Investigation of p75 neurotrophin receptor and the role of its post-translational modifications in tumour cell motility and invasiveness

The p75 neurotrophin receptor (p75NTR) is a member of the tumour necrosis factor superfamily, which relies on the recruitment of cytosolic protein partners - including the TNF receptor associated factor 6 (TRAF6) E3 ubiquitin ligase - to produce cellular responses such as apoptosis, survival, and inhibition of neurite outgrowth. Recently,p75NTR was also shown to undergo γ-secretase-mediated regulated intramembrane proteolysis, and the receptor ICD was found to migrate to the nucleus where it regulates gene transcription. Moreover, γ-secretase-mediated proteolysis was shown to be involved in glioblastoma cell migration and invasion. In this study we report that TRAF6-mediated K63-linked polyubiquitination at multiple or alternative lysine residues influences p75NTR-ICD stability in vitro. In addition, we found that TRAF6-mediated ubiquitination of p75NTR is not influenced by inhibition of dynamin. Moreover, we report beta-transducin repeats-containing protein (β-TrCP) as a novel E3- ligase that ubiquitinates p75NTR, which is independent of serine phosphorylation of the p75NTR destruction motif. In contrast to its influence on other substrates, co-expression of β-TrCP did not reduce p75NTR stability. We created U87-MG glioblastoma cell lines stably expressing wild type, γ-secretaseresistant and constitutively cleaved receptor, as well as the ICD-stabilized mutant K301R. Interestingly, only wild-type p75NTR induces increased glioblastoma cell migration, which could be reversed by application of γ-secretase inhibitor. Microarray and qRT-PCR analysis of mRNA transcripts in these cell lines yielded several promising genes that might be involved in glioblastoma cell migration and invasion, such as cadherin 11 and matrix metalloproteinase 12. Analysis of potential transcription factor binding sites revealed that transcription of these genes might be regulated by well known p75NTR signalling cascades such as NF-κB or JNK signalling, which are independent of γ-secretase-mediated cleavage of the receptor. In contrast, while p75NTR overexpression was confirmed in melanoma cell lines and a patient sample of melanoma metastasis to the brain, inhibition of γ-secretase did not influence melanoma cell migration. Collectively, this study provides several avenues to better understand the physiological importance of posttranslational modifications of p75NTR and the significance of the receptor in glioblastoma cell migration and invasion.

Identification and characterization of innate immune receptor substrates of γ-secretase enzyme complex

The γ-secretase protease complexes and associated regulated intramembrane proteolysis play an important role in controlling receptor-mediated intracellular signalling events, which have a central role in Alzheimer’s disease, cancer progression and immune surveillance. It has previously been reported that the Interleukin-1 receptor, type 1, (IL-1R1) is a substrate for regulated intramembrane proteolysis, mediated by presenilin (PS)-dependent γ-secretase activity. The aims of this project were twofold. Firstly, to determine the conservation of regulated intramembrane proteolysis as a physiological occurrence amongst other cytokine receptors. In this regard, similar to IL-1R1, we identified the Tumour necrosis factor receptor type 1 (TNFR1) and the Toll like receptor 4 (TLR4) as novel γ-secretase substrates. Secondly, given that the diversity of signalling events mediated by the IL-1R1, TLR4 and TNFR1 are spatially segregated, we investigated the spatial distribution, subcellular trafficking and subcellular occurrence of regulated intramembrane proteolysis of IL-1R1, TLR4 and TNFR1. Using dynasore an inhibitor of clathrin-dependent receptor endocytosis, both ectodomain shedding and γ-secretase-mediated cleavage of IL-1R1 were observed post-internalization. In contrast, TNFR-1 underwent ectodomain shedding at the cell surface followed by endosomal γ-secretase-mediated cleavage. Furthermore, immortalised fibroblasts from PS1-deficient mice showed impaired γ-secretasemediated cleavage of IL-1R1 and TNFR1, indicating that both are cleaved by PS1-and not PS2-containing γ-secretase complexes. Subcellular fractionation and immunofluorescence studies revealed that the γ-secretase generated IL-1R1 ICD translocates to the nucleus on IL-1β stimulation. These observations further demonstrate the novel PS-dependent means of modulating IL-1β, LPS and TNFα- mediated immune responses by regulating IL-1R1/TLR4/TNFR1 protein levels within the cells.

Oral cancer incidence and survival rates in the Republic of Ireland, 1994-2009

Background: Oral cancer is a significant public health problem world-wide and exerts high economic, social, psychological, and physical burdens on patients, their families, and on their primary care providers. We set out to describe the changing trends in incidence and survival rates of oral cancer in Ireland between 1994 and 2009. Methods: National data on incident oral cancers [ICD 10 codes C01-C06] were obtained from the National Cancer Registry Ireland from 1994 to 2009. We estimated annual percentage change (APC) in oral cancer incidence during 1994–2009 using joinpoint regression software (version 4.2.0.2). The lifetime risk of oral cancer to age 79 was estimated using Irish incidence and population data from 2007 to 2009. Survival rates were also examined using Kaplan-Meier curves and Cox proportional hazard models to explore the influence of several demographic/lifestyle covariates with follow-up to end 2012. Results: Data were obtained on 2,147 oral cancer incident cases. Men accounted for two-thirds of oral cancer cases (n = 1,430). Annual rates in men decreased significantly during 1994–2001 (APC = -4.8 %, 95 % CI: −8.7 to −0.7) and then increased moderately (APC = 2.3 %, 95 % CI: −0.9 to 5.6). In contrast, annual incidence increased significantly in women throughout the study period (APC = 3.2 %, 95 % CI: 1.9 to 4.6). There was an elevated risk of death among oral cancer patients who were: older than 60 years of age; smokers; unemployed or retired; those living in the most deprived areas; and those whose tumour was sited in the base of the tongue. Being married and diagnosed in more recent years were associated with reduced risk of death. Conclusion: Oral cancer increased significantly in both sexes between 1999 and 2009 in Ireland. Our analyses demonstrate the influence of measured factors such as smoking, time of diagnosis and age on observed trends. Unmeasured factors such as alcohol use, HPV and dietary factors may also be contributing to increased trends. Several of these are modifiable risk factors which are crucial for informing public health policies, and thus more research is needed.