title: Blockade of mitogen-activated protein kinase cascade signaling in interleukin 6-independent multiple myeloma cells.
abstract: Interleukin 6 (IL-6) is a growth factor for multiple myeloma (MM) cells, yet not all MM cell lines or patient cells require IL-6 for their growth. It is well known that IL-6 activates the signal transducers and activators of transcription (stat) 1-stat3 heterodimer, stat3 homodimer, and Ras-dependent mitogen-activated protein kinase (MAPK) cascades in multiple cell systems. We have shown previously that the MAPK pathway is an important pathway for IL-6-mediated MM cell growth. In this study, we delineate the pattern of upstream MAPK cascade activation in IL-6-responsive B9 cells and in IL-6-nonresponsive U266, OCI-My5, and RPMI8226 MM cells to define sites of blockade of this pathway associated with loss of responsiveness to IL-6. In B9 cells, IL-6 triggered the following in sequence: gp130 phosphorylation, gp130-to-protein tyrosine phosphatase 1D (PTP1D) binding, PTP1D phosphorylation, PTP1D complex formation with Grb2-Son of sevenless 1 (Sos1), and Sos1 phosphorylation. gp130 phosphorylation, gp130-to-PTP1D binding, PTP1D phosphorylation, and PTP1D-to-Grb2 binding are also induced by IL-6 in all IL-6-independent MM cell lines studied. However, Grb2 is not associated with Sos1, and neither Grb2-to-Sos1 binding nor Sos1 phosphorylation is triggered by IL-6 in OCI-My5 MM cells. On the other hand, Grb2 and Sos1 are associated constitutively in U266 and RPMI8226 MM cells, but phosphorylation of Sos1 is not induced by IL-6. These data suggest that lack of Sos1 activation is associated with loss of IL-6 responsiveness in MM cell lines that grow independently of IL-6.
authors.affiliation: Division of Hematologic Malignancies, Dana-Farber Cancer Institute, and Department of Medicine, Harvard Medical School, Boston, Massachusetts 02215, USA.
authors.forename: A
authors.initials: A
authors.lastname: Ogata
authors.forename: D
authors.initials: D
authors.lastname: Chauhan
authors.forename: M
authors.initials: M
authors.lastname: Urashima
authors.forename: G
authors.initials: G
authors.lastname: Teoh
authors.forename: S P
authors.initials: SP
authors.lastname: Treon
authors.forename: K C
authors.initials: KC
authors.lastname: Anderson
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002455:Cell Division; D051380:GRB2 Adaptor Protein; D020662:Guanine Nucleotide Exchange Factors; D006801:Humans; D015850:Interleukin-6 / Q000494:pharmacology* / Q000502:physiology; D051379:Mice; D009101:Multiple Myeloma; D010766:Phosphorylation; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism; D011506:Proteins / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D014162:Transfection; D014407:Tumor Cells, Cultured; D020663:ras Guanine Nucleotide Exchange Factors
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D051380:GRB2 Adaptor Protein; C495948:GRB2 protein, human; C495949:Grb2 protein, mouse; D020662:Guanine Nucleotide Exchange Factors; D015850:Interleukin-6; D011506:Proteins; D011993:Recombinant Fusion Proteins; D020663:ras Guanine Nucleotide Exchange Factors; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D017027:Protein Tyrosine Phosphatases