A computer-aided design tool for biomedical OBT sensor tuning in cell-culture assays

BACKGROUND AND OBJECTIVES

The biomedical engineering must frequently develop sensor designs by including information from performance of bio-samples (cell cultures or tissues), technical specifications of transducers, and constrains from electronic circuits. A computer program for real-time cell culture monitoring system design is developed; analyzing, modelling and integrating into the program design flow the electrodes, cell culture and test circuit's influences.

METHODS

The computer tool, first, generates an equivalent electric circuit model for the cell-electrode bio-systems based on the area covered by cells, which also considers the cell culture dynamics. Second, proposes an Oscillation Based Test (OBT) parameterized circuit, for Electrical Cell-Substrate Sensing (ECIS) measurements of the cell culture system bioimpedance. Third, simulates electrically the full system to define the best system parameter values for the sensor.

RESULTS

Reported experimental results are based on commercial gold electrodes and the AA8 cell line. Characteristics of the cell lines, as time-division or cell size, are incorporated into the program design flow, showing that for a given assay, the optimal OBT circuit parameters can be selected with the help of the computer tool. The electrical simulations of the full system demonstrate that the can be correctly predicted the output frequency and amplitude ranges of the voltage response, obtaining accurate results when cell culture approaches to confluence phase.

CONCLUSION

It is proposed a computer program for system design of biosensors applied to monitoring cell culture dynamics. The program allows obtaining confident system information by electrical stimulation. All system components (electrodes, cell culture and test circuits) are properly modelled. The employed procedure can be applied to any other 2D electrode layout or alternative circuit technique for ECIS test. Finally, deep insight information on cell size, number, and time-division can be extracted from the comparison with real cell culture assays in the future.

Relevance of the serial position effect in the differential diagnosis of mild cognitive impairment, Alzheimer-type dementia, and normal ageing

Serial position effects are observed when a person memorises a series of words exceeding his or her attention span. Cognitively normal individuals recall words at the beginning and end of the list more frequently than those in the middle, which reflects the way that short- and long-term episodic memory works.

OBJECTIVE

To study the serial position effect in patients with mild cognitive impairment (MCI) compared to subjects with Alzheimer-type dementia (AD) or normal ageing (NA).

METHODS

30 AD, 25 MCI and 20 NA subjects underwent neurological and neuropsychological assessment. The Rey Auditory Verbal Learning Test (RAVLT) was used to study primacy, middle, and recency effects and delayed recall for each group.

RESULTS

The general memory pattern of MCI subjects was very similar to that of AD subjects, and was characterised by reduced learning capacity, rapid forgetfulness and clear recency effect in learning. With regard to delayed recall, however, there were differences in performance; MCI subjects' ability to recall words at the beginning and middle of the list was similar to that of normal subjects, while their memory of words at the end of the list was poor, as in AD subjects.

CONCLUSIONS

RAVLT is a tool permitting us to distinguish between MCI and NA subjects. The recency index for the delayed recall task is a valid indicator for distinguishing between MCI patients and patients with normal ageing.

Comparison of three effective Hamiltonian models of increasing complexity: Triazene in water as a test case

A critical comparison of widely used solvation models is reported. It is illustrated by a study of the triazene molecule in liquid water. We consider the following approaches: (1) a continuum model based on multicentric multipole expansions of the charge distribution, (2) the averaged solvent electrostatic potential from molecular dynamics (ASEP/MD) method, and (3) molecular dynamics simulations using a combined quantum mechanics/molecular mechanics potential (QM/MM/MD). We find that the solvation induces appreciable changes in the geometry and charge distribution of triazene. These changes are only qualitatively reproduced by the dielectric continuum model, which clearly underestimates induced dipole moments and solute-solvent interaction energy. We also show that the use of effective point charges placed on solute nuclei during the classical simulations may cause significant errors in the description of the solvent structure. The addition of charges representing nitrogen atom lone pairs is compulsory to reproduce the QM/MM/MD simulation results. Moreover, our results validate the use of the mean field approximation in the study of solvent effects. A major conclusion of this study is that the ASEP/MD method constitutes a reliable alternative to the much more computationally demanding QM/MM/MD methods.

N-acetyl-cysteine abolishes hydrogen peroxide-induced modification of eukaryotic initiation factor 4F activity via distinct signalling pathways

During the oxidative stress generated by hydrogen peroxide (H2O2) in nerve growth factor (NGF)-differentiated PC12 cells, eIF4E binding protein (4E-BP1) and initiation factor 4E (eIF4E) phosphorylated levels decrease significantly, and an enhancement of the association of 4E-BP1 to eIF4E, which in turn decreases eIF4F formation is observed. The treatment with N-acetyl-cysteine (NAC) completely abolishes the H2O2-induced decrease in eIF4E phosphorylated levels, whereas the decrease in 4E-BP1 phosphorylated levels and eIF4F activity inhibition are significantly but not fully reversed. Rapamycin, the mammalian target of rapamycin (FRAP/mTOR) inhibitor, prevents the effect of NAC on H2O2-induced eIF4F complex formation inhibition. Besides the inhibitor induces a similar decrease in 4E-BP1 phosphorylated levels to that promote by H2O2. However, rapamycin has no effect on the NAC-induced recovery in phosphorylated eIF4E levels. Neither the MAP kinase inhibitors, PD98056 and SB203580, or the protein phosphatase 2A inhibitor, okadaic acid, mimic NAC effect on the H2O2-induced eIF4E dephosphorylation. Altogether our findings suggest that the effects caused by oxidative stress on eIF4s factors depends on two MAP kinase-independent signal transduction pathways, being at least one of them rapamycin-dependent.

A theoretical study of solvent effects on the 1(n→π*) electron transition in acrolein

The (1)(n-->pi(*)) electron transition of acrolein in liquid water was studied theoretically by using the averaged solvent electrostatic potential/molecular dynamics method. The model combines a multireference perturbational treatment in the description of the solute molecule with molecular dynamics calculations in the description of the solvent. We demonstrate the importance of the solvent electron polarization, bulk solvent effects, and the use of relaxed geometries in solution on the calculated solvent shift. It is also shown that the inclusion of the dynamic correlation does not change the solvent shift although it must be used to reproduce the transition energy.

Does phosphorylation of eukaryotic elongation factor eEF2 regulate protein synthesis in ischemic preconditioning?

Ischemia/reperfusion-associated translation inhibition in the hippocampus is attenuated significantly at reinitiation and elongation steps by ischemic preconditioning (Burda et al. [2003] Neurochem. Res. 28:1237-1243). To address potential regulation of the elongation step by changes in eukaryotic elongation factor 2 (eEF2) phosphorylation with and without acquired ischemic tolerance (IT), Wistar rats were preconditioned by 5-min sublethal ischemia and 2 days later, 30-min lethal ischemia was induced. Given the important role that oxidative stress plays in the ischemic process, eEF2 phosphorylation was also studied in a model of oxidative stress in vitro. Three blocks of our results support a lack of correlation between eEF2 phosphorylation status and protein synthesis rate. First, eEF2 was dephosphorylated significantly (activated) after transient cerebral ischemia in rats with and without IT or H2O2-treated cells; however, protein synthesis was significantly inhibited under these three conditions. Second, after 30-min reperfusion, the protein synthesis rate was maintained below control levels in cortex and hippocampus of rats without IT. Eukaryotic EF2 phosphorylated levels were notably low only in the cortex, whereas levels in the hippocampus were close to that of sham controls. In rats with IT, protein synthesis was virtually restored in both brain regions, but phosphorylated eEF2 levels were even higher than in rats without IT. Third, after 4-hr reperfusion, the protein synthesis rate in cortex and hippocampus was observed to be below sham control values in rats with and without IT. Conversely, phosphorylated eEF2 levels were below sham control in rats with IT and reached sham control values in rats without IT.

A new method to locate saddle points for reactions in solution by using the free-energy gradient method and the mean field approximation

A new method for calculating saddle points of reactions in solution is presented. The main characteristics of the method are: (1) the solute-solvent system is described by the averaged solvent electrostatic potential/molecular dynamics method (ASEP/MD). This is a quantum mechanics/molecular mechanics method (QM/MM) that makes use of the mean field approximation (MFA) and that permits one to simultaneously optimize the electronic structure and geometry of the solute molecule and the solvent structure around it. (2) The transition state is located by the joint use of the free-energy gradient method and the mean field approximation. An application to the study of the Menshutkin reaction between NH(3) and CH(3)Cl in aqueous solution is discussed. The accuracy and usefulness of the proposed method is checked through comparison with other methods.

Reversible inhibition of the protein phosphatase 1 by hydrogen peroxide. Potential regulation of eIF2 alpha phosphorylation in differentiated PC12 cells

Oxidative inactivation of protein tyrosine phosphatases and calcineurin is a well established mechanism; however, little information with regard to the effect of oxidants on PP1 and PP2A activity is available. Herein, we show that PP1 activity is inhibited by H(2)O(2) treatment in differentiated PC12 cells both in vitro and in vivo experiments. Thiol-antioxidant N-acetyl-cysteine (NAC) and reduced glutathione (GSH), when added in vitro to lysates from H(2)O(2)-treated cells, reversed PP1 inhibition. H(2)O(2) treatment increased eIF2 alpha phosphorylated levels (eIF2 alpha P) in a time- and dose-dependent fashion and promoted protein synthesis inhibition. Interestingly, NAC pretreatment protected cells from H(2)O(2)-induced PP1 inactivation and, consequently, it abolished increased H(2)O(2)-induced eIF2 alpha phosphorylation and protein synthesis inhibition. In addition, PP1 inhibitor tautomycin prevented both NAC-induced PP1 reactivation and eIF2 alpha P dephosphorylation in H(2)O(2)-treated cells. Taken together, our findings support a role for PP1 in eIF2 alpha phosphorylation and oxidative stress-triggered translation down regulation.

Possible mechanisms involved in the down-regulation of translation during transient global ischaemia in the rat brain

The striking correlation between neuronal vulnerability and down-regulation of translation suggests that this cellular process plays a critical part in the cascade of pathogenetic events leading to ischaemic cell death. There is compelling evidence supporting the idea that inhibition of translation is exerted at the polypeptide chain initiation step, and the present study explores the possible mechanism/s implicated. Incomplete forebrain ischaemia (30 min) was induced in rats by using the four-vessel occlusion model. Eukaryotic initiation factor (eIF)2, eIF4E and eIF4E-binding protein (4E-BP1) phosphorylation levels, eIF4F complex formation, as well as eIF2B and ribosomal protein S6 kinase (p70(S6K)) activities, were determined in different subcellular fractions from the cortex and the hippocampus [the CA1-subfield and the remaining hippocampus (RH)], at several post-ischaemic times. Increased phosphorylation of the alpha subunit of eIF2 (eIF2 alpha) and eIF2B inhibition paralleled the inhibition of translation in the hippocampus, but they normalized to control values, including the CA1-subfield, after 4--6 h of reperfusion. eIF4E and 4E-BP1 were significantly dephosphorylated during ischaemia and total eIF4E levels decreased during reperfusion both in the cortex and hippocampus, with values normalizing after 4 h of reperfusion only in the cortex. Conversely, p70(S6K) activity, which was inhibited in both regions during ischaemia, recovered to control values earlier in the hippocampus than in the cortex. eIF4F complex formation diminished both in the cortex and the hippocampus during ischaemia and reperfusion, and it was lower in the CA1-subfield than in the RH, roughly paralleling the observed decrease in eIF4E and eIF4G levels. Our findings are consistent with a potential role for eIF4E, 4E-BP1 and eIF4G in the down-regulation of translation during ischaemia. eIF2 alpha, eIF2B, eIF4G and p70(S6K) are positively implicated in the translational inhibition induced at early reperfusion, whereas eIF4F complex formation is likely to contribute to the persistent inhibition of translation observed at longer reperfusion times.

Carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) induces initiation factor 2 alpha phosphorylation and translation inhibition in PC12 cells

We have investigated the effect of the mitochondrial uncoupler carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) on protein synthesis rate and initiation factor 2 (eIF2) phosphorylation in PC12 cells differentiated with nerve growth factor. FCCP treatment induced a very rapid 2-fold increase in intracellular Ca(2+) concentration that was accompanied by a strong protein synthesis rate inhibition (68%). The translation inhibition correlated with an increased phosphorylation of the alpha subunit of eIF2 (eIF2 alpha) (25% vs. 7%, for FCCP-treated and control cells, respectively) and a 1.7-fold increase in the double-stranded RNA-dependent protein kinase activity. No changes in the PKR endoplasmic reticulum-related kinase or eIF2 alpha phosphatase were found. Translational regulation may play a significant role in the process triggered by mitochondrial calcium mobilization.

Ischemia-induced phosphorylation of initiation factor 2 in differentiated PC12 cells: role for initiation factor 2 phosphatase

An in vitro model of ischemia was obtained by subjecting PC12 cells differentiated with nerve growth factor to a combination of glucose deprivation plus anoxia. Immediately after the ischemic period, the protein synthesis rate was significantly inhibited (80%) and western blots of cell extracts revealed a significant accumulation of phosphorylated eukaryotic initiation factor 2, alpha subunit, eIF2(alphaP) (42%). Upon recovery, eIF2(alphaP) levels returned to control values after 30 min, whereas protein synthesis was still partially inhibited (33%) and reached almost control values within 2 h. The activities of the mammalian eIF2alpha kinases, double-stranded RNA-activated protein kinase, mammalian GCN2 homologue, and endoplasmic reticulum-resident kinase, were determined. None of the eIF2alpha kinases studied showed increased activity in ischemic cells as compared with controls. Exposure of cells to cell-permeable inhibitors of protein phosphatases 1 and 2A, calyculin A or tautomycin, induced dose- and time-dependent accumulation of eIF2(alphaP), mimicking an ischemic effect. Protein phosphatase activity, as measured with [(32)P]phosphorylase a as a substrate, diminished during ischemia and returned to control levels upon 30-min recovery. In addition, the rate of eIF2(alphaP) dephosphorylation was significantly lower in ischemic cells, paralleling both the greatest translational inhibition and the highest eIF2(alphaP) levels. The endogenous phosphatase activity from control and ischemic extracts showed different sensitivity to inhibitor 2 and fostriecin in in vitro assays, inhibitor-2 effect in ischemic cells being lower than in control cells. Together these results indicate that an eIF2alpha phosphatase, probably protein phosphatase 1, is implicated in the ischemia-induced eIF2(alphaP) accumulation in PC12 cells.

Ischaemia induces changes in the association of the binding protein 4E-BP1 and eukaryotic initiation factor (eIF) 4G to eIF4E in differentiated PC12 cells

Ischaemia was obtained in vitro by subjecting nerve-growth-factor-differentiated PC12 cells to glucose deprivation plus anoxia. During ischaemia the rate of protein synthesis was significantly inhibited, and eIF4E-binding protein (4E-BP1) and eukaryotic initiation factor 4E (eIF4E) were significantly dephosphorylated in parallel. In addition, ischaemia induced an enhancement of the association of 4E-BP1 to eIF4E, which in turn decreased eIF4F formation, whereas no degradation of initiation factor 4G was observed. The treatment of PC12 cells with the specific p38 mitogen-activated protein kinase inhibitor SB203580 induced eIF4E dephosphorylation but did not cause any effect on protein synthesis rate. Rapamycin, the inhibitor of mammalian target of rapamycin ('mTOR'), but not PD98059, the inhibitor of extracellular signal-regulated protein kinases ('ERK1/2'), induced similar effects on 4E-BP1 phosphorylation to ischaemia; nevertheless, 4E-BP1-eIF4E complex levels were higher in ischaemia than in rapamycin-treated cells. In addition, both protein synthesis rate and eIF4F formation were lower in ischaemic cells than in rapamycin-treated cells.

4E binding protein 1 expression is inversely correlated to the progression of gastrointestinal cancers

Several components of the eukaryotic protein synthesis apparatus have been associated with oncogenic transformation of cells. Overexpression of the initiation factor eIF4E occurs in a variety of human tumours. The aim of this study was to determine the level of expression and the phosphorylation state of eIF4E and 4E-binding protein 1 (4E-BP1) in gastrointestinal cancer, and to ascertain whether or not these factors can be used as diagnostic or prognostic markers within this type of cancer. The eIF4E levels were significantly higher in tumours compared with normal tissue (51. 5+/-4.4 vs 30.9+/-2.5 arbitrary units (A.U.)/mg of protein, p<0.001). However, phosphorylated eIF4E did not change in stomach cancers and decreased in colorectal cancers (67.1+/-1.2 vs 60.8+/-2.8%, p<0.05). 4E-BP1 expression increased in most of the gastrointestinal cancers studied. In addition, an inverse correlation between 4E-BP1 elevation and N and M stages was found, showing significant higher elevation of 4E-BP1 in Node-negative patients (11.21+/-5.74 vs 4. 03+/-2.36 n-fold, p<0.05) as well as in patients without distant metastasis (8.41+/-3.29 vs 0.97+/-0.35 n-fold, p<0.05). These results suggest that 4E-BP1 could function as a tumour suppressor. Moreover, the data show a significant dephosphorylation of 4E-BP1 in gastrointestinal tumours that correlated with an increase in the association of 4E-BP1 and eIF4E indicating a lower availability to eIF4E to recruit to the ribosomes. Our results support a possible role of 4E-BP1 as a prognostic factor in gastrointestinal carcinoma.

Levels, phosphorylation status and cellular localization of translational factor eIF2 in gastrointestinal carcinomas

The level of expression and the phosphorylation status of the alpha subunit of initiation factor 2 (eIF2alpha) protein have been determined by comparing samples from human stomach, colon and sigma-rectum carcinomas with normal tissue from the same patients. The unphosphorylated and phosphorylated levels of cytoplasmic eIF2alpha, as well as the percentage of phosphorylated factor over the total, were significantly higher in stomach, colon and sigma-rectum tumours compared with normal tissue. The expression of this factor was also studied by using immunocytochemical methods, where redistribution towards the nucleus in tumour cells as compared with normal tissue was observed. Our results support a likely implication of eIF2alpha in gastrointestinal cancer.

Trimeric G proteins modulate the dynamic interaction of PKAII with the Golgi complex

The Golgi complex represents a major subcellular location of protein kinase A (PKA) concentration in mammalian cells where it has been previously shown to be involved in vesicle-mediated protein transport processes. We have studied the factors that influence the interaction of PKA typeII subunits with the Golgi complex. In addition to the cytosol, both the catalytic (Calpha) and regulatory (RIIalpha) subunits of PKAII were detected at both sides of the Golgi stack, particularly in elements of the cis- and trans-Golgi networks. PKAII subunits, in contrast, were practically absent from the middle Golgi cisternae. Cell treatment with either brefeldin A, AlF(4-) or at low temperature induced PKAII dissociation from the Golgi complex and redistribution to the cytosol. This suggested the existence of a cycle of association/dissociation of PKAII holoenzyme to the Golgi. The interaction of purified RIIalpha with Golgi membranes was studied in vitro and found not to be affected by brefeldin A while it was sensitive to modulators of heterotrimeric G proteins such as AlF(4-), GTPgammaS, beta(gamma) subunits and mastoparan. RII(alphaa) binding was stimulated by recombinant, myristoylated Galpha(i3) subunit and inhibited by cAMP. Pretreatment of Golgi membranes with bacterial toxins known to catalyze ADP-ribosylation of selected Galpha subunits also modified RIIalpha binding. Taken together the data support a regulatory role for Golgi-associated Galpha proteins in PKAII recruitment from the cytosol.

[Congenital hydronephrosis. An evolutionary study of renal function]

Between 1986 and 1995, 24 newborn and young infants underwent to surgical repair of 32 renal units affected by congenital hydronephrosis in spite of their levels of renal function and dilation. 22 renal units were pelviureteral junction obstruction and 10 were vesico-ureteral obstruction. Isotopic studies were made pre- and post-operatively, resulting in a high percentage of kidneys with the highest values of relative renal function showing a downward after surgery, and a general improvement among the renal units with previously moderate function. Drainage slope curves showed an improvement of its partial obstruction, and no change when dilation without obstruction. The clearance half-time showed a reduction in the slower renal units. We conclude that the natural evolution of these age-group kidneys is a counterbalance with the healthy contralateral renal unit.

Resistance of initiation factor 2 (eIF-2alpha) kinases to staurosporine: an approach for assaying the kinases in crude extracts

We studied the effect of staurosporine on two well characterised mammalian eIF-2alpha kinases, the heme-regulated translational inhibitor (HRI), and interferon-inducible double-stranded RNA-activated protein kinase (PKR). Both pure eIF-2 and a synthetic peptide used to measure the activity of purified or immunoprecipitated enzymes (sequence ILLSELSRRRIRAI) were phosphorylated with purified enzymes and crude preparations of tissues or cells in the presence of the inhibitor. In the presence of 0.25 microM staurosporine (a concentration which completely inhibits a wide range of Ser/Thr protein kinases), the phosphorylation of eIF-2alpha by HRI and PKR was not inhibited. The lack of response of eIF-2alpha kinases to staurosporine allowed us to measure PKR activity in salt washed postmicrosomal supernatants without previous purification of the enzyme. In the presence of poly(I):poly(C), the PKR activator, we detected both an increased phosphorylation of eIF-2alpha and an increment in the autophosphorylation of PKR. We also confirmed an induction of PKR in cultured neuronal cells after treatment with interferon. The results obtained following phosphorylation of the synthetic peptide with crude extracts are less conclusive. Although its phosphorylation is specific because it displaces eIF-2 phosphorylation, and the presence of staurosporine prevents its phosphorylation by other serine/threonine kinases, it is a rather poor substrate for PKR.

Increased activity of eukaryotic initiation factor 2B in PC12 cells in response to differentiation by nerve growth factor

Translational rates, and activities and levels of initiation factors 2 and 2B were assessed in rat pheochromocytoma cells upon nerve growth factor (NGF) treatment. Two or 5 days of exposure to NGF caused significant quantitative increases in protein synthesis rate that are deemed necessary for neuronal differentiation. Changes in initiation factor 2 activity, as measured by its capacity to form a ternary complex, occur parallel to the observed changes in protein synthesis. Nevertheless, neither the intracellular levels of the initiation factor 2 nor the degree of phosphorylation of its alpha subunit can justify this increased activity. Interestingly, initiation factor 2B activity increases parallel to the neurite outgrowth, being significantly higher after 5 days of exposure to NGF, and could be responsible for the elevated rate of protein synthesis. No significant changes in the levels of eukaryotic initiation factor 2B, as determined with two different antibodies against the gamma and epsilon subunits of the factor, were observed, implying that the increased activity should be regulated by factors other than its cellular concentration. Our results support the hypothesis that initiation factor 2B may play a role in the biochemical events controlling the differentiative growth factor-induced signaling pathway in these cells.

The intraischemic and early reperfusion changes of protein synthesis in the rat brain. eIF-2 alpha kinase activity and role of initiation factors eIF-2 alpha and eIF-4E

Rats were subjected to the standard four-vessel occlusion model of transient cerebral ischemia (vertebral and carotid arteries). The effects of normothermic ischemia (37 degrees C) followed or not by 30-minute reperfusion, as well as 30-minute postdecapitative ischemia, on translational rates were examined. Protein synthesis rate, as measured in a cell-free system, was significantly inhibited in ischemic rats, and the extent of inhibition strongly depended on duration and temperature, and less on the model of ischemia used. The ability of reinitiation in vitro (by using aurintricarboxylic acid) decreased after ischemia, suggesting a failure in the synthetic machinery at the initiation level. Eukaryotic initiation factor 2 (eIF-2) presented almost basal activity and levels after 30-minute normothermic ischemia, and the amount of phosphorylated eIF-2 alpha in these samples, as well as in sham-control samples, was undetectable. The decrease in the levels of phosphorylated initiation factor 4E (eIF-4E) after 30-minute ischemia (from 32% to 16%) could explain, at least partially, the impairment of initiation during transient cerebral ischemia. After reperfusion, eIF-4E phosphorylation was almost completely restored to basal levels (29%), whereas the level of phosphorylated eIF-2 alpha was higher (13%) than in controls and ischemic samples (both less than 2%). eIF-2 alpha kinase activity in vitro as measured by phosphorylation of endogenous eIF-2 in the presence of ATP/Mg2+, was higher in ischemic samples (8%) than in controls (4%). It seems probable that the failure of the kinase in phosphorylating eIF-2 in vivo during ischemia is due to the depletion of ATP stores. The levels of the double-stranded activated eIF-2 alpha kinase were slightly higher in ischemic animals than in controls. Our results suggest that the modulation of eIF-4E phosphorylation could be implicated in the regulation of translation during ischemia. On the contrary, phosphorylation of eIF-2 alpha, by an eIF-2 alpha kinase already activated during ischemia, represents a plausible mechanism for explaining the inhibition of translation during reperfusion.

Protein kinase A activity is required for the budding of constitutive transport vesicles from the trans-Golgi network

We have examined the role played by protein kinase A (PKA) in vesicle-mediated protein transport from the trans-Golgi network (TGN) to the cell surface. In vivo this transport step was inhibited by inhibitors of PKA catalytic subunits (C-PKA) such as the compound known as H89 and a myristoylated form of the inhibitory peptide sequence contained in the thermostable PKA inhibitor. Inhibition by H89 occurred at an early stage during the transfer of vesicular stomatitis virus G glycoprotein from the TGN to the cell surface. Reversal from this inhibition correlated with a transient increase in the number of free coated vesicles in the Golgi area. Vesicle budding from the TGN was studied in vitro using vesicular stomatitis virus-infected, permeabilized cells. Addition to this assay of C-PKA stimulated vesicle release while it was suppressed by PKA inhibitory peptide, H89, and antibody against C-PKA. Furthermore, vesicle release was decreased when PKA-depleted cytosol was used and restored by addition of C-PKA. These results indicate a regulatory role for PKA activity in the production of constitutive transport vesicles from the TGN.

Purification and characterization of guanine nucleotide-exchange factor, eIF-2B, and p37 calmodulin-binding protein from calf brain

Eukaryotic initiation factor 2B, or guanine nucleotide-exchange factor, has been purified for the first time from the brain by a novel procedure that allows the purification of initiation factor 2 as well and uses a salt wash postmicrosomal supernatant as starting material. The procedure includes a three-part chromatographic step in heparin-Sepharose and in SP-5PW and diethylaminoethyl-5PW ion-exchange high-performance chromatographies. The purification of the factors was followed by measuring activity in the guanine nucleotide-exchange assay and the capacity of initiation factor 2 to form a ternary complex with the initiation form of methionyl-tRNA and GTP. The method yields guanine nucleotide-exchange factor (75%) and highly purified initiation factor 2 (> 95%), which are separated in the last step. The exchange factor from the brain is a multimeric protein with five subunits of molecular masses of 82, 65, 52, 42, and 30 kDa; it stimulates ternary complex formation in the presence of GDP, and this activity is inhibited by N-ethylmaleimide. A 37-kDa protein that copurifies with initiation factors is characterized in this study as a new calmodulin-binding protein (p37); it is highly phosphorylated by casein kinase activities and can comigrate with the alpha subunit of initiation factor 2 under standard sodium dodecyl sulfate electrophoresis conditions.

Protein synthesis in the developing rat liver: participation of initiation factors eIF-2 and eIF-2B

We studied the decline in protein synthesis in the developing liver in suckling rats (4 to 10 days) and adult rats (2 mo). The rate of protein synthesis was measured with a cell-free system and compared with the activity of two initiation factors, eukaryotic initiation factor-2 and eukaryotic initiation factor-2B, and with casein kinase II, which phosphorylates both factors in vitro. The specific activity of the three parameters decreased in adult rats compared with suckling rats and in parallel to the rate of protein synthesis. Quantification of eukaryotic initiation factor-2 in the ribosomal salt wash and in the postmicrosomal supernatant showed that both the specific activity and the levels of eukaryotic initiation factor-2, are much higher in the ribosomal salt wash fractions than in postmicrosomal supernatants, but no differences were found between the two age groups. The eukaryotic initiation factor-2/ribosome ratio was higher in adult rats than in suckling rats, and this parameter seems to be inversely proportional to the rate of protein synthesis. The phosphorylation state of eukaryotic initiation factor-2 alpha, as determined by isoelectric focusing followed by protein immunoblotting, revealed very low and equal levels of phosphorylation in the two animal groups. The lack of changes in eukaryotic initiation factor-2 levels and phosphorylation status suggests that a decrease in the activity or levels of eukaryotic initiation factor-2B could be responsible for the decrease in eukaryotic initiation factor-2 activity and account for, at least in part, the differences observed in the rates of protein synthesis.

Phosphorylation of the alpha subunit of initiation factor 2 correlates with the inhibition of translation following transient cerebral ischaemia in the rat

Rats were subjected to the standard four-vessel occlusion model of cerebral transient ischaemia (vertebral and carotid arteries) for 15 and 30 min. After a 30 min recirculation period, protein synthesis rate, initiation factor 2 (eIF-2) and guanine nucleotide exchange factor (GEF) activities, and the level of phosphorylation of the alpha subunit of eIF-2 (eIF-2 alpha) were determined in the neocortex region of the brain from sham-operated controls and ischaemic animals. Following reversible cerebral ischaemia, the protein synthesis rate, as measured in a cell-free system, was significantly inhibited (70%) in the ischaemic animals. eIF-2 activity, as measured by its ability to form a ternary complex, also decrease parallel to the decrease in protein synthesis. As eIF-2 activity was assayed in the presence of Mg2+ and GTP-regenerating capacity, the decrease in ternary-complex formation indicated the possible impairment of GEF activity. Since phosphorylated eIF-2 [eIF-2(alpha P)] is a powerful inhibitor of GEF, the levels of phosphorylated eIF-2 alpha were determined, and an increase from 7% phosphorylation in sham control rats to 20% phosphorylation in 15 min and 29% phosphorylation in 30 min in ischaemic rats was observed, providing evidence for a tight correlation of phosphorylation of eIF-2 alpha and inhibition of protein synthesis. Moreover, GEF activity measured in the GDP-exchange assay was in fact inhibited in the ischaemic animals, proving that protein synthesis is impaired by the presence of eIF-2(alpha P), which blocks eIF-2 recycling.

Translational initiation factor eIF-2 subcellular levels and phosphorylation status in the developing rat brain

We have quantified the levels of the alpha subunit of initiation factor 2 (eIF-2) in the postmicrosomal supernatant and the ribosomal salt wash fractions from suckling and adult rat brain. The levels of eIF-2 in the ribosomal salt wash decrease in adult with respect to that present in suckling rat brain, but the total amount remains fairly constant, and a very close parallelism exists between the eIF-2 associated with ribosomes and RNA levels in the microsomal fraction in the two age groups. The phosphorylation state of eIF-2 alpha, as determined by isoelectric focusing followed by protein immunoblotting, in the same subcellular fractions, did not reveal the presence of the phosphorylated form in any of the fractions studied. These results suggest that phosphorylation of the alpha subunit is not implied in the regulation of protein synthesis initiation during brain development, and some other component regulates both the number of active ribosomes and eIF-2 levels in microsomes.

Partial purification of a novel N-ethylmaleimide-activated translational inhibitor from adult rat brain

A translational inhibitor that is activated by N-ethylmaleimide treatment can be found in the postmicrosomal fraction prepared from the brain of adult rats, but it is almost undetectable in the same fraction prepared from suckling animals. The inhibitor is thermolabile and remains in the supernatant fraction after precipitation at pH 5. During the purification procedure, the inhibitor in its unactivated state binds to the anion exchanger (diethylaminoethyl-cellulose) but not to the cation exchanger (phosphocellulose). Treatment with N-ethylmaleimide increases inhibitor affinity for the cation exchanger, and this chromatographic step purifies the inhibitor by 143-fold. Both the thermolabile nature and the behavior of the inhibitory activity during the different steps of the purification procedure suggest that this activity is most probably due to a protein. Although the addition of initiation factor 2 reverses the inhibition of protein synthesis in the presence of ATP and Mg2+, the inhibitor does not phosphorylate any of the initiation factor subunits "in vitro," which indicates that it does not contain any intrinsic protein kinase activity. However, its presence in both a crude and a purified preparation of a kinase of the alpha subunit of a brain eukaryotic initiation factor increases the phosphorylation of the alpha subunit of the initiation factor. The mechanism of action of this inhibitor is discussed.

Heterogeneity in the beta-subunit of translational initiation factor eIF-2 during brain development

We have detected by immunoblotting analysis of crude fractions from suckling and adult rat brain, resolved by two-dimensional isoelectric focusing-dodecyl sulfate polyacrylamide gel electrophoresis, the presence of two different forms of the beta subunit of polypeptide initiation factor 2 (eIF-2). These two forms differ in their apparent molecular weights and also in their isoelectric point values. Quantitation of both forms in the crude fractions shows that, the most basic form beta 1 (pI: 6.1, 52 kDa), is present in higher levels of the salt wash ribosomal fractions obtained from both, suckling and adult animals, than in the postmicrosomal fraction corresponding to the same animals. The most acidic form, beta 2 (pI: 5.9, 50 kDa), is present in the highest level in the postmicrosomal supernatant from adult animals. A close parallelism is found between beta 1 levels and eIF-2 activity.

Purification of a novel eIF-2 alpha protein kinase from calf brain

A new eukaryotic initiation factor 2 kinase has been purified for the first time from calf brain cytosol. The purification of a nonabundant novel protein kinase activity, designated as PKI, that phosphorylates the alpha subunit of eukaryotic initiation factor 2 is described. The protein kinase activity was assayed using purified initiation factor 2 as a substrate and was purified by ammonium sulphate precipitation, conventional chromatography in heparin-Sepharose and phosphocellulose and by high performance size exclusion and anion exchange chromatographies. The protein kinase activity elutes in the region of 140,000 in the size exclusion chromatography and is associated with two different polypeptides a and b, with relative molecular masses of 38,000 and 20,000 and an approximate ratio of 2.5-3.0:1. The protein kinase does not phosphorylate casein or histones and it is independent of cyclic nucleotides. It can be classified as a serine kinase since the phosphorylation of the alpha subunit of eIF-2 is produced in serine residues. Under these conditions none of the kinase subunits are phosphorylated.

Subcellular and regional distribution of casein kinase II and initiation factor 2 activities during rat brain development

The possible relationship between the subcellular and regional distribution of the activities of initiation factor 2 and casein kinase II, responsible for the phosphorylation of the beta subunit of the factor, has been studied during postnatal rat brain development. Both activities have been measured in four brain regions: diencephalon, hemispheres, cerebellum and brain stem, and in two subcellular fractions: postmicrosomal supernatant and the protein fraction associated with ribosomes, or crude initiation factors fraction. The specific activity of both the factor and the protein kinase is much higher in the protein fraction associated with ribosomes than in the soluble fraction and slightly higher in the hemispheres than in the other three regions. Changes in the activity of both proteins are in parallel with development, the activities increase in the postmicrosomal supernatant and decrease in the fraction associated with ribosomes from suckling (5-day-old) to adult (60-day-old) animals. The total activity of the factor and its kinase, calculated by summation of the activities of both subcellular fractions, does not change during development, and the distribution of activities between the two subcellular fractions observed during brain development, appears as an attractive regulation mechanism for the function of both proteins.