Biomedical subjects

Qingjun Meng

Publications and source records attributed to Qingjun Meng.

5 recordsLinked to original sources

PubMed2006

Identification of Tctex2beta, a novel dynein light chain family member that interacts with different transforming growth factor-beta receptors.

Endoglin is a membrane-inserted protein that is preferentially synthesized in angiogenic vascular endothelial and smooth muscle cells. Endoglin associates with members of the transforming growth factor-beta (TGF-beta) receptor family and has been identified as the gene involved in hereditary hemorrhagic telangiectasia. Although endoglin is known to affect cell responses to TGF-beta, its mode of action is largely unknown. We performed yeast two-hybrid screening of a human placental cDNA library and isolated a new endoglin-binding partner, a novel 221-amino acid member of the Tctex1/2 family of cytoplasmic dynein light chains named Tctex2beta, as the founder of a new Tctex1/2 subfamily. The interaction was localized exclusively to the cytoplasmic domain of endoglin. Reverse transcription-PCR showed expression of Tctex2beta in a wide range of tissues, including vascular endothelial and smooth muscle cells, placenta, and testis, as well as in several tumor cell lines. High expression levels were found in human umbilical vein endothelial cells and the large cell lung cancer cell line. Forced expression of Tctex2beta had a profound inhibitory effect on TGF-beta signaling. Additional Tctex2beta-interacting receptors were identified to be the TGF-beta type II receptor and most likely beta-glycan, but not ALK5, ALK1, or the bone morphogenetic protein type II receptor. Upon fluorescence tagging, co-localization of Tctex2beta and endoglin, as well as Tctex2beta, endoglin, and the TGF-beta type II receptor, was observed by different microscopy techniques. Our findings link endoglin for the first time to microtubule-based minus end-directed transport machinery, suggesting that some endoglin functions might be regulated and directed by its interaction with the cytoplasmic dynein light chain Tctex2beta.

Amino Acid Sequence↗

PubMed2005

IFN-gamma-stimulated transcriptional activation by IFN-gamma-activated transcriptional element-binding factor 1 occurs via an inducible interaction with CAAAT/enhancer-binding protein-beta.

IFN-gamma-activated transcriptional element (GATE)-binding factor 1 (GBF1) was identified as a transactivator that induces gene expression through GATE, a novel IFN-inducible element. Although it can induce gene expression, it is an extremely weak DNA-binding protein on its own. GATE also binds another transcription factor, C/EBP-beta. Therefore, we explored whether GBF1 physically interacts with C/EBP-beta to induce IFN-gamma-regulated transcription. In response to IFN-gamma, C/EBP-beta undergoes phosphorylation at a critical ERK1/2 phosphorylation motif. Mutational inactivation of this motif and/or interference with the ERK1/2 activation prevented the IFN-gamma-induced interactions between GBF1 and C/EBP-beta. A 37-aa long peptide derived from the GBF1 protein can associate with C/EBP-beta in an IFN-inducible manner. These results identify a converging point for two transactivators that exert their effects through a single response element. Together, our studies identify a novel regulatory mechanism that controls IFN-induced transcription.

Amino Acid Motifs↗

PubMed2005

Development of monoclonal antibodies against GBF1 and their use in studying its functions.

Interferon-gamma (IFN-gamma) regulates a number of cellular genes using a variety of cellular signaling pathways. Previously, we identified a novel IFN-regulated element, IFN-gamma-activated transcriptional element (GATE), in the promoter of the murine IFN regulatory factor-9 (IRF-9) gene. This element binds to novel factors. We have recently characterized a novel regulatory factor, GATE binding factor 1 (GBF1), which promoted IFN-gamma-induced transcription. Although GBF1 was a potent inducer of transcription, it did not bind to DNA well in vitro. To understand its role in IFN-gamma-induced actions, we raised monoclonal antibodies (mAb) against GBF1. These antibodies are highly useful in Western, immunoprecipitation, and immunocytochemical analyses. Employing these antibodies, we show that GBF1 is recruited to the endogenous IRF-9 promoter. We also show GBF1 interacts with CAAAT/enhancer binding protein-beta (C/EBP-beta), the other GATE binding factor. Furthermore, other cytokines, such as interleukin-1 (IL-1) and IL-6, induced the expression of GBF1. These antibodies may be useful tools for investigating the role of GBF1 in cytokine-induced responses.

Animals↗

PubMed2002

A novel transactivating factor that regulates interferon-gamma-dependent gene expression.

We have previously identified a novel interferon (IFN)-stimulated cis-acting enhancer element, gamma-IFN-activated transcriptional element (GATE). GATE differs from the known IFN-stimulated elements in its primary sequence. Preliminary analysis has indicated that the GATE-dependent transcriptional response requires the binding of novel transacting factors. A cDNA expression library derived from an IFN-gamma-stimulated murine macrophage cell line was screened with a (32)P-labeled GATE probe to identify the potential GATE-binding factors. A cDNA coding for a novel transcription-activating factor was identified. Based on its discovery, we named it as GATE-binding factor-1 (GBF-1). GBF-1 homologs are present in mouse, human, monkey, and Drosophila. It activates transcription from reporter genes carrying GATE. It possesses a strong transactivating activity but has a weak DNA binding property. GBF-1 is expressed in most tissues with relatively higher steady-state levels in heart, liver, kidney, and brain. Its expression is induced by IFN-gamma treatment. GBF-1 is present in both cytosolic and nuclear compartments. These studies thus identify a novel transactivating factor in IFN signaling pathways.

Amino Acid Sequence↗

PubMed2002

MEKK1 plays a critical role in activating the transcription factor C/EBP-beta-dependent gene expression in response to IFN-gamma.

IFN-gamma induces a number of genes to up-regulate cellular responses by using specific transcription factors and the cognate elements. We recently discovered that CCAAT/enhancer-binding protein-beta (C/EBP-beta) induces gene transcription through an IFN-response element called gamma-IFN-activated transcriptional element (GATE). Using mutant cells, chemical inhibitors, and specific dominant negative inhibitors, we show that induction of GATE-driven gene expression depends on MEK1 (mitogen-activated protein kinase kinase/extracellular signal-regulated protein kinase kinase) and ERKs (extracellular signal-regulated protein kinases) but is independent of Raf-1. Interestingly in cells lacking the MEKK1 gene or expressing the dominant negative MEKK1, ERK activation, and GATE dependent gene expression is inhibited. A dominant negative MEKK1 blocks C/EBP-beta-driven gene expression stimulated by IFN-gamma. These studies describe an IFN-gamma-stimulated pathway that involves MEKK1-MEK1-ERK1/2 kinases to regulate C/EBP-beta-dependent gene expression.

Animals↗