p91 STAT1 activation in interleukin-3-stimulated primary acute myeloid leukemia cells.
Interleukin-3 (IL-3) stimulates in vitro blast cell proliferation in a consistent proportion of acute myeloid leukemia (AML) cases, however the degree of response varies from case to case and it is not related to the FAB subtype or to other clinical parameters. IL-3-induced proliferation of myeloid cells is mediated by the interaction with an heterodimeric receptor (IL-3R) comprised of a ligand binding subunit denoted alpha and a common transducing subunit designated as beta (beta). Ligand binding to the receptor activates a number of signaling molecules including proteins of the STATs (signal transducing and activators of transcription) family. To elucidate the mechanisms responsible for the abnormal proliferative response of AML cells to IL-3, we evaluated, both in the IL-3-dependent M-07e cell line and in 20 AML cases, the activation of STAT1 p91 and its association with the beta c subunit. On the basis of the in vitro proliferation assay, 11 out of 20 cases were found to be responsive to IL-3 and eight out of 16 to GM-CSF. Our results demonstrated that in M-07e cells and in six AML cases (five IL-3 responsive and one unresponsive) p91 tyrosine phosphorylation was ligand dependent. Ligand independent p91 tyrosine phosphorylation was detected in 10 AML cases (five responsive and five unresponsive). p91 association with the beta c subunit was consistent with its ligand dependent activation and with the ability to form a DNA-binding complex containing p91. In the remaining four cases (three unresponsive and one responsive) no p91 tyrosine phosphorylation and/or association were detected. These findings, together with the observation that in five IL-3 responsive cases p91 was constitutively phosphorylated, suggest that IL-3-mediated AML proliferation is only partially sustained by p91 activation and that other post-receptor molecules are required to achieve maximal proliferative response. Moreover structural abnormalities of the receptor or of post-receptor signaling proteins may account for the constitutive p91 phosphorylation and growth factor independent proliferation observed in the unresponsive AML cases.
Aronica
M G
MG
Dipartimento di Scienze Biomediche e Oncologia Umana, Università di Torino, Italy.
Brizzi
M F
MF
Dentelli
P
P
Rosso
A
A
Yarden
Y
Y
Pegoraro
L
L
D002455:Cell Division / Q000187:drug effects; D003593:Cytoplasm / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000187:drug effects* / Q000235:genetics* / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000494:pharmacology; D006801:Humans; D007140:Immunoglobulin Fab Fragments; D007377:Interleukin-3 / Q000494:pharmacology*; D007951:Leukemia, Myeloid / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology; D010766:Phosphorylation; D016185:Receptors, Interleukin-3 / Q000096:biosynthesis / Q000187:drug effects; D050794:STAT1 Transcription Factor; D015534:Trans-Activators / Q000187:drug effects* / Q000235:genetics* / Q000378:metabolism; D014407:Tumor Cells, Cultured; D014443:Tyrosine / Q000378:metabolism
D004268:DNA-Binding Proteins; D007140:Immunoglobulin Fab Fragments; D007377:Interleukin-3; D016185:Receptors, Interleukin-3; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D015534:Trans-Activators; D014443:Tyrosine; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D004247:DNA