Biomedical subjects

S Jaharul Haque

Publications and source records attributed to S Jaharul Haque.

14 recordsLinked to original sources

PubMed2006

Interleukins and STAT signaling.

Metazoan cells secrete small proteins termed cytokines that execute a variety of biological functions essential for the survival of organisms. Binding of cytokines that belong to the hematopoietin- or interferon-family, to their cognate receptors on the surface of target cells, induces receptor aggregation, which in turn sequentially triggers tyrosine-phosphorylation-dependent activation of receptor-associated Janus-family tyrosine kinases (JAKs), receptors, and signal transducers and activators of transcription (STATs). Phosphorylated STATs form dimers that migrate to the nucleus, bind to cognate enhancer elements and activate transcription of target genes. Each cytokine activates a specific set of genes to execute its biological functions with a certain degree of redundancy. Cytokine signals are, in general, transient in nature. Therefore, under normal physiological conditions, initiation and attenuation of cytokine signals are tightly controlled via multiple cellular and molecular mechanisms. Aberrant activation of cytokine signaling pathways is, however, found under a variety of patho-physiological conditions including cancer and immune diseases.

Animals↗

PubMed2005

PI3K-AKT pathway negatively controls EGFR-dependent DNA-binding activity of Stat3 in glioblastoma multiforme cells.

Glioblastoma multiforme (GBM) cells frequently harbor amplification and/or gain-of-function mutation of the EGFR gene leading to the activation of multiple signaling pathways. Blockade of EGFR activation inhibited the activation of both AKT and Stat3 in U87 and D54 GBM cells and induced spontaneous apoptosis, which were associated with reduction in the steady-state level of Mcl-1. Surprisingly, inhibition of PI3 kinase (PI3K) activity, which in turn inhibited AKT activation, significantly increased the DNA-binding activity of Stat3 in U87 and D54 cells. This was not due to an increase in the level of tyrosine-phosphorylated Stat3. Conversely, ectopic expression of constitutively activated AKT significantly decreased the DNA-binding activity of Stat3 in 293T cells. Interestingly, blockade of protein phosphatase 2A activity in GBM or 293T cells by calyculin A, which activated AKT, stabilized the phosphorylation of multiple Ser/Thr residues that were located in the transactivation domain (TAD) of Stat3 and this in turn completely ablated the DNA-binding activity of Stat3. Collectively, these results suggest that both Stat3 and AKT provide survival signals in U87 and D54 cells, and Ser/Thr phosphorylation of Stat3-TAD by the PI3K-AKT pathway negatively controls the DNA-binding function of Stat3.

Apoptosis↗

PubMed2005

Tyrosine 729 of the G-CSF receptor controls the duration of receptor signaling: involvement of SOCS3 and SOCS1.

Mutations in the granulocyte-colony stimulating factor receptor (G-CSF-R) gene resulting in carboxy terminal truncation have been associated with acute myeloid leukemia (AML). The truncated G-CSF-R from AML patients mediate enhanced and prolonged activation of signal transducer and activator of transcription 5 (Stat5). It has been shown that Src homology-2 (SH2)-containing tyrosine phosphatase-1 attenuates the intensity of G-CSF-induced Stat5 activation through interacting with the carboxy terminus of the G-CSF-R. Using a series of tyrosine-to-phenylalanine substitution mutants, we show here that tyrosine (Tyr) 729, located in the carboxy terminus of the G-CSF-R, controls the duration of G-CSF-stimulated activation of Stat5, Akt, and extracellular signal-regulated kinase 1/2. It is interesting that activation of these signaling molecules by G-CSF was prolonged by pretreating cells with actinomycin D or cyclohexamide, suggesting that de novo protein synthesis is required for appropriate termination of G-CSF-R signaling. The transcripts for suppressor of cytokine signaling 3 (SOCS3) and SOCS1 were up-regulated rapidly upon G-CSF stimulation. Expression of SOCS3 or SOCS1, but not SOCS2 and cytokine-inducible SH2 domain-containing protein, completely suppressed G-CSF-induced Stat5 activation but had only a weak effect on Stat5 activation mediated by the receptor mutant lacking Tyr 729. SOCS1 and SOCS3 also inhibited G-CSF-dependent cell proliferation, but the inhibitory effect of the two SOCS proteins on cell proliferation was diminished when Tyr 729 of the G-CSF-R was mutated. These data indicate that Tyr 729 of the G-CSF-R is required for SOCS1- and SOCS3-mediated negative regulation of G-CSF-R signaling and that the duration and intensity of G-CSF-induced Stat5 activation are regulated by two distinct mechanisms.

Animals↗

PubMed2005

Aberrant Stat3 signaling by interleukin-4 in malignant glioma cells: involvement of IL-13Ralpha2.

Interleukin (IL)-4 exhibits antitumor activity in rodent experimental gliomas, which is likely mediated by the actions of IL-4 on a variety of immune cells present in and around the tumor masses. Here, we show that IL-4, which activates Stat6 in normal human astrocytes and in a variety of other cells, induces an aberrant activation of Stat3 in glioblastoma multiforme (GBM) cells but not in normal human astrocytes. Previously, we have shown that autocrine IL-6 signaling induces a persistent activation of Stat3. Now, we show that Stat3 is further activated by IL-4 stimulation of GBM cells. Expression of IL-13Ralpha2, a decoy receptor for IL-13 that partly blocks IL-4-mediated activation of Stat6 in GBM cells, up-regulates the activation of Stat3 as shown by a small interfering RNA-mediated inhibition of IL-13Ralpha2 expression. In addition, transient expression of the IL-13Ralpha2 transgene in 293T cells increases the IL-4-mediated activation of Stat3 and subsequent expression of Stat3-targeted gene. Coimmunoprecipitation results reveal that IL-13Ralpha2-mediated activation of Stat3 does not require a direct physical interaction between Stat3 and IL-13Ralpha2. Chromatin immunoprecipitation assay employing anti-Stat3 antibody confirms the in vivo binding of activated Stat3 to the promoters of genes that encode antiapoptotic proteins Bcl-2, Bcl-x(L), and Mcl-1. IL-4 significantly up-regulates of the steady-state levels of Bcl-2, Bcl-x(L), and Mcl-1 in GBM cells. These results indicate that IL-4/IL-13 receptor-mediated Stat3 signaling may contribute to the pathogenesis of GBM cells by modulating the expression of the Bcl-2 family of antiapoptotic proteins.

Astrocytes↗

PubMed2005

Pediatric hypereosinophilic syndrome (HES) differs from adult HES.

The idiopathic hypereosinophilic syndrome (HES) developed in a 15-year-old boy who presented with colitis, cough, rash, and hepatitis. Molecular analysis failed to demonstrate the Fip1-like1-Platelet Derived Growth Factor Receptor alpha chain (FIP1L1-PDGFRA) mutation described in adult patients with HES. There are significant clinical differences between the pediatric and adult presentations of HES.

Adolescent↗

PubMed2005

Serine phosphorylation of Stat6 negatively controls its DNA-binding function.

In response to interleukin-4 (IL-4) or IL-13 stimulation of cells, Stat6 becomes phosphorylated on Tyr(641) and forms homodimers that migrate to the nucleus, bind to cognate DNA elements, and drive the transcription of target genes. Here, we show that phosphorylation of multiple serine residues ablates its DNA-binding activity in IL-4 stimulated cells. The phosphorylation sites are mapped to the transactivation domain (TAD) of Stat6. Importantly, serine phosphorylation of Stat6 TAD does not affect the phosphorylation of Tyr(641), nor does it affect the dimer formation or the ability of translocating to the nucleus in IL-4-stimulated cells. Collectively, these data suggest that phosphorylation of multiple serine residues in the TAD possibly induces conformational changes in Stat6 dimers that cause the loss of DNA binding and, thus, negatively control the expression of IL-4-responsive genes.

Cell Line↗

PubMed2004

Impaired nitric oxide synthase-2 signaling pathway in cystic fibrosis airway epithelium.

Cystic fibrosis (CF) airway epithelial cells are more susceptible to viral infection due to impairment of the innate host defense pathway of nitric oxide (NO). NO synthase-2 (NOS2) expression is absent, and signal transducer and activator of transcription (STAT) 1 activation is reduced in CF. We hypothesized that the IFN-gamma signaling pathway, which leads to NOS2 gene induction in CF airway epithelial cells, is defective. In contrast to a lack of NOS2 induction, the major histocompatibility complex class 2, an IFN-gamma-regulated delayed-responsive gene, is similarly induced in CF and non-CF airway epithelial (NL) cells, suggesting an NOS2-specific defect in the IFN-gamma signaling pathway. STAT1 and activator protein-1, both required for NOS2 gene expression, interact normally in CF cells. Protein inhibitor of activated STAT1 is not increased in CF cells. IFN-gamma induces NOS2 expression in airway epithelial cells through an autocrine mechanism involving synthesis and secretion of IFN-gamma-inducible mediator(s), which activates STAT1. Here, CF cells secrete IFN-gamma-inducible factor(s), which stimulate NOS2 expression in NL cells, but not in CF cells. In contrast, IFN-gamma-inducible factor(s) similarly inhibit virus in CF and NL cells. Thus autocrine activation of NOS2 is defective in CF cells, but IFN-gamma induction of antiviral host defense is intact.

Adenocarcinoma, Bronchiolo-Alveolar↗

PubMed2003

TGF-beta-induced SOCS3 expression augments TNF-alpha-induced osteoclast formation.

Osteoclast differentiation is dependent on TGF-beta to prime precursors to the osteoclast lineage. The mechanism by which TGF-beta enables osteoclast formation is unknown. One possibility is that TGF-beta opposes pro-inflammatory JAK/STAT signalling. Recently, we showed that TGF-beta-induces SOCS3, an inhibitor of the JAK/STAT pathway, in precursors and enhances SOCS3 in RANKL-induced osteoclasts. We therefore elected to test the role of SOCS3 in the effect of other regulators of osteoclastic differentiation. We found that TNF-alpha-induced osteoclasts also express SOCS3 and TGF-beta strongly up-regulates this. Moreover, TNF-alpha-induced osteoclast differentiation and total resorbed bone area were enhanced in SOCS3-retrovirally infected precursors, whereas antisense knockdown of SOCS3 suppressed formation and the augmentative effect of TGF-beta. Furthermore, SOCS3 overexpression blunted the anti-osteoclastic effect of IFN-beta but not IL-10. This suggests that TGF-beta-induced expression of SOCS3 may represent a crucial mechanism by which TGF-beta antagonizes specific anti-osteoclastic JAK/STAT signals, priming precursors for resorption rather than inflammatory functions.

Animals↗

PubMed2003

The possible role of TGF-beta-induced suppressors of cytokine signaling expression in osteoclast/macrophage lineage commitment in vitro.

Osteoclast formation is dependent on the ability of TGF-beta to enable receptor activator of NF-kappaB ligand (RANKL)-induced commitment of hemopoietic precursors to the osteoclastic lineage. The mechanism by which TGF-beta enables formation is unknown. One possibility is that TGF-beta opposes Janus kinase (JAK)/STAT signals generated by inhibitory cytokines such as IFN-beta. The JAK/STAT pathway is activated by cytokines that induce resistance to osteoclast formation, such as IFN-gamma and M-CSF, and the effect of these is opposed by TGF-beta. Recently, a group of STAT-induced factors, termed suppressors of cytokine signaling (SOCS), has been identified that inhibit JAK/STAT signals. Therefore, we tested the ability of TGF-beta to induce SOCS expression in osteoclast precursors and examined the effect of SOCS expression on osteoclast/macrophage lineage commitment. We found that while SOCS mRNA is undetectable in macrophages, osteoclasts express SOCS-3, and TGF-beta up-regulates this expression. Furthermore, TGF-beta rapidly induces sustained SOCS-3 expression in macrophage/osteoclast precursors. To determine whether SOCS-3 plays a role in osteoclast differentiation we expressed SOCS-3 in precursors using a retroviral system. We found that osteoclast differentiation was significantly enhanced in SOCS-3-infected precursors, and SOCS-3 expression enables formation in the presence of anti-TGF-beta Ab. On the other hand, antisense knockdown of SOCS-3 strongly suppressed osteoclast formation and significantly blunted the response to TGF-beta. Moreover, like TGF-beta, SOCS-3 expression opposed the inhibitory effect of IFN-beta. These data suggest that TGF-beta-induced expression of SOCS-3 may represent a mechanism by which TGF-beta suppresses inhibitory cytokine signaling, priming precursors for a role in bone resorption.

Animals↗

PubMed2003

Impaired innate host defense causes susceptibility to respiratory virus infections in cystic fibrosis.

Viral infection is the primary cause of respiratory morbidity in cystic fibrosis (CF) infants. Here, we identify that host factors allow increased virus replication and cytokine production, providing a mechanism for understanding the severity of virus disease in CF. Increased virus is due to lack of nitric oxide synthase 2 (NOS2) and 2', 5' oligoadenylate synthetase (OAS) 1 induction in response to virus or IFNgamma. This can be attributed to impairment of activation of signal transducer and activator of transcription (STAT)1, a fundamental component to antiviral defense. NO donor or NOS2 overexpression provides protection from virus infection in CF, suggesting that NO is sufficient for antiviral host defense in the human airway and is one strategy for antiviral therapy in CF children.

Antiviral Agents↗

PubMed2003

STAT-1 and c-Fos interaction in nitric oxide synthase-2 gene activation.

Interferon-gamma (IFN-gamma) is required for induction of the human nitric oxide synthase-2 (NOS2) gene in lung epithelium. Although the human NOS2 promoter region contains many cytokine-responsive elements, the molecular basis of induction is only partially understood. Here, the major cis-regulatory elements that control IFN-gamma-inducible NOS2 gene transcription in human lung epithelial cells are identified as composite response elements that bind signal transducer and activator of transcription 1 (STAT-1) and activator protein 1 (AP-1), which is comprised of c-Fos, Fra-2, c-Jun, and JunD. Notably, IFN-gamma activation of the human NOS2 promoter is shown to require functional AP-1 regulatory region(s), suggesting a role for AP-1 activation/binding in the IFN-gamma induction of genes. We show that c-Fos interacts with STAT-1 after IFN-gamma activation and the c-Fos/STAT-1 complex binds to the gamma-activated site (GAS) element in close proximity to AP-1 sites located at 4.9 kb upstream of the transcription start site. Taken together, our findings support a model in which a physical interaction between c-Fos and STAT-1 participates in NOS2 gene transcriptional activation.

5' Flanking Region↗

PubMed2002

Inhibition of constitutively active Stat3 suppresses proliferation and induces apoptosis in glioblastoma multiforme cells.

Glioblastoma multiforme (GBM), the most common and malignant central nervous system tumor in humans, is highly proliferative and resistant to apoptosis. Stat3, a latent transcription factor being activated by aberrant cytokine or growth factor signaling, acts as a suppressor of apoptosis in a number of cancer cells. Here we report that GBM tumors and cell lines contain high levels of constitutively activated Stat3 when compared with normal human astrocytes, white matter, and normal tissue adjacent to tumor. The persistent activation of Stat3 is in part, attributable to an autocrine action of interleukin-6 in the GBM cell line U251. Janus kinase inhibitor AG490 inhibits Stat3 activation with a concomitant reduction in steady-state levels of Bcl-X(L), Bcl-2 and Mcl-1 proteins and induces apoptosis in U251 cells as revealed by Poly (ADP-ribose) polymerase cleavage and Annexin-V staining. Expression of a dominant negative mutant Stat3 protein or treatment with AG490 markedly reduces the proliferation of U251 cells by inhibiting the constitutive activation of Stat3. These results provide evidence that constitutive activation of Stat3 contributes to the pathogenesis of glioblastoma by promoting both proliferation and survival of GBM cells. Therefore, targeting Stat3 signaling may provide a potential therapeutic intervention for GBM.

Acute-Phase Proteins↗

PubMed2002

IL-13R(alpha)2, a decoy receptor for IL-13 acts as an inhibitor of IL-4-dependent signal transduction in glioblastoma cells.

Interleukin (IL)-4 and IL-13 share the type II IL-4 receptor for cell signaling. We show that despite expressing the necessary signaling components, glioblastoma cells failed to respond to either IL-4 or IL-13. This was in part because of the expression of a high-affinity IL-13-binding transmembrane protein IL-13R(alpha)2 that inhibited IL-13-mediated Stat6 activation by acting as a decoy receptor. In contrast, normal human astrocytes that did not express the IL-13R(alpha)2 gene efficiently induced Stat6 activation in response to both IL-4 and IL-13. Transient expression of the IL-13R(alpha)2 transgene in nonexpressing heterologous cells inhibited not only IL-13- but also IL-4-mediated signal transduction and Stat6-responsive gene expression. The inhibition was likely mediated through the physical interaction between the short intracellular domain of the IL-13R(alpha)2 protein and the cytoplasmic domain of the IL-4R(alpha) chain that harbors the Stat6 docking sites. Thus, IL-13R(alpha)2 acts as an inhibitor of IL-4-dependent signal transduction pathways via a novel mechanism that is independent of ligand binding.

3T3 Cells↗

PubMed1996

Overexpression of mouse p140 subunit of replication factor C accelerates cellular proliferation.

Screening of a murine cDNA expression library with an IFN-stimulated response element (ISRE), as a recognition site DNA probe, resulted in the isolation of a cDNA encoding a polypeptide of 1145 amino acids designated ISRE-binding factor-1. This was subsequently shown to be identical to the M(r) 140,000 subunit of replication factor C (RFC). RFC is required, along with the proliferating cell nuclear antigen and DNA polymerase delta, for the synthesis of the leading strand during DNA replication. RFC exhibits a structure-specific DNA-binding activity that has been localized to its M(r) 140,000 subunit (p140). Sequence-specific binding of this polypeptide to the ISRE occurs only with low affinity. Based on DNA-binding activity of the truncated RFC-p140 encoded by the partial cDNA isolated, the DNA-binding domain of this polypeptide was mapped to a region encoded by amino acids 366 to 540. Transfection of NIH 3T3 cells with an expression plasmid containing murine RFC-p140 driven by cytomegalovirus early promoter led to the establishment of stable cell lines that expressed a 2.5- to 3.0-fold higher RFC-p140 protein level in comparison with control cells. The stable clones exhibited significantly accelerated cell proliferation, indicating that RFC-p140 is the limiting subunit of an active RFC complex in normal cells.

3T3 Cells↗