Insulinlike growth factor–I signaling in multiple myeloma: downstream elements, functional correlates, and pathway cross-talk

• Published in: Blood Vol. 99; no. 11; pp. 4138 - 4146
• Main Authors: Qiang, Ya-Wei, Kopantzev, Eugene, Rudikoff, Stuart
• Format: Journal Article
• Language: English
• Published: Washington, DC Elsevier Inc 01.06.2002; The Americain Society of Hematology
• Subjects: Apoptosis - drug effects; Biological and medical sciences; Cell Division - drug effects; Chromones - pharmacology; Dexamethasone - pharmacology; DNA Replication - drug effects; Enzyme Inhibitors - pharmacology; Humans; Immunodeficiencies. Immunoglobulinopathies; Immunoglobulinopathies; Immunopathology; Insulin-Like Growth Factor I - pharmacology; MAP Kinase Signaling System - drug effects; MAP Kinase Signaling System - physiology; Medical sciences; Morpholines - pharmacology; Multiple Myeloma - physiopathology; Phosphatidylinositol 3-Kinases - metabolism; Phosphorylation; Receptor Cross-Talk - physiology; Recombinant Proteins - pharmacology; Retroviridae - genetics; Ribosomal Protein S6 Kinases - antagonists & inhibitors; Ribosomal Protein S6 Kinases - metabolism; Signal Transduction - drug effects; Signal Transduction - physiology; Sirolimus - pharmacology; Transcription Factors - metabolism; Transfection; Tumor Cells, Cultured; Human; Cell proliferation; Immunopathology; Pathophysiology; Enzyme; Transferases; Mitogen-activated protein kinase; Malignant hemopathy; EC 2.4.1.21; Insulin like growth factor 1; Myeloma; 1-Phosphatidylinositol 3-kinase; Signal transduction; Regulation(control); Immunoglobulinopathy; Lymphoproliferative syndrome; Protein-tyrosine kinase; Tumor cell; Apoptosis
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood.V99.11.4138

In multiple myeloma cells, insulinlike growth factor–I (IGF-I) activates 2 distinct signaling pathways, mitogen-activated protein kinase (MAPK) and phosphoinositol 3-kinase (PI-3K), leading to both proliferative and antiapoptotic effects. However, it is unclear through which of these cascades IGF-I regulates these different responses. The present studies identify a series of downstream targets in the PI-3K pathway, including glycogen synthase kinase–3β, p70S6 kinase, and the 3 members of the Forkhead family of transcription factors. The contribution of the MAPK and PI-3K pathways and, where possible, individual elements to proliferation and apoptosis was evaluated by means of a series of specific kinase inhibitors. Both processes were regulated almost exclusively by the PI-3K pathway, with only minor contributions associated with the MAPK cascade. Within the PI-3K cascade, inhibition of p70S6 kinase led to significant decreases in proliferation and protection from apoptosis. Activation of p70S6 kinase could also be prevented by MAPK inhibitors, indicating regulation by both pathways. The Forkhead transcription factor FKHRL1 was observed to provide a dual effect in that phosphorylation upon IGF-I treatment resulted in a loss of ability to inhibit proliferation and induce apoptosis. The PI-3K pathway was additionally shown to exhibit cross-talk and to regulate the MAPK cascade, as inhibition of PI-3K prevented activation of Mek1/2 and other downstream MAPK elements. These results define important elements in IGF-I regulation of myeloma cell growth and provide biological correlates critical to an understanding of growth-factor modulation of proliferation and apoptosis.