1. Division of Molecular Carcinogenesis and Center for Biomedical Genetics, The Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands
2. These authors contributed equally to this work

Correspondence to: René Bernards¹ Email: r.bernards@nki.nl

Abstract

Protein modification by the conjugation of ubiquitin moieties—ubiquitination—plays a major part in many biological processes, including cell cycle and apoptosis¹. The enzymes that mediate ubiquitin-conjugation have been well-studied, but much less is known about the ubiquitin-specific proteases that mediate de-ubiquitination of cellular substrates^{2, 3}. To study this gene family, we designed a collection of RNA interference vectors to suppress 50 human de-ubiquitinating enzymes, and used these vectors to identify de-ubiquitinating enzymes in cancer-relevant pathways. We report here that inhibition of one of these enzymes, the familial cylindromatosis tumour suppressor gene (CYLD)⁴, having no known function, enhances activation of the transcription factor NF-B. We show that CYLD binds to the NEMO (also known as IKK) component of the IB kinase (IKK) complex, and appears to regulate its activity through de-ubiquitination of TRAF2, as TRAF2 ubiquitination can be modulated by CYLD. Inhibition of CYLD increases resistance to apoptosis, suggesting a mechanism through which loss of CYLD contributes to oncogenesis. We show that this effect can be relieved by aspirin derivatives that inhibit NF-B activity⁵, which suggests a therapeutic intervention strategy to restore growth control in patients suffering from familial cylindromatosis.