Biomedical subjects

Weiqi Huang

Publications and source records attributed to Weiqi Huang.

6 recordsLinked to original sources

PubMed2007

PU.1, interferon regulatory factor (IRF) 2, and the interferon consensus sequence-binding protein (ICSBP/IRF8) cooperate to activate NF1 transcription in differentiating myeloid cells.

Nf1 (neurofibromin 1) is a Ras-GAP protein that regulates cytokine-induced proliferation of myeloid cells. In previous studies, we found that the interferon consensus sequence-binding protein (ICSBP; also referred to as interferon regulatory factor 8) activates transcription of the gene encoding Nf1 (the NF1 gene) in differentiating myeloid cells. We also found that NF1 activation requires cytokine-stimulated phosphorylation of a conserved tyrosine residue in the interferon regulatory factor (IRF) domain of ICSBP/IRF8. In this study, we found that ICSBP/IRF8 cooperates with PU.1 and interferon regulatory factor 2 to activate a composite ets/IRF-cis element in the NF1 promoter. We found that PU.1 binds directly to the NF1-cis element, and DNA-bound PU.1 interacts with IRF2, recruiting IRF2 to the cis element. This interaction requires cytokine-induced phosphorylation of specific serine residues in the PU.1 PEST domain and of a conserved tyrosine residue in the IRF domain of IRF2. We found that ICSBP/IRF8 interaction with the NF1-cis element requires pre-binding of PU.1 and IRF2. The conserved IRF domain tyrosine in ICSBP/IRF8 is required for interaction with the DNA-bound PU.1-IRF2 heterodimer. NF1 deficiency in myeloid progenitor cells results in cytokine hypersensitivity and myeloproliferation. Therefore, these studies identify a target gene for the previously observed tumor-suppressor effect of PU.1. Additionally, these studies identify a tumor-suppressor function for the "oncogenic" transcription factor, IRF2.

Cell Differentiation↗

PubMed2006

Activation of SHP2 protein-tyrosine phosphatase increases HoxA10-induced repression of the genes encoding gp91(PHOX) and p67(PHOX).

The CYBB and NCF2 genes encode the phagocyte oxidase proteins gp91(PHOX) and p67(PHOX), respectively. These genes are transcribed after the promyelocyte stage of differentiation, and transcription continues until cell death. In undifferentiated myeloid cells, homologous cis-elements in the CYBB and NCF2 genes are repressed by the homeodomain transcription factor HoxA10. During cytokine-induced myelopoiesis, tyrosine phosphorylation of HoxA10 decreases binding affinity for the CYBB and NCF2 cis-elements. This abrogates HoxA10-induced transcriptional repression as differentiation proceeds. Therefore, mechanisms involved in differentiation stage-specific HoxA10 tyrosine phosphorylation are of interest because HoxA10 phosphorylation modulates myeloid-specific gene transcription. In this study, we found that HoxA10 is a substrate for SHP2 protein-tyrosine phosphatase in undifferentiated myeloid cells. In contrast, HoxA10 is a substrate for a constitutively active mutant form of SHP2 in both undifferentiated and differentiating myeloid cells. Expression of such SHP2 mutants results in persistent HoxA10 repression of CYBB and NCF2 transcription during myelopoiesis. Both HoxA10 overexpression and activating SHP2 mutations have been described in human myeloid malignancies. Therefore, our results suggest that these mutations could cooperate, leading to decreased myeloid-specific gene transcription and functional differentiation block in myeloid cells with both defects.

Animals↗

PubMed2006

Leukemia-associated, constitutively active mutants of SHP2 protein tyrosine phosphatase inhibit NF1 transcriptional activation by the interferon consensus sequence binding protein.

Deficiency in either the interferon consensus sequence binding protein (ICSBP) or neurofibromin 1 (Nf1) increases the proliferative response of myeloid progenitor cell to hematopoietic cytokines. Consistent with this, we previously demonstrated that ICSBP activates transcription of the gene encoding Nf1 (the NF1 gene). In the studies presented here, we determine that ICSBP tyrosine phosphorylation is necessary for the activation of NF1 transcription. Since ICSBP is tyrosine phosphorylated in response to hematopoietic cytokines, these studies identify a novel pathway by which cytokine-induced posttranslational modification of ICSBP results in NF1 transcription. Nf1 subsequently inactivates cytokine-activated Ras, thereby creating a negative feedback mechanism for cytokine-induced proliferation. In these studies, we also determine that ICSBP is a substrate for SHP2 protein tyrosine phosphatase (SHP2-PTP). We find that wild-type SHP2-PTP dephosphorylates ICSBP only in undifferentiated myeloid cells. In contrast, a leukemia-associated, constitutively activated mutant form of SHP2-PTP dephosphorylates ICSBP in both myeloid progenitors and differentiating myeloid cells. Activated SHP2-PTP mutants thereby inhibit ICSBP-dependent NF1 transcription, impairing this negative feedback mechanism on cytokine-activated Ras. Therefore, these studies suggest that leukemia-associated ICSBP deficiency cooperates with leukemia-associated activating mutants of SHP2-PTP to contribute to the proliferative phenotype in myeloid malignancies.

Animals↗

PubMed2005

Trichostatin A induces transforming growth factor beta type II receptor promoter activity and acetylation of Sp1 by recruitment of PCAF/p300 to a Sp1.NF-Y complex.

Transforming growth factor beta type II receptor (TbetaRII) is a tumor suppressor gene that can be transcriptionally silenced by histone deacetylases (HDACs) in cancer cells. In this report, we demonstrated the mechanism by which trichostatin A (TSA), an inhibitor of HDAC, induces the expression of TbetaRII in human pancreatic cancer cell lines by modulating the transcriptional components that bind a specific DNA region of the TbetaRII promoter. This region of the TbetaRII promoter possesses Sp1 and NF-Y binding sites in close proximity (located at -102 and -83, respectively). Treatment of cells with TSA activates the TbetaRII promoter in a time-dependent manner through the recruitment of p300 and PCAF into a Sp1.NF-Y.HDAC complex that binds this DNA element. The recruitment of p300 and PCAF into the complex is associated with a concomitant acetylation of Sp1 and an overall decrease in the amount of HDAC associated with the complex. Transient overexpression of p300 or PCAF potentiated TSA-induced TbetaRII promoter activity. The effect of PCAF was dependent on its histone acetyltransferase activity, whereas that of p300 was independent. Stable transfection of PCAF caused an increase in TbetaRII mRNA expression, the association of PCAF with TbetaRII promoter, and the acetylation of Sp1. Taken together, these results showed that TSA treatment of pancreatic cancer cells leads to transcriptional activation of the TbetaRII promoter through modulation of the components of a Sp1.NF-Y.p300.PCAF.HDAC-1 multiprotein complex. Moreover, the interaction of NF-Y with the Sp1-associated complex may further explain why this specific Sp1 site mediates transcriptional responsiveness to TSA.

Acetyltransferases↗

PubMed2004

Alterations of cell signaling pathways in pancreatic cancer.

Pancreatic ductal adenocarcinomas continue to have the worst prognosis of any adult malignancy with a five-year survival rate of less than 4%. One approach to improve patient survival from pancreatic cancer is to identify new biological targets that contribute to the aggressive pathogenecity of this disease and to develop reagents that will interfere with the function of these targets. Apart from the identification of the genetic profile of pancreatic cancer, a number of studies have focused on aberrant cell signaling pathways and their role in pancreatic cancer biology and response to therapy. This review, although not comprehensive, will discuss the salient features of several of these pathways. These include the roles of TGF beta signaling in both tumor suppression and tumor promotion and the effects of deregulation of phosphotyrosine kinase receptor signaling pathways in pancreatic cancer.

Adult↗

PubMed2000

Bone Marrow Endothelial Cell-Derived Factors Inhibit the Growth of Marrow CFU-F.

The present study investigated the effects of the serum-free conditioned media of the bone marrow endothelial cells on CFU-F for potential mechanisms upon which hematopoiesis may be regulated by them within the bone marrow microenvironment. After obtaining the serum-free conditioned media of human and murine purified bone marrow endothelial cells (hBMEC-CM and mBMEC-CM) in vitro, MW > 10 kD, 3 - 10 kD and < 3 kD components were sifted out from these media by means of serial ultrafiltration. Assays of CFU-F were performed to test the effects of BMEC-CM and their ultrafiltrated components. The results showed that every one of hBMEC-CM, mBMEC-CM and their MW < 3 kD components exerted a suppressive effect on the proliferation of corresponding CFU-F but MW > 10 kD and 3 - 10 kD components. The BMEC-CM and MW < 3 kD components decreased the number as well as the size of CFU-F. There were the markedly negative concentration-dependent relations between the concentrations of MW < 3 kD component and the numbers of CFU-F. These findings suggested that bone marrow endothelial cells in culture could secrete at least a humoral factor (molecular weight less than 3 kD) which has an inhibitory effect on the growth of CFU-F.

Journal Article↗