Abstract A31: Posttranslational modifications of Chmp1A and their effects on human pancreatic cancer cells
Authors: Park Maiyon 
Published: October 2015

Chromatin modifying protein 1A/Charged multivesicular body protein 1A (Chmp1A) is a member of the Endosomal Sorting Complex Required for Transport (ESCRT)-III family that functions in the sorting of receptor proteins for lysosomal degradation via the formation of endosomal multivesicular bodies. Like other ESCRT-III members, Chmp1A consists of a basic N-, and an acidic C-terminus that contains a motif required for MVB biogenesis. However, Chmp1A is unique among ESCRTs since it has a Nuclear Localization Signal (NLS) at the N-terminus. We have recently reported that Chmp1A, via its NLS, activates ataxia telangiectasia mutated (ATM) and p53 signaling that is partially responsible for the tumor suppressor function of Chmp1A in human pancreatic cancer cells. Through protein motif database searches, we found that Chmp1A contains a potential ubiquitin-interacting motif (UIM), and sumoylation sites, which overlap with NLS. These are new findings since none of the ESCRT-III complex has been reported to have UIMs or sumoylation sites for the interaction with ubiquitin or sumo proteins, respectively. UIM has potential dual functions with ubiquitin binding and promoting mono-ubiquitination. Since SUMO is identified as a “Small Ubiquitin-like MOdifier”, sumoylation sites may act similar to UIM by sumo binding and promoting sumoylation. The goal of our study is first to examine the binding and posttranslational modifications of Chmp1A with ubiquitin and sumo proteins. Second goal is to determine the detailed alterations of binding and modifications of Chmp1A with ubiquitin or sumo proteins in human pancreatic cancer cells, and to examine the effect of these processes on cancer cell growth and activation of ATM and p53 .

Our preliminary data indicates that full-length, but not NLS-deleted Chmp1A interacts with ubiquitin and sumo proteins, and serves as a substrate for ubiquitination or sumoylation in non-tumorigenic cells. In addition, in vitro sumoylation assays indicate that full-length but not NLS-deleted Chmp1A is cleaved upon sumoylation. The UIM- or sumoylation sites- overlapping NLS domain is required for the growth inhibition of Chmp1A in human pancreatic cancer cells. These indicate that the binding and modification with UIM and/or sumoylation sites is important in tumor suppressor function of Chmp1A. Thus, we investigated if the interaction and modification of Chmp1A with ubiquitin or sumo proteins are altered in human pancreatic cancer cells. In pancreatic cancer cells, the bindings of full-length Chmp1A with ubiquitin or sumo proteins are nearly abolished. Unlike in non-tumorigenic cells, full-length Chmp1A was not cleaved upon sumoylation and NLS-deleted Chmp1A showed robust sumoylation in human pancreatic cancer cells, insinuating the significance of these sites in pancreatic cancer cell growth. We generated mutant constructs to abolish specifically either UIM or sumoylation sites without interfering nuclear localization of Chmp1A. Using these constructs, we are investigating the detailed alteration of the binding and modifications of Chmp1A with ubiquitin or sumo proteins, and their effects on growth and signaling activities of ATM and p53 in pancreatic cancer cells. Collectively our study will advance our understanding on the molecular events involved in pancreatic cancers and may facilitate the development of new targets for anticancer therapy.

Citation Format: Maiyon Park. Posttranslational modifications of Chmp1A and their effects on human pancreatic cancer cells. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Innovations in Research and Treatment; May 18-21, 2014; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2015;75(13 Suppl):Abstract nr A31.