The E3 ubiquitin ligase UBR5 regulates centriolar satellite stability and primary cilia.

Primary cilia are crucial for signal transduction in a variety of pathways, including hedgehog and Wnt. Disruption of primary cilia formation (ciliogenesis) is linked to numerous developmental disorders (known as ciliopathies) and diseases, including cancer. The ubiquitin-proteasome system (UPS) component UBR5 was previously identified as a putative positive regulator of ciliogenesis in a functional genomics screen. UBR5 is an E3 ubiquitin ligase that is frequently deregulated in tumors, but its biological role in cancer is largely uncharacterized, partly due to a lack of understanding of interacting proteins and pathways. We validated the effect of UBR5 depletion on primary cilia formation using a robust model of ciliogenesis, and identified CSPP1, a centrosomal and ciliary protein required for cilia formation, as a UBR5-interacting protein. We show that UBR5 ubiquitylates CSPP1, and that UBR5 is required for cytoplasmic organization of CSPP1-comprising centriolar satellites in centrosomal periphery, suggesting that UBR5-mediated ubiquitylation of CSPP1 or associated centriolar satellite constituents is one underlying requirement for cilia expression. Hence, we have established a key role for UBR5 in ciliogenesis that may have important implications in understanding cancer pathophysiology.

Hypoxia-independent gene expression signature associated with radiosensitisation of prostate cancer cell lines by histone deacetylase inhibition.

BACKGROUND: Histone deacetylase inhibitors (HDACis) like vorinostat are promising radiosensitisers in prostate cancer, but their effect under hypoxia is not known. We investigated gene expression associated with radiosensitisation of normoxic and hypoxic prostate cancer cells by vorinostat. METHODS: Cells were exposed to vorinostat under normoxia or hypoxia and subjected to gene expression profiling before irradiation and clonogenic survival analysis. RESULTS: Pretreatment with vorinostat led to radiosensitisation of the intrinsically radioresistant DU 145 cells, but not the radiosensitive PC-3 and 22Rv1 cells, and was independent of hypoxia status. Knockdown experiments showed that the sensitisation was not caused by repression of hypoxia-inducible factor HIF1 or tumour protein TP53. Global deregulation of DNA repair and chromatin organisation genes was associated with radiosensitisation under both normoxia and hypoxia. A radiosensitisation signature with expression changes of 56 genes was generated and valid for both conditions. For eight signature genes, baseline expression also correlated with sensitisation, showing potential as pretreatment biomarker. The hypoxia independence of the signature was confirmed in a clinical data set. CONCLUSIONS: Pretreatment with HDACi may overcome radioresistance of hypoxic prostate tumours by similar mechanisms as under normoxia. We propose a gene signature to predict radiosensitising effects independent of hypoxia status.