Effects of arsenic on modification of promyelocytic leukemia (PML): PML responds to low levels of arsenite

Inorganic arsenite (iAs3+) is a two-edged sword. iAs3+ is a well-known human carcinogen; nevertheless, it has been used as a therapeutic drug for acute promyelocytic leukemia (APL), which is caused by a fusion protein comprising retinoic acid receptor-α and promyelocytic leukemia (PML). PML, a nuclear transcription factor, has a RING finger domain with densely positioned cysteine residues. To examine PML-modulated cellular responses to iAs3+, CHO-K1 and HEK293 cells were each used to establish cell lines that expressed ectopic human PML. Overexpression of PML increased susceptibility to iAs3+ in CHO-K1 cells, but not in HEK293 cells. Exposure of PML-transfected cells to iAs3+ caused PML to change from a soluble form to less soluble forms, and this modification of PML was observable even with just 0.1 μM iAs3+ (7.5 ppb). Western blot and immunofluorescent microscopic analyses revealed that the biochemical changes of PML were caused at least in part by conjugation with small ubiquitin-like modifier proteins (SUMOylation). A luciferase reporter gene was used to investigate whether modification of PML was caused by oxidative stress or activation of antioxidant response element (ARE) in CHO-K1 cells. Modification of PML protein occurred faster than activation of the ARE in response to iAs3+, suggesting that PML was not modified as a consequence of oxidative stress-induced ARE activation. - Highlights: • PML was found in nuclear microspecles in response to arsenite. • Arsenite triggers SUMOylation of PML. • Arsenite modifies PML at as low as 0.1 μM. • Modification of PML is not caused by ARE activation