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Biomedical subjects

G L Johnson

Publications and source records attributed to G L Johnson.

At least 19 recordsLinked to original sources
PubMed2006

Re-activation of a dormant tumor suppressor gene maspin by designed transcription factors.

The controlled and specific re-activation of endogenous tumor suppressors in cancer cells represents an important therapeutic strategy to block tumor growth and subsequent progression. Other than ectopic delivery of tumor suppressor-encoded cDNA, there are no therapeutic tools able to specifically re-activate tumor suppressor genes that are silenced in tumor cells. Herein, we describe a novel approach to specifically regulate dormant tumor suppressors in aggressive cancer cells. We have targeted the Mammary Serine Protease Inhibitor (maspin) (SERPINB5) tumor suppressor, which is silenced by transcriptional and aberrant promoter methylation in aggressive epithelial tumors. Maspin is a multifaceted protein, regulating tumor cell homeostasis through inhibition of cell growth, motility and invasion. We have constructed artificial transcription factors (ATFs) made of six zinc-finger (ZF) domains targeted against 18-base pair (bp) unique sequences in the maspin promoter. The ZFs were linked to the activator domain VP64 and delivered in breast tumor cells. We found that the designed ATFs specifically interact with their cognate targets in vitro with high affinity and selectivity. One ATF was able to re-activate maspin in cell lines that comprise a maspin promoter silenced by epigenetic mechanisms. Consistently, we found that this ATF was a powerful inducer of apoptosis and was able to knock down tumor cell invasion in vitro. Moreover, this ATF was able to suppress MDA-MB-231 growth in a xenograft breast cancer model in nude mice. Our work suggests that ATFs could be used in cancer therapeutics as novel molecular switches to re-activate dormant tumor suppressors.

Amino Acid Sequence↗
PubMed2006

Lymphoblastic leukemia/lymphoma in mice overexpressing the Mer (MerTK) receptor tyrosine kinase.

Mer (MerTK) is a receptor tyrosine kinase important in platelet aggregation, as well as macrophage cytokine secretion and clearance of apoptotic cells. Mer is not normally expressed in thymocytes or lymphocytes; however, ectopic Mer RNA transcript and protein expression is found in a subset of acute lymphoblastic leukemia cell lines and patient samples, suggesting a role in leukemogenesis. To investigate the oncogenic potential of Mer in vivo, we created a transgenic mouse line (Mer(Tg)) that expresses Mer in the hematopoietic lineage under control of the Vav promoter. Ectopic expression and activation of the transgenic Mer protein was demonstrated in lymphocytes and thymocytes of the Mer(Tg) mice. At 12-24 months of age, greater than 55% of the Mer(Tg) mice, compared to 12% of the wild type, developed adenopathy, hepatosplenomegaly, and circulating lymphoblasts. Histopathological analysis and flow cytometry were consistent with T-cell lymphoblastic leukemia/lymphoma. Mer may contribute to leukemogenesis by activation of Akt and ERK1/2 anti-apoptotic signals, which were upregulated in Mer(Tg) mice. Additionally, a significant survival advantage was noted in Mer(Tg) lymphocytes compared to wild-type lymphocytes after dexamethasone treatment. These data suggest that Mer plays a cooperative role in leukemogenesis and may be an effective target for biologically based leukemia/lymphoma therapy.

Animals↗
PubMed2006

MEKK1 controls matrix degradation and tumor cell dissemination during metastasis of polyoma middle-T driven mammary cancer.

Mammary tumor cells are required to degrade the surrounding matrix and disseminate in order to metastasize, and both of these processes are controlled by a tumor cell-signaling network that remains poorly defined. MEKK1 is a MAPKKK that regulates both the extracellular signal regulated kinase (ERK1/2) and the c-Jun amino terminal kinase (JNK) signaling pathways. MEKK1 signaling regulates migration through control of cell adhesion and is required for inducible expression of urokinase-type plasminogen activator (uPA). MEKK1-deficient mice with mammary gland-targeted expression of the polyoma middle T antigen (PyMT) transgene develop primary mammary tumors at a rate and frequency similar to wild-type littermates, indicating that MEKK1 deficiency does not affect PyMT-mediated transformation. However, MEKK1-/- mice display significantly delayed tumor cell dissemination and lung metastasis. Delayed MEKK1-dependent tumor dissemination is associated with markedly reduced tumor uPA expression, gelatinase activity, and prolonged tumor basement membrane integrity. siRNA-mediated MEKK1 knockdown inhibits uPA activity, cell migration and invasion in MDA-MB-231 human breast cancer cells. Thus MEKK1 controls tumor progression by regulating both the migration and proteolysis aspects of tumor cell invasiveness. To our knowledge, this is the first example of a MAPKKK that regulates metastasis through control of tumor invasiveness.

Animals↗
PubMed2001

Caspase 8-dependent sensitization of cancer cells to TRAIL-induced apoptosis following reovirus-infection.

TRAIL (TNF-related apoptosis-inducing ligand) induces apoptosis in susceptible cells by binding to death receptors 4 (DR4) and 5 (DR5). TRAIL preferentially induces apoptosis in transformed cells and the identification of mechanisms by which TRAIL-induced apoptosis can be enhanced may lead to novel cancer chemotherapeutic strategies. Here we show that reovirus infection induces apoptosis in cancer cell lines derived from human breast, lung and cervical cancers. Reovirus-induced apoptosis is mediated by TRAIL and is associated with the release of TRAIL from infected cells. Reovirus infection synergistically and specifically sensitizes cancer cell lines to killing by exogenous TRAIL. This sensitization both enhances the susceptibility of previously resistant cell lines to TRAIL-induced apoptosis and reduces the amount of TRAIL needed to kill already sensitive lines. Sensitization is not associated with a detectable change in the expression of TRAIL receptors in reovirus-infected cells. Sensitization is associated with an increase in the activity of the death receptor-associated initiator caspase, caspase 8, and is inhibited by the peptide IETD-fmk, suggesting that reovirus sensitizes cancer cells to TRAIL-induced apoptosis in a caspase 8-dependent manner. Reovirus-induced sensitization of cells to TRAIL is also associated with increased cleavage of PARP, a substrate of the effector caspases 3 and 7.

Antineoplastic Agents↗
PubMed2001

In vitro activity of MEKK2 and MEKK3 in detergents is a function of a valine to serine difference in the catalytic domain.

MEKK2 and MEKK3 are mitogen-activated protein kinase kinase kinases (MAP3 kinases) of 70 and 71 kDa respectively that are markedly homologous (94%) in their kinase domains. Both MEKK2 and MEKK3 are able to activate the Jun kinase pathway in vivo. However, following routine immunoprecipitation in Triton X-100, MEKK2 but not MEKK3 is able to effectively phosphorylate both SEK-1 and MEK-1 and to undergo autophosphorylation. Unexpectedly, both MEKK2 and MEKK3 are functional in an in vitro kinase assay when cells are solubilized with the closely related detergent, NP-40. Given the high homology between these kinases, we set out to relate this differential sensitivity to Triton X-100 to differences in primary structure. A set of chimeric molecules were generated and the loss of activity in Triton X-100 mapped to kinase domain II/III and specifically to serine 390 of MEKK3 and valine 384 of MEKK2, residues immediately N-terminal to the active site lysine. Mutation of serine 390 of MEKK3 to a valine (as is found in MEKK2) conferred catalytic activity to MEKK3 in Triton X-100 whereas the reciprocal alteration of valine 384 of MEKK2 to a serine conferred lack of activity in Triton X-100 to MEKK2. Search of the protein database identified only three kinases, MEKK3, Pbs2p and Dd-PKI, with a serine or threonine at this site. The presence of a serine or threonine adjacent to the active site lysine in protein kinases is rare and, in MEKK3, results in detergent instability.

Amino Acid Sequence↗
PubMed2001

Role of MEKK2-MEK5 in the regulation of TNF-alpha gene expression and MEKK2-MKK7 in the activation of c-Jun N-terminal kinase in mast cells.

Cross-linking of the high-affinity IgE receptor (FcepsilonRI) on mast cells with IgE and multivalent antigen triggers mitogen-activated protein (MAP) kinase activation and cytokine gene expression. We report here that MAP kinase kinase 4 (MKK4) gene disruption does not affect either MAP kinase activation or cytokine gene expression in response to cross-linking of FcepsilonRI in embryonic stem cell-derived mast cells. MKK7 is activated in response to cross-linking of FcepsilonRI, and this activation is inhibited by MAP/ERK kinase (MEK) kinase 2 (MEKK2) gene disruption. In addition, expression of kinase-inactive MKK7 in the murine mast cell line MC/9 inhibits c-Jun NH(2)-terminal kinase (JNK) activation in response to cross-linking of FcepsilonRI, whereas expression of kinase-inactive MKK4 does not affect JNK activation by this stimulus. However, FcepsilonRI-induced activation of the tumor necrosis factor-alpha (TNF-alpha) gene promoter is not affected by expression of kinase-inactive MKK7. We describe an alternative pathway by which MEKK2 activates MEK5 and big MAP kinase1/extracellular signal-regulated kinase 5 in addition to MKK7 and JNK, and interruption of this pathway inhibits TNF-alpha promoter activation. These findings suggest that JNK activation by antigen cross-linking is dependent on the MEKK2-MKK7 pathway, and cytokine production in mast cells is regulated in part by the signaling complex MEKK2-MEK5-ERK5.

Cell Line↗
PubMed2001

Reovirus infection activates JNK and the JNK-dependent transcription factor c-Jun.

Viral infection often perturbs host cell signaling pathways including those involving mitogen-activated protein kinases (MAPKs). We now show that reovirus infection results in the selective activation of c-Jun N-terminal kinase (JNK). Reovirus-induced JNK activation is associated with an increase in the phosphorylation of the JNK-dependent transcription factor c-Jun. Reovirus serotype 3 prototype strains Abney (T3A) and Dearing (T3D) induce significantly more JNK activation and c-Jun phosphorylation than does the serotype 1 prototypic strain Lang (T1L). T3D and T3A also induce more apoptosis in infected cells than T1L, and there was a significant correlation between the ability of these viruses to phosphorylate c-Jun and induce apoptosis. However, reovirus-induced apoptosis, but not reovirus-induced c-Jun phosphorylation, is inhibited by blocking TRAIL/receptor binding, suggesting that apoptosis and c-Jun phosphorylation involve parallel rather than identical pathways. Strain-specific differences in JNK activation are determined by the reovirus S1 and M2 gene segments, which encode viral outer capsid proteins (sigma1 and mu1c) involved in receptor binding and host cell membrane penetration. These same gene segments also determine differences in the capacity of reovirus strains to induce apoptosis, and again a significant correlation between the capacity of T1L x T3D reassortant reoviruses to both activate JNK and phosphorylate c-Jun and to induce apoptosis was shown. The extracellular signal-related kinase (ERK) is also activated in a strain-specific manner following reovirus infection. Unlike JNK activation, ERK activation could not be mapped to specific reovirus gene segments, suggesting that ERK activation and JNK activation are triggered by different events during virus-host cell interaction.

Animals↗
PubMed2001

Detection of caspase activation in situ by fluorochrome-labeled caspase inhibitors.

Apoptosis is dependent on the activation of a group of proteolytic enzymes called caspases. Caspase activation can be detected by immunoblotting using caspase-specific antibodies or by caspase activity measurement employing pro-fluorescent substrates that become fluorescent upon cleavage by the caspase. Most of these methods require the preparation of cell extracts and, therefore, are not suitable for the detection of active caspases within the living cell. Using FAM-VAD-FMK, we have developed a simple and sensitive assay for the detection of caspase activity in living cells. FAM-VAD-FMK is a carboxyfluorescein (FAM) derivative of benzyloxycarbonyl-valine-alanine-aspartic acid-fluoromethyl ketone (zVAD-FMK), which is a potent broad-spectrum inhibitor of caspases. FAM-VAD-FMK enters the cell and irreversibly binds to activated caspases. Cells containing bound FAM-VAD-FMK can be analyzed by flow cytometry, fluorescence microscopy, or a fluorescence plate reader. Using FAM-VAD-FMK, we have measured caspase activation in live non-adherent and adherent cells. We show that FAM-VAD-FMK labeled Jurkat and HeLa cells that had undergone apoptosis following treatment with camptothecin or staurosporine. Non-stimulated negative control cells were not stained. Pretreatment with the general caspase inhibitor zVAD-FMK blocked caspase-specific staining in induced Jurkat and HeLa cells. Pretreatment of staurosporine-induced Jurkat cells with FAM-VAD-FMK inhibited affinity labeling of caspase-3, -6, and -7, blocked caspase-specific cell staining, and led to the inhibition of apoptosis. In contrast, the fluorescent control inhibitor FAM-FA-FMK had no effect. Measurement of caspase activation in 96-well plates showed a 3- to 5-fold increase in FAM-fluorescence in staurosporine-treated cells compared to control cells. In summary, we show that FAM-VAD-FMK is a versatile and specific tool for detecting activated caspases in living cells.

Affinity Labels↗
PubMed2000

MEKK2 associates with the adapter protein Lad/RIBP and regulates the MEK5-BMK1/ERK5 pathway.

MEKK2 and MEKK3 are two closely related mitogen-activated protein kinase (MAPK) kinase kinases. The kinase domains of MEKK2 and MEKK3 are nearly identical, although their N-terminal regulatory domains are significantly divergent. By yeast two-hybrid library screening, we have identified MEK5, the MAPK kinase in the big mitogen-activated protein kinase 1 (BMK1)/ERK5 pathway, as a binding partner for MEKK2. MEKK2 expression stimulates BMK1/ERK5 activity, the downstream substrate for MEK5. Compared with MEKK3, MEKK2 activated BMK1/ERK5 to a greater extent, which might correlate with a higher affinity MEKK2-MEK5 interaction. A dominant negative form of MEK5 blocked the activation of BMK1/ERK5 by MEKK2, whereas activation of c-Jun N-terminal kinase (JNK) was unaffected, showing that MEK5 is a specific downstream effector of MEKK2 in the BMK1/ERK5 pathway. Activation of BMK1/ERK5 by epidermal growth factor and H2O2 in Cos7 and HEK293 cells was completely blocked by a kinase-inactive MEKK3 (MEKK3kin(-)), whereas MEKK2kin(-) had no effect. However, in D10 T cells, expression of MEKK2kin(-) but not MEKK3kin(-) inhibited BMK1/ERK5 activity. Two-hybrid screening also identified Lck-associated adapter/Rlk- and Itk-binding protein (Lad/RIBP), a T cell adapter protein, as a binding partner for MEKK2. MEKK2 and Lad/RIBP colocalize at the T cell contact site with antigen-loaded presenting cells, demonstrating cotranslocation of MEKK2 and Lad/RIBP during T cell activation. MEKK3 neither binds Lad/RIBP nor is recruited to the T cell contact with antigen presenting cell. MEKK2 and MEKK3 are differentially associated with signaling from specific upstream receptor systems, whereas both activate the MEK5-BMK1/ERK5 pathway.

Adaptor Proteins, Signal Transducing↗
PubMed2000

Tumor necrosis factor-alpha activation of the c-Jun N-terminal kinase pathway in human neutrophils. Integrin involvement in a pathway leading from cytoplasmic tyrosine kinases apoptosis.

The intensity and duration of an inflammatory response depends on the balance of factors that favor perpetuation versus resolution. At sites of inflammation, neutrophils adherent to other cells or matrix components are exposed to tumor necrosis factor-alpha (TNFalpha). Although TNFalpha has been implicated in induction of pro-inflammatory responses, it may also inhibit the intensity of neutrophilic inflammation by promoting apoptosis. Since TNFalpha is not only an important activator of the stress-induced pathways leading to p38 MAPk and c-Jun N-terminal kinase (JNK) but also a potent effector of apoptosis, we investigated the effects of TNFalpha on the JNK pathway in adherent human neutrophils and the potential involvement of this pathway in neutrophil apoptosis. Stimulation with TNFalpha was found to result in beta2 integrin-mediated activation of the cytoplasmic tyrosine kinases Pyk2 and Syk, and activation of a three-part MAPk module composed of MEKK1, MKK7, and/or MKK4 and JNK1. JNK activation was attenuated by blocking antibodies to beta2 integrins, the tyrosine kinase inhibitors, genistein, and tyrphostin A9, a Pyk2-specific inhibitor, and piceatannol, a Syk-specific inhibitor. Exposure of adherent neutrophils to TNFalpha led to the rapid onset of apoptosis that was demonstrated by augmented annexin V binding and caspase-3 cleavage. TNFalpha-induced increases in annexin V binding to neutrophils were attenuated by blocking antibodies to beta2 integrins, and the caspase-3 cleavage was attenuated by tyrphostin A9. Hence, exposure of adherent neutrophils to TNFalpha leads to utilization of the JNK-signaling pathways that may contribute to diverse functional responses including induction of apoptosis and subsequent resolution of the inflammatory response.

Apoptosis↗
PubMed2000

MEKK2 gene disruption causes loss of cytokine production in response to IgE and c-Kit ligand stimulation of ES cell-derived mast cells.

Ligation of the high-affinity IgE receptor (FcepsilonRI) or of c-Kit stimulates cytokine production in mast cells. We show that MEK kinase 2 (MEKK2), a MAPK kinase kinase (MAP3K) that regulates the JNK and ERK5 pathways, is required for cytokine production in embryonic stem (ES) cell-derived mast cells (ESMC). Targeted disruption of the MEKK2 or MEKK1 gene was used to abolish expression of the respective kinases in ESMC. Transcription of specific cytokines in response to IgE or c-Kit ligand was markedly reduced in MEKK2(-/-) ESMC relative to wild-type ESMC. Cytokine production in MEKK1(-/-) ESMC was similar to that of wild-type ESMC, demonstrating the specificity of MEKK2 in signaling cytokine gene regulation. MEKK2(-/-) ESMC also lost receptor-mediated stimulation of JNK. In contrast, JNK activation in response to UV irradiation was normal, showing that MEKK2 is required for receptor signaling but not for cellular stress responses. MEKK2 is the first MAP3K shown to be required for mast cell tyrosine kinase receptor signaling controlling cytokine gene expression.

Animals↗
PubMed2000

MEK kinase 2 binds and activates protein kinase C-related kinase 2. Bifurcation of kinase regulatory pathways at the level of an MAPK kinase kinase.

MEK kinase 2 (MEKK2) is a 70-kDa protein serine/threonine kinase that has been shown to function as a mitogen-activated protein kinase (MAPK) kinase kinase. MEKK2 has its kinase domain in the COOH-terminal moiety of the protein. The NH(2)-terminal moiety of MEKK2 has no signature motif that would suggest a defined regulatory function. Yeast two-hybrid screening was performed to identify proteins that bind MEKK2. Protein kinase C-related kinase 2 (PRK2) was found to bind MEKK2; PRK2 has been previously shown to bind RhoA and the Src homology 3 domain of Nck. PRK2 did not bind MEKK3, which is closely related to MEKK2. The MEKK2 binding site maps to amino acids 637-660 in PRK2, which is distinct from the binding sites for RhoA and Nck. This sequence is divergent in the closely related kinase PRK1, which did not bind MEKK2. In cells, MEKK2 and PRK2 are co-immunoprecipitated and PRK2 is activated by MEKK2. Similarly, purified recombinant MEKK2 activated PRK2 in vitro. MEKK2 activation of PRK2 is independent of MEKK2 regulation of the c-Jun NH(2)-terminal kinase pathway. MEKK2 activation of PRK2 results in a bifurcation of signaling for the dual control of MAPK pathways and PRK2 regulated responses.

Amino Acid Sequence↗
PubMed2000

MEK kinase 1 gene disruption alters cell migration and c-Jun NH2-terminal kinase regulation but does not cause a measurable defect in NF-kappa B activation.

MEK kinase 1 (MEKK1) is a 196-kDa mitogen-activated protein kinase (MAPK) kinase kinase that, in addition to regulating the c-Jun NH(2)-terminal kinase (JNK) pathway, is involved in the control of cell motility. MEKK1(-/-) mice are defective in eyelid closure, a TGFalpha-directed process involving the migration of epithelial cells. MEKK1 expression in epithelial cells stimulates lamellipodia formation, a process required for cell movement. In addition, mouse embryo fibroblasts derived from MEKK1(-/-) mice are inhibited in their migration relative to MEKK1(+/+) fibroblasts. MEKK1 is required for JNK but not NF-kappaB activation in response to virus infection, microtubule disruption, and stimulation of embryonic stem cells with lysophosphatidic acid. MEKK1 is not required for TNFalpha or IL-1 regulation of JNK or NF-kappaB activation in macrophages or fibroblasts. Thus, MEKK1 senses microtubule integrity, contributes to the regulation of fibroblast and epithelial cell migration, and is required for activation of JNK but not NF-kappaB in response to selected stress stimuli.

Animals↗
PubMed2000

Differential regulation of CD40-mediated human B cell responses by antibodies directed against different CD40 epitopes.

Ligation of CD40 using anti-CD40 or soluble CD40-ligand activates numerous intracellular kinases which transduce signals to the nucleus. The nature whereby these signaling events are coupled to distal functional events in B cells is poorly understood. In this study, using anti-CD40 monoclonal antibodies which recognize different epitopes on CD40, we compare the ability to activate the stress-activated protein kinases (SAPK) such as c-Jun NH(2) terminal kinase and p38 in human B cells with CD40 function. Activation of the SAPK pathway correlated with levels of activation of Rel/NF-kappaB transcription factors, but did not appear to be associated with rescue from anti-IgM induced apoptosis by suppressing caspase (CPP32) activity. Somewhat surprisingly, in the presence of IL-4, those antibodies to CD40 which failed to activate SAPK were most active in IgE production. IgE production was augmented in the presence of wortmannin. These studies suggest that rescue from apoptosis and IgE production mediated via CD40 may be independent of SAPK activation, induction of Rel/NF-kappaB, or suppression of CPP32 and that IgE production is, at least in part, regulated by signaling pathways that are dependent on phosphatidylinositol 3-kinase.

Antibodies↗
PubMed2000

Human neutrophil immunodeficiency syndrome is associated with an inhibitory Rac2 mutation.

A 5-week-old male infant presented with severe bacterial infections and poor wound healing, suggesting a neutrophil defect. Neutrophils from this patient exhibited decreased chemotaxis, polarization, azurophilic granule secretion, and superoxide anion (O(2)(-)) production but had normal expression and up-regulation of CD11b. Rac2, which constitutes >96% of the Rac in neutrophils, is a member of the Rho family of GTPases that regulates the actin cytoskeleton and O(2)(-) production. Western blot analysis of lysates from patient neutrophils demonstrated decreased levels of Rac2 protein. Addition of recombinant Rac to extracts of the patient neutrophils reconstituted O(2)(-) production in an in vitro assay system. Molecular analysis identified a point mutation in one allele of the Rac2 gene resulting in the substitution of Asp57 by an Asn (Rac2(D57N)). Asp57 is invariant in all defined GTP-binding proteins. Rac2(D57N) binds GDP but not GTP and inhibits oxidase activation and O(2)(-) production in vitro. These data represent the description of an inhibitory mutation in a member of the Rho family of GTPases associated with a human immunodeficiency syndrome.

Antigens, CD↗
PubMed2000

CD40 and adenosine A2 receptor agonist-cyclic adenosine monophosphate rescue B-cell antigen receptor-induced apoptosis through independent pathways and converge to prevent caspase activation.

BACKGROUND: Antigen receptor ligation induces apoptosis of B lymphocytes, but the molecular mechanisms underlying induction of apoptosis remain unclear, although the growing family of IL-1beta-converting enzyme cysteine proteases (caspases) are recognized to be major effectors of cellular death. OBJECTIVE: We sought to delineate and compare the rescue of B-cell apoptosis through CD40 ligand-CD40 interaction and cyclic adenosine monophosphate (cAMP)-dependent protein kinase A in human B cells. METHODS: By using tonsillar B cells and the B-lymphoblastoid cell line Ramos, rescue from B-cell apoptosis was compared, as were signaling pathways after activation of cells through CD40 and the adenosine A2 receptor. RESULTS: Both CD40 ligand-CD40 interaction and activation of intracellular cAMP rescue B cells from apoptosis after antigen receptor ligation. Although these pathways do not overlap, they converge by preventing the anti-IgM-induced activation of CPP32 (caspase 3), a member of the IL-1beta-converting enzyme protease family. CONCLUSION: These data indicate that the cAMP-protein kinase A-dependent and CD40-signaling pathways regulate B-cell survival and converge at a common point, the inhibition of antigen receptor-induced activation of caspases.

Antibodies↗