Molecular disorders in transitional vs. peripheral zone prostate adenocarcinoma

Prostate zones and cancer: lost in transition?

Localized prostate cancer shows great clinical, genetic and environmental heterogeneity; however, prostate cancer treatment is currently guided solely by clinical staging, serum PSA levels and histology. Increasingly, the roles of differential genomics, multifocality and spatial distribution in tumorigenesis are being considered to further personalize treatment. The human prostate is divided into three zones based on its histological features: the peripheral zone (PZ), the transition zone (TZ) and the central zone (CZ). Each zone has variable prostate cancer incidence, prognosis and outcomes, with TZ prostate tumours having better clinical outcomes than PZ and CZ tumours. Molecular and cell biological studies can improve understanding of the unique molecular, genomic and zonal cell type features that underlie the differences in tumour progression and aggression between the zones. The unique biology of each zonal tumour type could help to guide individualized treatment and patient risk stratification.

Population-based study of the association of variants in mismatch repair genes with prostate cancer risk and outcomes

BACKGROUND

Mismatch repair (MMR) gene activity may be associated with prostate cancer risk and outcomes. This study evaluated whether single nucleotide polymorphisms (SNP) in key MMR genes are related to prostate cancer outcomes.

METHODS

Data from two population-based case-control studies of prostate cancer among Caucasian and African-American men residing in King County, Washington were combined for this analysis. Cases (n = 1,458) were diagnosed with prostate cancer in 1993 to 1996 or 2002 to 2005 and were identified through the Seattle-Puget Sound Surveillance Epidemiology and End Results cancer registry. Controls (n = 1,351) were age-matched to cases and were identified through random digit dialing. Logistic regression was used to assess the relationship between haplotype-tagging SNPs and prostate cancer risk and disease aggressiveness. Cox proportional hazards regression was used to assess the relationship between SNPs and prostate cancer recurrence and prostate cancer-specific death.

RESULTS

Nineteen SNPs were evaluated in the key MMR genes: five in MLH1, 10 in MSH2, and 4 in PMS2. Among Caucasian men, one SNP in MLH1 (rs9852810) was associated with overall prostate cancer risk [odds ratio, 1.21; 95% confidence interval (95% CI), 1.02, 1.44; P = 0.03], more aggressive prostate cancer (odds ratio, 1.49; 95% CI, 1.15, 1.91; P < 0.01), and prostate cancer recurrence (hazard ratio, 1.83; 95% CI, 1.18, 2.86; P < 0.01), but not prostate cancer-specific mortality. A nonsynonymous coding SNP in MLH1, rs1799977 (I219V), was also found to be associated with more aggressive disease. These results did not remain significant after adjusting for multiple comparisons.

CONCLUSION

This population-based case-control study provides evidence for a possible association with a gene variant in MLH1 in relation to the risk of overall prostate cancer, more aggressive disease, and prostate cancer recurrence, which warrants replication.

Function of JunB in transient amplifying cell senescence and progression of human prostate cancer

PURPOSE

Replicative senescence in cells acts as a barrier against excessive proliferation and carcinogenesis. Transient amplifying cells (TAC) are a subset of basal cell populations within the prostate from which cancers are thought to originate; therefore, we focused on prostate TAC to investigate the molecular mechanisms by which the TAC may be able to evade senescence.

EXPERIMENTAL DESIGN

TAC clones were isolated from each zone within the whole prostate and analyzed in flow cytometry. Prostate cancer cells were transfected with junB small interfering RNA (siRNA) and examined by chorioallantoic membrane assay for cancer invasion. Immunohistochemical analysis was done in primary and metastatic prostate cancer specimens.

RESULTS

TAC populations showed increased expression of p53, p21, p16, and pRb, resulting in senescence. TAC clones with reduced p16 expression successfully bypassed this phase. We further found close correlation between the levels of junB and p16 expression. Repeated transfection of junB siRNA in prostatic TAC allowed the cells to escape senescence presumably through inactivation of p16/pRb. The chorioallantoic membrane invasion assay showed much lower in invasive cancer cells with high expression of junB; conversely, silencing of junB by transfection with junB siRNA promoted invasion. We also found that metastatic prostate cancers, as well as cancers with high Gleason scores, showed significantly low junB immunopositivity.

CONCLUSIONS

JunB is an essential upstream regulator of p16 and contributes to maintain cell senescence that blocks malignant transformation of TAC. JunB thus apparently plays an important role in controlling prostate carcinogenesis and may be a new target for cancer prevention and therapy.

Chromosomal imbalances, loss of heterozygosity, and immunohistochemical expression of TP53, RB1, and PTEN in intraductal cancer, intraepithelial neoplasia, and invasive adenocarcinoma of the prostate

Recent studies have shown that intraductal prostate carcinoma (IDC-P) should be considered as a separate lesion distinct from prostatic intraepithelial neoplasia (PIN). The purpose of the present study was to analyze the genetic relationship between benign prostatic tissue, PIN, invasive cancer, IDC-P, and extracapsular tumor tissue to get further information about the role of IDC-P in the development of prostate cancer. One hundred five radical prostatectomy specimens were investigated immunohistochemically, 77 cases were analyzed by PCR for LOH of the tumor suppressor genes TP53 and RB1, and 11 cases of IDC-P and 10 cases of PIN were investigated using comparative genomic hybridization (CGH). At CGH analysis, IDC-P showed several chromosomal imbalances in contrast to PIN, where no changes were found. We could demonstrate a significant increase of LOH for TP53 or RB1 from benign tissue to PIN. LOH of both TP53 and RB1 were frequently found in IDC-P (52%), followed by extracapsular tumor tissue (44%), invasive cancer (24%), PIN (19%), and benign prostatic tissue (17%). Increased immunohistochemical expression was found in invasive cancer for TP53, RB1, and for PTEN. Decreased expression could be demonstrated in extracapsular tumor tissue and in IDC-P. Our results indicate that IDC-P in general follows the genetic pathway from normal epithelium over PIN lesion. IDC-P represents a separate prostatic lesion and should be graded as a poorly differentiated carcinoma.

Elevated levels of the mismatch repair protein PMS2 are associated with prostate cancer

BACKGROUND

Defects in mismatch repair (MMR) proteins have been identified in various types of cancer. However, an association with prostate cancer has been controversial. Defective MMR results in genome instability with detrimental consequences that significantly contribute to tumorigenesis. This study determined alterations in key MMR protein levels in prostate cancer with the goal to identify prognostic markers.

METHODS

Prostatectomy samples were immunohistochemically stained and the relative presence or absence of key proteins MSH2, MLH1, and PMS2 determined. Cancer tissue of distinct grades was compared with the normal surrounding tissue. Microsatellite instability (MSI) in altered tissues was determined according to NCI guidelines.

RESULTS

In contrast to reports that associate a lack of individual MMR proteins with tumorigenesis, a significant increase in PMS2 levels was identified in PIN lesions and prostate cancer tissue. This elevation in PMS2 was independent of changes in levels in its heterodimeric partner, MLH1. Prostate tumors with elevated levels of PMS2 were genetically unstable, which was corrected by MLH1 co-elevation.

CONCLUSIONS

This is the first documentation of detrimental consequences associated with the increase in a MMR protein in human cancer. This study recognizes PMS2 elevation as a prognostic marker in pre-neoplastic and prostate cancer lesions. This result has significant implications for future diagnostic and treatment measures.

Analysis of differences in clinicopathological features between prostate cancers located in the transition and peripheral zones

BACKGROUND

The objective of this study was to retrospectively characterize differences in the clinicopathological features of prostate cancer according to the zonal origin.

METHODS

Among 185 consecutive patients who underwent radical prostatectomy without any neoadjuvant hormonal therapies, this study included 134 patients who were diagnosed as having either transition zone (TZ) or peripheral zone (PZ) cancer according to the following criteria: TZ or PZ cancers were considered when more than 70% of the cancer area was located in the TZ or PZ, respectively. The various clinicopathological features were then compared according to this classification.

RESULTS

In this series, 27 patients were diagnosed as having TZ cancer, while the remaining 107 were diagnosed as having PZ cancer. The percent of positive biopsy cores in TZ cancers was significantly lower than that in PZ cancers; however, there were no significant differences in the anatomical location of positive cores between these two groups except for the middle of prostate where TZ cancer showed a significantly lower rate of positive biopsies than PZ cancer. The preoperative serum prostate-specific antigen (PSA) value in patients with TZ cancer was significantly higher than that in those with PZ cancer. Furthermore, tumor volume in TZ cancers was significantly greater than that in PZ cancers. However, there was no significant difference in biochemical recurrence-free survival between patients with TZ and PZ cancers.

CONCLUSIONS

Despite the significantly high PSA value as well as great tumor volume compared with those of PZ cancers, TZ cancers had similar biochemical cure rates following radical prostatectomy, suggesting a less aggressive phenotype of TZ cancers than that of PZ cancers.

Gene expression profiling of the human prostate zones

OBJECTIVE

To investigate differences in gene expression in different zones of the prostate by microarray analyses, to better understand why aggressive tumours predominantly occur in the peripheral zone (PZ), whereas benign prostatic hyperplasia (BPH) occurs almost exclusively in the transition zone (TZ).

MATERIALS AND METHODS

Expression profiling of both prostate zones was done by microarray analysis. Reverse transcription-polymerase chain reaction (RT-PCR) of the top 18 genes confirmed the microarray analyses. RT-PCR with common cell-type markers indicated that the differential expression between the zones was not caused by an unequal distribution of different cell types. Primary stromal and epithelial prostate cells were used to study cell type expression in the 12 highest differentially expressed zonal-specific genes.

RESULTS

In all, 346 genes were identified as preferentially expressed in the TZ or PZ. A few of the TZ-specific genes, including ASPA, FLJ10970 and COCH, were also stroma-specific. Comparisons with other microarray studies showed that gene expression profiles of prostate cancer and BPH correlate with the expression profiles of the PZ and TZ, respectively.

CONCLUSION

Gene expression differs between the PZ and TZ of the prostate, and stromal-epithelial interactions might be responsible for the distinct zonal localization of prostate diseases.

Microsatellite instability and mismatch repair target gene mutations in cell lines and xenografts of prostate cancer

BACKGROUND

Mismatch repair (MMR) and microsatellite instability (MSI) occur in prostate cancer, but their role has not been well documented.

METHODS

In 6 cell lines and 22 xenografts from prostate cancer, PCR and gel electrophoresis were performed to detect MSI by analyzing microsatellite markers BAT-25 and BAT-26 and to detect frameshift mutations in mononucleotide repeats in BAX, IGF2R, MSH3, MSH6, and TGFBR2.

RESULTS

Four of 6 (67%) cell lines and 3 of 22 (14%) xenografts showed MSI. At least 1 frameshift mutation was detected in the same 4 (67%) cell lines and in 5 of 22 (23%) xenografts. While MSH3 was frequently mutated in cell lines, BAX and TGFBR2 showed frequent alterations in both cell lines and xenografts.

CONCLUSIONS

MSI related to MMR deficiency is relatively frequent in high-grade tumors, and mutations in MSI target genes involved in cell death and proliferation appeared to be selected for during prostatic carcinogenesis.

A comparison of the biological features between prostate cancers arising in the transition and peripheral zones

OBJECTIVES

To investigate differences in the biological features of prostate cancer according to the zonal origin.

PATIENTS AND METHODS

Among 172 consecutive patients who had a radical prostatectomy (RP), the study included 124 diagnosed as having either transition zone (TZ) or peripheral zone (PZ) cancer, defined according to whether there was > 70% of the cancer area in the TZ or PZ, respectively. The clinicopathological features were then compared between these groups. In addition, the RP specimens were stained immunohistochemically with antibodies to Ki-67, Bcl-2, matrix metalloproteinase-2 (MMP-2), MMP-9 and vascular endothelial growth factor (VEGF).

RESULTS

Twenty-four patients were diagnosed as having TZ cancer and the remaining 100 as having PZ cancer. Prostate specific antigen (PSA) values in patients with TZ cancer were significantly higher than in those with PZ cancer. Tumour volume in TZ cancer was significantly greater than that in PZ cancer, but there was no significant difference in biochemical recurrence-free survival between the groups. Immunohistochemistry showed that despite there being no differences in Bcl-2 and VEGF expression between TZ and PZ cancers, there was significantly greater expression of Ki-67, MMP-2 and MMP-9 in PZ than TZ cancers.

CONCLUSIONS

Despite there being no significant difference in biochemical recurrence-free survival after RP between patients with TZ and PZ cancers, there was less cell proliferation and biomarker levels related to invasive potential in TZ than in PZ cancers.

Comparison of the zones of the human prostate with the seminal vesicle: morphology, immunohistochemistry, and cell kinetics

BACKGROUND

The prostate contains three glandular zones (central, peripheral, transition) with widely differing susceptibilities to cancer and benign prostatic hyperplasia (BPH). Most of the prostate is derived from urogenital sinus, but the central zone may be derived from Wolffian duct, in common with the seminal vesicles (SV). The peripheral zone is the most frequent site of cancer and the transition zone is the almost exclusive site of BPH.

METHOD

We compared the histology and immunohistochemistry of the SV with those of the prostate zones in order to identify differences associated with susceptibility to disease or different embryological origins. Sections from the prostates of nine organ donors (aged 15-36) were stained for tissue-specific markers, antigens previously shown to stain differentially between the zones and markers of cell proliferation and cell death.

RESULTS

Neuroendocrine cells were absent from the SV and significantly fewer neuroendocrine cells were seen in the central zone compared to the peripheral zone. Most of the SV epithelium stained for lactoferrin, compared to approximately one-third of central zone and only 2% of peripheral zone epithelial cells. The proliferative index of the central zone was approximately 50% lower and the incidence of apoptotic cells approximately half that of the peripheral and transition zones.

CONCLUSIONS

The central zone has features in common with both the SV and the other zones of the prostate. The higher incidence of proliferative diseases in the transition and peripheral zones may be associated with the higher rate of cell turnover observed in these zones.

Molecular biology of prostate cancer

Development of any cancer reflects a progressive accumulation of alterations in various genes. Oncogenes, tumour suppressor genes, DNA repair genes and metastasis suppressor genes have been investigated in prostate cancer. Here, we review current understanding of the molecular biology of prostate cancer. Detailed understanding of the molecular basis of prostate cancer will provide insights into the aetiology and prognosis of the disease, and suggest avenues for therapeutic intervention in the future.