Suppression of CHK1 by ETS Family Members Promotes DNA Damage Response Bypass and Tumorigenesis

Novel frontiers in urogenital cancers: from molecular bases to preclinical models to tailor personalized treatments in ovarian and prostate cancer patients

Over the last few decades, the incidence of urogenital cancers has exhibited diverse trends influenced by screening programs and geographical variations. Among women, there has been a consistent or even increased occurrence of endometrial and ovarian cancers; conversely, prostate cancer remains one of the most diagnosed malignancies, with a rise in reported cases, partly due to enhanced and improved screening efforts.Simultaneously, the landscape of cancer therapeutics has undergone a remarkable evolution, encompassing the introduction of targeted therapies and significant advancements in traditional chemotherapy. Modern targeted treatments aim to selectively address the molecular aberrations driving cancer, minimizing adverse effects on normal cells. However, traditional chemotherapy retains its crucial role, offering a broad-spectrum approach that, despite its wider range of side effects, remains indispensable in the treatment of various cancers, often working synergistically with targeted therapies to enhance overall efficacy.For urogenital cancers, especially ovarian and prostate cancers, DNA damage response inhibitors, such as PARP inhibitors, have emerged as promising therapeutic avenues. In BRCA-mutated ovarian cancer, PARP inhibitors like olaparib and niraparib have demonstrated efficacy, leading to their approval for specific indications. Similarly, patients with DNA damage response mutations have shown sensitivity to these agents in prostate cancer, heralding a new frontier in disease management. Furthermore, the progression of ovarian and prostate cancer is intricately linked to hormonal regulation. Ovarian cancer development has also been associated with prolonged exposure to estrogen, while testosterone and its metabolite dihydrotestosterone, can fuel the growth of prostate cancer cells. Thus, understanding the interplay between hormones, DNA damage and repair mechanisms can hold promise for exploring novel targeted therapies for ovarian and prostate tumors.In addition, it is of primary importance the use of preclinical models that mirror as close as possible the biological and genetic features of patients' tumors in order to effectively translate novel therapeutic findings "from the bench to the bedside".In summary, the complex landscape of urogenital cancers underscores the need for innovative approaches. Targeted therapy tailored to DNA repair mechanisms and hormone regulation might offer promising avenues for improving the management and outcomes for patients affected by ovarian and prostate cancers.

Bibliometric analysis of PTEN in neurodevelopment and neurodegeneration

Phosphatase and tensin homologue deleted on chromosome ten (PTEN) was initially recognized as a significant regulator of cancer suppression and could impede cancer cell survival, proliferation, and energy metabolism. PTEN is highly expressed in neurons and performs crucial functions in neurogenesis, synaptogenesis, and neuronal survival. Disruption of PTEN activity may also result in abnormal neuronal function and is associated with various neurological disorders, including stroke, seizures, and autism. Although several studies have shown that PTEN is involved in the development and degenerative processes of the nervous system, there is still a lack of in-depth studies that summarize and analyse patterns of cooperation between authors, institutions, countries, and journals, as well as research hotspots and trends in this important field. To identify and further visualize the cooperation and comprehend the development and trends of PTEN in the nervous system, especially in neural development and neurological diseases, we used a bibliometric analysis to identify relevant publications on this topic. We first found that the number of publications displayed a growing trend with time, but this was not stable. Universities, institutions, and authors from the United States are leading in this area of research. In addition, many cutting-edge research results have been discovered, such as key regulatory molecules and cellular mechanisms of PTEN in the nervous system, which may provide novel intervention targets and precise therapeutic strategies for related pathological injuries and diseases. Finally, the literature published within the last 5 years is discussed to identify future research trends regarding PTEN in the nervous system. Taken together, our findings, analysed using bibliometrics, may reflect research hotspots and trends, providing a reference for studying PTEN in the nervous system, especially in neural development and neurological diseases. These findings can assist new researchers in developing their research interests and gaining basic information. Moreover, our findings also may provide precise clinical guidelines and strategies for treating nervous system injuries and diseases caused by PTEN dysfunction.

Targeting PEA3 transcription factors to mitigate small cell lung cancer progression

Small cell lung cancer (SCLC) remains a lethal disease with a dismal overall survival rate of 6% despite promising responses to upfront combination chemotherapy. The key drivers of such rapid mortality include early metastatic dissemination in the natural course of the disease and the near guaranteed emergence of chemoresistant disease. Here, we found that we could model the regression and relapse seen in clinical SCLC in vitro. We utilized time-course resolved RNA-sequencing to globally profile transcriptome changes as SCLC cells responded to a combination of cisplatin and etoposide-the standard-of-care in SCLC. Comparisons across time points demonstrated a distinct transient transcriptional state resembling embryonic diapause. Differential gene expression analysis revealed that expression of the PEA3 transcription factors ETV4 and ETV5 were transiently upregulated in the surviving fraction of cells which we determined to be necessary for efficient clonogenic expansion following chemotherapy. The FGFR-PEA3 signaling axis guided the identification of a pan-FGFR inhibitor demonstrating in vitro and in vivo efficacy in delaying progression following combination chemotherapy, observed inhibition of phosphorylation of the FGFR adaptor FRS2 and corresponding downstream MAPK and PI3K-Akt signaling pathways. Taken together, these data nominate PEA3 transcription factors as key mediators of relapse progression in SCLC and identify a clinically actionable small molecule candidate for delaying relapse of SCLC.

Identification of hub genes and their correlation with infiltration of immune cells in MYCN positive neuroblastoma based on WGCNA and LASSO algorithm

Background

The prognosis of MYCN positive NB is poor, and there is no targeted drug for N-myc at present. This study aims to screen out hub genes closely related to MYCN, analyze the relationship between hub genes and NB microenvironment, and provide basis for molecular targeted therapy of MYCN positive NB.

Methods

We combined the microarray data of GSE45547 (n=649) and GSE49710 (n=498), screened the DEGs between MYCN positive (n=185) and MYCN negative NB (n=951), performed WGCNA, Lasso regression and Roc analyses on the merged matrix, and obtained the hub genes related to MYCN in the training group. We performed ssGSEA on the experimental group to calculate the infiltration level of 28 kinds of immune cells in each sample, compared the differences of immune cell infiltration between MYCN positive and MYCN negative group. The influences of hub genes on the distribution of each immune cell were also analyzed by ssGSEA. The expression differences of the three hub genes were verified in the E-MTAB-8248 cohort (n=223), and the correlation between hub genes and prognosis of NB was calculated by Kaplan-Meier method in GSE62564 (n=498) and the validation group. We also verified the expression differences of hub genes by qRT-PCR in SK-N-BE(2), SKNDZ, Kelly and SH-SY5Y cell lines.

Results

Here were 880 DEGs including 420 upregulated and 460 downregulated genes in MYCN positive NB in the training group. Overlap of the DEGs and WGCNA networks identified four shared genes, namely, ZNF695, CHEK1, C15ORF42 and EXO1, as candidate hub genes in MYCN positive NB. Three core genes, ZNF695, CHEK1 and C15ORF42, were finally identified by Lasso regression and Roc analyses. ZNF695, CHEK1 and C15ORF42 were highly expressed in MYCN positive NB tissues and cell lines. These three genes were closely related to the prognosis of children with NB. Except that Activated CD4 T cell and Type2 T helper cell increased, the infiltration levels of the other 26 cells decreased significantly in MYCN positive NB tissues. The infiltration levels of Type2 T helper cell and Activated CD4 T cell were also significantly positively correlated with the expression levels of the three hub genes.

Conclusion

ZNF695, CHEK1 and C15ORF42 are highly expressed in MYCN positive NB, and their expression levels are negatively correlated with the prognosis of children with NB. The infiltration levels of Activated CD4 T cell and Type2 T helper cell increased in the microenvironment of MYCN positive NB and were significantly positively correlated with the expression levels of the three hub genes. The results of this study provide that ZNF695, CHEK1 and C15ORF42 may be potential prognostic markers and immunotherapy targets for MYCN positive NB.

HGF-mediated elevation of ETV1 facilitates hepatocellular carcinoma metastasis through upregulating PTK2 and c-MET

Background

Metastasis is a major determinant of death in patients with hepatocellular carcinoma (HCC). Dissecting key molecular mediators that promote this malignant feature may help yield novel therapeutic insights. Here, we investigated the role of E-twenty-six transformation-specific variant 1 (ETV1), a member of the E-twenty-six transformation-specific (ETS) family, in HCC metastasis. 

Methods

The clinical significance of ETV1 and its target genes in two independent cohorts of HCC patients who underwent curative resection were assessed by Kaplan–Meier analysis and Multivariate Cox proportional hazards model. Luciferase reporter assay and chromatin immunoprecipitation assay were used to detect the transcriptional regulation of target gene promoters by ETV1. The effect of ETV1 on invasiveness and metastasis of HCC were detected by transwell assays and the orthotopically metastatic model.

Results

ETV1 expression was frequently elevated in human HCC specimens. Increased ETV1 expression was associated with the malignant biological characteristics and poor prognosis of HCC patients. ETV1 facilitated invasion and metastasis of HCC cells in vitro and in vivo. Mechanistically, ETV1 promoted HCC metastasis via upregulating metastasis-related genes, including protein tyrosine kinase 2 (PTK2) and MET. Down-regulated the expression of PTK2 or tyrosine protein kinase Met (c-MET) decreased ETV1-mediated HCC metastasis. Hepatocyte growth factor (HGF) upregulated ETV1 expression through activating c-MET-ERK1/2-ELK1 pathway. Notably, in two independent cohorts, patients with positive coexpression of ETV1/PTK2 or ETV1/c-MET had worse prognosis. Furthermore, the combination of PTK2 inhibitor defactinib and c-MET inhibitor capmatinib significantly suppressed HCC metastasis induced by ETV1.

Conclusion

This study uncovers functional and prognostic roles for ETV1 in HCC and exposes a positive feedback loop of HGF-ERK1/2-ETV1-c-MET. Targeting this pathway may provide a potential therapeutic intervention for ETV1-overexpressing HCC.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-022-02475-2.

Role of Chk1 gene in molecular classification and prognosis of gastric cancer using immunohistochemistry and LORD-Q assay

Purpose: The aim of the current study was to assess the prognostic value of the Chk1 gene in the DNA damage response pathway in gastric cancer (GC). Methods: Expression levels of the Chk1 were measured in 220 GC tumor tissues and adjacent healthy/noncancerous tissues using real-time PCR and immunohistochemical staining. Genomic instability in GC patients was measured using the long-run real-time PCR technique for DNA-damage quantification assay and comet assay. Results: Significantly downregulated expression of Chk1 was observed at the mRNA level (p < 0.0001) and protein level (p < 0.0001). Significantly increased frequency of lesions/10 kb and comets was observed in tumor tissues compared with control tissues. Conclusion: The data suggest that downregulated expression of Chk1 and positive Heliobacter pylori infection status may have prognostic significance in GC.

Patient-matched analysis identifies deregulated networks in prostate cancer to guide personalized therapeutic intervention

Prostate cancer (PrCa) is the second most common malignancy in men. More than 50% of advanced prostate cancers display the TMPRSS2-ERG fusion. Despite extensive cancer genome/transcriptome data, little is known about the impact of mutations and altered transcription on regulatory networks in the PrCa of individual patients. Using patient-matched normal and tumor samples, we established somatic variations and differential transcriptome profiles of primary ERG-positive prostate cancers. Integration of protein-protein interaction and gene-regulatory network databases defined highly diverse patient-specific network alterations. Different components of a given regulatory pathway were altered by novel and known mutations and/or aberrant gene expression, including deregulated ERG targets, and were validated by using a novel in silico methodology. Consequently, different sets of pathways were altered in each individual PrCa. In a given PrCa, several deregulated pathways share common factors, predicting synergistic effects on cancer progression. Our integrated analysis provides a paradigm to identify druggable key deregulated factors within regulatory networks to guide personalized therapies.

Calcium cytotoxicity sensitizes prostate cancer cells to standard-of-care treatments for locally advanced tumors

Therapy resistance is a major roadblock in oncology. Exacerbation of molecular dysfunctions typical of cancer cells have proven effective in twisting oncogenic mechanisms to lethal conditions, thus offering new therapeutic avenues for cancer treatment. Here, we demonstrate that selective agonists of Transient Receptor Potential cation channel subfamily M member 8 (TRPM8), a cation channel characteristic of the prostate epithelium frequently overexpressed in advanced stage III/IV prostate cancers (PCa), sensitize therapy refractory models of PCa to radio, chemo or hormonal treatment. Overall, our study demonstrates that pharmacological-induced Ca²⁺ cytotoxicity is an actionable strategy to sensitize cancer cells to standard therapies.

Function and regulation of the PEA3 subfamily of ETS transcription factors in cancer

The PEA3 subfamily is a subgroup of the E26 transformation-specific (ETS) family. Its members, ETV1, ETV4, and ETV5, have been found to be overexpressed in multiple cancers. The deregulation of ETV1, ETV4, and ETV5 induces cell growth, invasion, and migration in various tumor cells, leading to tumor progression, metastasis, and drug resistance. Therefore, exploring drugs or therapeutic targets that target the PEA3 subfamily may contribute to the clinical treatment of tumor patients. In this review, we introduce the structures and functions of the PEA3 subfamily members, systematically review their main roles in various tumor cells, analyze their prognostic and diagnostic value, and, finally, introduce several molecular targets and therapeutic drugs targeting ETV1, ETV4, and ETV5. We conclude that targeting a series of upstream regulators and downstream target genes of the PEA3 subfamily may be an effective strategy for the treatment of ETV1/ETV4/ETV5-overexpressing tumors.

Rearranged ERG confers robustness to prostate cancer cells by subverting the function of p53

OBJECTIVE

ERG rearrangements are frequent and early events in prostate cancer. The functional role of rearranged ERG, however, is still incompletely understood. ERG rearrangements are maintained during prostate cancer progression suggesting that they may confer a selective advantage. The molecular basis of this notion is the subject of this study.

METHODS

A variety of immunological methods were used to characterize the effects of rearranged ERG on p53. Consequences of an overexpression of N-terminally deleted ERG on p53 function were interrogated by measuring apoptosis and cellular senescence in the presence or absence of exogenous DNA damage. Effects of N-terminally deleted ERG on the transactivation function of p53 were analyzed by qRT-PCR.

RESULTS

We show that overexpression of ERG leads to an increased basal level of DNA damage and a stabilization of p53 that involves a sequestration of its E3 ubiquitin ligase, MDM2, into nucleoli. A higher p53 expression was also observed in vivo in an ERG-overexpressing prostatic intraepithelial neoplasia mouse model. The correlation between ERG and p53 expression was corroborated in 163 patients with prostate cancer. ERG overexpression was found to inhibit both apoptosis and cellular senescence induced by exogenous DNA damage. Mechanistically, this protective effect of ERG involved an abrogation of the DNA damage-induced expression of p53 target genes.

CONCLUSIONS

By protecting tumor cells from the antiproliferative consequences of genotoxic stress, ERG may allow the survival and proliferation of genomically unstable tumor cells. Targeting ERG may therefore represent a promising strategy to suppress such adverse features during prostate cancer progression.

Comparative RNA-seq analysis reveals dys-regulation of major canonical pathways in ERG-inducible LNCaP cell progression model of prostate cancer

Prostate Cancer (CaP) is the second leading cause of cancer related death in USA. In human CaP, gene fusion between androgen responsive regulatory elements at the 5'-untranslated region of TMPRSS2 and ETS-related genes (ERG) is present in at least 50% of prostate tumors. Here we have investigated the unique cellular transcriptome associated with over-expression of ERG in ERG-inducible LNCaP cell model system of human CaP. Comprehensive transcriptome analyses reveal a distinct signature that distinguishes ERG dependent and independent CaP in LNCaP cells. Our data highlight a significant heterogeneity among the transcripts. Out of the 526 statistically significant differentially expressed genes, 232 genes are up-regulated and 294 genes are down-regulated in response to ERG. These ERG-associated genes are linked to several major cellular pathways, cell cycle regulation being the most significant. Consistently our data indicate that ERG plays a key role in modulating the expression of genes required for G1 to S phase transition, particularly those that affect cell cycle arrest at G1 phase. Moreover, cell cycle arrest in response to ERG appears to be promoted by induction of p21 in a p53 independent manner. These findings may provide new insights into mechanisms that promote growth and progression of CaP.

Molecular mechanisms and pathobiology of oncogenic fusion transcripts in epithelial tumors

Recurrent fusion transcripts, which are one of the characteristic hallmarks of cancer, arise either from chromosomal rearrangements or from transcriptional errors in splicing. DNA rearrangements include intrachromosomal or interchromosomal translocation, tandem duplication, deletion, inversion, or result from chromothripsis, which causes complex rearrangements. In addition, fusion proteins can be created through transcriptional read-through. Fusion genes can be transcribed to fusion transcripts and translated to chimeric proteins, with many having demonstrated transforming activities through multiple mechanisms in cells. Fusion proteins represent novel therapeutic targets and diagnostic biomarkers of diagnosis, disease status, or progression. This review focuses on the mechanisms underlying the formation of oncogenic fusion genes and transcripts and their impact on the pathobiology of epithelial tumors.

Genetically Engineered Mouse Models of Prostate Cancer in the Postgenomic Era

Recent genomic sequencing analyses have unveiled the spectrum of genomic alterations that occur in primary and advanced prostate cancer, raising the question of whether the corresponding genes are functionally relevant for prostate tumorigenesis, and whether such functions are associated with particular disease stages. In this review, we describe genetically engineered mouse models (GEMMs) of prostate cancer, focusing on those that model genomic alterations known to occur in human prostate cancer. We consider whether the phenotypes of GEMMs based on gain or loss of function of the relevant genes provide reliable counterparts to study the predicted consequences of the corresponding genomic alterations as occur in human prostate cancer, and we discuss exceptions in which the GEMMs do not fully emulate the expected phenotypes. Last, we highlight future directions for the generation of new GEMMs of prostate cancer and consider how we can use GEMMs most effectively to decipher the biological and molecular mechanisms of disease progression, as well as to tackle clinically relevant questions.

Mitochondrial Membrane Potential Regulates Nuclear Gene Expression in Macrophages Exposed to Prostaglandin E2

Metabolic engagement is intrinsic to immune cell function. Prostaglandin E2 (PGE2) has been shown to modulate macrophage activation, yet how PGE2 might affect metabolism is unclear. Here, we show that PGE2 caused mitochondrial membrane potential (Δψm) to dissipate in interleukin-4-activated (M(IL-4)) macrophages. Effects on Δψm were a consequence of PGE2-initiated transcriptional regulation of genes, particularly Got1, in the malate-aspartate shuttle (MAS). Reduced Δψm caused alterations in the expression of 126 voltage-regulated genes (VRGs), including those encoding resistin-like molecule α (RELMα), a key marker of M(IL-4) cells, and genes that regulate the cell cycle. The transcription factor ETS variant 1 (ETV1) played a role in the regulation of 38% of the VRGs. These results reveal ETV1 as a Δψm-sensitive transcription factor and Δψm as a mediator of mitochondrial-directed nuclear gene expression.

Roles and regulations of the ETS transcription factor ELF4/MEF

Most E26 transformation-specific (ETS) transcription factors are involved in the pathogenesis and progression of cancer. This is in part due to the roles of ETS transcription factors in basic biological processes such as growth, proliferation, and differentiation, and also because of their regulatory functions that have physiological relevance in tumorigenesis, immunity, and basal cellular homoeostasis. A member of the E74-like factor (ELF) subfamily of the ETS transcription factor family—myeloid elf-1-like factor (MEF), designated as ELF4—has been shown to be critically involved in immune response and signalling, osteogenesis, adipogenesis, cancer, and stem cell quiescence. ELF4 carries out these functions as a transcriptional activator or through interactions with its partner proteins. Mutations in ELF4 cause aberrant interactions and induce downstream processes that may lead to diseased cells. Knowing how ELF4 impinges on certain cellular processes and how it is regulated in the cells can lead to a better understanding of the physiological and pathological consequences of modulated ELF4 activity.

Chk1 Promotes DNA Damage Response Bypass following Oxidative Stress in a Model of Hydrogen Peroxide-Associated Ulcerative Colitis through JNK Inactivation and Chromatin Binding

Dysregulation of c-Jun N-terminal kinase (JNK) activation promoted DNA damage response bypass and tumorigenesis in our model of hydrogen peroxide-associated ulcerative colitis (UC) and in patients with quiescent UC (QUC), UC-related dysplasia, and UC-related carcinoma (UC-CRC), thereby adapting to oxidative stress. In the UC model, we have observed features of oncogenic transformation: increased proliferation, undetected DNA damage, and apoptosis resistance. Here, we show that Chk1 was downregulated but activated in the acute and quiescent chronic phases. In both phases, Chk1 was linked to DNA damage response bypass by suppressing JNK activation following oxidative stress, promoting cell cycle progression despite DNA damage. Simultaneously, activated Chk1 was bound to chromatin. This triggered histone acetylation and the binding of histone acetyltransferases and transcription factors to chromatin. Thus, chromatin-immobilized activated Chk1 executed a dual function by suppressing DNA damage response and simultaneously inducing chromatin modulation. This caused undetected DNA damage and increased cellular proliferation through failure to transmit the appropriate DNA damage signal. Findings in vitro were corroborated by chromatin accumulation of activated Chk1, Ac-H3, Ac-H4, and c-Jun in active UC (AUC) in vivo. Targeting chromatin-bound Chk1, GCN5, PCAF, and p300/CBP could be a novel therapeutic strategy to prevent UC-related tumor progression.

Phosphorylation of ETV4 at Ser73 by ERK kinase could block ETV4 ubiquitination degradation in colorectal cancer

It was reported that Src-mediated and RTK-dependent accumulation of key transcription factor, ETV4, which played an important role in the migration of embryonic cells and tumor cells, were regulated by their common downstream MAPK molecules. However, the detailed mechanism was not completely clear. In the present study, we revealed that ETV4 protein was significantly enhanced by ERK kinase activation in the colorectal cancer (CRC) patients and mouse models as well as in the CRC cell lines. It was further confirmed that the activation of ERK kinase led to the phosphorylation of ETV4 at Ser73 and the ETV4 phosphorylation could block its binding to COP1, thereby stabilized ETV4 via avoiding its ubiquitination degradation. In addition, this effect was not due to altering an E3 ubiquitin ligase, COP1 amount or p-COP1/COP1 ratio. Our results will help understand the mechanism of ETV4 overexpression in CRC patients and provide a clue to search new therapeutic target to treat the related tumors in clinical practice.

Prostate-derived ETS factor improves prognosis and represses proliferation and invasion in hepatocellular carcinoma

Prostate-derived E-twenty-six (ETS) factor (PDEF), an epithelium-specific ETS transcription factor, regulates carcinogenesis and tumor progression. The prognostic importance and biologic functions in hepatocellular carcinoma (HCC) have not been established. We investigated PDEF expression in 400 HCC patients using quantitative real-time polymerase chain reaction, western blot and immunohistochemistry analysis. PDEF expression was significantly lower in tumors than in peritumoral tissues. Lower PDEF levels were associated with poorer prognosis in patients. PDEF was an independent predictor of overall survival in multivariate analysis. PDEF expression was suppressed in highly metastatic HCC cell lines, and shRNA-mediated down-regulation of PDEF in low-metastatic HCC cell lines (with high PDEF) significantly increased cellular proliferative and invasive capacity in vitro and in vivo. RNA sequencing analysis indicated that PDEF may mediate transcription of several genes involved in apoptosis and the cell cycle. PDEF modulated epithelial-mesenchymal transition by up-regulating E-cadherin expression and down-regulating Slug and Vimentin expression, thereby lowering migration and invasion abilities of HCC cells. In conclusion, PDEF is associated with proliferation and invasiveness of HCC cells. It may serve as an independent predictor of prognosis in patients with HCC.

Distinct outcomes of CRL-Nedd8 pathway inhibition reveal cancer cell plasticity

Inhibition of protein degradation by blocking Cullin-RING E3 ligases (CRLs) is a new approach in cancer therapy though of unknown risk because CRL inhibition may stabilize both oncoproteins and tumor suppressors. Probing CRLs in prostate cancer cells revealed a remarkable plasticity of cells with TMPRSS2-ERG translocation. CRL suppression by chemical inhibition or knockdown of RING component RBX1 led to reversible G0/G1 cell cycle arrest that prevented cell apoptosis. Conversely, complete blocking of CRLs at a higher inhibitor dose-induced cytotoxicity that was amplified by knockdown of CRL regulator Cand1. We analyzed cell signaling to understand how varying degrees of CRL inhibition translated to distinct cell fates. Both tumor suppressor and oncogenic cell signaling pathways and transcriptional activities were affected, with pro-metastatic Wnt/β-catenin as the most upregulated. Suppression of the NF-κB pathway contributed to anti-apoptotic effect, and androgen receptor (AR) and ERG played decisive, though opposite, roles: AR was involved in protective quiescence, whereas ERG promoted apoptosis. These data define AR–ERG interaction as a key plasticity and survival determinant in prostate cancer and suggest supplementary treatments that may overcome drug resistance mechanisms regulated by AR–ERG interaction.

Nuclear Receptor Corepressor 1 Expression and Output Declines with Prostate Cancer Progression

PURPOSE

Castration therapy in advanced prostate cancer eventually fails and leads to the development of castration-resistant prostate cancer (CRPC), which has no cure. Characteristic features of CRPC can be increased androgen receptor (AR) expression and altered transcriptional output. We investigated the expression of nuclear receptor corepressor 1 (NCOR1) in human prostate and prostate cancer and the role of NCOR1 in response to antiandrogens.

EXPERIMENTAL DESIGN

NCOR1 protein levels were compared between matched normal prostate and prostate cancer in 409 patient samples. NCOR1 knockdown was used to investigate its effect on bicalutamide response in androgen-dependent prostate cancer cell lines and transcriptional changes associated with the loss of NCOR1. NCOR1 transcriptional signature was also examined in prostate cancer gene expression datasets.

RESULTS

NCOR1 protein was detected in cytoplasm and nuclei of secretory epithelial cells in normal prostate. Both cytoplasmic and nuclear NCOR1 protein levels were lower in prostate cancer than in normal prostate. Prostate cancer metastases show significant decrease in NCOR1 transcriptional output. Inhibition of LNCaP cellular proliferation by bicalutamide requires NCOR1. NCOR1-regulated genes suppress cellular proliferation and mediate bicalutamide resistance. In the mouse, NCOR1 is required for bicalutamide-dependent regulation of a subset of the AR target genes.

CONCLUSIONS

In summary, we demonstrated that NCOR1 function declines with prostate cancer progression. Reduction in NCOR1 levels causes bicalutamide resistance in LNCaP cells and compromises response to bicalutamide in mouse prostate in vivo Clin Cancer Res; 22(15); 3937-49. ©2016 AACR.

CHK1 and replicative stress in T-cell leukemia: Can an irreverent tumor suppressor end up playing the oncogene?

Replicative stress (RS) is a cell-intrinsic phenomenon enhanced by oncogenic transformation. Checkpoint kinase 1 (CHK1) is a key component of the ATR-dependent DNA damage response pathway that protects cells from RS by preventing replication fork collapse and activating homologous DNA repair. Taking this knowledge into account, one would predict CHK1 behaves strictly as a tumor suppressor. However, the reality seems far more complex. CHEK1 loss-of-function mutations have not been found in human tumors, and transgenic expression of Chek1 in mice promotes oncogene-induced transformation through RS inhibition. Moreover, CHK1 is overexpressed in various human cancers and CHK1 inhibitors have been developed as sensitizers to enhance the cytotoxicity of DNA damage-inducing chemotherapies. Here, we summarize the literature on the involvement of CHK1 in cancer progression, including our recent observation that CHK1 sustains T-cell acute lymphoblastic leukemia (T-ALL) cell viability. We also debate the importance of identifying patients that could benefit the most from treatment with CHK1 inhibitors, taking T-ALL as a model, and propose possible markers of therapeutic response.

Effective intra-S checkpoint responses to UVC in primary human melanocytes and melanoma cell lines

The objective of this study was to assess potential functional attenuation or inactivation of the intra-S checkpoint during melanoma development. Proliferating cultures of skin melanocytes, fibroblasts, and melanoma cell lines were exposed to increasing fluences of UVC and intra-S checkpoint responses were quantified. Melanocytes displayed stereotypic intra-S checkpoint responses to UVC qualitatively and quantitatively equivalent to those previously demonstrated in skin fibroblasts. In comparison with fibroblasts, primary melanocytes displayed reduced UVC-induced inhibition of DNA strand growth and enhanced degradation of p21Waf1 after UVC, suggestive of enhanced bypass of UVC-induced DNA photoproducts. All nine melanoma cell lines examined, including those with activating mutations in BRAF or NRAS oncogenes, also displayed proficiency in activation of the intra-S checkpoint in response to UVC irradiation. The results indicate that bypass of oncogene-induced senescence during melanoma development was not associated with inactivation of the intra-S checkpoint response to UVC-induced DNA replication stress.

The TMPRSS2-ERG Gene Fusion Blocks XRCC4-Mediated Nonhomologous End-Joining Repair and Radiosensitizes Prostate Cancer Cells to PARP Inhibition

Exposure to genotoxic agents, such as ionizing radiation (IR), produces DNA damage, leading to DNA double-strand breaks (DSB); IR toxicity is augmented when the DNA repair is impaired. We reported that radiosensitization by a PARP inhibitor (PARPi) was highly prominent in prostate cancer cells expressing the TMPRSS2-ERG gene fusion protein. Here, we show that TMPRSS2-ERG blocks nonhomologous end-joining (NHEJ) DNA repair by inhibiting DNA-PKcs. VCaP cells, which harbor TMPRSS2-ERG and PC3 cells that stably express it, displayed γH2AX and 53BP1 foci constitutively, indicating persistent DNA damage that was absent if TMPRSS2-ERG was depleted by siRNA in VCaP cells. The extent of DNA damage was enhanced and associated with TMPRSS2-ERG's ability to inhibit DNA-PKcs function, as indicated by its own phosphorylation (Thr2609, Ser2056) and that of its substrate, Ser1778-53BP1. DNA-PKcs deficiency caused by TMPRSS2-ERG destabilized critical NHEJ components on chromatin. Thus, XRCC4 was not recruited to chromatin, with retention of other NHEJ core factors being reduced. DNA-PKcs autophosphorylation was restored to the level of parental cells when TMPRSS2-ERG was depleted by siRNA. Following IR, TMPRSS2-ERG-expressing PC3 cells had elevated Rad51 foci and homologous recombination (HR) activity, indicating that HR compensated for defective NHEJ in these cells, hence addressing why TMPRSS2-ERG alone did not lead to radiosensitization. However, the presence of TMPRSS2-ERG, by inhibiting NHEJ DNA repair, enhanced PARPi-mediated radiosensitization. IR in combination with PARPi resulted in enhanced DNA damage in TMPRSS2-ERG-expressing cells. Therefore, by inhibiting NHEJ, TMPRSS2-ERG provides a synthetic lethal interaction with PARPi in prostate cancer patients expressing TMPRSS2-ERG.