Restoration of the DNA binding activity of estrogen receptor in MRL‐lpr/lpr mice by a polyamine biosynthesis inhibitor

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Abstract
Diverse data link estrogen influences to both the frequency and severity of systemic lupus erythematosus in humans and to murine lupus. A fundamental mechanism of action of estrogen involves the interaction of the hormone with its receptor protein, which is then transformed into the DNA binding form. We measured the concentration of uterine estrogen receptor and its DNA binding in normal BALB/c mice, lupus‐prone MRL‐lpr/lpr mice, and MRL‐lpr/lpr mice that had been treated with 1% difluoromethylornithine (DFMO). Uterine estrogen receptor levels in 20‐week‐old mice from the 3 groups were not significantly different. In contrast, DNA binding activity was significantly higher in BALB/c mice (mean ± SD 775 ± 100 fmoles/mg of DNA) than in untreated MRL‐lpr/lpr mice (80 ± 16 fmoles/mg of DNA) (P < 0.001). Treatment with 1% DFMO was associated with an increase in uterine estrogen receptor DNA binding (1,100 ± 218 fmoles/mg of DNA) in MRL‐lpr/lpr mice (P < 0.001). Polyamine levels were 2–6‐fold higher in the uterine tissues of untreated MRL‐lpr/lpr mice compared with the BALB/c mice and were significantly reduced by DFMO treatment. Our results link uterine polyamine production to a dysfunction of the estrogen receptors in MRL‐lpr/lpr mice. Reduction of the polyamine level by the irreversible inhibition of ornithine decarboxylase with DFMO restores estrogen receptor function.