Constitutive Stat3, Tyr705, and Ser727 phosphorylation in acute myeloid leukemia cells caused by the autocrine secretion of interleukin-6.
To explore the activation patterns of signal transducer and activator of transcription 3 (Stat3) in acute myeloid leukemia (AML), we examined whether the phosphorylation of tyrosine705 (Tyr705) and serine727 (Ser727) residues was abnormally regulated in cells from patients with AML. In 5 of 20 (25%) patients with AML, Stat3 was constitutively phosphorylated on Tyr705 and Ser727, which were not further up-regulated by treatment with IL-6. Furthermore, Stat3 was constitutively bound to the IRE response element in these cells as determined by electrophoretic mobility shift assay, and stimulation with IL-6 did not result in increased DNA binding. Interestingly, AML cells with constitutive Stat3 activation also secreted high levels of IL-6 protein. Treating these AML cells with anti-IL-6 resulted in restored IL-6-inducible Stat3 phosphorylation on both Tyr705 and Ser727 with low or undetectable basal phosphorylation levels in unstimulated cells. In contrast, treatment with anti-IL-1 did not result in altered Stat3 phosphorylation patterns. The constitutive IL-6 expression was associated with elevated levels of suppressor of cytokine signaling-1 (SOCS-1) and SOCS-3 mRNA expression, which were not down-regulated by anti-IL-6. These data indicate that the constitutive Stat3 activation in the investigated AML blasts is caused by high IL-6 secretion levels, thus stimulating the Jak/Stat pathway in an autocrine manner, a paracrine manner, or both. (Blood. 2000;95:3765-3770)
Schuringa
J J
JJ
Department of Hematology, University Hospital Groningen, Groningen, The Netherlands.
Wierenga
A T
AT
Kruijer
W
W
Vellenga
E
E
D000208:Acute Disease; D002352:Carrier Proteins / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D015850:Interleukin-6 / Q000097:blood* / Q000235:genetics; D047908:Intracellular Signaling Peptides and Proteins; D007951:Leukemia, Myeloid / Q000097:blood* / Q000145:classification / Q000276:immunology; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism*; D019000:Phosphotyrosine / Q000378:metabolism*; D011506:Proteins / Q000235:genetics*; D012097:Repressor Proteins; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050796:STAT3 Transcription Factor; D000071222:Suppressor of Cytokine Signaling 1 Protein; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D015534:Trans-Activators / Q000378:metabolism*; D014157:Transcription Factors; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D015850:Interleukin-6; D047908:Intracellular Signaling Peptides and Proteins; D011506:Proteins; D012097:Repressor Proteins; C108944:SOCS1 protein, human; C106644:SOCS3 protein, human; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; D000071222:Suppressor of Cytokine Signaling 1 Protein; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D010768:Phosphoserine; D019000:Phosphotyrosine