The influence of tyrosine nitration of cytochrome c and caspase 3 on apoptosis induction was investigated in an established squamous carcinoma cell line, OSC-4. The intracellular NO and O2(-) levels were increased up to about 110-120% and 140-180% of the control levels, respectively, after the treatment of OSC-4 cells with 5-FU (100 microg/ml), PLM (10 microg/ml), CDDP (10 microg/ml), or gamma-rays (20 Gy). The treatment of OSC-4 cells with ONOO(-) (1 mM) and the above anticancer agents induced tyrosine nitration of 14, 32 kDa protein among others and nitration of tyrosine residues of cytochrome c and caspase 3 was identified by the Western blotting of immunoprecipitates obtained by antibodies to these proapoptotic proteins. When cytochrome c and procaspase 3 were treated with ONOO(-), tyrosine nitration was increased in a ONOO(-)-dose dependent manner. Tyrosine nitration of cleaved (17 kDa) caspase 3, however, was not induced by ONOO(-). Procaspase 3 in the cytosol of HeLa cells was activated by the addition of ONOO(-)-treated as well as ONOO(-)-untreated cytochrome c. In addition, cleavage of ICAD and PARP were not suppressed in OSC-4 cells by pretreatment with ONOO(-). Activity of cleaved caspase 3 was not suppressed at low concentrations or by treatment with ONOO(-) or NO donors, SIN-1 and SNP. Furthermore, apoptosis of OSC-4 cells by the anticancer agents was not suppressed by ONOO(-). In conclusion, these results suggest that nitration of tyrosine residues of cytochrome c and procaspase 3 is induced by chemoradiotherapy but their nitration does not suppress cancer cell apoptosis.
Copyright 2002 Wiley-Liss, Inc.