RACK1 recruits STAT3 specifically to insulin and insulin-like growth factor 1 receptors for activation, which is important for regulating anchorage-independent growth.
Current understanding of the activation of STATs is through binding between the SH2 domain of STATs and phosphotyrosine of tyrosine kinases. Here we demonstrate a novel role of RACK1 as an adaptor for insulin and insulin-like growth factor 1 receptor (IGF-1R)-mediated STAT3 activation specifically. Intracellular association of RACK1 via its N-terminal WD domains 1 to 4 (WD1-4) with insulin receptor (IR)/IGF-1R is augmented upon respective ligand stimulation, whereas association with STAT3 is constitutive. Purified RACK1 or RACK1 WD1-4 associates directly with purified IR, IGF-1R, and STAT3 in vitro. Insulin induces multiprotein complex formation of RACK1, IR, and STAT3. Overexpression or downregulation of RACK1 greatly enhances or decreases, respectively, IR/IGF-1R-mediated activation of STAT3 and its target gene expression. Site-specific mutants of IR and IGF-1R impaired in RACK1 binding are ineffective in mediating recruitment and activation of STAT3 as well as in insulin- or IGF-1-induced protection of cells from anoikis. RACK1-mediated STAT3 activation is important for insulin and IGF-1-induced anchorage-independent growth in certain ovarian cancer cells. We conclude that RACK1 mediates recruitment of STAT3 to IR and IGF-1R specifically for activation, suggesting a general paradigm for the need of an adaptor in mediating activation of STATs by receptor protein tyrosine kinases.
Zhang
Weizhou
W
Department of Microbiology, Mount Sinai School of Medicine, New York, New York 10029-6574, USA.
Zong
Cong S
CS
Hermanto
Ulrich
U
Lopez-Bergami
Pablo
P
Ronai
Ze'ev
Z
Wang
Lu-Hai
LH
D000818:Animals; D023102:Anoikis; D002460:Cell Line; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation; D006801:Humans; D051379:Mice; D009154:Mutation; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D034741:RNA, Small Interfering / Q000235:genetics; D017526:Receptor, IGF Type 1 / Q000235:genetics / Q000378:metabolism*; D011972:Receptor, Insulin / Q000235:genetics / Q000378:metabolism*; D000075370:Receptors for Activated C Kinase; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*; D050796:STAT3 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction
D009363:Neoplasm Proteins; C419368:RACK1 protein, human; D034741:RNA, Small Interfering; D000075370:Receptors for Activated C Kinase; D011956:Receptors, Cell Surface; D050796:STAT3 Transcription Factor; D017526:Receptor, IGF Type 1; D011972:Receptor, Insulin; D019204:GTP-Binding Proteins