Amino acid chloramine damage to proliferating cell nuclear antigen in mammalian cells.

Unlabelled: Amino acid chloramines (AACLs) are reactive secondary products of activated neutrophils. To understand AACL damage in cell nuclei, we exploited proliferating cell nuclear antigen (PCNA) as a nuclear protein damage reporter, using western blotting and mass spectrometry. Chloramines of proline, arginine, and glycine caused significant damage to PCNA in cells. Chloramines of taurine and histidine caused slight damage to PCNA in cells. Other AACLs caused no PCNA damage in intact cells. Evidence supports a sulfonamide, sulfinamide, or sulfenamide crosslinking mechanism involving cysteine 148 at the PCNA subunit interface, methionine sulfoxide formation as the basis of electrophoretic mobility shifting, and tyrosine and/or methionine residues as the likely targets of AACL damage to the PCNA antibody epitope. An interstitial fluid model experiment showed that physiological amino acids can mediate HOCl damage to PCNA in the presence of proteins that would otherwise completely quench the HOCl.

Conclusion: PCNA is a sensitive biomarker of AACL damage in cell nuclei. Arginine chloramine and proline chloramine, or reactive species derived from them, were shown to enter cells and damage PCNA. Amino acids were shown to have at least two different mechanisms for suppressing PCNA damage in cells by their corresponding AACLs. Cysteine 148 was shown to be essential for PCNA subunit crosslinking by AACLs, and a crosslinking mechanism was proposed.