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 s itu (DCIS) specimens, which confer a high risk for the development of infil trating ductal carcinoma. If causally involved in the genesis of human brea st malignancy, cyclin D1 may represent an interesting target for chemopreve ntive approaches, as it sits at the junction of many growth factor and horm onal pathways. We have used the MCF-10A human breast cell line, derived fro m a mastectomy containing a low risk premalignant lesion, as a model system . Three cyclin D1 transfectants exhibited physiologically relevant levels o f transgene overexpression, but no coordinate overexpression of other cell cycle related genes. Proliferation assays, flow cytometry, and cdk enzymati c assays of anchorage-dependent proliferation indicated only a minimal and transient effect of cyclin D1. In contrast, cyclin D1 overexpression signif icantly stimulated anchorage-independent colonization in soft agar or methy lcellulose, accompanied by greater Gl-S progression. The cdk4 activity of t he control- and cyclin D1 transfectants in colonization assays was comparab le, but the cdk2 activity was higher in the latter. Injection of control- a nd 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 overexpre ssion is an early feature of breast neoplastic progression, and can contrib ute to cancer development through the promotion of colonization.