The clinical use of
anthracyclines to treat various canine
cancers is limited by the development of
cardiotoxicity. The intra-cardiac synthesis of
anthracycline C-13 alcohol metabolites (e.g.
daunorubicinol) contributes to the development of
cardiotoxicity. Canine
carbonyl reductase 1 (cbr1) catalyzes the reduction of
daunorubicin into
daunorubicinol. Recent mapping of the cbr1 locus by sequencing
DNA samples from dogs from various breeds revealed a cluster of conserved motifs for the
transcription factor Sp1 in the putative promoter region of cbr1. We hypothesized that the variable number of Sp1 motifs could impact the transcription of canine cbr1. In this study, we report the functional characterization of the canine cbr1 promoter. Experiments with reporter constructs and
chromatin immunoprecipitation show that cbr1 transcription depends on the binding of Sp1 to the proximal promoter. Site-directed mutagenesis experiments suggest that the variable number of Sp1 motifs impacts the transcription of canine cbr1. Inhibition of Sp1-DNA binding decreased canine cbr1
mRNA levels by 54% in comparison to controls, and also decreased enzymatic
carbonyl reductase activity for the substrates
daunorubicin (16%) and
menadione (23%). The transactivation of Sp1 increased the expression of cbr1
mRNA (67%), and increased
carbonyl reductase activity for
daunorubicin (35%) and
menadione (27%). These data suggest that the variable number of Sp1 motifs in the canine cbr1 promoter may impact the pharmacodynamics of
anthracyclines in canine
cancer patients.