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S Mahajan

Publications and source records attributed to S Mahajan.

At least 37 records · Page 2Linked to original sources
PubMed2001

CD2 stimulation leads to the delayed and prolonged activation of STAT1 in T cells but not NK cells.

OBJECTIVE: T lymphocytes can be activated by soluble factors such as cytokines or through direct cell-cell interactions. Although cytokine receptors are known to signal through STAT family transcription factors, the mechanisms by which other cell-surface molecules, such as CD2, transduce signals is unclear. The goal of this study was to determine whether stimulation of T cells through CD2 recapitulates aspects of cytokine-induced T-cell activation by use of STAT transcription factors. MATERIALS AND METHODS: T cells were treated with anti-CD2 antibodies or cells bearing the natural CD2 ligand CD58, after which signaling through STAT transcription factors was assessed. RESULTS: Stimulation of CD2 on primary T lymphocytes leads to the tyrosine phosphorylation, nuclear translocation, and DNA binding of STAT1. In contrast to stimulation by cytokines, the activation of STAT1 in response to CD2 ligation is delayed and does not involve Jak kinases. Furthermore, while STAT phosphorylation induced by cytokines is generally transient, STAT1 phosphorylation following CD2 stimulation persists for a period of days. Transcription of key target genes such as IRF1 and c-fos proceeds with delayed kinetics following CD2 stimulation, suggesting that this unique pattern of STAT activation may lead to a distinct cellular response following CD2 ligation. This pathway appears to be restricted to T cells, as stimulation of CD2 on NK cells does not lead to STAT1 activation. CONCLUSION: Stimulation of T cells through cell-surface molecules such as CD2 involves activation of STAT transcription factors, thus recapitulating elements of cytokine signaling.

Antibodies↗
PubMed2001

Tuberculosis of the vulva masquerading as a sexually transmitted disease.

Tuberculosis of the vulva is a rare condition usually seen by a gynecologist. We report a case of chronic ulcer on the vulva of four months duration, which, on detailed investigation, turned out to be a case of primary inoculation tuberculosis. The patient was subsequently put on antitubercular therapy with a good the therapeutic response. The rarity of this presentation in dermato-venereology is emphasized.

Adult↗
PubMed2001

Glutathione protects chemokine-scavenging and antioxidative defense functions in human RBCs.

Oxidant stress, in vivo or in vitro, is known to induce oxidative changes in human red blood cells (RBCs). Our objective was to examine the effect of augmenting RBC glutathione (GSH) synthesis on 1) degenerative protein loss and 2) RBC chemokine- and free radical-scavenging functions in the oxidatively stressed human RBCs by using banked RBCs as a model. Packed RBCs were stored up to 84 days at 1-6 degrees C in Adsol or in the experimental additive solution (Adsol fortified with glutamine, glycine, and N-acetyl-L-cysteine). Supplementing the conventional additive with GSH precursor amino acids improved RBC GSH synthesis and maintenance. The rise in RBC gamma-glutamylcysteine ligase activity was directly proportional to the GSH content and inversely proportional to extracellular homocysteine concentration, methemoglobin formation, and losses of the RBC proteins band 3, band 4.1, band 4.2, glyceraldehyde-3-phosphate dehydrogenase, and Duffy antigen (P < 0.01). Reduced loss of Duffy antigen correlated well with a decrease in chemokine RANTES (regulated upon activation, normal T-cell expressed, and secreted) concentration. We conclude that the concomitant loss of GSH and proteins in oxidatively stressed RBCs can compromise RBC scavenging function. Upregulating GSH synthesis can protect RBC scavenging (free radical and chemokine) function. These results have implications not only in a transfusion setting but also in conditions like diabetes and sickle cell anemia, in which RBCs are subjected to chronic/acute oxidant stresses.

Acetylcholinesterase↗
PubMed2000

STAT signaling in the pathogenesis and treatment of leukemias.

Leukemias continue to cause significant mortality in adults and children, and the use of standard cytotoxic chemotherapy has reached a therapeutic plateau. Thus, there is great interest in treatments directed against inappropriately activated cell signaling pathways which stimulate the uncontrolled growth of neoplastic cells. Increasing evidence suggests that the STAT signaling cascade may be one target of these therapies. Signal transducer and activator of transcription (STAT) proteins are critical in mediating the response of hematopoietic cells to a diverse spectrum of cytokines. Constitutive STAT activation is present in many malignancies and has been especially well characterized in acute and chronic leukemias. While STAT activation is a common characteristic of leukemias, the specific pattern of activated STATs and the manner by which STAT activation occurs vary with each disease. STAT tyrosine phosphorylation can occur through inappropriate Jak activation or by direct activation of an oncoprotein such as Bcr/Abl, and STAT serine phosphorylation may play an important role in leukemias as well. Thus, the STAT signaling pathway is an attractive target for therapeutic intervention, and strategies designed to inhibit STAT activation and STAT mediated gene transcription may play an important role in the next generation of anti-leukemia therapies. Oncogene (2000).

Acute Disease↗
PubMed2000

Inhibition of MAP kinase kinase causes morphological reversion and dissociation between soft agar growth and in vivo tumorigenesis in angiosarcoma cells.

Activated ras causes increased activity of several signal transduction systems, including the mitogen-activated protein kinase kinase (MAPKK) pathway and the phosphoinositol-3-kinase (PI-3-K) pathway. We have previously shown that the PI-3-K pathway plays a major role in regulation of ras-mediated tumor angiogenesis in angiosarcoma cells. However, the contribution of the MAPKK pathway to tumorigenesis and angiogenesis is not fully understood. Overexpression of constitutively active forms of MAPKK has previously been shown to transform nonmalignant NIH3T3 fibroblasts, but the effect of down-regulation of MAPKK on tumorigenesis and angiogenesis in a well established tumor has not been fully explored. We introduced a dominant negative MAPKK gene into SVR murine angiosarcoma cells. Introduction of a dominant negative MAPKK causes a significant decrease in proliferation rate in vitro and morphological reversion. Cells expressing the dominant negative MAPKK have a greatly decreased ability to form colonies in soft agar compared with wild-type cells. Despite the decreased cell growth in vitro and inability to grow in soft agar, the cells were equally tumorigenic in nude mice. Our results suggest that the MAPKK pathway is required for soft agar growth of angiosarcoma cells, and separates the phenotypes of soft agar growth versus in vivo tumorigenicity. These findings have implications in the development of signal transduction modulators as potential antineoplastic agents.

Agar↗
PubMed2000

TEL/PDGFbetaR fusion protein activates STAT1 and STAT5: a common mechanism for transformation by tyrosine kinase fusion proteins.

OBJECTIVE: TEL/PDGFbetaR is a tyrosine kinase fusion protein associated with the pathogenesis of chronic myelomonocytic leukemia. The following experiments were undertaken to understand the mechanisms whereby TEL/PDGFbetaR transforms cells. MATERIALS AND METHODS: Activation of JAK and STAT proteins was studied in an interleukin 3 (IL-3)-dependent cell line, Ba/F3, transformed to IL-3 independence by TEL/PDGFbetaR. RESULTS: TEL/PDGFbetaR activates STAT1 and STAT5 in transformed Ba/F3 cells through a JAK-independent pathway. Activation of STAT proteins requires the kinase activity of TEL/PDGFbetaR. JAK1, JAK2, JAK3, and TYK2 are not phosphorylated by TEL/PDGFbetaR. However, TEL/PDGFbetaR can phosphorylate STAT5 in transiently transfected COS cells, suggesting that TEL/PDGFbetaR may itself be the kinase involved in tyrosine phosphorylation of STAT proteins. In contrast, native PDGFbetaR stimulated by PDGF ligand does not activate STAT proteins to a significant degree in this hematopoietic context. STAT1 and STAT5 also are activated by TEL/ABL and TEL/JAK2 fusion proteins associated with human leukemia. CONCLUSIONS: STAT activation may be a common mechanism of transformation by leukemogenic tyrosine kinase fusion proteins.

Cell Line↗
PubMed2000

Cocaine differentially modulates chemokine production by mononuclear cells from normal donors and human immunodeficiency virus type 1-infected patients.

Earlier studies have supported a significant role for cocaine in the susceptibility to and the progression of human immunodeficiency virus type 1 (HIV-1) infection. Recently, several unique HIV-1 entry coreceptors (e.g., CCR5 and CCR3) and a trio of HIV-1-specific suppressor chemokines, namely, RANTES (regulated-upon-activation T expressed and secreted), macrophage inflammatory protein 1alpha (MIP-1alpha) and MIP-1beta, were identified. Although cocaine has been linked to the immunopathogenesis of HIV-1 infection, the corresponding cellular and molecular mechanism(s) have not been well defined. We hypothesize that cocaine mediates these pathologic effects through the downregulation of HIV-1-suppressing chemokines and/or upregulating HIV-1 entry coreceptors in HIV-1-infected subjects, resulting in disease progression to AIDS. Our results show that cocaine selectively downregulates endogenous MIP-1beta secretion by normal peripheral blood mononuclear cells (PBMC), while cocaine did not affect the MIP-1beta production by PBMC from AIDS patients. Cocaine also selectively suppresses lipopolysaccharide-induced MIP-1beta production by PBMC from HIV-infected patients. Further, cocaine significantly downregulates endogenous MIP-1beta gene expression, while it upregulates HIV-1 entry coreceptor CCR5 by normal PBMC. These studies suggests a role for cocaine as a cofactor in the pathogenesis of HIV infection and support the premise that cocaine increases susceptibility to and progression of HIV-1 infection by inhibiting the synthesis of HIV-1 protective chemokines and/or upregulating the HIV-1 entry coreceptor, CCR5.

Chemokine CCL3↗
PubMed2000

The stress hormone, cortisol, synergizes with HIV-1 gp-120 to induce apoptosis of normal human peripheral blood mononuclear cells.

Both quantitative and qualitative defects in immune functions in patients with AIDS may result from induction of programmed cell death or apoptosis of CD4 T lymphocytes. We postulate that neurohormones may interact with gp-120 that is shed during active HIV infection and cause apoptosis of immunocompetent cells leading to immunopathogenesis of HIV infections. In this study, we investigated the synergistic effect of cortisol plus HIV gp-120 in inducing apoptosis of lymphocytes from normal subjects. Total peripheral blood mononuclear cells and isolated CD4+ T-cells were treated with cortisol or gp-120 separately and in combination and RNA and DNA were extracted. RNA was reverse transcribed and amplified with specific primers for Fas and Fas ligand and analyzed on agarose gels. DNA was analyzed by gel electrophoresis for ladder formation, the hallmark for apoptosis, and Fas antigen expression by confocal microscopy. Results demonstrate that cortisol and gp-120 induce apoptosis of lymphocytes from normal donors as demonstrated by DNA ladder formation, TUNEL staining and Fas gene expression. Concentrations of cortisol and gp-120 that did not produce apoptosis when used separately, induced significant apoptosis when used in combination. Further, gp-120 induced DNA fragmentation was significant in the CD4+ T-cell subpopulation compared to the CD47 subpopulation. This study suggests that the stress-associated neurohormone, cortisol, synergizes with HIV peptides in causing apoptosis of normal lymphocytes. The synergistic effect of cortisol and gp- 120 in inducing apoptosis of lymphocytes is consistent with a model proposing that stress-associated and circulating HIV-1 derived soluble products may cause progression of HIV infections.

Apoptosis↗
PubMed1999

Rational design and synthesis of a novel anti-leukemic agent targeting Bruton's tyrosine kinase (BTK), LFM-A13 [alpha-cyano-beta-hydroxy-beta-methyl-N-(2, 5-dibromophenyl)propenamide].

In a systematic effort to design potent inhibitors of the anti-apoptotic tyrosine kinase BTK (Bruton's tyrosine kinase) as anti-leukemic agents with apoptosis-promoting and chemosensitizing properties, we have constructed a three-dimensional homology model of the BTK kinase domain. Our modeling studies revealed a distinct rectangular binding pocket near the hinge region of the BTK kinase domain with Leu460, Tyr476, Arg525, and Asp539 residues occupying the corners of the rectangle. The dimensions of this rectangle are approximately 18 x 8 x 9 x 17 A, and the thickness of the pocket is approximately 7 A. Advanced docking procedures were employed for the rational design of leflunomide metabolite (LFM) analogs with a high likelihood to bind favorably to the catalytic site within the kinase domain of BTK. The lead compound LFM-A13, for which we calculated a Ki value of 1.4 microM, inhibited human BTK in vitro with an IC50 value of 17.2 +/- 0.8 microM. Similarly, LFM-A13 inhibited recombinant BTK expressed in a baculovirus expression vector system with an IC50 value of 2.5 microM. The energetically favorable position of LFM-A13 in the binding pocket is such that its aromatic ring is close to Tyr476, and its substituent group is sandwiched between residues Arg525 and Asp539. In addition, LFM-A13 is capable of favorable hydrogen bonding interactions with BTK via Asp539 and Arg525 residues. Besides its remarkable potency in BTK kinase assays, LFM-A13 was also discovered to be a highly specific inhibitor of BTK. Even at concentrations as high as 100 micrograms/ml (approximately 278 microM), this novel inhibitor did not affect the enzymatic activity of other protein tyrosine kinases, including JAK1, JAK3, HCK, epidermal growth factor receptor kinase, and insulin receptor kinase. In accordance with the anti-apoptotic function of BTK, treatment of BTK+ B-lineage leukemic cells with LFM-A13 enhanced their sensitivity to ceramide- or vincristine-induced apoptosis. To our knowledge, LFM-A13 is the first BTK-specific tyrosine kinase inhibitor and the first anti-leukemic agent targeting BTK.

Agammaglobulinaemia Tyrosine Kinase↗
PubMed1999

Bruton's tyrosine kinase as an inhibitor of the Fas/CD95 death-inducing signaling complex.

Bruton's tyrosine kinase (BTK) is a member of the Src-related Tec family of protein tyrosine kinases. Mutations in the btk gene have been linked to severe developmental blocks in human B-cell ontogeny leading to X-linked agammaglobulinemia. Here, we provide unique biochemical and genetic evidence that BTK is an inhibitor of the Fas/APO-1 death-inducing signaling complex in B-lineage lymphoid cells. The Src homology 2, pleckstrin homology (PH), and kinase domains of BTK are all individually important and apparently indispensable, but not sufficient, for its function as a negative regulator of Fas-mediated apoptosis. BTK associates with Fas via its kinase and PH domains and prevents the FAS-FADD interaction, which is essential for the recruitment and activation of FLICE by Fas during the apoptotic signal. Fas-resistant DT-40 lymphoma B-cells rendered BTK-deficient through targeted disruption of the btk gene by homologous recombination knockout underwent apoptosis after Fas ligation, but wild-type DT-40 cells or BTK-deficient DT-40 cells reconstituted with wild-type human btk gene did not. Introduction of an Src homology 2 domain, a PH domain, or a kinase domain mutant human btk gene into BTK-deficient cells did not restore the resistance to Fas-mediated apoptosis. Introduction of wild-type BTK protein by electroporation rendered BTK-deficient DT-40 cells resistant to the apoptotic effects of Fas ligation. BTK-deficient RAMOS-1 human Burkitt's leukemia cells underwent apoptosis after Fas ligation, whereas BTK-positive NALM-6-UM1 human B-cell precursor leukemia cells expressing similar levels of Fas did not. Treatment of the anti-Fas-resistant NALM-6-UM1 cells with the leflunomide metabolite analog alpha-cyano-beta-methyl-beta-hydroxy-N-(2, 5-dibromophenyl)propenamide, a potent inhibitor of BTK, abrogated the BTK-Fas association without affecting the expression levels of BTK or Fas and rendered them sensitive to Fas-mediated apoptosis. The ability of BTK to inhibit the pro-apoptotic effects of Fas ligation prompts the hypothesis that apoptosis of developing B-cell precursors during normal B-cell ontogeny may be reciprocally regulated by Fas and BTK.

Agammaglobulinaemia Tyrosine Kinase↗
PubMed1999

Fludarabine-induced immunosuppression is associated with inhibition of STAT1 signaling.

Fludarabine is a nucleoside analog used in the treatment of hematologic malignancies that can induce severe and prolonged immunosuppression. Although it can be incorporated into the DNA of dividing cells, fludarabine is also a potent inhibitor of cells with a low growth fraction, thus it must have other mechanisms of action. STAT1, which is activated in response to many lymphocyte-activating cytokines including the interferons, is essential for cell-mediated immunity, as the absence of this protein is associated with prominent defects in the ability to control viral infections. Here we show that fludarabine, but not the immunosuppressant cyclosporine A, inhibits the cytokine-induced activation of STAT1 and STAT1-dependent gene transcription in normal resting or activated lymphocytes. Fludarabine caused a specific depletion of STAT1 protein (and mRNA) but not of other STATs. This loss of STAT1 was also seen in cells from patients treated with fludarabine in vivo. Brief exposure to fludarabine led to a sustained loss of STAT1, analogous to the prolonged period of immunosuppression induced by exposure to the drug in vivo. Thus, STAT1 may be a useful target in the development of new immunosuppressive and antineoplastic agents.

Alternative Splicing↗
PubMed1999

Structure-based design of specific inhibitors of Janus kinase 3 as apoptosis-inducing antileukemic agents.

A novel homology model of the kinase domain of Janus kinase (JAK) 3 was used for the structure-based design of dimethoxyquinazoline compounds with potent and specific inhibitory activity against JAK3. The active site of JAK3 in this homology model measures roughly 8 A x 11 A x 20 A, with a volume of approximately 530 A3 available for inhibitor binding. Modeling studies indicated that 4-(phenyl)-amino-6,7-dimethoxyquinazoline (parent compound WHI-258) would likely fit into the catalytic site of JAK3 and that derivatives of this compound that contain an OH group at the 4' position of the phenyl ring would more strongly bind to JAK3 because of added interactions with Asp-967, a key residue in the catalytic site of JAK3. These predictions were consistent with docking studies indicating that compounds containing a 4'-OH group, WHI-P131 [4-(4'-hydroxyphenyl)-amino-6,7-dimethoxyquinazoline], WHI-P154 [4-(3'-bromo-4'-hydroxylphenyl)-amino-6,7-dimethoxyquinazoline], and WHI-P97 [4-(3',5'-dibromo-4'-hydroxylphenyl)-amino-6,7-dimethoxyquinazolin e], were likely to bind favorably to JAK3, with estimated K(i)s ranging from 0.6 to 2.3 microM. These compounds inhibited JAK3 in immune complex kinase assays in a dose-dependent fashion. In contrast, compounds lacking the 4'-OH group, WHI-P79 [4-(3'-bromophenyl)-amino-6,7-dimethoxyquinazoline], WHI-P111 [4-(3'-bromo-4'-methylphenyl)-amino-6,7-dimethoxyquinazoline], WHI-P112 [4-(2',5'-dibromophenyl)-amino-6,7-dimethoxyquinazoline], WHI-P132 [4-(2'-hydroxylphenyl)-amino-6,7-dimethoxyquinazoline], and WHI-P258 [4-(phenyl)-amino-6,7-dimethoxyquinazoline], were predicted to bind less strongly, with estimated K(i)s ranging from 28 to 72 microM. These compounds did not show any significant JAK3 inhibition in kinase assays. Furthermore, the lead dimethoxyquinazoline compound, WHI-P131, which showed potent JAK3-inhibitory activity (IC50 of 78 microM), did not inhibit JAK1 and JAK2, the ZAP/SYK family tyrosine kinase SYK, the TEC family tyrosine kinase BTK, the SRC family tyrosine kinase LYN, or the receptor family tyrosine kinase insulin receptor kinase, even at concentrations as high as 350 microM. WHI-P131 induced apoptosis in JAK3-expressing human leukemia cell lines NALM-6 and LC1;19 but not in melanoma (M24-MET) or squamous carcinoma (SQ20B) cells. Leukemia cells were not killed by dimethoxyquinazoline compounds that were inactive against JAK3. WHI-P131 inhibited the clonogenic growth of JAK3-positive leukemia cell lines DAUDI, RAMOS, LC1;19, NALM-6, MOLT-3, and HL-60 (but not JAK3-negative BT-20 breast cancer, M24-MET melanoma, or SQ20B squamous carcinoma cell lines) in a concentration-dependent fashion. Potent and specific inhibitors of JAK3 such as WHI-P131 may provide the basis for the design of new treatment strategies against acute lymphoblastic leukemia, the most common form of childhood cancer.

Antineoplastic Agents↗
PubMed1999

Specificity of alpha-cyano-beta-hydroxy-beta-methyl-n-[4-(trifluoromethoxy)phe nyl]-propenamide as an inhibitor of the epidermal growth factor receptor tyrosine kinase.

The epidermal growth factor receptor (EGFR) tyrosine kinase has an essential function for the survival of human breast cancer cells. In a systematic effort to design potent and specific inhibitors of this receptor family protein tyrosine kinase (PTK) as antibreast cancer agents, we recently reported the construction of a three-dimensional homology model of the EGFR kinase domain. In this model, the catalytic site is defined by two beta-sheets that form an interface at the cleft between the NH2-terminal and COOH-terminal lobes of the kinase domain. Our modeling studies revealed a distinct, remarkably planar triangular binding pocket within the kinase domain with approximate dimensions of 15 A x 12 A x 12 A, and the thickness of the binding pocket is approximately 7 A with an estimated volume of approximately 600 A3 available for inhibitor binding. Molecular docking studies had identified alpha-cyano-beta-hydroxy-beta-methyl-N-[4-(trifluoromethoxy)phenyl]-p ropenamide (LFM-A12) as our lead inhibitor, with an estimated binding constant of 13 microM, which subsequently inhibited EGFR kinase in vitro with an IC50 value of 1.7 microM. LFM-A12 was also discovered to be a highly specific inhibitor of the EGFR. Even at very high concentrations ranging from 175-350 microM, this inhibitor did not affect the enzymatic activity of other PTKs, including the Janus kinases JAK1 and JAK3, the Src family kinase HCK, the Tec family member Bruton's tyrosine kinase, SYK kinase, and the receptor family PTK insulin receptor kinase. This observation is in contrast to the activity of a quinazoline inhibitor tested as a control, 4-(3-bromo, 4-hydroxyanilino)-6,7-dimethoxyquinazoline, which was shown to inhibit EGFR and other tyrosine kinases such as HCK, JAK3, and SYK.

Aniline Compounds↗
PubMed1998

Electromagnetic field-induced stimulation of Bruton's tyrosine kinase.

Here we present evidence that exposure of DT40 lymphoma B-cells to low energy electromagnetic fields (EMF) results in activation of phospholipase C-gamma 2 (PLC-gamma2), leading to increased inositol phospholipid turnover. PLC-gamma2 activation in EMF-stimulated cells is mediated by stimulation of the Bruton's tyrosine kinase (BTK), a member of the Src-related TEC family of protein tyrosine kinases, which acts downstream of LYN kinase and upstream of PLC-gamma2. B-cells rendered BTK-deficient by targeted disruption of the btk gene did not show enhanced PLC-gamma2 activation in response to EMF exposure. Introduction of the wild-type (but not a kinase domain mutant) human btk gene into BTK-deficient B-cells restored their EMF responsiveness. Thus, BTK exerts a pivotal and mandatory function in initiation of EMF-induced signaling cascades in B-cells.

Agammaglobulinaemia Tyrosine Kinase↗
PubMed1998

Altered interleukin-12 responsiveness in Th1 and Th2 cells is associated with the differential activation of STAT5 and STAT1.

T-cell activation in response to interleukin-12 (IL-12) is mediated through signaling events that include the tyrosine phosphorylation of STAT4. IL-12 responsiveness and the ability of IL-12 to activate STAT4 is different in T cells induced to differentiate into a Th1 or Th2 phenotype. In this report, we show that STAT5, STAT1alpha, and STAT1beta, in addition to STAT4, are tyrosine phosphorylated in response to IL-12 in phytohemagglutinin (PHA)-activated human T cells. To understand how the activation of these STATs contributes to T-cell IL-12 responsiveness, we analyzed the IL-12-induced activation of STAT5 and STAT1 in T cells stimulated to undergo Th1 or Th2 differentiation. The IL-12-induced tyrosine phosphorylation of STAT5 and STAT1, but not STAT4, is augmented in T cells activated into Th1 cells with PHA + interferon-gamma (IFN-gamma) compared with T cells activated with PHA alone. STAT5 DNA binding induced by IL-12 is also augmented in T cells activated with PHA + IFN-gamma compared with T cells activated with PHA alone, whereas STAT4 DNA binding is not increased. In contrast, the IL-12-induced activation of these STATs is inhibited in T cells activated into Th2 cells with PHA + IL-4. The enhancement of IL-12 signaling by IFN-gamma is not a direct effect of IFN-gamma on T cells, but rather is mediated by IL-12 that is produced by antigen-presenting cells in response to IFN-gamma. This positive autoregulatory effect of IL-12 on the activation of select STATs correlates with an increase in T-cell IFN-gamma production in response to IL-12. These findings suggest that the activation of STAT5 and STAT1 may augment select STAT4-dependent functional responses to IL-12 in Th1 cells.

Adult↗
PubMed1998

Alpha-cyano-beta-hydroxy-beta-methyl-N-[4-(trifluoromethoxy)phenyl] propenamide: an inhibitor of the epidermal growth factor receptor tyrosine kinase with potent cytotoxic activity against breast cancer cells.

Epidermal growth factor receptor (EGF-R) tyrosine kinase is known to be overexpressed in several malignancies and is an important target for anticancer drug design. We constructed a homology model to represent the structure of EGF-R and propose that this model can be used to design potent inhibitors of EGF-R. We used our EGF-R model and a docking procedure to rationally design compounds predicted to bind favorably to EGF-R. This approach led to the successful design of a leflunomide metabolite analogue, which was found to have an IC50 value of 1.7 microM in EGF-R inhibition assays and killed >99% of human breast cancer cells in vitro by triggering apoptosis. The reported studies may provide the basis for the development of a new class of potent and clinically useful anti-breast cancer agents.

Aniline Compounds↗
PubMed1997

B lymphocytes from patients with chronic lymphocytic leukemia contain signal transducer and activator of transcription (STAT) 1 and STAT3 constitutively phosphorylated on serine residues.

To explore the pathogenesis of chronic lymphocytic leukemia (CLL), we examined whether phosphorylation of one or more signal transducer and activator of transcription (STAT) factors was abnormal in cells from CLL patients. No constitutive tyrosine phosphorylation was detected on any STAT in CLL cells. To assess the phosphorylation of serine residues of STAT1 and STAT3 in CLL cells, we raised antibodies that specifically recognize the form of STAT1 phosphorylated on ser-727 and the form of STAT3 phosphorylated on ser-727. We found that in 100% of patients with CLL (n = 32), STAT1 and STAT3 were constitutively phosphorylated on serine. This was in contrast to normal peripheral blood B lymphocytes or CD5+) B cells isolated from tonsils, in which this phosphorylation was absent. Serine phosphorylation of STAT1 and STAT3 was seen occasionally in other leukemias, but it was a universal finding only in CLL. The serine phosphorylation of these STATs was a continuous process, as incubation of CLL cells with the kinase inhibitor H7 led to the dephosphorylation of these serine residues. The STAT serine kinase in CLL cells has not been identified, and appears to be neither mitogen-activated protein kinase nor pp70(s6k). In summary, the constitutive serine phosphorylation of STAT1 and STAT3 is present in all CLL samples tested to date, although the physiologic significance of this modification remains to be determined.

Antibody Formation↗