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Cyclin D1 in breast cancer is not associated with Ki67 but with ER
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Cyclin D1 is associated with cell cycle regulation and has more recently been shown to stimulate the transcriptional functions of the oestrogen receptor (ER). Furthermore, in normal breast there is a negative association between expression of ER and the proliferation marker Ki67 indicating that either ER positive cells are non-dividing or that the receptor is down-regulated as cells enter cycle. This important relationship breaks down in many ER-positive cancers and precancerous breast lesions where the receptor is often detected on proliferating cells. The aims of the present study were to determine the interplay between ER, Ki67 and cyclin D(1)in individual cells within the spectrum of human breast lesions ranging from normal to invasive carcinoma by using dual staining immunofluorescence. We found that in normal breast there was a strong positive association between ER and cyclin D(1)expression. In contrast there was a strong negative association between cyclin D(1)and Ki67 expression. Similar findings were seen for the other precancerous and cancerous breast lesions. Thus immunodetectable cyclin D(1)within individual cells does not appear to be associated with cell cycle progression in the benign or malignant breast but instead may have important interactions with ER.
Cyclin D1 overexpression, detected by standard immunohistochemistry, was correlated with other prognostic variables and its prognostic value was evaluated in a group of 148 invasive breast cancers with long-term follow-up. Overexpression of cyclin D1 (59% of cases) was negatively correlated (chi 2 test) with histological grade (P = 0.0001), mean nuclear area (P = 0.004), mean nuclear volume (P = 0.02), and mitotic activity (P = 0.03) and positively correlated with estrogen receptor (P = 0.0001). There was a strong correlation between cyclin D1 overexpression and histological type (P = 0.0001). Positive cyclin D1 staining was seen in 11 of 13 tubular carcinomas, 3 of 3 mucinous carcinomas, 4 of 4 invasive cribriform carcinomas, and 17 of 20 lobular carcinomas. Of 102 ductal cancers, 52 were positive, and all 6 medullary carcinomas were negative. There were no significant correlations with lymph node status, tumor size, or DNA ploidy. In survival analysis, cyclin D1 overexpression did not provide significant univariate or multivariate prognostic value. In conclusion, cyclin D1 is mainly overexpressed in the well differentiated and lobular types of invasive breast cancer and is strongly associated with estrogen receptor positivity. It is negatively correlated with the proliferation marker mitoses count and with the differentiation markers nuclear area and nuclear volume. However, cyclin D1 overexpression does not seem to have prognostic value in invasive breast cancer when no adjuvant treatment is given.
Both cyclin D1 and estrogens have an essential role in regulating proliferation of breast epithelial cells. We show here a novel role for cyclin D1 in growth regulation of estrogen-responsive tissues by potentiating transcription of estrogen receptor-regulated genes. Cyclin D1 mediates this activation independent of complex formation to a CDK partner. Cyclin D1 activates estrogen receptor-mediated transcription in the absence of estrogen and enhances transcription in its presence. The activation of estrogen receptor by cyclin D1 is not inhibited by anti-estrogens. A direct physical binding of cyclin D1 to the hormone binding domain of the estrogen receptor results in an increased binding of the receptor to estrogen response element sequences, and upregulates estrogen receptor-mediated transcription. These results highlight a novel role for cyclin D1 as a CDK-independent activator of the estrogen receptor.
The control of the cell-cycle-associated protein cyclin D1 and its variable behaviour in normal and transformed cells is described and contrasted with its activity in vivo. The role of cyclin D1 as a prognostic and predictive marker is examined in clinical breast cancer. High levels of the protein are seen in well differentiated, oestrogen receptor positive tumours, which respond well to tamoxifen treatment for metastatic disease.