The Cul4a Ubiquitin Ligase, A Putative Target Gene At The 13q34 Amplicon And Its Role In Breast Cancer Pathogenesis & Progression

Breast cancer is a complex and heterogeneous disease and one of the most frequent causes of cancer deaths in developed countries. DNA copy number alterations occur frequently in breast tumours. Regions of DNA amplification are of major interest since often contain oncogenes whose increased expression confers tumour cells a selective advantage and contributes to the carcinogenesis process. In our laboratory prior analysis of familiar and sporadic breast tumours by using array-CGH identified an amplification event at the 13q34 region with an overall frequency of 4.5% that increased to 8.1% in BRCA1-associated tumours. Comprehensive characterization of the amplicon allowed us to define CUL4A as one of the most likely putative oncogenes. CUL4A is an E3 Ubiquitin Ligase which is amplified and/or overexpressed in primary breast tumours and involved in functions such as chromatin regulation, cell cycle regulation or DNA repair through ubiquitylation of NER pathway members. Its deregulation could have implications for oncogenic transformation and treatment response to DNA-damaging agents. One of such compounds is Trabectedin a marine-derived drug that presents antitumor activity in sarcomas and ovarian cancer. To elucidate the possible implication of CUL4A in the initial steps of the tumorigenic process we conducted the stable up-regulation of CUL4A in human mammary epithelial cells (184B5), and in NIH3T3 mouse-derived cell line by lentiviral infection. We also stably silenced CUL4A in the human breast cancer cell lines MDA-MB-157 and HCC1937 that present amplification and/or overexpression of CUL4A. With these modified cell lines we performed functional assays in different in vitro systems such as viability experiments, colony formation both in plastic and in soft agar and 3-D cultures in Matrigel. In order to measure sensitivity to Trabectedin we used silenced CUL4A breast cancer cell lines to perform clonogenic assays. Our preliminary results in CUL4A overexpression in 184B5 model system showed increase in proliferation and colony formation ability. On the other hand, CUL4A silencing in breast cancer cell lines resulted in diminished proliferation and decreased colony-forming abilities in both anchorage dependent and independent conditions. Concerning DNA-repair implication, it seems that high levels of CUL4A could be a good predictor of Trabectedin response. Our results indicate that CUL4A would play a role in promoting oncogenesis and/or in modulating breast cancer progression. Further evaluation of CUL4A amplification/overexpression impact on the maintenance of genome integrity will help elucidate its full potential for therapeutic intervention in breast and other cancers. 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 91. doi:1538-7445.AM2012-91