Chronic IL-1 Exposure Drives Prostate Cancer Progression

Abstract

Prostate cancer (PCa) is the second most common cause of cancer-related deaths among American men. Androgen Receptor (AR) transcriptional activity is required for PCa tumor growth. Androgens regulate normal prostate tissue growth and differentiation via androgen receptor (AR) activation. Due to the role of androgens in prostate cancer, androgen-deprivation therapy (ADT), either through chemical or surgical castration or the use of anti-androgens, has become the standard therapy. However, ~10-20% of PCa patients will develop treatment resistance, referred to as castration-resistant PCa (CRPC). One mechanism of CRPC is the loss of dependence on AR for cell growth and survival. As such, over 84% of CRPC patients will develop incurable, lethal bone metastasis. Thus, it is important to uncover the mechanisms that drive CPRC. IL-1 is elevated in PCa patient tissue and serum and is associated with disease progression and metastasis. IL-1 is clinically relevant, but the role of IL-1 in CRPC development is not fully elucidated. Chronic inflammation is a known hallmark of cancer initiation and progression. Therefore, we exposed the cancer cells to IL-1 for several months to make the chronic IL-1 sublines, LNas1 and LNbs1. The chronic IL-1 sublines restore AR and AR activity but evolve AR independence and acquire a constitutive p62-KEAP1 interaction. p62 is a multi-domain, multifunctional pro-survival protein that mediates autophagic turnover of damaged proteins and organelles, promotes NF-κB inflammatory signaling and induces NRF2 antioxidant signaling through its binding to and sequestering of KEAP1 from NRF2. Despite constitutive p62- KEAP1 binding, the chronic IL-1 sublines only show elevated NRF2 signaling in the NRF2 target genes, HMOX1 and GCLC. Furthermore, the chronic IL-1 sublines evolve insensitivity to IL-1 extracellular signaling and, thus, do not activate NF-κB nor NRF2 signaling. Thus, the regulation and function of the constitutive p62-KEAP1 interaction in the chronic IL-1 sublines is novel. To investigate the regulation and function of the constitutive p62-KEAP1 interaction in PCa cells chronically exposed to IL-1, I dissected p62-KEAP1 regulation and function under the oxidative stress-inducing stimulus, androgen deprivation. Under androgen deplete conditions, there is attenuation of HMOX1 and overexpression of GCLC in the chronic IL-1 sublines. This suggests that there is active but aberrant NRF2 signaling that may allow these cells to be primed to withstand oxidative stress. Furthermore, knockdown of KEAP1 results in upregulation of HMOX1 suggesting that KEAP1 negatively regulates HMOX1. Both HMOX1 and GCLC function as an antioxidant to attenuate iron-induced lipid ROS and thus regulate iron- dependent cell death known as ferroptosis. Based on what we have found, we hypothesize that the sublines activate a novel pathway that primes them to withstand ferroptosis-induced cell death.