Identification of two distinct regions of allelic imbalance on chromosome 18Q in metastatic prostate cancer

A copy number gain on 18q present in primary prostate tumors is associated with metastatic outcome

BACKGROUND

Most prostate cancers (CaPs) grow slowly and remain indolent, yet some become aggressive and metastasize. Clinical decision-making requires prognostic markers that can be utilized at the time of diagnosis to identify aggressive tumors. Previous studies have shown a correlation between genomic alterations on the long arm of chromosome 18 (18q) and metastatic CaP.

OBJECTIVE

The goal of this study was to comprehensively profile copy number alterations found on 18q in prostate tumors with varying outcomes to identify putative biomarkers associated with more aggressive disease METHODS: A custom comparative genomic hybridization array was created composed of high-density tiling of 18q sequences. Primary prostate tumor tissues were gathered from men who underwent radical prostatectomy and were categorized based on the patient's long-term clinical outcome as either metastatic disease (MET) or no evidence of disease (NED). DNA was isolated from formalin-fixed, paraffin-embedded prostatectomy tumor tissues, and analyzed for copy number variations (CNVs). Protein levels of genes found within the region of CNVs were analyzed using immunohistochemistry.

RESULTS

Thirty-Four primary prostate tumors were analyzed: 17 NEDs and 17 METs. Two significant regions of copy number gains were found on 18q associated with outcome. One gain located at 18q11.2 was found exclusively in NED outcome tumors while another gain, located at 18q21.31, was found exclusively in MET outcome tumors (P -value< 0.0076). Immunohistochemistry analysis of protein levels showed more protein associated with copy number gain in the MET samples vs. those without the gain as indicated by H-scores of 184.7 and 121.0 respectively.

CONCLUSIONS

The latter of these CNVs represent a putative biomarker for aggressive disease and highlights a putative metastasis promoting gene. Further study of known connections to CaP suggests that the paracaspase MALT1 is the most likely target of the copy number gain and represents a potential therapeutic target. Future studies would be of interest to determine MALT1's role in aggressive CaP and the ability of this CNV region to differentiate CaP that will eventually metastasize.

Distinct genetic changes characterise multifocality and diverse histological subtypes in papillary thyroid carcinoma

AIMS

This study was undertaken to investigate the genetic factors underlying the development of multifocality and phenotypic diversity in multifocal papillary thyroid carcinoma (mPTC).

METHODS

Loss of heterozygosity (LOH) and BRAF(V600E) mutation status were analysed in a total of 55 individual tumour foci from 18 cases of mPTC. The genetic findings and morphology of tumour foci were then compared.

RESULTS

Multifocal PTC LOH rates were higher than observed previously in solitary PTC. Different patterns of LOH and BRAF(V600E) positivity separated follicular variant tumours and tumour foci from other PTC histological subtypes. In five cases, genetic alterations were detected in morphologically normal thyroid epithelium.

CONCLUSIONS

These findings support the concept that multifocal PTCs develop through clonal selection from a field of pre-neoplastic cells, with morphotype differentiation correlating with specific tumour-genetic alterations. The relatively high genetic disarray in multifocal PTC may underlie their ability to spread throughout the thyroid gland.

[Development of a three-dimensional primary prostate cancer cell culture model]

Much prostate cancer research is based on cell culture results. Recent genomic studies found major differences between primary prostate cancer tissue and established prostate cancer cell lines, which calls into question the clinical relevance of study results based on cell cultures.Using primary cultures of prostate cancer cells from prostatectomy specimens seems to be a reasonable solution, but primary cell cultures are much more difficult to establish. In this study, a primary cell culture model was combined with an invasion assay. With this combination it was possible not only to select invasive cell clones from the primary culture but also to culture these cells in a three-dimensional model, forming spheroids. A further characterization of this cell population was done by comparative genomic hybridization, showing numerous genetic alterations. The presented cell culture model offers, for the first time, an opportunity to isolate invasive growing cells from primary prostate cancer tissue and cultivate these cells for further analyses.

Allelic imbalance at 13q14.2 approximately q14.3 in localized prostate cancer is associated with early biochemical relapse

Allelic imbalance (AI), particularly at chromosomes 8p, 10q, and 13q, is the most frequently observed genetic change in sporadic prostate cancer. AI at these sites may inactivate tumor suppressor genes that regulate normal cell growth. To establish the relationship between AI and progression, we analyzed loci on 8p, 10q, and 13q14 in archival prostate tumors matched for Gleason grade, pre-operative prostate-specific antigen levels, and pathologic stage, and they were paired on the basis of relapse status after 3 years. AI was identified in 66% of patients without relapse and in 73% with relapse. There was no statistically significant difference for AI at 8p21.3 and 10q23.2 between the two groups of patients, but significant differences between relapsers and nonrelapsers in the frequency of AI at D13S165 at 13q14.2 (P=0.006) and D13S273 at 13q14.3 (P=0.03). There was also a significantly higher incidence of AI at both loci in the relapsers compared to the nonrelapsers (P=0.03). In three relapsers, AI occurred at all three loci between 13q14.2 and 13q14.3, with no nonrelapsers demonstrating AI at all three loci. These findings show that AI at 13q14.2 approximately q14.3 is an important event in the progression of localized prostate cancer, and suggest a possible role for microRNAs.

Genetic analysis of neuroendocrine tumor cells in prostatic carcinoma

BACKGROUND

Neuroendocrine differentiated tumor cells can be found in the majority of prostatic adenocarcinomas. During antiandrogen or androgen-withdrawal therapy the neuroendocrine differentiation is often increased but its prognostic value is discussed controversially. The origin of neuroendocrine tumor cells is under discussion. While double staining experiments suggest a non-neoplastic pluripotent stem cell, in vitro studies demonstrate a transdifferentiation of exocrine tumor cells to a neuroendocrine phenotype.

METHODS

Neuroendocrine differentiated LNCaP cells and laser captured microdissected cells of eight radical prostatectomies were allelotyped using 11 microsatellite markers from seven different loci.

RESULTS

Identical allelic profiles were detected in untreated and neuroendocrine differentiated LNCaP cells for all markers confirming their clonality. Neuroendocrine and exocrine tumor cells from radical prostatectomies shared identical allelic profiles for all markers, suggesting a common origin for both cell populations.

CONCLUSIONS

Our results support the concept of transdifferentiation of exocrine tumor cells to a neuroendocrine tumor cell phenotype.

Chromosome 18 suppresses tumorigenic properties of human prostate cancer cells

Although prostate cancer is still the most diagnosed cancer in men, most genes implicated in its progression are yet to be identified. Chromosome abnormalities have been detected in human prostate tumors, many of them associated with prostate cancer progression. Indeed, alterations (including deletions or amplifications) of more than 15 human chromosomes have been reported in prostate cancer. We hypothesized that transferring normal human chromosomes into human prostate cancer cells would interfere with their tumorigenic and/or metastatic properties. We used microcell-mediated chromosome transfer to introduce human chromosomes 10, 12, 17, and 18 into highly tumorigenic (PC-3M-Pro4) and highly metastatic (PC-3M-LN4) PC-3-derived cell lines. We tested the in vitro and in vivo properties of these hybrids. Introducing chromosome 18 into the PC-3M-LN4 prostate cancer cell line greatly reduced its tumorigenic phenotype. We observed retarded growth in soft agar, decreased invasiveness through Matrigel, and delayed tumor growth into nude mice, both subcutaneously and orthotopically. This phenotype is associated with a marker in the 18q21 region. Combined with the loss of human chromosome 18 regions often seen in patients with advanced prostate cancer, our results show that chromosome 18 encodes one or more tumor-suppressor genes whose inactivation contributes to prostate cancer progression.

Genetic pathways and new progression markers for prostate cancer suggested by microsatellite allelotyping

PURPOSE

At diagnosis, the biological behavior of prostate cancer is uncertain, making the choice of an adequate therapy option difficult. Performing microsatellite allelotyping on a large series of consecutive prostate cancers procured during radical prostatectomy at our institution, we sought to identify molecular markers associated with disease progression.

EXPERIMENTAL DESIGN

A total of 156 consecutive fresh tumor samples was prospectively collected and macroscopically dissected from the whole prostatectomy specimen immediately after operation. Histologically 100 samples contained >75% tumor cells and were therefore enrolled in the microsatellite allelotyping, using a total of 24 polymorphic markers for the chromosomal regions 5p, 5q, 7q, 8p, 9p, 9q, 13q, 17p, 17q, and 18q. Fresh paired normal and tumor DNA was investigated in fluorescent microsatellite analysis with automated laser product detection.

RESULTS

The incidence of tumor-DNA alterations [loss of heterozygosity or allelic imbalance (AI)] was highest for chromosomal regions 13q and 8p with 72 and 71%, respectively, followed by chromosomes 7q, 18q, 5q, and 17p with 57, 53, 41, and 39%, respectively. Alterations at chromosomes 8p, 9p, 13q, and 17p were significantly (P < 0.05) associated with advanced tumor stage, whereas AI at 8p and 17p was also associated with high Gleason score (P < 0.05). AI at 5q and 9p was associated with regional lymph node metastasis (P < 0.05). The combination of AI at 8p and 13q was strongly associated with advanced tumor stage (P < 0.0001).

CONCLUSIONS

With the obtained results, we are able to postulate three distinct pathways in prostate carcinogenesis, and we identified microsatellite markers of prognostic value.

Chromosome 18 suppresses prostate cancer metastases

Loss of heterozygosity and allelic imbalance data has shown that there are two distinct regions of loss on chromosome 18q associated with the progression of prostate cancer (CaP). To investigate the functional significance of chromosome 18q loci in CaP, we utilized the technique of microcell-mediated chromosome transfer to introduce an intact chromosome 18 into the human prostate cancer cell line, PC-3. Three of the resulting hybrid lines were compared to the PC-3 cells in vitro and in vivo. The hybrid cell lines, containing an intact copy of the introduced chromosome 18, exhibited a substantial reduction in anchorage-dependent and independent growth in vitro. These hybrid cell lines also made smaller tumors in nude mice following subcutaneous injection compared to PC-3 cells. Because tumor growth was not completely eliminated by introduction of chromosome 18, we assessed the ability of the hybrids to metastasize to bone after intra-cardiac inoculation in a nude mouse model. Mice inoculated with PC-3 hybrids containing intact copies of chromosome 18 had significantly fewer bone metastases and dramatically improved survival compared to PC-3 cells. In addition, the introduction of chromosome 18 significantly reduced tumor burden in extraskeletal sites. This was not because of differences in growth rates because mice bearing hybrids were monitored for metastases over twice as long as mice bearing PC-3 cells. Taken together, these data suggest that chromosome 18 has a functional role in CaP to suppress growth and metastases. Identification of the responsible gene(s) may lead to molecular targets for drug discovery.

Genetic evidence for a novel human desmosomal cadherin, desmoglein 4

Desmosomes are essential adhesion structures in most epithelia that link the intermediate filament network of one cell to its neighbor, thereby forming a strong bond. The molecular components of desmosomes belong to the cadherin superfamily, the plakin family, and the armadillo repeat protein family. The desmosomal cadherins are calcium-dependent transmembrane adhesion molecules and comprise the desmogleins and desmocollins. To date, three human desmoglein isoforms have been characterized, namely desmogleins 1, 2, and 3 that are expressed in a tissue- and differentiation-specific manner. Here we have identified and characterized, at the genetic level, a novel human desmoglein cDNA sharing homology with desmogleins 1, 2, 3 and we name this desmoglein 4. The human desmoglein 4 cDNA (3.6 kb) contains an open reading frame of 3120 bp that encodes a precursor protein of 1040 amino acids. The predicted mature protein comprises 991 amino acids with a molecular weight of 107822 Da at pI 4.38. Human desmoglein 4 shares 41% identity with human desmoglein 1, 37% with human desmoglein 2, and 50% with human desmoglein 3. Analysis of the exon/intron organization of the human desmoglein 4 gene (DSG4) demonstrates that it is composed of 16 exons spanning approximately 37 kb of 18q12 and is situated between DSG1 and DSG3. We have demonstrated using RT-PCR on multiple tissue cDNA samples that desmoglein 4 has very specific tissue expression in salivary gland, testis, prostate, and skin.

Genome-wide detection of LOH in prostate cancer using human SNP microarray technology

Loss of heterozygosity (LOH) of chromosomal regions is crucial in tumor progression. In this study we assessed the potential of the Affymetrix GeneChip HuSNP mapping assay for detecting genome-wide LOH in prostate tumors. We analyzed two human prostate cell lines, P69SV40Tag (P69) and its tumorigenic subline, M12, and 11 prostate cancer cases. The M12 cells showed LOH in chromosomes 3p12.1-p22.1, 11q22.1-q24.2, 19p13.12, and 19q13.42. All of the prostate cases with informative single-nucleotide polymorphism (SNP) markers showed LOH in 1p31.2, 10q11.21, 12p13.1, 16q23.1-q23.2, 17p13.3, 17q21.31, and 21q21.2. Additionally, a high percentage of cases showed LOH at 6p25.1-p25.3 (75%), 8p22-p23.2, and 10q22.1 (70%). Several tumor suppressor genes (TSGs) have been mapped in these loci. These results demonstrate that the HuSNP mapping assay can serve as an alternative to comparative genomic hybridization for assessing genome-wide LOH and can identify chromosomal regions harboring candidate TSGs implicated in prostate cancer.

Current status of the molecular genetics of human prostatic adenocarcinomas

Molecular genetic mechanisms involved in the progression of prostate cancer are not well understood due to extensive tumor heterogeneity and lack of suitable models. New methods such as fluorescence in-situ hybridization (FISH), comparative genomic hybridization (CGH) and microsatellite analysis have documented losses or gains on various chromosomes. Altered chromosomal regions have been associated with the activation of oncogenes and the inactivation of tumor suppressor genes or defects in mismatch repair (MMR) genes. It is suggested that increased genomic instability is associated with decreased androgen-responsive and progressive behavior of human prostate tumors, but it remains unclear whether this genomic instability is causing the progression of cancer or is the consequence of cancer. Extended studies on hereditary prostate cancer have identified 7 prostate cancer susceptibility loci on several chromosomes, but no specific gene has been confined for a large proportion of susceptibility. In this review we summarize the ongoing molecular genetic events associated with the sporadic and hereditary prostate cancer development and progression.

Androgen receptor length polymorphism associated with prostate cancer risk in Hispanic men

PURPOSE

The transcriptional activation domain of the androgen receptor gene includes a CAG repeat length polymorphism. A smaller number of repeats is reported to increase the risk of prostate cancer. We investigated the association of CAG repeat length and the risk of prostate cancer in a case-control study of Hispanic men.

MATERIALS AND METHODS

To estimate the magnitude of the association of repeat length with prostate cancer risk, samples from 82 white patients of Hispanic origin (Hispanic) with prostate cancer and 145 Hispanic controls were genotyped. To determine the allelic distribution of repeats by race/ethnicity we genotyped 132 black men, 163 white men of nonHispanic origin (white) and 175 Hispanic men with no family history of prostate cancer, and performed pairwise comparison.

RESULTS

In the case-control study of Hispanic men with a repeat length of 18 or less versus greater than 18 we found an approximately 3-fold increased risk of prostate cancer (OR 2.7, 95% CI 1.21 to 6.01, t test p = 0.013, age adjusted OR 3.03, 95% CI 1.27 to 7.26). The distribution of alleles differed significantly by race/ethnicity. The mean prevalence of short CAG repeat alleles plus or minus SD was higher in black than in white men (19.8 +/- 3.2 versus 21.8 +/- 2.7, t test p <0.0001) and lower in Hispanic men than in other white men (22.7 +/- 3.3, t test p = 0.014).

CONCLUSIONS

To our knowledge, our study represents the first case-control study of the androgen receptor gene in a Hispanic population and provides evidence of the increased prostate cancer risk associated with short CAG repeats. Our results suggest that short CAG repeats are associated with an increased prostate cancer risk in Hispanic men.

Chromosomal aberrations related to metastasis of human solid tumors

The central role of sequential accumulation of genetic alterations during the development of cancer has been firmly established since the pioneering cytogenetic studies successfully defined recurrent chromosome changes in specific types of tumor. In the course of carcinogenesis, cells experience several genetic alterations that are associated with the transition from a preneoplastic lesion to an invasive tumor and finally to the metastatic state. Tumor progression is characterized by stepwise accumulation of genetic alterations. So does the dominant metastatic clone. Modern molecular genetic analyses have clarified that genomic changes accumulate during the development and progression of cancers. In comparison with the corresponding primary tumor, additional events of chromosomal aberrations (including gains or allelic losses) are frequently found in metastases, and the incidence of combined chromosomal alterations in the primary tumor, plus the occurrence of additional aberrations in the distant metastases, correlated significantly with decreased postmetastatic survival. The deletions at 3p, 4p, 6q, 8p, 10q, 11p, 11q, 12p, 13q, 16q, 17p, 18q, 21q, and 22q, as well as the over-representations at 1q, 8q, 9q, 14q and 15q, have been found to associate preferentially with the metastatic phenotype of human cancers. Among of them, the deletions on chromosomes 8p, 17p, 11p and 13p seem to be more significant, and more detail fine regions of them, including 8p11, 8p21-12, 8p22, 8p23, 17p13.3, 11p15.5, and 13q12-13 have been suggested harboring metastasis-suppressor genes. During the past decade, several human chromosomes have been functionally tested through the use of microcell-mediated chromosome transfer (MMCT), and metastasis-suppressor activities have been reported on chromosomes 1, 6, 7, 8, 10, 11, 12, 16, and 17. However, it is not actually known at what stage of the metastatic cascade these alterations have occurred. There is still controversial with the association between the chromosomal aberrations and the metastatic phenotype of cancer. As the progression of human genome project and the establishment of more and more new techniques, it is hopeful to make clear the genetic mechanisms involved in the tumor metastasis in a not very long future, and provide new clues to predicting and controlling the metastasis.

Delineation and candidate gene mutation screening of the 18q22 minimal region of deletion in head and neck squamous cell carcinoma

The 18q chromosome arm is frequently lost in advanced head and neck squamous cell carcinoma. Twenty-four microsatellite markers located on chromosome 18q were genotyped in 145 primary tumors and 10 cell lines in order to identify putative tumor suppressor genes implicated in tumor progression. Two different minimal common regions of loss (MCRL) were identified at 18q22 and 18q23 respectively. To refine and delineate boundaries of an homozygous deletion found in one cell line, 44 extra markers located at 18q22 were analysed and the homozygous deletion was precisely defined within a critical region of 4.9 Mb. Four known genes (CDH7, CDH19, DNAM-1, FLJ23594) located in this critical region and two EST clusters (Hs.96900, Hs.98628) were selected for further investigations. For these six genes, genomic structures were established, somatic mutations were screened in 20 HNSCC and 10 cell lines and transcription levels were determined in eight cell lines. No somatic mutations were found in any of the candidate genes analysed (57 coding exons). However, differential transcription levels were observed for CDH19 and Hs.96900 in head and neck cancer cell lines supporting their putative involvement through down regulation mechanisms in head and neck cancer progression.

Permanent phenotypic and genotypic changes of prostate cancer cells cultured in a three-dimensional rotating-wall vessel

A three-dimensional (3D) integrated rotating-wall vessel cell-culture system was used to evaluate the interaction between a human prostate cancer cell line, LNCaP, and microcarrier beads alone, or microcarrier beads previously seeded with either prostate or bone stromal cells. Upon coculture of LNCaP cells with microcarrier beads either in the presence or in the absence of prostate or bone stromal cells, 3D prostate organoids were formed with the expected hormonal responsiveness to androgen, increased cell growth, and prostate-specific antigen production. In this communication, we define permanent phenotypic and genotypic changes of LNCaP cells upon coculture with microcarrier beads alone, or with microcarrier beads previously seeded with either prostate or bone stromal cells. Most notably, we observed selective genetic changes, i.e., chromosomal losses or gains, as evaluated by both conventional cytogenetic and comparative genomic hybridization, in LNCaP sublines derived from the prostate organoids. Moreover, the derivative LNCaP cells appear to have altered growth profiles, and exhibit permanent and stable changes in response to androgen, estrogen, and growth factors. The derivative LNCaP sublines showed increased anchorage-independent growth rate, and enhanced tumorigenicity and metastatic potential when inoculated orthotopically in castrated athymic mice. Our results support the hypothesis that further nonrandom genetic and phenotypic changes in prostate cancer epithelial cells can occur through an event that resembles "adaptive mutation" such as has been described in bacteria subjected to nutritional starvation. The occurrence of such permanent changes may be highly contact dependent, and appears to be driven by specific microenvironmental factors surrounding the tumor cell epithelium grown as 3D prostate organoids.

Chromosome 18 suppresses the tumorigenicity of prostate cancer cells

Microcell-mediated chromosome transfer allows for the introduction of normal chromosomes into tumor cells in an effort to identify putative tumor suppressor genes. We have used this approach to introduce an intact copy of chromosome 18 into the prostate cancer cell line DU145, and independently to introduce human chromosomes 8 and 18 into the prostate cancer cell line TSU-PR1. Introduction of an extra copy of human chromosome 8 had no effect on the growth properties in vitro or the tumorigenicity in vivo of TSU-PR1 cells. However, microcell hybrids containing an introduced copy of human chromosome 18 exhibited a longer population doubling time, retarded growth in soft agar, and slowed tumor growth in athymic nude mice. These experiments provide functional evidence for the presence of one or more tumor suppressor genes on human chromosome 18 that are involved in prostate cancer.