1. Department of Experimental Oncology, European Institute of Oncology, 20141 Milan
2. Department of Molecular and Cell Biology, Leiden University Medical Center, 2300 RA Leiden, The Netherlands
3. FIRC Institute of Molecular Oncology, 20139 Milan, Italy
4. Unit of Molecular Embryology, Free University of Brussels, B-6041 Gosselies
5. Laboratory of Molecular Cancer Biology, Flanders Interuniversity Institute for Biotechnology, B-9052 Ghent, Belgium