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Short Communications |






From the Departments of Urology, Kimmel Cancer Center,*
Pathology and Cell Biology,
and Microbiology
and Immunology,
Jefferson Medical College of
Thomas Jefferson University, Philadelphia, Pennsylvania; and the
Department of Urology,§
University of Padova,
Padua, Italy
| Abstract |
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| Introduction |
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Deletions of the short arm of chromosome 3 (3p) have been detected by loss of heterozygosity (LOH) and cytogenetic studies in TCC of the bladder.11-13 Three discrete regions spanning 3p1214, 3p2124, and 3p2426 often have been shown to be deleted, suggesting that these regions might harbor genes that are important in the development of TCC.13 Vieten et al12 have developed an in vitro multistep model of human uroepithelial transformation. In a study of chromosome 3 losses associated specifically with immortalization of five independent human papillomavirus-transformed urothelial cell lines, the smallest common region of deletion was 3p14.114.2. These results suggest that loss of a gene(s) in this region may be responsible for immortalization of the uroepithelial cells.
We cloned the tumor suppressor gene FHIT at 3p14.2,14 one of the most frequently deleted chromosomal regions in TCC of the bladder.11 FHIT gene lies on a region of over 1 Mb of chromosome 3p14.2 that encompasses the FRA3B fragile region and encodes a protein of 147 amino acids (16.8 kd) with diadenosine triphosphate hydrolase activity.15 A papillomavirus insertion site,16 plasmid integration sites,17 and cancer-specific translocation18,19 have been mapped within the FRA3B fragile site in the FHIT gene.
The purpose of this report is to show that loss of expression of the Fhit protein occurs in the majority of transitional cell carcinomas of the bladder, suggesting that loss of FHIT function plays a critical role in bladder carcinogenesis.
| Materials and Methods |
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TCC-derived cell lines (SW780, T24, Hs228T, CRL7930, CRL7833, HBT9) and 293 human kidney cells were obtained from the American Type Culture Collection (ATCC) and were maintained in the recommended media. A total of 30 transurethrally resected transitional carcinomas of the bladder were obtained from the Department of Urology, Jefferson Medical College of Thomas Jefferson University (Philadelphia, PA). Samples were taken immediately after resection and snap frozen in liquid nitrogen. In addition, sections from 85 formalin-fixed, paraffin-embedded specimens of TCC of the bladder were obtained from archival blocks of radical cystectomy cases. Forty-one of these specimens came from the Department of Urology, University of Padova (Padua, Italy), and 44 specimens came from the Department of Urology, Jefferson Medical College of Thomas Jefferson University. All samples were obtained from patients who gave informed consent to use excess pathological specimens for research purposes.
RNA Extraction and cDNA Synthesis
RNA was extracted from six TCC-derived cell lines (SW780, T24, Hs228T, CRL7930, CRL7833, HBT9) and from 30 frozen tissue samples with an RNeasy mini Kit (Qiagen, Valencia, CA), according to the manufacturers protocol. cDNA was synthesized from 2 µg of total RNA. Reverse transcription (RT) was carried out in a 22-µl volume with 300 units of Superscript II (Life Technologies, Gaithersburg, MD), 500 ng/µl oligo(dT), and 50 ng/µl random hexamers. The reaction was incubated at 42°C for 50 minutes and then was boiled for 5 minutes. The final reaction was diluted with distilled water to 30 µl, and 1 µl of cDNA was used for PCR in consecutive rounds of amplification with FHIT-specific nested primer pairs 5U2/3D2 and 5U1/3D1, as described previously.14
Amplified DNA fragments corresponding with full-sized and aberrant FHIT transcripts in the cell lines were excised from agarose gel, purified, and sequenced directly. Sequence analysis was performed on 373A and 377 DNA sequencers (Applied Biosystems, Foster City, CA.)
DNA Analysis
DNA from six TCC-derived cell lines (SW780, T24, Hs228T, CRL7930,
CRL7833, HBT9) was extracted by standard techniques and amplified by
PCR, using oligonucleotide primer pairs for 10 loci within introns 3
(12f/r for 1; 09f/r for 2), 4 (06f/r for 3; 03f/r for 4; Col10kf/r for
5; 0817EF/ER for 6), and 5 (36C3/36C4 for 7; N143kf/r for 8; N100Kf/r
for 9; N020Kf/r for 10) and for exons 5, 7, 8, and 9 of the
FHIT gene (Figure 1)
. PCR
amplification reactions were performed in a 25-µl volume, using 100
µg of template, 1 unit of Taq polymerase (Takara, Pan Vera
Corp., Madison, WI), 20 ng of primers, and 0.5 mmol/L of each
deoxynucleoside triphosphate. Amplifications were carried out in
a Perkin-Elmer thermal cycler for 35 cycles of 94°C for 20 seconds
(for denaturation), 57°C for 30 seconds (varied for specific primer
pairs), and 72°C for 30 seconds (for extension).
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Protein Extraction and Immunoblot Analysis
Cell lines from which protein was extracted were pelleted and rinsed with phosphate-buffered saline (PBS) (Gibco, Grand Island, NY) and were lysed in 400 µl of protein lysis buffer (10 mmol/L Tris, 1% NP-40, 0.1% bovine serum albumin, 1 mmol/L EDTA, PBS) and 50 µl phenylmethylsulfonyl fluoride (PMSF) (125 mmol/L PMSF in ethanol) on ice for 5 minutes. After a 6-minute centrifugation at 8500 rpm at room temperature, the lysate supernatant was removed and was assayed for protein concentration with the Protein Assay reagent (Bio-Rad Laboratories, Melville, NY). Protein was aliquoted and stored at -80°C.
For Western analysis, 100 µg of protein was boiled in loading buffer containing 5% sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), glycerol, bromophenol blue, and ß-mercaptoethanol for denaturing. Samples were electrophoresed on 420% precast Tris-glycine gels (Fisher Scientific, Pittsburgh, PA) with the Mini Protean II electrophoresis system (Bio-Rad Laboratories) and subsequently transferred to a nitrocellulose membrane (MSI, Westborough, MA) with the Mini trans-Blot cell apparatus (Bio-Rad Laboratories). Membranes were blocked for 3 hours at room temperature in 5% nonfat dry milk dissolved in TBS-T (Tris-buffered saline Tween20). Primary and secondary antibodies were diluted in 5% nonfat dry milk solution. Western analysis was performed overnight at 4°C with a 1:1000 dilution of the Fhit polyclonal antibody (Zymed Laboratories, San Francisco, CA). Secondary antibody solution (1:2000 dilution) containing anti-rabbit immunoglobulin labeled with horseradish peroxidase (Amersham Life Sciences, Buckinghamshire, England) was applied for 1 hour at room temperature. Membranes were treated with enhanced chemiluminescence detection reagents (Amersham Life Sciences) according to the manufacturers recommended protocol. Bands were detected by exposing the membrane to medical X-ray film (Fuji, Stamford, CT) for 110 minutes at room temperature.
Blots were stripped in a solution containing 100 mmol/L ß-mercaptoethanol, 2% SDS, and 62.5 mmol/L Tris-HCl (pH 6.7) for 30 minutes at 60°C. They were rinsed in TBS-T and reprobed for protein standardization under the previously mentioned conditions, with ß-actin (Sigma, St. Louis, MO) as the primary antibody and a 1:2000 dilution of the anti-mouse secondary antibody labeled with horseradish peroxidase (Amersham Life Sciences), and exposed for 1 minute at room temperature before the film was developed.
Immunohistochemistry
Routine deparaffinization of all sections mounted on positive charge slides was carried out according to standard procedures, followed by rehydration through an ethanol series. The slides were immersed in citrate buffer (0.01 mol/L sodium citrate, pH 6.0) and heated in a microwave oven at 600 W (three times for 5 minutes) to enhance antigen retrieval. Endogenous peroxidase was blocked with 0.3% hydrogen peroxidase in methanol for 30 minutes. The sections were then incubated with anti-Fhit antibody, 1:1000 dilution (Zymed Laboratories) overnight at room temperature. The primary antibody was omitted and replaced by PBS in the negative control. After this incubation, sections were treated with biotinylated anti-rabbit antibody and streptavidin-biotin-peroxidase (Histostain-SP Kit; Zymed Laboratories). Antibody localization was detected, with diaminobenzidine as a chromogen substrate. Finally, sections were washed in distilled water and weakly counterstained with Harrys modified hematoxylin.20
Statistical Analysis
We used the Fisher exact test with a two-tailed P for analysis of statistical significance of correlation between clinicopathological parameters and Fhit expression.
| Results |
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To determine whether genomic deletions occur in TCC cell lines, we analyzed six TCC-derived cell lines (SW780, T24, Hs228T, HBT9, CRL7833, CRL7930) by PCR amplification, using oligonucleotide primers appropriate for 10 STSs placed in introns 3, 4, and 5 and for exons 5, 7, 8, and 9 of the FHIT gene.
Three cell lines (SW780, CRL7930, CRL7833) exhibit discontinuous
homozygous deletions. As shown in Figure 1
, the fragments that are
commonly deleted overlap with regions of the FHIT gene that
were deleted in previously reported cancer-derived cell
lines.14,19
Homozygous deletions did not include
FHIT exons 5, 7, 8, and 9.
The three cell lines with homozygous deletions within the FHIT gene are the same three cell lines showing both absent or abnormal FHIT transcript and an absence of Fhit protein (see below).
Expression of FHIT Transcripts in TCCs
Using the RT-PCR amplification assay, FHIT cDNAs of altered size were identified in one (CRL7833) of the six cell lines (data not shown). Four cell lines (SW780, T24, Hs228T, HBT9) showed the presence of only a normal-sized FHIT transcript. FHIT cDNA could not be amplified from CRL7930 cells. Sequencing of the amplified DNA products revealed normal FHIT sequences in T24, HS228T, and HBT9 cells. The normal-sized band present in SW780 consisted of a mixture of abnormal FHIT transcripts.
Similar experiments then were performed using RNA extracted from
primary TCCs of the bladder. Overall, 26 of 30 (87%) primary TCCs
showed a combination of normal and one or more aberrant transcripts
(Figure 2)
. Abnormalities of the
FHIT transcripts consisted of the absence of one or more
exons of the FHIT gene or the absence of exons with
insertion of intronic sequences, as described
previously.14,19
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Immunoblot experiments using protein lysate from the six
transitional carcinoma-derived cell lines showed an absence of Fhit
protein in the three cell lines (SW780, CRL7930, CRL7833) with absent
or abnormal FHIT transcripts (Figure 3)
. Conversely, two cell lines, T24 and
HBT9, expressed abundant Fhit protein in concordance with the apparent
absence of FHIT gene alteration in these cells. The absence
of Fhit protein in Hs228T cells in discordance with the presence of a
normal FHIT transcript might be because of the expression of
a low level of FHIT transcript, as described previously for
RCC cell lines.20
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Statistical Analysis
Statistical studies showed a significant correlation (P = 0.0013) between absence and/or reduction of Fhit expression and advanced tumor stage. No correlation was found between Fhit expression and tumor differentiation grade.
| Discussion |
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Western blot analysis shows absence of Fhit protein in four of six TCC-derived cell lines examined. The observation of multiple separate homozygous deletions that did not include FHIT exons in three of the four cell lines showing absence of Fhit protein suggested that in these cells the homozygous deletions are the result of an overlap of independent deletions of the two FHIT alleles, as previously demonstrated in other tumors.24,25 The immunohistochemical study of 85 primary TCCs of all grades and stages has demonstrated that 30.6% of them were uniformly negative and another 30.6% were a mixture of Fhit-positive and -negative cells. Thus 61.2% of these primary tumors show reduced expression of Fhit. In addition, RT-PCR analysis of the integrity of FHIT transcripts in primary tumors and derived cell lines suggests frequent gene lesions. Similarly, 85% of clear cell renal carcinomas and more than 70% of cervical carcinomas have shown loss or reduction of Fhit expression.20,26 The inactivation of FHIT in bladder tumors is probably a result of deletions within both alleles, as described for other carcinomas, particularly tumors resulting from exposure to environmental carcinogens. These include cancers of the lung, esophagus, stomach, cervix, and pancreas.14,26-32 Further studies will be required to define the exact mechanisms leading to loss of Fhit in bladder cancer.
Our study of transitional cell carcinoma of the bladder shows a significant correlation (P = 0.0013) between the absence or reduction of Fhit expression and advanced stage of the primary tumor. The heterogeneous pattern of Fhit loss of expression in TCCs of the bladder is similar to the pattern observed in breast carcinoma.33 In addition, reduced Fhit expression is correlated with a more aggressive disease in both bladder and breast cancers. Conversely, a uniform pattern of loss of Fhit expression has been observed in tumors such as lung and gastric cancers, in which loss of Fhit has been suggested to be an early event in the tumorigenesis process.34,35 In conclusion, we show for the first time that FHIT is inactivated in the majority of transitional cell carcinomas of the urinary bladder and suggest that FHIT inactivation is a late event in neoplastic progression.
| Footnotes |
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Supported in part by National Institutes of Health grant CA56036 (to C. M. C.) and by the Martin Greitzer Fund.
Accepted for publication October 26, 1999.
| References |
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