Abstract PR09: Plac8 links oncogenic mutations to regulation of autophagy and is critical to pancreatic cancer progression
Authors: Balakrishnan Vijaya , Conan Kinsey , O'Dell Michael , Huang Jing Li , Newman Laurel , Whitney-Miller Christa , Land Hartmut , Hezel Aram 
Published: October 2015

Abstract
A) Pancreatic ductal adenocarcinoma (PDA) depends on a marked reprogramming of metabolic pathways, including the acquisition of autophagy dependence, for survival and growth. How common mutations in PDA cause autophagy dependence as well as the timing of autophagy activation in the course of cancer progression, have not been established. Here we show how Plac8, a gene synergistically up-regulated in response to the common cooperating oncogenic mutations found in PDA (RAS activation and functional loss of p53), is critical to the growth of PDA by sustaining autophagy via facititating autophagosome-lysosome fusion. Furthermore, we delineate that Kras and p53 mutations cooperate to induce autophagic flux. B) To establish Plac8’s role in PDA growth and autophagy we use murine cell lines and human PDA cell lines to determine 1) the lysosomal localization of Plac8, 2) its role in regulating autophagy using both loss of function and gain of function approaches, 3) the impact on lysosomal biology, and 4) the relationship between Plac8 and other genetic pathways governing autophagy. Using genetically engineered models of PDA we determine the timing of autophagy activation in PDA progression and the impact of Plac8 mutation. C) We identify Plac8 as a novel regulator of autophagosome-lysosome fusion required for PDA growth, thus providing a mechanistic link between oncogenic mutations and the activation of autophagy in cancer. Plac8 expression is required for growth of human PDA cells as xenografts in mice, as well as activation of autophagy. We find that concurrent mutation of KRAS and p53 is critical for maximal induction of autophagy in vitro. Correspondingly, using genetically engineered mouse models of PDA (Pdx1-Cre; LSL-KrasG12D; p53L/+), in which loss of p53 function occurs in a step-wise manner relying on the spontaneous loss of a heterozygous WT p53 allele, we see a step-wise incremental increase in LC3 puncta in vivo with each histological stage through the course of PDA progression. Thus, we find that the cooperative effects of KRAS and p53 drive activation of autophagy rather than either mutation alone. The overall survival of a Pdx1-Cre; LSL-KrasG12D; p53L/+; Plac8null murine cohort (OS 27.9 wks) was significantly longer than a Pdx1-Cre; LSL-KrasG12D; p53L/+; Plac8wt cohort (OS 17.0 wks, p=0.0006) demonstrating in vivo that genetic inactivation of Plac8 impedes cancer progression and resulting death. Our data suggest that the role of Plac8 in facilitating autophagy is critical to cancer, as the requirement of Plac8 for both tumorigenicity and autophagy can be compensated by over-expression of Atg12, a gene critical for autophagosome formation or by constitutively activated Rab7, a gene encoding a GTP-binding protein stimulating autophagosome-lysosome fusion. D) We conclude that Plac8 may offer a potential therapeutic window and point of intervention, as Plac8 mutation in the engineered PDA model inhibits cancer progression and significantly improves survival while having a minimal impact on the overall fitness of the animals. In fact, Plac8, and regulation of autophagosome-lysosome fusion, has specific relevance to regulation of autophagy during malignant cell transformation as Plac8 and the processes it regulates, appear to be largely dispensable to many normal physiologic processes.
This abstract is also presented as Poster B36.
Citation Format: Vijaya Balakrishnan, Kinsey Conan, Michael O'Dell, Jing Li Huang, Laurel Newman, Christa Whitney-Miller, Hartmut Land, Aram Hezel. Plac8 links oncogenic mutations to regulation of autophagy and is critical to pancreatic cancer progression. [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 PR09.