Persistent Oxidative Damage Accounts for the Origin of Mutations Observed in Uterine Pathology

Abstract

Endometrial adenocarcinoma and leiomyomas are prevalent disorders of the same organ. Endometrial cancer, the most prevalently diagnosed gynecological cancer, is associated with mutated PTEN tumor suppressor gene. The type I endometrial cancer PTEN hotspot mutation involves a cytosine to guanine transversion. The mechanism for C to G transversions in endometrial tissue has not been previously explained. For the first time, we show that the CpG dinucleotide of codon 130 is methylated, which increases the likelihood of oxidative damage to the adjacent guanine. 8oxoG, in the presence of peroxynitrite, can form guanidinohydantoin or spiroiminodihydantoin and mispair with guanine, explaining C:G>G:C mutations. We show that uterine tissue is persistently exposed to peroxynitrite, which can also generate nitrotyrosine by interaction with proteins. We have also detected nitrated proteins in benign human uterine tissue, and for the first time identified the predominantly nitrated protein as ACTBL2. Leiomyomas are frequently observed and are a common indication for hysterectomy. Leiomyomas are known to contain MED12 codon 44 mutations at high frequency, involving all 6 possible guanine substitutions in the codon GGT. We show that myometrium is persistently exposed to peroxynitrite, as is endometrium. Oxidative guanine damage, promoted by peroxynitrite exposure, explains the prevalence of guanine mutations observed in leiomyomas. Benign human endometrial tissue and normal myometrium are persistently exposed to peroxynitrite, indicating similar mutagenic pathways in both uterine tissues.