ADrosophilaortholog of the human cylindromatosis tumor suppressor gene regulates triglyceride content and antibacterial defense

Abstract

The cylindromatosis (CYLD) gene is mutated in human tumors of skin appendages. It encodes a deubiquitylating enzyme (CYLD) that is a negative regulator of the NF-B and JNK signaling pathways, in vitro. However, the tissue-specific function and regulation of CYLD in vivo are poorly understood. We established a genetically tractable animal model to initiate a systematic investigation of these issues by characterizing an ortholog of CYLD in Drosophila. Drosophila CYLD is broadly expressed during development and, in adult animals, is localized in the fat body, ovaries, testes, digestive tract and specific areas of the nervous system. We demonstrate that the protein product of Drosophila CYLD (CYLD), like its mammalian counterpart, is a deubiquitylating enzyme. Impairment of CYLD expression is associated with altered fat body morphology in adult flies, increased triglyceride levels and increased survival under starvation conditions. Furthermore, flies with compromised CYLD expression exhibited reduced resistance to bacterial infections. All mutant phenotypes described were reversible upon conditional expression of CYLD transgenes. Our results implicate CYLD in a broad range of functions associated with fat homeostasis and host defence in Drosophila.

The Drosophila Imd Signaling Pathway

“…CYLD is a deubiquitinating enzyme that downregulates mammalian TNFR signaling by inactivating TRAF2. Drosophila CYLD interacts with the IKK protein Kenny and also negatively regulates Imd signaling (75,76). Activated Relish is targeted for ubiquitination and proteasomal degradation by the SCF complex (77), possibly promoted by the ubiquitin-binding protein dRYBP (78).…”

CYLD: A Multifunctional Deubiquitinase

“…8 Two recent studies have shown that CYLD also regulates NF-κB and JNK signaling in Drosophila. 10,12 Xue et al 12 demonstrated that CYLD deficiency suppressed activated JNK signaling and abolished JNK dependent transcription during wing development, consistent with a positive role for CYLD. Furthermore, dTRAF2 exhibited enhanced ubiquitination concomitantly with reduced protein levels in this mutant, suggesting CYLD removes a degradative ubiquitin modification that stabilises dTRAF2 to promote JNK signaling (Fig.…”

“…The NF-κB inhibitory function of CYLD has been confirmed in mouse and Drosophila organisms, where mutations that strongly reduced CYLD mRNA/protein levels caused enhanced susceptibility to NF-κB stimuli. [7][8][9][10] CYLD was also shown to negatively regulate JNK activation in cultured mammalian cells and positively regulate the signaling pathway in developing Drosophila 11,12 (Fig. 1).…”

“…13 Recent studies have uncovered a role for CYLD in regulating mitosis, 14 spermatogenesis, 15 B cell homeostasis, 16,17 positively promoting T cell development, 18 and modulating the response to bacterial infection. 7,10,13 Part of this diversity in function arises from the involvement of CYLD in different signaling pathways, orchestrated by a variety of protein interactions. For example, the role of CYLD in regulating entry into mitosis appears to be IKK-complex independent and is most likely mediated by modulating Plk1 kinase activity; a protein shown to interact with CYLD and phenocopy the deubiquitinating enzymes activity regarding mitosis.…”

“…14 However, Drosophila CYLD contains only a single CAP-Gly domain, and consequently defects caused by deleting this region may result from disrupting the interaction between CYLD and Kenny (the Drosophila orthologue of NEMO/IKKg). Tsichritzis et al 10 identified an interaction between the Drosophila orthologues of CYLD and NEMO/ IKKg, and showed that CYLD negatively regulated NF-κB signaling in response to bacterial infection. In contrast to mammalian studies however, reducing the levels of Drosophila CYLD had a greater affect on stimulating basal NF-κB signaling than it did on increasing NF-κB signaling in response to pathway stimuli; this suggests an absolute requirement for Drosophila CYLD in restricting NF-κB activity.…”