Involvement of Rel and GATA transcription factors in the regulation of antimicrobial peptide gene expression in Drosophila melanogaster

Sammanfattning: Insects posses a powerful immune system related to the innate immune reactions present in vertebrates. When insects are infected by bacteria or other microorganisms, a vast production of different antimicrobial peptides is activated. The expression of antimicrobial peptides is regulated at the level of transcription. The aim of the studies presented in this thesis has been to characterize transcription factors and DNA regulatory elements necessary for expression of antimicrobial peptide genes in Drosophila melanogaster. In the upstream regulatory region of many inducible immunity genes in insects a kB motif and a GATA motif are located in proximity to each other. I demonstrate that the GATA motif is essential for expression of the Drosophila Cecropin A1 (CecA1) gene in the larval fat body and in the hemocytic cell line mbn-2 during infection, but dispensable for the infection-dependent expression in the adult fat body. I show that the Rel protein, dorsal-related immunity factor (DIF), and the GATA transcription factor, SERPENT (SRP), are sequence-specific activators of antimicrobial peptide genes. Co-transfection assays demonstrated that DIF is a more potent activator of the CecA1 promoter than DORSAL (DL). By using co-transfection experiments I found that DL has a negative effect on DIF activity. It is demonstrated that DIF and SRP are phospho-proteins within the cell, both in larvae and in mbn-2 cells. It is also shown that DIF is phosphorylated in response to infection. A GATA binding activity (GBA) is present in nuclear extracts from mbn-2 cells and larval fat body. Furthermore, it is demonstrated that SRP is expressed in immunocompetent tissues, i.e. larval fat body and hemocytes. Finally, it is shown that a specific antiserum against SRP interferes with GBA and generates a supershift, demonstrating that SRP is a component of the GBA.