Abstract 4277: Inhibition of autophagy (Plac8) prevents malignant transformation of cadmium induced prostate carcinogenesis

Abstract

Abstract Introduction: Cadmium (Cd) exposure is associated with an increased risk of prostate cancer (CaP). Previously we reported that Cd induces Plac8 expression may be responsible for defective autophagy which facilitates the transformation of prostate epithelial cells. The goal of this study is to decipher the molecular signaling responsible for defective autophagy by plac8 and whether inhibition of plac8 facilitates pro-apoptotic machinery in chronically exposed -Cd in prostate epithelial cells. Methods: Overexpression or silencing Plac8 in chronically exposed Cd in RWPE-1 cells or cadmium, transformed prostate epithelial (CTPE) cells were subjected to cell viability, apoptosis, autophagy functional studies, Western blot and in vivo analyses. For statistical analysis, data were analyzed using Student’s‘t’ test with a p-value less than 0.05 considered significant. Results: Our results suggest that during cellular transformation, Cd exposure induced Plac8 expression, which caused defective-autophagy that resulted in the proliferation of damaged cells. Inhibition of Plac8 resulted in suppression of pro-survival machinery and concomitantly induced severe endoplasmic reticulum (ER) stress that resulted in caspase-mediated cell death in Cd-exposed cells. More specifically, inhibition of Plac8 by shRNA resulted in induction of ER stress markers (PREK/ATF4) which facilitate caspase-mediated cell death in Cd- transformed prostate epithelial cells. Activation of NFKB is one of the downstream events of Plac8 that transcriptionally regulates NFKB activation in Cd-transformed cells. We identified, Plac8 binding sites in NFKB promoter. Hence inhibition of plac8 resulted in the complete shutdown of NFKB mediated pro-survival signaling in Cd-transformed prostate epithelial cells. While analyzing autophagy signaling network, we found induction of Atg family proteins, however, in the absence of Plac8, the induction of autophagy fails to protect the Cd-transformed cells. Similar results were observed in plac8 silenced cd-transformed cells in xenotransplanted mice, where Cd-transformed cells induced aggressive tumors, and Plac8 knockdown significantly inhibited the tumor growth. While ATF4, PLac8, NFKB were not expressed in normal human prostate tissues, their expression was significantly increased in BPH followed by CaP specimens; normal prostate < BPH << Gleason 6-7 CaP < Gleason 8-10 CaP. Cd levels were much higher in tumor tissues (21.43 μg/g) of CaP patients than in healthy controls (1.12 μg/g). The levels also correlated with Plac8 expression. These results demonstrate the clinical significance of Cd levels and of Plac8 expression as plausible drivers of Cd-induced transformation in prostate carcinogenesis. Conclusions: These results suggest that Plac8 may be an essential component in the Cd-induced transformation of normal prostate epithelial cells to a cancerous state. Citation Format: Venkatesh Kolluru, Ashish Tyagi, Balaji Chandrasekaran, Murali K. Ankem, Chendil Damodaran. Inhibition of autophagy (Plac8) prevents malignant transformation of cadmium induced prostate carcinogenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4277.