Arsenite induces DNA-protein crosslinks and cytokeratin expression in the WRL-68 human hepatic cell line

The induction of DNA-protein crosslinks (DPC) has been proposed as an indic ator of early biological effects due to the fact that known or suspected ca rcinogens induce an increased proportion of proteins tightly bound to DNA, Arsenic, a human carcinogen, is reduced and methylated mainly in liver cell s generating a number of intermediate reactive forms which could lead to th e formation of DNA-protein crosslinks, The induction of DPC by arsenite [As (III)] was investigated in the WRL-68 human hepatic cell line, testing the possibility that cytokeratins or cytokeratin-like proteins, due to their hi gh content of SH groups, could participate in DPC, The formation and decay of DPC was dose-related. Arsenite was the only intracellular species presen t since no methylated As forms could be detected. Thus, DPC can be attribut ed to the presence of arsenite, an important species present in liver durin g As exposure, whose permanence in the tissue would depend on the methylati on rate of the organism. Several cytokeratins were identified by immunoblot ting among the proteins crosslinked with DNA, including cytokeratin 18 (CK1 8), a specific fiver intermediate filament. An augmented presence of CK18 w as detected in treated cultures by immunoblotting of total protein PAGE. In liver cells cytokeratin synthesis is tightly correlated with differentiati on programs, thus arsenite could not only be damaging DNA but also modifyin g differentiation patterns in this tissue.