Pharmacogenomic studies in model systems have the potential to define previously unknown mechanisms of action of medications used in human illness and to discover new genes and signaling pathways in the model system, itself. We initiated pharmacogenomic studies in C. elegans to identify novel signal transduction pathways through which antipsychotic drugs (APDs), and in particular, the most effective APD, clozapine, exert their biological effects. These drugs have both growth stimulating and toxic effects in humans. Many of these drugs cause larval arrest and lethality in C. elegans. We took advantage of these phenotypes by performing a genome-wide feeding RNAi screen for suppressors of clozapine-induced larval arrest (Scla). The screen yielded 42 suppressors, one of which is F22B3.8, a gene we have named
scla-1.
scla-1 shares 31% identity with the nonreceptor tyrosine kinase IL-2-inducible T cell kinase (ITK), which is critical for the development, function and differentiation of T cells. We validated our RNAi result by backcrossing two deletions of
scla-1 six times and then confirming the Scla phenotype of each strain. In addition to suppression of clozapine-induced larval arrest, we found that these mutants suppress both developmental delay and lethality induced by other APDs, such as chlorpromazine and fluphenazine. We also found that clozapine induces expression of
scla-1 as assayed by q-RT-PCR. We are currently generating transgenic worms carrying transcriptional and translational GFP reporters for
scla-1. We will test our translational construct for rescue of the Scla phenotype of our two knockouts. Previous work by our laboratory1 and by Weeks et al.2 showed that APDs activate the insulin/IGF-1 signaling (IIS) in C. elegans. In mammals, activation of ITK depends on phosphatidylinositol-3-kinase3, which is a known target of the IIS effectors. Therefore, we are constructing an
scla-1;
daf-16::gfp animal to test the potential interaction of these pathways in C. elegans. The effects of APDs are likely determined by actions at multiple sites, and by defining the downstream interactions of pathways modulated by APDs, we may better understand their therapeutic and toxic effects. This knowledge may lead to improved treatments.
1. Karmacharya et al (2009) Neuropsychopharmacology 34, 1968-1978.
2. Weeks et al (2010) ACS Chem Neurosci 1, 463-473.
3. Fernandes et al (2009) MBC 20, 3690-3699.