Induction of Mammary Gland Hyperplasia and Carcinomas in Transgenic Mice Expressing Human Cyclin E

Abstract

Deregulated expression of several cell cycle regulatory genes has been demonstrated to be associated with cancer. In particular, a strong correlation has been established between inappropriate cyclin E expression and human breast cancer. To determine the ability of cyclin E to play a causative role in mammary tumorigenesis, regulatory sequences from the ovine ␤-lactoglobulin gene were utilized to specifically target expression of human cyclin E to the mammary glands of pregnant and lactating mice. Lactating mammary glands of transgenic mice expressing cyclin E contained areas of hyperplasia, primarily papillary projections of hyperplastic cells, which were rarely observed in lactating glands of control mice. Over 10% of female cyclin E transgenic mice have developed mammary carcinomas, with latencies ranging from 8 to 13 months. Tumor analysis revealed the presence of transgene-specific cyclin E RNA and protein, as well as cyclin E-and cdk2-associated kinase activity, suggesting that cyclin E is likely a contributing component of tumorigenic progression in this model system.The regulation of critical transitions through the cell cycle is mediated by distinct protein kinase complexes, each composed of a cyclin regulatory and a cyclin-dependent kinase (cdk) catalytic subunit (8,35,37,41). In mammalian cells, several structural classes of cyclins (A to H) have been identified and have been demonstrated to reach maximal abundance during particular phases of the cell cycle (8, 35). Individual cyclins associate in various combinations with specific members of the cdk family, which in mammalian cells contains at least six cdks (28,35). The temporal regulation of cellular events necessary for orderly cell cycle progression is thought to be achieved by the sequential activation of different cyclin-cdk complexes throughout the cell cycle.Much evidence indicates that progression through the G 1 phase of the cell cycle is dependent upon the activity of G 1 cyclins, which include the D-type cyclins and cyclin E. The D-type cyclins reach maximal levels of expression and form functional kinase complexes with cdk4 or cdk6 during mid-G 1 phase (3, 25-27, 44, 50), whereas cyclin E is expressed and associates with cdk2 in an active complex near the G 1 /S boundary (10, 19). Inhibition of cyclin D1 by microinjection of antisense plasmids or antibodies during mid-G 1 phase prevents entry into S phase (2, 36). Similarly, microinjection of cyclin E antibodies prior to S phase inhibits the occurrence of S phase (32), as does inhibition of cdk2 activity by dominant negative or antibody microinjection methods (34,45,46). Overexpression of cyclin D1 or E accelerates progression through G 1 , reduces growth factor requirements, and diminishes cell size (31,36,39,49), while an additive effect on G 1 phase shortening is observed when both cyclins D1 and E are overexpressed in the same cell (38). These data suggest that the D-type cyclins and cyclin E are essential for progression through G 1 phase, controlling events that are rate limiting f...

Deregulated cyclin E promotes p53 loss of heterozygosity and tumorigenesis in the mouse mammary gland

“…This phenomenon is transient, occurring in the epithelia during the lactogenic cycle, initially manifest in the final third of pregnancy and persisting until the litter is weaned at 4 weeks post partum. At this point, the mammary epithelia undergo involution and the hyperplastic epithelia are included in this process (Bortner and Rosenberg, 1997). By standard hematoxylin and eosin staining, hyperplasia in the epithelia of midlactation (2 weeks post partum) mice appeared generally more widespread in T380A transgenic mice than those with the CycE transgene, but no more severe.…”

“…Chromosomal instability and aneuploidy are thought to be mediators of tumorigenesis. Furthermore, a murine transgenic model expressing cyclin E in the mammary epithelium leads to hyperplasia and mammary tumors (Bortner and Rosenberg, 1997), albeit at a low frequency. In both instances the expression of cyclin E was deregulated with respect to the cell cycle.…”

Increased expression of cyclin E is associated with an increased resistance to doxorubicin in rat fibroblasts

“…In fact, doxorubicin is one of the most valuable anticancer drug in present day clinical use, being an integral part of the treatment of malignancies such as carcinoma of the breast, head and neck, thyroid and soft tissue sarcomas and leukaemias (DeVita et al, 2001). Moreover, on the other hand, increased expression of cyclin E is a common event in a variety of human malignancies (Donnellan and Chetty, 1999;Sandhu and Slingerland, 2000) and is believed to play an important role in cancer development and progression by causing cell growth deregulation and genomic instability (Bortner and Rosenberg, 1997;Spruck et al, 1999). Thus, it has been proposed that cyclin E may become a target for treatment of human cancers (Owa et al, 2001).…”

“…The proper timing and amplitude of cyclin E expression are important since their alterations cause deregulation of cell growth (Ohtsubo et al, 1995;Sgambato et al, 1997). Moreover, transgenic mice overexpressing cyclin E develop breast cancers (Bortner and Rosenberg, 1997) and increased levels of cyclin E have been reported in a variety of human malignancies, (Donnellan and Chetty, 1999;Sandhu and Slingerland, 2000).…”

Malignant transformation by cyclin E and Ha-Ras correlates with lower sensitivity towards induction of cell death but requires functional Myc and CDK4

“…Among human malignancies the strongest correlation was established between breast carcinoma and cyclin E overexpression; here the alterations of cyclin E expression have even been correlated with stage and grade of the disease (Keyomarsi et al, 1994). First experiments with transgenic mice showed that constitutive expression of cyclin E can predispose for the development of mammary tumours after a long latency period (Bortner and Rosenberg, 1997).…”