Dorit Ron, Ph.D., Director
The goal of this component is to study the role of the small G protein H-Ras in ethanol's action.
Previously the Ron lab found that the activity of H-Ras is increased upon ethanol exposure in the
hippocampus (Suvarna et al., 2004), and in the reward pathway. Furthermore, activation of H-Ras
contributes to the inhibitory actions of ethanol on the activity of the N-Methyl-D-Asparate receptor,
one of the main targets of ethanol in the brain. Systemic administration of a dominant negative form
of H-Ras decreased voluntary ethanol, but not water, intake. Interestingly, the H-Ras transcript
was recently shown to be up-regulated in brains of selected lines of mice that consume high levels
of ethanol (Mulligan et al., 2006). These findings led to the hypothesis that H-Ras plays an important
role in neuroadaptations that underlie behaviors associated with ethanol exposure, such as ethanol
drinking behaviors. This component is using a virus-mediated gene delivery approach to down-regulate
and up-regulate the level and activity of H-Ras in the reward pathway, and testing for possible
molecular, electrophysiological and behavioral consequences of ethanol-mediated activation of H-Ras.
In addition, the investigators are using similar approaches to test for possible mechanisms that
lead to the activation of H-Ras by ethanol.
Ras inhibitors are currently being developed by the pharmaceutical industry as potential drugs for the
treatment of cancer. Therefore, results obtained from these experiments could lead to rapid development
of new medications to treat alcohol addiction. Furthermore, Ras is a focal point in various signaling
cascades to be investigated within the ACTG (i.e., Component 7 - Tao kinases, Pilot Project 9B - Puckered
MAP kinase phosphatase and Pilot Project 9B - atypical PKCs). In addition, Ras and several of its
regulators are found in the C. elegans genome, thus providing a rapid genetic approach to characterize
the role of Ras in ethanol's actions (Component 6).
Ethanol alters trafficking and functional N-methyl-D-aspartate receptor NR2 subunit ratio via H-Ras.
Suvarna N, Borgland SL, Wang J, Phamluong K, Auberson YP, Bonci A, Ron D. J Biol Chem. 2005 Sep 9;280(36):31450-9.
Toward understanding the genetics of alcohol drinking through transcriptome meta-analysis.
Mulligan MK, Ponomarev I, Hitzemann RJ, Belknap JK, Tabakoff B, Harris RA, Crabbe JC, Blednov YA, Grahame NJ, Phillips TJ, Finn DA, Hoffman PL, Iyer VR, Koob GF, Bergeson SE. Proc Natl Acad Sci U S A. 2006 Apr 18;103(16):6368-73.
Steven McIntire, M.D., Ph.D., Director
This project stems from previous work in the McIntire lab using C. elegans as a model system to understand
the different molecular mechanisms of action of ethanol. We have identified two novel and highly
conserved genes, unc-79 and unc-80, which are required for ethanol responses in C. elegans. In the case
of unc-79, we have also identified a mouse with a mutation in the mouse homologue of unc-79, munc-79,
through a forward mutagenesis study in mice.
Munc-79 heterozygous mutant mice exhibit hypersensitivity to the acute effects of ethanol, as observed
in unc-79 mutants of C. elegans. Hence, studies in C. elegans and mice have both implicated the
UNC-79 protein in ethanol responses. This component is characterizing the role of munc-79 in ethanol
responses of mice.
These investigators are also simultaneously pursuing further screens in C. elegans to identify
additional mutants that exhibit ethanol hypersensitivity as seen in unc-79. They are screening
for suppressors of unc-79 to better define the molecular pathways in which unc-79 and munc-79 function.
These screens are likely to identify genes that encode relevant targets of ethanol, either as direct
targets or as members of a pathway affected by ethanol. The determination of the molecular mechansism
of action of ethanol may provide the basis for a directed approach to the development of therapeutics
to treat alcoholism and alcoholic neurologic disorders.
Ulrike Heberlein, Ph.D., Director
The goal of this component is to analyze the function of TAO (thousand-and-one amino acid) kinases and their
downstream signaling pathways in the regulation of ethanol-related behaviors. In a screen for ethanol-induced
hyperactivity mutants in Drosophila melanogaster, we recently identified a loss-of-function mutation in the
dtao gene that almost completely abolishes flies' hyperactivity response to ethanol. dtao encodes a putative
MAP3K of the GCK-VIII subfamily of Ste20p (sterile 20 protein) kinases. These proteins are characterized by
a highly conserved serine/threonine kinase domain, which regulates MAPK signaling cascades through ERK, JNK,
and/or p38. In addition to their catalytic function, TAO kinases have been shown to regulate cytoskeletal
organization through interaction with actin and tubulin, via a structurally divergent C-terminal tail
region. In mammals, dtao is represented by three orthologous genes: Taok1, Taok2 and Taok3, of which Taok1
and Taok2 are most highly expressed in the brain. To determine if the function of dTAO in regulating
ethanol-responsive behaviors is conserved in mammals, we are analyzing the behavioral response to ethanol
in mice in which the Taok1 and Taok2 genes have been conditionally disrupted. Our expectation is that these
data will: 1) identify new molecular pathways mediating the behavioral effects of ethanol, 2) provide new
mammalian models in which to study the effects of ethanol exposure, 3) identify potential genetic risk
factors for alcohol use disorders in humans, and 4) provide potential molecular targets for the development
of pharmacotherapies to treat alcoholism.
