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P Erhardt

Publications and source records attributed to P Erhardt.

At least 19 recordsLinked to original sources
PubMed1998

Intact Ras function is required for sustained activation and nuclear translocation of extracellular signal-regulated kinases in nerve growth factor-stimulated PC12 cells.

PC12 pheochromocytoma cell lines expressing the dominant negative Ha-Ras Asn-17 protein at different levels were used in this study to analyze the relationship between nerve growth factor (NGF)-induced activation of members of the mitogen-activated protein kinase (MAPK) family, and neuritogenesis. In wild-type PC12 cells, NGF rapidly stimulated the extracellular signal-regulated kinases (ERKs). Kinase activation was sustained and was followed by the translocation of ERK 1 and ERK 2 into the nucleus ultimately leading to neurite outgrowth. In cells expressing relatively high levels of the inhibitory Ras protein, NGF stimulation of ERK 1 and ERK 2 as well as nuclear translocation of these protein kinases were greatly inhibited. In contrast, in PC12 subclones expressing low amounts of Ha-Ras Asn-17 the peak of ERK activation was only slightly reduced, but became transient in nature and was not followed by nuclear translocation of ERKs 1 and 2. Since all PC12 subclones expressing detectable levels of the dominant inhibitory Ras protein are resistant to NGF induction of neurite formation, our observations support the notion that sustained activation and translocation of ERKs into the nucleus are essential for NGF-induced neuronal differentiation of PC12 cells.

Animals↗
PubMed1997

Identification of the MDM2 oncoprotein as a substrate for CPP32-like apoptotic proteases.

Programmed cell death is mediated by members of the interleukin 1-beta convertase family of proteases, which are activated in response to diverse cell death stimuli. However, the key substrates of these proteases that are responsible for apoptotic cell death have not been identified. Here we report that the MDM2 oncoprotein is cleaved by members of the CPP32 subfamily of interleukin 1-beta convertase proteases both in vitro and in vivo, resulting in the disappearance of MDM2 from apoptotic cells. Because MDM2 functions as a negative regulator of the p53 tumor suppressor and because p53 induces apoptosis in response to a variety of stimuli, this cleavage of MDM2 by CPP32-like proteases may result in deregulation of p53 and contribute directly to the process of apoptotic cell death.

Amino Acid Sequence↗
PubMed1997

p53-dependent induction of apoptosis by proteasome inhibitors.

Proteolysis by the ubiquitin/proteasome pathway controls the intracellular levels of a number of proteins that regulate cell proliferation and cell cycle progression. To determine whether this pathway of protein turnover was also linked to apoptosis, we treated Rat-1 and PC12 cells with specific proteasome inhibitors. The peptide aldehydes PSI and MG115, which specifically inhibit the chymotrypsin-like activity of the proteasome, induced apoptosis of both cell types. In contrast, apoptosis was not induced by inhibitors of lysosomal proteases or by an alcohol analog of PSI. The tumor suppressor p53 rapidly accumulated in cells treated with proteasome inhibitors, as did the p53-inducible gene products p21 and Mdm-2. In addition, apoptosis induced by proteasome inhibitors was inhibited by expression of dominant-negative p53, whereas overexpression of wild-type p53 was sufficient to induce apoptosis of Rat-1 cells in transient transfection assays. Although other molecules may also be involved, these results suggest that stabilization and accumulation of p53 plays a key role in apoptosis induced by proteasome inhibitors.

Animals↗
PubMed1997

Adenovirus-mediated gene transfer of dominant negative ras(asn17) in 3T3L1 adipocytes does not alter insulin-stimulated P13-kinase activity or glucose transport.

Recent studies suggest that the ras-map kinase and PI3-kinase cascades converge. We sought to determine whether PI3-kinase is downstream of ras in insulin signaling in a classic insulin target cell. We generated a recombinant adenovirus encoding dominant negative ras by cloning the human H-ras cDNA with a ser to asn substitution at amino acid 17 (ras(asn17)) into the pACCMVpLpA vector and cotransfecting 293 cells with the pJM17 plasmid containing the adenoviral genome. Efficiency of gene transfer was assessed by infecting fully differentiated 3T3L1 adipocytes with a recombinant adenovirus expressing beta-galactosidase (beta-gal); greater than 70% of cells were infected. Infection of adipocytes with ras(asn17) resulted in 10-fold greater expression than endogenous ras. This high efficiency gene transfer allowed biochemical assays. Insulin stimulation of ras-GTP formation was inhibited in ras(asn17)-expressing cells. Map kinase gel mobility shift revealed that insulin (1 UM) or epidermal growth factor (100 ng/ml) resulted in the appearance of a hyperphosphorylated species of p42 map kinase in uninfected cells and those expressing beta-gal but not in cells expressing ras(asn17). In contrast, insulin increased IRS-1-associated PI3-kinase activity approximately 10-fold in control cells and high level overexpression of ras(asn17) did not impair this effect. Similarly, insulin and epidermal growth factor activation of total (no immunoprecipitation) PI3-kinase activity in both cytosol and total cellular membranes and insulin stimulation of glucose transport were not affected by expression of dominant negative ras. Thus, adenovirus-mediated gene transfer is effective for studying insulin signaling in fully differentiated insulin target cells. Inhibition of ras activation abolishes insulin-stimulated phosphorylation of map kinase but does not affect insulin stimulation of PI3-kinase activity. In normal cell physiology, PI3-kinase does not appear to be downstream of ras in mediating the actions of insulin.

1-Methyl-3-isobutylxanthine↗
PubMed1997

Estimating xenobiotic half-lives in humans from rat data: influence of log P.

The nature of empirical allometric expressions relating dispositional and kinetic parameters for a given xenobiotic across multiple mammalian species is well known. It has also been demonstrated that a simple allometric relationship may be used to predict kinetic parameters for humans based merely on data for multiple xenobiotics from rats. We decided to explore reasons for the variance in the data arising from the latter method. We were particularly interested in learning whether any physicochemical characteristics of xenobiotics might account for outlying data points (i.e., poor prediction of human half-life from rat half-life). We have explored the influence of lipid solubility as reflected by a xenobiotic's log P value because adipose tissue comprises a significantly larger percentage of total body weight in humans than in rats. We used half-life data from the literature for 127 xenobiotics. A data subset of 102 xenobiotics for which we were able to find estimates of log P values, including several with extremely large log P values, was also analyzed. First and second order models, including and excluding log P, were compared. The simplest of these models can be recast as the familiar allometric relationship having the form Y = a(Xb). The remaining models can be seen as extensions of this relationship. Our results suggest that incorporation of log P into the prediction of xenobiotic half-life in humans from rat half-life data is important only for xenobiotics with extremely large log P values such as dioxins and polychlorinated biphenyls. Moreover, a second order model in logarithm of rat half-life accommodates all data points very well, without specifically accounting for log P values.

Animals↗
PubMed1996

Activation of the CPP32 apoptotic protease by distinct signaling pathways with differential sensitivity to Bcl-xL.

In the absence of growth factors, many types of mammalian cells undergo apoptosis. We and others have shown recently that growth factors promote cell survival by activating phosphatidylinositol 3-kinase (PI 3-kinase) in several cell types. In the present study, we have compared downstream elements of the apoptotic pathways induced by PI 3-kinase inhibitors and other stimuli. In U937 cells, both PI 3-kinase inhibitors (wortmannin and LY294002) and etoposide activated the CPP32 apoptotic protease by cleavage to active p17 subunits. In contrast, treatment with tumor necrosis factor alpha (TNFalpha) resulted in the accumulation of a distinct active CPP32 subunit, p20. Furthermore, overexpression of Bcl-xL blocked DNA fragmentation, CPP32 activation and cleavage of poly(ADP-ribose) polymerase in U937 cells treated with both PI 3-kinase inhibitors and etoposide, but not in cells treated with TNFalpha. Distinct patterns of CPP32 activation and differential sensitivities to Bcl-xL thus distinguish the cell death pathways activated by PI 3-kinase inhibition and DNA damage from that activated by TNFalpha.

Androstadienes↗
PubMed1995

Differential regulation of Raf-1 and B-Raf and Ras-dependent activation of mitogen-activated protein kinase by cyclic AMP in PC12 cells.

Growth factor stimulation of the mitogen-activated protein (MAP) kinase pathway in fibroblasts is inhibited by cyclic AMP (cAMP) as a result of inhibition of Raf-1. In contrast, cAMP inhibits neither nerve growth factor-induced MAP kinase activation nor differentiation in PC12 pheochromocytoma cells. Instead, in PC12 cells cAMP activates MAP kinase. Since one of the major differences between the Ras/Raf/MAP kinase cascades of these cell types is the expression of B-Raf in PC12 cells, we compared the effects of cAMP on Raf-1 and B-Raf. In PC12 cells maintained in serum-containing medium, B-Raf was refractory to inhibition by cAMP, whereas Raf-1 was effectively inhibited. In contrast, both B-Raf and Raf-1 were inhibited by cAMP in serum-starved PC12 cells. The effect of cAMP is thus dependent upon growth conditions, with B-Raf being resistant to cAMP inhibition in the presence of serum. These results were extended by studies of Rat-1 fibroblasts into which B-Raf had been introduced by transfection. As in PC12 cells, B-Raf was resistant to inhibition by cAMP in the presence of serum, whereas Raf-1 was effectively inhibited. In addition, the expression of B-Raf rendered Rat-1 cells resistant to the inhibitory effects of cAMP on both growth factor-induced activation of MAP kinase and mitogenesis. These results indicate that Raf-1 and B-Raf are differentially sensitive to inhibition by cAMP and that B-Raf expression can contribute to cell type-specific differences in the regulation of the MAP kinase pathway. In contrast to the situation in PC12 cells, cAMP by itself did not stimulate MAP kinase in B-Raf-expressing Rat-1 cells. The activation of MAP kinase by cAMP in PC12 cells was inhibited by the expression of a dominant negative Ras mutant, indicating that cAMP acts on a target upstream of Ras. Thus, it appears that a signaling component upstream of Ras is also require for cAMP stimulation of MAP kinase in PC12 cells.

Animals↗
PubMed1994

Complete coding sequence, deduced primary structure, chromosomal localization, and structural analysis of murine aggrecan.

We have isolated and sequenced overlapping cDNA clones encoding the entire core protein of aggrecan (the large aggregating chondroitin sulfate/keratan sulfate proteoglycan of cartilage) from three chondrocyte cDNA libraries of BALB/c mice and localized the aggrecan gene in mouse chromosome 7. We determined 7386 bp of the cDNA sequence, including 132 and 854 nucleotides of 5' and 3' untranslated regions, respectively. The core protein precursor is 2132 amino acids long (M(r) 222,008), including a 19-residue secretory signal peptide. The overall amino acid sequence of the mouse aggrecan shows 91.6% identity to rat and 72.5% to human aggrecan. Comparison of the amino acid sequences of various domains and subdomain structures of mouse aggrecan to known sequences of other species and related proteins (versican, neurocan, link protein, and lymphocyte homing receptor CD44) revealed high levels of identity of the G1, G2, and G3 globular domains and relatively less conserved structures in the interglobular and glycosaminoglycan-attachment regions. Epidermal growth factor (EGF)-like module was detected in only a minor fraction of aggrecan clones, while the complement regulatory protein (CRP)-like domain was regularly expressed in all samples.

Aggrecans↗
PubMed1993

ras-independent induction of rat brain type II sodium channel expression in nerve growth factor-treated PC12 cells.

Nerve growth factor (NGF) plays an important role in the development of the nervous system, and there is considerable interest in understanding the molecular mechanisms underlying its effects on neuronal differentiation. To determine if the activity of proteins of the ras gene family is necessary for the NGF-mediated induction of sodium channel expression in pheochromocytoma (PC12) cells, sodium channel expression was analyzed in PC12 sublines stably overexpressing the dominant inhibitory mutant c-Ha-ras(Asn-17). Northern blot analysis, RNase protection assays, and whole-cell patch clamp recordings indicate that the NGF-mediated increase in type II sodium channel mRNA and sodium current density can occur independent of ras activity and by doing so provide strong evidence for the importance of ras-independent mechanisms in NGF-mediated neuronal differentiation.

Amino Acid Sequence↗
PubMed1993

Hydrolysis of phosphatidylcholine couples Ras to activation of Raf protein kinase during mitogenic signal transduction.

We have investigated the relationship between hydrolysis of phosphatidylcholine (PC) and activation of the Raf-1 protein kinase in Ras-mediated transduction of mitogenic signals. As previously reported, cotransfection of a PC-specific phospholipase C (PC-PLC) expression plasmid bypassed the block to cell proliferation resulting from expression of the dominant inhibitory mutant Ras N-17. In contrast, PC-PLC failed to bypass the inhibitory effect of dominant negative Raf mutants, suggesting that PC-PLC functions downstream of Ras but upstream of Raf. Consistent with this hypothesis, treatment of quiescent cells with exogenous PC-PLC induced Raf activation, even when normal Ras function was blocked by Ras N-17 expression. Further, activation of Raf in response to mitogenic growth factors was blocked by inhibition of endogenous PC-PLC. Taken together, these results indicate that hydrolysis of PC mediates Raf activation in response to mitogenic growth factors.

3T3 Cells↗
PubMed1992

Hydrolysis of phosphatidylcholine is stimulated by Ras proteins during mitogenic signal transduction.

We have used a dominant inhibitory ras mutant (Ha-ras Asn-17) to investigate the relationship of Ras proteins to hydrolysis of phosphatidylcholine (PC) in the transduction of mitogenic signals. Expression of Ha-Ras Asn-17 inhibited NIH 3T3 cell proliferation induced by polypeptide growth factors or phorbol esters. In contrast, the mitogenic activity of PC-specific phospholipase C (PC-PLC) was not inhibited by Ha-Ras Asn-17 expression. Similarly, cotransfection with a cloned PC-PLC gene bypassed the block to NIH 3T3 cell proliferation resulting from expression of the inhibitory ras mutant. Hydrolysis of PC can therefore induce cell proliferation in the absence of normal Ras activity, suggesting that PC-derived second messengers may act downstream of Ras in mitogenic signal transduction. This was substantiated by the finding that Ha-Ras Asn-17 expression inhibited growth factor-stimulated hydrolysis of PC. Taken together, these results indicate that PC hydrolysis is a target of Ras during the transduction of growth factor-initiated mitogenic signals.

3T3 Cells↗
PubMed1992

Role of Ras in signal transduction from the nerve growth factor receptor: relationship to protein kinase C, calcium and cyclic AMP.

A dominant inhibitory ras mutant (Ha-ras Asn-17) has been used to investigate the role of Ras in nerve growth factor (NGF)-mediated signal transduction in PC12 cells. Expression of Ha-Ras Asn-17 blocks neuronal differentiation of these cells in response to NGF treatment. The Ha-Ras Asn-17 block was bypassed by treatment with NGF plus dibutyryl cAMP or NGF plus the Ca2+ ionophore ionomycin, but not by NGF plus 12-O-tetradecanoyl phorbol acetate (TPA). Direct stimulation of the cAMP or Ca2+ pathways thus appeared to act synergistically with a Ras-independent NGF signaling pathway. This Ras-independent pathway was also distinct from protein kinase C, since its activity was not affected by protein kinase C down-regulation. It thus appears that NGF stimulation generates a Ras-independent intracellular signal that contributes to neuronal differentiation independently of the cAMP, Ca2+ or protein kinase C second messenger systems. Since TPA did not bypass the Ha-Ras Asn-17 block to differentiation, protein kinase C also did not appear to be sufficient for Ras-dependent pathways mediating NGF-induced differentiation. Down-regulation experiments further indicated that protein kinase C was not required for NGF induction of early response genes via either Ras-dependent or Ras-independent pathways. Moreover, the formation of inositol phosphates and mobilization of intracellular calcium in response to NGF was not inhibited in PC12 cells expressing the Ha-Ras Asn-17 protein. Therefore, although calcium was able to bypass the Ha-Ras Asn-17 block to PC12 differentiation, Ras activity was not required for activation of phospholipase C in response to NGF. It thus appears that both Ras-dependent and Ras-independent signaling pathways contribute to NGF-induced PC12 cell differentiation independently of the cAMP, calcium and protein kinase C second messenger systems.

Animals↗
PubMed1991

Areca-nut toxicity in cultured human buccal epithelial cells.

In cultured human buccal epithelial cells, at doses of 3-540 micrograms/ml, areca-nut extract significantly decreased viability, as determined by colony-forming efficiency, clonal growth rate, ability to take up neutral red and ability to exclude trypan blue, and also caused significant formation of DNA single-strand breaks and DNA protein cross-links. Comparisons of the areca nut-related compounds, 3-(N-nitrosomethylamino)propion-aldehyde (NMPA), 3-(N-nitrosomethylamino)propionitrile (NMPN), N-nitrosoguvacoline, N-nitrosoguvacine, arecoline, arecaidine, guvacoline and guvacine, in terms of the above endpoints, indicate that NMPA is ten times more cytopathic to buccal cells than the other agents on a molar basis. Because metabolism of NMPA can potentially yield several reactive breakdown products, including aldehydes, this study indicates that both the parent compound and its metabolites may contribute to the observed pathobiological effects. Taken together, the observed pathobiological effects of areca-nut extract and certain related compounds in cultured human buccal epithelial cells indicate that these agents may contribute to the oral carcinogenicity associated with chewing betel quid.

Areca↗
PubMed1983

Glucose polymer supplementation of feeds for very low birthweight infants.

The feeds of 14 very low birthweight infants (birth weight less than 1500 g) were supplemented with a glucose polymer (Caloreen) at the rate of 6 g/kg body weight daily. Seven day periods of supplementation were alternated with seven day periods of normal feeding. Adding the glucose polymer significantly increased the rate of weight gain in these infants from 105 g/week to 140 g/week; growth rates in terms of length and head circumference were not affected. No adverse effects were noted. Glucose polymer is a useful energy supplement for very low birthweight infants.

Body Weight↗
PubMed1980

GLC determination of bretylium in biological fluids.

Bretylium [(o-bromobenzyl)ethyldimethylamine] is a quaternary ammonium compound used as the tosylate salt for treatment of ventricular fibrillation in humans. A sensitive assay was developed for the determination of low bretylium concentrations in plasma and urine. The internal standards were (p-bromobenzyl)ethyldimethylammonium p-toluenesulfonate and (o-methoxybenzyl)ethyldimethylammonium p-toluenesulfonate. Samples were deproteinized with acetonitrile and extracted with methylene chloride. After the evaporation of the organic phase, the residue was reacted with sodium 2,4,5-trichlorothiophenolate in methanol. This procedure yielded volatile compounds with excellent electron-capture capabilities for the GLC analysis. The assay sensitivity is 5 ng/ml. The extraction recovery of bretylium as determined by a direct radioactivity measurement was 90 and 97% for plasma and urine, respectively. The method is highly reproducible with no significant day-to-day variations. Comparisons of 60 standard plasma samples, 25 standard urine samples, and plasma samples from a dog that received [14C]bretylium showed excellent agreement between the GLC method and direct radioactivity measurement of bretylium.

Animals↗