Prenatal paternal anxiety symptoms predict child DHEA levels and internalizing symptoms during adrenarche

Introduction

This study examined (1) whether measures of paternal anxious and depressive symptoms collected prenatally and during a follow-up assessment when the child was in middle childhood, predict child neuroendocrine outcomes, and (2) whether neuroendocrine outcomes are intermediate factors between paternal mental health and child cognitive/behavioral outcomes. Middle childhood coincides with increased autonomy as the child transitions into grade school, and with adrenarche, as the maturing adrenal gland increases secretion of dehydroepiandrosterone (DHEA) and its sulfated metabolite (DHEA-S), hormones that are implicated in corticolimbic development which regulate emotions and cognition.

Methods

Participants were recruited from a subsample of a large prospective birth cohort study (3D study). We conducted a follow-up study when children were 6-8 years old (N = 61 families, 36 boys, 25 girls). Parental symptoms of anxiety, stress and depression were assessed via validated self-report questionnaires: prenatally using an in-house anxiety questionnaire, the Perceived Stress Scale (PSS) and the Center for Epidemiologic Studies Depression (CES-D), and at the follow up, using the Beck Anxiety and Beck Depression Inventories. Children provided salivary hormone samples, and their pituitary gland volume was measured from structural Magnetic Resonance Imaging (MRI) scans. Child behaviors were measured using the Strengths and Difficulties Questionnaire and cognitive outcomes using the WISC-V. Multiple regression analyses were used to test whether paternal mental health symptoms assessed prenatally and during childhood are associated with child neuroendocrine outcomes, adjusting for maternal mental health and child sex. Indirect-effect models assessed whether neuroendocrine factors are important intermediates that link paternal mental health and cognitive/behavioral outcomes.

Results

(1) Fathers' prenatal anxiety symptoms predicted lower DHEA levels in the children, but not pituitary volume. (2) Higher prenatal paternal anxiety symptoms predicted higher child internalizing symptoms via an indirect pathway of lower child DHEA. No associations were detected between paternal anxiety symptoms measured in childhood, and neuroendocrine outcomes. No child sex differences were detected on any measure.

Conclusion

These results highlight the often-overlooked role of paternal factors during pregnancy on child development, suggesting that paternal prenatal anxiety symptoms are associated with child neuroendocrine function and in turn internalizing symptoms that manifest at least up to middle childhood.

Longitudinal associations between paternal mental health and child behavior and cognition in middle childhood

Introduction

Paternal mental health has been associated with adverse consequences on offspring psychosocial development, and family environmental factors may partly explain those associations. To clarify this, we need comprehensive prospective studies, particularly in middle-childhood when the child enters school and is expected to make use of behavioral and cognitive skills as part of their interactions and learning.

Method

Using data from a sub-sample of the prospective 3D birth cohort study comprised of mother-father-child triads, and a follow-up of the parents and the children at 6-8 years of age (n = 61; 36 boys, 25 girls), we examined whether paternal anxious and depressive symptoms measured during the pregnancy period (i.e., prenatally) or concurrently when the child was assessed at 6-8 years old were associated with children's cognition/behavior.

Results

In contrast to our hypotheses, we found that greater prenatal paternal depressive symptoms predicted fewer child behavioral difficulties; and that greater concurrent childhood paternal depression or anxiety symptoms were associated with higher child full-scale IQ, controlling for the equivalent maternal mental health assessment and parental education. Father parenting perception did not mediate these associations, nor were they moderated by maternal mental health at the concurrent assessment, or paternal ratings of marital relationship quality.

Discussion

These findings suggest that higher symptoms of paternal mental health symptoms are associated with fewer child behavioral difficulties and higher cognitive performance in middle childhood. Potential clinical implications and future research directions are discussed.

Age-specific associations between oestradiol, cortico-amygdalar structural covariance, and verbal and spatial skills

Oestradiol is known to play an important role in the developing human brain, although little is known about the entire network of potential regions that might be affected and how these effects may vary from childhood to early adulthood, which in turn can explain sexually differentiated behaviours. In the present study, we examined the relationships between oestradiol, cortico-amygdalar structural covariance, and cognitive or behavioural measures typically showing sex differences (verbal/spatial skills, anxious-depressed symptomatology) in 152 children and adolescents (aged 6-22 years). Cortico-amygdalar structural covariance shifted from positive to negative across the age range. Oestradiol was found to diminish the impact of age on cortico-amygdalar covariance for the pre-supplementary motor area/frontal eye field and retrosplenial cortex (across the age range), as well as for the posterior cingulate cortex (in older children). Moreover, the influence of oestradiol on age-related cortico-amygdalar networks was associated with higher word identification and spatial working memory (across the age range), as well as higher reading comprehension (in older children), although it did not impact anxious-depressed symptoms. There were no significant sex effects on any of the above relationships. These findings confirm the importance of developmental timing on oestradiol-related effects and hint at the non-sexually dimorphic role of oestradiol-related cortico-amygdalar structural networks in aspects of cognition distinct from emotional processes.

Sex-specific contribution of DHEA-cortisol ratio to prefrontal-hippocampal structural development, cognitive abilities and personality traits

Although dehydroepiandrosterone (DHEA) may exert neuroprotective effects in the developing brain, prolonged or excessive elevations in cortisol may exert neurotoxic effects. The ratio between DHEA and cortisol (DC ratio) has been linked to internalising and externalising disorders, as well as cognitive performance, supporting the clinical relevance of this hormonal ratio during development. However, the brain mechanisms by which these effects may be mediated have not yet been identified. Furthermore, although there is evidence that the effects of cortisol in the central nervous system may be sexually dimorphic in humans, the opposite is true for DHEA, with human studies showing no sex-specific associations in cortical thickness, cortico-amygdalar or cortico-hippocampal structural covariance. Therefore, it remains unclear whether sex moderates the developmental associations between DC ratio, brain structure, cognition and behaviour. In the present study, we examined the associations between DC ratio, structural covariance of the hippocampus with whole-brain cortical thickness, and measures of personality, behaviour and cognition in a longitudinal sample of typically developing children, adolescents and young adults aged 6-22 years (N = 225 participants [F = 128]; 355 scans [F = 208]), using mixed effects models that accounted for both within- and between-subject variances. We found sex-specific interactions between DC ratio and anterior cingulate cortex-hippocampal structural covariance, with higher DC ratios being associated with a more negative covariance between these structures in girls, and a more positive covariance in boys. Furthermore, the negative prefrontal-hippocampal structural covariance found in girls was associated with higher verbal memory and mathematical ability, whereas the positive covariance found in boys was associated with lower cooperativeness and reward dependence personality traits. These findings support the notion that the ratio between DHEA and cortisol levels may contribute, at least in part, to the development of sex differences in cognitive abilities, as well as risk for internalising/externalising disorders, via an alteration in prefrontal-hippocampal structure during the transition from childhood to adulthood.

Role of DHEA and cortisol in prefrontal-amygdalar development and working memory

There is accumulating evidence that both dehydroepiandrosterone (DHEA) and cortisol play an important role in regulating physical maturation and brain development. High DHEA levels tend to be associated with neuroprotective and indirect anabolic effects, while high cortisol levels tend to be associated with catabolic and neurotoxic properties. Previous literature has linked the ratio between DHEA and cortisol levels (DC ratio) to disorders of attention, emotional regulation and conduct, but little is known as to the relationship between this ratio and brain development. Due to the extensive links between the amygdala and the cortex as well as the known amygdalar involvement in emotional regulation, we examined associations between DC ratio, structural covariance of the amygdala with whole-brain cortical thickness, and validated report-based measures of attention, working memory, internalizing and externalizing symptoms, in a longitudinal sample of typically developing children and adolescents 6-22 years of age. We found that DC ratio predicted covariance between amygdalar volume and the medial anterior cingulate cortex, particularly in the right hemisphere. DC ratio had a significant indirect effect on working memory through its impact on prefrontal-amygdalar covariance, with higher DC ratios associated with a prefrontal-amygdalar covariance pattern predictive of higher scores on a measure of working memory. Taken together, these findings support the notion, as suggested by animal and in vitro studies, that there are opposing effects of DHEA and cortisol on brain development in humans, and that these effects may especially target prefrontal-amygdalar development and working memory, in a lateralized fashion.

Dehydroepiandrosterone impacts working memory by shaping cortico-hippocampal structural covariance during development

Existing studies suggest that dehydroepiandrosterone (DHEA) may be important for human brain development and cognition. For example, molecular studies have hinted at the critical role of DHEA in enhancing brain plasticity. Studies of human brain development also support the notion that DHEA is involved in preserving cortical plasticity. Further, some, though not all, studies show that DHEA administration may lead to improvements in working memory in adults. Yet these findings remain limited by an incomplete understanding of the specific neuroanatomical mechanisms through which DHEA may impact the CNS during development. Here we examined associations between DHEA, cortico-hippocampal structural covariance, and working memory (216 participants [female=123], age range 6-22 years old, mean age: 13.6 +/-3.6 years, each followed for a maximum of 3 visits over the course of 4 years). In addition to administering performance-based, spatial working memory tests to these children, we also collected ecological, parent ratings of working memory in everyday situations. We found that increasingly higher DHEA levels were associated with a shift toward positive insular-hippocampal and occipito-hippocampal structural covariance. In turn, DHEA-related insular-hippocampal covariance was associated with lower spatial working memory but higher overall working memory as measured by the ecological parent ratings. Taken together with previous research, these results support the hypothesis that DHEA may optimize cortical functions related to general attentional and working memory processes, but impair the development of bottom-up, hippocampal-to-cortical connections, resulting in impaired encoding of spatial cues.

Sex-specific associations of testosterone with prefrontal-hippocampal development and executive function

Testosterone is thought to play a crucial role in mediating sexual differentiation of brain structures. Examinations of the cognitive effects of testosterone have also shown beneficial and potentially sex-specific effects on executive function and mnemonic processes. Yet these findings remain limited by an incomplete understanding of the critical timing and brain regions most affected by testosterone, the lack of documented links between testosterone-related structural brain changes and cognition, and the difficulty in distinguishing the effects of testosterone from those of related sex steroids such as of estradiol and dehydroepiandrosterone (DHEA). Here we examined associations between testosterone, cortico-hippocampal structural covariance, executive function (Behavior Rating Inventory of Executive Function) and verbal memory (California Verbal Learning Test-Children's Version), in a longitudinal sample of typically developing children and adolescents 6-22 yo, controlling for the effects of estradiol, DHEA, pubertal stage, collection time, age, handedness, and total brain volume. We found prefrontal-hippocampal covariance to vary as a function of testosterone levels, but only in boys. Boys also showed a specific association between positive prefrontal-hippocampal covariance (as seen at higher testosterone levels) and lower performance on specific components of executive function (monitoring the action process and flexibly shifting between actions). We also found the association between testosterone and a specific aspect of executive function (monitoring) to be significantly mediated by prefrontal-hippocampal structural covariance. There were no significant associations between testosterone-related cortico-hippocampal covariance and verbal memory. Taken together, these findings highlight the developmental importance of testosterone in supporting sexual differentiation of the brain and sex-specific executive function.

The 2S albumin allergens of Arachis hypogaea, Ara h 2 and Ara h 6, are the major elicitors of anaphylaxis and can effectively desensitize peanut-allergic mice

BACKGROUND

Ara h 2 and Ara h 6, co-purified together in a 13-25 kD fraction (Ara h 2/6; 20 kD fraction) on gel filtration chromatography, account for the majority of effector activity in a crude peanut extract (CPE) when assayed with RBL SX-38 cells sensitized with IgE from human peanut allergic sera.

OBJECTIVES

To determine if Ara h 2/6 are the primary peanut allergens responsible for allergic reactions in vivo and to determine if Ara h 2/6 would be sufficient to prevent allergic reactions to a complete CPE.

METHODS

An oral sensitization mouse model of peanut allergy was used to assess the activity of Ara h 2/6 (20 kD) and CPE without the 20 kD fraction (CPE w/o 20 kD) for allergic provocation challenge and immunotherapy. The activity of these preparations was also tested in an assay of histamine release from human basophils in whole blood.

RESULTS

Compared with mice challenged with control CPE, mice challenged with CPE w/o 20 kD experienced reduced symptoms (P < 0.05) and a smaller decrease in body temperature (P < 0.01). Results with the basophil histamine release assay corroborated these findings (P < 0.01). The mouse model was also used to administer Ara h 2/6 (20 kD) in an immunotherapy protocol, in which peanut-allergic mice treated with the 20 kD fraction experienced significantly reduced symptoms, changes in body temperature, and mast cell protease (MMCP-1) release compared with placebo (P < 0.01 for all parameters). Importantly, immunotherapy with the 20 kD fraction was just as effective as treatment with CPE, whereas CPE w/o 20 kD was significantly less effective for higher dose peanut challenges.

CONCLUSIONS AND CLINICAL RELEVANCE

Ara h 2/6 are the most potent peanut allergens in vivo and can be used to desensitize peanut-allergic mice. These results have potential implications for clinical research in the areas of diagnosis and immunotherapy for peanut allergy.

Effects of rice bran oil on plasma lipid concentrations, lipoprotein composition, and glucose dynamics in mares1

Plasma lipid concentrations, lipoprotein composition, and glucose dynamics were measured and compared between mares fed diets containing added water, corn oil (CO), refined rice bran oil (RR), or crude rice bran oil (CR) to test the hypothesis that rice bran oil lowers plasma lipid concentrations, alters lipoprotein composition, and improves insulin sensitivity in mares. Eight healthy adult mares received a basal diet fed at 1.5 times the DE requirement for maintenance and each of the four treatments according to a repeated 4 x 4 Latin square design consisting of four 5-wk feeding periods. Blood samples were collected for lipid analysis after mares were deprived of feed overnight at 0 and 5 wk. Glucose dynamics were assessed at 0 and 4 wk in fed mares by combined intravenous glucose-insulin tolerance tests. Plasma glucose and insulin concentrations were measured, and estimated values of insulin sensitivity (SI), glucose effectiveness, and net insulin response were obtained using the minimal model. Mean BW increased (P = 0.014) by 29 kg (range = 10 to 50 kg) over 5 wk. Mean plasma concentrations of NEFA, triglyceride (TG), and very low-density lipoprotein (VLDL) decreased (P < 0.001) by 55, 30, and 39%, respectively, and plasma high-density lipoprotein and total cholesterol (TC) concentrations increased (P < 0.001) by 15 and 12%, respectively, over 5 wk. Changes in plasma NEFA (r = 0.58; P < 0.001) and TC (r = 0.44; P = 0.013) concentrations were positively correlated with weight gain over 5 wk. Lipid components of VLDL decreased (P < 0.001) in abundance over 5 wk, whereas the relative protein content of VLDL increased by 39% (P < 0.001). Addition of oil to the basal diet instead of water lowered plasma NEFA and TG concentrations further (P = 0.002 and 0.020, respectively) and increased plasma TC concentrations by a greater magnitude (P = 0.072). However, only plasma TG concentrations and VLDL free cholesterol content were affected (P = 0.024 and 0.009, respectively) by the type of oil added to the diet. Mean plasma TG concentration decreased by 14.2 mg/dL over 5 wk in the CR group, which was a larger (P < 0.05) decrease than the one (-5.3 mg/dL) detected in mares that received water. Consumption of experimental diets lowered S(I), but glucose dynamics were not affected by oil supplementation. Addition of oil to the diet altered blood lipid concentrations, and supplementation with CR instead of water specifically affected plasma TG concentrations and VLDL free cholesterol content.

Suspected case of venous air embolism in an infant undergoing hip arthrogram

An otherwise well ten-week-old girl underwent an air contrast hip arthrogram and application of a hip spica for a developmentally dislocated hip. The child displayed signs consistent with venous air embolism after injection of 5 ml of air into the hip joint. These signs included a decrease in arterial haemoglobin oxygen saturation as measured by pulse oximetry, decreased end-tidal carbon dioxide level and tachycardia. The signs initially resolved, but the patient deteriorated with injection of a further 5 ml of air. The patient responded to cessation of injection and resuscitative measures. The infant remained well postoperatively. The need for the use of air to confirm intra-articular placement of the needle prior to injection of contrast during a hip arthrogram is questioned.

The complete pathway for catalytic activation of the mitogen-activated protein kinase, ERK2

The mitogen-activated protein (MAP) kinase ERK2 is an essential signal transduction molecule that mediates extracellular signaling by all polypeptide growth factors. Full activation of ERK2 requires phosphorylation at both a threonine residue (Thr(183)) conserved in most protein kinases as well as a tyrosine residue (Tyr(185)) unique to members of the mitogen-activated protein kinase family. We have characterized the kinetic role of phosphorylation at each site with respect to the overall activation mechanism, providing a complete picture of the reaction steps involved. Phosphorylation at Tyr(185) serves to configure the ATP binding site, while phosphorylation at both residues is required to stabilize binding of the protein substrate, myelin basic protein. Similar control mechanisms are employed to stabilize ATP and myelin basic protein in the phosphoryl group transfer reaction, accounting for the enormous increase in turnover rate. The mechanism of ERK2 activation is kinetically similar to that of the cell cycle control protein, cdk2/cyclinA. Phosphorylation of Tyr(185) in ERK2 and association of cyclinA with cdk2 both serve to stabilize ATP binding. Subsequent phosphorylation of both enzymes on threonine serves to stabilize binding of the phosphoacceptor substrate.

Induction of 7-ethoxyresorufin-O-deethylase activity by planar chlorinated hydrocarbons and polycyclic aromatic hydrocarbons in cell lines from the rainbow trout pituitary

The induction of 7-ethoxyresorufin-o-deethylase (EROD) activity was examined in three rainbow trout pituitary cell lines: RTP-91E, RTP-91F and RTP-2. RTP-91E and RTP-91F were developed from the pituitary of a male and have epithelial-like and fibroblast-like morphologies, respectively. RTP-2, which was described previously, was developed from the pituitary of a female and has an epithelial-like shape. In all cell lines EROD activity was induced by 2,3,7,8- tetrachlorodibenzo-p-dioxin (TCDD). Immunoblotting with the polyclonal antibody, anti-trout CYP1A1(277-294)/KLH, confirmed induction of a 58-kDa polypeptide. Potential inhibitors of the aryl hydrocarbon receptor, geldanamycin and alpha-naphthoflavone, inhibited EROD induction by TCDD. Other compounds inducing EROD activity were 1,2,3,7,8-pentachlorodibenzo-p-dioxin (PCDD), 2,3,7,8-tetrachlorodibenzofuran (TCDF), 3,3',4,4',5-pentachlorobiphenyl (PCB 126), and 3-methylcholanthrene (3MC). When judged by the concentration eliciting 50% of the maximal response (EC50), induction was similar in RTP-2 and RTP-91E, and less effective in RTP-91F. Regardless of the cell line, the rank order from most to least potent inducer on the basis of EC50 value was TCDD> or =PCDD>TCDF>PCB 126>>3MC. When induction potencies were expressed relative to TCDD, the values obtained with the pituitary cell lines were similar to previously published values derived with a rainbow trout liver cell line.

Mechanism of activation of ERK2 by dual phosphorylation

The mitogen-activated protein (MAP) kinases are characterized by their requirement for dual phosphorylation at a conserved threonine and tyrosine residue for catalytic activation. The structural consequences of dual-phosphorylation in the MAP kinase ERK2 (extracellular signal-regulated kinase 2) include active site closure, alignment of key catalytic residues that interact with ATP, and remodeling of the activation loop. In this study, we report the specific effects of dual phosphorylation on the individual catalytic reaction steps in ERK2. Dual phosphorylation leads to an increase in overall catalytic efficiency and turnover rate of approximately 600,000- and 50,000-fold, respectively. Solvent viscosometric studies reveal moderate decreases in the equilibrium dissociation constants (K(d)) for both ATP and myelin basic protein. However, the majority of the overall rate enhancement is due to an increase in the rate of the phosphoryl group transfer step by approximately 60,000-fold. By comparison, the rate of the same step in the ATPase reaction is enhanced only 2000-fold. This suggests that optimizing the position of the invariant residues Lys(52) and Glu(69), which stabilize the phosphates of ATP, accounts for only part of the enhanced rate of phosphoryl group transfer in the kinase reaction. Thus, significant stabilization of the protein phosphoacceptor group must also occur. Our results demonstrate similarities between the activation mechanisms of ERK2 and the cell cycle control enzyme, Cdk2 (cyclin-dependent kinase 2). Rather than dual phosphorylation, however, activation of the latter is controlled by cyclin binding followed by phosphorylation at Thr(160).

Kinetic basis for activation of CDK2/cyclin A by phosphorylation

The activation of most protein kinases requires phosphorylation at a conserved site within a structurally defined segment termed the activation loop. A classic example is the regulation of the cell cycle control enzyme, CDK2/cyclin A, in which catalytic activation depends on phosphorylation at Thr(160) in CDK2. The structural consequences of phosphorylation have been revealed by x-ray crystallographic studies on CDK2/cyclin A and include changes in conformation, mainly of the activation loop. Here, we describe the kinetic basis for activation by phosphorylation in CDK2/cyclin A. Phosphorylation results in a 100,000-fold increase in catalytic efficiency and an approximate 1,000-fold increase in the overall turnover rate. The effects of phosphorylation on the individual steps in the catalytic reaction pathway were determined using solvent viscosometric techniques. It was found that the increase in catalytic power arises mainly from a 3,000-fold increase in the rate of the phosphoryl group transfer step with a more moderate increase in substrate binding affinity. In contrast, the rate of phosphoryl group transfer in the ATPase pathway was unaffected by phosphorylation, demonstrating that phosphorylation at Thr(160) does not serve to stabilize ATP in the ATPase reaction. Thus, we hypothesize that the role of phosphorylation in the kinase reaction may be to specifically stabilize the peptide phosphoacceptor group.

Human immunodeficiency virus (HIV) type 1 antibodies in perinatal HIV-1 infection: association with human HIV-1 transmission, infection, and disease progression. For the Women and Infants Transmission Study

Anti -human immunodeficiency virus (HIV) type 1 antibodies in 242 pregnant women and 238 infants were measured at birth and at 1, 2, 4, and 6 months after birth, to estimate their association with perinatal transmission and infant disease progression. Maternal anti-p24 (P=.01) and anti-gp120 (P=.04) antibodies were inversely associated with vertical transmission rates, independent of maternal percentage of CD4 cells, hard drug use, duration of ruptured membranes, serum albumin levels, serum vitamin A levels, and quantitative HIV-1 peripheral mononuclear blood cell culture, but not with maternal plasma immune complex dissociated p24 or HIV-1 RNA copy number, both of which were highly correlated with antibodies. From ages 1-2 months, anti-gp120, -gp41, -p31, and -p66 decayed to a greater extent in infected than in uninfected infants. Infected infants produced anti-p24 antibody by age 2 months, anti-p17 by 4 months, and anti-p41 and anti-gp120 by 6 months. As early as birth, infants with rapid disease progression had lower levels of anti-p24 than did infants whose disease did not rapidly progress, but not independently of HIV-1 RNA levels.

Catalytic reaction pathway for the mitogen-activated protein kinase ERK2

The structural, functional, and regulatory properties of the mitogen-activated protein kinases (MAP kinases) have long attracted considerable attention owing to the critical role that these enzymes play in signal transduction. While several MAP kinase X-ray crystal structures currently exist, there is by comparison little mechanistic information available to correlate the structural data with the known biochemical properties of these molecules. We have employed steady-state kinetic and solvent viscosometric techniques to characterize the catalytic reaction pathway of the MAP kinase ERK2 with respect to the phosphorylation of a protein substrate, myelin basic protein (MBP), and a synthetic peptide substrate, ERKtide. A minor viscosity effect on k(cat) with respect to the phosphorylation of MBP was observed (k(cat) = 10 +/- 2 s(-1), k(cat)(eta) = 0.18 +/- 0.05), indicating that substrate processing occurs via slow phosphoryl group transfer (12 +/- 4 s(-1)) followed by the faster release of products (56 +/- 4 s(-1)). At an MBP concentration extrapolated to infinity, no significant viscosity effect on k(cat)/K(m(ATP)) was observed (k(cat)/K(m(ATP)) = 0.2 +/- 0.1 microM(-1) s(-1), k(cat)/K(m(ATP))(eta) = -0.08 +/- 0.04), consistent with rapid-equilibrium binding of the nucleotide. In contrast, at saturating ATP, a full viscosity effect on k(cat)/K(m) for MBP was apparent (k(cat)/K(m(MBP)) = 2.4 +/- 1 microM(-1) s(-1), k(cat)/K(m(MBP))(eta) = 1.0 +/- 0.1), while no viscosity effect was observed on k(cat)/K(m) for the phosphorylation of ERKtide (k(cat)/K(m(ERKtide)) = (4 +/- 2) x 10(-3) microM(-1) s(-1), k(cat)/K(m(ERKtide))(eta) = -0.02 +/- 0.02). This is consistent with the diffusion-limited binding of MBP, in contrast to the rapid-equilibrium binding of ERKtide, to form the ternary Michaelis complex. Calculated values for binding constants show that the estimated value for K(d(MBP)) (</=0.5 microM) is significantly lower than that of the measured K(m(MBP)) (4.2 +/- 0.8 microM). Furthermore, MBP binds to the ERK2 x ATP complex at least 1500-fold more tightly than does ERKtide (K(d(ERKtide)) >/= 1.5 mM). The dramatically higher catalytic efficiency of MBP in comparison to that of ERKtide ( approximately 600-fold difference) is largely attributable to the slow dissociation rate of MBP (</=1.2 s(-1)) versus that of the synthetic peptide (>/=56 s(-1)), from the ERK2 active site.

[Utilization of an equimolar mixture of oxygen-nitrous oxide in a general pediatric ward]

We report our experience of the utilization of the 50% oxygen-nitrous oxide mixture (nitrous oxide 50%) in our general pediatric ward after one year of use.

PATIENTS AND METHODS

Between 1st April 1997 and 31st March 1998, children who had to undergo a painful procedure were proposed to inhale 50% nitrous oxide before the procedure. We evaluate pain, restlessness and adverse effects.

RESULTS

The procedures (127 of them) were carried out in 90 children (61 boys). They were aged from 5 months to 15 years (mean: 5.7 years; median: 4.1 years). Indications were: lumbar puncture (n = 45), burning dressing (n = 29), venous cannulation (n = 12), minor surgery (n = 27), and miscellaneous (n = 14). Inhalation time was between 2 to 70 min (mean: 14.4 min; median: 11 min). Pain was absent or low in 106 cases (83.4%). Restlessness was absent or low in 100 cases (78.8%). Averse events were observed 12 times, but they were always minor and quickly reversible.

CONCLUSION

Nitrous oxide (50%) can be used successfully in a general pediatric ward. Other studies are necessary to define the best conditions.

Backbone flexibility of five sites on the catalytic subunit of cAMP-dependent protein kinase in the open and closed conformations

To develop an alternative approach to measure peptidyl backbone flexibility and to expand our understanding of the segmental flexibility of cAMP-dependent protein kinase (cAPK), the effect of protein kinase inhibitor peptide, PKIalpha(5-24), and MgATP on the mobility of fluorescein selectively conjugated to five sites on the catalytic subunit of cAPK was examined. Specifically, five full-length, single-site catalytic subunit mutants (K16C, K81C, I244C, C199A, and N326C) were prepared, and fluorescein maleimide was selectively attached to the side chains of each substituted cysteine or, in the case of the C199A mutant, to the unprotected native C343. The time-resolved anisotropy decay profiles of the five fluorescein maleimide-conjugated mutants were well fit to a biexponential equation. The fast rotational correlation times of the fluorescein conjugates ranged between 1.9 and 2.8 ns and were inversely correlated (r = -0.87) to the averaged crystallographic main-chain atom B factors around each site of conjugation. The slow correlation times ranged between 25 and 28 ns and were about the same magnitude as the value of 21 ns estimated from the Stokes-Einstein equation. The presence of MgATP and PKIalpha(5-24), which induces the closed conformation of cAPK, was associated with a reduction of the fast rotational correlation time of the K81C conjugate, indicating that the peptidyl backbone around K81 is measurably less flexible when the C subunit is in the closed compared with the open conformation. The results suggest (i) that time-resolved fluorescence anisotropy can assess the nanosecond flexibility of short segments of the peptidyl backbone around each site of labeling and (ii) that the substrate/pseudosubstrate binding differentially affects the backbone flexibility of cAPK.

Effects of mutations in the C-terminal region of NIa protease on cis-cleavage between NIa and NIb

Mutational analyses were carried out to investigate whether the nuclear inclusion protein a (NIa) C-terminal amino acids of turnip mosaic potyvirus play any roles in the cis-cleavage between NIa and NIb. The processing rate of the NIa-NIb junction sequence was decreased significantly by either V240D or Q243A mutation while little affected by F226D, V228E, K230E, I232D, or L235D mutation. The mutation of W212S, G213S, or I217D abolishing the cleavage at the NIb-CP or 6K1-cylindrical inclusion protein junction sequence decreased the processing rate to half the level of that of the wild type. Deletion of the C-terminal one (K230), two (S229 and K230), three (S229 to L231), or six amino acids (S229 to D234) as well as the insertion of five glycines between S229 and K230 or between S220 and Q221 did not affect significantly the cleavage while the deletion of 20 amino acids (Q218 to S237) decreased the processing rate to 73% of that of the wild type. These results rule out the possibility that the C-terminal region plays a role as a spacer in right placement of the NIa-NIb junction sequence and demonstrate that the C-terminal 20 amino acids from Q218 to S237 are not crucial for the cis-cleavage of the NIa-NIb junction sequence.

Absolute copy number and relative change in determinations of human immunodeficiency virus type 1 RNA in plasma: effect of an external standard on kit comparisons

Use of a common set of human immunodeficiency virus type 1 (HIV-1) RNA standards eliminated differences among absolute HIV-1 RNA copy number estimates made with three commercially available assays. The relative changes in the viral RNA levels determined by the commercial assays were similar and were unaffected by the use of a common set of standards.

Increased vertical transmission of human immunodeficiency virus from hepatitis C virus-coinfected mothers. Women and Infants Transmission Study

To determine if hepatitis C virus (HCV) infection affects vertical transmission of human immunodeficiency virus (HIV), 487 HIV-infected pregnant women in the prospective, multicenter, Women and Infants Transmission Study had HCV antibody (anti-HCV by second-generation ELISA) and HCV RNA (by quantitative polymerase chain reaction) measured in peripartum maternal plasma; 161 (33%) were anti-HCV-positive. HIV vertical transmission occurred from 42 HCV-infected mothers (26.1%) versus 53 HCV-uninfected mothers (16.3%; odds radio [OR], 1.82; P = .01). In a logistic regression model that included maternal drug use, a potential confounder, HCV infection was marginally associated with perinatal HIV transmission (OR, 1.64; P = .05), whereas drug use was not. Women who transmitted HIV had higher levels of HCV RNA (median, 721,254 copies/mL) than those who did not (337,561 copies/mL; P = .01). Maternal HCV infection is associated with increased HIV vertical transmission. Further studies are needed to ascertain if HCV directly affects perinatal HIV transmission or is a marker for another factor, such as maternal drug use.

Immune complex-dissociated p24 antigen in congenital or perinatal HIV infection: role in the diagnosis and assessment of risk of infection in infants

Immune complex-dissociated (ICD) HIV-1 p24 antigen assay is a rapid technique for assessing the presence of HIV gag or core protein in plasma or serum. In this study, ICD p24 antigen detection in HIV-1 infected mothers and their infants enrolled in the Women and Infants Transmission Study (WITS) was evaluated primarily as a diagnostic assay for HIV-1 detection in young infants and for its association with perinatal transmission. Plasma from 47 infected infants and 160 uninfected infants was examined, along with plasma from 197 of their mothers who had a delivery or close-to-delivery specimen. ICD p24 antigen was detected in plasma of 27.3% of infected infants at birth and in 70% to 81% at 1 to 6 months. The diagnostic specificity at birth was 90% and 98% to 100.0% at 1 to 6 months. The ICD p24 antigen concentration correlated with concurrent quantitative HIV culture results. The risk of transmission from mother to infant was higher if the mother had detectable ICD p24 antigen at or near the time of delivery (p = 0.002), but its presence did not accurately predict transmission (positive predictive value of 36%, negative predictive values of 85%). The relative ease of performing the ICD p24 antigen assay and the low cost compared with that of HIV culture or DNA PCR makes this test a useful adjunct for the diagnosis of perinatal HIV infection and for enhancing understanding of its pathogenesis, particularly where cost and availability limit access to more sensitive assays.

Identification of a partially rate-determining step in the catalytic mechanism of cAMP-dependent protein kinase: a transient kinetic study using stopped-flow fluorescence spectroscopy

The kinetics of nucleotide binding and phosphoryl group transfer were measured in the catalytic subunit of cAMP-dependent protein kinase using stopped-flow fluorescence spectroscopy and an acrylodan-labeled derivative of this enzyme, which we have previously shown to have kinetic properties similar to those for the wild-type enzyme (Lew et al., 1996). The fluorescence emission spectrum of this enzyme is quenched differentially by ATP and ADP so that both the binding of ligands and phosphoryl group transfer at the active site can be monitored selectively. The association and dissociation rate constants for both nucleotides were measured using two methods: relaxation and competition binding. The ratio of the observed dissociation and association rate constants by both methods are consistent with Kd measurements (25 microM) determined by equilibrium fluorescence quenching. The dissociation rate constant for ADP (100 s(-1)) is approximately 2.5-fold larger than k(cat) (39 s(-1)). A full viscosity effect was measured for k(cat), suggesting that a diffusive step or steps limit maximum turnover. Pre-steady-state kinetic transients are biphasic and were fitted to observed rate constants of 500 s(-1) and 60 s(-1) at 500 microM Kemptide (LRRASLG). Metal substitution studies (Mg2+ vs Mn2+) indicate that this first phase represents the phosphoryl group transfer step. Phosphopeptide release is faster than this second phase since the substrate is in rapid exchange with the enzyme and phosphorylation reduces the affinity of the peptide. The inability to assign this second phase to the chemical event or to product release implies that it reflects a viscosity-sensitive, protein conformational change that occurs after phosphoryl group transfer and prior to product release. Two conformational steps were detected in the binding of both ATP and ADP by relaxation methods that may be related to this second pre-steady-state kinetic phase. We suggest that this additional step in the kinetic mechanism may also occur in the wild-type enzyme and represents a large structural change in the enzyme during normal catalytic cycling.

Defining the time of fetal or perinatal acquisition of human immunodeficiency virus type 1 infection on the basis of age at first positive culture. Women and Infants Transmission Study (WITS)

It has been suggested that a positive diagnostic test for human immunodeficiency virus type 1 (HIV-1) during the first 48 h of life is indicative of intrauterine transmission, whereas negative tests during the first week with positive tests later indicate intrapartum transmission. On the basis of data from all 140 infected infants in the Women and Infants Transmission Study (WITS), the probability was estimated that an HIV-1 culture would be positive for the first time at each day of life if cultures were performed daily. The estimated probabilities (+/-SE) by days 0, 2, 4, 7, 9, 16, and 30 of life are 27.4% (+/-6.4%), 27.4% (+/-13.0%), 45.3% (+/-20.5%), 45.3% (+/-22.5%), 65.3% (+/-20.0%), 88.4% (+/-7.8%), and 89.3% (+/-7.0%), respectively. The initial 27% probability is consistent with the hypothesis that transmission usually occurs during the intrapartum period. However, the distribution of age at first positive culture does not separate clearly into two distinct intervals. More definitive methods for determining the timing of transmission are needed.

Identification of functional domains in the neuronal Cdk5 activator protein

Cyclin-dependent kinase 5 (Cdk5) is activated by the neuronal-specific activator protein, p35. In contrast to the activation of typical CDKs by cyclin subunits, p35.Cdk5 was not further activated by the CDK-activating kinase (CAK) and was neither phosphorylated nor inhibited by the Tyr-15-specific Wee1 kinase. The previously identified proteolytic active fragment of p35, p25 (residues 91-307) as well as the slightly smaller fragment containing residues 109-291, was found to be sufficient to bind and activate Cdk5. Other CDKs, including Cdk2, associated weakly with p25. However, their kinase activity was only activated to the low level observed for cyclin A.Cdk2 without Thr-160 phosphorylation, and phosphorylation of Thr-160 in Cdk2 did not activate the p25.Cdk2 complex further. We have identified distinct regions in p35 required for binding to Cdk5 or activation of Cdk5. Residues approximately 150-200 of p35 were sufficient for binding to Cdk5, but residues approximately 279-291 were needed in addition for activation of Cdk5 in vitro.

Synergistic binding of nucleotides and inhibitors to cAMP-dependent protein kinase examined by acrylodan fluorescence spectroscopy

We have engineered an acrylodan-modified derivative of the catalytic subunit of cyclic AMP-dependent protein kinase (cAPK) whose fluorescence emission signal has allowed the synergistic binding between nucleotides and physiological inhibitors of cAPK to be examined (Whitehouse, S., and Walsh, D. A. (1983) J. Biol. Chem. 258, 3682-3692). In the presence of the regulatory subunit, RI, the affinity of cAPK for adenosine, ADP, AMPPNP (adenosine 5'-(beta, gamma-imino)triphosphate), or ATP was 5-, 50-, 120-, and 15,000-fold enhanced, while in the presence of the heat-stable inhibitor protein of cAPK (PKI), there was a 3-, 20-, 33-, and 2000-fold enhancement in the binding of these nucleotides, respectively. A short inhibitor peptide, PKI-(14-22), enhanced the binding of ADP to the same degree as did full-length PKI (20-fold) but, in contrast, did not significantly enhance the binding of ATP or AMPPNP. The full binding synergism between PKI and either ATP (2000-fold) or AMPPNP (33-fold) to cAPK could, however, be mimicked by a longer peptide, PKI-(5-24), suggesting that the PKI NH2 terminus (residues 5-13) is most likely critical. Since this region is remote from the ATP gamma-phosphate, the binding synergism must arise through an extended network communication mechanism between the PKI NH2 terminus and the ATP binding site.

Effects of internal cleavages and mutations in the C-terminal region of NIa protease of turnip mosaic potyvirus on the catalytic activity

The nuclear inclusion protein a (NIa) of turnip mosaic potyvirus is a protease processing the viral polyprotein into functional proteins. It has been shown that the NIa C-terminal 27-kDa protease cleaves itself between Ser-223 and Gly-224 to generate a 25-kDa protein lacking the C-terminal 20 amino acids. We have found a second internal cleavage near the C-terminus resulting in the degradation of the 25-kDa protein into a 24-kDa protein. Substitution of the active site Asp-81 or Cys-151 with Asn or Ser, respectively, prevented the second cleavage, suggesting that the internal cleavage is also due to the proteolytic activity of the NIa protease. This second internal cleavage was found to occur between Thr-207 and Ser-208, eliminating the C-terminal 36 amino acids from the 27-kDa protease. The proteolytic activity of the 24-kDa protein was not detected at all when it was measured using a nonapeptide containing the cleavage site between 6K1 and Cl as a substrate, suggesting that the C-terminal region between residues 208 and 223 contains essential amino acids for the processing of 6K1-Cl polyprotein. The deletion analyses of the C-terminal region revealed that at least 217 amino acids from the N-terminus are required for the catalytic activity of the NIa protease. The point mutation of Trp-212 to Ser, Gly-213 to Ser, or Ile-217 to Asp drastically abolished the catalytic activity, demonstrating that Trp-212, Gly-213, and Ile-217 are important for the processing of 6K1-Cl polyprotein.

Localization and developmental changes in the neuron-specific cyclin-dependent kinase 5 activator (p35nck5a) in the rat brain

Mammalian brains contain a cde2-like protein kinase which is a heterodimer of cyclin-dependent kinase 5 (Cdk5) and a brain-specific regulatory subunit with a molecular weight of 35,000. In this study, we examined the temporal and spatial expression patterns of p35nck5a in the developing rat brain. Northern blot analysis showed that p35nck5a messenger RNA expression was low in the brain of 12-day postcoitum rats, and increased to a much higher level from 18 days postcoitum to two weeks after birth, and then declined at three weeks after birth. These developmental changes in p35nck5a expression correlated with the changes in Cdk5-associated kinase activity during brain development. These data suggest that p35nck5a is the specific activator for Cdk5 in the brain. Immunohistochemical and in situ hybridization studies demonstrated the presence of p35nck5a protein in postmitotic neurons but not in glial cells at all stages of brain development, indicating that p35nck5a is a neuron-specific protein. In the adult brain, the protein was rich in cell bodies and dendrites, and only very low amounts were detected in axons. In fetal and neonatal brains, however, axonal pathways such as the corpus callosum and external capsule were also stained with anti-p35nck5a antibody. Our findings suggest that p35nck5a is neuron specific, and a specific activator for Cdk5, and the subcellular localization of the two is strictly regulated depending on brain development. Neuronal Cdc2-like kinase may play key roles in neuronal maturation, synaptic formation, and neuronal plasticity.

Characterization of Nla protease from turnip mosaic potyvirus exhibiting a low-temperature optimum catalytic activity

Nuclear inclusion protein a (Nla) protease of turnip mosaic potyvirus is responsible for the processing of the viral polyprotein into functional proteins. The Nla protease was found to exhibit its optimum catalytic activity at approximately 15 degrees and a bell-shaped pH-dependent activity profile with a maximum at approximately pH 8.5. Kinetic studies showed that both Km and V(max) values were lower at 12 than at 25 degrees in all three different pH conditions, pH 7.0, 7.4, and 8.3, indicating that the higher activity at 12 degrees is due to the lower value of Km. Interestingly, the self-cleavage of the 27-kDa protease to generate the 25-kDa protease occurred more rapidly at 25 than at 12 degrees, implying that the C-terminal self-cleavage site may interfere with the binding of the peptide substrate to the active site of the protease. Mutations and deletions at the C-terminal cleavage site had no effect on the temperature dependence of the proteolytic activity, demonstrating that the C-terminal self-cleavage is not related to the low-temperature optimum catalytic activity. The fluorescence measurement of the Nla protease upon temperature variation revealed that the protease undergoes a large conformational change between 2 and 42 degrees and a drastic transition near 45 degrees, suggesting that the low-temperature optimum catalytic activity is due to the highly flexible structure of the Nla protease.

Early detection of human immunodeficiency virus on dried blood spot specimens: sensitivity across serial specimens. Women and Infants Transmission Study Group

OBJECTIVE

To evaluate the use of dried blood spot (DBS) specimens and the early diagnostic value of the polymerase chain reaction (PCR) for detection of the human immunodeficiency virus (HIV) in DBS specimens collected at predefined age intervals from a large cohort of U.S. infants at risk of congenital or perinatal HIV infection.

DESIGN

We assayed available DBS specimens (n = 272) obtained during the first 4 months of life from 144 infants (41 infected, 103 uninfected) born to HIV-infected mothers enrolled in the Women and Infants Transmission Study. The DBS PCR results were compared with infant HIV infection status, PCR on liquid blood, and viral culture results. Analyses also included sensitivity and specificity of assay as related to the age of the infant when the specimen was obtained.

RESULTS

The DBS specimen PCR results were concordant with results from liquid blood specimens and with results from viral culture. The DBS PCR was highly specific for all age groups. Sensitivity in detecting HIV infection status rapidly increased during the first month of life, from 19% (5/26) by 1 week to 96% (25/26) by 1 month of age. Specimens obtained on the day of birth or the next day were the least likely to have detectable HIV DNA.

CONCLUSIONS

The PCR assay of DBS specimens is a reliable tool for the early diagnosis of HIV infection and has important advantage over that of liquid blood DNA PCR and viral culture. These advantages include a lower volume of blood required for testing, increased safety, and ease of storage or transport of specimens. Thus DBS PCR is a useful test for clinical and epidemiologic tracking of infants at risk of HIV infection.

The utility of IgA antibody to human immunodeficiency virus type 1 in early diagnosis of vertically transmitted infection. National Institute of Allergy and Infectious Diseases and National Institute of Child Health and Human Development Women and Infants Transmission Study Group

OBJECTIVE

To determine the sensitivity and specificity of anti-human immunodeficiency virus (HIV) IgA in identifying infected infants at or before 6 months of age among the offspring of HIV-infected mothers.

DESIGN

Prospective comparison of anti-HIV IgA measurement performed in 2 different laboratories by 2 different methods with the criterion standard of blood culture.

SETTING

Five centers in the United States and Puerto Rico.

PATIENTS

Population-based sample of 156 infants of HIV-infected mothers in the Women and Infants Transmission Study.

MAIN OUTCOME MEASURES

Results of anti-HIV IgA test in relation to the infection status of the infants as measured by blood culture.

RESULTS

Six-month plasma or serum samples were first tested in the 2 laboratories. The sensitivity and specificity of anti-HIV IgA in detecting infected infants at this age by laboratories 1 and 2 were 69% and 63% and 100% and 99%, respectively. A look-back study of samples obtained at birth, 1, 2, and 4 months was then performed on all infected children and a matched set of uninfected children. The performance of the test at birth was unsatisfactory in both laboratories (sensitivity 44% and 33%, specificity 43% and 60%), whether peripheral or cord blood was examined. At 1, 2, and 4 months, the sensitivity of the test was lower than at 6 months, but specificity was high. A modest correlation of absent anti-HIV IgA antibody and low percentage of CD4 cells in peripheral blood was seen at 6 months of age.

CONCLUSIONS

The anti-HIV IgA test has moderate sensitivity and high specificity for the diagnosis of HIV infection at 6 months of age in the offspring of infected mothers.

Bound to activate: conformational consequences of cyclin binding to CDK2

The cyclin-dependent kinases (CDKs) are among the most highly regulated enzymes in the protein-kinase family. The crystal structures of cyclin A and the CDK2-cyclin A complex spectacularly reveal the atomic basis for regulation of these enzymes and provide a template for understanding the function and regulation of other members of the CDK family.

Expression, purification, and identification of a novel self-cleavage site of the Nla C-terminal 27-kDa protease of turnip mosaic potyvirus C5

The gene encoding the C-terminal protease domain (27 kDa) of the nuclear inclusion protein a of turnip mosaic potyvirus C5 was cloned and expressed as a fusion protein with glutathione S-transferase in Escherichia coli XL1-blue. Two forms of the protease (27 and 25 kDa) were purified from the fusion protein by glutathione affinity chromatography and Mono S chromatography and exhibited the specific proteolytic activity when a synthetic undecapeptide, Glu-Pro-Thr-Val-Tyr-His-Gln-Thr-Leu-Asn-Glu, or an in vitro translation product of the polyprotein containing the cleavage site between the nuclear inclusion protein b and the capsid protein, was used as a substrate. The purified proteases showed a Km of 1.15 +/- 0.16 mM and a Vmax of 0.74 +/- 0.091 mumol/mg/min with the synthetic peptide substrate. The 25-kDa protein was found to be generated by the cleavage between Ser223 and Gly224 near the C-terminus of the 27-kDa protease and to retain the specific proteolytic activity. The point mutation of Asp81 or Cys151, two putative active site residues in the 27-kDa protease, to Asn or Ser, respectively, prevented the generation of the 25-kDa protein and diminished the proteolytic activity of the protease drastically, suggesting that the 27-kDa protease cleaves itself between Ser223 and Gly224 to generate the 25-kDa protein.

Reconstitution of neuronal Cdc2-like kinase from bacteria-expressed Cdk5 and an active fragment of the brain-specific activator. Kinase activation in the absence of Cdk5 phosphorylation

Neuronal Cdc2-like kinase is a heterodimer of Cdk5 and a 25-kDa subunit which is derived from a brain-specific 35-kDa novel protein, p35 (Lew, J., Huang, Q.-Q., Qi, Z., Winkfein, R. J., Aebersold, R., Hunt, T., and Wang, J. H. (1994) Nature 371, 423-426). Three truncated forms of p35 including the one corresponding to the 25-kDa subunit of the kinase have been expressed in Escherichia coli and shown to activate a bacteria-expressed Cdk5 with equal efficacy. The shortest truncated form of p35, p21, spanning amino acid residues 88 to 291, has been used to reconstitute active Cdk5 kinase and to characterize the activation reaction. The purified kinase displays similar specific enzyme activity and similar phosphorylation site specificity as the neuronal Cdc2-like kinase purified from bovine brain. Bovine brain extract contains Cdk5 uncomplexed with p35 or p25 which has also been found to be activated by p21 or p25. The results substantiate the previous suggestion that p35 is a specific Cdk5 activator. Several observations suggest that, unlike other well characterized Cdc2-like kinases whose activities depend on the phosphorylation of the catalytic subunits at a specific site by a distinct kinase, the reconstituted Cdk5/p21 does not depend on the phosphorylation of Cdk5 for activity. The reconstitution of the highly active Cdk5 kinase was achieved without requiring any other kinase in the reconstitution reaction. The possibility of autophosphorylation of Cdk5 on the putative activation site has been ruled out as no phosphorylation occurred on Cdk5 during the enzyme reaction. The rate and extent of the kinase reconstitution were not significantly affected by Mg2+ ATP.

Structure, function, and regulation of neuronal Cdc2-like protein kinase

We have identified and purified from bovine brain a novel protein kinase which catalyzes in vitro phosphorylation of neurofilament proteins NF-H and NF-M and tau proteins at sites implicating the enzyme in the regulation of neurocytoskeleton dynamics and in Alzheimer pathology. The protein kinase displays a phosphorylation site specificity similar or identical to the cell cycle regulatory kinase, cdc2 kinase. The purified kinase is a heterodimer of a cdc2-like catalytic subunit, called cdk5, and a 25 kDa regulatory subunit. The regulatory subunit is essential for kinase activity, and it is derived from a 35 kDa protein, p35 by proteolysis. Northern blot analysis of tissue distribution indicates that cdk5 is widely distributed but especially rich in brain, whereas p35 expression is only found in brain. The protein kinase is therefore termed neuronal cdc2-like kinase. The neuron-specificity of the enzyme appears to be conferred by the regulatory subunit. During cell division, cdc2 kinase is regulated by complex phosphorylation mechanisms involving a network of specific protein kinases. Some of these kinases or their homologs have been found in mammalian brains and they may be involved in the regulation of neuronal cdc2-like kinase.

Neuronal cdc2-like kinase

Neurofilament proteins and the neuron-specific microtubule-associated protein tau are phosphorylated in vivo at sites conforming to the phosphorylation consensus motif of the cell-cycle-control protein kinase, p34cdc2-cyclin. Abnormalities in the phosphorylation of these proteins are associated with neurodegenerative disorders, such as amylotrophic lateral sclerosis and Alzheimer's disease. A cdc2-like kinase composed of cyclin-dependent kinase 5 (cdk5) and a brain-specific regulatory subunit is proposed to be responsible for the cdc2-like phosphorylation of these neuronal proteins.

A brain-specific activator of cyclin-dependent kinase 5

Phosphorylation of the neurofilament proteins of high and medium relative molecular mass, as well as of the Alzheimer's tau protein, is thought to be catalysed by a protein kinase with Cdc2-like substrate specificity. We have purified a novel Cdc2-like kinase from bovine brain capable of phosphorylating both the neurofilament proteins and tau. The purified enzyme is a heterodimer of cyclin-dependent kinase 5 (Cdk5) and a novel regulatory subunit, p25 (ref. 8). When overexpressed and purified from Escherichia coli, p25 can activate Cdk5 in vitro. Unlike Cdk5, which is ubiquitously expressed in human tissue, the p25 transcript is expressed only in brain. A full-length complementary DNA clone showed that p25 is a truncated form of a larger protein precursor, p35, which seems to be the predominant form of the protein in crude brain extract. Cdk5/p35 is the first example of a Cdc2-like kinase with neuronal function.

Butyrate increases colonocyte protein synthesis in ulcerative colitis

Butyrate promotes epithelial cell healing and improves symptoms when administered rectally in patients with distal ulcerative colitis (UC). It was hypothesized that butyrate may enhance healing in patients with UC by stimulating colonocyte proliferation and/or protein production. Mucosa from the descending colon was obtained from patients with UC (n = 5), Crohn's disease (n = 8), diverticulitis (n = 6), and cancer (normal tissue 10 cm from tumor; n = 10). Epithelial cells were isolated using dispase/collagenase and differential sedimentation and incubated for 4 hr at 37 degrees C with either Na butyrate (10 mM) or NaCl (10 mM). Protein synthesis was assessed by [14C]leucine incorporation and proliferation was determined with [3H]thymidine. Mean viability and purity were >88%. Spontaneous proliferation was significantly increased in UC when compared to diverticulitis and normal controls. Butyrate significantly increased protein synthesis in UC epithelial cells when compared to saline control. The therapeutic effects of butyrate in patients with UC may be due to its use by epithelial cells as a metabolic fuel to increase protein production and promote healing.

Purification of a 15-kDa cdk4- and cdk5-binding protein

Yeasts p13suc1/p18CKS and their human homologues, p9CKShs1/p9CKShs2, strongly interact with p34cdc2 and p34cdk2. While attempting to purify the starfish oocyte p13suc1 homologue, we discovered a 15-kDa protein cross-reactive with anti-p9CKShs2/anti-p13suc1 antibodies. p15cdk-BP-Sepharose binds an anti-PSTAIRE cross-reactive protein of 33 kDa when loaded with starfish oocyte extracts. The p15cdk-BP-bound "PSTAIRE signal" is part of a 250-kDa complex distinct from p34cdc2/cyclin B. p15cdk-BP-Sepharose beads retain a kinase phosphorylating HMG I/Y, P1, and myelin basic protein (among 24 substrates tested). Major cdc2 kinase substrates are not phosphorylated by the p15cdk-BP-bound kinase. Phosphopeptide maps of P1 phosphorylated by the p15cdk-BP-bound kinase, p34cdc2/cyclin B, p 33cdk5/p25, and casein kinase 2 showed that these kinases phosphorylate P1 on different sites. Phosphopeptide maps of P1 phosphorylated by the p15cdk-BP-bound starfish kinase and p15cdk-BP-bound human p34cdk4/cyclin D are largely coincident. To investigate the nature of the p15cdk-BP-bound kinase, extracts of mammalian tissues and cells were loaded on p9CKShs1- and p15cdk-BP-Sepharose and the bound proteins were analyzed using specific anti-cdk antibodies. cdc2 and cdk2 bind to p9CKShs1-Sepharose, but not to p15cdk-BP. cdk4 and cdk5 bind to p15cdk-BP-Sepharose, but not to p9CKShs1-Sepharose. We conclude that p15cdk-BP specifically binds the cdk4/cyclin D and cdk5 kinases and, along with p13suc1 and p9CKShs, may be part of a larger family of cdk-binding proteins.