Retinoblastoma gene mutations in primary human prostate cancer

Breast and prostate cancers harbor common somatic copy number alterations that consistently differ by race and are associated with survival

Background

Pan-cancer studies of somatic copy number alterations (SCNAs) have demonstrated common SCNA patterns across cancer types, but despite demonstrable differences in aggressiveness of some cancers by race, pan-cancer SCNA variation by race has not been explored. This study investigated a) racial differences in SCNAs in both breast and prostate cancer, b) the degree to which they are shared across cancers, and c) the impact of these shared, race-differentiated SCNAs on cancer survival.

Methods

Utilizing data from The Cancer Genome Atlas (TCGA), SCNAs were identified using GISTIC 2.0, and in each tumor type, differences in SCNA magnitude between African Americans (AA) and European Americans (EA) were tested using linear regression. Unsupervised hierarchical clustering of the copy number of genes residing in race-differentiated SCNAs shared between tumor types was used to identify SCNA-defined patient groups, and Cox proportional hazards regression was used to test for association between those groups and overall/progression-free survival (PFS).

Results

We identified SCNAs that differed by race in breast (n = 58 SCNAs; permutation p < 10^− 4) and prostate tumors (n = 78 SCNAs; permutation p = 0.006). Six race-differentiated SCNAs common to breast and prostate found at chromosomes 5q11.2-q14.1, 5q15-q21.1, 8q21.11-q21.13, 8q21.3-q24.3, 11q22.3, and 13q12.3-q21.3 had consistent differences by race across both tumor types, and all six were of higher magnitude in AAs, with the chromosome 8q regions being the only amplifications. Higher magnitude copy number differences in AAs were also identified at two of these race-differentiated SCNAs in two additional hormonally-driven tumor types: endometrial (8q21.3-q24.3 and 13q12.3-q21.3) and ovarian (13q12.3-q21.3) cancers. Race differentiated SCNA-defined patient groups were significantly associated with survival differences in both cancer types, and these groups also differentiated within triple negative breast cancers based on PFS. While the frequency of the SCNA-defined patient groups differed by race, their effects on survival did not.

Conclusions

This study identified race-differentiated SCNAs shared by two related cancers. The association of SCNA-defined patient groups with survival demonstrates the clinical significance of combinations of these race-differentiated genomic aberrations, and the higher frequency of these alterations in AA relative to EA patients may explain racial disparities in risk of aggressive breast and prostate cancer.

Deletion of the p16INK4a tumor suppressor and expression of the androgen receptor induce sarcomatoid carcinomas with signet ring cells in the mouse prostate

The tumor suppressor p16^Ink4a, encoded by the INK4a gene, is an inhibitor of cyclin D-dependent kinases 4 and 6, CDK4 and CDK6. This inhibition prevents the phosphorylation of the retinoblastoma protein (pRb), resulting in cellular senescence through inhibition of E2F-mediated transcription of S phase genes required for cell proliferation. The p16^Ink4a plays an important role in tumor suppression, whereby its deletion, mutation, or epigenetic silencing is a frequently observed genetic alteration in prostate cancer. To assess its roles and related molecular mechanisms in prostate cancer initiation and progression, we generated a mouse model with conditional deletion of p16^Ink4a in prostatic luminal epithelium. The mice underwent oncogenic transformation and developed prostatic intraepithelial neoplasia (PIN) from eight months of age, but failed to develop prostatic tumors. Given the prevalence of aberrant androgen signaling pathways in prostate cancer initiation and progression, we then generated R26hAR^L/wt:p16^L/L: PB-Cre4 compound mice, in which conditional expression of the human AR transgene and deletion of p16^Ink4a co-occur in prostatic luminal epithelial cells. While R26hAR^L/wt:PB-Cre4 mice showed no visible pathological changes, R26hAR^L/wt:p16^L/L: PB-Cre4 compound mice displayed an early onset of high-grade PIN (HGPIN), prostatic carcinoma, and metastatic lesions. Strikingly, we observed tumors resembling human sarcomatoid carcinoma with intermixed focal regions of signet ring cell carcinoma (SRCC) in the prostates of the compound mice. Further characterization of these tumors showed they were of luminal epithelial cell origin, and featured characteristics of epithelial to mesenchymal transition (EMT) with enhanced proliferative and invasive capabilities. Our results not only implicate a biological role for AR expression and p16^Ink4a deletion in the pathogenesis of prostatic SRCC, but also provide a new and unique genetically engineered mouse (GEM) model for investigating the molecular mechanisms for SRCC development.

Molecular alterations associated with prostate cancer

Introduction

The amount of information and knowledge about pathways and genetic alterations regarding prostate cancer, including the tools available for its study has been recently increasing. Additionally, a variety of molecular signaling pathways control cell proliferation, however, this incompletely understood process is disturbed in cancer cells.

Materials and methods

A literature review was made using the MEDLINE, Embase and LILACS databases searching for the following keywords: prostate neoplasms, prostate cancer, molecular medicine, genomics, pathways, and cell cycle.

Results

Different biological mechanisms have been associated with the development of prostate cancer, such as alterations in tumor suppressor genes, oncogenes (TP53, RB1, among others) and CDKIs; DNA methylation; chromosomal alterations and rearrangements; changes in PTEN and PI3K / mTOR; global defects in apoptosis; alterations in the androgen receptor (AR); and epigenetic mechanisms.

Conclusions

Good clinical practice and a practical approach have to be based on basic knowledge, thus, in this article, the main genetic alterations, mutations and pathways involved in prostate cancer development were reviewed.

Flavokawain A induces deNEDDylation and Skp2 degradation leading to inhibition of tumorigenesis and cancer progression in the TRAMP transgenic mouse model

S phase kinase-associated protein 2 (Skp2) has been shown to be required for spontaneous tumor development that occurs in the retinoblastoma protein (pRb) deficient mice. Here we have demonstrated that flavokawain A (FKA), a novel chalcone from the kava plant, selectively inhibited the growth of pRb deficient cell lines and resulted in a proteasome-dependent and ubiquitination-mediated Skp2 degradation. Degradation of Skp2 by FKA was found to be involved in a functional Cullin1, but independent of Cdh1 expression. Further studies have demonstrated that FKA docked into the ATP binding pocket of the precursor cell-expressed developmentally down-regulated 8 (NEDD8)-activating enzyme (NAE) complex, inhibited NEDD8 conjugations to both Cullin1 and Ubc12 in PC3 cells and Ubc12 NEDDylation in an in vitro assay. Finally, dietary feeding of the autochthonous transgenic adenocarcinoma of the mouse prostate (TRAMP) mice with FKA inhibited the formation of high-grade prostatic intra-epithelial neoplasia lesions (HG-PIN) and prostate adenocarcinomas, reduced the tumor burden and completely abolished distant organ metastasis. Immunohistochemistry studies revealed that dietary FKA feeding resulted in marked anti-proliferative and apoptotic effects via down-regulation of Skp2 and NEDD8 and up-regulation of p27/Kip1 in the prostate of TRAMP mice. Our findings therefore provide evidence that FKA is a promising NEDDylation inhibitor for targeting Skp2 degradation in prostate cancer prevention and treatment.

The N Terminus of the Retinoblastoma Protein Inhibits DNA Replication via a Bipartite Mechanism Disrupted in Partially Penetrant Retinoblastomas

The N-terminal domain of the retinoblastoma (Rb) tumor suppressor protein (RbN) harbors in-frame exon deletions in partially penetrant hereditary retinoblastomas and is known to impair cell growth and tumorigenesis. However, how such RbN deletions contribute to Rb tumor- and growth-suppressive functions is unknown. Here we establish that RbN directly inhibits DNA replication initiation and elongation using a bipartite mechanism involving N-terminal exons lost in cancer. Specifically, Rb exon 7 is necessary and sufficient to target and inhibit the replicative CMG helicase, resulting in the accumulation of inactive CMGs on chromatin. An independent N-terminal loop domain, which forms a projection, specifically blocks DNA polymerase α (Pol-α) and Ctf4 recruitment without affecting DNA polymerases ε and δ or the CMG helicase. Individual disruption of exon 7 or the projection in RbN or Rb, as occurs in inherited cancers, partially impairs the ability of Rb/RbN to inhibit DNA replication and block G1-to-S cell cycle transit. However, their combined loss abolishes these functions of Rb. Thus, Rb growth-suppressive functions include its ability to block replicative complexes via bipartite, independent, and additive N-terminal domains. The partial loss of replication, CMG, or Pol-α control provides a potential molecular explanation for how N-terminal Rb loss-of-function deletions contribute to the etiology of partially penetrant retinoblastomas.

NUSAP1 expression is upregulated by loss of RB1 in prostate cancer cells

BACKGROUND

Overexpression of NUSAP1 is associated with poor prognosis in prostate cancer, but little is known about what leads to its overexpression. Based on previous observations that NUSAP1 expression is enhanced by E2F1, we hypothesized that NUSAP1 expression is regulated, at least in part, by loss of RB1 via the RB1/E2F1 axis.

METHODS

Using Significance Analysis of Microarrays, we examined RB1, E2F1, and NUSAP1 transcript levels in prostate cancer gene expression datasets. We compared NUSAP1 expression levels in DU145, LNCaP, and PC-3 prostate cancer cell lines via use of cDNA microarray data, RT-qPCR, and Western blots. In addition, we used lentiviral expression constructs to knockdown RB1 in prostate cancer cell lines and transient transfections to knockdown E2F1, and investigated RB1, E2F1, and NUSAP1 expression levels with RT-qPCR and Western blots. Finally, in DU145 cells or PC-3 cells that stably underexpress RB1, we used proliferation and invasion assays to assess whether NUSAP1 knockdown affects proliferation or invasion.

RESULTS

NUSAP1 transcript levels are positively correlated with E2F1 and negatively correlated with RB1 transcript levels in prostate cancer microarray datasets. NUSAP1 expression is elevated in the RB1-null DU145 prostate cancer cell line, as opposed to LNCaP and PC-3 cell lines. Furthermore, NUSAP1 expression increases upon knockdown of RB1 in prostate cancer cell lines (LNCaP and PC-3) and decreases after knockdown of E2F1. Lastly, knockdown of NUSAP1 in DU145 cells or PC-3 cells with stable knockdown of RB1 decreases proliferation and invasion of these cells.

CONCLUSION

Our studies support the notion that NUSAP1 expression is upregulated by loss of RB1 via the RB1/E2F1 axis in prostate cancer cells. Such upregulation may promote prostate cancer progression by increasing proliferation and invasion of prostate cancer cells. NUSAP1 may thus represent a novel therapeutic target.

Retinoblastoma (RB1) pocket domain mutations and promoter hyper-methylation in head and neck cancer

BACKGROUND

The RB1 gene plays a pivotal role in cell cycle regulation. In this case-control study we searched for alterations in the RB1 pocket domain and its promoter region in head and neck cancer (HNC) patients in the Pakistani population.

METHODS

For germline mutation analyses, 380 blood samples from HNC patients and 350 blood samples from control individuals were included. Polymerase chain reaction (PCR) and single strand conformational polymorphism (SSCP) assays, followed by sequence analyses, were used for the RB1 pocket domain mutation screens. For the RB1 promoter methylation screens, 72 HNC tumor samples along with adjacent uninvolved tissues were tested using a methylation-specific polymerase chain reaction (MSP) assay.

RESULTS

RB1 (pocket domain and spacer region) sequence analysis revealed one frameshift and seven non-synonymous missense mutations. The frequency of missense mutations in exon 14, i.e., g76474C > T, g76475G > C and g76476A > G, resulting in Arg455Ser, was found to be highest (0.10). Missense mutations g76467G > C (exon14), g76468T > C (exon14), g77041A > T and g77043A > T (exon 16), when analyzed via Alamut biosoftware version 2.0, were found to be present in highly conserved amino acids with Align GVGD scores C15 (GV: 0.00-GD: 21.82), C65 (GV: 0.00-GD: 83.33) and C65 (GV: 0.00-GD: 98.69), respectively. These missense mutations were found to be deleterious by SIFT score: 0.00 (median 3.64). RB1 promoter methylation analysis revealed that 16% of its cytosines (3% in CpG) were methylated in the HNC tumor samples.

CONCLUSION

Our findings indicate that both genetic and epigenetic RB1 changes may contribute to the pathogenesis of HNC in the Pakistani population.

Breast cancer risk after radiotherapy for heritable and non-heritable retinoblastoma: a US-UK study

BACKGROUND

Retinoblastoma is a rare childhood eye cancer caused by germline or somatic mutations in the RB1 gene. Previous studies observed elevated breast cancer risk among retinoblastoma survivors. However, there has been no research on breast cancer risk in relation to radiation (primarily scatter radiation from the primary treatment) and genetic susceptibility of retinoblastoma survivors.

METHODS

Two groups of retinoblastoma survivors from the US and UK were selected, and breast cancer risk analysed using a case-control methodology, nesting within the respective cohorts, matching on heritability (that is to say, having bilateral retinoblastoma or being unilateral cases with at least one relative with retinoblastoma), and using exact statistical methods. There were a total of 31 cases and 77 controls.

RESULTS

Overall there was no significant variation of breast cancer risk with dose (P>0.5). However, there was a pronounced and significant (P=0.047) increase in the risk of breast cancer with increasing radiation dose for non-heritable retinoblastoma patients and a slight and borderline significant (P=0.072) decrease in risk of breast cancer with increasing radiation dose for heritable retinoblastoma patients, implying significant (P=0.024) heterogeneity in radiation risk between the heritable and non-heritable retinoblastoma groups; this was unaffected by the blindness status. There was no significant effect of any type of alkylating-agent chemotherapy on breast cancer risk (P>0.5).

CONCLUSIONS

There is significant radiation-related risk of breast cancer for non-heritable retinoblastoma survivors but no excess risk for heritable retinoblastoma survivors, and no significant risk overall. However, these results are based on very small numbers of cases; therefore, they must be interpreted with caution.

TFDP3 was expressed in coordination with E2F1 to inhibit E2F1-mediated apoptosis in prostate cancer

TFDP3 has been previously identified as an inhibitor of E2F molecules. It has been shown to suppress E2F1-induced apoptosis dependent P53 and to play a potential role in carcinogenesis. However, whether it indeed helps cancer cells tolerate apoptosis stress in cancer tissues remains unknown. TFDP3 expression was assessed by RT-PCR, in situ hybridization and immunohistochemistry in normal human tissues, cancer tissues and prostate cancer tissues. The association between TFDP3 and E2F1 in prostate cancer development was analyzed in various stages. Apoptosis was evaluated with annexin-V and propidium iodide staining and flow-cytometry. The results show that, in 96 samples of normal human tissues, TFDP3 could be detected in the cerebrum, esophagus, stomach, small intestine, bronchus, breast, ovary, uterus, and skin, but seldom in the lung, muscles, prostate, and liver. In addition, TFDP3 was highly expressed in numerous cancer tissues, such as brain-keratinous, lung squamous cell carcinoma, testicular seminoma, cervical carcinoma, skin squamous cell carcinoma, gastric adenocarcinoma, liver cancer, and prostate cancer. Moreover, TFDP3 was positive in 23 (62.2%) of 37 prostate cancer samples regardless of stage. Furthermore, immunohistochemistry results show that TFDP3 was always expressed in coordination with E2F1 at equivalent expression levels in prostate cancer tissues, and was highly expressed particularly in samples of high stage. When E2F1 was extrogenously expressed in LNCap cells, TFDP3 could be induced, and the apoptosis induced by E2F1 was significantly decreased. It was demonstrated that TFDP3 was a broadly expressed protein corresponding to E2F1 in human tissues, and suggested that TFDP3 is involved in prostate cancer cell survival by suppressing apoptosis induced by E2F1.

Expression of p 16 protein in prostatic adenocarcinomas, intraepithelial neoplasia, and benign/hyperplastic glands

The tumor suppressor gene CDKN2/MTSI(p16(INK4)) may be inactivated by point mutations, deletions, or methylation in many tumor types. In prostate cancer, a very low frequency of point mutations has been reported, but deletions of 9p21 and inactivation by methylation are observed more frequently. The purpose of this study was to assess the expression pattern of the CDKN2 protein product p 16 in a series of 104 prostatic adenocarcinomas treated by radical prostatectomy, using immunohistochemical detection on archival, paraffin-embedded material. Nuclear staining was completely absent in 13 (13%) of 104 cases, whereas cytoplasmic staining was found in 99 (95%) of 104 carcinomas. Significant differences were found when comparing the staining intensity of carcinomas and coexisting prostatic intraepithelial neoplasia (PIN) with benign/hyperplastic glands. In 86 (95%) of 91 cases the overall staining intensity of carcinomas was stronger than the reactivity in benign/hyperplastic glands, which were most often weakly stained. In 71 (95%) of 75 cases the staining intensity of PIN was stronger than in benign/hyperplastic glands, a contrast also observed within single glands. However, p16 immunostaining in carcinomas was not prognostically important and it was not associated with standard clinicopathologic parameters. Our results support that CDKN2/plb is inactivated in only a small proportion of localized prostate cancers. The increased p16 staining of carcinomas/PIN in comparison with benign/hyperplastic glands suggests that p 16 protein may be involved in early stages of prostate tumorigenesis by mechanisms other than CDKN2/p16 gene inactivation, and the possibility of using p(16) immunostaining as a marker for PIN is discussed.

Rb1/105 gene alterations and head and neck carcinogenesis

Retinoblastoma gene (Rb1) is a tumor suppressor gene, which plays a pivotal role in cell cycle regulation, promoting G1/S arrest and growth restriction through inhibition of the E2F transcription factor. Abnormalities in the genes involved in cell cycle, including Rb1, have been reported in head and neck cancer (HNC) patients. Studies regarding Rb1 have been observed in different world populations but data is missing for Pakistani population. This study was aimed to analyze the genetic aberrations of Rb1 and their association with the development of HNC in Pakistani population. Genomic DNA was isolated from blood samples of 300 HNC patients and 270 controls. Salient coding region of gene was amplified by using Polymerase Chain Reaction (PCR). PCR conditions were optimized for each exon separately. Amplified products were analyzed for mutational screening using Single strand confirmation polymorphism (SSCP) technique followed by sequence analysis. Sequence analysis revealed five missense mutations g77082G>C, g77083G>A, g170220A>T, g170221G>C, g170228T>A, two frameshift mutations, two stop codon and two intronic substitutions in this study. The overall frequency of these mutations was 0.71. Frequency of nonsense mutations; Lys462stop (Novel) and Ser834stop (CM952105) were 0.15 and 0.14 respectively. We also report here novel missense mutations, frameshift mutation and a stop codon Lys462stop in HNC patients of Pakistani origin.This study suggests that the Rb1 germline mutations may contribute to genetic susceptibility for HNC. To our knowledge, this is the first report that Rb1 gene may be associated with risk of cancer in Pakistani population.

Time to stratify? The retinoblastoma protein in castrate-resistant prostate cancer

It is generally held that the retinoblastoma (RB) tumor suppressor functions in multiple tissues to protect against tumor development. However, preclinical studies and analysis of tumor samples of early disease did not support an important role of RB loss in the origin of prostate cancer. By contrast, recent observations in the clinical setting and subsequent modeling of RB function indicate that the tumor suppressor has specialized roles in controlling androgen receptor expression in prostate cancer, and primarily functions to prevent progression to the castration-resistant stage of disease. Furthermore, preclinical models have now shown that loss of RB expression or functional activity decreases the effectiveness of hormone therapy, yet seems to increase sensitivity to a subset of chemotherapeutic agents. Here, the current state of knowledge regarding the implications of RB loss for prostate cancer progression will be reviewed, and potential opportunities for developing RB as a metric to predict therapeutic response will be considered.

Alterations of the retinoblastoma gene in metastatic breast cancer

Germline mutations affecting the retinoblastoma gene (RB1) predispose to inherited retinoblastomas but also other malignancies, including breast cancer. While somatic RB1 mutations have been detected in different malignancies, information about the potential role of RB1 mutations in breast cancer is limited. Recently, we discovered RB1 mutations to be associated with resistance to anthracyclines/mitomycin in primary breast cancer. The present work is the first report evaluating RB1 mutation and epigenetic status in metastatic breast cancer. Among 148 breast cancer samples analyzed by MLPA, four samples harbored intragenic deletions/duplications: Thus, exons 1–2 were deleted in two tumors and exons 21–23 in one tumor, while one sample harbored duplication of exons 18–23. The entire RB1 gene was duplicated in two tumors and multiple amplifications were revealed in one sample. Reduced copy number was observed in 17 samples (11.5%). No point mutation or promoter hypermethylation was discovered (n = 38 and 114 tumors analyzed, respectively). Interestingly, among seven tumors expressing lack of response to epirubicin, two samples harbored alterations in RB1, contrasting none out of 16 tumors with stable disease or an objective response (P = 0.08). In summary, the frequency of RB1 alterations in metastatic lesions was not increased when compared to primary breast cancer, indicating that RB1 alterations do not play a major role in metastatic development. While a non-significant association suggesting RB1 alterations to be linked to therapy resistance was observed, our data do not suggest a major role for RB1 alterations explaining acquired drug resistance.

Identification and characterization of retinoblastoma gene mutations disturbing apoptosis in human breast cancers

Background

The tumor suppressor pRb plays a key role regulating cell cycle arrest, and disturbances in the RB1 gene have been reported in different cancer forms. However, the literature reports contradictory findings with respect to a pro - versus anti - apoptotic role of pRb, and the consequence of alterations in RB1 to chemotherapy sensitivity remains unclear. This study is part of a project investigating alterations in pivotal genes as predictive factors to chemotherapy sensitivity in breast cancer.

Results

Analyzing 73 locally advanced (stage III) breast cancers, we identified two somatic and one germline single nucleotide changes, each leading to amino acid substitution in the pRb protein (Leu607Ile, Arg698Trp, and Arg621Cys, respectively). This is the first study reporting point mutations affecting RB1 in breast cancer tissue. In addition, MLPA analysis revealed two large multiexon deletions (exons 13 to 27 and exons 21 to 23) with the exons 21-23 deletion occurring in the tumor also harboring the Leu607Ile mutation. Interestingly, Leu607Ile and Arg621Cys point mutations both localize to the spacer region of the pRb protein, a region previously shown to harbor somatic and germline mutations. Multiple sequence alignment across species indicates the spacer to be evolutionary conserved. All three RB1 point mutations encoded nuclear proteins with impaired ability to induce apoptosis compared to wild-type pRb in vitro. Notably, three out of four tumors harboring RB1 mutations displayed primary resistance to treatment with either 5-FU/mitomycin or doxorubicin while only 14 out of 64 tumors without mutations were resistant (p = 0.046).

Conclusions

Although rare, our findings suggest RB1 mutations to be of pathological importance potentially affecting sensitivity to mitomycin/anthracycline treatment in breast cancer.

Regulation of cell proliferation in a stratified culture system of epithelial cells from prostate tissue

Mechanisms controlling epithelial proliferation and differentiation in the prostate have been primarily investigated in mouse models. The regulation of proliferation and differentiation is poorly understood in human prostate epithelial cells. In vivo, the glandular prostate epithelium consists of a p63-positive proliferating basal cell layer and a post-mitotic p27-positive secretory cell layer. We have established an organized stratified culture system of human primary prostate epithelial cells to gain insight into mechanisms regulating proliferation and differentiation. In this system, expression of p63 is observed in the bottom layer. In addition, BrdU incorporation persists even though cells are confluent. In contrast, in the upper layer, p63 expression is greatly diminished, p27 is expressed, and the cells are growth arrested. Overexpression of cyclin D1 or knockdown of p27 does not increase proliferation. After inactivation of the nuclear phosphoprotein Rb, the cell layers remain organized and cell proliferation increases only in the bottom layer. Furthermore, the expression of p63 remains confined to the bottom layer after Rb inactivation. Altogether, this in vitro model recapitulates certain aspects of in vivo growth regulation and differentiation and suggests that the loss of Rb family proteins in human cells trigger hyperplasia but is not sufficient for transformation.

Receptor for advanced glycation end products (RAGE) and its ligand, amphoterin are overexpressed and associated with prostate cancer development

BACKGROUND

Advanced glycation end products (AGE) are produced with normal aging. Recently, some reports indicated that the interaction between AGE and the cognate receptor (RAGE) has a role in cancer dependent.

METHODS

We investigated RAGE and amphoterin mRNA expression in prostate cancer cell lines (DU145, PC-3, and LNCaP cells), hormone-refractory prostate cancer tissues, and paired untreated primary prostate cancer and normal prostate (including benign prostatic hypertrophy (BPH)) tissues using real-time quantitative PCR. Moreover, to confirm the AGE-RAGE interaction in prostate cancer, DU145 cells stimulated with AGE-bovine serum albumin (AGE-BSA) were examined by in vitro matrigel assay, cell viability assay, MTT assay, reverse transcription-polymerase chain reaction (RT-PCR), and Western blot.

RESULTS

DU145 cells, a hormone-independent prostate cancer cell line, showed the highest RAGE mRNA expression. Amphoterin mRNA was expressed in all three cell lines. In prostate tissues, untreated prostate cancer tissue and hormone-refractory prostate cancer tissue showed higher RAGE and amphoterin mRNA expression than normal prostate tissue. The AGE-RAGE interaction induced the invasion and growth in DU145 cells stimulated with AGE-BSA.

CONCLUSIONS

The AGE-RAGE interaction is important in prostate cancer development, and inhibition of this interaction has potential as a new molecular target for cancer therapy or prevention.

Liver-Specific pRB Loss Results in Ectopic Cell Cycle Entry and Aberrant Ploidy

The liver exhibits an exquisitely controlled cell cycle, wherein hepatocytes are maintained in quiescence until stimulated to proliferate. The retinoblastoma tumor suppressor, pRB, plays a central role in proliferative control by inhibiting inappropriate cell cycle entry. In many cases, liver cancer arises due to aberrant cycles of proliferation, and correspondingly, pRB is functionally inactivated in the majority of hepatocellular carcinomas. Therefore, to determine how pRB loss may provide conditions permissive for deregulated hepatocyte proliferation, we investigated the consequence of somatic pRB inactivation in murine liver. We show that liver-specific pRB loss results in E2F target gene deregulation and elevated cell cycle progression during post-natal growth. However, in adult livers, E2F targets are repressed and hepatocytes become quiescent independent of pRB, suggesting that other factors may compensate for pRB loss. Therefore, to probe the consequences of acute pRB inactivation in livers of adult mice, we gave adenoviral-Cre by i.v. injection. We show that acute pRB loss is sufficient to elicit E2F target gene expression and cell cycle entry in adult liver, demonstrating a critical role for pRB in maintaining hepatocyte quiescence. Finally, we show that liver-specific pRB loss results in the development of nuclear pleomorphism associated with elevated ploidy that is evident in adult mice harboring both acute and chronic pRB loss. Together, these results show the crucial role played by pRB in maintaining hepatocyte quiescence and ploidy in adult liver in vivo and underscore the critical importance of delineating the consequences of acute pRB loss in adult animals.

Genetically engineered murine models of prostate cancer: insights into mechanisms of tumorigenesis and potential utility

There has been substantial progress made recently in the effort to model human prostate cancer in mice. Several mutant mice have been generated which mimic various aspects of the human disease, including the development of preneoplastic lesions, invasive carcinoma, and metastases. These mouse reagents provide the research community with valuable new tools for dissecting the mechanisms of tumorigenesis, as well as for testing new targeted therapies. This review will summarize some of these models and their utility, as well as propose future challenges for developing improved models.

Synthetic lethality of retinoblastoma mutant cells in the Drosophila eye by mutation of a novel peptidyl prolyl isomerase gene

Mutations that inactivate the retinoblastoma (Rb) pathway are common in human tumors. Such mutations promote tumor growth by deregulating the G1 cell cycle checkpoint. However, uncontrolled cell cycle progression can also produce new liabilities for cell survival. To uncover such liabilities in Rb mutant cells, we performed a clonal screen in the Drosophila eye to identify second-site mutations that eliminate Rbf(-) cells, but allow Rbf(+) cells to survive. Here we report the identification of a mutation in a novel highly conserved peptidyl prolyl isomerase (PPIase) that selectively eliminates Rbf(-) cells from the Drosophila eye.

Epigenetic changes in prostate cancer: implication for diagnosis and treatment

Prostate cancer is the most common noncutaneous malignancy and the second leading cause of cancer death among men in the United States. DNA methylation and histone modifications are important epigenetic mechanisms of gene regulation and play essential roles both independently and cooperatively in tumor initiation and progression. Aberrant epigenetic events such as DNA hypo- and hypermethylation and altered histone acetylation have both been observed in prostate cancer, in which they affect a large number of genes. Although the list of aberrantly epigenetically regulated genes continues to grow, only a few genes have, so far, given promising results as potential tumor biomarkers for early diagnosis and risk assessment of prostate cancer. Thus, large-scale screening of aberrant epigenetic events such as DNA hypermethylation is needed to identify prostate cancer-specific epigenetic fingerprints. The reversibility of epigenetic aberrations has made them attractive targets for cancer treatment with modulators that demethylate DNA and inhibit histone deacetylases, leading to reactivation of silenced genes. More studies into the mechanism and consequence of demethylation are required before the cancer epigenome can be safely manipulated with therapeutics as a treatment modality. In this review, we examine the current literature on epigenetic changes in prostate cancer and discuss the clinical potential of cancer epigenetics for the diagnosis and treatment of this disease.

Genetic aberrations in prostate carcinoma detected by comparative genomic hybridization and microsatellite analysis: association with progression and angiogenesis

BACKGROUND

In spite of increasing knowledge about the tumor biology of prostate cancer (PC), molecular events involved in tumor progression are not well characterized. There is evidence that a number of genetic alterations play a role in tumor progression and in addition, angiogenesis also contributes. In this study, comparative genomic hybridization (CGH), a sensitive method for detecting regional DNA copy number abnormalities, and microsatellite analysis was used to identify frequent genome changes in PC. Correlation of these data with microvessel density (MVD) and clinical follow-up data was performed to determine genetic alterations that are associated with angiogenesis and subsequent tumor progression.

METHODS

Fifty-seven paraffin embedded radical prostatectomy (RP) specimens were microdissected. DNA from the microdissected PC tissue was amplified by degenerate oligonucleoitide primed (DOP)-polymerase chain reaction (PCR), and CGH was performed on the PCR product. Quantitative analyses of the CGH profiles were performed using a t-statistic. Additionally, a microsatellite analysis of chromosome 13q was performed on a subgroup of 31 of the tumors. Using a polyclonal antibody against factor VIII, MVD was determined for all RP specimens. The results of CGH and microsatellite analysis were correlated with the clinical data of the patients and with MVD.

RESULTS

Forty-two of the tumors (75%) showed one or more gains while 39 (70%) showed one or more losses per tumor. The most frequent DNA copy number gains were on chromosome 3, 4, 7, 8, 10, 11, 12, 13, and X. The most frequent losses were on chromosomes 2, 5, 6, 8, 10, 13, 15, and 16. Cancer recurrence occurred in 15 patients. The total number of DNA copy number losses was significantly higher in patients with this progression (86%) than without (52%) (P < 0.001). There was no significant difference in the number of gains in patients with or without progression. Contingency table analysis showed a significant correlation between progression and losses in regions of chromosomes 6q and 13q and a gain of chromosome 7q. In multivariate analysis, only loss of chromosome 6 was independently prognostic. The gains that correlated most closely with MVD > 35 were on chromosomes 2q, 7q, and Xq, while the losses most closely associated with MVD > 35 were on chromosomes 8q, 10q, and 13q. However, only the association between loss of chromosome 13q and MVD > 35 was statistically significant. Microsatellite analysis revealed a statistically significant correlation between MVD and instability of locus 171.

CONCLUSIONS

This study indicates that the frequency of genetic alterations in PC as detected by CGH correlates with clinical outcome, and that losses of DNA from chromosomes 6q and 13q are important events that correlate with tumor progression, with loss of 13q, especially instability of locus 171, also associated with angiogenesis.

Induction of Androgen Receptor-Dependent Apoptosis in Prostate Cancer Cells by the Retinoblastoma Protein

Re-expression of a tumor suppressor in tumor cells that lack it is an effective way to study its functional activities. However, because tumor cells contain multiple mutations, tumor suppressor functions that are dependent on (an)other regulators are unlikely to be identified by its re-expression alone if the other regulators are also mutated. In this study, we show that re-expression of retinoblastoma (RB) together with the androgen receptor (AR) in RB- and AR-deficient prostate cancer DU-145 cells resulted in an apoptotic activity, acting through the mitochondria damage-initiated caspase activation pathway, which was not present when RB, or the AR, was re-expressed alone. The ability of RB + AR to induce mitochondria damage was dependent on the proapoptotic proteins Bax and Bak and could be blocked by the antiapoptotic protein Bcl-x(L). Coexpressed AR did not detectably change RB's regulation of E2F and cell cycle progression in culture. On the other hand, coexpressed RB could activate the transactivation activity of the AR in an androgen-depleted media. Although androgen induced greater AR transactivation activity in this condition, it did not induce apoptosis in the absence of coexpressed RB. Analysis of mutants of RB and the AR indicated that intact pocket function of RB and the transactivation activity of the AR were required for RB + AR-induced apoptosis. These results provide direct functional data for an AR-dependent apoptosis-inducing activity of RB and highlight the importance of cell type-specific regulators in obtaining a more complete understanding of RB.

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.

The significance of key regulators of apoptosis in the development and prognosis of prostate carcinoma. II. Products of suppressor genes Rb and PTEN, CDKI, Fas

The molecular basis for the transition of carcinoma of the prostate from androgen-dependent to androgen-independent growth is largely unknown. Currently for example, it is not clear whether the androgen-independent phenotype is a result of selection of a subgroup of genetically distinct prostate tumour cells which are already hormone-resistant or a genetic adaptation of prostate tumour cells to the hormone therapy itself. It has also been established that prostate tumour transformation is a result of homeostatic control defects, a line of thinking directed toward elucidating the apoptotic profile of prostate tumour cells that may be important in determining prognosis, response to therapy and illness progression. Main consideration in this part of rewiev is given to the role of tumour suppressor genes pRb and PTEN and also the natural inhibitors of cyclin dependent kinases - proteins p21(Waf1/Cip1) and p27(Kip1). Attention is also given to the role of FAS-mediated pathways in apoptosis induction.

Prostate Development and Carcinogenesis

The process involved in the development and carcinogenesis of the prostate gland is complex. During early prostate development, the androgenic hormone from embryonic testicles is required for ductal formation, growth, and branching morphogenesis of the prostate gland. From this early stage, interactions between the epithelium and mesenchyme become firmly established through paracrine influence (i.e., growth factors) from mesenchyme (stroma), in response to testosterone, acting on epithelium to stimulate its proliferation, morphogenetic differentiation, and function. In return, the epithelium also exerts its paracrine effects on mesenchyme by regulating the differentiation and specific organizational pattern of its stromal smooth muscle. In a normal adult prostate, the maintenance of normal glandular structure and function is dependent not only on the constant presence of testosterone, but also on a normal intact and stable stroma. This chapter will concentrate first on factors involved in the normal development of the prostate gland and then on the aberrant changes in the homeostatic balance arising either from within (i.e., mutations) or outside (i.e., changes in hormonal balance) that result in derangements of the prostate gland. Finally, environmental and genetic factors that lead to prostate carcinogenesis including activation of oncogenes and mutations of tumor suppressor genes are also discussed.

Expression of G1-S modulators (p53, p16, p27, cyclin D1, Rb) and Smad4/Dpc4 in intrahepatic cholangiocarcinoma

Aberrations of G1-S cell cycle arrest and TGF-beta/Smad pathway are critical events in human carcinogenesis. We studied alterations of both pathways by immunohistochemical staining for p53, p16, p27, cyclin D1, Rb and Smad4/Dpc4 in 42 intrahepatic cholangiocarcinomas (ICCs). Abnormal nuclear overexpression of p53 and cyclin D1 was noted in 15 (35.7%) and 26 (61.9%) cases, respectively. Total loss of p16, p27, Rb and Smad4 was detected in 15 (35.7%), 13 (31.0%), 5 (11.9%) and 19 (45.2%) cases, respectively. Forty cases (95.2%) showed aberrations of at least one of the pathways, of which 21 (50%) revealed abnormality in G1-S pathway only, 17 (40.5%) had abnormalities in both pathways and 2 (4.8%) had an abnormality in TGF-beta/Smad pathway only. Among the examined genes, loss of Smad4 was found to have a positive relationship with the pTNM stage (P < 0.05). The overall stage of the high-altered group (alterations in 2 to 5 of the genes, n = 29) was significantly higher than that of the low-altered group (alteration of one or no gene, n = 13) (P < 0.01). We also examined the expression of above genes in the accompanying biliary dysplasia and found out abnormal expression of p53, cyclin D1 or p16 in 7 out of 13 dysplastic lesions. Our data suggest that abnormal G1-S cell cycle and altered TGF-beta/Smad pathway are major events in cholangiocarcinogenesis. Moreover, there might be a possible cumulative effect of the alterations in the examined genes upon the clinical outcome of patients with resectable ICCs.

Tumor suppression by a severely truncated species of retinoblastoma protein

Rb(+/+):Rb(-/-) chimeric mice are healthy until early in adulthood when they develop lethal pituitary tumors composed solely of Rb(-/-) cells. In an effort to delineate the minimal structures of the retinoblastoma protein necessary for RB tumor suppression function, chimeric animals derived from stably transfected RB(-/-) embryonic stem (ES) cells were generated. One such ES cell transfectant expressed a human RB allele encoding a stable, truncated nuclear derivative lacking residues 1 to 378 (Delta 1-378). Others encoded either wild-type human RB or an internally deleted derivative of the Delta 1-378 mutant. All gave rise to viable chimeric animals with comparable degrees of chimerism. However, unlike control mice derived, in part, from naive Rb(-/-) ES cells or from ES cells transformed by the double RB mutant, Delta 1-378/Delta exon22, animals derived from either wild-type RB- or Delta 1-378 RB-producing ES cells failed to develop pituitary tumors. Thus, in this setting, a substantial fraction of the RB sequence is unnecessary for RB-mediated tumor suppression.

An 800-kb region of deletion at 13q14 in human prostate and other carcinomas

Deletions of regions at 13q14 have been detected by various genetic approaches in human cancers including prostate cancer. Several studies have defined one region of loss of heterozygosity (LOH) at 13q14 that seems to reside in a DNA segment of 7.1 cM between genetic markers D13S263 and D13S153. To define the smallest region of overlap (SRO) for deletion at 13q14, we first applied tissue microdissection and multiplex PCR to detect homozygous deletion and/or hemizygous deletion at 13q14 in 134 prostate cancer specimens from 114 patients. We detected deletions at markers D13S1227, D13S1272, and A005O48 in 13 (10%) of these tumor specimens. Of the 13 tumors with deletions, 12 were either poorly differentiated primary tumors or metastases of prostate cancer. To fine-map the deletion region, we then constructed a high-resolution YAC/BAC/STS/EST physical map based on experimental and database analyses. Several markers encompassing the deletion region were analyzed for homozygous deletion and/or hemizygous deletion in 61 cell lines/xenografts derived from human cancers of the prostate, breast, ovary, endometrium, cervix, and bladder, and a region of deletion was defined by duplex PCR assay between markers A005X38 and WI-7773. We also analyzed LOH at 13q14 in the 61 cell lines/xenografts using the homozygosity mapping of deletion approach and 26 microsatellite markers. We found 24 (39%) of the cell lines/xenografts to show LOH at 13q14 and defined a region of LOH by markers M1 and M5. Combination of homozygous or hemizygous deletion and LOH results defined the SRO for deletion to be an 800-kb DNA interval between A005X38 and M5. There are six known genes located in or close to the SRO for deletion. This region of deletion is at least 2 Mb centromeric to the RB1 tumor-suppressor gene and the leukemia-associated genes 1 and 2, each of which is located at 13q14. These data suggest that the 800-kb DNA segment with deletion contains a gene whose deletion may be important for the development of prostate and other cancers. This study also provides a framework for the fine-mapping, cloning, and identification of a novel tumor-suppressor gene at 13q14.

Gene therapy for prostate cancer: current status and future prospects

PURPOSE

Locally advanced, relapsed and metastatic prostate cancer has a dismal prognosis with conventional therapies offering no more than palliation. In recent years advances achieved in understanding the molecular biology of cancer have afforded clinicians and scientists the opportunity to develop a range of novel genetic therapies for this disease.

MATERIALS AND METHODS

We performed a detailed review of published reports of gene therapy for prostate cancer. Particular emphasis was placed on recent developments in the arena of nonviral (plasmid DNA, DNA coated gold particles, liposomes and polymer DNA complexes) and viral (adenovirus, retrovirus, adeno-associated virus, herpes virus and pox virus) vectors. Therapeutic strategies were categorized as corrective, cytoreductive and immunomodulatory gene therapy for the purpose of data analysis and comparison.

RESULTS

Locoregional administration of nonviral and viral vectors can yield impressive local gene expression and therapeutic effects but to our knowledge no efficient systemically delivered vector is available to date. Corrective gene therapy to restore normal patterns of tumor suppressor gene (p53, Rb, p21 and p16) expression or negate the effect of mutated tumor promoting oncogenes (ras, myc, erbB2 and bcl-2) have efficacy in animal models but this approach suffers from the fact that each cancer cell must be targeted. A wide variety of cytoreductive strategies are under development, including suicide, anti-angiogenic, radioisotopic and pro-apoptotic gene therapies. Each approach has strengths and weaknesses, and may best be suited for use in combination. Immunomodulatory gene therapy seeks to generate an effective local immune response that translates to systemic antitumor activity. Currently most studies involve immunostimulatory cytokine genes, such as granulocyte-macrophage colony-stimulating factor, or interleukin-2 or 12.

CONCLUSIONS

Various therapeutic genes have proved activity against prostate cancer in vitro and in vivo. However, the chief challenge facing clinical gene therapy strategies is the lack of efficient gene delivery by local and systemic routes. For the foreseeable future vector development may remain a major focus of ongoing research. Despite this caveat it is anticipated that gene therapy approaches may significantly contribute to the management of prostate cancer in the future.

Replicating adenoviral vector-mediated transfer of a heat-inducible double suicide gene for gene therapy

Tumor cells that express a fusion gene of Escherichia coli cytosine deaminase (CD) and herpes simplex virus type 1 thymidine kinase (TK) sequences activate and are subsequently killed by the nontoxic prodrugs 5-fluorocytosine and ganciclovir. We have previously developed a recombinant adenovirus containing the CD-TK fusion gene controlled by the human inducible heat shock protein 70 promoter so that heat at 41 degrees C for 1 hour induces therapeutic gene expression. This adenovirus effectively transduces heat-inducible expression of the CD-TK gene into human prostate carcinoma cells. However, because a limited number of cells in a tumor can actually be infected, we created a replicating adenoviral vector to increase CD-TK gene expression. This vector is a replication-competent, E1B-attenuated adenoviral vector containing the hsp70 promoter-driven CD-TK gene (Ad.E1A(+)HS-CDTK). When human prostate adenocarcinoma DU-145 cells (mutant p53) were infected with the virus at a multiplicity of infection (MOI) of 1 or 10, the viral replication was detected within 2 days at both MOIs. Similar results were observed in human colorectal carcinoma CX-1 cells. When DU-145 cells were infected with the virus at an MOI of 10, incubated for 24 hours, heated at 41 degrees C for 4 hours, and then harvested 20 hours later, Western blot analysis demonstrated that this virus successfully produced viral E1A proteins and heat shock stimulated the CD-TK gene expression by 12.3-fold. In addition, Ad.E1A(+)HS-CDTK effectively suppressed cell proliferation by viral cytopathic effect). Unlike with a replication-incompetent virus (Ad.HS-CDTK), the cytopathic effect of the virus and cytotoxicity in the presence of the prodrugs were still observed even at low MOI (MOI=1.0).

Reduced expression of hMSH2 and hMLH1 and risk of prostate cancer: a case-control study

BACKGROUND

Although prostate cancer is the most common incident cancer in men, not much is known about its etiology. We tested the hypothesis that expression levels of hMSH2 and hMLH1 in unaffected (normal) tissue play a role in the etiology of prostate cancer.

METHODS

Total RNA was extracted from peripheral blood lymphocytes of subjects ascertained by a case-control study (70 patients and 97 age- and ethnicity-matched controls). A multiplex reverse transcription-polymerase chain reaction assay was used to simultaneously evaluate the relative expression of hMSH2 and hMLH1, using beta-actin as the internal control.

RESULTS

The relative gene expression levels of hMSH2 and hMLH1 were significantly lower in cases than in controls (P < 0.05 for both genes). When compared with the highest tertile of the controls, low expression levels (the middle and lowest tertiles) of hMLH1 were associated with significantly increased risk of prostate cancer in a dose-response relationship (ORs = 2.68, and 4.31; 95% confidence interval = 1.00-7.23 and 1.64-11.30, respectively) after adjustment for age, ethnicity, smoking status, and family history of prostate cancer.

CONCLUSIONS

These results suggest that reduced expression of hMLH1 in peripheral lymphocytes may be a risk factor for prostate cancer. However, it cannot be ruled out that the reduced expression we observed may be caused by the disease status. Our findings and the factors that may affect the expression of hMLH1 need further confirmation in larger prospective studies.

The use of multicolor fluorescence technologies in the characterization of prostate carcinoma cell lines: a comparison of multiplex fluorescence in situ hybridization and spectral karyotyping data

Recent studies have identified several chromosome regions that are altered in primary prostate cancer and prostatic carcinoma cell lines. These targeted regions may harbor genes involved in tumor suppression. We used multiplex fluorescence in situ hybridization (M-FISH) to screen for genetic rearrangements in four prostate cancer cell lines, LNCaP, LNCaP.FCG, DU145, and PC3, and compared our results with those recently obtained using spectral karyotyping (SKY). A number of differences was noted between abnormalities characterized by SKY and M-FISH, suggesting variation in karyotype evolution and characterization by these two methodologies. M-FISH analysis showed that hormone-resistant cell lines (DU145 and PC3) contained many genetic alterations (> or =15 per cell), suggesting high levels of genetic instability in hormone-refractory prostate cancer. Most chromosome regions previously implicated in prostate cancer were altered in one or more of these cell lines. Several specific chromosome aberrations were also detected, including a del(4)(p14) and a del(6)(q21) in the hormone-insensitive cell lines, a t(1;15)(p?;q?) in LNCaP, LNCaP, and PC3, and a i(5p) in LNCaP.FCG, DU145, and PC3. These clonal chromosome abnormalities may pinpoint gene loci associated with prostate tumourigenesis, cancer progression, and hormone sensitivity.

Growth factors and epithelial-stromal interactions in prostate cancer development

Epithelial-stromal interactions are important not only in growth, development, and functional cytodifferentiation of the prostate but also in derangements of prostate gland such as BPH and prostate carcinoma. This chapter explores the roles of epithelium and stroma during this delicate process and highlights the role and mutual influence of each on the other. It also examines the importance of ECM in mediating the effects of androgens and drawn attention to estrogen and genetic factors in the process. During this process of epithelial-stromal interaction, growth factors play a central role in mediating the interactions. This chapter focuses on the role of several growth factors including epidermal growth factor, fibroblast growth factor, transforming growth factor alpha, transforming growth factor beta, insulin-like growth factor-1, vascular endothelial growth factor, nerve growth factor, platelet-derived growth factor, and hepatocyte growth factor. This chapter emphasizes the importance of epithelial-stromal interactions in tumorigenesis and highlights the switch of paracrine to autocrine mode during the process of carcinogenesis.

Analysis of cyclin-dependent kinase inhibitor expression and methylation patterns in human prostate cancers

BACKGROUND

Downregulation of genes which negatively control cell cycle progression represents a possible mechanism for prostate tumorigenesis. We examined the expression levels of the p16, p15, p14, and retinoblastoma-susceptibility (RB) genes in primary prostate cancers and human prostate cancer cell lines, and correlated this with the DNA methylation levels of two loci in p16.

METHODS

The mRNA levels of p16, p15, and p14 were examined by reverse transcriptase-PCR (RT-PCR). DNA methylation of the p16 5' CpG island was determined by bisulfite genomic sequencing, while methylation of exon 2 shared by the p16 and p14 genes was measured by a quantitative bisulfite-based technique, methylation-sensitive single-nucleotide primer extension (Ms-SNuPE). RB protein levels were assessed by immunohistochemical staining of histologic sections of normal and tumor prostate tissues, using a monoclonal antibody (mAB).

RESULTS

Overexpression of p16 mRNA was found in 6/9 (67) of prostate tumors compared to the adjacent normal prostate, whereas elevated p14 and p15 levels were only observed in 2/9 (22) and 1/6 (17) of prostate cases, respectively. There was no statistically significant association of grade (P = 0.18) and stage (P = 1.00) of prostate cancer to the elevated p16 levels in the tumors. The p16 5' CpG island was completely unmethylated in these tissues. In contrast, exon 2 of p16/p14 was methylated in both the tumor and normal adjacent prostates, and was increased in 8/11 (73) of tumors relative to normal tissues. There was no association between p16 overexpression and increased p16/p14 exon 2 methylation in these tumors (P = 1.00). Diminished RB levels in prostate tumors that had upregulated p16 mRNA were found, although absent RB was also detected in tumors without elevated p16 levels. The expression levels of the two genes, RB and p16, were not correlated statistically (P = 0.16).

CONCLUSIONS

Our studies show that although the levels of the cell cycle regulators p16, p15, p14, and Rb are altered in prostate cancers, there is no apparent correlation to grade, stage, or any pattern of regulation between the related genes. Exon 2 of p16/p14 is methylated in a majority of prostate tumors compared to the unmethylated upstream 5' region, and may be a potential tumor marker for human prostate cancer.

Loss of heterozygosity at chromosome arm 13q and RB1 status in human prostate cancer

Aberrations of the long arm of chromosome 13 are common in prostate cancer and were initially attributed to alterations of the RB1 gene in band q14 of the chromosome. However, prostate tumors generally yield normal p110RB1 nuclear staining despite loss of heterozygosity (LOH) at the RB1 locus. Our previous analysis of chromosome arm 13q showed allelic loss in 41% of primary prostate tumors. To refine our knowledge of 13q, we extended our previous LOH study by using more polymorphic markers to analyze more prostate tumors. Sixty human prostate carcinomas were screened for allelic loss on 13q by using 13 13q-specific markers. LOH on the long arm of chromosome 13 was found in 39 (65%) of the 60 tumors. Furthermore, 33 of these 39 tumors had evidence of allelic loss involving a region of 13q14 containing RB1. Because immunohistochemical assessment of pRb expression is controversial in prostate tumors, we used a quantitative reverse transcription polymerase chain reaction (RT-PCR) method to determine whether RB1 is the target tumor suppressor gene in this region. RB1 mRNA steady-state levels were determined in 12 prostate tumors preselected on the basis of presumed deletion at the RB1 locus and four prostate tumors without LOH at the RB1 locus; five normal prostate specimens were used as controls. One of the 12 assessable prostate tumors with presumed LOH at RB1 showed a corresponding decreased in RB1 mRNA expression, whereas none of the four tumors without LOH at RB1 locus showed such a decrease. This study, based on another technical approach, confirms that RB1 is not the main target of the observed LOH at 13q14.3, and raises the possibility that another tumor suppressor gene in this region plays a key role in prostate cancer.