No abstract

In mammals, TAK1, a MAPKKK kinase, is implicated in multiple signaling processes, including the regulation of NF-B activity via the IL1-R/TLR pathways. TAK1 function has largely been studied in cultured cells, and its in vivo function is not fully understood. We have isolated null mutations in the Drosophila dTAK1 gene that encodes dTAK1, a homolog of TAK1. dTAK1 mutant flies are viable and fertile, but they do not produce antibacterial peptides and are highly susceptible to Gram-negative bacterial infection. This phenotype is similar to the phenotypes generated by mutations in components of the Drosophila Imd pathway. Our genetic studies also indicate that dTAK1 functions downstream of the Imd protein and upstream of the IKK complex in the Imd pathway that controls the Rel/NF-B like transactivator Relish. In addition, our epistatic analysis places the caspase, Dredd, downstream of the IKK complex, which supports the idea that Relish is processed and activated by a caspase activity. Our genetic demonstration of dTAK1's role in the regulation of Drosophila antimicrobial peptide gene expression suggests an evolutionary conserved role for TAK1 in the activation of Rel/NF-B-mediated host defense reactions.

Salivary gland tumors, a group of histologically diverse benign and malignant neoplasms, represent a challenging problem for diagnosis and treatment. A specific recurring t(11;19)(q21;p13) translocation is associated with two types of salivary gland tumors, mucoepidermoid carcinomas and Warthin's tumors. This translocation generates a fusion protein comprised of the N-terminal CREB (cAMP response element-binding protein)-binding domain of the CREB regulator MECT1 (Mucoepidermoid carcinoma translocated-1) and the C-terminal transcriptional activation domain of the Notch coactivator Mastermind-like 2 (MAML2). Here, we demonstrate that the MECT1-MAML2 fusion protein induces expression of multiple genes known to be CREB transcriptional targets. MECT1-MAML2 was found to bind to CREB, recruit p300/CBP into the CREB complex through a binding domain on MAML2, and constitutively activate CREB-dependent transcription. The transforming activity of MECT1-MAML2 was markedly reduced by blocking CREB DNA binding. Thus, this fusion oncogene mimics constitutive activation of cAMP signaling, by activating CREB directly. This study has identified a novel, critical mechanism of transformation for an oncogene associated very specifically with salivary gland tumors, and identified potential targets for the development of novel therapies.

Cell 91, 531-541). Binding assay and cell culture studies indicate that both PCE-1 and OTX elements and at least two different regulatory factors RX and CRX are necessary for high level, photoreceptor cell-restricted gene expression. Thus, photoreceptor specificity can be achieved by multiple promoter elements interacting with a combination of both photoreceptor-specific regulatory factors and factors present in closely related cell lineages.

Wnt/Wingless directs many cell fates during development. Wnt/Wingless signaling increases the amount of beta-catenin/Armadillo, which in turn activates gene transcription. Here the Drosophila protein D-Axin was shown to interact with Armadillo and D-APC. Mutation of d-axin resulted in the accumulation of cytoplasmic Armadillo and one of the Wingless target gene products, Distal-less. Ectopic expression of d-axin inhibited Wingless signaling. Hence, D-Axin negatively regulates Wingless signaling by down-regulating the level of Armadillo. These results establish the importance of the Axin family of proteins in Wnt/Wingless signaling in Drosophila.