCLC cell migration and provides a potential target for NSCLC diagnosis and treatment.

From cancer to rejuvenation: incomplete regeneration as the missing link (part II: rejuvenation circle)

In the first part of our study, we substantiated that the embryonic reontogenesis and malignant growth (disintegrating growth) pathways are the same, but occur at different stages of ontogenesis, this mechanism is carried out in opposite directions. Cancer has been shown to be epigenetic-blocked redifferentiation and unfinished somatic embryogenesis. We formulated that only this approach of aging elimination has real prospects for a future that is fraught with cancer, as we will be able to convert this risk into a rejuvenation process through the continuous cycling of cell dedifferentiation-differentiation processes (permanent remorphogenesis). Here, we continue to develop the idea of looped ontogenesis and formulate the concept of the rejuvenation circle.

Cellular census of human fibrosis defines functionally distinct stromal cell types and states

Fibrotic disorders are some of the most devastating and poorly treated conditions in developed nations, yet effective therapeutics are not identified for many of them. A major barrier for the identification of targets and successful clinical translation is a limited understanding of the human fibrotic microenvironment. Here, we construct a stromal cell atlas of human fibrosis at single cell resolution from patients with Dupuytren’s disease, a localized fibrotic condition of the hand. A molecular taxonomy of the fibrotic milieu characterises functionally distinct stromal cell types and states, including a subset of immune regulatory ICAM1⁺ fibroblasts. In developing fibrosis, myofibroblasts exist along an activation continuum of phenotypically distinct populations. We also show that the tetraspanin CD82 regulates cell cycle progression and can be used as a cell surface marker of myofibroblasts. These findings have important implications for targeting core pathogenic drivers of human fibrosis.

New anti-fibrotics aided by a better understanding of fibrotic cell subsets and their functions are needed. Here the authors perform single-cell RNA-seq and CyTOF on nodules from patients with Dupuytren’s disease to map subsets and the state of mesenchymal cells during pathogenic fibrogenesis.

Transcriptional suppression of AMPKα1 promotes breast cancer metastasis upon oncogene activation

Oncogenic hotspot mutations in PIK3CA and overexpression of HER2 are known as a driving force for human breast cancer metastasis. AMPK is pivotal in maintaining cellular energy homeostasis. In this study, we demonstrate that transcription inhibition of AMPKα1 is critically important in human advanced breast cancer with poor clinical outcomes, that AMPKα1 is transcriptionally inhibited in response to activation of PI3K/HER2, and that ΔNp63α, a tumor metastasis suppressor, is a direct transcriptional factor mediating oncogenic PI3K/HER2-induced transcriptional suppression of AMPKα1. In addition, inhibition of AMPK leads to disruption of cell–cell adhesion and promotes cancer metastasis. This study highlights a critical role for AMPK in the connection of cell–cell adhesion and cancer metastasis.

AMP-activated protein kinase (AMPK) functions as an energy sensor and is pivotal in maintaining cellular metabolic homeostasis. Numerous studies have shown that down-regulation of AMPK kinase activity or protein stability not only lead to abnormality of metabolism but also contribute to tumor development. However, whether transcription regulation of AMPK plays a critical role in cancer metastasis remains unknown. In this study, we demonstrate that AMPKα1 expression is down-regulated in advanced human breast cancer and is associated with poor clinical outcomes. Transcription of AMPKα1 is inhibited on activation of PI3K and HER2 through ΔNp63α. Ablation of AMPKα1 expression or inhibition of AMPK kinase activity leads to disruption of E-cadherin-mediated cell–cell adhesion in vitro and increased tumor metastasis in vivo. Furthermore, restoration of AMPKα1 expression significantly rescues PI3K/HER2-induced disruption of cell–cell adhesion, cell invasion, and cancer metastasis. Together, these results demonstrate that the transcription control is another layer of AMPK regulation and suggest a critical role for AMPK in regulating cell–cell adhesion and cancer metastasis.

Role of p53 Family Proteins in Metformin Anti-Cancer Activities

Metformin has been used as therapy for type 2 diabetes for many years. Clinical and basic evidence as indicated that metformin has anti-cancer activities. It has been well-established that metformin activates AMP-activated protein kinase (AMPK), which in turn regulates energy homeostasis. However, the mechanistic aspects of metformin anti-cancer activity remain elusive. p53 family proteins, including p53, p63 and p73, have diverse biological functions, including regulation of cell growth, survival, development, senescence and aging. In this review, we highlight the evidence and mechanisms by which metformin inhibits cancer cell survival and tumor growth. We also aimed to discuss the role of p53 family proteins in metformin-mediated suppression of cancer growth and survival.

ΔNp63 in squamous cell carcinoma: defining the oncogenic routes affecting epigenetic landscape and tumour microenvironment

Squamous cell carcinoma (SCC) is a treatment‐refractory tumour which arises from the epithelium of diverse anatomical sites such as oesophagus, head and neck, lung and skin. Accumulating evidence has revealed a number of genomic, clinical and molecular features commonly observed in SCC of distinct origins. Some of these genetic events culminate in fostering the activity of ΔNp63, a potent oncogene which exerts its pro‐tumourigenic effects by regulating specific transcriptional programmes to sustain malignant cell proliferation and survival. In this review, we will describe the genetic and epigenetic determinants underlying ΔNp63 oncogenic activities in SCC, and discuss some relevant transcriptional effectors of ΔNp63, emphasizing their impact in modulating the crosstalk between tumour cells and tumour microenvironment (TME).

Serine 195 phosphorylation in the RNA-binding protein Rbm38 increases p63 expression by modulating Rbm38's interaction with the Ago2-miR203 complex

The p63 transcription factor, a p53 family protein, regulates genes involved in various cellular processes, including cell growth and differentiation. We previously showed that RNA-binding motif protein (Rbm38) is a p63 target and, in turn, regulates p63α mRNA stability by binding to the AU/U-rich element in its 3'UTR. Interestingly, Rbm38 can be phosphorylated at serine 195, altering its ability to regulate mRNA translation. However, whether the Ser-195 phosphorylation affects Rbm38's ability to destabilize p63 mRNA remains unclear. Here, using MCF7 and HaCaT cells, we showed that ectopic expression of phosphomimetic Rbm38-S195D increases, whereas WT Rbm38 and nonphosphorylatable Rbm38-S195A decrease p63α protein and transcript levels. We also found that upon activation of glycogen synthase kinase 3β (GSK3β), phosphorylation of Rbm38 at Ser-195 is increased, enhancing p63α expression in an Rbm38-dependent manner. To confirm this, we generated mouse embryo fibroblasts (MEFs) in which Ser-193 in mouse Rbm38 (equivalent to Ser-195 in human Rbm38) was substituted with aspartic acid (Rbm38^S193D/S193D ) or alanine (Rbm38^S193A/S193A ). We observed that the p63 transcript level was increased in Rbm38^S193D/S193D MEFs, but decreased in Rbm38^S193A/S193A MEFs. Mechanistically, we found that WT Rbm38, but not Rbm38-S195D, is required for p63 mRNA degradation mediated by microRNA 203 (miR203). Furthermore, we noted that Argonaute 2 (Ago2), a key regulator in microRNA-mediated mRNA decay, associates with WT Rbm38, and this association was reduced by Ser-195 phosphorylation. Together, our results reveal a critical mechanism by which Ser-195 phosphorylation in Rbm38 increases p63 expression by attenuating the association of Rbm38 with the Ago2-miR203 complex.

Alternative splicing is an important mechanism behind KAI1 loss of function in breast cancer patients from Saudi Arabia

PURPOSE

KAI1 (also called CD82) is a metastasis suppressor gene known to be downregulated in breast cancer and other solid tumors. The downregulation of KAI1 or loss of its function is usually associated with bad prognosis. The mechanism behind KAI1 loss of function is complex. In this study, we investigated "alternative splicing" as a possible mechanism that underlies KAI1 loss of function in breast cancer patients from a tertiary hospital in Saudi Arabia.

METHODS

Expression of KAI1 was studied in FFPE breast cancer and control tissue sections by IHC using two different antibodies targeting different domains of the protein. The TS82B antibody targets the extracellular loop, which constitutes most of the protein, while the second EPR4112 antibody targets the C-terminal intracellular domain of the protein.

RESULTS

Out of 90 breast cancer samples, 67% showed loss of KAI1 expression. The remaining 33% showed KAI1 expression with (TS82B) antibody; however, the protein was detected in only 11% of cancers when using the antibody (EPR4112) indicating a truncation of the protein at the C-terminus (truncated-KAI1) in 22% of the studied cancer samples. A significant correlation was found between truncated-KAI1 expression and advanced cancer stage (association with lymph node metastasis, P value 0.008).

CONCLUSION

Alternative splicing is an important mechanism underlying KAI1 loss of function in breast cancer, and it is associated with bad prognosis (advanced cancer stage).

A double dealing tale of p63: an oncogene or a tumor suppressor

As a member of tumor suppressor p53 family, p63, a gene encoding versatile protein variant, has been documented to correlate with cancer formation and progression, though it is rarely mutated in cancer patients. However, it has long been controversial on whether p63 is an oncogene or a tumor suppressor. Here, we comprehensively reviewed reports on roles of p63 in development, tumorigenesis and tumor progression. According to data from molecular cell biology, genetic models and clinic research, we conclude that p63 may act as either an oncogene or a tumor suppressor gene in different scenarios: TA isoforms of p63 gene are generally tumor-suppressive through repressing cell proliferation, survival and metastasis; ΔN isoforms, however, may initiate tumorigenesis via promoting cell proliferation and survival, but inhibit tumor metastasis and progression; effects of p63 on tumor formation and progression depend on the context of the whole p53 family, and either amplification or loss of p63 gene locus can break the balance to cause tumorigenesis.

Setdb1, a novel interactor of ΔNp63, is involved in breast tumorigenesis

ΔNp63 has been recently involved in self-renewal potential of breast cancer stem cells. Although the p63 transcriptional profile has been extensively characterized, our knowledge of the p63-binding partners potentially involved in the regulation of breast tumour progression is limited. Here, we performed the yeast two hybrid approach to identify p63α interactors involved in breast tumorigenesis and we found that SETDB1, a histone lysine methyl transferases, interacts with ΔNp63α and that this interaction contributes to p63 protein stability. SETDB1 is often amplified in primary breast tumours, and its depletion confers to breast cancer cells growth disadvantage. We identified a list of thirty genes repressed by ΔNp63 in a SETDB1-dependent manner, whose expression is positively correlated to survival of breast cancer patients. These results suggest that p63 and SETDB1 expression, together with the repressed genes, may have diagnostic and prognostic potential.

Metabolic pathways regulated by TAp73 in response to oxidative stress

Reactive oxygen species are involved in both physiological and pathological processes including neurodegeneration and cancer. Therefore, cells have developed scavenging mechanisms to maintain redox homeostasis under control. Tumor suppressor genes play a critical role in the regulation of antioxidant genes. Here, we investigated whether the tumor suppressor gene TAp73 is involved in the regulation of metabolic adaptations triggered in response to oxidative stress. H₂O₂ treatment resulted in numerous biochemical changes in both control and TAp73 knockout (TAp73−/−) mouse embryonic fibroblasts, however the extent of these changes was more pronounced in TAp73−/− cells when compared to control cells. In particular, loss of TAp73 led to alterations in glucose, nucleotide and amino acid metabolism. In addition, H₂O₂ treatment resulted in increased pentose phosphate pathway (PPP) activity in null mouse embryonic fibroblasts. Overall, our results suggest that in the absence of TAp73, H₂O₂ treatment results in an enhanced oxidative environment, and at the same time in an increased pro-anabolic phenotype. In conclusion, the metabolic profile observed reinforces the role of TAp73 as tumor suppressor and indicates that TAp73 exerts this function, at least partially, by regulation of cellular metabolism.

p73 promotes glioblastoma cell invasion by directly activating POSTN (periostin) expression

Glioblastoma Multiforme is one of the most highly metastatic cancers and constitutes 70% of all gliomas. Despite aggressive treatments these tumours have an exceptionally bad prognosis, mainly due to therapy resistance and tumour recurrence. Here we show that the transcription factor p73 confers an invasive phenotype by directly activating expression of POSTN (periostin, HGNC:16953) in glioblastoma cells. Knock down of endogenous p73 reduces invasiveness and chemo-resistance, and promotes differentiation in vitro. Using chromatin immunoprecipitation and reporter assays we demonstrate that POSTN, an integrin binding protein that has recently been shown to play a major role in metastasis, is a transcriptional target of TAp73. We further show that POSTN overexpression is sufficient to rescue the invasive phenotype of glioblastoma cells after p73 knock down. Additionally, bioinformatics analysis revealed that an intact p73/POSTN axis, where POSTN and p73 expression is correlated, predicts bad prognosis in several cancer types. Taken together, our results support a novel role of TAp73 in controlling glioblastoma cell invasion by regulating the expression of the matricellular protein POSTN.

TAp73 inhibits cell invasion and migration by directly activating KAI1 expression in colorectal carcinoma

p73 is a member of the p53 family of transcription factors and, like p53, plays a role as a tumor suppressor. p73 is involved in development, proliferation, apoptosis and metastasis. However, the precise molecular mechanisms underlying its function in inhibiting metastasis remain largely unknown. Here, we show that induction of TAp73 decreased invasion and migration activity of colorectal cancer cells, whereas knockdown of TAp73 led to increased invasion and migration activity. KAI1 was identified as a transcriptional target of TAp73 and its expression is indispensable for TAp73-mediated inhibition of cell invasion and migration. Furthermore, induction of TAp73 in colorectal cancer cells elevated KAI1 expression and decreased the frequency of hepatic metastasis in vivo. Whereas, the decreased invasion and migration activities caused by TAp73 induction were abrogated by knockdown of KAI1. Interestingly, TAp73 and KAI1 are overexpressed in primary colorectal cancers and a significant correlation between TAp73 and KAI1 expression was detected, but their expressions were significantly down-regulated in metastatic cancers. Taken together, our results support a novel role for TAp73 in controlling colorectal cancer cell invasion, migration and metastasis by regulating transcription of KAI1.

Ultraconserved long non-coding RNA uc.63 in breast cancer

Transcribed-ultraconserved regions (T-UCRs) are long non-coding RNAs (lncRNA) encoded by a subset of long ultraconserved stretches in the human genome. Recent studies revealed that the expression of several T-UCRs is altered in cancer and growing evidences underline the importance of T-UCRs in oncogenesis, offering also potential new strategies for diagnosis and prognosis. We found that overexpression of one specific T-UCRs named uc.63 is associated with bad outcome in luminal A subtype of breast cancer patients. uc.63 is localized in the third intron of exportin-1 gene (XPO1) and is transcribed in the same orientation of its host gene. Interestingly, silencing of uc.63 induces apoptosis in vitro. However, silencing of host gene XPO1 does not cause the same effect suggesting that the transcription of uc.63 is independent of XPO1. Our results reveal an important role of uc.63 in promoting breast cancer cells survival and offer the prospect to identify a signature associated with poor prognosis.

ΔNp63α is a common inhibitory target in oncogenic PI3K/Ras/Her2-induced cell motility and tumor metastasis

Activation of phosphatidylinositol 3 kinase (PI3K), Ras, and Her2 signaling plays a critical role in cancer development. Hotspot constitutive activating mutations in oncogenes, such as PIK3CA encoding the p110α catalytic subunit or RAS, as well as overexpression of Her2, are frequently found in human tumors and cancers. It has been well established that activation of these oncogenes profoundly promotes tumor metastasis, whereas decreased expression of ΔNp63α, the major protein isoform of the p53-related p63 expressed in epithelial cells, has been associated with cancer metastasis. In this study, we demonstrate that hotspot oncogenic mutations on PIK3CA and RAS, including p110α^H1047R, K-Ras^G12V, and H-Ras^G12V, as well as activation of Her2, all led to suppression of ΔNp63α expression via Akt-fork-head transcription factor 3a (Akt-FOXO3a) signaling, resulting in increased cell motility and tumor metastasis. Expression of ΔNp63α effectively reversed p110α^H1047R-, K-Ras^G12V-, H-Ras^G12V-, or Her2-induced cell motility in vitro and tumor metastasis in mouse models. We show that ΔNp63α was a direct FOXO3a transcriptional target and that expression of FOXO3a and ΔNp63α was correlated in human cancer biopsy samples. Together, these results demonstrate that ΔNp63α is a common inhibitory target of oncogenic PI3K, Ras, and Her2, and that ΔNp63α may function as a critical integrator of oncogenic signaling in cancer metastasis.

ΔNp63α promotes adhesion of metastatic prostate cancer cells to the bone through regulation of CD82

ΔNp63α is a critical mediator of epithelial development and stem cell function in a variety of tissues including the skin and breast, while overexpression of ΔNp63α acts as an oncogene to drive tumor formation and cancer stem cell properties in squamous cell carcinoma. However, with regards to the prostate, while ΔNp63α is expressed in the basal stem cells of the mature gland, during adenocarcinoma development, its expression is lost and its absence is used to clinically diagnose the malignant state. Surprisingly, here we identify a sub-population of bone metastatic prostate cancer cells in the PC3 cell line that express ΔNp63α. Interestingly, we discovered that ΔNp63α favors adhesion and stem-like growth of these cells in the bone microenvironment. In addition, we show that these properties require expression of the target gene CD82. Together, this work uncovers a population of bone metastatic prostate cancer cells that express ΔNp63α, and provides important information about the mechanisms of bone metastatic colonization. Finally, we identify metastasis-promoting properties for the tetraspanin family member CD82.

Metformin Promotes AMP-activated Protein Kinase-independent Suppression of ΔNp63α Protein Expression and Inhibits Cancer Cell Viability

The blood glucose modifier metformin is used to treat type II diabetes and has also been shown to possess anticancer activities. Recent studies indicate that glucose deprivation can greatly enhance metformin-mediated inhibition of cell viability, but the molecular mechanism involved in this inhibition is unclear. In this study, we report that, under glucose deprivation, metformin inhibited expression of ΔNp63α, a p53 family member involved in cell adhesion pathways, resulting in disruption of cell matrix adhesion and subsequent apoptosis in human squamous carcinoma cells. We further show that metformin promoted ΔNp63α protein instability independent of AMP-activated protein kinase and that WWP1, an E3 ligase of ΔNp63α, was involved in metformin-mediated down-regulation of ΔNp63α levels. In addition, we demonstrate that a combination of metformin and the glycolysis inhibitor 2-deoxy-d-glucose significantly inhibited ΔNp63α expression and also suppressed xenographic tumor growth in vivo In summary, this study reveals a new mechanism for metformin-mediated anticancer activity and suggests a new strategy for treating human squamous cell carcinoma.

Tetraspanin CD82: a suppressor of solid tumors and a modulator of membrane heterogeneity

Tetraspanin CD82 suppresses the progression and metastasis of a wide range of solid malignant tumors. However, its roles in tumorigenesis and hematopoietic malignancy remain unclear. Ubiquitously expressed CD82 restrains cell migration and cell invasion by modulating both cell-matrix and cell-cell adhesiveness and confining outside-in pro-motility signaling. This restraint at least contributes to, if not determines, the metastasis-suppressive activity and, also likely, the physiological functions of CD82. As a modulator of cell membrane heterogeneity, CD82 alters microdomains, trafficking, and topography of the membrane by changing the membrane molecular landscape. The functional activities of membrane molecules and the cytoskeletal interaction of the cell membrane are subsequently altered, followed by changes in cellular functions. Given its pathological and physiological importance, CD82 is a promising candidate for clinically predicting and blocking tumor progression and metastasis and also an emerging model protein for mechanistically understanding cell membrane organization and heterogeneity.

Effects of mutations in Wnt/β-catenin, hedgehog, Notch and PI3K pathways on GSK-3 activity-Diverse effects on cell growth, metabolism and cancer

Glycogen synthase kinase-3 (GSK-3) is a serine/threonine kinase that participates in an array of critical cellular processes. GSK-3 was first characterized as an enzyme that phosphorylated and inactivated glycogen synthase. However, subsequent studies have revealed that this moon-lighting protein is involved in numerous signaling pathways that regulate not only metabolism but also have roles in: apoptosis, cell cycle progression, cell renewal, differentiation, embryogenesis, migration, regulation of gene transcription, stem cell biology and survival. In this review, we will discuss the roles that GSK-3 plays in various diseases as well as how this pivotal kinase interacts with multiple signaling pathways such as: PI3K/PTEN/Akt/mTOR, Ras/Raf/MEK/ERK, Wnt/beta-catenin, hedgehog, Notch and TP53. Mutations that occur in these and other pathways can alter the effects that natural GSK-3 activity has on regulating these signaling circuits that can lead to cancer as well as other diseases. The novel roles that microRNAs play in regulation of the effects of GSK-3 will also be evaluated. Targeting GSK-3 and these other pathways may improve therapy and overcome therapeutic resistance.

ΔNp63α Silences a miRNA Program to Aberrantly Initiate a Wound-Healing Program That Promotes TGFβ-Induced Metastasis

Primary cancer cell dissemination is a key event during the metastatic cascade, but context-specific determinants of this process remain largely undefined. Multiple reports have suggested that the p53 (TP53) family member p63 (TP63) plays an antimetastatic role through its minor epithelial isoform containing the N-terminal transactivation domain (TAp63). However, the role and contribution of the major p63 isoform lacking this domain, ΔNp63α, remain largely undefined. Here, we report a distinct and TAp63-independent mechanism by which ΔNp63α-expressing cells within a TGFβ-rich microenvironment become positively selected for metastatic dissemination. Orthotopic transplantation of ΔNp63α-expressing human osteosarcoma cells into athymic mice resulted in larger and more frequent lung metastases than transplantation of control cells. Mechanistic investigations revealed that ΔNp63α repressed miR-527 and miR-665, leading to the upregulation of two TGFβ effectors, SMAD4 and TβRII (TGFBR2). Furthermore, we provide evidence that this mechanism reflects a fundamental role for ΔNp63α in the normal wound-healing response. We show that ΔNp63α-mediated repression of miR-527/665 controls a TGFβ-dependent signaling node that switches off antimigratory miR-198 by suppressing the expression of the regulatory factor, KSRP (KHSRP). Collectively, these findings reveal that a novel miRNA network involved in the regulation of physiologic wound-healing responses is hijacked and suppressed by tumor cells to promote metastatic dissemination. Cancer Res; 76(11); 3236-51. ©2016 AACR.

Estrogen Enhances the Cell Viability and Motility of Breast Cancer Cells through the ERα-ΔNp63-Integrin β4 Signaling Pathway

Estrogen induces ERα-positive breast cancer aggressiveness via the promotion of cell proliferation and survival, the epithelial-mesenchymal transition, and stem-like properties. Integrin β4 signaling has been implicated in estrogen/ERα-induced tumorigenicity and anti-apoptosis; however, this signaling cascade poorly understood. ΔNp63, an N-terminally truncated isoform of the p63 transcription factor, functions as a transcription factor of integrinβ4 and therefore regulates cellular adhesion and survival. Therefore, the aim of the present study was to investigate the estrogen-induced interaction between ERα, ΔNp63 and integrin β4 in breast cancer cells. In ERα-positive MCF-7 cells, estrogen activated ERα transcription, which induced ΔNp63 expression. And ΔNp63 subsequently induced integrin β4 expression, which resulted in AKT phosphorylation and enhanced cell viability and motility. Conversely, there was no inductive effect of estrogen on ΔNp63-integrinβ4-AKT signaling or on cell viability and motility in ERα-negative MDA-MB-231 cells. ΔNp63 knockdown abolishes these estrogen-induced effects and reduces cell viability and motility in MCF-7 cells. Nevertheless, ΔNp63 knockdown also inhibited cell migration in MDA-MB-231 cells through reducing integrin β4 expression and AKT phosphorylation. In conclusion, estrogen enhances ERα-positive breast cancer cell viability and motility through activating the ERα-ΔNp63-integrin β4 signaling pathway to induce AKT phosphorylated activation. Those findings should be useful to elucidate the crosstalk between estrogen/ER signaling and ΔNp63 signaling and provide novel insights into the effects of estrogen on breast cancer progression.

P53 functional abnormality in mesenchymal stem cells promotes osteosarcoma development

It has been shown that p53 has a critical role in the differentiation and functionality of various multipotent progenitor cells. P53 mutations can lead to genome instability and subsequent functional alterations and aberrant transformation of mesenchymal stem cells (MSCs). The significance of p53 in safeguarding our body from developing osteosarcoma (OS) is well recognized. During bone remodeling, p53 has a key role in negatively regulating key factors orchestrating the early stages of osteogenic differentiation of MSCs. Interestingly, changes in the p53 status can compromise bone homeostasis and affect the tumor microenvironment. This review aims to provide a unique opportunity to study the p53 function in MSCs and OS. In the context of loss of function of p53, we provide a model for two sources of OS: MSCs as progenitor cells of osteoblasts and bone tumor microenvironment components. Standing at the bone remodeling point of view, in this review we will first explain the determinant function of p53 in OS development. We will then summarize the role of p53 in monitoring MSC fidelity and in regulating MSC differentiation programs during osteogenesis. Finally, we will discuss the importance of loss of p53 function in tissue microenvironment. We expect that the information provided herein could lead to better understanding and treatment of OS.

ΔNp63α Transcriptionally Regulates the Expression of CTEN That Is Associated with Prostate Cell Adhesion

p63 is a member of the p53 transcription factor family and a linchpin of epithelial development and homeostasis. p63 drives the expression of many target genes involved in cell survival, adhesion, migration and cancer. In this study, we identify C-terminal tensin-like (CTEN) molecule as a downstream target of ΔNp63α, the predominant p63 isoform expressed in epithelium. CTEN belongs to the tensin family and is mainly localized to focal adhesions, which mediate many biological events such as cell adhesion, migration, proliferation and gene expression. Our study demonstrate that ΔNp63 and CTEN are both highly expressed in normal prostate epithelial cells and are down-regulated in prostate cancer. In addition, reduced expression of CTEN and ΔNp63 is correlated with prostate cancer progression from primary tumors to metastatic lesions. Silencing of ΔNp63 leads to decreased mRNA and protein levels of CTEN. ΔNp63α induces transcriptional activity of the CTEN promoter and a 140-bp fragment upstream of the transcription initiation site is the minimal promoter region required for activation. A putative binding site for p63 is located between -61 and -36 within the CTEN promoter and mutations of the critical nucleotides in this region abolish ΔNp63α-induced promoter activity. The direct interaction of ΔNp63α with the CTEN promoter was demonstrated using a chromatin immunoprecipitation (ChIP) assay. Moreover, impaired cell adhesion caused by ΔNp63α depletion is rescued by over-expression of CTEN, suggesting that CTEN is a downstream effector of ΔNp63α-mediated cell adhesion. In summary, our findings demonstrate that ΔNp63α functions as a trans-activation factor of CTEN promoter and regulates cell adhesion through modulating CTEN. Our study further contributes to the potential regulatory mechanisms of CTEN in prostate cancer progression.

Neuroblastoma: oncogenic mechanisms and therapeutic exploitation of necroptosis

Neuroblastoma (NB) is the most common extracranial childhood tumor classified in five stages (1, 2, 3, 4 and 4S), two of which (3 and 4) identify chemotherapy-resistant, highly aggressive disease. High-risk NB frequently displays MYCN amplification, mutations in ALK and ATRX, and genomic rearrangements in TERT genes. These NB subtypes are also characterized by reduced susceptibility to programmed cell death induced by chemotherapeutic drugs. The latter feature is a major cause of failure in the treatment of advanced NB patients. Thus, proper reactivation of apoptosis or of other types of programmed cell death pathways in response to treatment is relevant for the clinical management of aggressive forms of NB. In this short review, we will discuss the most relevant genomic rearrangements that define high-risk NB and the role that destabilization of p53 and p73 can have in NB aggressiveness. In addition, we will propose a strategy to stabilize p53 and p73 by using specific inhibitors of their ubiquitin-dependent degradation. Finally, we will introduce necroptosis as an alternative strategy to kill NB cells and increase tumor immunogenicity.

Amino-terminal residues of ΔNp63, mutated in ectodermal dysplasia, are required for its transcriptional activity

p63, a member of the p53 family, is a crucial transcription factor for epithelial development and skin homeostasis. Heterozygous mutations in TP63 gene have been associated with human ectodermal dysplasia disorders. Most of these TP63 mutations are missense mutations causing amino acidic substitutions at p63 DNA binding or SAM domains that reduce or abolish the transcriptional activity of mutants p63. A significant number of mutants, however, resides in part of the p63 protein that apparently do not affect DNA binding and/or transcriptional activity, such as the N-terminal domain. Here, we characterize five p63 mutations at the 5' end of TP63 gene aiming to understand the pathogenesis of the diseases and to uncover the role of ΔNp63α N-terminus residues in determining its transactivation potential.

Hippo Component TAZ Functions as a Co-repressor and Negatively Regulates ΔNp63 Transcription through TEA Domain (TEAD) Transcription Factor

Transcriptional co-activator with a PDZ binding domain (TAZ) is a WW domain-containing transcriptional co-activator and a core component of an emerging Hippo signaling pathway that regulates organ size, tumorigenesis, metastasis, and drug resistance. TAZ regulates these biological functions by up-regulating downstream cellular genes through transactivation of transcription factors such as TEAD and TTF1. To understand the molecular mechanisms underlying TAZ-induced tumorigenesis, we have recently performed a gene expression profile analysis by overexpressing TAZ in mammary cells. In addition to the TAZ-up-regulated genes that were confirmed in our previous studies, we identified a large number of cellular genes that were down-regulated by TAZ. In this study, we have confirmed these down-regulated genes (including cytokines, chemokines, and p53 gene family members) as bona fide downstream transcriptional targets of TAZ. By using human breast and lung epithelial cells, we have further characterized ΔNp63, a p53 gene family member, and shown that TAZ suppresses ΔNp63 mRNA, protein expression, and promoter activity through interaction with the transcription factor TEAD. We also show that TEAD can inhibit ΔNp63 promoter activity and that TAZ can directly interact with ΔNp63 promoter-containing TEAD binding sites. Finally, we provide functional evidence that down-regulation of ΔNp63 by TAZ may play a role in regulating cell migration. Altogether, this study provides novel evidence that the Hippo component TAZ can function as a co-repressor and regulate biological functions by negatively regulating downstream cellular genes.

The microRNA feedback regulation of p63 in cancer progression

The transcription factor p63 is a member of the p53 gene family that plays a complex role in cancer due to its involvement in epithelial differentiation, cell cycle arrest and apoptosis. MicroRNAs are a class of small, non-coding RNAs with an important regulatory role in various cellular processes, as well as in the development and progression of cancer. A number of microRNAs have been shown to function as transcriptional targets of p63. Conversely, microRNAs also can modulate the expression and activity of p63. However, the p63-microRNA regulatory circuit has not been addressed in depth so far. Here, computational genomic analysis was performed using miRtarBase, Targetscan, microRNA.ORG, DIANA-MICROT, RNA22-HSA and miRDB to analyze miRNA binding to the 3'UTR of p63. JASPAR (profile score threshold 80%) and TFSEARCH datasets were used to search transcriptional start sites for p53/p63 response elements. Remarkably, these data revealed 63 microRNAs that targeted p63. Furthermore, there were 39 microRNAs targeting p63 that were predicted to be regulated by p63. These analyses suggest a crosstalk between p63 and microRNAs. Here, we discuss the crosstalk between p63 and the microRNA network, and the role of their interactions in cancer.