Functional consequences of cyclin D1 overexpression in human mammary luminal epithelial cells

Changing molecular profile of brain metastases compared with matched breast primary cancers and impact on clinical outcomes

Background:

Breast cancer commonly metastasises to the brain, but little is known about changes in the molecular profile of the brain secondaries and impact on clinical outcomes.

Methods:

Patients with samples from brain metastases and matched breast cancers were included. Immunohistochemical analysis for oestrogen receptor, progesterone receptor, p27kip1, cyclin D1, epidermal growth factor receptor, insulin like growth factor 1, insulin like growth factor 1 receptor, vascular endothelial growth factor A, transforming growth factor-β and HER2 receptor was performed. Borderline HER2 results were analysed by fluorescent in situ hybridisation. Levels of expression were compared, with review of effect on clinical outcomes.

Results:

A total of 41 patients were included. Of the patients, 20% had a change in oestrogen receptor or HER2 in their brain metastasis that could affect therapeutic decisions. There were statistically significant rises in brain metastases for p27kip1 (P=0.023) and cyclin D1 (P=0.030) and a fall in vascular endothelial growth factor A (P=0.012). Overall survival from the time of metastasis increased significantly with oestrogen receptor-positive (P=0.005) and progesterone receptor-positive (P=0.013) brain lesions and with a longer duration from diagnosis of the breast primary (P<0.001).

Conclusions:

In this cohort there were phenotypic differences in metastatic brain tumours compared with matched primary breast tumours. These could be relevant for aetiology, and have an impact on prognostication, current and future therapies.

Cyclin D-1 protein over-expression is not associated with gene amplification in benign and atypical apocrine lesions of the breast

Cyclin D-1 protein over-expression and/or gene amplification have been shown to be frequent events in subsets of breast carcinomas. Cyclin D-1 is generally considered as a weak oncogene, and its over-expression has been shown to occur in occasional benign breast lesions. In a previous series, we have shown that cyclin D-1 was over-expressed in subsets of apocrine metaplasia (APM) and apocrine adenosis (AA) of the breast and that such over-expression was mostly associated with a significant increase in the proliferative capacity of these lesions. We examined the mechanisms involved in cyclin D-1 over-expression in apocrine lesions. A total of 41 cases were analysed in this study. The cases were divided into: 18 cases of APM and 23 cases of AA. All cases analysed had been previously analysed by immunohistochemistry, and all showed over-expression of the cyclin D-1 protein. Fluorescence in situ hybridisation (FISH) was performed using a dual cyclin D-1 (spectrum orange)/chromosome 11 centromere (spectrum green) DNA probe. The results showed that none of the cases studied had concomitant gene amplification. These results suggest that other post-transcriptional mechanisms might be responsible for cyclin D-1 protein over-expression in benign apocrine lesions. Further studies are needed to understand the mechanisms involved in abnormal cyclin D-1 expression in these lesions.

Alterations of the cell cycle regulators cyclin D1, cyclin A, p27, p21, p16, and pRb in apocrine metaplasia of the breast

G1/S transition defects have been a proposed requirement for tumor development. Apocrine metaplasia (APM) in the breast has been held as a sign of benignity. Yet, a number of studies have reported the presence of molecular abnormalities in some forms of APM suggesting a possible oncogenic potential for some of these lesions. We currently investigate the role of some of the cell cycle proteins, previously reported to be de-regulated in breast cancer, in an attempt to assess their significance in APM. Using immunohistochemistry, the expression of cyclin D1, cyclin A, p27, p21, p16, pRb and Ki-67 was examined in 93 cases of APM. The cases were divided into nonpapillary (NAPM) (30 cases) and papillary metaplasia (PAPM) (63 cases). PAPM was further subdivided into simple papillary (SPAPM) (29 cases), complex papillary (28 cases) and highly complex papillary (six cases). For statistical analysis, the last two groups were merged together (CPAPM). The results showed that increased histological complexity was associated with significant increase of proliferative capacity and alterations of the cell cycle control. The median Ki-67 index was 1.5% in SPAPM and 4.8% in the CPAPM. Also, alterations of the cell cycle regulators were significantly higher in the CPAPM than in the SPAPM. NAPM was generally similar to normal breast epithelium. Apocrine cells were negative for p16 while pRb was expressed in all cases. These findings suggest that in complex forms of APM, there is a considerable degree of cellular unrest. This may contribute to increased susceptibility to carcinogenesis.

Requirement for IGF-I in epidermal growth factor-mediated cell cycle progression of mammary epithelial cells

Induction of cyclin proteins is required for progression of cells through the G(1)-S and G(2)-M cell cycle checkpoints and is a primary mechanism by which mitogens regulate cell cycle progression. IGF-I and the epidermal growth factor (EGF)-related ligands are mitogens for mammary epithelial cells in vitro and are essential for growth of the mammary epithelium during development. We report here that IGF-I in combination with EGF or TGFalpha is synergistic in promoting DNA synthesis in mammary epithelial cells in the intact mammary gland cultured in vitro. We further investigated the role of IGF-I and EGF in cyclin expression and cell cycle progression in the mammary gland and demonstrate that IGF-I and EGF induce expression of early G(1) cyclins. However, we show that IGF-I, but not EGF, induces late G(1) and G(2) cyclins and is required for mammary epithelial cells to overcome the G(1)-S checkpoint. These data demonstrate that IGF-I is essential for cell cycle progression in mammary epithelial cells and that it is required for EGF-mediated progression past the G(1)-S checkpoint in these cells.

Cyclin D1 overexpression in a model of human breast premalignancy: preferential stimulation of anchorage-independent but not anchorage-dependent growth is associated with increased cdk2 activity

Cyclin D1 is frequently overexpressed in human breast ductal carcinoma in situ (DCIS) specimens, which confer a high risk for the development of infiltrating ductal carcinoma. If causally involved in the genesis of human breast malignancy, cyclin D1 may represent an interesting target for chemopreventive approaches, as it sits at the junction of many growth factor and hormonal pathways. We have used the MCF-10A human breast cell line, derived from a mastectomy containing a low risk premalignant lesion, as a model system. Three cyclin D1 transfectants exhibited physiologically relevant levels of transgene overexpression, but no coordinate overexpression of other cell cycle related genes. Proliferation assays, flow cytometry, and cdk enzymatic assays of anchorage-dependent proliferation indicated only a minimal and transient effect of cyclin D1. In contrast, cyclin D1 overexpression significantly stimulated anchorage-independent colonization in soft agar or methylcellulose, accompanied by greater Gl-S progression. The cdk4 activity of the control- and cyclin D1 transfectants in colonization assays was comparable, but the cdk2 activity was higher in the latter. Injection of control- and cyclin D1 transfected MCF-10A cells in matrigel into nude mice failed to produce tumors within 1.5 years. The data suggest that cyclin D1 overexpression is an early feature of breast neoplastic progression, and can contribute to cancer development through the promotion of colonization.