p53 mutations in human bladder cancer

Competition between p53 and YY1 determines PHGDH expression and malignancy in bladder cancer

PURPOSE

Serine metabolism is frequently dysregulated in many types of cancers and the tumor suppressor p53 is recently emerging as a key regulator of serine metabolism. However, the detailed mechanism remains unknown. Here, we investigate the role and underlying mechanisms of how p53 regulates the serine synthesis pathway (SSP) in bladder cancer (BLCA).

METHODS

Two BLCA cell lines RT-4 (WT p53) and RT-112 (p53 R248Q) were manipulated by applying CRISPR/Cas9 to examine metabolic differences under WT and mutant p53 status. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) and non-targeted metabolomics analysis were adopted to identify metabolomes changes between WT and p53 mutant BLCA cells. Bioinformatics analysis using the cancer genome atlas and Gene Expression Omnibus datasets and immunohistochemistry (IHC) staining was used to investigate PHGDH expression. Loss-of-function of PHGDH and subcutaneous xenograft model was adopted to investigate the function of PHGDH in mice BLCA. Chromatin immunoprecipitation (Ch-IP) assay was performed to analyze the relationships between YY1, p53, SIRT1 and PHGDH expression.

RESULTS

SSP is one of the most prominent dysregulated metabolic pathways by comparing the metabolomes changes between wild-type (WT) p53 and mutant p53 of BLCA cells. TP53 gene mutation shows a positive correlation with PHGDH expression in TCGA-BLCA database. PHGDH depletion disturbs the reactive oxygen species homeostasis and attenuates the xenograft growth in the mouse model. Further, we demonstrate WT p53 inhibits PHGDH expression by recruiting SIRT1 to the PHGDH promoter. Interestingly, the DNA binding motifs of YY1 and p53 in the PHGDH promoter are partially overlapped which causes competition between the two transcription factors. This competitive regulation of PHGDH is functionally linked to the xenograft growth in mice.

CONCLUSION

YY1 drives PHGDH expression in the context of mutant p53 and promotes bladder tumorigenesis, which preliminarily explains the relationship between high-frequency mutations of p53 and dysfunctional serine metabolism in bladder cancer.

Influence of GSTM1, GSTT1, GSTP1 and NAT2 genotypes on the p53 mutational spectrum in bladder tumours

Genetic polymorphisms affecting expression or activity of the corresponding enzymes can influence the risk of acquiring gene mutations and various cancers. We have studied 327 bladder cancer patients with regard to the functionally related polymorphisms of GSTM1, GSTT1, GSTP1 and NAT2 and analysed the p53 mutational status of their tumours. Fifty p53 mutations, 26% transversions and 74% transitions, were detected in 44 patients. P53 mutation frequency was significantly higher in higher-grade tumours than in low-grade tumours (OR = 2.09, 95% CI 1.44-3.02, adjusted for age and sex). Also, a significant association was found between tumour stage (Tis and T2+ vs. Ta and T1) and presence of the GSTP1 val allele (adjusted OR = 2.00, CI 1.14-3.52). Overall, there was no significant difference in frequency of p53 mutation among patients with different genotypes. Among patients with p53 mutation, transversions were significantly more frequent in GSTM1-negative as compared to GSTM1-positive individuals (OR = 5.18, CI 1.07-25.02, adjusted for age, sex and tumour stage). With one exception, all tumours with the most common type of transversion, G:C-C:G, occurred in GSTM1-negative patients. Among smokers, all transversions (3 of 3), but only 2 of 13 transitions, were found among carriers of the GSTP1 variant allele, and samples carrying at least 1 variant GSTP1 allele had more transitions at CpG sites than wild-type samples (adjusted OR = 4.61, CI 0.82-26.04). No significant associations were found for the NAT2 gene. Our results suggest that impaired glutathione conjugation may affect the mutation spectrum in critical target genes.

Mutations in the p53 gene in acute myeloid leukemia patients correlate with poor prognosis

Inactivation of tumor suppressor genes, whose products exert an inhibitory influence on cell cycle progression, can lead to neoplastic transformation. In acute myeloid leukemia (AML), the frequency of p53 gene mutations ranges from 4 to 15% in populations from USA and Europe. In an attempt to investigate the frequency of point mutations in the p53 gene in AML Brazilian patients, DNA samples of 35 patients were studied using PCR-SSCP techniques, screening exons 4-10. Mutations were identified in bone marrow DNA in 5 of the 35 AML patients (14.3%), a frequency similar to those reported for Northern American and European populations. The overall survival of patients with mutations in the p53 gene was significantly shorter than for patients without mutations.

p53 mutations in hairy cell leukemia

We have studied the frequency of p53 mutations in genomic DNA extracted from peripheral blood or the spleen of 61 patients with hairy cell leukemia using PCR-SSCP and automated cycle sequencing. We identified exon 5-8 mutations in 17 cases, corresponding to a frequency of 28%. In four cases, mutations were localized in exon 5; one patient with atypical HCL had a mutation in exon 6 at the 3' boundary; five cases showed mutations in exon 7, while exon 8 was found to be mutated in seven cases. The mutations found could be divided into three major categories: structural (n=9), inactivating (n= 6), and neutral (n= 2) mutations. None of the three transitions found occurred at CpG dinucleotides. The rate of p53 mutations found in this large cohort of HCL patients is unexpectedly high as in other non-Hodgkin lymphomas p53 mutations predict for poor treatment outcome. The character of the mutations we have found is entirely different from that described in other hematologic malignancies.

Mutation of cell cycle regulators and their impact on superficial bladder cancer

Early cytogenetic studies in bladder cancer identify regions of chromosomal gain or loss that can be candidate loci for oncogenes and tumor suppressor genes. Oncogenes with potential prognostic significance identified in bladder cancer the RAS family, epidermal growth factor receptor, ERBB-2, MDM2, and cyclin D1. The TP53 gene has been the most thoroughly characterized tumor suppressor gene in bladder cancer, with correlation of TP53 alterations with type of carcinogenic exposure, tumor stage and grade, as well as prognosis. Studies evaluating alterations of the retinoblastoma pathway have identified the retinoblastoma gene, RB, p161NK4A/CDKN2, and E2F-1 as tumor suppressor genes with potential prognostic significance in patients with bladder cancer. Better understanding of the genetic mechanisms underlying bladder tumor development and progression will allow better prevention, diagnosis, and treatment strategies.

Carcinomas of the renal pelvis associated with smoking and phenacetin abuse: p53 mutations and polymorphism of carcinogen-metabolising enzymes

Phenacetin abuse and smoking are established risk factors for transitional cell carcinomas of the urinary tract. In the present study, we analysed exposure and the clinical course of patients who underwent nephrectomy for transitional cell carcinoma of the renal pelvis. PCR-SSCP of archival, paraffin-embedded histological sections followed by direct DNA sequencing revealed that 29 of 89 (33%) renal pelvic carcinomas contained a p53 mutation. Double mutations were found in 4 tumours and triple mutations in 1 tumour. The incidence of p53 mutations was significantly higher in tumours with grades 3 and 4 than in those with grades 1 and 2 and higher in invasive than in non-invasive tumours. Furthermore, patients with carcinomas carrying a p53 mutation showed poorer survival than those without mutation. The type of p53 mutation in renal pelvic carcinomas was similar to that reported for bladder cancer, G:C-->A:T transition mutations being most frequent (45%, 33% of these at CpG sites), followed by G:C-->T:A and G:C-->C:G transversions. The incidence and type of p53 mutation did not differ significantly in patients with a history of phenacetin abuse, smoking or neither of these habits. This was also true for G:C-->T:A transversions (17.5% of mutations), which are considered typical of smoking-induced carcinomas at other sites, e.g., lung, oral cavity and oesophagus. Our results indicate that the frequency and pattern of p53 mutations are similar in transitional cell carcinomas of the bladder and the renal pelvis and do not reflect exposure to phenacetin and/or smoking. The frequency of genetic polymorphism in genes coding for carcinogen-metabolising enzymes (CYP1A1, NAT1, GSTT1 and GSTM1) was also independent of exposure. Although the sample size of our study does not allow definite conclusions, these data are compatible with chronic tissue damage as a causative factor in the evolution of urothelial carcinomas rather than pointing to a direct mutagenic effect of phenacetin and tobacco-specific carcinogens.

Alterations of TP53 in microdissected transitional cell carcinoma of the human urinary bladder: high frequency of TP53 accumulation in the absence of detected mutations is associated with poor prognosis

We have used microdissection of paraffin-embedded histological sections and polymerase chain reaction (PCR)-based direct DNA sequencing for 54 transitional cell carcinoma (TCC) of the bladder, to examine critically the association between TP53 nuclear accumulation determined by immunohistochemistry and the presence of TP53 mutations, and to examine their relationship to tumour stage and grade, as well as patient survival. There was a significant association between the presence of TP53-positive nuclei (> 10%) and a higher histological stage and grade (P = 0.0115, P = 0.0151 respectively; Fisher's exact). A significant association between TP53 gene mutations and TP53 nuclear reactivity in more than 10% of tumour cell nuclei was also observed (P = 0.0003; Fisher's exact). Mutations were detected in 18/54 (33%) cases together with the wild-type sequence when analysed from bulk frozen samples, with significant clustering of mutations in exons 7 and 8. The microdissection method distinguished more clearly between heterozygous and/or homozygous alterations of the TP53 tumour-suppressor gene, and clearly showed frequent accumulation of TP53 in the absence of mutations. When microdissecting immunonegative regions from the same paraffin sections, three out of ten samples showed the identical mutations detected in the immunopositive regions. There was a significant association between TP53 immunoreactivity in more than 50% of tumour cell nuclei and decreased survival among all patients (P = 0.0325; log-rank test). The patients with TP53 mutations showed a trend for a shorter survival period; however, the association was not statistically significant at the 95% confidence level (P = 0.132; log-rank test). In conclusion, our observations show that accumulation of TP53 occurs frequently in the absence of mutations, and that such accumulation is nevertheless associated with poor survival when it occurs in a high proportion (> 50%) of tumour cell nuclei.

Frequent p53 mutations and occasional loss of chromosome 4 in invasive bladder carcinoma induced by N-butyl-N-(4-hydroxybutyl)nitrosamine in B6D2F1 mice

B6D2F1 mice (45/group) were treated with N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) or uracil as follows: Group 1 received 0.05% BBN in drinking water for the entire experiment, Group 2 received 5 mg of BBN by gastric gavage in 0.1 mL of 20% ethanol twice per week for 10 wk, Group 3 received a 2.5% uracil-containing diet for the entire experiment, and Group 4 was controls (received 0.1 ml of 20% ethanol by gavage twice per week for 10 wk). The surviving mice in Group 1 were killed after week 26 and those in the other groups after week 30. By week 15, three of 11 Group 1 and one of 15 Group 2 mice had bladder carcinoma. By 26 and 30 wk, respectively, invasive carcinomas were observed in 33 of 34 and six of 21 mice in Groups 1 and 2 and renal pelvic carcinomas in 11 of 34 and three of 21 mice in Groups 1 and 2. Four of 19 uracil-treated mice had bladder nodular hyperplasia. By polymerase chain reaction-single-strand conformation polymorphism and sequence analyses, 16 of 20 and two of five bladder carcinomas from Groups 1 and 2, respectively, showed mutations in the p53 gene. Ha-ras mutation was present in one case. Loss of heterozygosity analysis with simple-sequence length polymorphism markers for chromosome 4 showed that 10 of 21, two of 15, and nine of 13 mice in Groups 1-3, respectively, had heterozygous or homozygous deletions. B6D2F1 mice are therefore susceptible to the urothelial carcinogenic effects of BBN and develop frequent p53 mutations and chromosome 4 deletions. Chromosome 4 deletions were also seen with uracil.

Significance of p53 overexpression in urinary bladder transitional cell carcinoma in situ before and after bacillus Calmette-Guérin treatment

OBJECTIVES

Overexpression of p53, normally secondary to gene mutation, in invasive uroepithelial neoplasms (transitional cell carcinoma) and a high percentage of transitional cell carcinoma in situ (CIS) has been described; however, the role of p53 before and after bacillus Calmette-Guérin (BCG) treatment of CIS needs to be defined.

METHODS

Immunohistochemical reaction for p53 overexpression was performed on 12 patients with CIS before and after BCG treatment. Thirty cystectomy specimens with invasive TCC were also evaluated for the presence of CIS, hyperplasia, and dysplasia.

RESULTS

Twenty-three cases of CIS were identified. Approximately 90% of CIS cases (21 of 23) were positive for p53 overexpression, whereas transitional cell hyperplasia was uniformly negative. Less than 5% of the cells in morphologically dysplastic lesions were positively stained. Ten of 12 CIS patients displayed p53 overexpression before BCG treatment. After BCG treatment, 4 patients displayed residual CIS with p53 overexpression, and 8 patients showed no residual CIS or p53 overexpression. Three of the 4 patients with residual CIS and overexpression rapidly developed invasive transitional cell carcinoma requiring cystectomy. The 1 remaining patient was treated with a second course of BCG; further biopsies displayed the development of grade 1 papillary transitional cell carcinoma without invasion, and the patient is currently being followed

CONCLUSIONS

Our data suggest that follow-up biopsy procedures are essential in all patients with CIS treated with BCG. The biopsy specimens should be evaluated for p53 overexpression, because our data indicate that persistent p53 overexpression in uroepithelial lesions after BCG treatment is an ominous finding for probable tumor progression.

Molecular and genetic events in schistosomiasis-associated human bladder cancer: role of oncogenes and tumor suppressor genes

Carcinoma of the urinary bladder is the most common malignancy in many tropical and subtropical countries and is mainly due to endemic schistosomal infection. Schistosomiasis-associated bladder cancer defines a characteristic pathology and cellular and molecular biology that differs from urothelial carcinoma of non-schistosomal origin. N-Nitroso compounds are suspected etiologic agents in the process of bladder cancer induction during schistosomiasis. Elevated levels of DNA alkylation damage have been detected in schistosome-infected bladders and are accompanied by an inefficient capacity of DNA repair mechanisms. Consequently, high frequency of G --> A transition mutations were observed in the H-ras gene and at the CpG sequences of the p53 tumor suppressor gene. Genetic changes have also been detected in the c-erbB-1 and c-erbB-2 oncogenes and in the cdkn2 and Rb tumor suppressor genes. The potential application of these mutational patterns in providing a biological marker suitable for the biomonitoring and early detection of this neoplasm could indicate new avenues of approach that might alleviate the problem in the future. It can also assist in elucidating the mechanisms by which schistosomiasis augments human bladder cancers.