Cactus-independent nuclear translocation of Drosophila RELISH

Insects can effectively and rapidly clear microbial infections by a variety of innate immune responses including the production of antimicrobial pepti des. Induction of these antimicrobial peptides in Drosophila has been well established to involve NF-K-B elements. We present evidence here for a mole cular mechanism of Lipopolysaccharide (LPS)-induced signaling involving Dro sophila NF-kappaB, RELISH, in Drosophila S2 cells. We demonstrate that LPS induces a rapid processing event within the RELISH protein releasing the C- terminal ankyrin-repeats from the N-terminal Rel homology domain (RHD). Exa mination of the cellular localization of RELISH reveals that the timing of this processing coincides with the nuclear translocation of the RHD and the retention of the ankyrin-repeats within the cytoplasm. Both the processing and the nuclear translocation immediately precede the expression of antiba cterial peptide genes cecropin A1, attacin, and diptericin. Over-expression of the RHD but not full-length RELISH results in an increase in the promot er activity of the cecropin A1 gene in the absence of LPS. Furthermore, the LPS induced expression of these antibacterial peptides is greatly reduced when RELISH expression is depleted via RNA-mediated interference. In additi on, loss of cactus expression via RNAi revealed that RELISH activation and nuclear translocation is not dependent on the presence of cactus. Taken tog ether, these results suggest that this signaling mechanism involving the pr ocessing of RELISH followed by nuclear translocation of the RHD is central to the induction of at least part of the antimicrobial response in Drosophi la, and is largely independent of cactus regulation.