Effects of Inorganic Arsenic on Human Prostate Stem-Progenitor Cell Transformation, Autophagic Flux Blockade, and NRF2 Pathway Activation

Abstract

BACKGROUND: Inorganic arsenic (iAs) is an environmental toxicant associated with an increased risk of prostate cancer in chronically exposed populations worldwide. However, the biological mechanisms underlying iAs-induced prostate carcinogenesis remain unclear. OBJECTIVES: We studied how iAs affects normal human prostate stem-progenitor cells (PrSPCs) and drives transformation and interrogated the molecular mechanisms involved. METHODS: PrSPCs were enriched by spheroid culture from normal human primary or immortalized prostate epithelial cells, and their differentiation capability was evaluated by organoid culture. Microarray analysis was conducted to identify iAs-dysregulated genes, and lentiviral infection was used for stable manipulation of identified genes. Soft agar colony growth assays were applied to examine iAs-induced transformation. For in vivo study, PrSPCs mixed with rat urogenital sinus mesenchyme were grafted under the renal capsule of nude mice to generate prostatelike tissues, and mice were exposed to 5 ppm (∼ 65 lM) iAs in drinking water for 3 months. RESULTS: Low-dose iAs (1 lM) disturbed PrSPC homeostasis in vitro, leading to increased self-renewal and suppressed differentiation. Transcriptomic analysis indicated that iAs activated oncogenic pathways in PrSPCs, including the KEAP1-NRF2 pathway. Further, iAs-exposed proliferative progenitor cells exhibited NRF2 pathway activation that was sustained in their progeny cells. Knockdown of NRF2 inhibited spheroid formation by driving PrSPC differentiation, whereas its activation enhanced spheroid growth. Importantly, iAs-induced transformation was suppressed by NRF2 knockdown. Mechanistically, iAs suppressed Vacuolar ATPase subunit VMA5 expression, impairing lysosome acidification and inhibiting autophagic protein degradation including p62, which further activated NRF2. In vivo, chronic iAs exposure activated NRF2 in both epithelial and stroma cells of chimeric human prostate grafts and induced premalignant events. CONCLUSIONS: Low-dose iAs increased self-renewal and decreased differentiation of human PrSPCs by activating the p62-NRF2 axis, resulting in epithelial cell transformation. NRF2 is activated by iAs through specific autophagic flux blockade in progenitor cells, which may have potential therapeutic implications.

Reciprocal regulation of NRF2 by autophagy and ubiquitin–proteasome modulates vascular endothelial injury induced by copper oxide nanoparticles

“…Consistently, several autophagy inhibitors 3-MA, Wort and CQ prevented HMOX1 transcription in CuONPs-treated HUVECs (F i g. 5 E–I). Our data are consistent to a recent report uncovering that arsenic activated NRF2 pathway in primary human prostate epithelial cells via an autophagy-dependent manner [ 62 ]. These data indicate autophagy is involved in CuONPs-mediated NRF2 activation in HUVECs via a novel singling pathway but not classical SQSTM1-KEAP1-NRF2 pathway.…”

Heavy Metals in the Environment and Thyroid Cancer

“…This observation could translate into clinical consequences: during sensitive life stages (such as prenatal life and early childhood), metals in the environment could cause thyroid stem cell damage at a low level of exposure that would have little or no adverse effects in well-differentiated thyroid cells. As suggested by previous studies in hormone-sensitive tissues like the prostate [46] and the thyroid [109], stem/progenitor cells may be the long-lived targets of toxicants that alter their differentiation capacity and increase their transformation susceptibility. Preliminary in vitro evidence with W indicates that thyroid cell progenitors exposed to slightly increased metal concentrations may be the origin of mature thyrocytes with abnormal characteristics typical of transformed cells [61].…”

“…In vitro, there were no effects in human thyroid cell morphology, viability, or proliferation when thyrocytes in primary cultures were chronically (72 h) exposed to several heavy metals (Cd, Cu, Hg, Mn, Pd, W, and Zn) at concentrations that are 0.1-100-fold relative to those measured in the urines of residents of the volcanic area. Based on previous observations [45][46][47][48] that immature progenitor cells may be more sensitive to the toxic effect of pollutants, we tested the same heavy metals, at the same low concentrations, in undifferentiated human thyrocytes in the form of thyrospheres. Thyrospheres are aggregates of thyroid stem cells and precursors of thyrocytes at a different level of differentiation [49] that, depending on the culture conditions, are able to differentiate into mature thyrocytes or produce additional thyrospheres by a process involving stem cells and named selfrenewal [50].…”

AS3MT facilitates NLRP3 inflammasome activation by m6A modification during arsenic-induced hepatic insulin resistance

“…Although the limit of arsenic content in groundwater set by the WHO is 10 μg/L, the arsenic content of groundwater in most arsenic-contaminated areas is much higher than this limit. Therefore, in the current study, we selected a concentration of 4 mg/L for animal experiments, based on the concentration of arsenic in arsenic-contaminated areas and the results of previous literature studies (Perry et al 2013 ; Rodriguez et al 2016 ; Castriota et al 2020 ; Xie et al 2020 ).…”