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From the Centre for Cell and Molecular Medicine,*
University of Keele School of Postgraduate Medicine, North
Staffordshire Hospital, Stoke-on-Trent, United Kingdom; the Department
of Pathology,
Stafford District General
Hospital, Stafford, United Kingdom; the Department of
Otorhinolaryngology,
Charite-Hospital,
Humboldt-University, Berlin, Germany; and the Department of
Pathology,
Virchow-Hospital,
Humboldt-University, Berlin, Germany
| Abstract |
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| Introduction |
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5% of newly diagnosed malignancies in
Northern Europe and the United States. Annually, more than 500,000 new
cases are registered worldwide and the incidence of the disease is
increasing.1
Survival rates for the disease are poor,
clinical outcome can vary among patients with tumors from the same
site, with comparable tumor stage, nodal status, and histological
grade.2-4
Chronic consumption of tobacco and alcohol are
recognized risk factors although it is unclear which traits determine
tumor behavior and therefore prognosis. Studies have demonstrated
elevated levels of cell proliferation in a high proportion of SCCHN
tumors, and proliferation rates have been related to patient survival,
and used in patient treatment strategies.5-7
Thus, genes
that encode regulators of cell proliferation may prove useful in
establishing patient prognosis or as targets in therapy regimens. The cyclin D1 gene (CCND1) encodes cyclin D1 protein, which is expressed in response to mitogenic signals promoting transition through the restriction point in the G1 phase of the cell cycle.8 Increased expression of cyclin D1 has been associated with increased cell proliferation.9,10 CCND1 amplification leading to deregulated CCND1 expression is common in tumors from patients with SCCHN.11,12 Cyclin D1 protein overexpression has been shown to correlate with reduced 5-year and overall survival in SCCHN patients.13 Other studies have shown that cyclin D1 protein overexpression is associated with poor prognosis in primary hypopharyngeal, laryngeal, esophageal, and oral squamous cell carcinomas.14-16 Furthermore cyclin D1 antisense experiments have demonstrated that the gene may be a potential target for therapeutic intervention in SCCHN.17
CCND1 is polymorphic with a common A/G substitution at nucleotide 870 in the conserved splice donor region of exon 4 of the gene.18 CCND1 alleles have been shown to be associated with splicing of CCND1 mRNA in both normal and tumorous lung tissue. In heterozygotes, transcript a is spliced equally from CCND1 G870 and A870 alleles, whereas transcript b is spliced mainly from the CCND1 A870 allele.18 In non-small cell lung cancer patients, CCND1 AA870 genotype is associated with poor prognosis.18 In contrast we have recently demonstrated in SCCHN that the CCND1 GG870 genotype was associated with poorly differentiated tumors and independently from tumor differentiation, with reduced patient disease-free interval.19,20 A second common G/C polymorphism at nucleotide 1722 within CCND1 3'UTR has also been described (G/C1722 sequence information is available at the NCBI SNP database at http://www.ncbi.nlm.nih.gov/SNP), although the influence of this polymorphism on tumorigenesis has not been examined.21
In this study we have further investigated the role of CCND1 allelism in SCCHN. We have examined the relationship of the CCND1 G/C1722 polymorphism with A/G870 alleles and clinical outcome. In addition we have further studied the influence of CCND1 alleles on mRNA splicing and protein expression in head and neck tissue.
| Materials and Methods |
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SCCHN patients (n = 294) were studied from our original cohort of 384 patients previously described.19,20 These patients were selected because of the availability of DNA and do not represent a clinical subgroup. The clinical pathological characteristics are similar to those of the total cohort.19 Briefly, the case group comprised German Caucasians suffering a single histologically confirmed oral cavity pharyngeal or laryngeal squamous cell carcinoma. Patients were recruited at first presentation or during follow-up between 1994 and 1996. Malignancies were staged using the TMN classification system.22 All tumors were squamous cell carcinoma and were histologically graded as: well (G01), moderately (G2), and poorly (G3) differentiated. Margins of the resected specimen were examined by a histopathologist and judged for tumor-free margins using the international R0-R2 system; R0, microscopically proven free tumor margins; R1, microscopic infiltration and macroscopically free margin; R2, macroscopic tumor infiltration of the margin. Where details were available we examined the association of cyclin D1 genotype and protein expression with factors known to influence clinical outcome: tumor site (n = 268), tumor size (T1 to T4) (n = 258), histological differentiation (G0/1 to G3) (n = 168) and the presence of nodes at time of surgery (n = 166). We also examined the association of genotypes and protein expression with tumor recurrence (defined as disease-free interval) in 151 patients. The study to identify associations with disease-free interval was performed only in patients in which a R0 resection could be achieved during initial treatment. Patients suffering a tumor re-growth during the first 6 months after initial treatment and those suffering extra-capsular tumor spread in any of the resected lymph nodes were excluded to avoid misjudged recurrences because of residual tumor growth. Lymph node involvement was determined before surgery using ultrasound, computed tomography, and nuclear magnetic resonance imaging and later histologically proven in the neck dissection specimen.
DNA and RNA Extraction
Peripheral blood samples were collected in ethylenediaminetetraacetic acid. Tumor and histologically normal head and neck tissues (salivary gland or muscle) were collected at time of surgery and snap-frozen in liquid nitrogen and stored at -70°C before use. DNA was extracted from frozen tissue and blood using a phenol-chloroform method.23 mRNA was isolated from frozen normal and tumor tissues using the MicrofastTrack RNA isolation kit (Invitrogen, Groningen, The Netherlands).
Restriction Fragment Length Polymorphism-Polymerase Chain Reaction (PCR) Genotyping
CCND1 G/C1722 genotypes were identified in DNA isolated from peripheral blood using a restriction fragment length polymorphism-PCR based assay.24 Briefly reactions were performed in 25 µl containing 1x Taq polymerase buffer (Promega, Southampton, UK), 100 µmol/L dNTPs, 0.25 µg of each primer, 2% dimethyl sulfoxide, 0.25 U of Taq polymerase (Promega, UK) and 0.1 µg of DNA. Reactions were performed on an automated thermal cycler with an initial denaturation of 94°C (2 minutes) and cycled 34 times with annealing temperature of 57°C (1 minute), an extension at 72°C (1 minute), and denaturation of 94°C (1 minute). PCR products were digested with HaeIII following the manufacturers guidelines (New England Biolabs, Hitchin, Hertfordshire, UK). Alleles were resolved on 3% agarose gels stained with ethidium bromide.
Reverse Transcriptase-PCR Analysis of CCND1 mRNA
mRNA extracted from snap-frozen tissues was reverse-transcribed to cDNA using a superscript preamplification system (Gibco-BRL Life Technologies, Paisley, UK). Analysis of CCND1 transcripts a and b was performed using a nested PCR strategy.18 Reactions containing 2 µl of cDNA were performed in 100-µl volumes containing 1x PCR buffer (Promega), 100 µmol/L dNTPs, 0.5 µg each primer, 2 U of Taq polymerase (Promega). Primary reactions were cycled 32 times, following which 1 µl of PCR product was nested for 22 cycles. PCR conditions were initial denaturation temperature 94°C (2 minutes), annealing 55°C (1 minute), elongation 74°C (1 minute), and denaturation 94°C (1 minute). PCR products were digested with the restriction enzyme ScrFI (New England Biolabs) and alleles visualized on 8% acrylamide gels and silver stained.
Immunohistochemistry
Paraffin-embedded tumor material was available in 135 cases from the cohort of 294 patients. Immunohistochemistry was performed using a Shandon Sequenza (Shandon Scientific Limited, Cheshire, UK) as described.25 A mouse monoclonal cyclin D1 antibody (DCS-6; Novocastra, Newcastle-upon-Tyne, UK) was used. A cyclin D1-positive breast tumor provided positive control material. Negative controls had no primary antibody applied and included a section of normal head and neck tissue. Slides were graded as negative (0 to <10% cells stained), low (>10 to 50% cells stained), moderate (>50 to 75% cells stained), and strong (>75% cells stained).
Statistics
Statistical analysis was performed using Stata, version 5 (Stata Corporation, College Station, TX). Pearson chi-square tests were used to identify linkage between CCND1 genotypes and associations of genotypes with gender. Association of genotypes and protein expression with clinicopathological parameters were analyzed and corrected for imbalances in age and gender using logistic regression. Associations between cyclin D1 protein and genotype and cyclin D1 protein expression with gender were analyzed using the Armitage trend test. Coxs proportional hazard regression model was used in the analysis of the effects of cyclin D1 staining and genotypes on disease-free interval. Kaplan-Meier curves were generated for graphical representation of associations with disease-free interval. A probability level of 5% was considered statistically significant.
| Results |
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Cyclin D1 expression was detected in 112 of 135 (83%) of tumors
examined (Table 1)
. The proportion of tumor cells expressing cyclin D1
was variable between different tumors. Thus expression was low in 35 of
135 (25.9%) cases, moderate in 56 of 135 (41.4%) cases, and high in
21 of 135 (15.5%) cases. Cyclin D1 protein expression was not
associated with patient age at presentation neither did we find an
association with tumor stage, differentiation, or the presence of tumor
nodes (Table 1)
. Analysis of cyclin D1 expression with patient gender
revealed that tumor expression of cyclin D1 was high in both sexes
(Table 1)
. However, significantly more tumors from females expressed
cyclin D1 compared with those from males (Table 1)
. Furthermore, a
significant trend was observed between an increase in the proportion of
cells expressing cyclin D1 in the tumors from female patients, compared
with those from males (Table 3)
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| Discussion |
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We have also examined the expression of cyclin D1 protein in these tumors. Cyclin D1 expression was frequently deregulated, with the proportion of cells expressing the protein varying between different tumors. Our data are consistent with findings in other studies.26,27 However, surprisingly, in our cohort of patients, absence of expression of cyclin D1 correlated with reduced disease-free interval. In contrast previous work has associated up-regulated expression of cyclin D1 with poor outcome in SCCHN.13-16 Although it is assumed, that deregulated expression leads to poor outcome directly through increased cellular proliferation of tumor cells, in a recent study cyclin D1 expression in SCCHN tumors has been associated with an increase in apoptosis and cyclin D1-negative tumors were more proliferatively active.27 Cyclin D1 expression has been associated with good prognosis in non-small cell lung cancer and bladder cancer24,28 and both good and bad prognosis in studies on breast and cancer.29-32 It is possible that these contradictory results in part reflect the many different mechanisms through which deregulated expression of cyclin D1 can occur in cancer.11,12,24,29,33 It would be interesting in the future, to examine the association between CCND1 alleles with the mechanism of protein overexpression such as CCND1 amplification in addition to biological markers of cellular proliferation and to relate these findings to clinical parameters including tumor differentiation and patient disease-free interval. Further understanding of these mechanisms and their effect on tumor biology in specific tissues may increase understanding of cyclin D1 as a prognostic marker.
To explore mechanisms underlying the link between CCND1 genotypes and clinical outcome in SCCHN, we investigated the data for associations with gene expression. Firstly, we found a significant trend between a reduction in the proportion of cyclin D1-expressing cells within the tumors of patients with CCND1 GG870. Furthermore, CCND1 GG870 was associated with reduced disease-free interval in our patients thus providing a link between CCND1 A/G870 alleles with cyclin D1 expression and clinical outcome in SCCHN. Secondly, we found that CCND1 A/G870 alleles modulate the splicing of CCND1 mRNA in head and neck tissues. CCND1 transcripts a and b were detected from each CCND1 A/G870 allele. However, transcript b was spliced mainly from the CCND1 A870, whereas transcript a was spliced equally from CCND1 G870 and CCND1 A870 alleles. It would be expected therefore, that CCND1 AA870 homozygotes express more transcript b than CCND1 GG870 homozygotes. Although we did not measure transcript levels, it is possible that physiological differences in the ratio of CCND1 transcripts a to b because of interindividual genotypic variation may influence the development of SCCHN. Interestingly, we found that in four of nine of the tumors allele-specific splicing of the transcripts was deregulated (S. L. Holley and P. R. Hoban, unpublished data). It is not clear from this preliminary data whether this is a specific mechanism for tumor development or indicates a general loss of splicing fidelity in these tumors.
CCND1 transcript a is identical to the reported cyclin D1 cDNA,34 however, transcript b fails to splice at the exon 4/intron 4 boundary, terminates downstream of exon 4 and does not contain exon 5.18 The difference between the proteins predicted by the nucleotide sequences of the two transcripts is in the carboxy terminal PEST rich region (destruction box) encoded by exon 5, which facilitates turnover of the START cyclins.35 The terminal region of transcript b has no PEST-rich sequence. Functional differences in the expression of the alternate CCND1 transcripts have also been demonstrated.36 Further, the monoclonal antibody, DCS-6, used in our immunohistochemical analysis, cross-reacts with recombinant cyclin D1 proteins from both CCND1 transcript a and b and protein from transcript b has been detected with this antibody in lymphoma cells and solid tissues.36-38 Therefore it is not clear in our immunohistochemical analysis which specific protein is being detected in the SCCHN tumors. We did not find any associations between CCND1 G/C1722 alleles and protein expression. Because of its location in exon 5, we assume that CCND1 G/C1722 is a marker reflecting the activity of CCND1 transcript a. Alternatively CCND1 G/C1722 alleles may be in linkage with other alleles that influence cyclin D1 function or that of a gene close by.
Our study has highlighted potential differences in the genetics and biology of tumors from SCCHN patients of different gender. The distribution of G/C1722 genotypes was different between male and female patients. We also found that significantly more tumors from female patients and a higher proportion of cells in those tumors expressed cyclin D1, than those from male patients. Our cohort was too small to significantly examine the data for differences in outcome based on CCND1 and gender. However it was noted that tumor site significantly differed with patient gender. Thus oral (21% female versus 7% male) and pharyngeal (38% female versus 21% male) tumors were more common in female patients whereas laryngeal tumors were more common in male patients (40% females versus 71% males). SCCHN is documented as a predominantly elderly male disease associated with heavy smoking and high alcohol consumption.1-3 In our cohort, female patients were associated with less alcohol (30% females compared with 73% of males) and tobacco (62% females compared with 88% males) consumption. This data would indicate that SCCHN etiology in males and females may be different. The role of cyclin D1 in tumor development in patients of differing gender is unclear and the gene may merely be a marker for these differences. However, CCND1 amplification and protein expression has been related to tobacco exposure in SCCHN.39 In breast cancer patients cyclin D1 expression and estrogen receptor status are significantly correlated and associated with clinical outcome.40 Furthermore, previous functional studies have suggested that cyclin D1 interacts in a ligand-specific manner with the estrogen receptor in breast cells and the androgen receptor in prostate cells.41,42
In conclusion, accumulating data demonstrate that CCND1 is important in the development of SCCHN and that the gene has potential both as a prognostic marker, and as a target in the treatment of the disease. Our data suggest that CCND1 A/G870 alleles influence expression of CCND1, and that specific antibodies to transcript b are required to validate expression studies and to identify the specific cyclin D1 protein in SCCHN tumors. We realize, in some cases, numbers were small, and that our findings require independent confirmation in a separate and larger cohort, however, for the first time, we demonstrate the potential of CCND1 G/C1722 alleles as an independent prognostic marker in this disease. Our data also highlights differences in the molecular genetics of SCCHN tumors associated with patient gender. Collectively these findings have implications in rationalizing the protein as a target for treatment of patients with SCCHN.
| Footnotes |
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Supported by the North Staffordshire Medical Institute (grant no. 51272958).
Accepted for publication August 3, 2001.
| References |
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