Cyclin D1 Amplification Research Articles

Amplification and overexpression of cyclin D1 in aggressive human esophageal cancer.

Cyclin D1 is a cell-cycle regulator essential for G1 phase progression and a candidate proto-oncogene implicated in pathogenesis of several human tumor types including esophageal cancers. Association between cyclin D1 gene amplification and clinical outcome was examined using southern blotting in 45 patients with primary esophageal cancer. In cases showing gene amplification, expression levels of mRNA and gene product were further examined by northern blotting, western blotting and immunohistochemical analyses. Amplification of cyclin D1 gene was found in 14 of 45 patients (31. 1%). There was no association between gene amplification and clinicopathological parameters but the frequency of hematogenous recurrence in cases with gene amplification was significantly higher than that in cases without amplification in 30 patients undergoing curative surgery (70.0% vs 25.0%, p<0.05). Furthermore, cumulative survival rate of cases with gene amplification was significantly lower than that of cases without amplification (p<0.05). Overexpression of cyclin D1 mRNA was observed in 12 of 14 cases (85. 7%) showing gene amplification but overexpression of its protein was found in only four cases (28.6%). Amplification of the cyclin D1 gene is a reliable prognostic factor and post-translational modification of this gene may play a functionally important role in development of primary esophageal cancer.

Expression of cyclin Ds in relation to p53 status in human breast carcinomas.

Cyclin D1 has been reported to be overexpressed in many tumours, including breast carcinomas. Cyclin D1 was first identified as a protooncogene (BCL1/PRAD1), and its overexpression was related to tumour proliferation. The product has also recently been identified as important in mediating cell cycle growth arrest via the p53 pathway in murin fibroblast cell lines. Ninety breast carcinomas previously analysed for p53 status were analysed for amplification of cyclin D1, D2 and D3 genes by Southern blot analysis and for protein expression by immunhistochemistry. In 10 samples gene amplification was detected at the cyclin D1 locus. No gene amplification was detected at the cyclin D2 and D3 loci. Immunoreactivity for cyclin D1 was detected in 38 (42.2%) tumour tissue samples. Fifty samples were immunostained for cyclin D2 and D3. Only 2 samples (4%) showed immunoreactivty for cyclin D2, and 9 samples (18%) for cyclin D3. Cyclin D1 protein overexpression was significantly more often found in tumours with wild type p53 and in tumours with higher grades of differentiation expressing ER. No association was seen between gene amplification of the cyclin D1 gene and p53 status. We conclude there is a relationship between wild type p53 and cyclin D1 protein overexpression in clinical material, indicating that cyclin D1 may be another downstream effector of p53.

Molecular analysis of INK4 genes in breast carcinomas

Cell cycle regulators have recently been implicated in oncogenic transformation of cells, including the cyclins active in the G1 phase of the cell cycle and their respective cyclin-dependent kinases (CDK) whose activities are regulated by a set of inhibitors of CDK (CDKI). Since CDKIs can inhibit cell proliferation, they may have a role as tumor suppressor genes. To determine if alterations of CDKI genes may be involved in tumorigenesis of breast cancer, we examined the mutational status of p16(INK4A), p15(INK4B), p18(INK4C), p19(INK4D) CDKI genes in 36 primary breast carcinomas and 9 breast cancer cell lines using polymerase chain reaction-single strand conformational polymorphism (PCR-SSCP), direct DNA sequencing, and Southern blot analysis. Furthermore, amplification of cyclin D1, D2, D3 genes were also examined in these samples. One mutation of p15(INK4B) gene occurred, resulting in change of aspartic acid to asparagine at codon 85. Since aspartic acid at this position is conserved between all four human and murine INK4 proteins, this missense mutation may have functional significance. The sample with a p15(INK4B) point mutation was accompanied by amplification of the cyclin D1 gene. A deletion of the p18(INK4C) gene was found in a primary tumor. Three deletions of the p16(INK4A) gene and two deletions of the p15(INK4B) gene were found in the cell lines. Also, we found amplification of the p15(INK4B) and p16(INK4A) loci in a clinical sample as well as amplification of the p19(INK4D) in another sample, and amplification of the myeloperoxidase (MPO) gene in one cell line and two primary tumors. We suspect that a critical gene for breast cancer is amplified near the MPO gene. These data indicate that CDKI mutations are moderately rare in breast cancer and are often associated with the simultaneous alteration of more than one cell-cycle regulatory gene.

Altered expression of cyclin D1 and CDK4 genes in ovarian carcinomas.

We analyzed the expression and amplification of cyclin D1 and CDK4 genes in ovarian carcinomas. Northern blot analysis revealed overexpression of cyclin D1 in 12 of 65 (18%) ovarian carcinomas while CDK4 was overexpressed in 7 of 48 cases (14%). None of the tumors showed amplification of any of the 2 genes. Overexpression of cyclin D1 and CDK4 transcripts was correlated, suggesting a role of both genes in altered growth control of ovarian cancer cells. Elevated levels of cyclin D1 were significantly associated with a well-moderately differentiated grade (G1-G2) (p < 0.005). No significant association was found between cyclin D1 expression and estrogen receptor, progesterone and epidermal growth factor receptor content. Cyclin D1 expression does not appear to be associated with clinical outcome in human ovarian cancer, although a longer follow-up period and screening of other molecules involved in the same pathway would be necessary to assess this hypothesis.

Altered expression of cyclin D1 and CDK4 genes in ovarian carcinomas

We analyzed the expression and amplification of cyclin D1 and CDK4 genes in ovarian carcinomas. Northern blot analysis revealed overexpression of cyclin D1 in 12 of 65 (18%) ovarian carcinomas while CDK4 was overexpressed in 7 of 48 cases (14%). None of the tumors showed amplification of any of the 2 genes. Overexpression of cyclin D1 and CDK4 transcripts was correlated, suggesting a role of both genes in altered growth control of ovarian cancer cells. Elevated levels of cyclin D1 were significantly associated with a well-moderately differentiated grade (G1-G2) (p < 0.005). No significant association was found between cyclin D1 expression and estrogen receptor, progesterone and epidermal growth factor receptor content. Cyclin D1 expression does not appear to be associated with clinical outcome in human ovarian cancer, although a longer follow-up period and screening of other molecules involved in the same pathway would be necessary to assess this hypothesis. Int. J. Cancer 74:390–395, 1997. © 1997 Wiley-Liss, Inc.

Cyclin-D1-gene amplification and expression in breast carcinoma: relation with clinicopathologic characteristics and with retinoblastoma gene product, p53 and p21WAF1 immunohistochemical expression.

Cyclin D1 is a major positive regulator of the G1 restriction point promoting inactivation of the retinoblastoma protein (RB). The cyclin D1 gene is rearranged, amplified and/or over-expressed in several human neoplasms. In the present series of 64 human breast carcinomas, cyclin D1 amplification (4- to 8-fold) was seen in 24% of cases, and cyclin-D1 immunohistochemical over-expression was seen in 50% of cases. Amplification and over-expression were statistically associated; however, divergent result were seen in 30% of cases. Some of these discrepancies may reflect the fact that cyclin-D1 expression may be due to mechanisms other than gene amplification. Cyclin-D1 over-expression, but not cyclin-D1 amplification, was associated with positive oestrogen-receptor immunoreactivity. Cyclin-D1 amplification was associated with high RB expression, and 4 cases (7%) with absent RB immunoreactivity showed no cyclin-D1 amplification nor expression. Our data support the hypothesis that cyclin-D1 amplification may be associated with enhanced gene transcription and with high RB expression, that high ER expression may cooperate in maintaining high levels of cyclin-D1 protein, and that loss of RB function, as assessed by the lack of RB immunoreactivity, may be related to normal cyclin-D1 gene copy number and low cyclin-D1 expression.

Amplification and expression of the cyclin D1 gene in anal and esophageal squamous cell carcinomas

Cyclin Dl is a cell-cycle regulator and candidate proto-oncogene implicated in the pathogenesis of numerous tumor types. Amplification of the cyclin Dl gene occurs commonly in esophageal squamous cell carcinomas. However, no studies have examined the role of cyclin D1 in anal carcinogenesis. We examined 20 esophageal squamous cell carcinomas and 24 anal carcinomas for cyclin Dl alterations. Protein expression was evaluated by immunohistochemistry using the cyclin D1GM antibody (Novocastra, Newcastle upon Tyne, UK). Cyclin D1 amplification was examined by fluorescent in situ hybridization (FISH), using a cyclin D1 probe obtained from Toshiya Inaba at St. Jude Children's Research Hospital, Memphis, TN. The FISH sections were analyzed using a Leica (Deerfield, IL) confocal microscope. By immunohistochemistry, 75% of esophageal carcinomas showed evidence of cyclin D1 expression. Cyclin Dl amplification was detected by FISH in 65% of esophageal cancers. There was good correlation between cyclin D1 protein expression and gene amplification, although some tumors showed protein overexpression in the absence of gene amplification. Among the 24 anal carcinomas studied, 8% showed weak cyclin D1 immunoreactivity in rare tumor cells. None of the anal tumors showed cyclin D1 amplification. We conclude that cyclin Dl alterations are common in esophageal carcinomas but do not appear to be important in anal carcinogenesis. Immunohistochemical detection of cyclin D1 protein overexpression is a good predictor of cyclin D1 amplification.

Overexpression of Cyclin D1 in Epithelial Ovarian Cancers

Amplification and overexpression of the cell cycle-related gene cyclin D1 have been demonstrated in several human malignancies and have been shown to be directly oncogenic in breast epithelium and lymphocytes. Overexpression of the gene can occur in the absence of gene amplification. We have investigated whether cyclin D1 is overexpressed in a panel of 43 sporadic epithelial ovarian cancers using immunohistochemistry. Cyclin D1 was overexpressed in 26% of these tumors. Overexpression of cyclin D1 is associated with borderline or well-differentiated, grade 1 tumors but does not correlate with a particular histological type, overexpression of the c-erb-B2 oncogene, or presence of estrogen receptors. It is suggested that overexpression of cyclin D1 may contribute to the pathogenesis of epithelial ovarian cancers, including a subset of tumors different from those overexpressing the c-erb-B2 oncogene.

Amplification of cyclin D1 in squamous cell carcinoma of the head and neck and the prognostic value of chromosomal abnormalities and cyclin D1 overexpression

Abnormalities of chromosome band 11q13 are frequent in squamous cell carcinoma of the head and neck (SCCHN). The oncogene CCND1 is located at 11q13 and encodes cyclin D1, a cell cycle-regulating protein. The authors investigated the clinical relevance and associations between amplification and overexpression of cyclin D1 and 11q13 rearrangements. The study involved two series of patients. In Series 1, overexpression of cyclin D1 and 11q13 rearrangements, assessed by immunohistochemistry and cytogenetics, respectively, were compared with clinical data in 75 patients with SCCHN. Patients were monitored for at least 18 months or until death. In another 23 patients (Series 2), the authors investigated the association between DNA amplification (by slot blot hybridization), overexpression of cyclin D1, and cytogenetics. In Series 1, 9 of 75 tumors (12%) had 11q13 aberrations, 6 of which manifested elevated expression of cyclin D1. Patients with tumors strongly positive for cyclin D1 (n = 9) and those with tumors showing 11q13 rearrangements had poorer survival (P = 0.047 and 0.005, respectively). However, the correlation between these two variables was weak (P = 0.12). In Series 2, 17 of 23 tumors (74%) showed elevated cyclin D1 protein expression, and 6 of these showed gene amplification as well. Of these six, only one revealed 11q13 rearrangements. Overexpression of cyclin D1 and 11q13 rearrangements are independent prognostic factors for SCCHN. In general, DNA amplification results in overexpression of cyclin D1, but additional genetic mechanisms are involved in the deregulation. Furthermore, oncogenes at 11q13 besides CCND1 may be involved in the tumorigenesis.

Amplification of cyclin D1 in squamous cell carcinoma of the head and neck and the prognostic value of chromosomal abnormalities and cyclin D1 overexpression

BACKGROUND Abnormalities of chromosome band 11q13 are frequent in squamous cell carcinoma of the head and neck (SCCHN). The oncogene CCND1 is located at 11q13 and encodes cyclin D1, a cell cycle-regulating protein. The authors investigated the clinical relevance and associations between amplification and overexpression of cyclin D1 and 11q13 rearrangements. METHODS The study involved two series of patients. In Series 1, overexpression of cyclin D1 and 11q13 rearrangements, assessed by immunohistochemistry and cytogenetics, respectively, were compared with clinical data in 75 patients with SCCHN. Patients were monitored for at least 18 months or until death. In another 23 patients (Series 2), the authors investigated the association between DNA amplification (by slot blot hybridization), overexpression of cyclin D1, and cytogenetics. RESULTS In Series 1, 9 of 75 tumors (12%) had 11q13 aberrations, 6 of which manifested elevated expression of cyclin D1. Patients with tumors strongly positive for cyclin D1 (n = 9) and those with tumors showing 11q13 rearrangements had poorer survival (P = 0.047 and 0.005, respectively). However, the correlation between these two variables was weak (P = 0.12). In Series 2, 17 of 23 tumors (74%) showed elevated cyclin D1 protein expression, and 6 of these showed gene amplification as well. Of these six, only one revealed 11q13 rearrangements. CONCLUSIONS Overexpression of cyclin D1 and 11q13 rearrangements are independent prognostic factors for SCCHN. In general, DNA amplification results in overexpression of cyclin D1, but additional genetic mechanisms are involved in the deregulation. Furthermore, oncogenes at 11q13 besides CCND1 may be involved in the tumorigenesis. Cancer 1997; 79:380-9. © 1997 American Cancer Society.

Correlation between p53 mutation and cyclin D1 amplification in head and neck squamous cell carcinoma

Mutations in the p53 tumour suppressor gene and amplification of the cyclin D1 (CCND1) oncogene have been commonly reported in various malignancies. In the present study of 39 squamous cell carcinomas of the head and neck, p53 mutations were manifest in 11 (28%) of the cases, whereas CCND1 amplification was seen in 6 (16%) of 37 analysed tumours. The 10 mutations occurring in coding sequences of p53 were found in exon 5 (4 cases), exon 6 (3 cases),f and exon 8 (3 cases). No mutation was found in exon 7. Eight of the 10 exon nucleotide substitutions were missense mutations and two were nonsense mutations. All six tumours with CCND1 amplification also had p53 mutations, while an additional five tumours manifested p53 mutations in the absence of CCND1 amplification. There was a statistically significant positive correlation between these two gene alterations. This raises the possibility that mutation of p53 precedes CCND1 amplification in carcinogenesis.

Cyclin gene amplification and overexpression in breast and ovarian cancers: evidence for the selection of cyclin D1 in breast and cyclin E in ovarian tumors.

Evidence of the involvement of cyclin genes in genetic alterations in human cancer is growing. In the present study, we investigated the amplification, in human breast and ovarian cancer, of 5 cyclin genes; cyclin A, cyclin D1, cyclin D2, cyclin D3 and cyclin E. For this purpose, a series of 1,171 breast and 237 ovarian tumors tested for DNA amplification by Southern blotting and a subset of 132 breast and 22 ovarian cancers were analyzed for RNA expression levels by slot-blot and Northern blotting. In breast tumors, only cyclin D1 was found to be activated in a sizeable fraction of the tumors (amplification 12.6%, overexpression 19%). Cyclin A, D2, D3, and E genes never, or only on rare occasions, showed increased DNA copy numbers and were never found overexpressed at the RNA level. Amplification of cyclin D1 correlated with ER+ breast cancer and the presence of lymph-node metastasis. Interestingly, we were also able to determine an association with invasive lobular carcinoma. Our data suggest that cyclin D1 activation determines the evolution of a particular subset of estrogen-responsive tumors. Data obtained in ovarian tumors contrasted with observations in breast cancer. Cyclin D1 DNA amplification was much less frequent in ovarian than in breast tumors (3.3% vs. 12.6%), whereas cyclin E amplification and overexpression were observed in a significant number of cases (12.5% and 18.0% respectively). Cyclin A, cyclin D2 and D3 rarely showed anomalies at the DNA level and were never overexpressed. No clear correlation could be observed between amplification of the cyclin E gene and tumor type, stage or grade in ovarian cancer. Data presented here suggest distinct pathways of cyclin activation in human breast and ovarian cancer.

A clinicopathological study on overexpression of cyclin D1 and of p53 in a series of 248 patients with operable breast cancer.

Overexpression of cyclin D1 is frequently found in various types of human tumours and results from clonal rearrangement and/or amplification involving chromosomal region 11q13. In order to evaluate the pathological relevance of cyclin D1 overexpression in human breast cancer, we generated a polyclonal antiserum against the carboxy-terminal part of the cyclin D1 protein. After affinity purification, the antiserum specifically detected overexpression of cyclin D1 in formalin-fixed, paraffin-embedded tumour material also. The intensity of the nuclear stainings was, in general, proportional to the degree of cyclin D1 amplification. We did not encounter significant variability of staining within individual tumours with overexpression of cyclin D1. Overexpression of cyclin D1 appeared to be associated with oestrogen receptor-positive breast tumours, but not with any other clinicopathological parameter tested. Overexpression of cyclin D1 was not prognostic value for recurrence of survival in a consecutive series of 248 operable breast cancer patients (stage I and II). Overexpression of p53 was also not of prognostic significance in this series, but was associated with undifferentiated histology and oestrogen receptor-negative breast tumours, as has been reported previously by others. A high proportion of breast tumours with a low grade of malignancy in this series of operable breast cancer patients may explain discrepancies concerning the prognostic value of amplification and of overexpression of cyclin D1.

Cyclin D1 amplification and expression in human breast carcinoma: correlation with histological prognostic markers and oestrogen receptor expression

Aims-To study the amplification of the Cyclin D1 gene (CCND1) in human breast carcinoma; to relate this to Cyclin D1 protein expression; to relate these parameters to recognised pathological prognostic factors, including oestrogen receptor (ER) status.Methods-DNA extracted from frozen sections of breast tumours (n = 36) was used for Southern blotting. Probes for CCND1, c-myc and the immunoglobulin heavy chain locus (IgH) were hybridised to tumour DNA. Immunocytochemical expression of Cyclin D1 protein and ER was studied in paraffin wax sections from the same tumours.Results-Amplification of CCND1 was observed in 11% (four of 36) of tumours studied. Over expression of Cyclin D1 protein was observed in 73% (30/41) of tumours. There was no correlation between recognised histological prognostic markers and either gene amplification or expression. However, a weak association was seen between Cyclin D1 expression and ER status.Conclusions-A disparity exists between locus amplification and over expression of Cyclin D1, suggesting the existence of another mechanism for raised protein expression. No significant correlation was detected between either Cyclin D1 amplification or over expression and established prognostic markers.

Cyclin D1 protein expression in lung cancer.

Cyclin D1, a G1 cyclin, has been implicated in the oncogenesis of various types of malignancies via deregulation of cell cycles. Amplification of cyclin D1 as a part of 11q13 amplicon has been reported in lung cancer as well as a subset of carcinomas arising from various organs including breast, head and neck, and esophagus. In addition to its role as an oncogene, several recent studies have suggested that amplification is indicative of poor prognosis. In this study we examined the cyclin D1 protein expression in 102 consecutive cases of lung cancers using the microwave enhanced immunohistochemical staining method and correlated the data with the histologic subtype and grade, Ki-67 (MIB-1) labeling index, and survival. Nuclear positive staining was observed in 18 cases (18 %) of lung cancers. Although squamous cell carcinoma demonstrated a higher rate of expression (12 /58, 21%), three of 33 adenocarcinomas (9%) revealed overexpression and both adenocarcinoma and squamous cell carcinoma components within the adenosquamous carcinoma showed nuclear staining. There was no correlation between cyclin D1 overexpression and histologic grade, Ki-67 (MIB-1) labeling index, and survival. These observations indicate that cyclin D1 protein overexpression might be implicated in the oncogenesis of the various histologic types of non-small cell lung carcinomas but it has no usefulness as a prognostic marker.

Genetic Alterations of Cyclins, Cyclin-Dependent Kinases, and Cdk Inhibitors in Human Cancer

Publisher Summary This chapter focuses on the genetic alterations of cyclins, cyclin dependent kinases (Cdk), and Cdk inhibitors in human cancer. Contemporary research into the molecular basis of cancer has two central tenets. The first is that cancer arises through alterations in the genetic make-up of the tumor cell. The second is that these changes are manifested in the breakdown of the processes that regulate cell growth and differentiation. In simplistic terms, cancer cells proliferate uncontrollably and fail to differentiate. The large numbers of tumors that show perturbations in the D cyclins themselves, their upstream regulators, or their downstream targets suggest that this pathway is extremely important in human cancer and holds great promise for therapeutic intervention. The conventional view of the cell division cycle is as a series of checkpoints or transitions at which certain criteria must be met before the cell proceeds to the next phase. The cyclin D1 gene, now given the locus designation CCNDI, maps to band q13 on the long arm of chromosome 11. The chapter also discusses the amplification of cyclin D1 in human tumors. When the gene for Cdk4 was located on chromosome 12q13, it was quickly realized that it too lies within a tumor-specific amplicon, which had been previously observed in human sarcomas of various types and in tumors of the central nervous system, particularly gliomas. There has been a great deal of interest in the cyclin-dependent kinase inhibitors that have been identified in mammalian cells. The chapter describes cyclin D1-p16-pRb pathway.

Human cyclin D1 oncogene and esophageal squamous cell carcinoma.

Oncogene activation and tumor suppressor gene inactivation have been implicated in the genetic basis of esophageal squamous cell carcinoma (ESCC). Cyclin D1, an oncogene that has a critical role in G1 progression of the cell cycle, has been observed to be amplified in carcinomas of the breast and head and neck, and translocated in parathyroid adenomas and centrocytic lymphomas. Established ESCC cell lines were assayed for cyclin D1 amplification and overexpression by Southern, Northern, and Western blot analyses. In addition, cyclin D1 overexpression was determined in primary tumors and adjacent normal mucosa by differential polymerase chain reaction (PCR) and immunohistochemical staining. The authors observed that approximately 50% of ESCC cell lines with cyclin D1 DNA amplification also had RNA and protein overexpression. Related genes, cyclin D2 and D3, were not amplified or overexpressed in these cell lines with rare exception. The cyclin D1 protein was able to associate with the cell-cycle-dependent kinases, cdk4 and cdk6, but not always with proliferating cell nuclear antigen in selected cell lines tested, representing a novel finding. In addition, approximately 50% of primary tumors had cyclin D1 overexpression that was not present in adjacent normal mucosa. Cyclin D1 overexpression based on PCR correlated with enhanced cyclin D1 protein nuclear staining in malignant cells. Cyclin D1 is amplified and overexpressed in ESCC and may be important in its molecular pathogenesis.

Differential Polymerase Chain Reaction Assay of Cyclin Dl Gene Amplification in Esophageal Carcinoma

The cyclin D1 gene, located on chromosome 11q13, is frequently rearranged in parathyroid neoplasms and amplified in some carcinomas of other organs. Recent studies have detected amplification of cyclin D1 and other markers on chromosome 11q13 (evaluated by Southern or slot blot assays) in approximately 25-50% of squamous cell carcinomas of the esophagus and noted that amplification was associated with lessened survival time. We applied the technique of differential polymerase chain reaction to the evaluation of cyclin D1 gene amplification in squamous cell carcinomas of the esophagus. Cyclin D1 was found to be amplified in 10 of 45 (22%) primary tumors and three of 12 (25%) lymph node metastases. Lymph node metastases tended to be more common in patients with cyclin D1 amplification (70%) than in those without amplification (37%). In 36 patients with follow-up, cyclin D1 amplification was associated with decreased 1 year survival (28% vs. 59%). Cyclin D1 gene amplification in esophageal carcinomas can be evaluated by differential polymerase chain reaction and may provide useful prognostic information.

Highly Frequent Homozygous Deletion of the p16 Gene in Esophageal Cancer Cell Lines

To study the involvement of the p16 tumor suppressor gene in esophageal cancer development, we examined homozygous deletion of the p16 gene in 13 human esophageal cancer cell lines and 9 gastric cancer cell lines, in which some of genetic alterations have already been characterized. By Southern blot analysis, homozygous deletion was observed in 12 out of the 13 esophageal cancer cell lines (92%), in 2 out of a total of 9 gastric cancer cell lines (22%). It was also found that the p16 gene loss, cyclin D1 amplification and p53 gene mutations occurred independently in these cell lines. These findings suggest that loss or mutations of the p16 gene are involved in most esophageal cancers and that mutation of this gene plays a critical role in the development of esophageal cancer.

Cyclin D1 induction in breast cancer cells shortens G1 and is sufficient for cells arrested in G1 to complete the cell cycle.

The sequential transcriptional activation of cyclins, the regulatory subunits of cell-cycle-specific kinases, is thought to regulate progress through the cell cycle. Cyclins are therefore potential oncogenes, and cyclin D1 overexpression and/or amplification at its genomic locus, 11q13, are common features of several human cancers. Induction of cyclin D1 is an early response to mitogenic stimulation in several cell types, but the consequences of altered expression of this gene in human cells of epithelial origin remain undefined. We assessed the effects of alterations of cyclin D1 expression in human breast cancer cells by generating T-47D cells expressing human cyclin D1 under the control of a zinc-responsive metallothionein promoter. In cycling cells induction of cyclin D1 after zinc treatment resulted in an increase in the number of cells progressing through G1 and in the rate of transition from G1 to S phase, indicating that cyclin D1 is rate-limiting for progress through G1 phase. In cells arrested in early G1 phase after growth factor deprivation, zinc induction of cyclin D1 was sufficient for completion of the cell cycle, a process requiring growth factor stimulation in control cells. These data demonstrate a critical role for cyclin D1 in human breast cancer cell-cycle control and suggest that deregulated expression of cyclin D1 is likely to reduce dependence on normal physiological growth stimuli, thereby providing a growth advantage to tumor cells and a potential mechanism of resistance to endocrine therapy.