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

B ACKGROUND : Inorganic arsenic (iAs) is an environmental toxicant associated with an increased risk of prostate cancer in chronically exposed popu- lations worldwide. However, the biological mechanisms underlying iAs-induced prostate carcinogenesis remain unclear. O BJECTIVES : We studied how iAs a ff ects normal human prostate stem -progenitor cells (PrSPCs) and drives transformation and interrogated the mo- lecular mechanisms involved. M ETHODS : PrSPCs were enriched by spheroid culture from normal human primary or immortalized prostate epithelial cells, and their di ff erentiation capability was evaluated by organoid culture. Microarray analysis was conducted to identify iAs-dysregulated genes, and lentiviral infection was used for stable manipulation of identi fi ed 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. R ESULTS : Low -dose iAs (1 lM) disturbed PrSPC homeostasis in vitro , leading to increased self -renewal and suppressed di ff erentiation. Transcriptomic analysis indicated that iAs activated oncogenic pathways in PrSPCs, including the KEAP1-NRF2 pathway. Further, iAs-exposed pro- liferative progenitor cells exhibited NRF2 pathway activation that was sustained in their progeny cells. Knockdown of NRF2 inhibited spheroid for- mation by driving PrSPC di ff erentiation, 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 acidi fi cation 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. C ONCLUSIONS : Low -dose iAs increased self -renewal and decreased di ff erentiation of human PrSPCs by activating the p62-NRF2 axis, resulting in epithelial cell transformation. NRF2 is activated by iAs through speci fi c autophagic fl ux blockade in progenitor cells, which may have potential thera- peutic implications. https://doi.org/10.1289/EHP6471