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[Cancer Research 64, 5963-5972, September 1, 2004]
© 2004 American Association for Cancer Research


Regular Articles

Molecular Features of the Transition from Prostatic Intraepithelial Neoplasia (PIN) to Prostate Cancer

Genome-wide Gene-expression Profiles of Prostate Cancers and PINs

Shingo Ashida1,2, Hidewaki Nakagawa1, Toyomasa Katagiri1, Mutsuo Furihata3, Megumi Iiizumi1, Yoshio Anazawa1, Tatsuhiko Tsunoda4, Ryo Takata1,6, Kotaro Kasahara2, Tsuneharu Miki5, Tomoaki Fujioka6, Taro Shuin2 and Yusuke Nakamura1

1 Laboratory of Molecular Medicine, Human Genome Center, Institute of Medical Science, The University of Tokyo, Tokyo; Departments of 2 Urology, and 3 Tumor Pathology, Kochi Medical School, Nankoku; 4 Laboratory for Medical Informatics, SNP Research Center, RIKEN (Institute of Physical and Chemical Research), Yokohama; 5 Department of Urology, Kyoto Prefectural University of Medicine, Kyoto; and 6 Department of Urology, Iwate Medical University, Morioka, Japan.


    ABSTRACT
 Top
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
To characterize the molecular feature in prostate carcinogenesis and the putative transition from prostatic intraepithelial neoplasia (PIN) to invasive prostate cancer (PC), we analyzed gene-expression profiles of 20 PCs and 10 high-grade PINs with a cDNA microarray representing 23,040 genes. Considering the histological heterogeneity of PCs and the minimal nature of PIN lesions, we applied laser microbeam microdissection to purify populations of PC and PIN cells, and then compared their expression profiles with those of corresponding normal prostatic epithelium also purified by laser microbeam microdissection. A hierarchical clustering analysis separated the PC group from the PIN group, except for three tumors that were morphologically defined as one very-high-grade PIN and two low-grade PCs, suggesting that PINs and PCs share some molecular features and supporting the hypothesis of PIN-to-PC transition. On the basis of this hypothesis, we identified 21 up-regulated genes and 63 down-regulated genes commonly in PINs and PCs compared with normal epithelium, which were considered to be involved in the presumably early stage of prostatic carcinogenesis. They included AMACR, OR51E2, RODH, and SMS. Furthermore, we identified 41 up-regulated genes and 98 down-regulated genes in the transition from PINs to PCs; those altered genes, such as POV1, CDKN2C, EPHA4, APOD, FASN, ITGB2, LAMB2, PLAU, and TIMP1, included elements that are likely to be involved in cell adhesion or the motility of invasive PC cells. The down-regulation of EPHA4 by small interfering RNA in PC cells lead to attenuation of PC cell viability. These data provide clues to the molecular mechanisms underlying prostatic carcinogenesis, and suggest candidate genes the products of which might serve as molecular targets for the prevention and treatment of PC.


    INTRODUCTION
 Top
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Prostate cancer (PC) is the most common malignancy in males and the second-leading cause of cancer-related deaths in the United States and Europe (1) . Despite surgery and radiation therapy that often cure localized disease, and the possibility of early diagnosis through testing for prostate-specific antigen in serum, up to 30% of treated PC patients suffer relapse (2, 3, 4) . Most patients with relapsed or advanced disease initially respond to androgen-ablation therapy because early PC growth is androgen dependent, but they eventually progress to androgen-independent disease, which no longer responds to androgen ablation. The most important issue to be solved in this context is that this advanced stage of PC does not respond to other therapies either.

Investigations designed to clarify the molecular mechanisms that underlie the initiation and progression of PC have revealed altered expression of PTEN, p27KIPS, and Nkx3.1 tumor suppressor genes, the c-myc oncogene, and the Bcl-2 antiapoptotic gene in human and/or mouse PCs (5 , 6) . However, the overall molecular events are still largely unknown. High-grade PIN (prostatic intraepithelial neoplasia) has been considered to be a putative precursor of cancer (7) , and some clinical and scientific evidence supports a relationship between high-grade PINs and PCs. However, that hypothesis is still controversial (8 , 9) . Added to the difficulties of proving a PIN-to-PC transition is that human PCs are histopathologically very heterogeneous, and PIN is generally a very small lesion. Most previous molecular-based studies have analyzed bulk cancer tissues that were contaminated by a large proportion of noncancerous cells including fibromascular, microvasculature, and inflammatory cells, but such strategies do not yield precise molecular profiles of the respective lesions.

To overcome that limitation, we obtained purified populations of PC and PIN cells, as well as normal prostatic epithelial cells as a control, by LMM (laser microbeam microdissection), before analyzing genome-wide gene-expression profiles of 20 PCs and 10 PINs on a cDNA microarray representing 23,040 genes. This is the first report to show precise expression profiles of PC and PIN tumors, and to disclose molecular features confirming a relationship between PINs and PCs.


    MATERIALS AND METHODS
 Top
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Patients and Tissue Samples.
Tissue samples were obtained with informed consent from 26 cancer patients undergoing radical prostatectomy. All of the surgical specimens were at clinical stages T2a to T3a with or without N1, and their Gleason scores were 5–9. All of the samples were embedded in TissueTek OCT medium (Sakura, Tokyo, Japan) immediately after surgical resection and stored at –80°C until use. Histopathological diagnoses were made by a single pathologist (M. F.) before LMM. H&E-stained sections from adjacent frozen tissues were prepared to confirm the histological diagnosis. High-grade PINs included in the surgical specimen of PC were characterized and identified by the following criteria: (a) a basal cell layer consistently enveloped the intraductal/acinar proliferation; and (b) atypical cells that had large nuclei of relatively uniform size increased the chromatin content, which might be irregularly distributed, and had prominent nucleoli that were similar to those of carcinoma cells (7 , 10) . Once high-grade PIN cells, PC cells, and normal epithelium were identified by H&E study, we microdissected them by LMM from the adjacent frozen slides. Normal prostatic epithelial cells were microdissected from the prostatic lobe opposite to the prostate cancer, or the normal prostatic tissue apparently far from the cancer. From among the 26 resected tissues, 20 cancers and 10 high-grade PINs had sufficient amounts and quality of RNA for microarray analysis.

Laser Microbeam Microdissection and T7-based RNA Amplification.
LMM and T7-based RNA amplification were performed as described previously (11) . Prostate tumor cells and normal prostatic epithelial cells were isolated selectively by the EZ cut system with a pulsed UV narrow beam-focus laser (SL Microtest GmbH, Germany) in accordance with the manufacturer’s protocols. After DNase treatment, total RNAs were subjected to two rounds of T7-based amplification, which yielded 50 to 100 µg of amplified RNA (3) from each sample. Then 2.5-µg aliquots of amplified RNA from PC or PIN cells and from normal prostatic ductal epithelial cells were labeled by reverse transcription with Cy5-dCTP (tumor cells) or Cy3-dCTP (normal cells (Amersham Biosciences, Buckinghamshire, United Kingdom), as described previously (12) .

cDNA Microarray Analysis and Acquisition of Data.
We fabricated a genome-wide cDNA microarray with 23,040 cDNAs selected from the UniGene database (build no.131) of the National Center for Biotechnology Information (NCBI).7 Construction, hybridization, washing, and scanning were carried out according to methods described previously (11 , 12) . Signal intensities of Cy3 and Cy5 from the 23,040 spots were quantified and analyzed by substituting backgrounds with ArrayVision software (Imaging Research, Inc., St. Catharines, Ontario, Canada). Subsequently, the fluorescent intensities of Cy5 (tumor) and Cy3 (control) for each target spot were adjusted so that the mean Cy3/Cy5 ratio of 52 housekeeping genes was equal to one. Because data derived from low-signal intensities are less reliable, we determined a cutoff value on each slide (12) , and we excluded genes from further analysis when both the Cy3 and the Cy5 dyes yielded signal intensities lower than that of the cutoff. For other genes, we calculated the Cy5/Cy3 ratio using the raw data of each sample.

Cluster Analysis of 20 Prostate Cancers and 10 PINs According to Gene-expression Profiles.
We applied a hierarchical clustering method to both genes and tumors, excluding genes whose Cy3- and Cy5-fluorescence intensities were both below the cutoff value. To obtain reproducible clusters for classification of the 30 tumors, we selected 63 genes for which valid data were obtained in 80% of the experiments and whose expression ratios varied by SDs of more than 1.5. The analysis was performed with web-available software (Cluster and TreeView) written by Eisen.8 Before applying the clustering algorithm, we log-transformed the fluorescence ratio for each spot and then median-centered the data for each sample to remove experimental biases.

Identification of Genes That Were Up- or Down-regulated Commonly from Normal Epithelium to PINs and PCs.
We identified genes the expression of which was altered from normal epithelium to 10 PINs and 20 PCs according to the following criteria: (a) genes for which we were able to obtain expression data in more than 50% of the cases examined; and (b) genes the expression ratio of which was more than 3.0 or less than 0.33 in more than 50% of informative cases.

Identification of Genes That Were Up- or Down-regulated from PINs to PCs.
We identified genes with changed expression in 20 PCs and 10 PINs according to the following criteria: (a) genes for which we were able to obtain expression data in more than 50% of the cases examined; and (b) genes the expression ratio of which was more than 3.0 in PCs and between 0.5 and 2.0 in PINs (defined as up-regulated genes) or genes whose expression ratio was less than 0.33 in cancers and between 0.5 and 2.0 in PINs (defined as down-regulated genes) in more than 50% of informative cases.

Immunohistochemistry.
Formalin-fixed and paraffin-embedded prostatic tumor sections were immunostained with a mouse anti-APOD (apolipoprotein D) monoclonal antibody (NeoMarkers, Fremont, CA) or a rabbit anti-EPHA4 (EphA4) polyclonal antibody (Santa Cruz Biotechnology Inc., Santa Cruz, CA) for APOD or EPHA4 expression. PC tissues included PC cells, PIN cells, and normal prostatic epithelium heterogeneously. Deparaffinized tissue sections were placed in 10 mmol/L citrate buffer (pH 6.0) and were heated to 108°C in an autoclave for 15 minutes for antigen retrieval. Sections were incubated with a 1:10 dilution or a 1:100 dilution of primary antibody for APOD or EPHA4, respectively, in a humidity chamber for 1 hour at room temperature and were developed with peroxidase labeled-dextran polymer followed by diaminobenzidine (DAKO Envision Plus System; DAKO Corporation, Carpinteria, CA). Sections were counterstained with hematoxylin. For negative controls, primary antibody was omitted.

Small Interfering RNA-expressing Constructs and Colony Formation/MTT Assay.
We used small interfering RNA (siRNA)-expression vector (psiU6BX) for RNA interference effect to the target genes. The U6 promoter was cloned upstream of the gene-specific sequence (19-nucleotide sequence from the target transcript, separated by a short spacer TTCAAGAGA from the reverse complement of the same sequence) and five thymidines as a termination signal as well as neocassette for selection with Geneticin (Sigma). The target sequences for EphA4 are 5'-TCCGAACCTACCAAGTGTG-3' (198si), 5'-TCATGAAGCTGAACACCGA-3' (468si) and 5'-GCAGCACCATCATCCATTG-3' (1313si). The sequence of 5'-GAAGCAGCACGACTTCTTC-3' (EGFPsi) corresponding to EGFP was as a negative control. PC3 PC cells were plated onto 10-cm dishes (5 x 105 cells/dish) and transfected with psiU6BX containing EGFP target sequence (EGFP) or psiU6BX containing EPHA4 target sequence with LipofectAMINE 2000 (Invitrogen) according to the manufacturer’s instruction. Cells were selected by 500 µg/mL Geneticin for 1 week, harvested 48 hours after transfection, and analyzed by reverse transcription (RT)-PCR to validate knockdown effect on EPHA4. The primers of RT-PCR were 5'-GAAGGCGTGGTCACTAAATGTAA-3' and 5'- TTTAATTTCAGAGGGCGAAGAC-3' for EPHA4, and 5'-GAGAGAGAATGAAAAGTGGAGCA-3' and 5'-GATTAACCACAACCATGCCTTAC-3' for ß2-MG, used to quantify the amount of cDNA input. These cells were also stained by Giemsa solution and applied for 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay to evaluate the colony formation and the cell number, respectively.


    RESULTS
 Top
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Hierarchical Clustering Analyses of Expression Patterns in PCs and PINs.
To avoid contamination of PC or PIN tissues with stromal cells as much as possible, we performed LMM of 26 surgical specimens of PCs. Because PCs and PINs originate from prostatic epithelial ductal cells, we also purified normal ductal epithelial cells as controls for our microarray study. Normal prostatic ductal cells, PC cells (PC), and PIN cells (PIN) were clearly microdissected from each clinical specimen as shown (N) in Fig. 1Citation .



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Fig. 1. Laser microbeam microdissection. Normal prostatic ductal epithelial cells (N), prostate cancer cells (PC), and prostatic intraepithelial neoplasia cells (PIN) from a single specimen (patient 16) were microdissected from H&E-stained sections. Lane A, premicrodissected tissue; Lane B, postmicrodissected tissue; Lane C, microdissected cells.

 
RNA from each microdissected specimen was amplified for analysis on a genome-wide cDNA microarray. We generated the expression profiles of 30 prostatic tumors (20 PCs and 10 PINs) from 26 patients (cancer and PIN coexisted in four patients, in which cases both lesions were examined). On the basis of expression patterns of 63 genes that we selected applying strict conditions (i.e., valid data obtained in 80% of the experiments and expression ratios that varied by SDs of more than 1.5), all of the tumors fell into two major groups according to their status of malignancy in an unsupervised way, except for three cases (Fig. 2A)Citation in which two PCs (12T and 20T) with low Gleason scores (score 5) were included in the branch corresponding to the PIN group, and one PIN (23PIN) belonged to the PC group. Histological re-examination of this misplaced PIN diagnosed it as a very-high-grade PIN (Fig. 2B)Citation that pathologically resembled PC and probably represented a transitional lesion to invasive PC. These experiments showed that, although it was generally possible to distinguish PC from PIN by molecular classification on the basis of expression profiles, the distinction was not as obvious as we expected, and some molecular features were commonly shared. These results offered considerable validity to the concept that high-grade PINs can become invasive PCs.



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Fig. 2. A, dendrogram of unsupervised clustering analysis of 63 genes (vertical axis) across 30 prostatic tumors (horizontal axis). Red, the transcript level above the median for that gene across all samples; green, below the median for that gene across all samples; black, unchanged expression; gray, no detectable expression. In the horizontal axis, PCs and PINs were separated in two trunks (column A on left and column B on right); above top of dendrogram, numbers below patient identification numbers, Gleason scores. In the vertical axis, the 63 genes were clustered in different branches according to similarities in relative expression ratios. Genes that appear more than once, identical genes spotted on different sets of slides. B, histological examination of samples from patient 23PIN, which fell in the PC cluster on the basis of its molecular profile. This tumor was later confirmed to be a very-high-grade PIN.

 
Identification of Genes That Were Up- or Down-regulated Commonly in PINs and PCs As Compared with Normal Epithelium.
Because we have obtained supportive evidence for the concept that PIN is a precursor of invasive PC through our hierarchical-clustering analysis of molecular profiles, it seemed likely that genes involved in an early stage of prostatic carcinogenesis would be deregulated from normal epithelium to PIN and also their deregulation should be retained in PCs (Fig. 3A)Citation . On the basis of this hypothesis of prostatic carcinogenesis, we identified 21 genes that were commonly up-regulated in PINs and PCs according to the criteria mentioned in Materials and Methods (Fig. 3ACitation ; Table 1Citation ); they included AMACR, OR51E2, RODH and SMS. On the other hand, 63 genes were selected as commonly down-regulated in PINs and PCs (Fig. 3ACitation ; Table 2Citation ); that list included several proteinases such as SERPINB1, SERPING1, and MMP7.



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Fig. 3. In A, 21 genes were up-regulated (21 up) and 63 genes were down-regulated (63 down) commonly in PINs and PCs as genes involved in an early step of prostatic carcinogenesis. In B, on the other hand, 41 genes were up-regulated (41 up) and 98 genes were down-regulated (98 down) in the transition from PINs to PCs. Red, the transcript level up-regulated compared with normal prostatic epithelial cells; green, the transcript level down-regulated compared with normal prostatic epithelial cells; black, unchanged expression; gray, no detectable expression. The detail of the genes in the gene lists that were differentially expressed in each step of this prostatic carcinogenesis hypothesis are shown in Tables 1Citation 2Citation 3Citation 4Citation Citation . C, immunohistochemical analysis of genes, apolipoprotein D (APOD) and EPHA4, which were identified to be differentially expressed in the transition from PIN to PC in B. APOD was abundantly expressed in PC cells, whereas PINs and normal prostatic epithelium (N) from the same patient showed no expression of APOD protein. The EPHA4 protein was also strongly expressed in PC cells, whereas PINs and normal prostatic epithelium (N) from the same patient showed no, or very weak, expression of EPHA4 protein. The PC, PIN, and normal prostate epithelium were included on one PC tissue. x200.

 

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Table 1 Up-regulated genes from normal epithelium to prostate tumors (PINs and PCs)

 

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Table 2 Down-regulated genes from normal epithelium to prostate tumors (PINs and PCs)

 
Identification of Genes Up- or Down-regulated during Malignant Transformation from PINs to Prostate Cancers.
We then focused on differential expression patterns between PINs and PCs to search for genes likely to be involved in the transition from non-invasive precursor PINs to malignant cancers (Fig. 3B)Citation . Comparing the expression profiles of 20 PCs with those of 10 PINs, we identified 41 up-regulated genes (Table 3)Citation and 98 down-regulated genes (Table 4)Citation Citation . The list included POV1, CDKN2C, EPHA4, APOD, FASN, and VWF as up-regulated, and ITGB2, LAMB2, PLAU, and TIMP1 as down-regulated; the altered genes might be involved with cell adhesion or motility in invasive PC cells.


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Table 3 Up-regulated genes in the transition from PIN to PC

 

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Table 4 Down-regulated genes in the transition from PIN to PC

 

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Table 4A Continued

 
To validate the differential expression pattern in the transition from PIN to PC, we performed immunohistochemical analysis of apolipoprotein D (APOD) and EPHA4, listed in Table 3Citation as up-regulated genes in the PIN-to-PC transition. In general, PC tissues include PC cells, PIN cells, and normal prostatic epithelium heterogeneously, and we compared the staining pattern of each kind of cells associated with prostatic carcinogenesis on the same tissues from the same patient. As shown in Fig. 3CCitation , APOD was abundantly expressed in PC cells, whereas PINs and normal prostatic epithelium from the same patient had no expression of APOD protein. The EPHA4 protein was also strongly expressed in PC cells while PINs and normal prostatic epithelium from the same patient had no, or very weak, expression of EPHA4 protein.

Growth Suppression Mediated by EPHA4-specific siRNA in Prostate Cancer Cells.
To investigate the growth or survival effect of EPHA4 on PC cells, we knocked down their endogenous expression by mammalian vector-based RNA interference technique by using the PC cell line. The transfection of one of the siRNA-expressing vectors, 1313si, clearly reduced the endogenous expression of EPHA4 (Fig. 4A)Citation . This knocking-down effect by the siRNA on EPHA4 mRNA resulted in drastic growth suppression in colony formation assay as well as in MTT assay (Fig. 4B and C)Citation . These findings strongly suggested that overexpression of EPHA4 in PC cells was associated with the enhanced growth of cancer cells.



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Fig. 4. Knocking-down effect of EPHA4 in PC cell line by siRNA. In A, RT-PCR experiments indicate knockdown effect of EPHA4 mRNA by transfection of siRNA expression vectors 1313si, but not 198si, 468si1, or EGFPsi. Each of the sequences of 198si, 468si, and 1313si corresponded to a part of the EPHA4 sequence, and that of EGFPsi corresponded to a part of the EGFP sequence. Cells were harvested 48 hours after transfection and analyzed. ß2-MG was used as the quantitative standard. In B, colony formation assay showed a drastic decrease of colony numbers in PC cells 1 week after transfection with 1313si. In C, MTT assay also showed the drastic decrease of the number of PC cells transfected with 1313si, but not with 198si, 468si1, or EGFPsi. *, P 0.01. (ABS, antibodies)

 

    DISCUSSION
 Top
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
PC is one of the most common malignant diseases in Western countries. A number of research groups have investigated gene-expression profiles of PCs (13, 14, 15, 16) , but the results presented here are markedly different from theirs. Compared with a meta-analysis of four representative microarray datasets (17) , only three (7.5%) of the 40 genes listed as being commonly up-regulated in PCs, and seven (17.5%) of the 40 down-regulated genes, coincided with our data. We attribute these discrepancies to the fact that prostate tumors are histopathologically very heterogeneous, containing a large proportion of stromal cells, and expression profiles from bulk tissues could be substantially influenced by contamination with surrounding noncancerous cells and by the proportions of various cell types. For example, genes that are highly expressed in stromal cells, but not in epithelial cells, may be selected as down-regulated elements in microarray analyses of bulk tissues, because stromal components are less abundant in cancer tissues than in normal prostate (~17 versus 60%; ref. 15 ). SDF1 (stromal cell-derived factor 1), which is highly expressed in stroma, showed low signal (under the cutoff) in our experiments (data not shown). However, Stamey et al. (15) reported that gene as down-regulated in PCs, probably because stromal components were present in the normal control. Similarly, genes that are expressed in normal epithelial cells and cancer cells, but not in stromal cells, may be selected as up-regulated elements during microarray analysis of bulk tissue if noncancerous epithelial cells are enriched in the tumor tissue. For instance, PRSS8 (prostasin) was reportedly up-regulated in many microarray studies that used bulk tissues (17) , but in our experiments, expression of this gene was either unchanged or down-regulated in some PCs as compared with normal epithelium. PRSS8 is predominantly expressed in normal prostatic epithelial cells; several studies using in situ techniques have revealed its down-regulation in PC cells (18 , 19) . These observations make clear that contamination of cancer tissues with stromal cells or normal prostate epithelium can mislead efforts to understand the molecular pathology of PC; therefore, microdissection is definitely required for precision in microarray analyses of PCs. In this study, we applied the LMM system (11) to purify populations of cancer cells, PIN cells, and normal prostatic epithelial cells from surgical specimens, in an effort to obviate influences from stromal components and normal prostate.

Several lines of clinical and pathological evidence have linked PINs to PCs, and high-grade PIN has been widely considered the precursor of invasive PC (8 , 10) . PINs and PCs can show certain genetic alterations in common (20) . However, some data have argued against this hypothesis; for example, early-stage PCs are not always accompanied by PIN (9 , 10) and some genetic markers of PINs are not always observed in PCs (21) . Hence, considerable controversy has arisen about the natural history of high-grade PIN and the mechanism of PIN development, and the putative transition from PIN to invasive PC has remained unsettled.

We analyzed the precise molecular profiles of purified populations of PC and PIN cells to investigate the molecular mechanism of prostate carcinogenesis and to examine the molecular linkage between PINs and PCs. Our unsupervised hierarchical clustering analysis was able to distinguish most PCs from PINs on the basis of their expression profiles, although two low-grade PCs with Gleason scores of 5 fell in the PIN cluster and one high-grade PIN was classified into the PC group. The latter turned out to be a very-high-grade PIN in a retrospective histological review and probably represented a transitional lesion to invasive PC. These results implied that the gene-expression profile of very-high-grade PIN is very similar to that of PC, supporting the concept that at least some high-grade PINs are precursors of PC. It should also be added that prostate pathologists have long recognized a phenomenon in which PC spreads along prostatic ducts to mimic PIN (22) . In fact, an early controversy that arose when the concept of PIN was first introduced was that the lesions merely reflected intraductal spread of invasive cancer. Except for the one PIN case, our microarray data comparing PIN cells with PC cells rejects this criticism and clearly supports the concept that PINs are precursor lesions of PC, not ductal spread of PC cells.

We identified genes that were up- or down-regulated (Tables 1Citation and 2Citation ) commonly in PINs and PCs comparing with normal epithelium; those genes may be involved in an early step of prostatic carcinogenesis. The up-regulated elements in PINs and PCs included AMACR ({alpha}-methyl acyl-CoA racemase), OR51E2 (olfactory receptor, family 51, subfamily E, member 2), RDOH (3-hydroxysteroid epimerase), and SMS (spermine synthase). AMACR has a key role in ß-oxidation of dietary branched-chain fatty acids and is often overexpressed in PCs (23 , 24) . OR51E2 is also overexpressed in PCs (25) , but its function is unknown. RDOH functions in androgen catabolism and is likely to be associated with androgen-dependent prostate tumorigenesis. SMS is a polyamine-biosynthesis enzyme; polyamines such as spermine have been implicated in the growth of PC cells and protection from apoptosis (26) . On the other hand, SERPIN-B1 [serine (or cysteine) proteinase inhibitor, clade B (ovalbumin) member 1] and SERPIN-G1 [serine (or cysteine) proteinase inhibitor, clade G (ovalbumin), member 1] were down-regulated from normal prostate epithelium to PIN. The pigment epithelium-derived factor encoded by SERPIN-F1 was recently reported to be a key inhibitor of stromal vasculature and growth of epithelial tissue in mouse prostate (27) ; in pigment epithelium-derived factor-deficient mice, stromal vessels were increased and associated with epithelial-cell hyperplasia. Those observations suggest to us that SERPIN-B1 and SERPIN-G1 may also be key regulators of prostate growth. Almost all genes that were up- or down-regulated in PINs were also up- or down-regulated, respectively, in PCs compared with normal prostate epithelium, implying that PCs retain the molecular features of their putative precursor PINs. These data supported the notion of PIN-to-PC transition.

Next, we focused on genes showing differential expression after the transition from PINs to PCs (see Fig. 3BCitation ; Tables 3Citation and 4Citation Citation ). The list included POV1, CDKN2C, EPHA4, APOD, and FAM as up-regulated genes and LAMB2, ITGB2, PLAU, and TIMP1 as down-regulated genes. EPHA4 is one of the receptor tyrosine kinase receptors and is likely to play a critical role in neuronal circuit development and angiogenesis by regulating cell shape and motility (28) . However, EPHA4 overexpression in PCs is novel and may involve PC cell viability and motility. Some of the latter are associated with cell adhesion and proteinase activity, suggesting that their expression changes may contribute to the invasive phenotype by abolishing ductal structures during the transition from PIN to PC. We validated the differential expression of APOD and EPHA4 by the immunohistochemical analysis on several PC tissues (Fig. 3C)Citation , which was consistent with our precise RNA profiles and indicated that our profile analysis was highly reliable.

Furthermore, we investigated by the small interfering RNA strategy whether overexpression of EPHA4 was associated with enhanced growth of PC cells. As shown in Fig. 4Citation , down-regulation of EPHA4 in PC cell line resulted in a drastic reduction in PC cell viability, suggesting that the overexpression of EPHA4 in the transition of PIN to PC cells is likely to be essential in PC cell growth, indicating that targeting to EPHA4 may be a promising approach to develop novel PC treatments.

Overall, it is interesting that our lists of differentially expressed genes in prostate carcinogenesis via PINs to invasive PCs included many genes associated with lipid metabolism, including AMACR, FASN (fatty acid synthase), MFGE8 (milk fat globule-EGF factor 8 protein), APOD (apolipoprotein D), APOL1 (apolipoprotein L1), PLA2G2A (phospholipase A2, group IIA), and SORL1 (sortilin-related receptor L). Epidemiological aspects suggest that the development of PC is strongly associated with high fat intake (1) ; our data concerning these genes may help to explain the apparent association between fat intake and prostate carcinogenesis.

In conclusion, our extensive list of genes derived from precise expression profiles of PCs and PINs should provide useful information for identifying molecular targets for the prevention and treatment of PC, as well as for understanding the molecular mechanism of prostatic carcinogenesis, especially the transition from PIN to PC.


    ACKNOWLEDGMENTS
 
We thank Noriko Sudo, Saori Osawa, and Miwako Ando for fabrication of the cDNA microarray; Emi Ichihashi for analysis of the data; Tae Makino and Noriko Ikawa for preparation of samples by cryostat; and Drs. Soji Kakiuchi and Takefumi Kikuchi for helpful discussions.


    FOOTNOTES
 
Grant support: Supported in part by Research for the Future Program Grant 00L01402 from the Japan Society for the Promotion of Science (Y. Nakamura).

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Requests for reprints: Y. Nakamura. Laboratory of Molecular Medicine, Human Genome Center, Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108--8639, Japan. Phone: 81-3-5449-5372; Fax: 81-3-5449-5433; E-mail: yusuke{at}ims.u-tokyo.ac.jp

7 Internet address of database: http://www.ncbi.nlm.nih.gov. Back

8 Internet address: http://genome-www5.stanford.edu/MicroArray/SMD/restech.html. Back

Received 1/ 5/04. Revised 6/ 8/04. Accepted 6/21/04.


    REFERENCES
 Top
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 

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