Abstract 5113: Carboxyl terminal region of MUC16 is critical for tumor cell invasion and drug resistance.
Authors: Das Srustidhar , Torres-Gonzalez Maria P. , Majhi Prabin D. , Lakshmanan Imayavaramban , Ponnusamy Moorthy P. , Rachagani Satyanarayana , Cruz Eric , Haridas Dhanya , Batra Surinder K. 
Published: August 2014

Abstract
MUC16, also known as CA125, is routinely used to monitor the progression (as a biomarker) and response to therapeutics (as a prognostic marker) for epithelial ovarian cancer (EOC), but the deregulated expression is not restricted only to EOC. Recent studies from our lab have shown that normal breast and pancreas (ducts) do not express MUC16; however its expression progressively increases in primary and metastatic breast and pancreatic cancers. In addition, we have observed the involvement of MUC16 in enhancing the tumorigenic potential by shRNA studies. In the present study, to understand the mechanistic involvement of MUC16, we have focused on its C-terminal region. MUC16 is a type-I membrane-bound mucin with a heavily glycosylated N-terminal domain, a transmembrane region (TM) and a 32-residue cytoplasmic tail (CT) domain. Though it has been predicted that MUC16 undergoes cleavage/shedding in the extracellular SEA domain(s) by proteases such as MMP7 and neutrophil elastase, the exact nature and site of cleavage and the fate of the membrane bound portion (C-terminal) after release of extracellular portion is not entirely understood. The post cleavage C-ter region is interesting due to presence of (a) stretch of polybasic aminoacids, the site of interaction for cytoskeletal proteins like Ezrin/Radixin/Moesin, (b) potential nuclear localization signal (bioinformatics prediction) which might facilitate its nuclear localization with associated transcription factors modulating the transcription of various target genes and (c) several potential serine, threonine and tyrosine phosphorylation sites facilitating its interaction(s) with proteins influencing oncogenic signaling pathways. Therefore, we hypothesized that the oncogenic potential of MUC16 is in part, mediated by the potential involvement of C-terminal domain of MUC16. Thusly, we have made several truncated versions of MUC16 from the C-terminal end with N-terminal FLAG tag and C-terminal HA-tag and are in the process of characterization. To understand the functional significance of this C-terminal region, we have stably transfected MCF7 (breast cancer), MiaPaCa and T3M4 (pancreatic cancer) cells with an empty vector, FLAG-MUC16-114AA-HA and FLAG-MUC16-114AA-dCT (32 AA in the CT is deleted). Our results from in vitro functional assays indicate that C-terminal region of MUC16 is responsible for enhancing the invasive potential of cancer cells and confers resistance to chemotherapeutic agents such as Cisplatin and Gemcitabine. Moreover, we see that the function of the carboxyl terminal MUC16 is dependent on the stability of the protein, which is a function of N-glycosylation and ubiquitylation. Overall, our studies indicate that C-terminal region of MUC16 is an important mediator of cancer cell invasion and drug resistance. (This work is supported from the Department of Defense BC101014).
Citation Format: Srustidhar Das, Maria P. Torres-Gonzalez, Prabin D. Majhi, Imayavaramban Lakshmanan, Moorthy P. Ponnusamy, Satyanarayana Rachagani, Eric Cruz, Dhanya Haridas, Surinder K. Batra. Carboxyl terminal region of MUC16 is critical for tumor cell invasion and drug resistance. [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 5113. doi:10.1158/1538-7445.AM2013-5113