IN-VIVO REGULATION OF THE I-KAPPA-B HOMOLOG CACTUS DURING THE IMMUNE-RESPONSE OF DROSOPHILA

The dorsoventral regulatory gene pathway (spatzlel Toll/cactus) contro ls the expression of several antimicrobial genes during the immune res ponse of Drosophila. This regulatory cascade shows striking similariti es with the cytokine-induced activation cascade of NF-kappa B during t he inflammatory response in mammals. Here, we have studied the regulat ion of the I kappa B homologue Cactus in the fat body during the immun e response. We observe that the cactus gene is up-regulated in respons e to immune challenge. Interestingly, the expression of the cactus gen e is controlled by the spatzle/Toll/cactus gene pathway, indicating th at the cactus gene is auto-regulated. We also show that two Cactus iso forms are expressed in the cytoplasm of fat body cells and that they a re rapidly degraded and resynthesized after immune challenge. This deg radation is also dependent on the Toll signaling pathway. Altogether, our results underline the striking similarities between the regulation of I kappa B and cactus during the immune response.