43 research outputs found
Evidence for a role of TRIB3 in the regulation of megakaryocytopoiesis
Megakaryocytopoiesis is a complex differentiation process driven by the hormone
thrombopoietin by which haematopoietic progenitor cells give rise to
megakaryocytes, the giant bone marrow cells that in turn break down to form blood
platelets. The Tribbles Pseudokinase 3 gene (TRIB3) encodes a pleiotropic protein
increasingly implicated in the regulation of cellular differentiation programmes.
Previous studies have hinted that TRIB3 could be also involved in
megakaryocytopoiesis but its role in this process has so far not been investigated.
Using cellular model systems of haematopoietic lineage differentiation here we
demonstrate that TRIB3 is a negative modulator of megakaryocytopoiesis. We found
that in primary cultures derived from human haematopoietic progenitor cells,
thrombopoietin-induced megakaryocytic differentiation led to a time and dosedependent
decrease in TRIB3 mRNA levels. In the haematopoietic cell line UT7/mpl,
silencing of TRIB3 increased basal and thrombopoietin-stimulated megakaryocyte
antigen expression, as well as basal levels of ERK1/2 phosphorylation. In primary
haematopoietic cell cultures, silencing of TRIB3 facilitated megakaryocyte
differentiation. In contrast, over-expression of TRIB3 in these cells inhibited the
differentiation process. The in-vitro identification of TRIB3 as a negative regulator of
megakaryocytopoiesis suggests that in-vivo this gene could be important for the
regulation of platelet production
ANKRD26 and Its Interacting Partners TRIO, GPS2, HMMR and DIPA Regulate Adipogenesis in 3T3-L1 Cells
Partial inactivation of the Ankyrin repeat domain 26 (Ankrd26) gene causes obesity and diabetes in mice and increases spontaneous and induced adipogenesis in mouse embryonic fibroblasts. However, it is not yet known how the Ankrd26 protein carries out its biological functions. We identified by yeast two-hybrid and immunoprecipitation assays the triple functional domain protein (TRIO), the G protein pathway suppressor 2 (GPS2), the delta-interacting protein A (DIPA) and the hyaluronan-mediated motility receptor (HMMR) as ANKRD26 interacting partners. Adipogenesis of 3T3-L1 cells was increased by selective down-regulation of Ankrd26, Trio, Gps2, Hmmr and Dipa. Furthermore, GPS2 and DIPA, which are normally located in the nucleus, were translocated to the cytoplasm, when the C-terminus of ANKRD26 was introduced into these cells. These findings provide biochemical evidence that ANKRD26, TRIO, GPS2 and HMMR are novel and important regulators of adipogenisis and identify new targets for the modulation of adipogenesis
Amino Acid Availability Controls TRB3 Transcription in Liver through the GCN2/eIF2α/ATF4 Pathway
In mammals, plasma amino acid concentrations are markedly affected by dietary or pathological conditions. It has been well established that amino acids are involved in the control of gene expression. Up to now, all the information concerning the molecular mechanisms involved in the regulation of gene transcription by amino acid availability has been obtained in cultured cell lines. The present study aims to investigate the mechanisms involved in transcriptional activation of the TRB3 gene following amino acid limitation in mice liver. The results show that TRB3 is up-regulated in the liver of mice fed a leucine-deficient diet and that this induction is quickly reversible. Using transient transfection and chromatin immunoprecipitation approaches in hepatoma cells, we report the characterization of a functional Amino Acid Response Element (AARE) in the TRB3 promoter and the binding of ATF4, ATF2 and C/EBPβ to this AARE sequence. We also provide evidence that only the binding of ATF4 to the AARE plays a crucial role in the amino acid-regulated transcription of TRB3. In mouse liver, we demonstrate that the GCN2/eIF2α/ATF4 pathway is essential for the induction of the TRB3 gene transcription in response to a leucine-deficient diet. Therefore, this work establishes for the first time that the molecular mechanisms involved in the regulation of gene transcription by amino acid availability are functional in mouse liver