RESUMO
The secretion of sex hormone-binding globulin (SHBG) by the human hepatocarcinoma cell line Hep G2 was increased significantly not only by estradiol (E2) but also by testosterone (T), dihydrotestosterone, and the synthetic androgen danazol in the presence, but not the absence, of fetal calf serum. The secretion of SHBG also was stimulated by the antiestrogen tamoxifen, although this required the use of longer incubation periods and higher concentrations than were required for the steroids. The antiandrogen cyproterone acetate and cortisol (5 microM) decreased SHBG secretion. Pregnanediol (5 microM) had no discernible effect. These changes were considered specific as none of the compounds altered either the secretion of total protein by the cells or their total protein content. Cells incubated with a mixture of E2 (0.5 microM) and T (0.5 microM) secreted significantly more SHBG than did cells incubated with E2 (1.0 microM), indicating these steroids exert their effects through different mechanisms. The increases with E2 and T were reduced significantly by tamoxifen and cyproterone acetate, respectively, suggesting receptor mediation of the steroid effects. The E2-related increase was abolished by cycloheximide, indicating that the changes were due to alterations in the synthesis of SHBG rather than to alterations in the release of previously synthesized protein. These findings suggest the T-related decrease in plasma SHBG levels may be due to causes other than a decrease in the hepatic synthesis of the protein. Additionally, they indicate that Hep G2 cells may prove suitable for examining the regulation of the SHBG gene by a variety of compounds.
Assuntos
Carcinoma Hepatocelular/metabolismo , Di-Hidrotestosterona/farmacologia , Estradiol/farmacologia , Neoplasias Hepáticas/metabolismo , Globulina de Ligação a Hormônio Sexual/metabolismo , Testosterona/farmacologia , Linhagem Celular , Antagonistas de Hormônios/farmacologia , Humanos , Hidrocortisona/farmacologia , Pregnanodiol/farmacologia , Proteínas/metabolismoRESUMO
Lysosomal ceroid/lipofuscinosis storage in human, canine, and ovine forms of neuronal ceroidlipofuscinosis is predominantly in neurons and retinal pigment epithelial cells. Despite problems in identifying individual storage materials, it is believed that non-enzymic oxidation of unsaturated fatty acids in phospholipids and inhibition of lysosomal proteolysis, leading to massive deposition of autofluorescent pigment, is the cause of the disease. We have, therefore, studied cellular phospholipases and find a marked deficiency of lysosomal phospholipase A1 (PLA1) in canine NCL brain. Other lysosomal hydrolases, and cytosolic/mitochondrial forms of phospholipase A2 are completely normal. We believe that the PLA1 deficiency leads to transient lysosomal storage of phospholipids containing peroxy fatty acids which are then chemically converted to hydroxynonenal, a potent inhibitor of a thiol-dependent enzymes. Inhibition of proteases is believed to be intrinsic to the formation of lipofuscin. An inherited deficiency of a thiol protease (the lysosomal cathepsin H) in two siblings with NCL can also lead to build up of peptides which are then cross-linked and converted into ceroid-containing curvilinear bodies. Thus there is evidence for molecular and genetic heterogeneity in Batten disease.
Assuntos
Ceroide/biossíntese , Lipofuscinoses Ceroides Neuronais/enzimologia , Fosfolipases A/deficiência , Animais , Encéfalo/enzimologia , Doenças do Cão/enzimologia , Cães , Humanos , Lipofuscinoses Ceroides Neuronais/metabolismo , Lipofuscinoses Ceroides Neuronais/veterinária , Fosfolipases A/genética , Fosfolipases A1 , Fosfolipases A2 , Especificidade da EspécieRESUMO
Cell differentiation and myelination involve a fine balance between stasis and programmed cell death, yet the genes that regulate this have not been clearly defined. We therefore studied two key gene products involved in oligodendrocyte plasma membrane lipid metabolism and their antagonistic role in ceramide-mediated cell death signaling. Overexpression of palmitoyl:protein thioesterase (PPT1; verified by Western blot of the V5-tagged protein and increased enzyme activity) resulted in decreased ceramide in the detergent-resistant microdomain (DRM, or raft) relative to cholesterol and sphingomyelin (SM). This PPT1 overexpression also resulted in protection against cell death induced by either staurosporine or C(2)-ceramide. In contrast, overexpression of neutral sphingomyelinase 2 (NSMase2; verified by Western blot of the FLAG-tagged protein and increased enzyme activity) resulted in increased membrane NSMase and increased ceramide in rafts relative to cholesterol and SM. The difference in SM and ceramide turnover was quantitated by [(3)H]palmitate pulse-chase labeling. Furthermore, when NBD-SM was added to cells, it was hydrolyzed by NSMase-transfected cells at more than twofold the rate in untransfected cells. NSMase2 overexpression enhanced cell death induced by staurosporine or C(2)-ceramide, in contrast to the protective effect of PPT1 overexpression. The presence of a fraction of both PPT1 and NSMase2 in rafts together with their substrates (palmitoylated proteins and SM, respectively) suggests a mechanism for dynamic palmitoylation/depalmitoylation of certain proteins in controlling cell death via NSMase activation.
Assuntos
Membrana Celular/enzimologia , Ceramidas/metabolismo , Microdomínios da Membrana/metabolismo , Oligodendroglia/enzimologia , Esfingomielina Fosfodiesterase/metabolismo , Tioléster Hidrolases/metabolismo , Animais , Apoptose/fisiologia , Células CHO , Diferenciação Celular/fisiologia , Cricetinae , Humanos , Lipídeos de Membrana/metabolismo , Células Tumorais CultivadasRESUMO
Dying children have special needs related to their age and stage of development. Family physicians are sometimes asked to care for children at home or in hospital in the final days of life. Working with families and other caregivers, family physicians are well placed to care for dying children.
Assuntos
Medicina de Família e Comunidade/métodos , Papel do Médico , Assistência Terminal/métodos , Adolescente , Canadá/epidemiologia , Criança , Desenvolvimento Infantil , Pré-Escolar , Família/psicologia , Necessidades e Demandas de Serviços de Saúde , Humanos , Lactente , Mortalidade Infantil , Recém-Nascido , Medição da DorRESUMO
The polyphosphoinositides play important roles in transmembrane signalling but are also involved in anchoring cell surface proteins, organellar transport, cytoskeleton organization, and cell survival. The polyphosphoinositides synthesized by phosphatidylinositol-3 kinase (PI-3K), (Ptd(3,4)InsP2, and PtdIns(3,4,5)P3), appear to play a critical role in cell survival by membrane recruitment and activation of Akt kinase. Inhibitors of PI3K, wortmannin, and LY294002, induced a time-dependent activation of caspase-3 (CPP32), with a peak at 6 hr, leading to subsequent cell death by apoptosis in a dorsal root ganglion cell line (F-11). Lowering cyclic AMP (cAMP) levels enhanced both caspase-3 activation and cell death induced by PI3K inhibitors, whereas a nonhydrolyzable cAMP analog (Bt2cAMP), lowered CPP32 and was protective. We stably transfected the F-11 cells with the constitutively active p110 catalytic subunit of PI-3 kinase and observed resistance to both caspase-3 (CPP32) activation and subsequent apoptosis induced by either wortmannin or LY294002. Treatment of F-11 cells with bradykinin (BK) stimulated the hydrolysis of a different polyphosphoinositide, PtdIns(4,5)P2, and enhanced both wortmannin-induced caspase-3 (CPP32) activation and subsequent apoptosis. PtdIns(4,5)P2 is also a precursor of the anti-apoptotic PtdIns(3,4,5) P3 and lowering cAMP levels with opioid agonists for 30 min enhanced both the hydrolysis of PtdIns(4,5) P2 and cellular apoptosis. The enhancement was opioid dose-dependent and opioid antagonist (naloxone)-reversible and was also seen following 24-hr exposure to opioids such as U69,593 and Dala2, Dleu5 enkephalin (DADLE). However, unlike the bradykinin stimulation of PtdIns(4,5)P2 hydrolysis following activation of phospholipase C, the opioid-enhanced hydrolysis was independent of external Ca2+ and was blocked by pertussis toxin, suggesting a different mechanism involving GI, GO, or betagamma-subunits. In summary, both the receptor-mediated lowering of cAMP levels and the hydrolysis of 4,5-polyphosphoinositides have no direct effect on caspase-3 activity or apoptosis but do exacerbate the activation of caspase-3-like activity and subsequent cell death by apoptosis induced by inhibitors of 3-polyphosphoinositide synthesis. We suggest that multiple polyphosphoinositide pathways are involved in the regulation of apoptosis.
Assuntos
Apoptose/fisiologia , Gânglios Espinais/metabolismo , Fosfatos de Fosfatidilinositol/metabolismo , Transdução de Sinais/fisiologia , Androstadienos/farmacologia , Bradicinina/farmacologia , Caspase 3 , Caspases/efeitos dos fármacos , Caspases/metabolismo , Células Cultivadas , AMP Cíclico/metabolismo , Inibidores Enzimáticos/farmacologia , Entorpecentes/farmacologia , Fosfatidilinositol 3-Quinases/genética , Fosfatidilinositol 3-Quinases/metabolismo , Inibidores de Fosfoinositídeo-3 Quinase , Receptores Opioides/efeitos dos fármacos , WortmaninaRESUMO
Chronic exposure of embryonic brain to opioids leads to microcephaly and developmental abnormalities. An immortalized mouse neuroblastoma x dorsal root ganglion hybrid cell line stably transfected to overexpress kappa-opioid receptors (F-11kappa7) showed complete loss of kappa-receptor binding to [3H]U69,593 after exposure to the kappa-agonist U69,593 for 24 h. U69,593 had no measurable effect on cell viability as determined by either cell viability or DNA fragmentation assays. However, when cell death (apoptosis) was induced by either staurosporine or the phosphatidylinositol 3-kinase inhibitors wortmannin and LY294002, cells pretreated with U69,593 for 24 h showed increased apoptosis compared with untreated cells. Thus, staurosporine (50 nM), wortmannin (4 microM), and LY294002 (30 microM) treatment for 24 h induced a 50% loss of cell viability and DNA fragmentation in 24 h. U69,593 pretreatment produced the same killing at lower concentrations, namely, 20 nM staurosporine, 2 microM wortmannin, and 14 microM LY294002, respectively. The effects of U69,593 were time-, dose-, and naloxone-reversible, suggesting that they are receptor-mediated. However, coaddition of U69,593 at the same time as staurosporine, wortmannin, or LY294002 did not enhance apoptosis. All three drugs that induced apoptosis were found to increase the level of ceramide, and pretreatment with U69,593 further increased the rate of formation of ceramide, a lipid that induces apoptosis in cells. We propose that chronic exposure to kappa-receptor agonists promotes increased vulnerability of neurons to apoptosis.
Assuntos
Apoptose/efeitos dos fármacos , Benzenoacetamidas , Ceramidas/metabolismo , Entorpecentes/farmacologia , Receptores Opioides kappa/agonistas , Analgésicos/farmacologia , Androstadienos/farmacologia , Animais , Linhagem Celular Transformada/citologia , Linhagem Celular Transformada/efeitos dos fármacos , Sobrevivência Celular/efeitos dos fármacos , Ceramidas/biossíntese , Cromonas/farmacologia , DNA/análise , Fragmentação do DNA/efeitos dos fármacos , Relação Dose-Resposta a Droga , Inibidores Enzimáticos/farmacologia , Gânglios Espinais/citologia , Expressão Gênica/fisiologia , Camundongos , Morfolinas/farmacologia , Neuroblastoma , Neurônios/química , Neurônios/citologia , Neurônios/efeitos dos fármacos , Pirrolidinas/farmacologia , Receptores Opioides kappa/genética , Estaurosporina/farmacologia , Fatores de Tempo , WortmaninaRESUMO
The mechanism by which opiates affect fetal development is unknown, but one potential target is the programmed cell death (apoptosis) pathway of neurons. Apoptosis was induced in both primary neuronal cultures from embryonic day 7 cerebral hemispheres of chick brain (E7CH) and the F-11kappa7 cell line (an immortalized mouse neuroblastoma x dorsal root ganglion hybrid stably transfected to overexpress kappa-opioid receptors) by either staurosporine or the phosphatidylinositol 3-kinase inhibitors wortmannin and LY294002. Cells pretreated with either the mu-specific opioid agonist morphiceptin (E7CH) or the kappa-specific opioid agonist U69,593 (F-11kappa7) for 24 h showed increased apoptosis in response to staurosporine or wortmannin when compared with non-pretreated cells. The effects of morphiceptin and U69,593 were time- and dose-dependent and antagonist-reversible, suggesting that they were receptor-mediated. Neither morphiceptin nor U69,593 by themselves had any measurable effect on cell viability or DNA fragmentation, and coaddition of opiates at the same time as staurosporine, wortmannin, or LY294002 did not enhance apoptosis. Time course studies indicated a maximal opioid effect at a time (16-24 h) when inhibition of adenylate cyclase had been maximal for many hours. Addition of dibutyryl cyclic AMP either before or at the time of opioid addition protected against apoptosis and reduced fragmentation to levels seen for staurosporine plus dibutyryl cyclic AMP alone. The specificity for cyclic AMP was confirmed by showing protection with the specific agonist Sp-adenosine 3',5'-cyclic monophosphothioate and increased killing with the antagonist Rp-adenosine 3',5'-cyclic monophosphothioate. We conclude that the opioid enhancement of apoptosis is based on the inhibition of adenylate cyclase and that the effect is time-dependent.
Assuntos
Androstadienos/farmacologia , Apoptose/efeitos dos fármacos , Apoptose/fisiologia , Benzenoacetamidas , AMP Cíclico/fisiologia , Inibidores Enzimáticos/farmacologia , Entorpecentes/farmacologia , Neurônios/fisiologia , Estaurosporina/farmacologia , Androstadienos/antagonistas & inibidores , Animais , Linhagem Celular , Sobrevivência Celular/efeitos dos fármacos , Embrião de Galinha , AMP Cíclico/antagonistas & inibidores , Endorfinas/farmacologia , Camundongos , Pirrolidinas/farmacologia , Receptores Opioides kappa/agonistas , Estaurosporina/antagonistas & inibidores , WortmaninaRESUMO
Human glioma cell line U-373 MG expresses CMP-NeuAc : Galbeta1,3GlcNAc alpha2,3-sialyltransferase [EC No. 2.4.99.6] (alpha2,3ST), UDP-GlcNAc : beta-d-mannoside beta1,6-N-acetylglucosaminyltransferase V [EC 2.4.1.155] (GnT-V) and UDP-GlcNAc3: beta-d-mannoside beta1,4-N-acetylglucosaminyltransferase III [EC 2.4.1.144] (GnT-III) but not CMP-NeuAc : Galbeta1,4GlcNAc alpha2,6-sialyltransferase [EC 2.4.99.1] (alpha2,6ST) under normal culture conditions. We have previously shown that transfection of the alpha2,6ST gene into U-373 cells replaced alpha2,3-linked sialic acids with alpha2,6 sialic acids, resulting in a marked inhibition of glioma cell invasivity and a significant reduction in adhesivity. We now show that U-373 cells, which are typically highly resistant to cell death induced by chemotherapeutic agents (< 10% death in 18 h), become more sensitive to apoptosis following overexpression of these four glycoprotein glycosyltransferases. U-373 cell viability showed a three-fold decrease (from 20 to 60% cell death) following treatment with staurosporine, C2-ceramide or etoposide, when either alpha2,6ST and GnT-V genes were stably overexpressed. Even glycosyltransferases typically raised in cancer cells, such as alpha2,3ST and GnT-III, were able to decrease viability two-fold (from 20 to 40% cell death) following stable overexpression. The increased susceptibility of glycosyltransferase-transfected U-373 cells to pro-apoptotic drugs was associated with increased ceramide levels in Rafts, increased caspase-3 activity and increased DNA fragmentation. In contrast, the same glycosyltransferase overexpression protected U-373 cells against a different class of apoptotic drugs, namely the phosphatidylinositol 3-kinase inhibitor LY294002. Thus altered surface protein glycosylation of a human glioblastoma cell line can lead to lowered resistance to chemotherapeutic agents.
Assuntos
Glioma/enzimologia , Glicoconjugados/biossíntese , N-Acetilglucosaminiltransferases/genética , Sialiltransferases/genética , Esfingosina/análogos & derivados , Antineoplásicos/farmacologia , Caspase 3 , Caspases/metabolismo , Morte Celular/genética , Linhagem Celular Tumoral , Membrana Celular/metabolismo , Sobrevivência Celular/efeitos dos fármacos , Sobrevivência Celular/genética , Cromonas/farmacologia , Relação Dose-Resposta a Droga , Resistencia a Medicamentos Antineoplásicos/genética , Inibidores Enzimáticos/farmacologia , Etoposídeo/farmacologia , Glioma/genética , Glicosilação , Humanos , Morfolinas/farmacologia , N-Acetilglucosaminiltransferases/metabolismo , Oligossacarídeos/metabolismo , Sialiltransferases/metabolismo , Esfingosina/farmacologia , Estaurosporina/farmacologia , Transfecção , beta-D-Galactosídeo alfa 2-6-SialiltransferaseRESUMO
Oligodendroglial cells express many specific proteins, such as myelin basic protein (MBP), which are physiologically phosphorylated by protein kinase C (PKC). Diacylglycerols are physiological activators of PKC and can be liberated from phospholipids by the direct receptor-mediated activation of phospholipase C (PL-C) or indirectly via the activation of phospholipase D (PL-D). In a well-characterized human oligodendroglioma (HOG) cell line, PL-C (measured by release of [3H]inositol phosphates) and PL-D (formation of [3H]myristoylated or palmitoylated phosphatidylethanol) were activated by both carbachol (blocked by pirenzepine, suggesting an M1 receptor) and histamine (H1 receptor) but not glutamate, bradykinin, or phenylephrine. PL-C stimulation by carbachol or histamine was completely inhibited by short-term treatment (< 30 min) with phorbol ester (TPA), a PKC activator. In contrast, PL-D activation by either carbachol or histamine was stimulated in additive fashion by TPA, suggesting at least two distinct mechanisms for PL-D activation. Down regulation of PKC by prolonged (24 hr) treatment with TPA reversed the inhibitory effects of TPA on PL-C and the stimulatory effects on PL-D. However, the PKC inhibitors H-7 and galactosylsphingosine did not inhibit the TPA-mediated stimulation of PLD while the less-specific PKC inhibitor, staurosporine, was only partially inhibitory. Preexposure of cells to carbachol, greatly reduced both PL-C and PL-D activation by carbachol, suggesting homologous desensitization. Time-course studies indicated that PL-D activation (10 sec or less) was at least as fast as PL-C activation, and the affinity of carbachol and histamine for the receptor coupled to either phospholipase (EC50 = 5-10 microM) was about the same.(ABSTRACT TRUNCATED AT 250 WORDS)
Assuntos
Neoplasias do Sistema Nervoso/enzimologia , Oligodendroglioma/enzimologia , Fosfolipase D/metabolismo , Alcaloides/farmacologia , Carbacol/farmacologia , Cromatografia em Camada Fina , Regulação para Baixo/efeitos dos fármacos , Ativação Enzimática/efeitos dos fármacos , Histamina/farmacologia , Humanos , Hidrólise , Fosfatos de Inositol/metabolismo , Palmitatos/metabolismo , Ésteres de Forbol/farmacologia , Proteína Quinase C/antagonistas & inibidores , Estaurosporina , Células Tumorais Cultivadas , Fosfolipases Tipo C/metabolismoRESUMO
An immortalized dorsal root ganglion cell line F-11 exhibits many properties of spinal cord neurons and undergoes apoptosis in response to growth factor withdrawal and the exogenous addition of inhibitors of phosphatidylinositol-3-kinase (PI3K). To elucidate the mechanism of apoptosis we generated F-11 clones which overexpressed either the p110 subunit of PI3K, a constitutively active form of protein kinase B/Akt (Myristoylated Akt), or a dominant-negative form (c-Akt). The first two constructs were protective against apoptosis induced by PI3K inhibitors such as wortmannin and LY294002. Caspase-3 (CPP32) levels peaked at 4 hr to 6 hr in response to pro-apoptotic drugs, and this increase was attenuated by 50% in F-11 with constitutively active Akt. The Akt protection was confirmed by DNA fragmentation studies. Both neo-transfected and the c-Akt dominant-negative transfected F-11 cells showed increased ceramide formation (twofold) in response to staurosporine, wortmannin, or LY294002; whereas cells with a constitutively active Akt (Myr-Akt) showed no increase in ceramide when treated with staurosporine, wortmannin, or LY294002. Ceramide was a more potent activator of CPP32 and an inducer of apoptosis when added as the native form (hydroxy- or nonhydroxy-), rather than the more water-soluble C(2)-ceramide. Overexpression of PI3K (p110) and Akt protected cells against ceramide-induced apoptosis, suggesting that Ceramide action is upstream of Akt in these cells and suggesting that Akt might be a target for inhibition by ceramide. Both staurosporine and C(2)-ceramide activated the Jun kinase (JNK) cascade and C(2)-ceramide increased caspase-3 (CPP32) activity in cells expressing wild-type c-Jun, but not dominant-negative (TAM-67) c-Jun. We suggest that this pathway is also involved in apoptosis, consistent with the idea that ceramide has multiple kinase and kinase-modulating targets in the apoptotic pathway of neurons. J. Neurosci. Sci. 57:884-893, 1999.