Expression Pattern Of Cyclin D1 Research Articles

Prognostic Significance of Cyclin D1 Over-expression in Colorectal Cancer: An Experience from Madinah, Saudi Arabia.

Background and study aim: Cyclin D1 is a key regulatory protein in the cell cycle and is over-expressed in many tumors, including endometrial, thyroid, urothelial, breast, brain gliomas, and esophageal cancers. The main aim of the present study is to examine the expression pattern of cyclin D1 and its correlation with the different clinicopathological features in patients with colorectal camcer (CRC) from the Madinah region of Saudi Arabia. Patients and methods:The archival tumor blocks were analyzed using immunohistochemistry for Cyclin D1 over-expression in 324 CRC patients diagnosed from January 2006 to December 2017, at the Department of Pathology, King Fahad Hospital, Madinah, Saudi Arabia.Results: Cyclin D1 over-expression was absent in normal mucosa, while 15% cases of adenoma showed its over-expression. In CRC, Cyclin D1 was expressed at high levels in 24.1% of case. No significant correlation was observed between Cyclin D1 over-expression and age, gender, tumor size, type and location. However, Cyclin D1 over-expression exhibited a significant correlation with tumor differentiation (p=0.04), lymph node involvement (p=0.001), lymphovascular invasion (p=0.001), distant metastasis (p=0.006) and AJCC staging (p=0.001). The Kaplan-Meir analysis revealed a shorter period of survival with Cyclin D1 over-expression (p=0.000). The Cox-regression model analysis showed that Cyclin D1 over-expression was an independent prognostic marker in CRC (p=0.000). Conclusion: Cyclin D1 over-expression increases during normal-adenoma-carcinoma sequence. The significant association observed between Cyclin D1 over-expression, advanced tumor stage and short survival period clearly suggest the role of Cyclin D1 in the carcinogenesis and progression of CRC.

Regulation of cyclin D1 by arsenic and microRNA inhibits adipogenesis

Low-dose chronic exposure to arsenic in drinking water represents a global public health concern with established risks for metabolic and cardiovascular disease, as well as cancer. While the linkage between arsenic and disease is strong, further understanding of the molecular mechanisms of its pathogenicity is required. Previous reports demonstrated the ability of arsenic to interfere with adipogenesis, which may mediate its effects in promoting metabolic disease. We hypothesized that microRNA are important regulators of most if not all mesenchymal stem cell processes that are dysregulated by arsenic exposure to impair lipogenesis. Arsenic increased the expression of miR-29b in white adipose tissue, as well as human mesenchymal stem cells (hMSCs) isolated from adipose tissue. Exposing hMSCs to arsenic increased abundance of miR-29b and cyclin D1 to promote proliferation over differentiation. Paradoxically, inhibition of miR-29b enhanced the inhibitory effect of arsenic on differentiation. This paradox was attributed to a requirement for miR-29 in regulating cyclin D1 expression as stable inhibition of miR-29b eliminated the cyclic pattern of cyclin D1 expression. Temporal regulation of cyclin D1 is critical for adipogenic differentiation, and the data suggest a paradigm where arsenic disruption of miR-29b regulatory pathways impairs adipogenic differentiation and ultimately adipose metabolic homeostasis.

Up-Regulation of PKM2 Relates to Retinal Ganglion Cell Apoptosis After Light-Induced Retinal Damage in Adult Rats.

Pyruvate kinase isozyme type M2 (PKM2), a key glycolytic enzyme, which is involved in ATP generation and pyruvate production, participates in tumor metabolism, growth, and other multiple cellular processes. However, one attractive biological function of PKM2 is that it translocates to the nucleus and induces cell apoptosis. Recently, increased PKM2 has been found in age-related macular degeneration (AMD), but little is known regarding its function in the AMD pathophysiology. To investigate whether PKM2 participated in retinal degeneration, we performed a light-induced retinal damage model in adult rats. Western blot and immunohistochemistry analysis showed a significant up-regulation of PKM2 in retinal ganglion cells (RGCs) layer (GCL) after light exposure. Immunofluorescent labeling indicated that PKM2 located mainly in RGCs. Co-localization of PKM2 and active caspase-3 as well as TUNEL in RGCs suggested that PKM2 might participate in RGC apoptosis. In addition, the expression patterns of cyclin D1 and phosphorylated extracellular signal-regulated kinase (p-ERK) were parallel with that of PKM2. Furthermore, PKM2, cyclin D1, and active caspase-3 protein expression decreased by intravitreal injection of U0126, a highly selective inhibitor of MAPK/ERK kinase. Collectively, we hypothesized that PKM2 might participate in RGC apoptosis after light-induced retinal damage medicated by p-ERK through cycle re-entry mechanism.

Cyclin D1 expression in multiple myeloma by immunohistochemistry: Case series of 14 patients and literature review

Background:Cyclin D1 dysregulation is an early and unifying oncogenic event in patients of multiple myeloma (MM). This may be detected up to 30% cases by immunohistochemistry (IHC) and up to 40-50% cases by molecular studies. However, studies on the clinical significance of cyclin D1 dysregulation in MM have been inconclusive. We aimed to study the pattern of cyclin D1 expression in MM by IHC and correlate with selected clinicopathologic features.Materials and Methods:Formalin fixed, decalcified, bone marrow trephine sections from 14 symptomatic patients of MM (13 newly diagnosed and one relapsed) were subjected to cyclin D1 IHC by using a rabbit monoclonal antibody to cyclin D1 (clone EPR2241).Results:Cyclin D1 expression (in ≥10% tumor cell nuclei) was observed in 8 of 14 cases (57%). Cyclin D1 positive (+) group had significantly lower hemoglobin level (P = 0.03) than cyclin D1 negative (−) group (n = 6); though both groups showed no statistical significance (P > 0.05) in regard to age, gender, Durie and Salmon stage, lytic bone lesions, light chain phenotype, creatinine, calcium, lactate dehydrogenase, leukocyte and platelet count and bone marrow histology. Ten of 14 (71.5%) showed a favorable response (follow-up; 7 days to 34 months) to thalidomide and/or bortezomib based chemotherapeutic regimen. Four of eight cyclin D1− patients showed complete response, two had a partial response (PR) and two died of the disease; whereas 4/6 cyclin D1 − patients had PR, one refused definitive therapy and one was lost to follow-up (P > 0.05, Fischer's exact test).Conclusion:IHC may be a feasible tool for the demonstration of cyclin D1 expression on adequately processed trephine biopsy specimen in MM patients in a resource poor setting. Negative IHC results should be correlated with molecular techniques for prognostication.

Expression of β-catenin and cyclin D1 in Merkel cell carcinomas of the head and neck

Merkel cell carcinomas (MCC) are very aggressive tumors of the sun-exposed skin with a high potential to metastasize. Little is known about the genesis of MCC and very few prognostic markers have been detected so far. The Wnt pathway protein β-catenin and the cell cycle protein cyclin D1 are two promotors of tumor growth and are expressed in a variety of malignant neoplasms such as lymphomas, thyroid, breast cancer, and many others. Tissue samples of 27 patients with MCC were immunohistochemically stained for β-catenin and cyclin D1 and correlated with overall survival of patients. In addition, western blot analysis was carried out in the two MCC cell lines MCC-13 and MCC-26. β-catenin showed a cytoplasmatic expression of 10-30 % in 11 samples and an expression lower than 10 % in eight samples. Nuclear staining was visible in two samples. None of the 27 samples expressed cyclin D1. Neither cyclin D1 nor β-catenin was expressed in a statistically significant manner, concluding that the development of MCCs is independent of β-catenin and cyclin D1 expression and these proteins are not suitable as prognostic markers. We could describe the expression pattern of cyclin D1 for the first time.

Cyclin D1 an early biomarker in oral carcinogenesis

Background:Dysregulation of cell cycle is a fundamental hallmark of cancer progression. Cyclin D1, part of complex molecular system regulating G1-S point of cell cycle is overexpressed in variety of tumors.Aims:To look for its immunohistochemical expression in clinically normal mucosa from patients with and without tobacco habits, leukoplakia; and correlate its expression to individual atypical morphologic features, as seen in hematoxylin and eosin (H and E) sections of leukoplakia exhibiting dysplasia.Materials and Methods:We examined the expression of cyclin D1 in immunohistochemically stained sections of 15 normal buccal mucosa without any habits (group 1), 30 clinically normal mucosa from tobacco habituιs (group 2) and 30 leukoplakias exhibiting dysplasias (group 3). Descriptive statistical analysis performed. Results presented on Mean ± Standard deviation and in number (%). Adjusted Wald 95% Confidence Interval (CI) computed, percentages of morphological features assessed by Laplace estimate. Mann-Whitney U, Kruskal-Wallis test used to find the percentage expression of cyclin D1.Results:Expression of cyclin D1 in group 3 was significantly higher than in group 1 and 2 (P < 0.001, P = 0.028), expression in group 2 was significantly higher than in group 1 (P = 0.003) and were statistically significant. Generally expression of cyclin D1 was confined to lower one-third of epithelium and was highest in mild dysplasias. Among 13 atypical morphologic features, cyclin D1 expression consistently correlated with basilar hyperplasia.Conclusion:The altered pattern of cyclin D1 expression here may be an early event in conversion of normal epithelium into dysplastic epithelium and may serve as a biomarker of oral carcinogenesis. Its expression may be increased in tobacco habitués. Basilar hyperplasia should be given additional weightage in the grading system in predicting the fate of affected epithelium.

Cycling D1 negatively regulates the expression of differentiation genes in HT-29 M6 mucus-secreting colon cancer cells

HT-29 M6 colon cancer cells differentiate to a mucus-secreting phenotype in culture. We found that the pattern of cyclin D1 expression in HT-29 M6 cells did not correlate with instances of cell proliferation but was specifically induced during a dedifferentiation process following disaggregation of epithelial cell layers, even under conditions that did not allow cell cycle reentrance. Interestingly, ectopic expression of cyclin D1 in differentiated cells led to the inhibition of the transcriptional activity of differentiation gene promoters, such as the mucin MUC1. We thus propose that the overexpression of cyclin D1 found in colon cancer favours tumour dedifferentiation as one mechanism of tumour progression.

Wnt pathway in pulmonary fibrosis in the bleomycin mouse model.

The Wnt/beta-catenin signaling pathway plays an important role in regulating cellular differentiation, proliferation, and polarity. We used bleomycin to induce lung fibrosis in a transgenic Wnt reporter mouse to characterize the expression pattern of cyclin D1, MMP-7, and TGF-beta in conjunction with the Wnt/beta-catenin signaling pathway. LacZ expression reveals the Wnt/beta-catenin signaling pathway through the activated (nuclear) beta-catenin and coactivation of LEF/TCF transcription factors. X-gal staining and immunohistochemical staining of beta-catenin, cyclin D1, MMP-7, and TGF-beta were assessed after bleomycin administration. We observed LacZ expression in bronchiolar proliferative lesions and the epithelium in remodeled cystic and fibrotic areas at both 1 and 3 weeks. Nuclear beta-catenin staining was prominent in epithelial cells of remodeled and fibrotic areas at 3 weeks. MMP-7 was faint in basement membranes of airways and matrix zones in fibrotic areas at 3 weeks. Cyclin D1 was observed in alveolar macrophages (AM), alveolar epithelium, and fibrotic areas consistent with rapid cell turnover in these areas at both 1 and 3 weeks. TGF-beta was faintly staining in alveolar macrophages and epithelial cells at 3 weeks. The Wnt/beta-catenin pathway is activated in bleomycin-induced lung fibrosis, and downstream genes were localized in AM, alveolar epithelium, and interstitium.

Multiple Myeloma with IGH-Involving del(14q): Report of 34 Cases.

Chromosomal translocations involving the IGH locus on 14q32 are a hallmark of B-cell malignancies. These translocations are particularly frequent in non-hyperdiploid (NHD) multiple myeloma (MM), representing approximately 50% of myeloma cases. MM-associated primary t(14q32) target at least 7 partner genes including cyclins D (CCND1, −D3), MAF transcription factors (CMAF, MAF B and A) and MMSET/FGFR3. Some of the translocations are predictive of clinical outcome. Recently, we identified a novel interstitial del(14q) involving IGH and recurrent in chronic lymphocytic leukaemia and MM (Pospisilova et al, Leukemia, 2007). In spite of extensive studies, the mechanism(s) and molecular consequences of del(14q) remain unknown. We report here 34 cases of plasma cell (PC) malignancies with del(14q) involving IGH, as proven by FISH. Cases were collected in UK and Belgium. The estimated incidence of these aberrations in PC malignancies was 1.4%. There were 13 female and 21 male patients ranging in age from 49 to 86 years (average 68). Twenty seven patients had MM, one had SMM and 6 had MGUS. In almost all cases, the del(14q) was detected at diagnosis. Clinical data of the reported cases have been collected. The del(14q) were roughly mapped by FISH and grouped into 3 categories according to the proximal breakpoint:1.del(14)(q24.1q32.33) involving the ZFP36L1 region (11 cases);2.deletions proximal to ZFP36L1 (14 cases) and3.deletions distal to ZFP36L1 (7 cases).The size of del(14q) was not determined in 2 cases. Biallelic deletion of TRAF3/14q32.33 recurrently occurring in MM, was detected by FISH in 1 out of 9 analyzed cases. Additional FISH analysis showed that the del(14q) was predominantly associated with NHD tumors (62% vs 38% with hyperdiploid karyotypes) and frequently (60%) accompanied by del(13q), regarded as a poor prognostic factor. All reported cases were negative for t(4;14) and t(11;14); they also showed a normal status of CCND3, CMAF, MAFB and CMYC, when examined. A gain of 1q/CKS1B was found in 57% (8/14) of analyzed cases. The expression pattern of cyclin D1−D3 has been examined.

Cyclin D1 Is Not an Immediate Target of β-Catenin following Apc Loss in the Intestine

Cyclin D1 is postulated to be a target of the canonical Wnt pathway and critical for intestinal adenoma development. We show here that, unlike cyclin D1 reporter assays, endogenous cyclin D1 levels are not affected following antagonism of the Wnt pathway in vitro, nor is cyclin D1 immediately up-regulated following conditional loss of Apc in vivo. Cyclin D1 levels do, however, increase in a delayed manner in a small subset of cells, suggesting such up-regulation occurs as a secondary event. We also analyzed the immediate consequences of Apc loss in a cyclin D1(-/-) background and failed to find any cyclin D1-dependent phenotypes. However, we did observe elevated cyclin D1 expression in lesions developing 20 days after Apc loss. In these circumstances, all adenomas (but not smaller lesions) showed cyclin D1 up-regulation. Finally in a smaller study, we analyzed whether cyclin D1 deficiency affected adenoma formation 20 days following induced loss of Apc. Unlike AhCre(+) Apc(fl/fl) mice (which all developed adenomas), doubly mutant AhCre(+) Apc(fl/fl) cyclin D1(-/-) mice only developed small lesions. Taken together, this argues that cyclin D1 up-regulation in intestinal neoplasia is important for tumor progression rather than initiation.

Immunohistochemical expression of cyclin D1, cyclin E, p21/waf1 and p27/kip1 in inflammatory bowel disease: correlation with other cell-cycle-related proteins (Rb, p53, ki-67 and PCNA) and clinicopathological features.

The expression patterns of cyclins D1 and E as well as cyclin-dependent kinase inhibitors p21/waf1 and p27/kip1 and their correlation with clinical parameters and other cell cycle regulators was investigated in inflammatory bowel disease (IBD). These molecular markers were localized immunohistochemically using the monoclonal antibodies anti-cyclin D1 (DCS-6), anti-cyclin E (13A3), anti-p21 (4D10) and anti-p27 (1B4) in 70 patients with IBD, 30 patients with colorectal cancer and eight healthy subjects. Data were analyzed statistically using the software program. Cyclin D1 expression was higher in both UC and CD compared with the healthy control group. In addition, CD cyclin D1 expression was higher compared with UC cases and colorectal carcinomas. Cyclin D1 expression was correlated with disease activity and cell proliferation in UC cases. A positive relationship of cyclin D1 with p27/kip1 in both UC and CD was detected. Cyclin E expression was higher in UC, CD and carcinomas compared with healthy control group and its expression correlated with proliferative activity in both UC and CD cases. p21/waf1 expression was higher in IBD cases compared with that of the control group, while a decreased p21/waf1 expression in the group of carcinomas was noted. This expression was correlated with disease activity in UC and the proliferative activity in both UC and CD. The expression of cyclins D1 and E as well as p21/waf1 was also correlated with the existence of dysplastic lesions. A lower p27/kip1 expression in the group of carcinomas compared with IBD cases and healthy controls was found. The expression patterns of cyclin D1, cyclin E, p21/waf1 and p27/kip1 in IBD may indicate their contribution in epithelial cell turnover and their possible implication in IBD-related dysplasia-carcinoma.

Cell-cycle mechanisms involved in podocyte proliferation in cellular lesion of focal segmental glomerulosclerosis

Background: Podocyte injury may induce podocyte proliferation, which results in glomerular scarring. The cellular lesion, seen in some patients with primary focal segmental glomerulosclerosis (FSGS), is characterized by proliferation of cells covering the sclerotic or collapsed glomerular tufts. Cell-cycle mechanisms by which podocyte proliferation occurs in the cellular lesion of FSGS are unclear. Methods: We examined expression patterns of cyclin D1; cyclin E; cyclin A; cyclin B1; cyclin-dependent kinase (CDK)2; CDK4; such CDK inhibitors as p21WAF1/CIP1 (p21), p27kip1 (p27), and p57kip2 (p57); and Wilms’ tumor protein-1 (WT-1) in 12 renal biopsy specimens with the cellular lesion of FSGS and 6 renal biopsy specimens with no detectable abnormalities by immunohistochemistry and immunoelectron microscopy. Messenger RNA (mRNA) expression patterns of cyclin D1, cyclin E, p21, p27, and p57 were evaluated further by in situ hybridization. Results: In controls, immunostaining for cyclin A, cyclin B1, CDK2, CDK4, and p21 was almost negligible, but positive signals for cyclin D1, cyclin E, p27, and p57 were observed in glomerular epithelial cells (GECs). In the cellular lesion of FSGS, positive signals for cyclin E, cyclin A, cyclin B1, CDK2, and p21 were present in GEC nuclei, in which WT-1, p27, p57, and cyclin D1 were undetected. Immunoelectron microscopy showed that cyclin E-, CDK2-, and p21-specific gold particles were increased significantly in GEC nuclei in the cellular lesion in which cyclin D- and p57-specific particles were absent compared with controls. An in situ hybridization study showed specific signals of cyclin D1, cyclin E, p21, p27, and p57 mRNA in GECs forming the cellular lesion of FSGS. Conclusion: Our results suggest that damaged podocytes may inhibit p27 and p57 protein expression, but activate a cyclin D1–independent cell-cycle mechanism and mitotic cell cyclins to promote GEC proliferation in the cellular lesion of FSGS.

Expression of cyclin D1 in normal, metaplastic, hyperplastic endometrium and endometrioid carcinoma suggests a role in endometrial carcinogenesis.

Endometrioid carcinoma is often preceded by characteristic histopathologic lesions known as endometrial hyperplasia. Estrogen appears to be involved in the development of endometrioid carcinoma. Other mechanisms of endometrial carcinogenesis include mutations in p53 and PTEN tumor suppressor genes and overexpression of cyclin D1. However, the pattern of cyclin D1 expression is not well defined in normal, hyperplastic, neoplastic, and metaplastic endometrium. Cyclin D1 immunohistochemical analysis was used to evaluate 108 fixed, paraffin-embedded endometrial biopsy specimens and uterine resections obtained from 108 patients. Specimens included proliferative and secretory endometria, simple and complex hyperplastic lesions, and endometrioid adenocarcinoma. Normal and metaplastic surface epithelia were also evaluated independently of glandular morphologic features. Cyclin D1 was significantly overexpressed in glands with complex hyperplasia and endometrioid adenocarcinoma compared with proliferative or secretory endometrium and simple hyperplasia. Significant overexpression was also noted in papillary, syncytial, and squamous metaplasias compared with normal surface epithelium or epithelium with tubal metaplasia. Overexpression of cyclin D1 increases from normal endometrium to hyperplasia and carcinoma, suggesting that it may play a role in endometrial carcinogenesis. Overexpression of cyclin D1 in endometrial glands was independent from overexpression of cyclin D1 in surface metaplastic epithelium.

Cyclin D1 expression in dysplastic nevi: an immunohistochemical study.

Objective We previously surveyed cyclin D1 expression in common acquired nevi, Spitz nevi, and malignant melanomas and reported that benign nevi maintain a zonal pattern of cyclin D1 expression, in contrast with malignant melanomas. Our aim was to extend those observations by examining cyclin D1 expression in dysplastic nevi. Methods Cyclin D1 overexpression in 23 dysplastic nevi was detected by an immunohistochemical technique. The extent of atypia of the nevi was graded as mild, moderate, or severe, using previously established criteria. Results Cyclin D1 overexpression in dysplastic nevi maintained a zonal pattern, similar to Spitz nevi. Cyclin D1 overexpression was greatest in the region of the epidermal-dermal junction and was significantly less prominent in the papillary and reticular dermis, suggesting that cyclin D1 expression is under cell control and correlates with maturation of nevus cells. Cyclin D1 overexpression also correlated with cytologic atypia, as dysplastic nevi with moderate or severe cytologic atypia contained a greater percentage of cyclin D1-positive cells than did nevi with mild atypia. Six dysplastic nevi with many cyclin D1--positive cells were assessed by fluorescence in situ hybridization studies using cyclin D1--specific and chromosome 11 centromeric probes. In all cases, there was no evidence of 11q13 translocation, amplification, or trisomy of chromosome 11. Conclusions Cyclin D1 may be involved in the pathogenesis of dysplastic nevi. Cyclin D1 overexpression does not appear to be explained by cyclin D1 locus amplification or translocation in most cases, and it may be a result of other cell abnormalities that up-regulate the protein level of cyclin D1.

Cyclin D1 expression in dysplastic nevi: an immunohistochemical study.

We previously surveyed cyclin D1 expression in common acquired nevi, Spitz nevi, and malignant melanomas and reported that benign nevi maintain a zonal pattern of cyclin D1 expression, in contrast with malignant melanomas. Our aim was to extend those observations by examining cyclin D1 expression in dysplastic nevi. Cyclin D1 overexpression in 23 dysplastic nevi was detected by an immunohistochemical technique. The extent of atypia of the nevi was graded as mild, moderate, or severe, using previously established criteria. Cyclin D1 overexpression in dysplastic nevi maintained a zonal pattern, similar to Spitz nevi. Cyclin D1 overexpression was greatest in the region of the epidermal-dermal junction and was significantly less prominent in the papillary and reticular dermis, suggesting that cyclin D1 expression is under cell control and correlates with maturation of nevus cells. Cyclin D1 overexpression also correlated with cytologic atypia, as dysplastic nevi with moderate or severe cytologic atypia contained a greater percentage of cyclin D1-positive cells than did nevi with mild atypia. Six dysplastic nevi with many cyclin D1--positive cells were assessed by fluorescence in situ hybridization studies using cyclin D1--specific and chromosome 11 centromeric probes. In all cases, there was no evidence of 11q13 translocation, amplification, or trisomy of chromosome 11. Cyclin D1 may be involved in the pathogenesis of dysplastic nevi. Cyclin D1 overexpression does not appear to be explained by cyclin D1 locus amplification or translocation in most cases, and it may be a result of other cell abnormalities that up-regulate the protein level of cyclin D1.

Expression patterns of cyclin D1 and related proteins regulating G1-S phase transition in uveal melanoma and retinoblastoma

BACKGROUND/AIMSA checkpoint mechanism in late G1, whose regulation via loss of retinoblastoma protein (pRB) or p16, or overexpression of cyclin D1 or cyclin dependent kinase 4 (CDK4), has been proposed...

Expression of G1-->S transition regulatory molecules in human urothelial cancer.

Growth of cancer cells is characterized by accelerated passage through the cell cycle, which is often caused by deregulation of the G1→S transition. In this study the expression of G1→S transition regulatory molecules was analyzed in 32 transitional cell carcinoma specimens and fifteen normal tissues obtained by cystectomy or nephroureterectomy of mainly locally advanced tumors, as well as six bladder cancer cell lines. Expression of mRNAs for cyclins D1 and D2 and cyclin‐dependent kinases (CDK) 2 and 4 was investigated by quantitative reverse transcription‐poly‐merase chain reaction. Overexpression of cyclin D1 compared to normal mucosa was observed in 3 tumors (9.4%), but in neither of the cell lines. All tumors with overexpression were moderately differentiated (G2) pT1 or pT2 tumors, and thus among the less advanced specimens. Cyclin D2 was not expressed in normal bladder mucosa or in tumors. The expression of CDK4 mRNA varied within the same range in mucosa, tumors, and cell lines. CDK2 mRNA expression varied more strongly and was diminished in individual tumors and in four cell lines. It is concluded that cyclin D1 overexpression can play an important role in the early stage of urothelial tumorigenesis, driving cell proliferation. Ectopic expression of cyclin D2 or amplification of CDK4 does not occur at a significant frequency in urothelial carcinomas. Different expression patterns of cyclin D1 and CDK2 indicate heterogeneity in the mechanisms of G1→S transition deregulation in individual bladder tumors which may elicit differences in their biological and clinical behavior.