Characterization of Drosophila Menin Protein Interactions and a Potential Role for Menin in the Insulin Signalling Pathway

Abstract

<p>Menin is a tumour suppressor protein associated with the MEN1 hereditary cancer syndrome. Numerous protein interactions have been identified for menin but its specific function in tumour suppression remains enigmatic. Since the protein is well conserved, the <em>Drosophila</em> model system was used to study menin protein interactions in hopes of further elucidating menin function. In this study, two menin protein interactions were examined; the first was a novel interaction with <em>Drosophila</em> fas-associated death domain (dFADD), an important protein in innate immune signalling and the second was a conserved interaction with Trithorax (Trx), a histone methyltransferase important for activation of gene expression. Both these interactions were confirmed through co-immunoprecipitation in <em>Drosophila</em> S2 cells. Unlike <em>dFADD</em> mutants that are highly susceptible to bacterial infection, <em>Mnn1</em> mutants display normal resistance, suggesting that menin does not play an essential role in innate immune signalling. Moreover, <em>dFADD</em> mutants do not display a heat shock sensitivity phenotype, as previously reported for <em>Mnn1</em> mutants. The importance of the menin-Trx interaction in the regulation of heat shock gene expression was examined since both proteins were independently shown to be necessary for proper expression of <em>hsp70</em>. Chromatin immunoprecipitation analyses demonstrate that menin and Trx co-localize in the coding region of <em>hsp70</em>. Heat shock results in a loss of menin and an increase in Trx localization at <em>hsp70</em> and the proteins fail to co-immunoprecipitate with prolonged heat stress, suggesting a complex regulation of the interaction. Due to the recently identified interactions between mammalian menin and proteins of the insulin signalling pathway, a potential role for <em>Drosophila</em> menin in this pathway was examined. <em>Mnn1</em> mutants display increased desiccation and starvation resistance, similar to other positive regulators of insulin signalling. Overall, this thesis describes a novel interaction between menin and dFADD and a conserved interaction with Trx and also proposes a potential role for menin in the <em>Drosophila</em> insulin signalling pathway.</p>