Precisely regulated cell proliferation is essential for embryonic development as well as homeostasis in adult organs and tissues, whereas uncontrolled cell proliferation is a hallmark of cancer. Thus, elucidating how the cell cycle machinery is controlled is an important area of research in cancer cell biology. A large body of evidence has established a basic paradigm of the control of cell cycle progression involving the Retinoblastoma (Rb) protein family in conjunction with the E2F family of transcription factors. During G0/G1, interaction of hypo-phosphorylated Rb proteins with E2Fs prevents the transcription of E2F target genes. Cyclin-CDK complexes generated during cell cycle progression hyper-phosphorylate Rb, leading to release of Rb from E2Fs; this allows E2F target gene transcription and cell cycle progression. We previously identified the mammalian ortholog of Drosophila ecdysoneless (Ecd) protein as a novel and essential regulator of Rb-E2F-dependent cell cycle progression. Loss of Ecd retards the separation of Rb from E2F, arrests cells at G1/S boundary and prevents cell cycle progression. Consistent with role of Ecd in cell cycle, our recent studies show Ecd is overexpressed in breast cancer cell lines as well as in ductal carcinoma in situ and infiltrating ductal carcinomas of the breast. To understand the mechanism of Ecd overexpression and its correlation with oncogenesis, we overexpressed either Ecd alone, 61L-HRas alone or both genes together in hTERT-immortalized hMECs. These transfectants were then examined for their oncogenic properties. We observed while vector infected cells do not exhibit anchorage independence, all three transfectants showed anchorage independent proliferation, particularly Ecd+Ras showed a dramatic increase in anchorage independence in comparison with either Ecd or H-Ras. Similarly, other oncogenic traits such as proliferation on matrigel, invasion and migration were dramatically increased when both genes were expressed in comparison with individual genes. Considering the known oncogenic role of Ras in human cancer and the known role of Ecd in cell cycle, these data are highly significant and present a novel synergistic pathway for mammary cell transformation. We are currently defining the molecular mechanism of this synergistic oncogenic effect. In addition, we are generating Ecd overexpressed transgenic mice to examine the role of Ecd in oncogenesis in in vivo models.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4177. doi:1538-7445.AM2012-4177