title: X-linked and cellular IAPs modulate the stability of C-RAF kinase and cell motility.
abstract: Inhibitor of apoptosis proteins (IAP) are evolutionarily conserved anti-apoptotic regulators. C-RAF protein kinase is a direct RAS effector protein, which initiates the classical mitogen-activated protein kinase (MAPK) cascade. This signalling cascade mediates diverse biological functions, such as cell growth, proliferation, migration, differentiation and survival. Here we demonstrate that XIAP and c-IAPs bind directly to C-RAF kinase and that siRNA-mediated silencing of XIAP and c-IAPs leads to stabilization of C-RAF in human cells. XIAP binds strongly to C-RAF and promotes the ubiquitylation of C-RAF in vivo through the Hsp90-mediated quality control system, independently of its E3 ligase activity. In addition, XIAP or c-IAP-1/2 knockdown cells showed enhanced cell migration in a C-RAF-dependent manner. XIAP promotes binding of CHIP (carboxy terminal Hsc70-interacting protein), a chaperone-associated ubiquitin ligase, to the C-RAF-Hsp90 complex in vivo. Interfering with CHIP expression resulted in stabilization of C-RAF and enhanced cell migration, as observed in XIAP knockdown cells. Our data show an unexpected role of XIAP and c-IAPs in the turnover of C-RAF protein, thereby modulating the MAPK signalling pathway and cell migration.
authors.affiliation: Emmy Noether Group of DFG, Institut für Biochemie II, Goethe University Medical School, Frankfurt, Germany.
authors.forename: Taner
authors.initials: T
authors.lastname: Dogan
authors.forename: Gregory S
authors.initials: GS
authors.lastname: Harms
authors.forename: Mirko
authors.initials: M
authors.lastname: Hekman
authors.forename: Christiaan
authors.initials: C
authors.lastname: Karreman
authors.forename: Tripat Kaur
authors.initials: TK
authors.lastname: Oberoi
authors.forename: Emad S
authors.initials: ES
authors.lastname: Alnemri
authors.forename: Ulf R
authors.initials: UR
authors.lastname: Rapp
authors.forename: Krishnaraj
authors.initials: K
authors.lastname: Rajalingam
mesh_terms: D002465:Cell Movement; D004795:Enzyme Stability; D020868:Gene Silencing; D018841:HSP90 Heat-Shock Proteins / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D011485:Protein Binding; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism*; D014162:Transfection; D044767:Ubiquitin-Protein Ligases; D051636:X-Linked Inhibitor of Apoptosis Protein / Q000378:metabolism*
chemical_list: D018841:HSP90 Heat-Shock Proteins; D051636:X-Linked Inhibitor of Apoptosis Protein; D044767:Ubiquitin-Protein Ligases; D019908:Proto-Oncogene Proteins c-raf