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 indicator of early biological effects due to the fact that known or suspected carcinogens induce an increased proportion of proteins tightly bound to DNA, Arsenic, a human carcinogen, is reduced and methylated mainly in liver cells generating a number of intermediate reactive forms which could lead to the 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 high content of SH groups, could participate in DPC, The formation and decay of DPC was dose-related. Arsenite was the only intracellular species present since no methylated As forms could be detected. Thus, DPC can be attributed to the presence of arsenite, an important species present in liver during As exposure, whose permanence in the tissue would depend on the methylation rate of the organism. Several cytokeratins were identified by immunoblotting among the proteins crosslinked with DNA, including cytokeratin 18 (CK18), a specific fiver intermediate filament. An augmented presence of CK18 was detected in treated cultures by immunoblotting of total protein PAGE. In liver cells cytokeratin synthesis is tightly correlated with differentiation programs, thus arsenite could not only be damaging DNA but also modifying differentiation patterns in this tissue.