title: Characterization of 14-3-3sigma dimerization determinants: requirement of homodimerization for inhibition of cell proliferation.
abstract: The seven highly conserved 14-3-3 proteins expressed in mammalian cells form a complex pattern of homo- and hetero-dimers, which is poorly characterized. Among the 14-3-3 proteins 14-3-3sigma is unique as it has tumor suppressive properties. Expression of 14-3-3sigma is induced by DNA damage in a p53-dependent manner and mediates a cell cycle arrest. Here we show that the 14-3-3sigma protein exclusively forms homodimers when it is ectopically expressed at high levels, whereas ectopic 14-3-3zeta formed heterodimers with the five other 14-3-3 isoforms. The x-ray structure of 14-3-3sigma revealed five residues (Ser5, Glu20, Phe25, Q55, Glu80) as candidate determinants of dimerization specificity. Here we converted these amino-acids to residues present in 14-3-3zeta at the analogous positions. Thereby, Ser5, Glu20 and Glu80 were identified as key residues responsible for the selective homodimerization of 14-3-3sigma. Conversion of all five candidate residues was sufficient to switch the dimerization pattern of 14-3-3sigma to a pattern which is very similar to that of 14-3-3zeta. In contrast to wildtype 14-3-3sigma this 14-3-3sigma variant and 14-3-3zeta were unable to mediate inhibition of cell proliferation. Therefore, homodimerization by 14-3-3sigma is required for its unique functions among the seven mammalian 14-3-3 proteins. As inactivation of 14-3-3sigma sensitizes to DNA-damaging drugs, substances designed to interfere with 14-3-3sigma homodimerization may be used to inactivate 14-3-3sigma function for cancer therapeutic purposes.
authors.affiliation: Molecular Oncology, Independent Max-Planck Research Group, Max-Planck-Institute of Biochemistry, Munich, Germany.
authors.forename: Berlinda
authors.initials: B
authors.lastname: Verdoodt
authors.forename: Anne
authors.initials: A
authors.lastname: Benzinger
authors.forename: Grzegorz M
authors.initials: GM
authors.lastname: Popowicz
authors.forename: Tad A
authors.initials: TA
authors.lastname: Holak
authors.forename: Heiko
authors.initials: H
authors.lastname: Hermeking
mesh_terms: D048948:14-3-3 Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D019943:Amino Acid Substitution; D049109:Cell Proliferation; D019281:Dimerization; D006801:Humans; D008958:Models, Molecular; D050505:Mutant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D013379:Substrate Specificity
chemical_list: D048948:14-3-3 Proteins; D050505:Mutant Proteins