Ishtiaq Rehman

iTRAQ underestimation in simple and complex mixtures: "the good, the bad and the ugly".

The increasing popularity of iTRAQ for quantitative proteomics applications makes it necessary to evaluate its relevance, accuracy, and precision for biological interpretation. Here, we have assessed (a) the accuracy and precision of iTRAQ quantification in a controlled experimental setup, using low- and high-complexity protein mixtures; and (b) the potential pitfalls that hamper the applicability and attainable dynamic range of iTRAQ: isotopic contamination, background interference, and signal-to-noise ratio. Our data suggest greater dynamic crosstalk between interfering factors affecting underestimations, and that these interferences were largely scenario-specific, dependent on sample complexity. The good is the potential for iTRAQ to provide accurate quantification spanning 2 orders of magnitude. This potential is however limited by two factors. (1) The bad: the existence of isotopic impurities that can be corrected for; provided accurate isotopic factors are at ones disposal. (2) The ugly: we demonstrate here the interference of mixed MS/MS contribution occurring during precursor selection, an issue that is currently very difficult to minimize. In light of our results, we propose a list of advice for iTRAQ data analysis that could routinely ameliorate quantitative interpretation of proteomic data sets.

Promoter hypermethylation is associated with tumor location, stage, and subsequent progression in transitional cell carcinoma.

PURPOSE Transitional cell carcinoma (TCC) is a pan-urothelial disease characterized by multiplicity. Although little is known about the molecular events in upper-tract TCC, similar carcinogenic mechanisms are thought to occur throughout the urinary tract. However, we have previously shown that distinct patterns of microsatellite instability occur in upper and lower urinary tract TCC, suggesting biologic differences between these tumors. Here we investigate the extent of promoter hypermethylation in TCC throughout the urinary tract. PATIENTS AND METHODS Tissue was obtained from 280 patients (median follow-up, 56 months) whose tumors comprised 116 bladder and 164 upper-tract tumors (UTT). Analysis for hypermethylation at 11 CpG islands, using methylation-sensitive polymerase chain reaction and bisulfite sequencing, was performed for each sample and compared with the tumors clinicopathologic details, microsatellite instability status, and subsequent behavior. RESULTS Promoter methylation was present in 86% of TCC and occurred both more frequently and more extensively in UTT (94%) than in bladder tumors (76%; P < .0001). Methylation was associated with advanced tumor stage (P = .0001) and higher tumor progression (P = .03) and mortality rates (P = .04), when compared with tumors without methylation. Multivariate analysis revealed that methylation at the RASSF1A and DAPK loci, in addition to tumor stage and grade, were associated with disease progression (P < .04). CONCLUSION Despite morphologic similarities, there are genetic and epigenetic differences between TCC in the upper and lower urinary tracts. Methylation occurs commonly in urinary tract tumors, may affect carcinogenic mechanisms, and is a prognostic marker and a potential therapeutic target.

Distinct MicroRNA Alterations Characterize High- and Low-Grade Bladder Cancer

Urothelial carcinoma of the bladder (UCC) is a common disease that arises by at least two different molecular pathways. The biology of UCC is incompletely understood, making the management of this disease difficult. Recent evidence implicates a regulatory role for microRNA in cancer. We hypothesized that altered microRNA expression contributes to UCC carcinogenesis. To test this hypothesis, we examined the expression of 322 microRNAs and their processing machinery in 78 normal and malignant urothelial samples using real-time rtPCR. Genes targeted by differentially expressed microRNA were investigated using real-time quantification and microRNA knockdown. We also examined the role of aberrant DNA hypermethylation in microRNA downregulation. We found that altered microRNA expression is common in UCC and occurs early in tumorogenesis. In normal urothelium from patients with UCC, 11% of microRNAs had altered expression when compared with disease-free controls. This was associated with upregulation of Dicer, Drosha, and Exportin 5. In UCC, microRNA alterations occur in a tumor phenotype-specific manner and can predict disease progression. High-grade UCC were characterized by microRNA upregulation, including microRNA-21 that suppresses p53 function. In low-grade UCC, there was downregulation of many microRNA molecules. In particular, loss of microRNAs-99a/100 leads to upregulation of FGFR3 before its mutation. Promoter hypermethylation is partly responsible for microRNA downregulation. In conclusion, distinct microRNA alterations characterize UCC and target genes in a pathway-specific manner. These data reveal new insights into the disease biology and have implications regarding tumor diagnosis, prognosis and therapy.

Expression of S100 proteins in normal human tissues and common cancers using tissue microarrays: S100A6, S100A8, S100A9 and S100A11 are all overexpressed in common cancers

Aims : To survey the expression of members of the S100 family of calcium‐binding proteins in normal human tissues and common cancers using tissue microarrays. S100A6, S100A8, S100A9 and S100A11 have all been suggested to have potential roles in carcinogenesis and tumour progression but their expression has not been described in a wide range of human tissues and tumours.

Promoter hypermethylation identifies progression risk in bladder cancer.

Purpose: New methods to accurately predict an individual tumor behavior are urgently required to improve the treatment of cancer. We previously found that promoter hypermethylation can be an accurate predictor of bladder cancer progression, but it is not cancer specific. Here, we investigate a panel of methylated loci in a prospectively collected cohort of bladder tumors to determine whether hypermethylation has a useful role in the management of patients with bladder cancer. Experimental Design: Quantitative methylation-specific PCR was done at 17 gene promoters, suspected to be associated with tumor progression, in 96 malignant and 30 normal urothelial samples. Statistical analysis and artificial intelligence techniques were used to interrogate the results. Results: Using log-rank analysis, five loci were associated with progression to more advanced disease (RASSF1a, E-cadherin, TNFSR25, EDNRB, and APC; P < 0.05). Multivariate analysis revealed that the overall degree of methylation was more significantly associated with subsequent progression and death (Cox, P = 0.002) than tumor stage (Cox, P = 0.008). Neuro-fuzzy modeling confirmed that these five loci were those most associated with tumor progression. Epigenetic predictive models developed using artificial intelligence techniques identified the presence and timing of tumor progression with 97% specificity and 75% sensitivity. Conclusion: Promoter hypermethylation seems a reliable predictor of tumor progression in bladder cancer. It is associated with aggressive tumors and could be used to identify patients with either superficial disease requiring radical treatment or a low progression risk suitable for less intensive surveillance. Multicenter studies are warranted to validate this marker.

Molecular Detection of Localized Prostate Cancer Using Quantitative Methylation-Specific PCR on Urinary Cells Obtained Following Prostate Massage

Purpose: The diagnosis of localized prostate cancer is difficult due to a lack of cancer-specific biomarkers. Many patients require repeat prostate biopsies to diagnose the disease. We investigated whether aberrant promoter hypermethylation in prostatic fluid could reliably detect prostate cancer. Experimental Design: Urine samples were collected after prostate massage from 95 patients with localized prostate cancer undergoing radical prostatectomy (63 pT1, 31 pT2, and 1 pT3) and from 38 control patients. Ten genes (GSTP1, RASSF1a, ECDH1, APC, DAPK, MGMT, p14, p16, RARβ2, and TIMP3) were investigated using quantitative real-time methylation-specific PCR. Receiver operator curves were generated. Results: The frequency of gene methylation ranged from 6.3% (p14) to 83.2% (GSTP1) in prostate cancer patients. At least one gene was hypermethylated in 93% of cancer patients. The specificity of methylation was 0.74. Methylation was significantly more frequent (P < 0.05) in cancer than control patients for all genes except p14 and p16. According to receiver operator curve analysis, the four-gene combination of GSTP1 (0.86), RASSF1a (0.85), RARβ2 (0.80), and APC (0.74) best discriminated malignant from nonmalignant cases. The sensitivity and accuracy of this four-gene set were 86% and 89%, respectively. Conclusions: The presence of aberrant methylation in urinary cells obtained after prostate massage is significantly associated with prostate cancer. A panel of four genes could stratify patients into low and high risk of having prostate cancer and optimize the need for repeat prostatic biopsies.

Distinct patterns of microsatellite instability are seen in tumours of the urinary tract.

To date, two forms of microsatellite instability (MSI) have been described in human cancer. MSI typical of hereditary nonpolyposis colon cancer (HNPCC), is due to deficient DNA mismatch repair (MMR) and is defined with mono- and dinucleotide repeat microsatellites. A second variety of instability is best seen at selective tetranucleotide repeats (EMAST; elevated microsatellite alterations at select tetranucleotides). While MSI occurs infrequently in bladder cancers, EMAST is common. Sporadic tumours with the largest proportion showing MSI are those found most frequently in HNPCC kindreds. While bladder cancer is not frequently seen in HNPCC, upper urinary tract tumours (UTTs) are. Having previously found a low frequency of MSI in bladder cancer, we sought to determine the relative levels of MSI and EMAST in transitional cell carcinoma (TCC) of the upper and lower urinary tracts. Microsatellite analysis was performed at 10 mono- and dinucleotide and eight tetranucleotide loci, in 89 bladder and 71 UTT TCC. Contrasting patterns of instability were seen in urinary tumours. In bladder cancer, MSI was rare and EMAST was common. The presence of EMAST was not related to tumour grade, stage, subsequent outcome or immunohistochemical expression of the MMR proteins. In UTT, while MSI occurred frequently, EMAST was seen less frequently than in bladder cancer. When TCC of the upper and lower urinary tracts are compared, MSI-H is more frequent in UTT and EMAST more frequent in bladder cancer. Our findings show that, as for colorectal cancer, the pattern of MSI varies with location in the urinary tract. In addition, we have confirmed that MSI and EMAST are discrete forms of MSI, and that the presence of EMAST does not affect tumour phenotype.

iTRAQ-facilitated proteomic analysis of human prostate cancer cells identifies proteins associated with progression.

The unpredictable behavior of prostate cancer presents a major clinical challenge during patient management. In order to gain an insight into the molecular mechanisms associated with prostate cancer progression, we employed the shot-gun proteomic approach of isobaric tags for relative and absolute quantitation (iTRAQ), followed by 2D-LC-MS/MS, using the poorly metastatic LNCaP cell line and its highly metastatic variant LNCaP-LN3 cell line as a model. A total number of 280 unique proteins were identified (> or =95% confidence), and relative expression data was obtained for 176 of these. Ten proteins were found to be significantly up-regulated (> or =1.50 fold), while 4 proteins were significantly down-regulated (> or = -1.50 fold), in LNCaP-LN3 cells. Differential expression of brain creatine kinase (CKBB), soluble catechol-O-methyltransferase (S-COMT), tumor rejection antigen (gp96), and glucose regulated protein, 78 kDa (grp78), was confirmed by Western blotting or independent 2D-PAGE analysis. Additionally, iTRAQ analysis identified absence of the lactate dehydrogenase-B (LDH-B) subunit in LNCaP-LN3 cells, confirming our published data. The clinical relevance of gp96 was assessed by immunohistochemistry using prostate tissues from benign ( n = 95), malignant ( n = 66), and metastatic cases ( n = 3). Benign epithelium showed absent/weak gp96 expression in the basal cells, in contrast to the moderate/strong expression seen in malignant epithelium. Furthermore, there was a statistically significant difference in the intensity of gp96 expression between benign and malignant cases ( p < 0.0005, Mann-Whitney U). Our study is the first to report the application of iTRAQ technology and its potential for the global proteomic profiling of prostate cancer cells, including the identification of absent protein expression.

FGFR3 Mutations Indicate Better Survival in Invasive Upper Urinary Tract and Bladder Tumours

BACKGROUND Promoter hypermethylation and microsatellite instability are frequent in tumours of the upper urinary tract (UTT) and infrequent in bladder tumours. FGFR3 mutations are common findings in bladder tumours and are associated with a good prognosis. OBJECTIVE To investigate the occurrence of FGFR3 mutations in UTT and determine the prognostic effect of these genetic changes. DESIGN, SETTING, AND PARTICIPANTS Tissue from the initial tumour was obtained from 280 patients (117 bladder tumours and 163 UTT). Patients were selected from pathologic archives to represent the disease spectrum of UCC throughout the urinary tract. Following UCC excision, patients underwent surveillance for a median of 56 mo (range 1-216 mo) or until death. MEASUREMENTS FGFR3 mutation analysis was successfully performed on 252 of the 280 primary tumours using the SNaPshot method. Two-tailed statistical analyses were done using the chi(2), Fisher exact tests, and log rank tests. Cox proportional hazard ratios were estimated to obtain risks of recurrence, progression, and death, and to find independent prognostic factors in a multivariate model. RESULTS AND LIMITATIONS FGFR3 mutations occurred with the same frequency in bladder and upper tract tumours. Mutations were associated with low-stage tumours and a milder disease course in bladder, ureter, and renal pelvis tumours. Strikingly, our data suggest that these mutations indicate a better survival in patients with invasive tumours from the bladder and upper urinary tract. CONCLUSIONS FGFR3 mutation status might be used to select patients with invasive UCC who have a lower risk of death.

Methylational urinalysis: a prospective study of bladder cancer patients and age stratified benign controls.

Tumour suppressor gene (TSG) methylation has been proposed as a diagnostic marker for urothelial cancer (UC). Here, we compare the frequency of urinary TSG methylation in young and elderly patients, with and without UC. Urine samples were obtained prospectively from 35 UC patients, 35 benign controls over the age of 70 years and 34 healthy volunteers under the age of 40 years. Methylation analysis was performed for eight gene promoters using quantitative methylation-specific PCR. Methylation was detected in urine DNA from all three patient groups. The highest frequencies were seen in UC patients. Significantly less methylation was present in control samples than UC cases for RASSF1a and APC (P<0.034). The ‘methylation index’ and level of methylation was highest in the UC group and lowest in the young control group. A marker panel of RASSF1a, E-cad and APC generated a sensitivity of 69%, a specificity of 60% and a diagnostic accuracy of 86%. TSG methylation is detectable in urine DNA from patients with and without bladder cancer. The frequency and extent of methylation appears to increase with age and malignancy. The lack of tumour specificity suggests that further investigation is required before this test is introduced into clinical practice.