RESUMO
THOC5 is a nuclear/cytoplasmic protein member of the spliceosome complex which potentiates C/EBP expression in adipocyte differentiation. As C/EBP family members are important regulators of myelopoiesis and THOC5 is highly expressed in neutrophil/macrophage progenitor cells we assessed the role of THOC5 in cytokine-stimulated monocytic development. M-CSF stimulated maturation of the NFS60 cell line was associated with enhanced THOC5 expression and phosphorylation. THOC5 was also shown to form a complex with C/EBPbeta. Ectopic expression of THOC5 mimicked M-CSF mediated cell maturation and enhanced protein expression of the myeloid transcription factors C/EBPbeta, C/EBPalpha, Pu-1 and also GAB2 (a PI-3 Kinase and macrophage development regulator). Increased THOC5 expression also mimicked M-CSF stimulated increases in the lipid second messenger PtdInsP(3). Inhibition of THOC5-induced increases in PtdInsP(3) levels abrogated the elevated levels of C/EBPbeta. Thus THOC5 expression can potentiate receptor signalling to transcription factor expression and monocyte differentiation.
Assuntos
Fator Estimulador de Colônias de Macrófagos/farmacologia , Proteínas Nucleares/metabolismo , Receptor de Fator Estimulador de Colônias de Macrófagos/metabolismo , Fatores de Transcrição/metabolismo , Animais , Proteína beta Intensificadora de Ligação a CCAAT/metabolismo , Linhagem Celular , Humanos , Fator Estimulador de Colônias de Macrófagos/metabolismo , Camundongos , Monócitos/citologia , Monócitos/metabolismo , Proteínas Nucleares/imunologia , Fosfatidilinositol 3-Quinases/metabolismo , Fosforilação , Transdução de Sinais , Fatores de Transcrição/genética , TransfecçãoRESUMO
The fusion protein TEL/PDGFRB is associated with chronic myelomonocytic leukaemia and has intrinsic tyrosine kinase activity. The effects of TEL/PDGFRB were assessed using the multipotent haemopoietic cell line FDCP-Mix. In the absence of growth factors, TEL/PDGFRB expression increased survival that was associated with elevated levels of phosphatidylinositol 3,4,5 trisphosphate (PIP3). Whilst TEL/PDGFRB had subtle effects on the growth factor requirements it had a profound effect on differentiation. The cells became refractory to cytokine-stimulated development, showing limited maturation but failing to produce fully mature cells. We have previously identified the spliceosome protein THOC5 as a target in macrophage colony-stimulating factor signalling and a protein involved in the regulation of transcription factor expression. TEL/PDGFRB expression increased the expression and phosphorylation of THOC5. Elevated expression of THOC5 increased PIP3 levels and decreased apoptosis. Mass spectrometry was used to identify a site for TEL/PDGFRB-mediated phosphorylation on THOC5, which was shown to be a target for a number of other leukaemogenic tyrosine kinases. Thus, THOC5 is a novel target for modulation of signal transduction with a potential role in leukaemogenesis.
