Abstract 3875: Effect of Nutlin and E3 ligase inhibitor on p53 and p21 levels in HDM2 expressing LNCaP cells.

Abstract

Abstract HDM2 is a human homologue of murine double minute 2 protein (MDM2), which is also a negative regulator for p53 mediated tumor suppressor mechanisms. The latter is involved in regulating cell proliferation and induction of apoptosis as a means of controlling tumor growth. HDM2 can directly bind to p53 and neutralize its ability to induce p21 transcription. HDM2 also contains E3 ligase activity that is responsible for p53 ubiquitination and proteosomal degradation. Hence, compounds that inhibit E3 ligase activity of HDM2 are expected to lead to elevated p53 levels via inhibition of ubiquitination-mediated degradation. Similarly, blocking HDM2 by Nutlin was also expected to restore the levels of p53. According to existing literature, up-regulation of p53 should lead to activation of downstream pathways, such as induction of p21 protein. To confirm this hypothesis the prostate cancer cell line (LNCaP) was treated with HDM2-E3 ligase inhibitor and Nutlin for a 24-hour time period. The levels of p53 and p21 proteins were measured by Western Blot analysis and the mRNA levels were measured by RT-PCR amplification. Our preliminary results showed that HDM2-E3 ligase inhibitor increased p53 levels in LNCaP cells. The increase in p53 levels was greater in Nutlin treated samples compared to E3 ligase inhibited treated samples. In addition, we suspect that induction of p53 expression may also activate downstream pathways that will eventually lead to inhibition of cyclin-dependent kinases (CDKs) and phospho-retinoblastoma (pRB) protein mediated cell proliferation. To confirm our hypothesis further studies will be conducted. (The financial support from the Royal Dames of Cancer Research Inc., Ft. Lauderdale, Florida is gratefully acknowledged). Citation Format: Saamia Shaikh, Melanie Reddy, Sivanesan Dhandayuthapani, Karthikeyan Alagarsamy, Emily Schmitt, Appu Rathinavelu. Effect of Nutlin and E3 ligase inhibitor on p53 and p21 levels in HDM2 expressing LNCaP cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3875. doi:10.1158/1538-7445.AM2013-3875