Expression of death-associated protein kinase during tumour progression of human renal cell carcinomas: Hypermethylation-independent mechanisms of inactivation

The Role of Death-Associated Protein Kinase-1 in Cell Homeostasis-Related Processes

Tremendous amount of financial resources and manpower have been invested to understand the function of numerous genes that are deregulated during the carcinogenesis process, which can be targeted for anticancer therapeutic interventions. Death-associated protein kinase 1 (DAPK-1) is one of the genes that have shown potential as biomarkers for cancer treatment. It is a member of the kinase family, which also includes Death-associated protein kinase 2 (DAPK-2), Death-associated protein kinase 3 (DAPK-3), Death-associated protein kinase-related apoptosis-inducing kinase 1 (DRAK-1) and Death-associated protein kinase-related apoptosis-inducing kinase 2 (DRAK-2). DAPK-1 is a tumour-suppressor gene that is hypermethylated in most human cancers. Additionally, DAPK-1 regulates a number of cellular processes, including apoptosis, autophagy and the cell cycle. The molecular basis by which DAPK-1 induces these cell homeostasis-related processes for cancer prevention is less understood; hence, they need to be investigated. The purpose of this review is to discuss the current understanding of the mechanisms of DAPK-1 in cell homeostasis-related processes, especially apoptosis, autophagy and the cell cycle. It also explores how the expression of DAPK-1 affects carcinogenesis. Since deregulation of DAPK-1 is implicated in the pathogenesis of cancer, altering DAPK-1 expression or activity may be a promising therapeutic strategy against cancer.

Inhibition of miR-34a-5p can rescue disruption of the p53-DAPK axis to suppress progression of clear cell renal cell carcinoma

DAPK, a transcriptional target of the p53 protein, has long been characterized as a tumor suppressor that acts as a negative regulator in multiple cellular processes. However, increasing studies have suggested that the role of DAPK may vary depending on cell type and cellular context. Thus far, the expression and function of DAPK in clear cell renal cell carcinoma (ccRCC) remain ambiguous. Since ccRCC behaves in an atypical way with respect to p53, whether the p53‐DAPK axis functions normally in ccRCC is also an intriguing question. Here, tissue specimens from 61 ccRCC patients were examined for DAPK expression. Functional studies regarding apoptosis, growth, and migration were used to determine the role of DAPK in renal cancer cells. The validity of the p53‐DAPK axis in ccRCC was also determined. Our study identified DAPK as a negative regulator of ccRCC, and its expression was reduced in certain subgroups. However, the p53‐DAPK axis was disrupted due to upregulation of miR‐34a‐5p under stressed conditions. miR‐34a‐5p was identified as a novel repressor of DAPK acting downstream of p53. Inhibition of miR‐34a‐5p can correct the p53‐DAPK axis disruption by upregulating DAPK protein and may have potential to be used as a therapeutic target to improve outcomes for ccRCC patients.

CYP1B1 promotes tumorigenesis via altered expression of CDC20 and DAPK1 genes in renal cell carcinoma

BACKGROUND

Cytochrome P450 1B1 (CYP1B1) has been shown to be up-regulated in many types of cancer including renal cell carcinoma (RCC). Several reports have shown that CYP1B1 can influence the regulation of tumor development; however, its role in RCC has not been well investigated. The aim of the present study was to determine the functional effects of CYP1B1 gene on tumorigenesis in RCC.

METHODS

Expression of CYP1B1 was determined in RCC cell lines, and tissue microarrays of 96 RCC and 25 normal tissues. To determine the biological significance of CYP1B1 in RCC progression, we silenced the gene in Caki-1 and 769-P cells by RNA interference and performed various functional analyses.

RESULTS

First, we confirmed that CYP1B1 protein expression was significantly higher in RCC cell lines compared to normal kidney tissue. This trend was also observed in RCC samples (p < 0.01). Interestingly, CYP1B1 expression was associated with tumor grade and stage. Next, we silenced the gene in Caki-1 and 769-P cells by RNA interference and performed various functional analyses to determine the biological significance of CYP1B1 in RCC progression. Inhibition of CYP1B1 expression resulted in decreased cell proliferation, migration and invasion of RCC cells. In addition, reduction of CYP1B1 induced cellular apoptosis in Caki-1. We also found that these anti-tumor effects on RCC cells caused by CYP1B1 depletion may be due to alteration of CDC20 and DAPK1 expression based on gene microarray and confirmed by real-time PCR. Interestingly, CYP1B1 expression was associated with CDC20 and DAPK1 expression in clinical samples.

CONCLUSIONS

CYP1B1 may promote RCC development by inducing CDC20 expression and inhibiting apoptosis through the down-regulation of DAPK1. Our results demonstrate that CYP1B1 can be a potential tumor biomarker and a target for anticancer therapy in RCC.

Epigenetics of kidney cancer and bladder cancer

This article focuses on the epigenetic alterations of aberrant promoter hypermethylation of genes, and histone modifications or RNA interference in cancer cells. Current knowledge of the hypermethylation of allele(s) in classical tumor suppressor genes in inherited and sporadic cancer, candidate tumor suppressor and other cancer genes is summarized gene by gene. Global and array-based studies of tumor cell hypermethylation are discussed. The importance of standardization of scoring of the methylation status of a gene is highlighted. The histone marks associated with hypermethylated genes, and the miRNAs with dysregulated expression, in kidney or bladder tumor cells are also discussed. Kidney cancer has the highest mortality rate of the genito-urinary cancers. There are management issues associated with the high recurrence rate of superficial bladder cancer, while muscle-invasive bladder cancer has a poor prognosis. These clinical problems are the basis for the translational application of gene hypermethylation in the diagnosis and prognosis of kidney and bladder cancer.

Latent membrane protein 1 of Epstein-Barr virus regulates death-associated protein kinase 1 in lymphoblastoid cell line

The Epstein-Barr virus (EBV) infects and transforms primary B cells into lymphoblastoid cell lines (LCLs). We observed death-associated protein kinase 1 (DAPK1) upregulation in B cells following EBV infection and high DAPK1 levels in LCLs. DAPK1 participates in several apoptosis-inducing pathways, yet DAPK1 expression increased during B cell transformation. Data from LMP1 overexpression in LCLs and HeLa cells and from knocked down LMP1 in LCLs suggest LMP1 regulation of DAPK1 expression. We observed NF-κB signaling in DAPK1 upregulation by LMP1 with CTAR deletion mutants failing to induce DAPK1 expression and with Bay11 blocking DAPK1 expression. DAPK1 is inactive in LCLs due to insufficient stimuli, and is not regulated by Ser308 phosphorylation. However, DAPK1 in LCLs is functional, as evidenced by its quick mediation of cell death following UV or H(2)O(2) exposure, and increased survival among LCLs knocked down with DAPK. DAPK roles in EBV-infected B cells remain to be identified.

Death-associated protein kinase (DAPK) and signal transduction: regulation in cancer

Death-associated protein kinase (DAPK) is a pro-apoptotic serine/threonine protein kinase that is dysregulated in a wide variety of cancers. The mechanism by which this occurs has largely been attributed to promoter hypermethylation, which results in gene silencing. However, recent studies indicate that DAPK expression can be detected in some cancers, but its function is still repressed, suggesting that DAPK activity can be subverted at a post-translational level in cancer cells. This review will focus on recent data describing potential mechanisms that may alter the expression, regulation or function of DAPK.

Promoter hypermethylation profile of kidney cancer with new proapoptotic p53 target genes and clinical implications

PURPOSE

Risk stratification of renal cell carcinoma is based on the histopathologic classification. Promoter hypermethylation as a mechanism of gene inactivation in renal cell carcinoma has been shown for only a small number of genes. We examined the usefulness of quantitative methylation analysis with a new set of p53 target genes for determining the clinical outcome and aggressiveness of the tumor disease.

EXPERIMENTAL DESIGN

The genes selected were APAF-1, CASPASE-8, DAPK-1, IGFBP-3, and PML. The tissue samples analyzed were taken from tumor specimens obtained from 90 consecutive patients with clear cell renal carcinoma and from 20 normal kidney specimens. Quantitative methylation analysis of CpG sites in the promoter region was done by methylation-specific real-time PCR and the normalized index of methylation (NIM) was determined for each sample.

RESULTS

Hypermethylation of the promoter region was common for APAF-1 (97%) and DAPK-1 (41%) but not for IGFBP-3 (3%), PML (3%), or CASP-8 (0%). The tumor patients had a median follow-up of 55 months. A correlation was found between the methylation level of APAF-1 and tumor size and nodal status, but not for tumor stage, grade, and age of patient. Kaplan-Meier analysis was able to identify patients with a higher risk of recurrence and tumor-related death by using APAF-1 (>or=56% NIM) and DAPK-1 (>or=10% NIM) methylation levels. In multivariate analysis, APAF-1 and DAPK-1 methylation levels were independent prognostic markers for metastatic disease and death from renal cell carcinoma.

CONCLUSIONS

Our findings indicate that promoter hypermethylation of APAF-1 and DAPK-1 is a marker of aggressive renal cell carcinoma and provides independent prognostic information on disease outcome.

EZH2 polycomb transcriptional repressor expression correlates with methylation of the APAF-1 gene in superficial transitional cell carcinoma of the bladder

The EZH2 gene controls methylation of various EZH2 target promoters. The APAF-1, DAPK-1 und IGFBP-3 genes are frequently methylated in bladder cancer, and methylation of these genes is found in more aggressive tumor types. The aim of our study was to investigate a potential link between EZH2 mRNA expression and the extent of APAF-1, DAPK-1 and IGFBP-3 methylation in urothelial transitional cell carcinoma (TCC) and to correlate the data with histopathological parameters and follow-up data. EZH2 mRNA expression was measured by real-time reverse transcription polymerase chain reaction, and the methylation analysis was performed using methylation-specific real-time polymerase chain reaction. Tissue specimens were obtained from 35 patients with TCC. EZH2 mRNA expression was detected in all tumor specimens investigated. The EZH2 expression levels correlated well with the differentiation grade of the tumor specimens (p = 0.03), and the APAF-1 methylation correlated with tumor stage (p = 0.0001) and grade (p = 0.004). Matched pair analysis demonstrated a statistically significant correlation between elevated EZH2 mRNA expression and higher methylation levels of APAF-1 in superficial (p = 0.024) and well- differentiated (p = 0.04) TCC. In patients with recurrent TCC, APAF-1 and IGFBP-3 methylation levels were significantly higher (p = 0.03 and p = 0.01, respectively), which was not observed when EZH2 mRNA expression or DAPK-1 methylation levels were related to the clinical outcome. In conclusion, our data show that EZH2 expression and APAF-1 methylation are related to tumor progression and invasiveness. Moreover, these data present first evidence that APAF-1 methylation is related to transcriptional activity of EZH2 expression in early-stage tumor disease of the bladder.

A Germ Line Mutation in the Death Domain of DAPK-1 Inactivates ERK-induced Apoptosis

p53 is activated genetically by a set of kinases that are components of the calcium calmodulin kinase superfamily, including CHK2, AMP kinase, and DAPK-1. In dissecting the mechanism of DAPK-1 control, a novel mutation (N1347S) was identified in the death domain of DAPK-1. The N1347S mutation prevented the death domain module binding stably to ERK in vitro and in vivo. Gel filtration demonstrated that the N1347S mutation disrupted the higher order oligomeric nature of the purified recombinant death domain miniprotein. Accordingly, the N1347S death domain module is defective in vivo in the formation of high molecular weight oligomeric intermediates after cross-linking with ethylene glycol bis(succinimidylsuccinate). Full-length DAPK-1 protein harboring a N1347S mutation in the death domain was also defective in binding to ERK in cells and was defective in formation of an ethylene glycol bis(succinimidylsuccinate)-cross-linked intermediate in vivo. Full-length DAPK-1 encoding the N1347S mutation was attenuated in tumor necrosis factor receptor-induced apoptosis. However, the N1347S mutation strikingly prevented ERK:DAPK-1-dependent apoptosis as defined by poly(ADP-ribose) polymerase cleavage, Annexin V staining, and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling imaging. Significant penetrance of the N1347S allele was identified in normal genomic DNA indicating the mutation is germ line, not tumor derived. The frequency observed in genomic DNA was from 37 to 45% for homozygous wild-type, 41 to 47% for heterozygotes, and 12 to 15% for homozygous mutant. These data highlight a naturally occurring DAPK-1 mutation that alters the oligomeric structure of the death domain, de-stabilizes DAPK-1 binding to ERK, and prevents ERK:DAPK-1-dependent apoptosis.

Identification of a dominant negative functional domain on DAPK-1 that degrades DAPK-1 protein and stimulates TNFR-1-mediated apoptosis

DAPK-1 is a stress-activated tumor suppressor protein that plays a role in both proapoptotic or antiapoptotic signal transduction pathways. To define mechanisms of DAPK-1 protein regulation, we have determined that DAPK-1 protein has a long half-life, and therefore its activity is primarily regulated at the protein level. Changes in DAPK-1 protein levels occur by a cathepsin B-dependent pathway, prompting us to evaluate whether cathepsin B plays positive or negative role in DAPK-1 function. The transfection of p55-TNFR-1 induced complex formation between DAPK-1 and cathepsin B. Depletion of cathepsin B protein using small interfering RNA stimulated TNFR-1 dependent apoptosis. The minimal binding region on DAPK-1 for cathepsin B was mapped to amino acids 836-947. The transfection of the DAPK-1-(836-947) miniprotein acted in a dominant negative manner inducing endogenous DAPK-1 protein degradation in a TNFR-1-dependent manner. These data suggest that DAPK-1 forms a multiprotein survival complex with cathepsin B countering the rate of TNFR-1-dependent apoptosis and highlights the importance of developing DAPK-1 inhibitors as agents to sensitize cells to stress-induced apoptosis.

A gene expression profile of tumor suppressor genes commonly methylated in bladder cancer

PURPOSE

The functional relationship between promoter hypermethylation and gene inactivation has been demonstrated for few genes only. We examined the promoter methylation status of two important tumor suppressor genes APAF-1 and DAPK-1 in bladder cancer as well as the mRNA expression pattern of these two genes for possible correlation between promoter hypermethylation and transcriptional repression.

METHODS

The methylation status and mRNA expression levels were related to clinicopathological features in 34 patients with transitional cell carcinoma (TCC) of the bladder with a median clinical follow-up of more than 45 months. Tissue from ten patients with nonmalignant disease served as a control group. Quantitative real-time PCR-based detection methods were used for determination of the normalized index of methylation (NIM) as well as the mRNA expression level.

RESULTS

APAF-1 and DAPK-1 methylation and mRNA expression was observed in all tumor and normal control samples investigated. Methylation (NIM) levels were significantly higher in tumor tissue for APAF-1 and DAPK-1, but median mRNA expression levels did not differ significantly comparing tumorous and non tumorous tissue. No correlation between expression levels of APAF-1 and DAPK-1 mRNA and tumor stage or grade was observed. However, in superficial TCC a strong correlation between higher NIM levels and lower mRNA expression of the APAF-1 gene was observed (P = 0.014).

CONCLUSIONS

Our results, although preliminary, provide first time in vivo expression analysis of the APAF-1 gene in bladder cancer specimen, suggesting expression control by promoter methylation in early stage tumor disease of the bladder.

Methylation of tumour suppressor genes APAF-1 and DAPK-1 and in vitro effects of demethylating agents in bladder and kidney cancer

To examine the significance of the methylation level of the p53 target and tumour suppressor genes apoptotic protease activating factor-1 (APAF-1) and death-associated protein kinase-1 (DAPK-1) in 80 microdissected tumour samples from transitional cell carcinoma (TCC) of the bladder and 80 tumour samples from clear-cell renal cell carcinoma (RCC) as well as from non-tumourous bladder and kidney tissue. Growth-inhibitory effects of the demethylating agents 5-Aza-2′-deoxycytidine (5-Aza-CdR) and zebularine were investigated in TCC and RCC cell lines. The methylation frequency of APAF-1 (DAPK-1) was 100% (77%) in TCC and 100% (33%) in RCC. The methylation levels of APAF-1 could differentiate between the individual tumour stages in TCC as well as in RCC. The APAF-1 methylation levels in RCC were significantly higher in tumours larger than 4 cm and in high-grade tumours. The methylation frequencies in normal tissue for APAF-1 (DAPK-1) were 11% (8%) in bladder tissue and 9% (5%) in kidney tissue. The growth-inhibitory effect of the demethylating agents in TCC (RT4, T24) and RCC (A498, ClearCa-5) cell lines resulted in a 17–132% prolongation of the doubling time (DT). In RCC cell lines, zebularine was superior to 5-Aza-CdR in achieving a DT prolongation. Quantitative real time RT-PCR detected a re-expression of mRNA transcripts of APAF-1 or DAPK-1. In conclusion, demethylating agents effectively retard growth of TCC and RCC cell lines. Methylation level analysis of specific genes has the potential for further tumour characterisation in TCC and RCC.