1. ¹Division of Experimental Medicine, Department of Medicine, McGill University, Montreal, Quebec, Canada
2. ²Lady Davis Institute, Jewish General Hospital, McGill University, Montréal Quebec, Canada
3. ³Division of Urology, Department of Surgery, McGill University and the Research Institute of the McGill University Health Centre, Montreal, Quebec, Canada

Correspondence: Dr M Chevrette, The Research Institute of the McGill University Health Centre, 1650 Cedar Ave, Room R4-113, Montreal, Quebec, Canada H3G 1A4. E-mail: mario.chevrette@mcgill.ca

⁴These authors have contributed equally to this work.

⁵Current address: Thallion Pharmaceuticals, St-Laurent, Quebec, Canada.

⁶Current address: McMaster University Medical Centre, Hamilton, Ontario, Canada.

Received 11 May 2007; Revised 26 July 2007; Accepted 7 August 2007; Published online 11 September 2007.

Abstract

CD9, a member of the tetraspanin family of proteins, is involved in a variety of cellular interactions with many other proteins and molecules. Although CD9 has been implicated in cell fusion, migration and cancer progression, the detailed function of this protein is not completely understood and likely depends on interactions with different protein partners, which are not yet all known. Using co-immunoprecipitation and mass-spectrometric protein sequencing, we have identified in prostate cancer cells, a novel CD9 partner, the 75-kDa protein HSPA9B, also known as mortalin. We further show that introduction and overexpression of wild-type CD9 into human PC-3 prostate cancer cells induces mitotic catastrophe. We also demonstrate, by immunocolocalisation studies, the interaction of CD9 and mortalin in PC-3 cells undergoing mitotic catastrophe. Our results not only identified mortalin as a new CD9 partner, but also clarify the mechanisms by which CD9 may control prostate cancer progression.