Abstract 1001: Protein Kinase D1 induces autophagic cell death through activation of endoplasmic reticulum stress in prostate cancer cells
Authors: Gara Rishi K. , Kumari Sonam , Khan Sheema , Chauhan Neeraj , Ganju Aditya , Chauhan Subhash C. , Jaggi Meena 
Published: August 2015

Background: Advanced stage of prostate cancer is difficult to treat and manage. Autophagy facilitates both disease progression and therapeutic resistance in prostate cancer. In fact, different forms of therapies such as androgen-deprivation, taxane-based chemotherapy, targeted kinase inhibition, and nutrient restriction, all induce significant cellular distress, and subsequently autophagy, which plays cyto-protective role in prostate cancer. The differential role of autophagy in prostate cancer cells is mainly dependent on the type of tumors, stage, and genetic context of cancer cells. Protein Kinase D1 is a serine-threonine kinase, a tumor-suppressor, which is down-regulated in advanced stage of prostate tumors. PKD1 is involved in many cellular functions, such as cell proliferation, apoptosis, cell adhesion and invasion. In this study we try to determine whether PKD1 causes autophagic cell death by activation of ER stress in prostate cancer cells.

Methods: Prostate cancer cells expressing PKD1 (LNCaP and C4-2; C4-2-GFP; C4-2-GFP-PKD1) and null PKD1 (DU-145/PC-3) were used for the experiments. Cell viability assay was performed by MTS assay. CCL2 expression levels were quantified by ELISA. Cell migration assays were performed with cells pre-incubated with 3-Methyladenine (3-MA; autophagy inhibitor), or Salubrinal (SAL; ER stress inhibitor) or exogenously added CCL2 (100ng/mL). Immmunoblot experiments were performed using specific antibodies.

Results: Our results suggest that PKD1 inhibits cell proliferation, migration and colonization, and arrest cells at G2/M phase. Our data strongly suggests that PKD1overexpressing cell activates Endoplasmic Reticulum (ER) stress-mediated autophagic cell death in prostate cancer cells compared to PKD1-null cells. Immunoblotting experiment suggested that C4-2-PKD1-GFP cells have suppressed ATG5/ATG7 and free ATG12 expression as compared to PKD1-null DU-145/PC-3 cells. These proteins are involved in the cyto-protective role of autophagy in prostate cancer cells. PKD1 also interacts and activates PERK expression, which is an initiator of Endoplasmic Reticulum stress (ER stress). PKD1-overexpressing C4-2-PKD-1-GFP and C4-2-GFP (vector control) cells inhibited nuclear translocation of oncogenic proteins such as c-Myc, ATG-5, p-NFKB-65 and β-catenin, and enhanced PERK and GSK-3β expression. Interestingly, PKD1 also suppressed the expression of p-AKT and mTOR and decreased glucose uptake in prostate cancer cells. Thus, PKD1 regulates glucose uptake with the involvement of AKT-mTOR-GSK-3β axis and decreases the nuclear translocation of c-Myc, ATG-5, p-NFKB-65 and β-catenin in prostate cancer cells.

Conclusions: Our results strongly suggest that the PKD1 mediated modulation of autophagy and ER stress induced cell death can be useful for the augmentation of current chemotherapies used for prostate cancer treatment.

Citation Format: Rishi K. Gara, Sonam Kumari, Sheema Khan, Neeraj Chauhan, Aditya Ganju, Subhash C. Chauhan, Meena Jaggi. Protein Kinase D1 induces autophagic cell death through activation of endoplasmic reticulum stress in prostate cancer cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1001. doi:10.1158/1538-7445.AM2015-1001