ABSTRACT
Previously, we showed that the mouse LIM-domain only 4 (Lmo4) gene, which encodes a protein containing two zinc-finger LIM domains that interact with various DNA-binding transcription factors, attenuates behavioral sensitivity to repeated cocaine administration. Here we show that transcription of anaplastic lymphoma kinase (Alk) is repressed by LMO4 in the striatum and that Alk promotes the development of cocaine sensitization and conditioned place preference, a measure of cocaine reward. Since LMO4 is known to interact with estrogen receptor α (ERα) at the promoters of target genes, we investigated whether Alk expression might be controlled by a similar mechanism. We found that LMO4 and ERα are associated with the Alk promoter by chromatin immunoprecipitation and that Alk is an estrogen-responsive gene in the striatum. Moreover, we show that ERα knock-out mice exhibit enhanced cocaine sensitization and conditioned place preference and an increase in Alk expression in the nucleus accumbens. These data define a novel regulatory network involved in behavioral responses to cocaine. Interestingly, sex differences in several behavioral responses to cocaine in humans and rodents have been described, and estrogen is thought to mediate some of these differences. Our data suggest that estrogen regulation of Alk may be one mechanism responsible for sexually dimorphic responses to cocaine.
Subject(s)
Adaptor Proteins, Signal Transducing/biosynthesis , Cocaine/pharmacology , Estrogen Receptor alpha/biosynthesis , Gene Targeting/methods , LIM Domain Proteins/biosynthesis , Receptor Protein-Tyrosine Kinases/biosynthesis , Reward , Transcription, Genetic/physiology , Adaptor Proteins, Signal Transducing/genetics , Anaplastic Lymphoma Kinase , Animals , Animals, Newborn , Cells, Cultured , Cocaine/metabolism , Estrogen Receptor alpha/genetics , HEK293 Cells , Humans , LIM Domain Proteins/genetics , Male , Mice , Mice, Inbred C57BL , Mice, Knockout , Motor Activity/drug effects , Motor Activity/genetics , Receptor Protein-Tyrosine Kinases/genetics , Transcription, Genetic/drug effectsABSTRACT
BACKGROUND: Previous work from our laboratory demonstrated a role for the Drosophila Lim-only (dLmo) gene in regulating behavioral responses to cocaine. Herein, we examined whether dLmo influences the flies' sensitivity to ethanol's sedating effects. We also investigated whether 1 of the mammalian homologs of dLmo, Lmo3, is involved in behavioral responses to ethanol in mice. METHODS: To examine dLmo function in ethanol-induced sedation, mutant flies with reduced or increased dLmo expression were tested using the loss of righting (LOR) assay. To determine whether mouse Lmo3 regulates behavioral responses to ethanol, we generated transgenic mice expressing a short-hairpin RNA targeting Lmo3 for RNA interference-mediated knockdown by lentiviral infection of single cell embryos. Adult founder mice, expressing varying amounts of Lmo3 in the brain, were tested using ethanol loss-of-righting-reflex (LORR) and 2-bottle choice ethanol consumption assays. RESULTS: We found that in flies, reduced dLmo activity increased sensitivity to ethanol-induced sedation, whereas increased expression of dLmo led to increased resistance to ethanol-induced sedation. In mice, reduced levels of Lmo3 were correlated with increased sedation time in the LORR test and decreased ethanol consumption in the 2-bottle choice protocol. CONCLUSIONS: These data describe a novel and conserved role for Lmo genes in flies and mice in behavioral responses to ethanol. These studies also demonstrate the feasibility of rapidly translating findings from invertebrate systems to mammalian models of alcohol abuse by combining RNA interference in transgenic mice and behavioral testing.
