<b>Background:</b> Aryl Hydrocarbon Receptor Interacting Protein-Like 1 (AIPL1) interacts with NUB1 and restricts the entry of NUB1 protein into the nucleus. The interferon-induced NEDD8 ultimate buster (NUB1) protein causes degradation of neddylated and FAT10ylated proteins through the ubiquitin proteasome system. We observed AIPL1 were frequently down-regulated in various cancers compared to normal tissues. The mechanistic roles of AIPL1 and NUB1 protein in cancer cell cycle regulation remain unexplored. <b>Results:</b> Meta-analysis of cancer databases revealed that expression transcripts of chaperones, including AIPL1, were down-regulated in lung, pancreatic cancer and breast cancer relative to the adjacent normal tissues. Opposite levels of both AIPL1 and NUB1 transcripts were observed in the breast cancer. So it triggers the in vitro experiments using breast cancer cells. METABRIC breast cancer clinical cohort highlighted that patients with low NUB1 transcripts had poor survival in the ER-negative subgroup (but not in ER-positive) of breast cancer patients: hazard ratio (HR)=0.66, 95% confidence interval (CI)=0.5-0.87, p=0.003 and triple negative subgroup of breast cancer patients: HR=0.67, 95% CI=0.47-0.96, p=0.028. NUB1 silencing significantly inhibits in vitro cell growth in MDA-MB-231 and MCF7 under hypoxia. AIPL1 protein forms multimers in cancer cells. NUB1 protein moved into the nucleus in hypoxia (0.1% O2 48hrs) with final confluency at 80-90%. p21 (marker of senescence) & p27 (marker of cell cycle arrest) accumulated in NUB1-silent MDA-MB-231 and RCC4 cells. It suggested that low NUB1 nuclear localisation in hypoxia cause cancer cell cycle arrest. In MDA-MB-231 cell, upon hypoxia, neddylation inhibitor (MLN4924) treated and siNUB1 transfected cells showed decreased CUL1 and further accumulated p21 & p27. The evidence suggested lower neddylated CUL1 and reduced NUB1 cooperatively stabilise p21 and p27 as the substrate of CUL1-ubiquitin ligase. The neddylation inhibitor MLN4924 treated and NUB1 knockdown group exhibited more cells in sub-G1 stage as compared to the control group. In connection to higher p21/p27, it is associated with prolonged arrested cellular aging with depletion. After silencing of NUB1, the increases in cell death of cancer cells upon hypoxia happen through the neddylation-dependent CUL1-p27-p21 and CUL2-VHL axis. We then demonstrated that HIF1α protein could be both neddylated and FAT10ylated upon reoxygenation. In a tissue microarray study of breast cancer, lower cytoplasmic expression (n=57) had worse overall survival than higher cytoplasmic expression (n=57): HR=1.779, 95% CI=1.006-3.346, p=0.048. <b>Conclusions:</b> AIPL1 and NUB1 proteins exert a role in cell cycle regulation in breast cancer. Low cytoplasmic NUB1 levels are observed in the G<sub>1</sub>-S transition of cancer cells. NUB1 depletion causes G<sub>0</sub>/G<sub>1</sub> phase arrest due to CUL1 and CUL2 ubiquitin E3 ligase-dependent pathways.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:736085 |
| Date | January 2017 |
| Creators | Tan, Ka-Liong |
| Contributors | Acuto, Oreste ; Pezzella, Francesco |
| Publisher | University of Oxford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://ora.ox.ac.uk/objects/uuid:9b0e5061-bf81-4006-af9e-5018f113cb97 |
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