RACK1 Is an Insulin-like Growth Factor 1 (IGF-1) Receptor-interacting Protein That Can Regulate IGF-1-mediated Akt Activation and Protection from Cell Death

Abstract

The insulin receptor and insulin-like growth factor 1 receptor (IGF-1R), activated by their ligands, control metabolism, cell survival, and proliferation. Although the signaling pathways activated by these receptors are well characterized, regulation of their activity is poorly understood. To identify regulatory proteins we undertook a two-hybrid screen using the IGF-1R ␤-chain as bait. This screen identified Receptor for Activated C Kinases (RACK1) as an IGF-1R-interacting protein. RACK1 also interacted with the IGF-1R in fibroblasts and MCF-7 cells and with endogenous insulin receptor in COS cells. Interaction with the IGF-1R did not require tyrosine kinase activity or receptor autophosphorylation but did require serine 1248 in the C terminus. Overexpression of RACK1 in either R؉ fibroblasts or MCF-7 cells inhibited IGF-1-induced phosphorylation of Akt, whereas it enhanced phosphorylation of Erks and Jnks. Src, the p85 subunit of phosphatidylinositol 3-kinase, and SHP-2 were all associated with RACK1 in these cells. Interestingly, the proliferation of MCF-7 cells was enhanced by overexpression of RACK1, whereas IGF-1-mediated protection from etoposide killing was greatly reduced. Altogether the data indicate that RACK1 is an IGF-1R-interacting protein that can modulate receptor signaling and suggest that RACK1 has a particular role in regulating Akt activation and cell survival.The insulin and IGF-1 1 receptors (IR and IGF-1R) belong to a family of tyrosine kinase receptors that also includes the insulin-related receptor. They are tetrameric receptors made up of two ␣-subunits that bind the ligands insulin, IGF-1 or IGF-2, and two ␤-subunits that share high homology in their kinase domains (reviewed in Ref. 1). These receptors are homologous to a receptor found in the nematode Caenorhabditis elegans and in Drosophila, and they activate an evolutionarily conserved metabolic and survival signaling pathway that includes insulin-related substrate 1 (IRS-1), phosphatidylinositol 3-kinase (PI3-K), the serine/threonine kinase Akt, and the Forkhead family of transcription factors (2-5).

RACK1 inhibits the serum‐ and anchorage‐independent growth of v‐Src transformed cells

“…RACK1's influence on normal cellular responses is broadreaching, affecting biologic functions as diverse as those that regulate cell growth [7], adhesion [31][32][33], migration [32,33], protrusion [33], death [35,36] and cell-cell interactions [37]. Some of the RACK1 effects (e.g., cell protrusion) appear to be due to RACK1's influence on Src kinase activity, others (e.g., cell migration) do not.…”

The Insulin‐Like Growth Factor System

“…This interaction delays progression of the cell cycle, but enhances FAK and paxillin phosphorylation, thereby altering integrin signaling (Hermanto et al, 2002). RACK1 may also modulate the antiapoptotic effects of the IGF-IR via Akt (Kiely et al, 2002).…”

Gene expression profiling of colon cancer by DNA microarrays and correlation with histoclinical parameters

“…GNB2L1 interacts with IGF1R, an important player in colorectal oncogenesis (Furstenberger and Senn, 2002). This interaction can regulate IGF1-mediated AKT activation and protection from cell death (Kiely et al, 2002) as well as IGF1-dependent integrin signalling and promote cell spreading and contact with the extracellular matrix (ECM) (Hermanto et al, 2002).…”