Cylindromas are benign adnexal skin tumors caused by germline mutations in the CYLD gene. In most cases the second wild-type allele is lost in tumor tissue, suggesting that CYLD functions as tumor suppressor. CYLD is a protein of 956 amino acids harboring a functional deubiquitinating domain at the COOH-terminal end. To shed more light on the function of CYLD, we have performed a yeast two hybrid screen using an HaCaT cDNA library that identified the RING finger protein TRIP (TRAF-interacting protein) as interactor with full-length CYLD. Mapping of the interacting domains revealed that the central domain of CYLD binds to the COOH-terminal end of TRIP. Far Western analysis and coimmunoprecipitations in mammalian cells confirmed that full-length CYLD binds to the COOH-terminal domain of TRIP. Because TRIP is an inhibitor of nuclear factor (NF)-kappaB activation by tumor necrosis factor (TNF), the effect of CYLD on NF-kappaB activation was investigated in HeLa cells. The results established that CYLD down-regulates NF-kappaB activation by TNF-alpha. The inhibition by CYLD depends on the presence of the central domain interacting with TRIP and its deubiquitinating activity. These findings indicate that cylindromas arise through constitutive NF-kappaB activation leading to hyperproliferation and tumor growth.

The characterization of cells with tumour initiating potential is significant for advancing our understanding of cancer and improving therapy. Aggressive, triple-negative breast cancers (TNBCs) are enriched for tumour-initiating cells (TICs). We investigated that hypothesis that VEGF receptors expressed on TNBC cells mediate autocrine signalling that contributes to tumour initiation. We discovered the VEGF receptor neuropilin-2 (NRP2) is expressed preferentially on TICs, involved in the genesis of TNBCs and necessary for tumour initiation. The mechanism by which NRP2 signalling promotes tumour initiation involves stimulation of the α6β1 integrin, focal adhesion kinase-mediated activation of Ras/MEK signalling and consequent expression of the Hedgehog effector GLI1. GLI1 also induces BMI-1, a key stem cell factor, and it enhances NRP2 expression and the function of α6β1, establishing an autocrine loop. NRP2 can be targeted in vivo to retard tumour initiation. These findings reveal a novel autocrine pathway involving VEGF/NRP2, α6β1 and GLI1 that contributes to the initiation of TNBC. They also support the feasibility of NRP2-based therapy for the treatment of TNBC that targets and impedes the function of TICs.