Expression of Eukaryotic Translation Initiation Factors in the Urothelial Carcinoma of the Bladder.

BACKGROUND/AIM: Urothelial carcinoma (UC) of the urinary bladder is the second most common tumor in the field of urology and is characterized by a relatively aggressive growth behavior. New therapeutic approaches are required to improve the prognosis of affected patients. We hypothesized a link between dysregulation of eIFs and the development of UC. Therefore, in the present work, we investigated the expression behavior of eIF1, eIF1AY, eIF1AX, eIF2α, eIF3a, eIF3b, eIF4B, eIF4E, eIF4G, eIF5A, eIF5B, and eIF6 in UC compared with that in urothelial tissue. MATERIALS AND METHODS: Paraffin-embedded tumor tissue samples from 107 patients suffering from UC were examined. Seventy-six patients contained adjacent urothelial tissue. Three tumor tissue cylinders (tumor collective) and two urothelial tissue cylinders (control collective) were collected per patient and embedded in tissue microarray (TMA) blocks. Immunohistochemical staining of the TMA sections was then performed. The staining results were assessed semi-quantitatively. Staining intensities and immunoreactive scores (IRS) of both collectives were compared. In each case, a distinction was made between cytoplasmic and nuclear staining. RESULTS: Significant up-regulation of eIF1AY, eIF2α, eIF3a, eIF3b, eIF4B, eIF4G, eIF5B, and eIF6 was found in the cytoplasm of UC. In contrast, eIF1 and eIF5A were significantly down-regulated in the cytoplasm of UC. eIF5A and eIF6 were significantly down-regulated in the nuclei of UC. CONCLUSION: Dysregulation of eIFs in the urothelium of the urinary bladder is linked to carcinogenesis at this site.

A Molecularly Characterized Preclinical Platform of Subcutaneous Renal Cell Carcinoma (RCC) Patient-Derived Xenograft Models to Evaluate Novel Treatment Strategies.

Renal cell carcinoma (RCC) is a kidney cancer with an onset mainly during the sixth or seventh decade of the patient's life. Patients with advanced, metastasized RCC have a poor prognosis. The majority of patients develop treatment resistance towards Standard of Care (SoC) drugs within months. Tyrosine kinase inhibitors (TKIs) are the backbone of first-line therapy and have been partnered with an immune checkpoint inhibitor (ICI) recently. Despite the most recent progress, the development of novel therapies targeting acquired TKI resistance mechanisms in advanced and metastatic RCC remains a high medical need. Preclinical models with high translational relevance can significantly support the development of novel personalized therapies. It has been demonstrated that patient-derived xenograft (PDX) models represent an essential tool for the preclinical evaluation of novel targeted therapies and their combinations. In the present project, we established and molecularly characterized a comprehensive panel of subcutaneous RCC PDX models with well-conserved molecular and pathological features over multiple passages. Drug screening towards four SoC drugs targeting the vascular endothelial growth factor (VEGF) and PI3K/mTOR pathway revealed individual and heterogeneous response profiles in those models, very similar to observations in patients. As unique features, our cohort includes PDX models from metastatic disease and multi-tumor regions from one patient, allowing extended studies on intra-tumor heterogeneity (ITH). The PDX models are further used as basis for developing corresponding in vitro cell culture models enabling advanced high-throughput drug screening in a personalized context. PDX models were subjected to next-generation sequencing (NGS). Characterization of cancer-relevant features including driver mutations or cellular processes was performed using mutational and gene expression data in order to identify potential biomarker or treatment targets in RCC. In summary, we report a newly established and molecularly characterized panel of RCC PDX models with high relevance for translational preclinical research.

Molecular margin status after radical prostatectomy using glutathione S-transferase P1 (GSTP1) promoter hypermethylation.

OBJECTIVE: To assess the potential for molecular staging in biopsies of the prostatic fossa after radical prostatectomy (RP) by searching for occult tumour cells through analysis of glutathione S-transferase P1 (GSTP1) methylation status. PATIENTS AND METHODS: We analysed 2446 biopsies: 2286 biopsies from a group of 254 patients with clinically organ-confined prostate cancer who underwent RP and 160 biopsies from a control group of 32 patients. After prostate gland excision, biopsies were obtained from defined areas of the prostatic fossa and bisected for histopathological and molecular genetics analyses. Results were related to clinicopathological data including tumour stage, lymph node status, resection status, tumour grading, initial PSA level, and biochemical recurrence. RESULTS: In total, 34 patients (13.4%) had at least one core positive for the GSTP1 promoter hypermethylation, six of whom (17.6%) were characterised as having a clinically localised tumour stage (pT2, pN0) and 28 (82.4%) as an advanced tumour stage (≥pT3 and/or pN1). GSTP1 promoter hypermethylation significantly correlated with tumour stage (P < 0.001), International Society of Urological Pathology grading (P = 0.001), lymph node status (P < 0.001), surgical margin status (P < 0.001), and biochemical recurrence (P = 0.001). Furthermore, in 46 patients (18.1%) further analysis led to a down- or upgrading of conventional surgical margin status. Classical R-status (margins of the specimen) is significantly superior to histological sampling from the fossa (P = 0.006) but not to GSTP1 analysis from the fossa (P = 0.227). CONCLUSION: For the detection of residual tumour in the fossa after RP in order to better predict recurrence, molecular GSTP1 promoter hypermethylation has some value; however, the classical R-status (margins of the specimen) is simpler and more widely applicable with similar results.

Functional and mutational analysis after radiation and cetuximab treatment on prostate carcinoma cell line DU145.

BACKGROUND: Epidermal Growth Factor Receptor is often overexpressed in advanced prostate carcinoma. In-vitro-studies in prostate carcinoma cell line DU145 have demonstrated increased sensibility to radiation after cetuximab treatment, but clinical data are not sufficient to date. METHODS: We analyzed effects of radiation and cetuximab in DU145 and A431 using proliferation, colony-forming-unit- and annexin-V-apoptosis-assays. Changes in protein expression of pEGFR and pERK1/2 after radiation and cetuximab treatment were analyzed. Using NGS we also investigated the impact of cetuximab long-term treatment. RESULTS: Cell counts in DU145 were reduced by 44% after 4 Gy (p = 0.006) and 55% after 4 Gy and cetuximab (p < 0.001). The surviving fraction (SF) was 0.69 after 2 Gy, 0.41 after 4 Gy and 0.15 after 6 Gy (each p < 0.001). Cetuximab treatment did not alter significantly growth reduction in 4 Gy radiated DU145 cells, p > 0.05 or SF, p > 0.05, but minor effects on apoptotic cell fraction in DU145 were detected. Using western blot, there were no detectable pEGFR and pERK1/2 protein signals after cetuximab treatment. No RAS mutation or HER2 amplification was detected, however a TP53 gen-mutation c.820G > T was found. CONCLUSIONS: Radiation inhibits cell-proliferation and colony-growth and induces apoptosis in DU145. Despite blocking MAP-Kinase-pathway using cetuximab, no significant radiation-sensitizing-effect was detected. Cetuximab treatment did not induce resistance-mutations. Further research must clarify which combination of anti-EGFR treatment strategies can increase radiation-sensitizing-effects.

Hamster Polyomavirus Research: Past, Present, and Future.

Hamster polyomavirus (Mesocricetus auratus polyomavirus 1, HaPyV) was discovered as one of the first rodent polyomaviruses at the end of the 1960s in a colony of Syrian hamsters (Mesocricetus auratus) affected by skin tumors. Natural HaPyV infections have been recorded in Syrian hamster colonies due to the occurrence of skin tumors and lymphomas. HaPyV infections of Syrian hamsters represent an important and pioneering tumor model. Experimental infections of Syrian hamsters of different colonies are still serving as model systems (e.g., mesothelioma). The observed phylogenetic relationship of HaPyV to murine polyomaviruses within the genus Alphapolyomavirus, and the exclusive detection of other cricetid polyomaviruses, i.e., common vole (Microtus arvalis polyomavirus 1) and bank vole (Myodes glareolus polyomavirus 1) polyomaviruses, in the genus Betapolyomavirus, must be considered with caution, as knowledge of rodent-associated polyomaviruses is still limited. The genome of HaPyV shows the typical organization of polyomaviruses with an early and a late transcriptional region. The early region encodes three tumor (T) antigens including a middle T antigen; the late region encodes three capsid proteins. The major capsid protein VP1 of HaPyV was established as a carrier for the generation of autologous, chimeric, and mosaic virus-like particles (VLPs) with a broad range of applications, e.g., for the production of epitope-specific antibodies. Autologous VLPs have been applied for entry and maturation studies of dendritic cells. The generation of chimeric and mosaic VLPs indicated the high flexibility of the VP1 carrier protein for the insertion of foreign sequences. The generation of pseudotype VLPs of original VP1 and VP2-foreign protein fusion can further enhance the applicability of this system. Future investigations should evaluate the evolutionary origin of HaPyV, monitor its occurrence in wildlife and Syrian hamster breeding, and prove its value for the generation of potential vaccine candidates and as a gene therapy vehicle.

Autoantibodies directed against α1-adrenergic receptor and endothelin receptor A in patients with prostate cancer.

BACKGROUND: For prostate cancer, signaling pathways induced by over-boarding stimulation of G-protein coupled receptors (GPCR) such as the endothelin, α1- and ß-adrenergic, muscarinic and angiotensin 1 receptors were accused to support the carcinogenesis. However, excessive receptor stimulation by physiological receptor ligands is minimized by a control system that induces receptor sensitization and down-regulation. This system is missing when so-called "functional autoantibodies" bind to the GPCR (GPCR-AAB). If GPCR-AAB were found in patients with prostate cancer, uncontrolled GPCR stimulation could make these autoantibodies an additional supporter in prostate cancer. METHODS: Using the bioassay of spontaneously beating cultured rat neonatal cardiomyocytes, GPCR-AAB were identified, quantified and characterized in the serum of 25 patients (aged 56-78 years, median 70 years) with prostate cancer compared to 10 male patients (aged 48-82 years, median 64) with urinary stone disorders (controls). RESULTS: Of the cancer patients, 24 (96%) and 17 (68%), respectively, carried autoantibodies directed against the α1-adrenergic receptor (α1-AAB) and endothelin receptor A (ETA-AAB). No patient was negative for both GPCR-AAB. In contrast, ETA-AAB and α1-AAB were absent in all (100%) and 9 (90%) of the 10 control patients, respectively. While α1-AAB targeted a specific epitope of the first extracellular loop of the α1-adrenergic receptor subtype A, an epitope of the second extracellular loop of the ETA receptor was identified as a target of ETA-AAB. As demonstrated in vitro, the functional activity of both autoantibodies found in prostate cancer can be neutralized by the aptamer BC007. CONCLUSIONS: We hypothesized that α1-AAB and ETA-AAB, which are highly present in prostate cancer patients, could by their functional activity support carcinogenesis by excessive receptor stimulation. The in vitro demonstrated neutralization of α1- and ETA-AAB by the aptamer BC007 could open the door to complement the treatments already available for prostate cancer.

The natural history of renal cell carcinoma with pulmonary metastases illuminated through mathematical modeling.

The goal of this study is to uncover some unobservable aspects of the individual-patient natural history of metastatic renal cell carcinoma (RCC) through mathematical modeling. We analyzed four clear cell RCC patients who at the time of primary tumor resection already had pulmonary metastases. Our description of the natural history of cancer in these patients was based on a parameterized version of a previously proposed very general mathematical model adjusted to these clinical cases. For each patient, identifiable model parameters were estimated by the method of maximum likelihood from the volumes of lung metastases computed from CT scans taken at or around the time of surgery. The model-based distribution of the volumes of lung metastases with likelihood maximizing parameters provided an excellent fit to the data for all patients analyzed. We found that, according to the model, the most likely scenario in all four patients had the following clinically important features: (1) duration of metastatic latency was very small compared to the growth period; (2) seeding of the first lung metastasis occurred before primary tumor reached detectable size, which implies that early cancer detection would not have prevented metastasis; (3) primary tumor contained a relatively fast growing subpopulation of metastasis-producing cells, which is consistent with the observed aggressive course of the disease; and (4) the volume of the primary tumor at the time of metastasis survey does not seem to be correlated with such characteristics of the metastatic burden as the number of detected lung metastases, their total volume, and the volume of the largest detected lung metastasis.

Crosstalk between Akt signaling and cold shock proteins in mediating invasive cell phenotypes.

Cold shock proteins are up-regulated by cellular stress and orchestrate inflammatory responses, cell proliferation, and differentiation. Enhanced cold shock protein expression promotes malignant cell transformation; up-regulation is detected in most cancers and associated with poor prognosis. Akt1, a serine/threonine kinase, is a potent oncogene, which activates pro-proliferative and anti-apoptotic signaling pathways, and phosphorylates the cold shock domain. Unexpectedly, chicken-YB-1 abrogates PI3K-Akt-dependent oncogenic cell transformation in embryonic fibroblasts. Here, we addressed the question whether chicken and human Y-box binding protein-1 (YB-1) act differently on cell transformation, and how a related protein, DNA-binding protein-A (DbpA) behaves in comparison. NIH3T3 cells were transduced with lentiviral vectors encoding for myristoylated (constitutive active) Akt1, YB-1, DbpA, or shRNA targeting YB-1 expression. Colony formation assays showed that human YB-1 acts similar to chicken on Akt-dependent cell transformation. This activity was not titratable. Given the correlation of nuclear YB-1 and upregulated DbpA expression in a series of clear cell renal cell carcinomas (n = 40) the colony formation assay was extended to include ectopic DbpA expression. DbpA alone prominently induced cell transformation, which was enhanced when constitutive active Akt1 or concomitant YB-1 expression was present. Notably, co-expression of DbpA together with YB-1 abrogated the repressive effect on Akt1 signaling observed with YB-1 alone. Macroscopically, some colonies yielded a remarkable "invasive" phenotype. Thus, cold shock proteins may convey profound anti- and pro-oncogenic effects on Akt-dependent cell transformation. DbpA is able to overcome the anti-oncogenic effects seen with combined YB-1 and Akt signaling in an in vitro model of colonial growth.

RANKL/RANK/OPG cytokine receptor system: mRNA expression pattern in BPH, primary and metastatic prostate cancer disease.

BACKGROUND: The cytokine system RANKL (receptor activator of NF-κB ligand), its receptor RANK and the antagonist OPG (osteoprotegerin) play a critical role in bone turnover. Our investigation was conducted to describe the gene expression at primary tumour site in prostate cancer patients and correlate the results with Gleason Score and PSA level. METHODS: Seventy-one samples were obtained from prostate cancer patients at the time of radical prostatectomy and palliative prostate resection (n = 71). Patients with benign prostate hyperplasia served as controls (n = 60). We performed real-time RT-PCR after microdissection of the samples. RESULTS: The mRNA expression of RANK was highest in tumour tissue from patients with bone metastases (p < 0.001) as compared to BPH or locally confined tumours, also shown in clinical subgroups distinguished by Gleason Score (< 7 or ≥ 7, p = 0.028) or PSA level (< 10 or ≥ 10 µg/l, p = 0.004). RANKL and OPG mRNA expression was higher in tumour tissue from patients with metastatic compared to local disease. The RANKL/OPG ratio was low in normal prostate tissue and high tumours with bone metastases (p < 0.05). Expression of all three cytokines was high in BPH tissue but did not exceed as much as in the tumour tissue. CONCLUSION: We demonstrated that RANK, RANKL and OPG are directly expressed by prostate cancer cells at the primary tumour site and showed a clear correlation with Gleason Score, serum PSA level and advanced disease. In BPH, mRNA expression is also detectable, but RANK expression does not exceed as much as compared to tumour tissue.

PBRM1 and VHL expression correlate in human clear cell renal cell carcinoma with differential association with patient's overall survival.

OBJECTIVE: To identify the clinicopathological association of PBRM1 (Polybromo-1 gene) and VHL (von Hippel-Lindau gene) expression at mRNA and protein levels in clear cell renal cell carcinoma (ccRCC) and its role in tumor progression. PATIENTS AND METHODS: Immunohistochemical analysis, Western blotting and qPCR analysis of PBRM1 and VHL were performed on fresh-frozen ccRCC and adjacent normal tissue obtained from 70 patients who underwent radical nephrectomy. In addition, a tissue microarray (TMA) from specimens of 326 ccRCC patients was used to evaluate the effect of loss of PBRM1 and VHL immunohistological expression on clinicopathological features as well as patient survival. RESULTS: In frozen tissue, PBRM1 and VHL mRNA were significantly down-regulated in most ccRCC tumors (77.6%/80.6%). Simultaneous weak PBRM1 and VHL protein expression was observed in 21.4% of frozen tumors. In the TMA samples, weak PBRM1 and VHL immunohistochemical staining was observed in 60.4% of the cases and was correlated (P<0.001). The association of PBRM1 and VHL immunohistochemical expression with clinicopathological parameters depicts a variable picture: predominantly weak PBRM1 and VHL expression were significantly associated with higher Fuhrman grade (P = 0.012 and 0.024, respectively) but only weak VHL expression was associated with a higher pT stage (P = 0.023). PBRM1 expression did not affect the overall survival, whereas weak VHL expression was associated with decreased patient overall survival (P = 0.013). CONCLUSIONS: Our data suggest that reduced expression of PBRM1 and VHL is correlated with an increased tumor aggressiveness. Low VHL expression was identified as a risk factor for worse patient overall survival, independently from PBRM1 expression pattern.

Autoantibodies Directed Against the Endothelin A Receptor in Patients With Benign Prostatic Hyperplasia.

BACKGROUND: Over-stimulation of G-protein coupled receptors (GPCRs) such as α1-adrenergic, muscarinic, endothelin, and AT1 receptors is considered to drive benign prostatic hyperplasia (BHP) which is often associated with lower urinary tract syndrome (LUTS). However, in addition to physiologic GPCR ligands, there is a new class of autoantibodies called functional autoantibodies that target the same GPCRs (GPCR-AABs) for over-stimulation, thus, presenting pathogenic potency. We hypothesize that patients with BPH/LUTS could carry GPCR-AABs representing potential targets for treatment. METHODS: GPCR-AABs were identified, quantified, and characterized in the serum from 20 patients (aged 55-82 years, median 71 years) with BPH using the bioassay of spontaneously beating cultured neonatal rat cardiomyocytes. RESULTS: A sum of 60% of the patients were positive for agonistic autoantibodies directed against the endothelin A receptor (ETA-AABs). ETA-AABs were associated with the IgG 1 subclass, targeted an epitope located on the second extracellular receptor loop and their agonistic activity could be neutralized by the aptamer BC007. CONCLUSIONS: Agonistic ETA-AABs could-via uncontrolled over-boarding endothelin A receptor stimulation-contribute to the pathogenesis of BPH/LUTS. The in vitro demonstrated ETA-AAB neutralization by the aptamer BC007 could open the door for a new treatment strategy in patients with BPH/LUTS. Prostate 77:458-465, 2017. © 2016 Wiley Periodicals, Inc.

Lymphoma outbreak in a GASH:Sal hamster colony.

We have detected a high incidence of lymphomas in a colony of GASH:Sal Syrian golden hamsters (Mesocricetus auratus). This strain is characterised by its ability to present convulsive crises of audiogenic origin. Almost 16 % (90 males and 60 females) of the 975 animals were affected during a 5-year period by the development of a progressing lymphoid tumour and exhibited similar clinical profiles characterised by lethargy, anorexia, evident abdominal distension, and a rapid disease progression resulting in mortality within 1 to 2 weeks. A TaqMan® probe-based real-time PCR analysis of genomic DNA from different tissue samples of the affected animals revealed the presence of a DNA sequence encoding the hamster polyomavirus (HaPyV) VP1 capsid protein. Additionally, immunohistochemical analysis using HaPyV-VP1-specific monoclonal antibodies confirmed the presence of viral proteins in all hamster tumour tissues analysed within the colony. An indirect ELISA and western blot analysis confirmed the presence of antibodies against the VP1 capsid protein in sera, not only from affected and non-affected GASH:Sal hamsters but also from control hamsters from the same breeding area. The HaPyV genome that accumulated in tumour tissues typically contained deletions affecting the noncoding regulatory region and adjacent sequences coding for the N-terminal part of the capsid protein VP2.

Generation of an antibody against the protein phosphatase 1 inhibitor KEPI and characterization of the epitope.

A monoclonal antibody against the potential tumor suppressor kinase-enhanced protein phosphatase 1 (PP1) inhibitor KEPI (PPP1R14C) was generated and characterized. Human KEPI was expressed in Escherichia coli and used to immunize Balb/c mice. Using hybridoma technology, one clone, G18AF8, was isolated producing antibodies which bound specifically to the KEPI protein in ELISA, immunoblotting and flow cytometry. The antibody was also successfully applied to stain KEPI protein in paraffin sections of human brain. The epitope was mapped using peptide array technology and confirmed as GARVFFQSPR. This corresponds to the N-terminal region of KEPI. Amino acid substitution analysis revealed that two residues, F and Q, are essential for binding. Affinity of binding was determined by competitive ELISA as 1 microM. In Western blot assays testing G18AF8 antibody on brain samples of several species, reactivity with hamster, rat and chicken samples was found, suggesting a broad homology of this KEPI epitope in vertebrates. This antibody could be used in expression studies at the protein level e.g. in tumor tissues.

Aberrant methylation of human L- and M-fructose 1,6-bisphosphatase genes in cancer.

A possible epigenetic regulation of the two isoenzymes of fructose 1,6-bisphosphatase (FBPase) was studied in liver, muscle, mamma, breast cancer and in different cancer cell lines. Results obtained after bisulfite sequencing revealed a different CpG methylation of both promoters in liver, muscle and breast tissue which is putatively involved in the cell-type specific gene expression of the two enzymes. In tumor cell lines, demethylation with 5-aza-deoxycytidine activated the expression of both isoenzymes. Additional inhibition of histone deacetylase with trichostatin A further increased FBPase mRNA concentrations. Since cancers typically have an abnormal energy metabolism and exhibit a low gluconeogenic phenotype, it was studied whether promoter methylation contributes to the decreased expression of FBPase in breast cancer. When non-malignant and malignant tissue samples from the same patient were compared a correlation between an increase of FBPase promoter methylation and a decrease of FBPase mRNA levels was observed.

Epitope mapping of antibodies against S-tagged fusion proteins and molecular weight markers.

Monoclonal antibodies against S-tagged fusion proteins expressed in pET vectors were generated and further characterized. Most pET vectors contain a 15-meric S-tag as a fusion tag for the detection of recombinant proteins. Two antibodies, G18BA3 and G18BE8, recognized this S-tag in enzyme immunoassay and Western blot. Their epitopes were mapped using peptide array technology and were confirmed to be AAKFERQHMDSPD. This corresponds to the C-terminal region of the S-tag plus additional amino acids P and D, which are also present in most available pET vectors. Amino acid substitution analysis revealed several essential residues for binding. The binding motif was therefore FExxHxDxxD for G18BA3 and AxxFExxH for G18BE8. Since some commercially available protein standards are expressed in pET vectors, G18BA3 and G18BE8 were also found to detect the ladder bands of a molecular weight marker on immunoblot analysis. Both antibodies should be highly useful for the simultaneous detection of recombinant pET vector-expressed fusion proteins and protein molecular weight standards in Western blotting, especially when chemoluminescent detection systems are used.

Chimeric polyomavirus-derived virus-like particles: the immunogenicity of an inserted peptide applied without adjuvant to mice depends on its insertion site and its flanking linker sequence.

We inserted the sequence of the carcinoembryonic antigen-derived T cell epitope CAP-1-6D (CEA) into different positions of the hamster polyomavirus major capsid protein VP1. Independently from additional flanking linkers, yeast-expressed VP1 proteins harboring the CEA insertion between VP1 amino acid residues 80 and 89 (site 1) or 288 and 295 (site 4) or simultaneously at both positions assembled to chimeric virus-like particles (VLPs). BALB/c mice immunized with adjuvant-free VLPs developed VP1- and epitope-specific antibodies. The level of the CEA-specific antibody response was determined by the insertion site, the number of inserts, and the flanking linker. The strongest CEA-specific antibody response was observed in mice immunized with VP1 proteins harboring the CEA insert at site 1. Moreover, the CEA-specific antibodies in these mice were still detectable 6 mo after the final booster immunization. Our results indicate that hamster polyomavirus-derived VLPs represent a highly immunogenic carrier for foreign insertions that might be useful for clinical and therapeutic applications.

Expression of the protein phosphatase 1 inhibitor KEPI is downregulated in breast cancer cell lines and tissues and involved in the regulation of the tumor suppressor EGR1 via the MEK-ERK pathway.

KEPI is a protein kinase C-potentiated inhibitory protein for type 1 Ser/Thr protein phosphatases. We found no or reduced expression of KEPI in breast cancer cell lines, breast tumors and metastases in comparison to normal breast cell lines and tissues, respectively. KEPI protein expression and ubiquitous localization was detected with a newly generated antibody. Ectopic KEPI expression in MCF7 breast cancer cells induced differential expression of 95 genes, including the up-regulation of the tumor suppressors EGR1 (early growth response 1) and PTEN (phosphatase and tensin homolog), which is regulated by EGR1. We further show that the up-regulation of EGR1 in MCF7/KEPI cells is mediated by MEK-ERK signaling. The inhibition of this pathway by the MEK inhibitor UO126 led to a strong decrease in EGR1 expression in MCF7/KEPI cells. These results reveal a novel role for KEPI in the regulation of the tumor suppressor gene EGR1 via activation of the MEK-ERK MAPK pathway.