Abstract P4-10-02: Transmembrane protein 33 (TMEM33) induces apoptosis via UPR signaling and autophagy in breast cancer cells

Breast cancer is the most common cancer diagnosed in women. Endoplasmic reticulum stress (EnR stress) and the related unfolded protein response (UPR) are activated in breast cancer cells and can promote cell survival and endocrine resistance. TMEM33 is a novel transmembrane protein that resides in the endoplasmic reticulum (EnR) and has been shown to activate the PERK and IRE1α branches of the UPR. However, the underlying mechanism of action of this EnR resident protein TMEM33 and the cellular functions that it regulates remain largely unknown. In this study, we show that overexpression of TMEM33 induces robust cell death in breast cancer cells. TMEM33 overexpression strongly activates UPR associated pro-death JNK-p53 signaling. We also observed a significant inhibition of the downstream survivin, which blocks cell death activation by binding to caspases and inhibiting their activation. We further show that the blockage of JNK activation with either an inhibitor or overexpression of survivin, protects cells against TMEM33 induced apoptosis. In addition, we show that TMEM33 overexpression induces autophagy in breast cancer cells. Inhibition of autophagy with using either the inhibitor chloroquine or knockdown of the Atg5 gene, further sensitizes breast cancer cells to the effects of TMEM33 overexpression. Cell death induced by TMEM33 is also decreased by overexpression of the autophagy gene Beclin 1. The findings in this study demonstrate that the novel EnR resident protein TMEM33 induces cell death by activating IRE1α-JNK-p53-survivin signaling in breast cancer cells. Concurrently, autophagy is also activated by TMEM33, and functions as a pro-survival mechanism. Cell fate reflects the balance between the pro-death and pro-survival activities as regulated by TMEM33. Citation Format: Clarke R, Hu R, Zhang X, Hilakivi-Clarke L, Kasid U. Transmembrane protein 33 (TMEM33) induces apoptosis via UPR signaling and autophagy in breast cancer cells [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P4-10-02.