1. Department of Molecular Cell Biology, Institute for Cancer Research, Oslo University Hospital, 0379 Oslo, Norway
2. Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo, 0379 Oslo, Norway
3. Current address: Department of Molecular Medicine, Division of Biochemistry, University of Oslo, 0379 Oslo, Norway
4. Department of Molecular Biosciences, Faculty of Mathematics and Natural Sciences, University of Oslo, 0379 Oslo, Norway