Loss of heterozygosity and overexpression of p53 gene in human primary prostatic adenocarcinoma

In vitro and in vivo model systems used in prostate cancer research

New incidence of prostate cancer is a major public health issue in the Western world, and has been rising in other areas of the globe in recent years. In an effort to understanding the molecular pathogenesis of this disease, numerous cell models have been developed, arising mostly from patient biopsies. The introduction of the genetically engineered mouse in biomedical research has allowed the development of murine models that allow for the investigation of tumorigenic and metastatic processes. Current challenges to the field include lack of an animal model that faithfully recapitulates bone metastasis of prostate cancer.

Elevated microsatellite alterations at selected tetranucleotides (EMAST) and mismatch repair gene expression in prostate cancer

Elevated microsatellite alterations at selected tetranucleotides (EMAST), a new form of microsatellite instability (MSI) affecting tetranucleotide repeats, was recently described to be frequent in several tumor types (e.g., bladder, lung, ovarian, and skin cancers). EMAST was found as a form of microsatellite alteration distinct from the MSI phenotype in hereditary nonpolyposis colorectal cancer (HNPCC)-related tumors which mostly affects mono- and dinucleotide repeats. To date, no study has investigated the role of EMAST in prostate cancer. We therefore analyzed 81 prostate tumors using 10 markers frequently detecting EMAST in other cancer types and the National Cancer Institute-consensus panel for HNPCC detection plus BAT40. In addition, we investigated p53 gene alterations [loss of heterozygosity (LOH)] and the expression of p53 and the mismatch repair (MMR) genes hMLH1 and hMSH2 on tissue microarrays. EMAST was detected in 4/81 (5%) cases and MSI in 6/79 (7.6%) cases. LOH of p53 was found in 9/45 (20%) informative cases. There was no correlation between MSI status and the histopathological or molecular characteristics of the tumors. Immunohistochemistry revealed p53 positivity in 5/61 (8%) tumors. There was a significant correlation between tumors showing a recurrence within 3 years after treatment and p53 positivity (p=0.029). Reduced hMLH1 expression, but no complete loss, was detected in 9/41 (22%) tumors without any correlations to histopathological or clinical features. Analysis of hMSH2 expression was available from 58/81 (72%) tumors. Staining intensity was as follows: negative in 7/58 (12%), weak staining in 16/58 (27.5%) samples, moderate staining in 19/58 (33%) samples, and strong staining in 16/58 (27.5%) samples. When negative/weak staining and moderate/strong staining were considered as two groups, there was a significant association between hMSH2 expression and tumor recurrence (p=0.039). In conclusion, our data show that MSI and EMAST are infrequent but distinct patterns of MSI in prostate tumors not related to MMR defects, p53 alterations, and histopathological characteristics. p53 positivity and moderate to strong hMSH2 expression of prostate tumors are correlated with early disease recurrence and indicate an unfavorable clinical course of the disease. These two genes could be useful biomarkers for the prediction of patients' outcome and should be analyzed in prospective studies.

Human prostate cancer risk factors

Prostate cancer has the highest prevalence of any nonskin cancer in the human body, with similar likelihood of neoplastic foci found within the prostates of men around the world regardless of diet, occupation, lifestyle, or other factors. Essentially all men with circulating androgens will develop microscopic prostate cancer if they live long enough. This review is a contemporary and comprehensive, literature-based analysis of the putative risk factors for human prostate cancer, and the results were presented at a multidisciplinary consensus conference held in Crystal City, Virginia, in the fall of 2002. The objectives were to evaluate known environmental factors and mechanisms of prostatic carcinogenesis and to identify existing data gaps and future research needs. The review is divided into four sections, including 1) epidemiology (endogenous factors [family history, hormones, race, aging and oxidative stress] and exogenous factors [diet, environmental agents, occupation and other factors, including lifestyle factors]); 2) animal and cell culture models for prediction of human risk (rodent models, transgenic models, mouse reconstitution models, severe combined immunodeficiency syndrome mouse models, canine models, xenograft models, and cell culture models); 3) biomarkers in prostate cancer, most of which have been tested only as predictive factors for patient outcome after treatment rather than as risk factors; and 4) genotoxic and nongenotoxic mechanisms of carcinogenesis. The authors conclude that most of the data regarding risk relies, of necessity, on epidemiologic studies, but animal and cell culture models offer promise in confirming some important findings. The current understanding of biomarkers of disease and risk factors is limited. An understanding of the risk factors for prostate cancer has practical importance for public health research and policy, genetic and nutritional education and chemoprevention, and prevention strategies.

Expression of fas ligand in metastatic prostatic carcinoma: suggestive of possible clonal expansion of subpopulation with metastatic potential

Fas ligand (FasL) is a type II transmembrane tumor necrosis factor family protein, known to trigger apoptosis in cells that bear the FasL receptor, Fas. The authors found that normal prostate, benign hyperplasia, and most prostatic carcinoma cells at the primary site did not express FasL, whereas metastatic prostatic carcinoma cells in lymph nodes and bone marrow displayed almost uniform, immunohistochemically detectable, FasL expression. However, small foci of FasL-positive prostatic carcinoma cells amid a vast majority of FasL-negative tumor cells were noted at the primary sites in patients with distant metastases. Analysis of the FasL gene and its mRNA by polymerase chain reaction and reverse transcriptase-polymerase chain reaction, respectively, suggested that the expression of immunohistochemically detectable FasL in metastatic tumor cells was not due to mutation in the FasL gene with resulting overexpression. Further, FasL expression was detectable in the acinar epithelial cells of prostates with morphologic atrophic changes, suggesting that FasL also plays a role in the physiologic apoptosis process of noncancerous prostate. The current data suggest that a subpopulation of prostate carcinoma cells clonally expresses FasL, and this subpopulation may have metastatic potential. Evaluation of FasL expression in the primary tumor thus may provide a useful parameter for predicting metastatic potential of the tumor.

Mutations within the tumour suppressor gene p53 are not confined to a late event in prostate cancer progression. a review of the evidence

Mutations in the p53 tumour suppressor gene are generally believed to be a late event in the progression of prostate cancer, and are associated with androgen independence, metastasis, and a worse prognosis. In this review, we examine the current literature available on p53 mutations and focus on stages A (T1) and B (T2) of prostate cancer. We report here that p53 mutations can be found in approximately one third of prostate cancers that are clinically localized to the prostate. In addition, high levels of p53 mutation are found in normal prostate tissue of prostate cancer patients, prostatic intraepithelial neoplasia, and benign prostatic hyperplasia. The limitations of techniques used to determine p53 mutations are discussed, as well as other modes of p53 loss in early stage prostate cancer.

Overexpression and genetic abnormality of p53 in parathyroid adenomas

To study the significance of p53 abnormality in parathyroid tumors, 32 parathyroid adenomas and 22 hyperplastic glands from 14 cases of secondary hyperparathyroidism were analysed using immunohistochemistry, polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP), single-strand conformation polymorphism (SSCP) and DNA sequencing. Immunohistochemical study revealed p53 overexpression in four parathyroid adenomas, of which two showed diffuse and one showed focal nuclear pleomorphism. Genetic analysis disclosed allelic loss in one, and a point mutation (R290H) and a polymorphism (L257 L) in another of the two other adenomas with diffuse nuclear pleomorphism. No abnormalities were discovered in the other two adenomas, although one had a R72P polymorphism in exon 4. There was no evidence of malignancy of the four tumors in either clinical or pathological terms. None of the 22 hyperplastic glands showed p53 overexpression. These results demonstrate that p53 abnormality can occur in benign parathyroid adenomas and is more prevalent in those with nuclear pleomorphism than in those without.

Expression of p21 and mutant p53 gene products in residual prostatic tumor cells after radical radiotherapy

BACKGROUND

In a previous study, sextant core biopsies revealed residual tumor in the prostate in 37/55 investigated patients, with an average of 6.8 years after external beam radiation therapy (RRT). More than half of the biopsies exhibited Ki-67 and PCNA proliferation activity.

METHODS

The present study aims at further characterizing residual tumor cells post-RRT by investigating whether the tumor cells exhibit immunohistochemical expression of p21 and mutant p53 gene products, which reflect the state of cell cycle regulatory mechanisms.

RESULTS

Positive p53 staining was observed in 11% and p21 positivity in 47% of biopsies. The proportion of positively stained cells was low for both antigens. The staining patterns point to the existence of wild-type p53-dependent, as well as alternative pathways for p21 protein induction.

CONCLUSIONS

A low proportion of tumor cells exhibited p53 protein accumulation post-RRT. G1 arrest, as assessed by p21 immunoexpression, was demonstrated in a low percentage of tumor cells in < 50% of post-RRT biopsies, indicating that the vast majority of residual tumor cells following RRT escape the G1/S checkpoint control and propagate into S-phase, presumably with a maintained malignant potential.

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 biology of prostatic intraepithelial neoplasia

High-grade PIN is the most likely precursor of prostatic adenocarcinoma, according to virtually all available evidence to date. The clinical importance of recognizing PIN is based on its strong association with prostatic carcinoma. PIN has a high predictive value as a marker for adenocarcinoma. Its identification in biopsy specimens of the prostate warrants further search for concurrent invasive carcinoma. PIN is associated with progressive abnormalities of phenotype and genotype intermediate between normal prostatic epithelium and cancer, indicating impairment of cell differentiation and regulatory control with advancing stages of prostatic carcinogenesis. There is progressive gain or loss of a wide variety of biomarkers, including morphometric markers, differentiation markers, stromal markers, growth factors and associated receptors, oncogenes, tumor suppressor genes, and chromosomes. Abnormalities in expression of most biomarkers are amplified in the progression from high-grade PIN to localized cancer, metastatic cancer, and hormone-refractory cancer. Oncogenesis of prostatic carcinoma probably occurs through the selection of several genetic changes, each modifying the expression or function of genes controlling cell growth and differentiation. Further studies are needed to evaluate the function and prognostic value of oncogene expression in the normal, preneoplastic, and neoplastic prostate.