Absence Of Phorbol Ester Research Articles

PF240 COMBINED INHIBITION OF SHP1 AND SHP2 WITH PHORBOL ESTERS AS A DIFFERENTIATION THERAPY AGAINST ACUTE MYELOID LEUKEMIA

Background:The differentiation‐based therapy for acute promyelocytic leukemia (APL) is an inspiring example for the search of novel strategies aimed at treatment of other subtypes of acute myeloid leukemia (AML). Thus, the discovery of new molecular players in cell differentiation becomes a paramount research area to achieve this goal.Aims:To assess the involvement of the protein tyrosine phosphatases SHP1 and SHP2 on leukemic cells differentiation along with the therapeutic possibilities of their targeting to enhance the differentiation induction effect of phorbol esters.Methods:The oxidation status and enzymatic activity of SHP1 and SHP2 during PMA‐induced differentiation of HEL cells was evaluated. Additionally, the effects of RNAi‐mediated downregulation of these phosphatases on cell differentiation was studied. Afterwards, the impact of chemical inhibition of SHP1 and SHP2 on differentiation both in the presence and absence of phorbol esters was tested. Finally, the anti‐leukemic potential of phorbol esters and chemical inhibitors of SHP1 and SHP2 was addressed in several AML model cell lines, a xenograft mouse model and AML primary cells in vitro. Results:An increase of oxidation with a concomitant decrease of activity was observed for both phosphatases at the onset of PMA‐induced differentiation. Consistently, silencing of these proteins favored the process, with an enhanced effect upon their simultaneous downregulation. Moreover, the proteins SRC and β‐catenin were identified as downstream targets of SHP1 and SHP2 in this context. In agreement with these findings, chemical inhibition of the phosphatases promoted cell differentiation itself and enhanced the effect of phorbol esters. Interestingly, treatment with the phorbol ester prostratin and the dual inhibitor of SHP1 and SHP2 NSC87877 synergistically hampered the proliferation of AML cell lines, prolonged the survival of xenografted mice and reduced the clonogenic potential of AML primary cells.Summary/Conclusion:SHP1 and SHP2 are relevant mediators of differentiation in AML cells and their inhibition either alone or in combination with prostratin seems a promising differentiation‐based therapeutic strategy against different subtypes of AML beyond APL.

SHP1 and SHP2 inhibition enhances the pro-differentiative effect of phorbol esters: an alternative approach against acute myeloid leukemia

BackgroundThe differentiation-based therapy for acute promyelocytic leukemia (APL) is an inspiring example for the search of novel strategies aimed at treatment of other subtypes of acute myeloid leukemia (AML). Thus, the discovery of new molecular players in cell differentiation becomes a paramount research area to achieve this goal. Here, the involvement of the protein tyrosine phosphatases SHP1 and SHP2 on leukemic cells differentiation is shown, along with the therapeutic possibilities of their targeting to enhance the differentiation induction effect of phorbol esters.MethodsThe oxidation status and enzymatic activity of SHP1 and SHP2 during PMA-induced differentiation of HEL cells was evaluated. Additionally, the effects of RNAi-mediated downregulation of these phosphatases on cell differentiation was studied. Afterwards, the impact of chemical inhibition of SHP1 and SHP2 on differentiation both in the presence and absence of phorbol esters was tested. Finally, the anti-leukemic potential of phorbol esters and chemical inhibitors of SHP1 and SHP2 was addressed in several AML model cell lines, a xenograft mouse model and AML primary cells in vitro.ResultsAn increase of oxidation with a concomitant decrease of activity was observed for both phosphatases at the onset of PMA-induced differentiation. Consistently, silencing of these proteins favored the process, with an enhanced effect upon their simultaneous downregulation. Moreover, the proteins SRC and β-catenin were identified as downstream targets of SHP1 and SHP2 in this context. In agreement with these findings, chemical inhibition of the phosphatases promoted cell differentiation itself and enhanced the effect of phorbol esters. Interestingly, treatment with the phorbol ester prostratin and the dual inhibitor of SHP1 and SHP2 NSC87877 synergistically hampered the proliferation of AML cell lines, prolonged the survival of xenografted mice and reduced the clonogenic potential of AML primary cells.ConclusionsSHP1 and SHP2 are relevant mediators of differentiation in AML cells and their inhibition either alone or in combination with prostratin seems a promising differentiation-based therapeutic strategy against different subtypes of AML beyond APL.

English

The plant, jatropha has attracted worldwide attention for its high oil content. The use of high performance liquid chromatography (HPLC) to separate and quantify, for the first time, the phytic acid (inositol hexaphosphate) and lower inositol phosphates (tri-, tetra- and penta-phosphates; IP6, IP5, IP4 and IP3) in toxic and non-toxic (NT) Jatropha curcas seeds from different locations in Mexico was proposed. There are reports on the total phytic acids but the method of precipitation used was not specific to distinguish between the phytic acid (IP6) and its hydrolysis products; therefore, this technique underestimates the IP6 content. It was observed that the total inositol concentration is independent on the presence or absence of phorbolesters (PE). The analysis showed that the toxic seeds from Villaflores and Chiapa de Corzo had high concentrations of total IP (46.2 and 42.5 mg/g, respectively) but the NT seeds from Huitzilan is the highest (56.88 mg/g) followed by Pueblillo (41.427 mg/g), Cuautla (37.832 mg/g) and Xochitlan (35.868 mg/g) showed higher values of IP. Finally, the toxic seeds from Coatzacoalcos (22.5 mg/g) showed lower value. This is the first work showing the different inositol phosphates present in jatropha seed samples, highlighting the presence of hexaphosphate acid as the major component. Key words: Phytic acid, high performance liquid chromatography (HPLC), anti-nutrients, phytates, IP5, IP6, hexaphosphate.

Abstract 3928: Structural basis for the failure of the C1 domain of RasGRP2 to bind phorbol ester

Abstract C1 domains represent the recognition motif for the second messenger diacylglycerol (DAG) and for the phorbol esters in protein kinase C, RasGRP, and several other families of signaling proteins. In addition to such typical C1 domains, atypical C1 domains have been identified which possess varying levels of sequence and structural homology with the typical C1 domains but fail to bind DAG or phorbol ester. Among RasGRP family members, RasGRP1 and RasGRP3 possess typical C1 domains, whereas the C1 domain of RasGRP2 stands out as being atypical. In order to better understand the structural constraints for ligand binding, we have analyzed the basis for the failure of the C1 domain of RasGRP2 to bind ligands. Using site-directed mutagenesis, we have identified four critical amino acid residues responsible for the lack of phorbol ester sensitivity. We found that the C1 domain of RasGRP2 had weak binding affinity (Kd = 2890 ± 240 nM) in vitro for [3H]phorbol 12,13-dibutyrate ([3H]PDBu). Replacing all four of critical amino acid residues (Asn7, Ser8, Ala19 and Ile21) with the corresponding residues (Thr7, Tyr8, Gly19 and Leu21, respectively) of RasGRP1 resulted in potent [3H]PDBu binding affinity (Kd = 1.47 ± 0.03 nM) and translocation in response to PMA in the LNCaP cell line. The mutant C1 domains incorporating one to three of these critical residues showed intermediate binding and translocation properties. Of the four substitutions, S8Y made the greatest contribution. Phospholipid requirements for [3H]PDBu binding to the mutant C1 domains were determined; at constant total phospholipid, the requirement for the proportion of phosphatidylserine in phosphatidylserine : phosphatidylcholine mixtures decreased in going from the single S8Y mutant to the quadruple mutant. Binding activity for DAG was also restored in the mutant C1 domains, in parallel with that for phorbol ester. The full length RasGRP2 protein containing the mutated C1 domains likewise showed strong phorbol ester binding, albeit modestly weaker than that of the purified C1 domain (Kd = 8.2 ± 1.1 nM for the full length protein containing all four mutations) and displayed translocation in the LNCaP (human prostate adenocarcinoma) cells in response to phorbol ester. RasGRP2 is a guanyl exchange factor for Rap1. A Rap1 GTPase pull-down assay was used to compare the guanine nucleotide exchange activity of wild type and mutated full length RasGRP2 in human embryonic kidney 293 (HEK 293) cells in the presence or absence of phorbol ester. These cells were transfected with either the wild type or the mutant RasGRP2. Consistent with the ability of phorbol ester to induce translocation of the full length RasGRP2 with the mutated C1 domain, phorbol ester enhanced the ability of the mutated RasGRP2 to activate Rap1. Citation Format: Agnes Czikora, Daniel J. Lundberg, Nancy E. Lewin, Noemi Kedei, Peter M. Blumberg. Structural basis for the failure of the C1 domain of RasGRP2 to bind phorbol ester. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3928. doi:10.1158/1538-7445.AM2015-3928

Genetic Improvement of Jatropha for Biodiesel Production

Jatropha curcas L. is a perennial oilseed crop belonging to the Euphorbiaceae family, whose oil content in seeds varies from 33 to 38%, giving a yield potential of over 1200 kg of oil per hectare. However, it is a non-domesticated species and research is required for commercial exploration of this species for biodiesel production. The strategies of Embrapa’s jatropha breeding program aim at developing cultivars with high yield and oil content, non-toxic (absence of phorbol esters), resistant to biotic and abiotic stresses and adapted to the main producing regions of Brazil. The program activities started with the enrichment and characterization of the germplasm bank, currently with over 200 accessions from different regions of Brazil. Depending on the specific objectives of the program, different selection and breeding methods are employed. In order to understand the genetic control of specific traits and to generate segregating populations, experimental designs such as diallel crosses, which allow the estimation of heterosis, general combining ability and specific combining ability among genotypes, have been adopted. In addition, molecular markers such as SSR and SNPs are being developed and may help in early selection for characters such as the absence of toxicity in the grains. The program also includes the study on genotype × environment interaction with the evaluation of the progenies/improved clones in different regions of Brazil, which is essential for recommending cultivars for specific or broad climatic conditions. In conclusion, considering that J. curcas is a perennial species and still not domesticated, approximately 5-7 years will be required to obtain improved cultivars and evidence-based information on crop production systems to support commercial cultivation.

γ‐Secretase and metalloproteinase activity regulate the distribution of endoplasmic reticulum to hippocampal neuron dendritic spines

The neuronal endoplasmic reticulum (ER) contributes to many physiological and pathological processes in the brain. A subset of dendritic spines on hippocampal neurons contains ER that may contribute to synapse-specific intracellular signaling. Distribution of ER to spines is dynamic, but knowledge of the regulatory mechanisms is lacking. In live cell imaging experiments we now show that cultured hippocampal neurons rapidly lost ER from spines after phorbol ester treatment. ER loss was reduced by inhibiting gamma-secretase (DAPT at 2 microM) and metalloproteinase (TAPI-0 and GM6001 at 4 microM) activity. Inhibition of protein kinase C also diminished loss of ER by preventing exit of ER from spines. Furthermore, gamma-secretase and metalloproteinase inhibition, in the absence of phorbol ester, triggered a dramatic increase in spine ER content. Metalloproteinases and gamma-secretase cleave several transmembrane proteins. Many of these substrates are known to localize to adherens junctions, a structural specialization with which spine ER interacts. One interesting possibility is thus that ER content within spines may be regulated by proteolytic activity affecting adherens junctions. Our data demonstrate a hitherto unknown role for these two proteolytic activities in regulating dynamic aspects of cellular ultrastructure, which is potentially important for cellular calcium homeostasis and several intracellular signaling pathways.

The nature of the hydrophobic n-alkanol binding site within the C1 domains of protein kinase Calpha.

The activator-binding sites within the C1 domains of protein kinase C (PKC) are also able to bind alcohols and anesthetics. In this study, the nature of the interaction of these agents with the hydrophobic region within the C1 domains was investigated and a structure-activity relationship for the alcohol effects was obtained. The effects of a series of n-alkanols on PKCalpha activity, determined using an in vitro assay system that lacked lipids, were found to be a nonlinear function of the chain length. In the absence of phorbol ester or diacylglycerol, 1-octanol potently activated PKCalpha in a concentration-dependent manner, while 1-heptanol was completely without effect, despite differing by one methylene unit. The minimal structural requirement for the activating effect corresponded to R-CH(OH)-(CH(2))(n)-CH(3), where R = H or an alkyl group and n >or= 6. Consistent with this, 2-octanol, for which n = 5, was without effect on the activity, even though this alcohol is only marginally less hydrophobic than 1-octanol, whereas 2-nonanol, for which n = 6, was able to produce activity. Importantly, it was found that PKCalpha was activated to a greater extent by R-2-nonanol than by the S enantiomer. The potentiation of phorbol ester-induced, membrane-associated PKCalpha activity by long-chain n-alkanols reported previously (Slater, S. J., Kelly, M. B., Larkin, J. D., Ho, C, Mazurek, A, Taddeo, F. J., Yeager, M. D., Stubbs, C. D. (1997) J. Biol. Chem. 272, 6167-6173), was also found here for nonmembrane associated PKC, indicating that this effect is an intrinsic property of the enzyme rather than a result of membrane perturbation. Overall, the results suggest that the alcohol-binding sites within the C1 domains of PKCalpha contain spatially distinct hydrophilic and hydrophobic regions that impose a high degree of structural specificity on the interactions of alcohols and other anesthetic compounds, as well as diacylglycerols and phorbol esters.

Protein Kinase C Isoforms Are Translocated to Microtubules in Neurons

Activation of protein kinase C (PKC) increases microtubule (MT) growth lifetimes, resulting in extension of a nocodazole-sensitive population of MTs in Aplysia growth cones. We examined whether the two phorbol ester-activated PKCs in Aplysia, the Ca(2+)-activated PKC Apl I and the Ca(2+)-independent PKC Apl II, are associated with these MTs. Phorbol esters translocated PKC to the Triton X-100-insoluble fraction, and a significant portion of this translocated pool was sensitive to low concentrations of nocodazole. Low doses of nocodazole had no effect on the amount of PKC in the Triton X-100-insoluble fraction in the absence of phorbol esters, whereas higher doses of nocodazole reduced basal levels of PKC Apl II. The F-actin cytoskeletal disrupter, latrunculin A, removed both PKCs from the Triton X-100-insoluble fraction in both control and phorbol ester-treated nervous systems. PKC Apl II also directly interacted with purified MTs. In detergent-extracted cells, both PKCs immunolocalized predominantly with MTs. PKCs were associated with newly formed MTs invading the actin-rich peripheral growth cone domain after PKC activation. Our results are consistent with a central role for PKCs in regulating MT extension.

Phorbol Ester-regulated Oligomerization of Diacylglycerol Kinase δ Linked to Its Phosphorylation and Translocation

Diacylglycerol kinase (DGK) plays an important role in signal transduction through modulating the balance between two signaling lipids, diacylglycerol and phosphatidic acid. In yeast two-hybrid screening, we unexpectedly found a self-association of the C-terminal part of DGKdelta containing a sterile alpha-motif (SAM) domain. We then bacterially expressed the SAM domain fused with maltose-binding protein and confirmed the formation of dimeric and tetrameric structures. Moreover, gel filtration and co-immunoprecipitation analyses demonstrated that DGKdelta formed homo-oligomeric structures in intact cells and that the SAM domain was critically involved in the oligomerization. Interestingly, phorbol ester stimulation induced dissociation of the oligomeric structures with concomitant phosphorylation of DGKdelta. Furthermore, we found that DGKdelta was translocated from cytoplasmic vesicles to the plasma membrane upon phorbol ester stimulation. In this case, DGKdelta mutants lacking the ability of self-association were localized at the plasma membranes even in the absence of phorbol ester. A protein kinase C inhibitor, staurosporine, blocked all of the effects of phorbol ester, i.e. oligomer dissociation, phosphorylation, and translocation. We confirmed that tumor-promoting phorbol esters did not directly bind to DGKdelta. The present studies demonstrated that the formation and dissociation of oligomers serve as the regulatory mechanisms of DGKdelta and that DGKdelta is a novel downstream effector of phorbol ester/protein kinase C signaling pathway.

Effect of Ca2+ ATPase Inhibitors on MCP-1 Release from Bone Marrow-Derived Mast Cells and the Involvement of p38 MAP Kinase Activation

The effect of two Ca²⁺ ATPase inhibitors, cyclopiazonic acid (CPA) and 2,5-di-(tert-butyl)-1,4-hydroquinone (DTBHQ), on the release of MCP-1 from bone marrow-derived mast cells (BMMCs) were investigated. CPA and DTBHQ increased the intracellular free Ca²⁺ concentration ([Ca²⁺]_i) and induced MCP-1 release in a dose-dependent manner. These Ca²⁺ ATPase inhibitors induced MCP-1 release in the absence of phorbol ester, in contrast to their induction of TNF-α. MCP-1 release reached a maximum at 6–9 h. It was inhibited by treatment with actinomycin D, the immunosuppressant cyclosporin A, and the cytosolic Ca²⁺ chelator BAPTA-AM. Furthermore, RT-PCR showed a time-dependent increase of MCP-1 mRNA. Thus MCP-1 release seems to depend on Ca²⁺-dependent transcriptional activation. MCP-1 release was dose-dependently inhibited by the p38 MAP kinase inhibitor SB202190, but not by the p44/42 MAP kinase inhibitor PD98059. Therefore, transcriptional activation of MCP-1 production and its release seem to be dependent on the nuclear factor of activated T cells and p38 MAP kinase activation. This is the first report to show the regulation of MCP-1 production in BMMCs.

Phosphorylation of class I MHC molecules in the absence of phorbol esters is an intracellular event and may be characteristic of trafficking molecules

Class I Major Histocompatibility Complex (MHC) molecules are displayed at the cell surface where they present antigenic peptides to T lymphocytes. Class I MHC molecules undergo cytoplasmic domain phosphorylation on a serine residue late in their biosynthesis. Here we show that phosphorylation occurs on mature, β 2-microglobulin-associated class I MHC molecules in a mouse lymphoid cell line. Both recently synthesized class I MHC molecules and molecules which are at least 3 h old become phosphorylated. Approximately 14% of phosphorylated class I MHC molecules occur at the cell surface. Density gradient analysis indicates that phosphorylated class I MHC molecules also occur in lamp + intracellular compartments and in fractions containing rab4, a GTP-binding protein associated with recycling endosomes. Class I MHC molecules are endocytosed and recycled to the cell surface in these cells. Furthermore, the lysosomotropic drug, primaquine, inhibits both class I MHC phosphorylation and its recycling back to the cell surface, suggesting that phosphorylation is related to class I MHC recycling. These observations are intriguing since several studies have shown that class I MHC molecules can acquire antigenic peptides in NH 4Cl-sensitive compartments. Hence, class I MHC phosphorylation may play a role in regulating intracellular sorting through these compartments.

Heat-killed Streptococcus suis capsular type 2 strains stimulate tumor necrosis factor alpha and interleukin-6 production by murine macrophages.

Streptococcus suis capsular type 2 is an important etiological agent of swine meningitis, and it is also a zoonotic agent. Since mononuclear phagocytes have been suggested to play a central role in the pathogenesis of meningitis, the objective of the present study was to evaluate the capacity of whole killed S. suis type 2 organisms to induce the release of the proinflammatory cytokines tumor necrosis factor alpha (TNF-alpha) and interleukin-6 (IL-6) by murine macrophages. Induction of cytokines was evaluated in the presence or absence of phorbol ester (phorbol 12-myristate 13-acetate [PMA]) costimulation. Results showed that S. suis type 2 stimulated the production of both cytokines in a concentration- and time-dependent fashion. Although large doses of bacteria were required for maximal cytokine release, titers were similar to those obtained with the lipopolysaccharide (LPS) positive control. An increase in cytokine release was observed with both S. suis and LPS with PMA costimulation. Experiments with cytochalasin-treated macrophages showed that the stimulation of cytokine production was phagocytosis independent. When macrophages were stimulated with an unencapsulated mutant, an increase in TNF production was observed, but the absence of the capsule had no effect on IL-6 production. In fact, whereas purified capsular polysaccharide of S. suis failed to induce cytokine release, purified S. suis cell wall induced both TNF and, to a lesser extent, IL-6. IL-6 secretion probably requires some distinct stimuli which differ from those of TNF. Finally, the S. suis putative virulence factors suilysin and extracellular protein EF showed no cytokine-stimulating activity. The ability of S. suis to trigger macrophages to produce proinflammatory cytokines may have an important role in the initiation and development of meningitis caused by this microorganism.

Formation of reactive oxygen species following bioactivation of gentamicin

The present study investigated the ability of gentamicin to catalyze free radical reactions and probed the underlying mechanisms by hydroethidine imaging, oxygen consumption, and reduction of cytochrome c. In Epstein-Barr virus-transformed lymphoblastoid cells, a respiratory burst was induced by phorbol ester and detected by hydroethidine, a fluorescent indicator of superoxide radical. The addition of gentamicin increased the fluorescence two-fold while gentamicin did not produce fluorescence in the absence of phorbol ester. In membrane preparations, gentamicin did not enhance NADPH consumption ruling out a direct activation of NADPH oxidase. The formation of reactive oxygen species by gentamicin was additionally supported by experiments that showed gentamicin increased oxygen consumption two-fold in intact cells and a cell-free system. In addition, generation of superoxide was indicated by the gentamicin-stimulated reduction of cytochrome c. The stimulation by gentamicin depended upon the presence of iron (Fe II/Fe III) and of arachidonic acid as an electron donor. These results support the hypothesis that an iron-gentamicin complex can increase reactive oxygen species in nonenzymatic and in biological systems. The requirement for a reductive activation in intact cells (e.g., by a respiratory burst) is interpreted as the conversion of an inactive Fe III-gentamicin to a redox-active Fe II-gentamicin complex.

Binding of protein kinase C isoforms to actin in Aplysia.

Recently, two of the 10 vertebrate protein kinase C (PKC) isoforms, PKC betaII and PKC epsilon, have been shown to bind specifically to actin filaments, suggesting that these kinases may regulate cytoskeletal dynamics. Here, we present evidence that two PKCs from the marine mollusk Aplysia californica, PKC Apl I, a Ca2+-activated PKC, and PKC Apl II, a Ca2+-independent PKC most similar to PKC epsilon and eta, also bind F-actin. First, they both cosedimented with purified actin filaments in a phorbol ester-dependent manner. Second, they both translocated to the Triton-insoluble fraction of the nervous system after phorbol ester treatment. PKC Apl II could also partially translocate to actin filaments and associate with the Triton-insoluble fraction in the absence of phorbol esters. Translocation to purified actin filaments was increased in the presence of a PKC inhibitor, suggesting that PKC phosphorylation reduces PKC bound to actin. Although both kinases bound F-actin, actin was not sufficient to activate the kinases. In support of a physiological role for actin-PKC interactions, immunochemical localization of PKC Apl II in neuronal growth cones revealed a striking colocalization with F-actin. Our results are consistent with a role for actin-PKC interactions in regulating cytoskeletal dynamics in Aplysia.

1,25-Dihydroxyvitamin D 3 enhances degranulation of mast cells

The mast cell lines rat basophilic leukemia (RBL) and mouse C57 cells respond to IgE/antigen complexes by degranulation. Treatment of these cells with 1,25-dihydroxyvitamin D 3 (1,25(OH) 2D 3), (10–100 nM) for 24–48 h enhanced IgE/antigen-induced exocytosis as monitored by release of hexosaminidase. A short term incubation with the hormone did not affect exocytosis, ruling out a rapid non genomic mechanism. The presence of vitamin D receptors, demonstrated by immunoblotting and the lack of effect of 24,25(OH) 2D 3 suggest a role for these receptors in the enhancing effect. 1,25(OH) 2D 3 also enhanced exocytosis induced by the calcium ionophore A23187 in the presence or absence of phorbol ester indicating modulation of events distal to signal transduction. 1,25(OH) 2D 3 enhanced exocytosis in the presence of cytochalasin D, indicating that the action of the hormone is not due to effects on microfilament structure. The results of this study suggest that 1,25(OH) 2D 3 may affect the allergic or pro-inflammatory potential of mast cells.

Tyrosine phosphorylation of myelin protein PO.

Po (M(r) 30 kDa), the major protein component of peripheral nervous system (PNS) myelin, is known to be phosphorylated by protein kinase C on serine residues at multiple sites. This study was conducted to assess whether other amino acids might be phosphorylated in the protein. Segments of rat sciatic nerve were incubated with 32P in either the presence or absence of phorbol ester. Labeled Po was isolated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and subjected to partial acid hydrolysis. Upon separation of the hydrolysis products by either thin-layer electrophoresis or thin-layer chromatography, a radioactive spot was detected which comigrated with authentic phosphotyrosine. In other experiments, nerves were incubated with the tyrosine phosphatase inhibitors vanadate or vanadyl hydroperoxide (pervanadate). When the nerve homogenate proteins were separated on gels and probed with a monoclonal antibody to phosphotyrosine on Western blots, a positive immune reaction was obtained for a protein species which migrated with the same mobility as PO on Coomassie Blue-stained gels. In the absence of 2-mercaptoethanol, this immunoreactive band displayed increased mobility on gels which is characteristic of the migration pattern of Po. The same immunostaining results were obtained using a purified peripheral myelin fraction prepared from nerve homogenates. Furthermore, the positions of immunoreactive bands produced by anti-Po and antiphosphotyrosine antibodies coincided on the same immunoblot of myelin proteins and purified Po. These data indicate that one or more tyrosyl residues in Po can be phosphorylated in intact sciatic nerve.

Regulation of the Plasminogen Activator Inhibitor Type-2 Gene in Monocytes: Localization of an Upstream Transcriptional Silencer

Transcriptional regulation of the plasminogen activator inhibitor type-2 (PAI-2) gene appears to be an important factor in the response of mononuclear phagocytes to inflammation. We have investigated here the molecular basis for PAI-2 synthesis in monocytic cells by reporter gene deletion analysis. A DNA fragment containing 5.1 kb of 5' flanking region through to the start of the second exon was fused to a chloramphenicol acetyl transferase (CAT) reporter gene, transfected into macrophage and nonmacrophage cells and tested for PAI-2 promoter-directed CAT activity in the presence and absence of phorbol ester. Deletion analysis showed the existence of three major transcription regulatory regions. (1) A positive regulatory region contained in the proximal promoter mediates basal transcription and 12-phorbol 13-myristate acetate inducibility. (2) A negative regulatory region, or silencer, present between -1977 and -1675, was found to repress PAI-2 promoter activity in an orientation- and position-independent manner, but not in a cell-specific manner. (3) A second positive regulatory element, located upstream between approximately -5100 and -3300, appears to overcome inhibition mediated by the silencer in a cell-specific manner, suggesting a mechanism for the regulation of this gene. We have localized the motif responsible for silencer activity to a 28-bp DNA sequence containing a unique 12-bp palindrome centered at an Xba I restriction enzyme site, CTCTCTAGAGAG, which is designated the PAI-2-upstream silencer element-1 (PAUSE-1). This element binds a specific PAUSE-1 binding factor as determined by mobility shift analysis. We conclude that PAI-2 gene transcription is regulated by both positive and negative control mechanisms that may be important for the regulation of other genes as well.

Differential Translocation of Protein Kinase C ε during HeLa Cell Adhesion to a Gelatin Substratum

The spreading of HeLa cells, following attachment to a collagen or gelatin substratum, requires the activation of protein kinase C (PKC). Membrane-bound PKC was previously shown to be activated during cell attachment and in response to the activation of a series of lipid second messengers turned on by the ligation of beta1-integrin collagen receptors. HeLa cells express the alpha, gamma, epsilon, zeta, lambda, and iota isozymes of PKC as determined by Western blotting with specific antibodies. Only PKCepsilon redistributed from the cytosol to the membrane during cell adhesion. Most of the PKCepsilon in cells that were in suspension was in the cytosolic fraction. During cell attachment to a gelatin matrix, all of the PKCepsilon moved out of the cytosol, with most going to the membrane fraction. After the cells became fully spread, PKCepsilon began to reappear in the cytosol. Translocation of PKCepsilon was not observed during the adhesion of cells to culture dishes where cells nonspecifically attach but do not spread. The conventional PKCalpha and -gamma isozymes were translocated from the cytosol to the membrane only when phorbol ester was present at a concentration that increases the rate and extent of cell spreading. Under normal conditions, i.e. in the absence of phorbol ester, PKCepsilon appears to be the PKC isozyme responsible for the regulation of HeLa cell adhesion to the extracellular matrix.

Retinoic acid-induced gene expression of tissue transglutaminase via protein kinase C-dependent pathway in mouse peritoneal macrophages.

Culture of mouse resident peritoneal macrophages with retinoic acid resulted in increased expression of the tissue transglutaminase gene as revealed by increases in the maximal velocity of the enzyme reaction in the cytosol and in the enzyme mRNA level. Protein kinase C-activating phorbol esters and okadaic acid, both of which were without effect on the enzyme induction by themselves, enhanced the retinoic acid-induced gene expression, which was in turn inhibited partially by pertussis toxin and totally by inhibitors of protein kinase C in either the presence or absence of phorbol esters. Retinoic acid was more effective in the "conditioned" medium, in which macrophages had been cultured for a time longer than 4 h, than in the "fresh" medium. The retinoic acid induction of transglutaminase was accompanied by increased phosphatidylinositol turnover and phosphatidic acid generation, which were efficiently suppressed by prior exposure of cells to pertussis toxin. It is likely that certain autocrine factor(s) liberated during culture of macrophages may afford conditions favorable for retinoic acid-induced gene expression, presumably via pertussis toxin-sensitive G protein-mediated phosphoinositide metabolism leading to activation of protein kinase C.

Growth of melanocytic cells is associated with down-regulation of protein kinase C alpha, delta, and epsilon isoforms. Possible role of diacylglycerol.

Protein kinase C (PKC) down-regulation has been shown to correlate with the growth of murine melanocytic cells in culture (Brooks, G., Wilson, R. E., Dooley, T. P., Goss, M. W., and Hart, I. R. (1991) Cancer Res. 51, 3281-3288). We now show that PKC alpha, delta, epsilon, and zeta isoforms are present at the protein level in quiescent, non-transformed Mel-ab melanocytes, maintained in the absence of phorbol ester. Proliferation of Mel-ab cells, achieved by incubation in the continual presence of phorbol 12,13-dibutyrate, was associated with a down-regulation of the PKC alpha, delta, and epsilon isozymes. Examination of two transformed syngeneic lines (the B16 murine melanoma and the long terminal repeat Ras.2 line), that grew in the absence of exogenous phorbol esters, showed that PKC alpha protein levels were either partially down-regulated or unaffected, the PKC delta and epsilon isoforms were down-regulated completely, and the levels of PKC zeta protein remained unaltered relative to quiescent Mel-ab cells. Basal levels of total diacylglycerol were elevated 5-fold in B16 melanoma cells compared with levels found in quiescent or proliferating Mel-ab melanocytes and appear to arise largely from the breakdown of phosphatidylinositol phospholipids accompanied by a significant rise in phospholipase C activity. Hourly treatments of quiescent Mel-ab melanocytes with the synthetic diacylglycerol analogue, 1,2-dioctanoyl-sn-glycerol, for 24 h, resulted in an induction of DNA synthesis which was associated with a significant down-regulation of PKC levels mediated largely via post-translational rather than transcriptional mechanisms. These results show for the first time that specific isoforms of PKC are down-regulated at the protein level during proliferation of murine melanocytic cells and suggest that the constitutive down-regulation of PKC in transformed melanoma cells may arise as a consequence of elevated endogenous phosphatidylinositol-derived diacylglycerol levels.