Differential activation of AP‐1 in human bladder epithelial cells by inorganic and methylated arsenicals

Abstract

Chronic exposures to inorganic arsenic (iAs) have been linked to increased incidences of various cancers, including cancer of the urinary bladder. Mechanisms by which iAs promotes cancer may include stimulation of activator protein-1 (AP-1) DNA binding through increased expression and/or phosphorylation of the AP-1 constituents. However, the role of methylated metabolites of iAs in AP-1 activation has not been thoroughly examined. In this study, we show that short-time exposures to 0.1-5 microM arsenite (iAsIII) or the methylated trivalent arsenicals methylarsine oxide (MAsIIIO), or iododimethylarsine (DMAsIIII) induce phosphorylation of c-Jun and increase AP-1 DNA binding activity in human bladder epithelial cells. DMAsIIII and especially MAsIIIO are considerably more potent than iAsIII as inducers of c-Jun phosphorylation and AP-1 activation. Phosphorylated c-Jun, JunB, JunD, and Fra-1, but not c-Fos, FosB, or ATF-2, are detected in the AP-1-DNA binding complex in cells exposed to trivalent arsenicals. In cells transiently transfected with an AP-1-dependent promoter-reporter construct, MAsIIIO was more potent than iAsIII in inducing the AP-1-dependent gene transcription. Exposures to trivalent arsenicals induce phosphorylation of extracellular signal-regulated kinase (ERK), but not c-Jun N-terminal kinases or p38 kinases. These results indicate that an ERK-dependent signal transduction pathway is at least partially responsible for c-Jun phosphorylation and AP-1 activation in UROtsa cells exposed to inorganic or methylated trivalent arsenicals.

Metabolism and toxicity of arsenic in human urothelial cells expressing rat arsenic (+3 oxidation state)-methyltransferase

“…We have also shown that UROtsa cells do not express AS3MT . Importantly, comparison of our previous work (Drobná et al, 2003;Lin et al, 2002;) with results of the present study suggests that serum starvation for 16 h has no effect on AS3MT expression or on the metabolic pattern of iAs in UROtsa cells.…”

“…However, no details regarding the speciation technique or data validation are provided. Our studies on the metabolism and toxic effects of As in UROtsa cells (Drobná et al, 2003;Styblo et al, 2000Styblo et al, , 2002 have consistently shown that these cells do not methylate iAs. Notably, T24 cells, another cell line derived from human bladder epithelium, also lack the capacity to methylate iAs (Styblo et al, 2000).…”

“…Confluent cell cultures were serum starved for 16 h before use in experiments. These or similar culture conditions, including serum starvation, have previously been used by this and other laboratories in studies that examined the metabolism and toxic effects of iAs in UROtsa cells (Drobná et al, 2003;Simeonova et al, 2000Simeonova et al, , 2002Styblo et al, 2000Styblo et al, , 2002. Notably, serum starvation for 16 h had no effect on the integrity or morphology of cultured cells.…”

“…For this assay, cells were cultured in 96-well plates to confluence and then exposed to iAs III , MAs III , or DMAs III for 24 h. The MTT assay was performed as previously described (Drobná et al, 2003).…”

“…However, unlike iAs species, DMAs V and TMAs V O at high doses are complete carcinogens in adult rats (Shen et al, 2003;Wei et al, 1999). In contrast, methylated trivalent arsenicals, methylarsonous acid (MAs III ) and dimethylarsonous acid (DMAs III ), are more toxic than iAs in vivo (Petrick et al, 2001) and are more potent than iAs as enzyme inhibitors (Lin et al, 2001;Petrick et al, 2001;, cytotoxins (Petrick et al, 2000;Styblo et al, 2000, and as modulators of cell signaling pathways (Drobná et al, 2003;. In addition, MAs III and DMAs III are more potent than iAs as DNA-damaging agents in vitro and in cultured cells (Kligerman et al, 2003;Mass et al, 2001).…”