Signal pathways involved in activation of p70S6K and phosphorylation of 4E-BP1 following exposure of multiple myeloma tumor cells to interleukin-6.
Interleukin-6 (IL-6) is a prominent tumor growth factor for malignant multiple myeloma cells. In addition to its known activation of the Janus tyrosine kinase-STAT and RAS-MEK-ERK pathways, recent work suggests that IL-6 can also activate the phosphatidylinositol 3-kinase (PI3-K)/AKT kinase pathway in myeloma cells. Because activation of the PI3-K/AKT as well as RAS-MEK-ERK pathways may result in downstream stimulation of the p70(S6K) (p70) and phosphorylation of the 4E-BP1 translational repressor, we assessed these potential molecular targets in IL-6-treated myeloma cells. IL-6 rapidly activated p70 kinase activity and p70 phosphorylation. Activation was inhibited by wortmannin, rapamycin, and the ERK inhibitors PD98059 and UO126, as well as by a dominant negative mutant of AKT. The concurrent requirements for both ERK and PI3-K/AKT appeared to be a result of their ability to phosphorylate p70 on different residues. In contrast, IL-6-induced phosphorylation of 4E-BP1 was inhibited by rapamycin, wortmannin, and dominant negative AKT but ERK inhibitors had no effect, indicating ERK function was dispensable. In keeping with these data, a dominant active AKT mutant was sufficient to induce 4E-BP1 phosphorylation but could not by itself activate p70 kinase activity. Prevention of IL-6-induced p70 activation and 4E-BP1 phosphorylation by the mammalian target of rapamycin inhibitors rapamycin and CCI-779 resulted in inhibition of IL-6-induced myeloma cell growth. These results indicate that both ERK and PI3-K/AKT pathways are required for optimal IL-6-induced p70 activity, but PI3-K/AKT is sufficient for 4E-BP1 phosphorylation. Both effects are mediated via mammalian target of rapamycin function, and, furthermore, these effects are critical for IL-6-induced tumor cell growth.
Shi
Yijiang
Y
Department of Medicine, West Los Angeles Veterans Affairs-UCLA Medical Center, Los Angeles, California 90073, USA.
Hsu
Jung-hsin
JH
Hu
Liping
L
Gera
Joseph
J
Lichtenstein
Alan
A
D048868:Adaptor Proteins, Signal Transducing; D000730:Androstadienes / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism*; D018797:Cell Cycle Proteins; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D015850:Interleukin-6 / Q000494:pharmacology*; D007700:Kinetics; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology; D009101:Multiple Myeloma; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D011994:Recombinant Proteins / Q000494:pharmacology; D012097:Repressor Proteins / Q000378:metabolism; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D020123:Sirolimus / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D000077191:Wortmannin
D048868:Adaptor Proteins, Signal Transducing; D000730:Androstadienes; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D004791:Enzyme Inhibitors; D005419:Flavonoids; D007334:Insulin-Like Growth Factor I; D015850:Interleukin-6; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D011994:Recombinant Proteins; D012097:Repressor Proteins; D019893:Ribosomal Protein S6 Kinases; D020123:Sirolimus; D000077191:Wortmannin; C087000:EIF4EBP1 protein, human; C494918:AKT1 protein, human; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one