PEA-15 Inhibits Tumorigenesis in an MDA-MB-468 Triple-Negative Breast Cancer Xenograft Model through Increased Cytoplasmic Localization of Activated Extracellular Signal-Regulated Kinase

Maternal Embryonic Leucine Zipper Kinase is Associated with Metastasis in Triple-negative Breast Cancer

Triple-negative breast cancer (TNBC) has high relapse and metastasis rates and a high proportion of cancer stem-like cells (CSC), which possess self-renewal and tumor initiation capacity. MELK (maternal embryonic leucine zipper kinase), a protein kinase of the Snf1/AMPK kinase family, is known to promote CSC maintenance and malignant transformation. However, the role of MELK in TNBC metastasis is unknown; we sought to address this in the current study. We found that MELK mRNA levels were higher in TNBC tumors [8.11 (3.79-10.95)] than in HR+HER2- tumors [6.54 (2.90-9.26)]; P < 0.001]. In univariate analysis, patients with breast cancer with high-MELK-expressing tumors had worse overall survival (P < 0.001) and distant metastasis-free survival (P < 0.01) than patients with low-MELK-expressing tumors. In a multicovariate Cox regression model, high MELK expression was associated with shorter overall survival after adjusting for other baseline risk factors. MELK knockdown using siRNA or MELK inhibition using the MELK inhibitor MELK-In-17 significantly reduced invasiveness, reversed epithelial-to-mesenchymal transition, and reduced CSC self-renewal and maintenance in TNBC cells. Nude mice injected with CRISPR MELK-knockout MDA-MB-231 cells exhibited suppression of lung metastasis and improved overall survival compared with mice injected with control cells (P < 0.05). Furthermore, MELK-In-17 suppressed 4T1 tumor growth in syngeneic BALB/c mice (P < 0.001). Our findings indicate that MELK supports metastasis by promoting epithelial-to-mesenchymal transition and the CSC phenotype in TNBC.

Significance

These findings indicate that MELK is a driver of aggressiveness and metastasis in TNBC.

Transcription Factor FOSL1 Enhances Drug Resistance of Breast Cancer Through DUSP7-Mediated Dephosphorylation of PEA15

Breast cancer (BC) represents one of the commonest and deadliest malignancies in women. However, drug resistance has always been a major obstacle to cancer treatment. Transcription factors have been reported to have close association with drug resistance of tumors. Recently, by analyzing the data from Gene Expression Omnibus (GEO) database (id: GSE76540), we found that transcription factor FOSL1 was significantly up-regulated in the transcriptome of doxorubicin-resistant BC cells compared with that in sensitive parental cells. Therefore, we aim to explore the regulatory mechanism of FOSL1 in affecting the drug resistance of BC cells. FOSL1 expression in doxorubicin-resistant BC cells was firstly examined through RT-qPCR, and then its influence on the drug resistance of BC cells was explored through a series of in vitro and in vivo mechanism assays. Results showed that FOSL1 promoted the drug resistance of BC cells to doxorubicin both in intro and in vivo. It positively regulated the transcription of DUSP7 in BC doxorubicin-resistant cells and DUSP7 also enhanced the drug resistance of BC cells. Furthermore, FOSL1 promoted the dephosphorylation of PEA15 through DUSP7. In conclusion, it was verified that FOSL1 promoted the drug resistance in breast cancer through DUSP7-mediated dephosphorylation of PEA15. Implications: These initial findings suggest that the FOSL1/DUSP7/PEA15 pathway may provide a theoretical guidance for BC treatment.

Nonphosphorylatable PEA15 mutant inhibits epithelial-mesenchymal transition in triple-negative breast cancer partly through the regulation of IL-8 expression

Background

Triple-negative breast cancer (TNBC) is an aggressive breast cancer subtype that lacks targeted therapies. Patients with TNBC have a very poor prognosis because the disease often metastasizes. New treatment approaches addressing drivers of metastasis and tumor growth are crucial to improving patient outcomes. Developing targeted gene therapy is thus a high priority for TNBC patients. PEA15 (phosphoprotein enriched in astrocytes, 15 kDa) is known to bind to ERK, preventing ERK from being translocated to the nucleus and hence blocking its activity. The biological function of PEA15 is tightly regulated by its phosphorylation at Ser104 and Ser116. However, the function and impact of phosphorylation status of PEA15 in the regulation of TNBC metastasis and in epithelial-to-mesenchymal transition (EMT) are not well understood.

Methods

We established stable cell lines overexpressing nonphosphorylatable (PEA15-AA) and phospho-mimetic (PEA15-DD) mutants. To dissect specific cellular mechanisms regulated by PEA15 phosphorylation status, we performed RT-PCR immune and metastasis arrays. In vivo mouse models were used to determine the effects of PEA15 phosphorylation on tumor growth and metastasis.

Results

We found that the nonphosphorylatable mutant PEA15-AA prevented formation of mammospheres and expression of EMT markers in vitro and decreased tumor growth and lung metastasis in in vivo experiments when compared to control, PEA15-WT and phosphomimetic PEA15-DD. However, phosphomimetic mutant PEA15-DD promoted migration, mesenchymal marker expression, tumorigenesis, and lung metastasis in the mouse model. PEA15-AA-mediated inhibition of breast cancer cell migratory capacity and tumorigenesis was the partial result of decreased expression of interleukin-8 (IL-8). Further, we identified that expression of IL-8 was possibly mediated through one of the ERK downstream molecules, Ets-1.

Conclusions

Our results show that PEA15 phosphorylation status serves as an important regulator for PEA15’s dual role as an oncogene or tumor suppressor and support the potential of PEA15-AA as a therapeutic strategy for treatment of TNBC.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10549-021-06316-2.

Birinapant Enhances Gemcitabine's Antitumor Efficacy in Triple-Negative Breast Cancer by Inducing Intrinsic Pathway-Dependent Apoptosis

Triple-negative breast cancer (TNBC) is the most aggressive subgroup of breast cancer, and patients with TNBC have few therapeutic options. Apoptosis resistance is a hallmark of human cancer, and apoptosis regulators have been targeted for drug development for cancer treatment. One class of apoptosis regulators is the inhibitors of apoptosis proteins (IAPs). Dysregulated IAP expression has been reported in many cancers, including breast cancer, and has been shown to be responsible for resistance to chemotherapy. Therefore, IAPs have become attractive molecular targets for cancer treatment. Here, we first investigated the antitumor efficacy of birinapant (TL32711), a biindole-based bivalent mimetic of second mitochondria-derived activator of caspases (SMACs), in TNBC. We found that birinapant as a single agent has differential antiproliferation effects in TNBC cells. We next assessed whether birinapant has a synergistic effect with commonly used anticancer drugs, including entinostat (class I histone deacetylase inhibitor), cisplatin, paclitaxel, voxtalisib (PI3K inhibitor), dasatinib (Src inhibitor), erlotinib (EGFR inhibitor), and gemcitabine, in TNBC. Among these tested drugs, gemcitabine showed a strong synergistic effect with birinapant. Birinapant significantly enhanced the antitumor activity of gemcitabine in TNBC both in vitro and in xenograft mouse models through activation of the intrinsic apoptosis pathway via degradation of cIAP2 and XIAP, leading to apoptotic cell death. Our findings demonstrate the therapeutic potential of birinapant to enhance the antitumor efficacy of gemcitabine in TNBC by targeting the IAP family of proteins.

ZNF703 promotes tumor progression in ovarian cancer by interacting with HE4 and epigenetically regulating PEA15

Background

It is known that the transcription factor zinc finger protein 703 (ZNF703) plays an important role in physiological functions and the occurrence and development of various tumors. However, the role and mechanism of ZNF703 in ovarian cancer are unclear.

Materials and methods

Immunohistochemistry was used to analyze the expression of ZNF703 in ovarian cancer patients and to assess the effect of ZNF703 expression on the survival and prognosis of ovarian cancer patients. ZNF703 overexpression and suppression expression experiments were used to evaluate the effect of ZNF703 on malignant biological behavior of ovarian cancer cells in vitro. Detecting the interaction between HE4 and ZNF703 by immunofluorescence colocalization and coprecipitation, and nuclear translocation. Chromatin immunoprecipitation-sequencing (ChIP-Seq), dual luciferase reporter assay, ChIP-PCR, in vivo model were applied to study the molecular mechanism of ZNF703 affecting the development of ovarian cancer.

Results

ZNF703 was highly expressed in ovarian cancer tissues, and its expression level is related to the prognosis of ovarian cancer patients. In vivo and in vitro experiments confirmed that ZNF703 overexpression/inhibition expression will promoted/inhibited the malignant biological behavior of ovarian cancer. Mechanically, ZNF703 interacted with HE4, and HE4 promoted nuclear translocation of ZNF703. ChIP-Seq identified multiple regulatory targets of ZNF703, of which ZNF703 directly binds to the enhancer region of PEA15 to promote the transcription of PEA15 and thereby promoted the proliferation of cancer cells.

Conclusion

The results showed that ZNF703 as an oncogene played an important role in the epigenetic modification of ovarian cancer proliferation, and suggested that ZNF703 as a transcription factor may become a prognostic factor and a potential therapeutic target for ovarian cancer.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-020-01770-0.

Modulating multi-functional ERK complexes by covalent targeting of a recruitment site in vivo

Recently, the targeting of ERK with ATP-competitive inhibitors has emerged as a potential clinical strategy to overcome acquired resistance to BRAF and MEK inhibitor combination therapies. In this study, we investigate an alternative strategy of targeting the D-recruitment site (DRS) of ERK. The DRS is a conserved region that lies distal to the active site and mediates ERK-protein interactions. We demonstrate that the small molecule BI-78D3 binds to the DRS of ERK2 and forms a covalent adduct with a conserved cysteine residue (C159) within the pocket and disrupts signaling in vivo. BI-78D3 does not covalently modify p38MAPK, JNK or ERK5. BI-78D3 promotes apoptosis in BRAF inhibitor-naive and resistant melanoma cells containing a BRAF V600E mutation. These studies provide the basis for designing modulators of protein-protein interactions involving ERK, with the potential to impact ERK signaling dynamics and to induce cell cycle arrest and apoptosis in ERK-dependent cancers.

Targetting PED/PEA-15 for diabetes treatment

INTRODUCTION

PED/PEA-15 is an ubiquitously expressed protein, involved in the regulation of proliferation and apoptosis. It is commonly overexpressed in Type 2 Diabetes (T2D) and in different T2D-associated comorbidities, including cancer and certain neurodegenerative disorders. Areas covered: In mice, Ped/Pea-15 overexpression impairs glucose tolerance and, in combination with high fat diets, further promotes insulin resistance and T2D. It also controls β-cell mass, altering caspase-3 activation and the expression of pro- and antiapoptotic genes. These changes are mediated by PED/PEA-15-PLD1 binding. Overexpression of PLD1 D4 domain specifically blocks Ped/Pea-15-PLD1 interaction, reverting the effect of Ped/Pea-15 in vivo. D4α, a D4 N-terminal peptide, is able to displace Ped/Pea-15-PLD1 binding, but features greater stability in vivo compared to the entire D4 peptide. Here, we review early mechanistic studies on PED/PEA-15 relevance in apoptosis before focusing on its role in cancer and T2D. Finally, we describe potential therapeutic opportunities for T2D based on PED/PEA-15 targeting. Expert opinion: T2D is a major problem for public health and economy. Thus, the identification of new molecules with pharmacological activity for T2D represents an urgent need. Further studies with D4α will help to identify smaller pharmacologically active peptides and innovative molecules of potential pharmacological interest for T2D treatment.

Discovery of a potent inhibitor of MELK that inhibits expression of the anti-apoptotic protein Mcl-1 and TNBC cell growth

Despite recent advances in molecularly directed therapy, triple negative breast cancer (TNBC) remains one of the most aggressive forms of breast cancer, still without a suitable target for specific inhibitors. Maternal embryonic leucine zipper kinase (MELK) is highly expressed in TNBC, where level of overexpression correlates with poor prognosis and an aggressive disease course. Herein, we describe the discovery through targeted kinase inhibitor library screening, and structure-guided design of a series of ATP-competitive indolinone derivatives with subnanomolar inhibition constants towards MELK. The most potent compound, 17, inhibits the expression of the anti-apoptotic protein Mcl-1 and proliferation of TNBC cells exhibiting selectivity for cells expressing high levels of MELK. These studies suggest that further elaboration of 17 will furnish MELK-selective inhibitors with potential for development in preclinical models of TNBC and other cancers.

Inhibition of miR-155 Protects Against LPS-induced Cardiac Dysfunction and Apoptosis in Mice

Sepsis-induced myocardial dysfunction represents a major cause of death in intensive care units. Dysregulated microRNAs (miR)-155 has been implicated in multiple cardiovascular diseases and miR-155 can be induced by lipopolysaccharide (LPS). However, the role of miR-155 in LPS-induced cardiac dysfunction is unclear. Septic cardiac dysfunction in mice was induced by intraperitoneal injection of LPS (5 mg/kg) and miR-155 was found to be significantly increased in heart challenged with LPS. Pharmacological inhibition of miR-155 using antagomiR improved cardiac function and suppressed cardiac apoptosis induced by LPS in mice as determined by echocardiography, terminal deoxynucleotidyl transferase nick-end labeling (TUNEL) assay, and Western blot for Bax and Bcl-2, while overexpression of miR-155 using agomiR had inverse effects. Pea15a was identified as a target gene of miR-155, mediating its effects in controlling apoptosis of cardiomyocytes as evidenced by luciferase reporter assays, quantitative real time-polymerase chain reaction, Western blot, and TUNEL staining. Noteworthy, miR-155 was also found to be upregulated in the plasma of patients with septic cardiac dysfunction compared to sepsis patients without cardiac dysfunction, indicating a potential clinical relevance of miR-155. The receiver-operator characteristic curve indicated that plasma miR-155 might be a biomarker for sepsis patients developing cardiac dysfunction. Therefore, inhibition of miR-155 represents a novel therapy for septic myocardial dysfunction.

On the Quest of Cellular Functions of PEA-15 and the Therapeutic Opportunities

Phosphoprotein enriched in astrocytes, 15 KDa (PEA-15), a ubiquitously expressed small protein in all mammals, is known for decades for its potent interactions with various protein partners along distinct biological pathways. Most notable interacting partners of PEA-15 include extracellular signal-regulated kinase 1 and 2 (ERK1/2) in the mitogen activated protein kinase (MAPK) pathway, the Fas-associated death domain (FADD) protein involving in the formation of the death-inducing signaling complex (DISC), and the phospholipase D1 (PLD1) affecting the insulin sensitivity. However, the actual cellular functions of PEA-15 are still mysterious, and the question why this protein is expressed in almost all cell and tissue types remains unanswered. Here we synthesize the most recent structural, biological, and clinical studies on PEA-15 with emphases on its anti-apoptotic, anti-proliferative, and anti-inflammative properties, and propose a converged protective role of PEA-15 that maintains the balance of death and survival in different cell types. Under conditions that this delicate balance is unsustainable, PEA-15 may become pathological and lead to various diseases, including cancers and diabetes. Targeting PEA-15 interactions, or the use of PEA-15 protein as therapeutics, may provide a wider window of opportunities to treat these diseases.

Immunotherapy targeting folate receptor induces cell death associated with autophagy in ovarian cancer

PURPOSE

Cancer cells are highly dependent on folate metabolism, making them susceptible to drugs that inhibit folate receptor activities. Targeting overexpressed folate receptor alpha (FRα) in cancer cells offers a therapeutic opportunity. We investigated the functional mechanisms of MORAB-003 (farletuzumab), a humanized mAb against FRα, in ovarian cancer models.

EXPERIMENTAL DESIGN

We first examined FRα expression in an array of human ovarian cancer cell lines and then assessed the in vivo effect of MORAB-003 on tumor growth and progression in several orthotopic mouse models of ovarian cancer derived from these cell lines. Molecular mechanisms of tumor cell death induced by MORAB-003 were investigated by cDNA and protein expression profiling analysis. Mechanistic studies were performed to determine the role of autophagy in MORAB-003-induced cell death.

RESULTS

MORAB-003 significantly decreased tumor growth in the high-FRα IGROV1 and SKOV3ip1 models but not in the low-FRα A2780 model. MORAB-003 reduced proliferation, but had no significant effect on apoptosis. Protein expression and cDNA microarray analyses showed that MORAB-003 regulated an array of autophagy-related genes. It also significantly increased expression of LC3 isoform II and enriched autophagic vacuolization. Blocking autophagy with hydroxychloroquine or bafilomycin A1 reversed the growth inhibition induced by MORAB-003. In addition, alteration of FOLR1 gene copy number significantly correlated with shorter disease-free survival in patients with ovarian serous cancer.

CONCLUSIONS

MORAB-003 displays prominent antitumor activity in ovarian cancer models expressing FRα at high levels. Blockade of folate receptor by MORAB-003 induced sustained autophagy and suppressed cell proliferation.

Development of PEA-15 using a potent non-viral vector for therapeutic application in breast cancer

Advanced breast cancer requires systemic treatment, therefore developing an efficient and safe strategy is urgently needed. To ensure the success of target therapy, we have developed a breast cancer-specific construct (T-VISA) composed of the human telomerase reverse transcriptase (hTERT; T) promoter and a versatile transgene amplification vector VISA (VP16-GAL4-WPRE integrated systemic amplifier) to target PEA-15 (phosphoprotein enriched in astrocytes) in advanced breast tumors. PEA-15 contains a death effector domain that sequesters extracellular signal-regulated kinase (ERK) in the cytoplasm, thereby inhibiting cell proliferation and inducing apoptosis. T-VISA-PEA-15 was found to be highly specific, selectively express PEA-15 in breast cancer cells, and induce cancer-cell killing in vitro and in vivo without affecting normal cells. Moreover, intravenous treatment with T-VISA-PEA-15 coupled with liposome nanoparticles attenuated tumor growth and prolonged survival in mice bearing advanced breast tumors. Importantly, there was virtually no severe toxicity when PEA-15 is expressed by our T-VISA system compared with cytomegalovirus (CMV) promoter. Thus, our findings demonstrate an effective cancer-targeted therapy that is worthy of development in clinical trials eradicating advanced breast cancer.

Linking signaling pathways to transcriptional programs in breast cancer

Cancer cells acquire genetic and epigenetic alterations that often lead to dysregulation of oncogenic signal transduction pathways, which in turn alters downstream transcriptional programs. Numerous methods attempt to deduce aberrant signaling pathways in tumors from mRNA data alone, but these pathway analysis approaches remain qualitative and imprecise. In this study, we present a statistical method to link upstream signaling to downstream transcriptional response by exploiting reverse phase protein array (RPPA) and mRNA expression data in The Cancer Genome Atlas (TCGA) breast cancer project. Formally, we use an algorithm called affinity regression to learn an interaction matrix between upstream signal transduction proteins and downstream transcription factors (TFs) that explains target gene expression. The trained model can then predict the TF activity, given a tumor sample’s protein expression profile, or infer the signaling protein activity, given a tumor sample’s gene expression profile. Breast cancers are comprised of molecularly distinct subtypes that respond differently to pathway-targeted therapies. We trained our model on the TCGA breast cancer data set and identified subtype-specific and common TF regulators of gene expression. We then used the trained tumor model to predict signaling protein activity in a panel of breast cancer cell lines for which gene expression and drug response data was available. Correlations between inferred protein activities and drug responses in breast cancer cell lines grouped several drugs that are clinically used in combination. Finally, inferred protein activity predicted the clinical outcome within the METABRIC Luminal A cohort, identifying high- and low-risk patient groups within this heterogeneous subtype.

PEA15 regulates the DNA damage-induced cell cycle checkpoint and oncogene-directed transformation

Regulation of the DNA damage response and cell cycle progression is critical for maintaining genome integrity. Here, we report that in response to DNA damage, COPS5 deubiquitinates and stabilizes PEA15 in an ATM kinase-dependent manner. PEA15 expression oscillates throughout the cell cycle, and the loss of PEA15 accelerates cell cycle progression by activating CDK6 expression via the c-JUN transcription factor. Cells lacking PEA15 exhibit a DNA damage-induced G2/M checkpoint defect due to increased CDC25C activity and, consequentially, higher cyclin-dependent kinase 1 (CDK1)/cyclin B activity, and accordingly they have an increased rate of spontaneous mutagenesis. We find that oncogenic RAS inhibits PEA15 expression and that ectopic PEA15 expression blocks RAS-mediated transformation, which can be partially rescued by ectopic expression of CDK6. Finally, we show that PEA15 expression is downregulated in colon, breast, and lung cancer samples. Collectively, our results demonstrate that tumor suppressor PEA15 is a regulator of genome integrity and is an integral component of the DNA damage response pathway that regulates cell cycle progression, the DNA-damage-induced G2/M checkpoint, and cellular transformation.

Antagonism of tumoral prolactin receptor promotes autophagy-related cell death

Therapeutic upregulation of macroautophagy in cancer cells provides an alternative mechanism for cell death. Prolactin (PRL) and its receptor (PRLR) are considered attractive therapeutic targets because of their roles as growth factors in tumor growth and progression. We utilized G129R, an antagonist peptide of PRL, to block activity of the tumoral PRL/PRLR axis, which resulted in inhibition of tumor growth in orthotopic models of human ovarian cancer. Prolonged treatment with G129R induced the accumulation of redundant autolysosomes in 3D cancer spheroids, leading to a type II programmed cell death. This inducible autophagy was a noncanonical beclin-1-independent pathway and was sustained by an astrocytic phosphoprotein (PEA-15) and protein kinase C zeta interactome. Lower levels of tumoral PRL/PRLR in clinical samples were associated with longer patient survival. Our findings provide an understanding of the mechanisms of tumor growth inhibition through targeting PRL/PRLR and may have clinical implications.

Phosphoprotein enriched in astrocytes (PEA)-15: a potential therapeutic target in multiple disease states

Phosphoprotein enriched in astrocytes-15 (PEA-15) is a cytoplasmic protein that sits at an important junction in intracellular signalling and can regulate diverse cellular processes, such as proliferation and apoptosis, dependent upon stimulation. Regulation of these processes occurs by virtue of the unique interaction of PEA-15 with other signalling proteins. PEA-15 acts as a cytoplasmic tether for the mitogen-activated protein kinases, extracellular signal-regulated kinase 1/2 (ERK1/2) preventing nuclear localisation. In order to release ERK1/2, PEA-15 requires to be phosphorylated via several potential pathways. PEA-15 (and its phosphorylation state) therefore regulates many ERK1/2-dependent processes, including proliferation, via regulating ERK1/2 nuclear translocation. In addition, PEA-15 contains a death effector domain (DED) which allows interaction with other DED-containing proteins. PEA-15 can bind the DED-containing apoptotic adaptor molecule, Fas-associated death domain protein (FADD) which is also dependent on the phosphorylation status of PEA-15. PEA-15 binding of FADD can inhibit apoptosis as bound FADD cannot participate in the assembly of apoptotic signalling complexes. Through these protein–protein interactions, PEA-15-regulated cellular effects have now been investigated in a number of disease-related studies. Changes in PEA-15 expression and regulation have been observed in diabetes mellitus, cancer, neurological disorders and the cardiovascular system. These changes have been suggested to contribute to the pathology related to each of these disease states. As such, new therapeutic targets based around PEA-15 and its associated interactions are now being uncovered and could provide novel avenues for treatment strategies in multiple diseases.

Association of the breast cancer antiestrogen resistance protein 1 (BCAR1) and BCAR3 scaffolding proteins in cell signaling and antiestrogen resistance

Most breast cancers are estrogen receptor-positive and treated with antiestrogens, but aberrant signaling networks can induce drug resistance. One of these networks involves the scaffolding protein BCAR1/p130CAS, which regulates cell growth and migration/invasion. A less investigated scaffolding protein that also confers antiestrogen resistance is the SH2 domain-containing protein BCAR3. BCAR1 and BCAR3 bind tightly to each other through their C-terminal domains, thus potentially connecting their associated signaling networks. However, recent studies using BCAR1 and BCAR3 interaction mutants concluded that association between the two proteins is not critical for many of their interrelated activities regulating breast cancer malignancy. We report that these previously used BCAR mutations fail to cause adequate loss-of-function of the complex. By using structure-based BCAR1 and BCAR3 mutants that lack the ability to interact, we show that BCAR3-induced antiestrogen resistance in MCF7 breast cancer cells critically depends on its ability to bind BCAR1. Interaction with BCAR3 increases the levels of phosphorylated BCAR1, ultimately potentiating BCAR1-dependent antiestrogen resistance. Furthermore, antiestrogen resistance in cells overexpressing BCAR1/BCAR3 correlates with increased ERK1/2 activity. Inhibiting ERK1/2 through overexpression of the regulatory protein PEA15 negates the resistance, revealing a key role for ERK1/2 in BCAR1/BCAR3-induced antiestrogen resistance. Reverse-phase protein array data show that PEA15 levels in invasive breast cancers correlate with patient survival, suggesting that PEA15 can override ERK1/2 activation by BCAR1/BCAR3 and other upstream regulators. We further uncovered that the BCAR3-related NSP3 can also promote antiestrogen resistance. Thus, strategies to disrupt BCAR1-BCAR3/NSP3 complexes and associated signaling networks could ultimately lead to new breast cancer therapies.

PEP-1-PEA-15 protects against toxin-induced neuronal damage in a mouse model of Parkinson's disease

BACKGROUND

PEA-15 is abundantly expressed in both neurons and astrocytes throughout the brain. It is a multifunctional protein with the ability to increase cell survival via anti-apoptotic and anti-proliferative properties. However, the function of PEA-15 in neuronal diseases such as Parkinson's disease (PD) remains unclear. In this study, we investigated the protective effects of PEA-15 on neuronal damage induced by MPP(+) in neuroblastoma SH-SY5Y and BV2 microglia cells and in a MPTP-induced PD mouse model using cell-permeable PEP-1-PEA-15.

METHODS

PEP-1-PEA-15 was purified using affinity chromatography. Cell viability and DNA fragmentation were examined by MTT assay and TUNEL staining. Dopaminergic neuronal cell death in the animal model was examined by immunohistochemistry.

RESULTS

PEP-1-PEA-15 transduced into the SH-SY5Y and BV2 cells in a time- and dose-dependent manner. Transduced PEP-1-PEA-15 protected against MPP(+)-induced toxicity by inhibiting intracellular ROS levels and DNA fragmentation. Further, it enhanced the expression levels of Bcl-2 and caspase-3 while reducing the expression levels of Bax and cleaved caspase-3. We found that PEP-1-PEA-15 transduced into the substantia nigra and prevented dopaminergic neuronal cell death in a MPTP-induced PD mouse. Also, we showed the neuroprotective effects in the model by demonstrating that treatment with PEP-1-PEA-15 ameliorated MPTP-induced behavioral dysfunctions and increased dopamine levels in the striatum.

CONCLUSIONS

PEP-1-PEA-15 can efficiently transduce into cells and protects against neurotoxin-induced neuronal cell death in vitro and in vivo.

GENERAL SIGNIFICANCE

These results demonstrate the potential for PEP-1-PEA-15 to provide a new strategy for protein therapy treatment of a variety of neurodegenerative diseases including PD.

Characterizing the metabolic heterogeneity in human breast cancer xenografts by 3D high resolution fluorescence imaging

We previously reported that tumor mitochondrial redox state and its heterogeneity distinguished between the aggressive and the indolent breast cancer xenografts, suggesting novel metabolic indices as biomarkers for predicting tumor metastatic potential. Additionally, we reported that the identified redox biomarkers successfully differentiated between the normal breast tissue and the cancerous breast tissue from breast cancer patients. The aim of the present study was to further characterize intratumor heterogeneity by its distribution of mitochondrial redox state and glucose uptake pattern in tumor xenografts and to further investigate the metabolic heterogeneity of the clinical biopsy samples. We employed the Chance redox scanner, a multi-section cryogenic fluorescence imager to simultaneously image the intratumor heterogeneity in the mitochondrial redox state and glucose uptake at a high spatial resolution (down to 50 × 50 × 20 μm(3)). The mitochondrial redox state was determined by the ratio of the intrinsic fluorescence signals from reduced nicotinamide adenine dinucleotide (NADH) and oxidized flavoproteins (Fp including FAD, i.e., flavin adenine dinucleotide), and the glucose uptake was measured using a near-infrared fluorescent glucose-analogue, pyropheophorbide 2-deoxyglucosamide (Pyro-2DG). Significant inter- and intratumor metabolic heterogeneity were observed from our imaging data on various types of breast cancer xenografts. The patterns and degrees of heterogeneity of mitochondrial redox state appeared to relate to tumor size and metastatic potential. The glucose uptake was also heterogeneous and generally higher in tumor peripheries. The oxidized and reduced regions mostly corresponded with the lower and the higher pyro-2DG uptake, respectively. However, there were some regions where the glucose uptake did not correlate with the redox indices. Pronounced glucose uptake and high NADH were observed in certain localized areas within the tumor necrotic regions, indicative of the existence of viable cells which was also supported by the H&E staining. Significant heterogeneity of the redox state indices was also observed in clinical specimens of breast cancer patients. As abnormal metabolism including the Warburg effect (high glycolysis) plays important roles in cancer transformation and progression, our observations that reveal the 3D intratumor metabolic heterogeneity as a characteristic feature of breast tumors are of great importance for understanding cancer biology and developing diagnostic and therapeutic methods.

Structure of ERK2 bound to PEA-15 reveals a mechanism for rapid release of activated MAPK

ERK1/2 kinases are the principal effectors of a central signaling cascade that converts extracellular stimuli into cell proliferation and migration responses and, when deregulated, can promote cell oncogenic transformation. The scaffolding protein PEA-15 is a death effector domain (DED) protein that directly interacts with ERK1/2 and affects ERK1/2 subcellular localization and phosphorylation. Here, to understand this ERK1/2 signaling complex, we have solved the crystal structures of PEA-15 bound to three different ERK2 phospho-conformers. The structures reveal that PEA-15 uses a bipartite binding mode, occupying two key docking sites of ERK2. Remarkably, PEA-15 can efficiently bind the ERK2 activation loop in the critical Thr-X-Tyr region in different phosphorylation states. PEA-15 binding triggers an extended allosteric conduit in dually phosphorylated ERK2, disrupting key features of active ERK2. At the same time PEA-15 binding protects ERK2 from dephosphorylation, thus setting the stage for immediate ERK activity upon its release from the PEA-15 inhibitory complex.

Bisphosphorylated PEA-15 sensitizes ovarian cancer cells to paclitaxel by impairing the microtubule-destabilizing effect of SCLIP

Paclitaxel is a standard chemotherapeutic agent for ovarian cancer. PEA-15 (phosphoprotein enriched in astrocytes-15 kDa) regulates cell proliferation, autophagy, apoptosis, and glucose metabolism and also mediates AKT-dependent chemoresistance in breast cancer. The functions of PEA-15 are tightly regulated by its phosphorylation status at Ser104 and Ser116. However, the effect of PEA-15 phosphorylation status on chemosensitivity of cancer cells remains unknown. Here, we tested the hypothesis that PEA-15 phosphorylated at both Ser104 and Ser116 (pPEA-15) sensitizes ovarian cancer cells to paclitaxel. We first found that knockdown of PEA-15 in PEA-15-high expressing HEY and OVTOKO ovarian cancer cells resulted in paclitaxel resistance, whereas re-expression of PEA-15 in these cells led to paclitaxel sensitization. We next found that SKOV3.ip1-DD cells (expressing phosphomimetic PEA-15) were more sensitive to paclitaxel than SKOV3.ip1-AA cells (expressing nonphosphorylatable PEA-15). Compared with SKOV3.ip1-vector and SKOV3.ip1-AA cells, SKOV3.ip1-DD cells displayed reduced cell viability, inhibited anchorage-independent growth, and augmented apoptosis when treated with paclitaxel. Furthermore, HEY and OVTOKO cells displayed enhanced paclitaxel sensitivity when transiently overexpressing phosphomimetic PEA-15 and reduced paclitaxel sensitivity when transiently overexpressing nonphosphorylatable PEA-15. These results indicate that pPEA-15 sensitizes ovarian cancer cells to paclitaxel. cDNA microarray analysis suggested that SCLIP (SCG10-like protein), a microtubule-destabilizing protein, is involved in pPEA-15-mediated chemosensitization. We found that reduced expression and possibly posttranslational modification of SCLIP following paclitaxel treatment impaired the microtubule-destabilizing effect of SCLIP, thereby promoting induction of mitotic arrest and apoptosis by paclitaxel. Our findings highlight the importance of pPEA-15 as a promising target for improving the efficacy of paclitaxel-based therapy in ovarian cancer.

The PEA-15/PED protein regulates cellular survival and invasiveness in colorectal carcinomas

The PEA-15/PED (phosphoprotein enriched in astrocytes 15kD/phosphoprotein enriched in diabetes) protein is a multifunctional phosphoprotein involved in various signaling pathways which determine survival, proliferation, and migration of cancer cells. Here, we investigated the expression and cellular functions of PEA-15 in colorectal carcinoma (CRC). PEA-15 is expressed in the majority of human CRC, predominantly in well differentiated tumor areas. A tissue microarray analysis of 1262 human CRC specimens from the DACHS study showed that PEA-15 expression is significantly associated with a low pT stadium as defined by limited invasion into the bowel wall. Moreover, patients with PEA-15-positive CRC exhibited a significantly longer tumor-specific survival time. To investigate the functional relevance of PEA-15 expression on a cellular level, we over-expressed PEA-15 in several CRC cell lines. Increased expression of PEA-15 resulted in a strong inhibition of clonogenicity, proliferation, and invasiveness of CRC cells. These effects were associated with a PEA-15-dependent down-regulation of integrin αvβ5 as well as with elevated levels of the phosphorylated MAP kinase ERK1/2. Moreover, expression of PEA-15 resulted in significant protection from cell death induced by cytotoxic drugs (5-FU, cisplatin), by the death ligand TRAIL, or by serum withdrawal. In conclusion, the PEA-15 protein regulates invasiveness, proliferation, and apoptosis resistance in CRC cells. PEA-15 might play an important role in chemoresistance, progression and metastasis in CRC.

Profound conformational changes of PED/PEA-15 in ERK2 complex revealed by NMR backbone dynamics

PED/PEA-15 is a small, non-catalytic, DED containing protein that is widely expressed in different tissues and highly conserved among mammals. PED/PEA-15 has been found to interact with several protein targets in various pathways, including FADD and procaspase-8 (apoptosis), ERK1/2 (cell cycle entry), and PLD1/2 (diabetes). In this research, we have studied the PED/PEA-15 in a complex with ERK2, a MAP kinase, using NMR spectroscopic techniques. MAP Kinase signaling pathways are involved in the regulation of many cellular functions, including cell proliferation, differentiation, apoptosis and survival. ERK1/2 are activated by a variety of external stimuli, including growth factors, hormones and neurotransmitters. Inactivated ERK2 is primarily found in the cytosol. Once the ERK/MAPK cascade is initiated, ERK2 is phosphorylated and stimulated, allowing it to redistribute in the cell nucleus and act as a transcription factor. Previous studies have shown that PED/PEA-15 complexes with ERK2 in the cytoplasm and prevents redistribution into the nucleus. Although the NMR structure and dynamics of PED/PEA-15 in the free form have been documented recently, no detailed structural and dynamic information for the ERK2-bound form is available. Here we report NMR chemical shift perturbation and backbone dynamic studies at the fast ps-ns timescale of PED/PEA-15, in its free form and in the complex with ERK2. These analyses characterize motions and conformational changes involved in ERK2 recognition and binding that orchestrate the reorganization of the DED and immobilization of the C-terminal tail. A new induced fit binding model for PED/PEA-15 is proposed.

PEA-15 unphosphorylated at both serine 104 and serine 116 inhibits ovarian cancer cell tumorigenicity and progression through blocking β-catenin

Ovarian cancer is a major cause of death among women; there remains an urgent need to develop new effective therapies to target this cancer. Phosphoprotein enriched in astrocytes (PEA-15) is a 15-kDa phosphoprotein that is known to bind ERK1/2, thus blocking cell proliferation. The physiological activity of PEA-15 is dependent on the phosphorylation status of serine 104 (Ser104) and Ser116. However, little is known about the impact of PEA-15 phosphorylation on tumor progression. We have previously shown that overexpression of PEA-15 has an antitumor effect against both breast and ovarian cancer cells. Here, we report that using a human ovarian cancer tissue microarray, we found that tissues from patients with ovarian cancer were significantly more likely than adjacent normal tissues to express PEA-15 phosphorylated at both sites. Using phosphomimetic and nonphosphorylatable mutants of PEA-15, we found that mutant double-unphosphorylated PEA-15 in which Ser104 and Ser116 were substituted with alanine (PEA-15-AA) had a more potent antitumorigenic effect in ovarian cancer than did phosphomimetic PEA-15 in which Ser104 and Ser116 were substituted with aspartic acid (PEA-15-DD). Further, we observed that the antitumorigenic effect of PEA-15-AA was a result of inhibition of the migration capacity of cells and inhibition of in vivo angiogenesis. This inhibition was partially dependent on inhibition of β-catenin expression and nuclear translocalization. Taken together, our results suggest that phosphorylated PEA-15 is an important contributor to the aggressiveness of ovarian cancer and justify the development of PEA-15-AA as an effective therapeutic molecule in the treatment of ovarian cancer.

Phosphorylation is the switch that turns PEA-15 from tumor suppressor to tumor promoter

Abnormal ERK signaling is implicated in many human diseases including cancer. This signaling cascade is a good target for the therapy of certain malignancies because of its important role in regulating cell proliferation and survival. The small phosphoprotein PEA-15 is a potent regulator of the ERK signaling cascade, and, by acting on this pathway, has been described to have both tumor-suppressor and tumor-promoter functions. However, the exact mechanism by which PEA-15 drives the outcome one way or the other remains unclear. We propose that the cellular environment is crucial in determining PEA-15 protein function by affecting the protein's phosphorylation state. We hypothesize that only unphosphorylated PEA-15 can act as a tumor-suppressor and that phosphorylation alters the interaction with binding partners to promote tumor development. In order to use PEA-15 as a prognostic marker or therapeutic target it is therefore important to evaluate its phosphorylation status.

High ERK protein expression levels correlate with shorter survival in triple-negative breast cancer patients

The mitogen-activated protein kinase (MAPK) signaling pathway is known to be activated in triple-negative breast cancer (TNBC). Extracellular signal-related kinase (ERK), a member of the MAPK pathway, promotes cell proliferation, angiogenesis, cell differentiation, and cell survival. To assess the prognostic impact of ERK in TNBC patients, relative quantities of ERK (ERK-2 and pMAPK) and direct targets of the ERK pathway (MAPK/ERK kinase 1, phospho-enriched protein in astrocytes [PEA]-15, phosphorylated (p)PEA-15, tuberous sclerosis protein 2, p70S6 kinase, and p27) were measured using reverse-phase protein arrays in tumor tissue from patients with TNBC (n = 97) and non-TNBC (n = 223). Protein levels in patients with TNBC were correlated with clinical and tumor characteristics and outcome. The median age of patients with TNBC was 55 years (range, 27-86 years). Disease stage was I in 21%, II in 60%, and III in 20% of the patients. In a multivariate analysis, among patients with TNBC, those with ERK-2-overexpressing tumors had a lower overall survival rate than those with low ERK-2-expressing tumors (hazard ratio [HR], 2.76; 95% confidence interval [CI], 1.19-6.41). However, high pMAPK levels were associated with a significantly higher relapse-free survival rate (HR, 0.66; 95% CI, 0.46-0.95). In conclusion, ERK-2 and pMAPK are valuable prognostic markers in TNBC. Further studies are justified to elucidate ERK's role in TNBC tumorigenicity and metastasis.

PEA15 impairs cell migration and correlates with clinical features predicting good prognosis in neuroblastoma

ERK and RSK2 drive proliferation and invasion of many cancers. Phosphoprotein enriched in astrocytes 15 (PEA15) binds ERK and RSK2 and high PEA15 levels can impair ERK- and RSK2-dependent transcription. PEA15 expression also inversely correlates with cell motility and invasiveness. We therefore tested PEA15 effects on neuroblastoma cells in vitro. We further analyzed PEA15 expression in the context of clinical and genetic features of neuroblastoma in tumor samples to determine its correlation with disease progression. Affymetrix microarray analysis was performed using 24 different neuroblastoma cell lines. Cell lines expressing low to intermediate levels of PEA15 were chosen for in vitro functional studies. The cell line results were verified by Affymetrix analysis of three different neuroblastic tumor types (total of 110 samples) PEA15 overexpression inhibited neuroblastoma migration in vitro. We verified that inhibition of motility required PEA15 interaction with its binding partners ERK and RSK2. Additionally, synthetic inhibitors of RSK2 suppressed integrin-dependent migration. PEA15 expression correlates with clinical parameters and a 25% increase in patient survival rate. The highest PEA15 levels were found in low stage, more differentiated and less metastatic neuroblastic tumors, and correlated with lack of MYCN amplification. PEA15 blocks neuroblastoma migration through inhibition of ERK/RSK2 signaling. PEA15 expression levels correlate with favorable clinical features suggesting that PEA15 limits metastatic progression of neuroblastoma. Thus, PEA15 and its partners ERK and RSK2 are potential targets for the development of new therapeutics to impede progression of minimal residual disease in patients with high-risk neuroblastoma.

The Role of Proteomics in the Diagnosis and Treatment of Women's Cancers: Current Trends in Technology and Future Opportunities

Technological and scientific innovations over the last decade have greatly contributed to improved diagnostics, predictive models, and prognosis among cancers affecting women. In fact, an explosion of information in these areas has almost assured future generations that outcomes in cancer will continue to improve. Herein we discuss the current status of breast, cervical, and ovarian cancers as it relates to screening, disease diagnosis, and treatment options. Among the differences in these cancers, it is striking that breast cancer has multiple predictive tests based upon tumor biomarkers and sophisticated, individualized options for prescription therapeutics while ovarian cancer lacks these tools. In addition, cervical cancer leads the way in innovative, cancer-preventative vaccines and multiple screening options to prevent disease progression. For each of these malignancies, emerging proteomic technologies based upon mass spectrometry, stable isotope labeling with amino acids, high-throughput ELISA, tissue or protein microarray techniques, and click chemistry in the pursuit of activity-based profiling can pioneer the next generation of discovery. We will discuss six of the latest techniques to understand proteomics in cancer and highlight research utilizing these techniques with the goal of improvement in the management of women's cancers.

Activation of Toll-like receptor 5 on breast cancer cells by flagellin suppresses cell proliferation and tumor growth

Increasing evidence showed that Toll-like receptors (TLR), key receptors in innate immunity, play a role in cancer progression and development but activation of different TLRs might exhibit the exact opposite outcome, antitumor or protumor effects. TLR function has been extensively studied in innate immune cells, so we investigated the role of TLR signaling in breast cancer epithelial cells. We found that TLR5 was highly expressed in breast carcinomas and that TLR5 signaling pathway is overly responsive in breast cancer cells. Interestingly, flagellin/TLR5 signaling in breast cancer cells inhibits cell proliferation and an anchorage-independent growth, a hallmark of tumorigenic transformation. In addition, the secretion of soluble factors induced by flagellin contributed to the growth-inhibitory activity in an autocrine fashion. The inhibitory activity was further confirmed in mouse xenografts of human breast cancer cells. These findings indicate that TLR5 activation by flagellin mediates innate immune response to elicit potent antitumor activity in breast cancer cells themselves, which may serve as a novel therapeutic target for human breast cancer therapy.

Targeted therapies in cancer - challenges and chances offered by newly developed techniques for protein analysis in clinical tissues

In recent years, new anticancer therapies have accompanied the classical approaches of surgery and radio- and chemotherapy. These new forms of treatment aim to inhibit specific molecular targets namely altered or deregulated proteins, which offer the possibility of individualized therapies.The specificity and efficiency of these new approaches, however, bring about a number of challenges. First of all, it is essential to specifically identify and quantify protein targets in tumor tissues for the reasonable use of such targeted therapies. Additionally, it has become even more obvious in recent years that the presence of a target protein is not always sufficient to predict the outcome of targeted therapies. The deregulation of downstream signaling molecules might also play an important role in the success of such therapeutic approaches. For these reasons, the analysis of tumor-specific protein expression profiles prior to therapy has been suggested as the most effective way to predict possible therapeutic results. To further elucidate signaling networks underlying cancer development and to identify new targets, it is necessary to implement tools that allow the rapid, precise, inexpensive and simultaneous analysis of many network components while requiring only a small amount of clinical material.Reverse phase protein microarray (RPPA) is a promising technology that meets these requirements while enabling the quantitative measurement of proteins. Together with recently developed protocols for the extraction of proteins from formalin-fixed, paraffin-embedded (FFPE) tissues, RPPA may provide the means to quantify therapeutic targets and diagnostic markers in the near future and reliably screen for new protein targets.With the possibility to quantitatively analyze DNA, RNA and protein from a single FFPE tissue sample, the methods are available for integrated patient profiling at all levels of gene expression, thus allowing optimal patient stratification for individualized therapies.