Abstract 1118: Nuclear-mediated function of Chmp1A in the regulation of ATM signaling activity for the control of human pancreatic tumor cell growth

Abstract

Abstract The American Cancer Society estimated that pancreatic cancer is the 4th leading cause of cancer death, following lung and bronchus, colon and rectum, and breast. However, the survival rate of pancreatic cancer patients is the lowest among all the cancer types combined. This poor prognosis underscores the need for innovative understanding of its molecular mechanisms, which would aid in the development of new therapeutics for pancreatic cancer patients. Chromatin modifying protein 1A/Charged multivesicular body protein (Chmp1A) is a member of the Endosomal Sorting Complex Required for Transport (ESCRT-III) family that functions in the sorting and/or degradation of receptor mediated proteins via the endocytic pathway. However, recent reports indicate that Chmp1A has additional functions: Howard's group reported that Chmp1A regulates cell cycle progression and chromatin condensation. We demonstrated that Chmp1A over-expression leads to inhibition of cell and xenograft tumor growth, and that nuclear localization of Chmp1A is required for the mediation of the inhibitory effects of all-trans retinoic acid (ATRA) of human pancreatic tumor cells. Chmp1A appears to regulate tumor growth through the stabilization of P53. P53 is a substrate of an ataxia-telangiectasia mutated (ATM) kinase, and ATM activation is closely related to chromatin modification. Thus, we hypothesize that Chmp1A, through its nuclear localization, regulates nuclear ATM signaling activity and subsequent pancreatic tumor growth. We are in the process of testing our hypotheses in human pancreatic ductal tumor (PanC-1) cells. Our preliminary data indicates that Chmp1A over-expression led to an increase in phospho-ATM at serine 1981 (an indicator of activation) in the nucleus. Immuno-staining identified the co-localization of ectopically induced Chmp1A with phospho-ATM and its target P53 whose intensity was closely reflecting that of Chmp1A expression. ATM kinase assay indicated that Chmp1A over-expression increased ATM kinase activity as evidenced by an increase in the level of phospho-P53 compared to control. In addition, ATM inhibitor-treated PanC-1 cells de-repressed Chmp1A mediated-growth inhibition and P53 stabilization. To test the significance of the nuclear localization signal (NLS) domain of Chmp1A we generated NLS-deletion and minimal NLS-domain of Chmp1A that was detected mainly in the cytoplasm and nucleus, respectively. We are in the process of generating stable clones of PanC-1 cells to conditionally over-express these deletion constructs. Once it is generated, we will test the effect of the NLS domain of Chmp1A on signaling activity of ATM and P53, and pancreatic tumor cell growth. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1118.