Biomedical subjects

Saghi Ghaffari

Publications and source records attributed to Saghi Ghaffari.

6 recordsLinked to original sources

PubMed2005

AKT induces erythroid-cell maturation of JAK2-deficient fetal liver progenitor cells and is required for Epo regulation of erythroid-cell differentiation.

AKT serine threonine kinase of the protein kinase B (PKB) family plays essential roles in cell survival, growth, metabolism, and differentiation. In the erythroid system, AKT is known to be rapidly phosphorylated and activated in response to erythropoietin (Epo) engagement of Epo receptor (EpoR) and to sustain survival signals in cultured erythroid cells. Here we demonstrate that activated AKT complements EpoR signaling and supports erythroid-cell differentiation in wild-type and JAK2-deficient fetal liver cells. We show that erythroid maturation of AKT-transduced cells is not solely dependent on AKT-induced cell survival or proliferation signals, suggesting that AKT transduces also a differentiation-specific signal downstream of EpoR in erythroid cells. Down-regulation of expression of AKT kinase by RNA interference, or AKT activity by expression of dominant negative forms, inhibits significantly fetal liver-derived erythroid-cell colony formation and gene expression, demonstrating that AKT is required for Epo regulation of erythroid-cell maturation.

Animals↗

PubMed2005

Erythropoietin stimulates phosphorylation and activation of GATA-1 via the PI3-kinase/AKT signaling pathway.

Erythropoietin (Epo) stimulation of its receptor's downstream signaling pathways and optimum function of GATA-1 transcription factor are both essential for normal erythroid cell development. Epo-receptor (EpoR) signaling and GATA-1 regulate proliferation, survival, differentiation, and maturation of erythroid cells. Whether any signal that is generated by EpoR targets GATA-1 or affects GATA-1 transcriptional activity is not known. Here, we demonstrate that stimulation of EpoR results in phosphorylation of GATA-1 at serine 310 (S310) in primary fetal liver erythroid progenitors and in cultured erythroid cells. We show that phosphorylation of GATA-1 is important for Epo-induced maturation of fetal liver erythroid progenitor cells. The PI3-kinase/AKT signaling pathway is identified as a mediator of Epo-induced phosphorylation of GATA-1. AKT serine threonine kinase phosphorylates GATA-1S310 in vitro and in erythroid cells and enhances GATA-1 transcriptional activity. These data demonstrate that EpoR signaling phosphorylates GATA-1 and modulates its activity via the PI3-kinase/AKT signaling pathway.

Animals↗

PubMed2003

Cytokines and BCR-ABL mediate suppression of TRAIL-induced apoptosis through inhibition of forkhead FOXO3a transcription factor.

Cytokine-provided survival signals are known to suppress apoptosis through inhibition of mitochondrial pathways that involve Bcl-2 family members. Here we show that in hematopoietic cells, cytokines also regulate death receptor-mediated pathways. We demonstrate that hematopoietic cytokines such as IL-3 and erythropoietin in normal cells, as well as BCR-ABL oncoprotein in transformed cells, inhibit transcription of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). Using small interfering RNAs, we show that the inhibition of TRAIL function is sufficient to partially rescue cytokine-deprived cells from apoptosis. Finally, we demonstrate that cytokine and BCR-ABL suppression of TRAIL transcription is mediated through phosphorylation and inhibition of the forkhead FOXO3a transcription factor. BCR-ABL-induced inhibition of TRAIL transcription in hematopoietic cells may provide a novel mechanism for tumorigenicity in chronic myeloid leukemia.

Apoptosis↗

PubMed2003

Phosphotyrosine mapping in Bcr/Abl oncoprotein using phosphotyrosine-specific immonium ion scanning.

Bcr/Abl is a fusion oncoprotein that is of paramount importance in chronic myelogenous leukemia and acute lymphocytic leukemia. The tyrosine-phosphorylated fraction of the p185 form of Bcr/Abl was isolated by immunoprecipitation with an anti-phosphotyrosine antibody and SDS-PAGE. The tryptic digest of the gel-separated protein was prefractionated on POROS R2/OLIGO R3 microcolumns and subjected to phosphotyrosine mapping by precursor ion scanning in positive ion mode utilizing the immonium ion of phosphotyrosine, also called phosphotyrosine-specific immonium ion scanning, on a quadrupole time-of-flight tandem mass spectrometer. In total, nine different phosphorylated tyrosine residues were unambiguously localized in 12 different precursor ions. These phosphorylation sites correspond to three previously described phosphotyrosine residues and six novel tyrosine phosphorylation sites, and most of them were not predicted by the phosphorylation motif prediction programs ProSite, NetPhos, or ScanSite. This study shows the power of phosphotyrosine-specific immonium ion scanning for sensitive phosphotyrosine mapping when limited amounts of samples are available.

Amino Acid Sequence↗

PubMed2003

Development of human protein reference database as an initial platform for approaching systems biology in humans.

Human Protein Reference Database (HPRD) is an object database that integrates a wealth of information relevant to the function of human proteins in health and disease. Data pertaining to thousands of protein-protein interactions, posttranslational modifications, enzyme/substrate relationships, disease associations, tissue expression, and subcellular localization were extracted from the literature for a nonredundant set of 2750 human proteins. Almost all the information was obtained manually by biologists who read and interpreted >300,000 published articles during the annotation process. This database, which has an intuitive query interface allowing easy access to all the features of proteins, was built by using open source technologies and will be freely available at http://www.hprd.org to the academic community. This unified bioinformatics platform will be useful in cataloging and mining the large number of proteomic interactions and alterations that will be discovered in the postgenomic era.

BRCA1 Protein↗

PubMed2002

Structure of the Bcr-Abl oncoprotein oligomerization domain.

The Bcr-Abl oncoprotein is responsible for a wide range of human leukemias, including most cases of Philadelphia chromosome-positive chronic myelogenous leukemia. Oligomerization of Bcr-Abl is essential for oncogenicity. We determined the crystal structure of the N-terminal oligomerization domain of Bcr-Abl (residues 1-72 or Bcr1-72) and found a novel mode of oligomer formation. Two N-shaped monomers dimerize by swapping N-terminal helices and by forming an antiparallel coiled coil between C-terminal helices. Two dimers then stack onto each other to form a tetramer. The Bcr1-72 structure provides a basis for the design of inhibitors of Bcr-Abl transforming activity by disrupting Bcr-Abl oligomerization.

Amino Acid Sequence↗