Social impairment in survivors of pediatric brain tumors via reduced social attention and emotion-specific facial expression recognition

BACKGROUND/OBJECTIVES

Survivors of pediatric brain tumors (SPBT) experience significant social challenges, including fewer friends and greater isolation than peers. Difficulties in face processing and visual social attention have been implicated in these outcomes. This study evaluated facial expression recognition (FER), social attention, and their associations with social impairments in SPBT.

METHODS

SPBT (N = 54; ages 7-16) at least 2 years post treatment completed a measure of FER, while parents completed measures of social impairment. A subset (N = 30) completed a social attention assessment that recorded eye gaze patterns while watching videos depicting pairs of children engaged in joint play. Social Prioritization scores were calculated, with higher scores indicating more face looking. Correlations and regression analyses evaluated associations between variables, while a path analysis modeling tool (PROCESS) evaluated the indirect effects of Social Prioritization on social impairments through emotion-specific FER.

RESULTS

Poorer recognition of angry and sad facial expressions was significantly correlated with greater social impairment. Social Prioritization was positively correlated with angry FER but no other emotions. Social Prioritization had significant indirect effects on social impairments through angry FER.

CONCLUSION

Findings suggest interventions aimed at improving recognition of specific emotions may mitigate social impairments in SPBT. Further, reduced social attention (i.e., diminished face looking) could be a factor in reduced face processing ability, which may result in social impairments. Longitudinal research is needed to elucidate temporal associations between social attention, face processing, and social impairments.

Ethical considerations for integrating multimodal computer perception and neurotechnology

Background

Artificial intelligence (AI)-based computer perception technologies (e.g., digital phenotyping and affective computing) promise to transform clinical approaches to personalized care in psychiatry and beyond by offering more objective measures of emotional states and behavior, enabling precision treatment, diagnosis, and symptom monitoring. At the same time, passive and continuous nature by which they often collect data from patients in non-clinical settings raises ethical issues related to privacy and self-determination. Little is known about how such concerns may be exacerbated by the integration of neural data, as parallel advances in computer perception, AI, and neurotechnology enable new insights into subjective states. Here, we present findings from a multi-site NCATS-funded study of ethical considerations for translating computer perception into clinical care and contextualize them within the neuroethics and neurorights literatures.

Methods

We conducted qualitative interviews with patients (n = 20), caregivers (n = 20), clinicians (n = 12), developers (n = 12), and clinician developers (n = 2) regarding their perspective toward using PC in clinical care. Transcripts were analyzed in MAXQDA using Thematic Content Analysis.

Results

Stakeholder groups voiced concerns related to (1) perceived invasiveness of passive and continuous data collection in private settings; (2) data protection and security and the potential for negative downstream/future impacts on patients of unintended disclosure; and (3) ethical issues related to patients' limited versus hyper awareness of passive and continuous data collection and monitoring. Clinicians and developers highlighted that these concerns may be exacerbated by the integration of neural data with other computer perception data.

Discussion

Our findings suggest that the integration of neurotechnologies with existing computer perception technologies raises novel concerns around dignity-related and other harms (e.g., stigma, discrimination) that stem from data security threats and the growing potential for reidentification of sensitive data. Further, our findings suggest that patients' awareness and preoccupation with feeling monitored via computer sensors ranges from hypo- to hyper-awareness, with either extreme accompanied by ethical concerns (consent vs. anxiety and preoccupation). These results highlight the need for systematic research into how best to implement these technologies into clinical care in ways that reduce disruption, maximize patient benefits, and mitigate long-term risks associated with the passive collection of sensitive emotional, behavioral and neural data.

Creation of a versatile automated two-step purification system with increased throughput capacity for preclinical mAb material generation

The ever-increasing speed of biotherapeutic drug discovery has driven the development of automated and high throughput purification capabilities. Typically, purification systems require complex flow paths or third-party components that are not found on a standard fast protein liquid chromatography instrument (FPLC) (e.g., Cytiva's ÄKTA) to enable higher throughput. In early mAb discovery there is often a trade-off between throughput and scale where a high-throughput process requires miniaturized workflows necessitating a sacrifice in the amount of material generated. At the interface of discovery and development, flexible automated systems are required that can perform purifications in a high-throughput manner, while also generating sufficient quantities of preclinical material for biophysical, developability, and preclinical animal studies. In this study we highlight the engineering efforts to generate a highly versatile purification system capable of balancing the purification requirements between throughput, chromatographic versatility, and overall product yields. We incorporated a 150 mL Superloop into an ÄKTA FPLC system to expand our existing purification capabilities. This allowed us to perform a range of automated two-step tandem purifications including primary affinity captures (protein A (ProA)/immobilized metal affinity chromatography (IMAC)/antibody fragment (Fab)) followed by secondary polishing with either size exclusion (SEC) or cation exchange (CEX) chromatography. We also integrated a 96 deep-well plate fraction collector into the ÄKTA FPLC system with purified protein fractions being analyzed by a plate based high performance liquid chromatography instrument (HPLC). This streamlined automated purification workflow allowed us to process up to 14 samples within 24 hr, enabling purification of ∼1100 proteins, monoclonal antibodies (mAbs), and mAb related protein scaffolds during a 12-month period. We purified a broad range of cell culture supernatant volumes, between 0.1 - 2 L, with final purification yields up to 2 g. The implementation of this new automated, streamlined protein purification process greatly expanded our sample throughput and purification versatility while also enabling the accelerated production of greater quantities of biotherapeutic candidates for preclinical in vivo animal studies and developability assessment.

Sleep problems in autism: Sex differences in the school-age population

Clinically significant sleep problems affect up to 86% of the autistic population in school-age. Sleep problems can have negative impacts on child cognition, behavior, and health. However, sex differences in the prevalence and types of sleep problems are not well understood in autism. To evaluate sex differences in sleep problems in the school-age autistic population, we obtained parent-report of sleep problems on the Children's Sleep Habits Questionnaire and conducted direct assessments to establish diagnosis and intellectual ability in 6-12-year-old children (autism n = 250; typical development [TD] n = 114). Almost 85% of autistic females demonstrated sleep problems compared to 65.8% of autistic males, 44.8% of TD females, and 42.4% of TD males; a statistically significant increase for autistic females. Autistic females demonstrated increased bedtime resistance, sleep anxiety, and sleepiness, and decreased sleep duration, but did not differ in sleep onset delay, night wakings, parasomnias, or disordered breathing compared with autistic males. Intellectual ability was not related to increased sleep problems. Higher anxiety scores were associated with more sleep problems for males but not females. In one of the first studies to evaluate sex differences in sleep in the school-age, autistic population, autistic females demonstrated increased sleep problems compared to autistic males, TD females, and TD males. Current autism assessment and intervention practices may benefit from increased attention to sleep problems in autistic school-age females and to anxiety in autistic males to enhance well-being and behavioral and health outcomes.

Face Processing and Social Functioning in Pediatric Brain Tumor Survivors

OBJECTIVE

Pediatric brain tumor survivors (PBTS) experience deficits in social functioning. Facial expression and identity recognition are key components of social information processing and are widely studied as an index of social difficulties in youth with autism spectrum disorder (ASD) and other neurodevelopmental conditions. This study evaluated facial expression and identity recognition among PBTS, youth with ASD, and typically developing (TD) youth, and the associations between these face processing skills and social impairments.

METHODS

PBTS (N = 54; ages 7-16) who completed treatment at least 2 years prior were matched with TD (N = 43) youth and youth with ASD (N = 55) based on sex and IQ. Parents completed a measure of social impairments and youth completed a measure of facial expression and identity recognition.

RESULTS

Groups significantly differed on social impairments (p < .001), with youth with ASD scoring highest followed by PBTS and lastly TD youth. Youth with ASD performed significantly worse on the two measures of facial processing, while TD youth and PBTS were not statistically different. The association of facial expression recognition and social impairments was moderated by group, such that PBTS with higher levels of social impairment performed worse on the expression task compared to TD and ASD groups (p < .01, η2 = 0.07).

CONCLUSIONS

Variability in face processing may be uniquely important to the social challenges of PBTS compared to other neurodevelopmental populations. Future directions include prospectively examining associations between facial expression recognition and social difficulties in PBTS and face processing training as an intervention for PBTS.

Profiles of Autonomic Activity in Autism Spectrum Disorder with and without Anxiety

Both anxiety and autism spectrum disorder (ASD) are associated with atypical physiological activity. Few studies have systematically assessed the resting physiological activity in ASD with co-occurring anxiety disorders. We tested 75 participants divided in four groups: youth with ASD, with (ASD + Anxiety = 22, 6F, 12.29 ± 2.83 years old) and without co-occurring anxiety (ASD Alone = 15, 6F, 11.59 ± 2.85 years old) and compared their physiological profile with that of matched typically developing controls (TDC) with (Anxiety Alone = 16, 6F, 11.24 ± 3.36 years old) and without co-occurring anxiety disorders (TDC = 22, 8F, 11.88 ± 2.88 years old). Results indicated reduced sympathetic and parasympathetic activity at rest in ASD as compared to TDC youth. ASD + Anxiety and Anxiety Alone groups showed different sympathetic, but similar parasympathetic activity. These findings suggest that autonomic profile-based approaches may advance research, diagnosis, and treatment of ASD and anxiety.

Heart rate increase predicts challenging behavior episodes in preschoolers with autism

Identifying triggers for challenging behavior is difficult in some children with autism because of their limited communication abilities. Physiological indicators of stress may provide important insights. This study examined whether heart rate (HR) predicts challenging behavior in children with autism. While wearing an electrocardiograph monitor, 41 children with autism aged 2- to 4-years participated in tasks designed to induce low-level stress (e.g. waiting for a snack). Coders identified 106 time periods during which challenging behaviors occurred and also coded 106 randomly selected time samples that did not include challenging behaviors. Thirteen (32%) participants exhibited challenging behaviors and were included in the study. Baseline-corrected HR was computed for each behavior/time sample. On average, children with autism showed a 22 ± 16% HR increase from baseline 58 ± 22 seconds before the onset of a challenging behavior episode. Peak HR change had moderate predictive utility (area under the curve = .72, p < .001). The increase in HR before challenging behaviors was similar for children of different characteristics (age, autism severity, expressive language ability, overall developmental ability). Results highlight the promise of using physiological stress to predict challenging behavior in preschoolers with autism; although, they need to be replicated in larger samples. Given recent advances in wearable biosensing, it may be useful to incorporate HR monitoring in autism intervention. Lay summary In children with autism, changes in heart rate (HR) may help us predict when challenging behavior is about to occur - but this hypothesis has not been well studied. In this study, HR increase moderately predicted challenging behavior in preschoolers with autism. Given recent advances in wearable sensors, it may be useful to incorporate HR monitoring in autism intervention.

Zika and travel in the news: a content analysis of US news stories during the outbreak in 2016-2017

OBJECTIVES

This study aimed to understand what information the US media communicated about Zika virus (ZIKV) and travel in 2016 and 2017.

STUDY DESIGN

We conducted a content analysis of news coverage about ZIKV and travel from April 5, 2016 to March 31, 2017.

METHODS

We obtained a stratified, random sample of English language, US print newspaper and television news coverage about ZIKV and travel. We developed a coding scheme to assess key messages in the news, including how ZIKV is transmitted, the symptoms and outcomes of ZIKV infection, and recommended prevention behaviors.

RESULTS

Almost all news stories mentioned mosquito-borne transmission (96.8%) and just over half mentioned sexual transmission (55.3%). News stories were more likely to talk about ZIKV outcomes (78.8%) than ZIKV symptoms (40.6%). However, outcomes affecting babies were mentioned more frequently than outcomes affecting adults. Recommendations included a wide array of protective behaviors, such as delaying or avoiding travel (77.6%) and using mosquito repellent (41.0%). However, few studies (10.9%) mentioned barriers to practicing ZIKV prevention behaviors.

CONCLUSIONS

Public health organizations and professionals can use these findings to help improve communication about future outbreaks of mosquito-borne illnesses. We also recommend conducting real-time monitoring of news media and frequent content analysis of news stories to ensure coverage provides the information the public needs.

Phenotypic characterisation of cell populations in the brains of horses experimentally infected with West Nile virus

BACKGROUND

West Nile virus (WNV), a mosquito borne member of the Flaviviridae, is one of the most commonly diagnosed agents of viral encephalitis in horses and people worldwide.

OBJECTIVES

A cassette of markers for formalin-fixed paraffin-embedded tissue and an archive of tissues from experimental infections in the horse were used to investigate the equine neuroimmune response to WNV meningoencephalomyelitis to phenotype the early response to WNV infection in the horse.

STUDY DESIGN

Quantitative analysis using archived tissue from experimentally infected horses.

METHODS

The thalamus and hindbrain from 2 groups of 6 horses were compared and consisted of a culture positive tissues from WNV experimentally horses, in the other, normal horses. Formalin-fixed paraffin-embedded tissue from the thalamus and hindbrain were immunolabeled for microglia, astrocytes, B cells, macrophages/neutrophils, CD3⁺ T cells. Fresh frozen tissues were immunolabeled for CD4⁺ and CD8⁺ T lymphocyte cell markers. Cell counts were obtained using a computer software program. Differences, after meeting assumptions of abnormality, were computed using a general linear model with a Tukey test (P<0.05) for pairwise comparisons.

RESULTS

In WNV-challenged horses, Iba-1⁺ microglia, CD3⁺ T lymphocyte and MAC387⁺ macrophage staining were significantly increased. The T cell response for the WNV-challenged horses was mixed, composed of CD4⁺ and CD8⁺ T lymphocytes. A limited astrocyte response was also observed in WNV-challenged horses, and MAC387⁺ and B cells were the least abundant cell populations.

MAIN LIMITATIONS

The results of this study were limited by a single collection time post-infection. Furthermore, a comprehensive analysis of cellular phenotypes is needed for naturally infected horses. Unfortunately, in clinical horses, there is high variability of sampling in terms of days post-infection and tissue handling.

CONCLUSIONS

The data show that WNV-challenged horses recruit a mixed T cell population at the onset of neurologic disease.

Methodological quality, completeness of reporting and use of systematic reviews as evidence in clinical practice guidelines for paediatric overweight and obesity

Paediatric obesity rates remain high despite extensive efforts to prevent and treat obesity in children. We investigated the quality of the methodology and reporting within systematic reviews (SRs) underpinning paediatric content in US clinical practice guidelines (CPGs). In June 2016 we searched guideline clearinghouses and professional organization websites for guidelines published by national or professional organizations in the United States from January 2007 onwards. In our primary, a priori analysis, we used PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) and AMSTAR (A Measurement Tool to Assess Systematic Reviews) instruments to score SRs and meta-analyses that included paediatric populations and were cited by included CPGs. In a secondary, post hoc analysis, we determined the extent to which US CPGs use available, relevant SRs and meta-analyses compared with non-US CPGs. Eight US-based CPGs with 27 references to 22 unique SRs were found. AMSTAR and PRISMA scores were low overall, with only three SRs having 'high' methodological quality. Items dealing with bias assessments and search strategies had especially low scores. US CPGs were also older on average and cited fewer SRs than their international counterparts. Low quality scores and dated guidelines should be a cause for concern among practicing clinicians and a call to action for future guideline developers, publishers and research institutions.

Brief measures of anxiety in non-treatment-seeking youth with autism spectrum disorder

This study investigated the accuracy of brief anxiety scales for non-treatment-seeking youth with autism spectrum disorder. In all, 54 youth (7-17 years; IQ: 67-158) with autism spectrum disorder and their parents completed (a) an expanded version of the Anxiety Disorders Interview Schedule-Child/Parent designed to capture typical and atypical fears and (b) brief scales of anxiety symptoms (Behavior Assessment Schedule for Children, Second Edition; Screen for Child Anxiety and Related Emotional Disorders; Negative Affective Self-Statement Questionnaire; Pediatric Anxiety Rating Scale). The results indicate that measures lacked adequate sensitivity and specificity, and the detection of atypical fears was particularly poor. Revised cut scores are offered, but refined and/or revised instruments are likely needed for research on youth with autism spectrum disorder.

Not to be overshadowed or overlooked: functional impairments associated with comorbid anxiety disorders in youth with ASD

This study's objective was to examine associations between comorbid anxiety disorders and difficulties commonly attributed to both anxiety and ASD (autism spectrum disorder) including self-injury, depressive symptoms, functional communication, social skill deficits and parent stress, in a well-characterized sample of youth with ASD. Fifty-nine verbally fluent participants (7-17 years; 93% Caucasian) diagnosed with ASD and their parents completed semistructured diagnostic interviews to confirm ASD diagnosis and assess for anxiety disorders. Parents completed questionnaires on child behavior and social skill as well as parental stress. Co-occurring anxiety disorders were associated with more parent-reported self-injurious behavior, depressive symptoms, and parental stress in youth with ASD, after controlling for other influential variables (e.g., ASD severity, cognitive ability, medication status). In contrast, youth with co-occurring anxiety disorders appeared to have significantly stronger parent-reported functional communication than youth with ASD alone as well as a comparable ability, according to parents, to initiate social interaction and develop relationships. Findings support a profile of challenges and relative strengths associated with the presence of anxiety disorders in youth with ASD. Though more research is needed to determine the direction of these associations, results provide further rationale for improving recognition and targeted treatment of this comorbidity in clinical practice.

Traditional and atypical presentations of anxiety in youth with autism spectrum disorder

We assessed anxiety consistent (i.e., "traditional") and inconsistent (i.e., "atypical") with diagnostic and statistical manual (DSM) definitions in autism spectrum disorder (ASD). Differential relationships between traditional anxiety, atypical anxiety, child characteristics, anxiety predictors and ASD-symptomology were explored. Fifty-nine participants (7-17 years, M(age) = 10.48 years; IQ > 60) with ASD and parents completed semi-structured interviews, self- and parent-reports. Seventeen percent of youth presented with traditional anxiety, 15 % with atypical anxiety, and 31 % with both. Language ability, anxious cognitions and hypersensitivity predicted traditional anxiety, whereas traditional anxiety and ASD symptoms predicted atypical anxiety. Findings suggest youth with ASD express anxiety in ways similar and dissimilar to DSM definitions. Similarities support the presence of comorbid anxiety disorders in ASD. Whether dissimilarities are unique to ASD requires further examination.

The role of emotion regulation in autism spectrum disorder

OBJECTIVE

Autism spectrum disorder (ASD) is associated with amplified emotional responses and poor emotional control, but little is known about the underlying mechanisms. This article provides a conceptual and methodologic framework for understanding compromised emotion regulation (ER) in ASD.

METHOD

After defining ER and related constructs, methods to study ER were reviewed with special consideration on how to apply these approaches to ASD. Against the backdrop of cognitive characteristics in ASD and existing ER theories, available research was examined to identify likely contributors to emotional dysregulation in ASD.

RESULTS

Little is currently known about ER in youth with ASD. Some mechanisms that contribute to poor ER in ASD may be shared with other clinical populations (e.g., physiologic arousal, degree of negative and positive affect, alterations in the amygdala and prefrontal cortex), whereas other mechanisms may be more unique to ASD (e.g., differences in information processing/perception, cognitive factors [e.g., rigidity], less goal-directed behavior and more disorganized emotion in ASD).

CONCLUSIONS

Although assignment of concomitant psychiatric diagnoses is warranted in some cases, poor ER may be inherent in ASD and may provide a more parsimonious conceptualization for the many associated socioemotional and behavioral problems in this population. Further study of ER in youth with ASD may identify meaningful subgroups of patients and lead to more effective individualized treatments.

Neural evidence for an association between social proficiency and sensitivity to social reward

Data from developmental psychology suggests a link between the growth of socio-emotional competences and the infant's sensitivity to the salience of social stimuli. The aim of the present study was to find evidence for this relationship in healthy adults. Thirty-five participants were recruited based on their score above the 85th or below the 15th percentile of the empathy quotient questionnaire (EQ, Baron-Cohen and Wheelwright, 2004). Functional magnetic resonance imaging (fMRI) was used to compare neural responses to cues of social and non-social (monetary) reward. When compared to the high-EQ group, the low-EQ group showed reduced activity of the brain s reward system, specifically the right nucleus accumbens, in response to cues predictive of social reward (videos showing gestures of approval)-but increased activation in this area for monetary incentives. Our data provide evidence for a link between self-reported deficits in social proficiency and reduced sensitivity to the motivational salience of positive social stimuli.

The responsiveness of biological motion processing areas to selective attention towards goals

A growing literature indicates that visual cortex areas viewed as primarily responsive to exogenous stimuli are susceptible to top-down modulation by selective attention. The present study examines whether brain areas involved in biological motion perception are among these areas-particularly with respect to selective attention towards human movement goals. Fifteen participants completed a point-light biological motion study following a two-by-two factorial design, with one factor representing an exogenous manipulation of human movement goals (goal-directed versus random movement), and the other an endogenous manipulation (a goal identification task versus an ancillary color-change task). Both manipulations yielded increased activation in the human homologue of motion-sensitive area MT+ (hMT+) as well as the extrastriate body area (EBA). The endogenous manipulation was associated with increased right posterior superior temporal sulcus (STS) activation, whereas the exogenous manipulation was associated with increased activation in left posterior STS. Selective attention towards goals activated a portion of left hMT+/EBA only during the perception of purposeful movement-consistent with emerging theories associating this area with the matching of visual motion input to known goal-directed actions. The overall pattern of results indicates that attention towards the goals of human movement activates biological motion areas. Ultimately, selective attention may explain why some studies examining biological motion show activation in hMT+ and EBA, even when using control stimuli with comparable motion properties.

Kindling and Oxidative Stress as Contributors to Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

Myalgic Encephalomyelitis/chronic fatigue syndrome (ME/CFS) is one of the more complex illnesses involving multiple systems within the body. Onset of ME/CFS frequently occurs quickly, and many patients report a prior exposure to a viral infection. This debilitating illness can affect the immune, neuroendocrine, autonomic, and neurologic systems. Abnormal biological findings among some patients have included aberrant ion transport and ion channel activity, cortisol deficiency, sympathetic nervous system hyperactivity, EEG spike waves, left ventricular dysfunction in the heart, low natural killer cell cytotoxicity, and a shift from Th1 to Th2 cytokines. We propose that the kindling and oxidative stress theories provide a heuristic template for better understanding the at times conflicting findings regarding the etiology and pathophysiology of this illness.

Efficacy of moxifloxacin for treatment of penicillin-, macrolide- and multidrug-resistant Streptococcus pneumoniae in community-acquired pneumonia

This pooled analysis of six prospective, multicentre trials aimed to determine the efficacy of moxifloxacin in community-acquired pneumonia (CAP) due to penicillin-, macrolide- and multidrug-resistant Streptococcus pneumoniae (MDRSP). At a central laboratory, isolates were identified and antimicrobial susceptibility determined (microbroth dilution). MDRSP was defined as resistance > or =3 drug classes. Patients received oral or sequential intravenous/oral 400 mg moxifloxacin once daily for 7-14 days. The primary endpoint was clinical success at test-of-cure for efficacy-valid patients with proven pretherapy S. pneumoniae infection. Of 140 S. pneumoniae isolated (112 respiratory, 28 blood), 23 (16.4%) were penicillin resistant, 26 (18.6%) macrolide resistant and 31 (22.1%) MDRSP. The moxifloxacin MIC90 was 0.25 microg/ml. Clinical cure with moxifloxacin was 95.4% (125/131) overall, and 100% (21/21) for penicillin-, 95.7% (22/23) for macrolide- and 96.4% (27/28) for multidrug-resistant strains. Moxifloxacin provided excellent clinical and bacteriological cure rates in CAP due to drug-resistant pneumococci.

Paying attention to emotion: an fMRI investigation of cognitive and emotional stroop tasks

In this research, we investigated the degree to which brain systems involved in ignoring emotionally salient information differ from those involved in ignoring nonemotional information. The design allowed examination of regional brain activity, using fMRI during color-word and emotional Stroop tasks. Twelve participants indicated the color of words while ignoring word meaning in conditions in which neutral words were contrasted to emotionally negative, emotionally positive, and incongruent color words. Dorsolateral frontal lobe activity was increased by both negative and incongruent color words, indicating a common system for maintaining an attentional set in the presence of salient distractors. In posterior regions of the brain, activity depended on the nature of the information to be ignored. Ignoring color-incongruent words increased left parietal activity and decreased parahippocampal gyrus activity, whereas ignoring negative emotional words increased bilateral occipito-temporal activity and decreased amygdala activity. The results indicate that emotion and attention are intimately related via a network of regions that monitor for salient information, maintain attention on the task, suppress irrelevant information, and select appropriate responses.

Signaling pathways activated by the growth hormone receptor

In recent years, significant progress has been made in elucidating the signaling pathways activated by the growth hormone (GH) receptor. An initiating event is probably the activation of JAK2 (Janus kinase 2), a GH receptor-associated tyrosine kinase. Identification of the proteins recruited to the GH receptor-JAK2 complex and dissection of the signaling pathways that are subsequently activated will ultimately provide a basis for understanding GH action at the molecular level.

Mutation of the SHP-2 binding site in growth hormone (GH) receptor prolongs GH-promoted tyrosyl phosphorylation of GH receptor, JAK2, and STAT5B

Binding of GH to GH receptor (GHR) rapidly and transiently activates multiple signal transduction pathways that contribute to the growth-promoting and metabolic effects of GH. While the events that initiate GH signal transduction, such as activation of the Janus tyrosine kinase JAK2, are beginning to be understood, the signaling events that terminate GH signaling, such as dephosphorylation of tyrosyl-phosphorylated signaling molecules, are poorly understood. In this report, we examine the role of the SH2 (Src homology-2) domain-containing protein tyrosine phosphatase SHP-2 in GH signaling. We demonstrate that the SH2 domains of SHP-2 bind directly to tyrosyl phosphorylated GHR from GH-treated cells. Tyrosine-to-phenylalanine mutation of tyrosine 595 of rat GHR greatly diminishes association of the SH2 domains of SHP-2 with GHR, and tyrosine-to-phenylalanine mutation of tyrosine 487 partially reduces association of the SH2 domains of SHP-2 with GHR. Mutation of tyrosine 595 dramatically prolongs the duration of tyrosyl phosphorylation of the signal transducer and activator of transcription STAT5B in response to GH, while mutation of tyrosine 487 moderately prolongs the duration of STAT5B tyrosyl phosphorylation. Consistent with the effects on STAT5B phosphorylation, tyrosine-to-phenylalanine mutation of tyrosine 595 prolongs the duration of tyrosyl phosphorylation of GHR and JAK2. These data suggest that tyrosine 595 is a major site of interaction of GHR with SHP-2, and that GHR-bound SHP-2 negatively regulates GHR/JAK2 and STAT5B signaling.

Role of the tyrosine kinase JAK2 in signal transduction by growth hormone

Chronic renal failure in children results in impaired body growth. This effect is so severe in some children that not only does it have a negative impact on their self-image, but it also affects their ability to carry out normal day-to-day functions. Yet the mechanism by which chronic renal failure causes short stature is not well understood. Growth hormone (GH) therapy increases body height in prepubertal children, suggesting that a better understanding of how GH promotes body growth may lead to better insight into the impaired body growth in chronic renal failure and therefore better therapies. This review discusses what is currently known about how GH acts at a cellular level. The review discusses how GH is known to bind to a membrane-bound receptor and activate a cytoplasmic tyrosine kinase called Janus kinase (JAK) 2. The activated JAK2 in turn phosphorylates tyrosines within itself and the associated GH receptor, forming high-affinity binding sites for a variety of signaling molecules. Examples of such signaling molecules include signal transducers and activators of transcription (Stats), which regulate the expression of a variety of GH-dependent genes, and the adapter protein Shc, which leads to activation of the Ras-Raf-MEK-MAP kinase pathway. In response to GH, JAK2 is also known to phosphorylate the insulin receptor substrates, leading to activation of phosphatidyl inositol 3' kinase and most likely other molecules that have been implicated in the regulation of metabolism. Finally, the ability of JAK2 to bind and activate the presumed adapter protein SH2-B is discussed. SH2-B has been shown to be a potent activator of GH-promoted JAK2 activity and downstream signaling events. Presumably these and other pathways initiated by GH combine to result in its ability to regulate body growth and metabolism.

The role of STAT proteins in growth hormone signaling

Growth hormone (GH) has long been known to be the body's primary regulator of body growth and a regulator of metabolism, yet the mechanisms by which GH regulates the transcription of specific genes required for these processes are just now being delineated. GH binding to its receptor recruits and activates the receptor-associated JAK2 that in turn phosphorylates tyrosines within itself and the GH receptor. These tyrosines form binding sites for a number of signaling proteins, including members of the family of signal transducers and activators of transcription (STAT). Among the known signaling molecules for GH, STAT proteins play a particularly prominent role in the regulation of gene transcription. This paper will review what is currently understood about which STAT proteins are regulated by GH, how they are regulated by GH, the GH-dependent genes they regulate, and discuss current theories about how GH-activated STAT signaling is regulated. Particular attention will be given to the novel role that STAT5 plays in sexually dimorphic gene expression in the liver as determined by the secretory pattern of GH and the role of STAT5 in body growth. Oncogene (2000).

Differential binding to and regulation of JAK2 by the SH2 domain and N-terminal region of SH2-bbeta

SH2-Bbeta has been shown to bind via its SH2 (Src homology 2) domain to tyrosyl-phosphorylated JAK2 and strongly activate JAK2. In this study, we demonstrate the existence of an additional binding site(s) for JAK2 within the N-terminal region of SH2-Bbeta (amino acids 1 to 555) and the ability of this region of SH2-B to inhibit JAK2. Four lines of evidence support the existence of this additional binding site(s). In a glutathione S-transferase pull-down assay, wild-type SH2-Bbeta and SH2-Bbeta(R555E) with a defective SH2 domain bind to both tyrosyl-phosphorylated JAK2 from growth hormone (GH)-treated cells and non-tyrosyl-phosphorylated JAK2 from control cells, whereas the SH2 domain of SH2-Bbeta binds only to tyrosyl-phosphorylated JAK2 from GH-treated cells. Similarly, JAK2 is present in alphaSH2-B immunoprecipitates in the absence and presence of GH, with GH substantially increasing the coprecipitation of JAK2 with SH2-B. When coexpressed in COS cells, SH2-Bbeta coimmunoprecipitates not only wild-type, tyrosyl-phosphorylated JAK2 but also kinase-inactive, non-tyrosyl-phosphorylated JAK2(K882E), although to a lesser extent. DeltaC555 (amino acids 1 to 555 of SH2-Bbeta) that lacks most of the SH2 domain binds similarly to wild-type JAK2 and kinase-inactive JAK2(K882E). Experiments using a series of N- and C-terminally truncated SH2-Bbeta constructs indicate that the pleckstrin homology (PH) domain (amino acids 269 to 410) and amino acids 410 to 555 are necessary for maximal binding of SH2-Bbeta to inactive JAK2, but neither region alone is sufficient for maximal binding. The SH2 domain of SH2-Bbeta is necessary and sufficient for the stimulatory effect of SH2-Bbeta on JAK2 and JAK2-mediated tyrosyl phosphorylation of Stat5B. In contrast, DeltaC555 lacking the SH2 domain, and to a lesser extent the PH domain alone, inhibits JAK2. DeltaC555 also blocks JAK2-mediated tyrosyl phosphorylation of Stat5B in COS cells and GH-stimulated nuclear accumulation of Stat5B in 3T3-F442A cells. These data indicate that in addition to the SH2 domain, SH2-Bbeta has one or more lower-affinity binding sites for JAK2 within amino acids 269 to 555. The interaction via this site(s) in SH2-B with inactive JAK2 seems likely to increase the local concentration of SH2-Bbeta around JAK2, thereby facilitating binding of the SH2 domain to ligand-activated JAK2. This would result in a more rapid and robust cellular response to hormones and cytokines that activate JAK2. This interaction between inactive JAK2 and SH2-B may also help prevent abnormal activation of JAK2.

SH2-B is required for growth hormone-induced actin reorganization

The Src homology-2 (SH2) domain-containing protein SH2-Bbeta is a substrate of the growth hormone (GH) receptor-associated tyrosine kinase JAK2. Here we tested whether SH2-Bbeta is involved in GH regulation of the actin cytoskeleton. Based on cell fractionation and confocal microscopy, we find SH2-Bbeta present at the plasma membrane and in the cytosol. SH2-Bbeta colocalized with filamentous actin in GH and platelet-derived growth factor (PDGF)-induced membrane ruffles. To test if SH2-Bbeta is required for actin reorganization, we transiently overexpressed wild-type or mutant SH2-Bbeta in 3T3-F442A cells and assayed for GH- and PDGF-induced membrane ruffling and fluid phase pinocytosis. Overexpression of wild-type SH2-Bbeta enhanced ruffling and pinocytosis produced by submaximal GH but not submaximal PDGF. Point mutant SH2-Bbeta (R555E) and truncation mutant DeltaC555, both lacking a functional SH2 domain, inhibited membrane ruffling and pinocytosis induced by GH and PDGF. Mutant DeltaN504, which possesses a functional SH2 domain and enhances JAK2 kinase activity in overexpression systems, also inhibited GH-stimulated membrane ruffling. DeltaN504 failed to inhibit GH-induced nuclear localization of Stat5B, indicating JAK2 is active in these cells. Taken together, these results show that SH2-Bbeta is required for GH-induced actin reorganization by a mechanism discrete from the action of SH2-Bbeta as a stimulator of JAK2 kinase activity.

SH2-B, a membrane-associated adapter, is phosphorylated on multiple serines/threonines in response to nerve growth factor by kinases within the MEK/ERK cascade

SH2-B has been shown to be required for nerve growth factor (NGF)-mediated neuronal differentiation and survival, associate with NGF receptor TrkA, and be tyrosyl-phosphorylated in response to NGF. In this work, we examined whether NGF stimulates phosphorylation of SH2-B on serines/threonines. NGF promotes a dramatic upward shift in mobility of SH2-B, resulting in multiple forms that cannot be attributed to tyrosyl phosphorylation. Treatment of SH2-B with protein phosphatase 2A, a serine/threonine phosphatase, reduces the many forms to two. PD98059, a MEK inhibitor, dramatically inhibits NGF-promoted phosphorylation of SH2-B on serines/threonines, whereas depletion of 4beta-phorbol 12-myristate 13-acetate-sensitive protein kinase Cs does not. ERKs 1 and 2 phosphorylate SH2-Bbeta primarily on Ser-96 in vitro. However, NGF still stimulates serine/threonine phosphorylation of SH2-Bbeta(S96A). SH2-Bbeta(S96A), like wild-type SH2-Bbeta, enhances NGF-induced neurite outgrowth. In contrast, SH2-Bbeta(R555E) containing a defective SH2 domain blocks NGF-induced neurite outgrowth and displays greatly reduced phosphorylation on serines/threonines in response to NGF. SH2-Bbeta(R555E), like wild-type SH2-Bbeta, associates with the plasma membrane, suggesting that the dominant negative effect of SH2-Bbeta(R555E) cannot be explained by an abnormal subcellular distribution. In summary, NGF stimulates phosphorylation of SH2-B on serines/threonines by kinases downstream of MEK, which may be important for NGF-mediated neuronal differentiation and survival.

SH2-B is required for nerve growth factor-induced neuronal differentiation

Nerve growth factor (NGF) is essential for the development and survival of sympathetic and sensory neurons. NGF binds to TrkA, activates the intrinsic kinase activity of TrkA, and promotes the differentiation of pheochromocytoma (PC12) cells into sympathetic-like neurons. Several signaling molecules and pathways are known to be activated by NGF, including phospholipase Cgamma, phosphatidylinositol-3 kinase, and the mitogen-activated protein kinase cascade. However, the mechanism of NGF-induced neuronal differentiation remains unclear. In this study, we examined whether SH2-Bbeta, a recently identified pleckstrin homology and SH2 domain-containing signaling protein, is a critical signaling protein for NGF. TrkA bound to glutathione S-transferase fusion proteins containing SH2-Bbeta, and NGF stimulation dramatically increased that binding. In contrast, NGF was unable to stimulate the association of TrkA with a glutathione S-transferase fusion protein containing a mutant SH2-Bbeta(R555E) with a defective SH2 domain. When overexpressed in PC12 cells, SH2-Bbeta co-immunoprecipitated with TrkA in response to NGF. NGF stimulated tyrosyl phosphorylation of endogenous SH2-Bbeta as well as exogenously expressed GFP-SH2-Bbeta but not GFP-SH2-Bbeta(R555E). Overexpression of SH2-Bbeta(R555E) blocked NGF-induced neurite outgrowth of PC12 cells, whereas overexpression of wild type SH2-Bbeta enhanced NGF-induced neurite outgrowth. Overexpression of either wild type or mutant SH2-Bbeta(R555E) did not alter tyrosyl phosphorylation of TrkA, Shc, or phospholipase Cgamma in response to NGF or NGF-induced activation of ERK1/2, suggesting that SH2-Bbeta may initiate a previously unknown pathway(s) that is essential for NGF-induced neurite outgrowth. Taken together, these data indicate that SH2-Bbeta is a novel signaling molecule required for NGF-induced neuronal differentiation.

A functional DNA binding domain is required for growth hormone-induced nuclear accumulation of Stat5B

The mechanisms regulating the cellular distribution of STAT family transcription factors remain poorly understood. To identify regions of Stat5B required for ligand-induced nuclear accumulation, we constructed a cDNA encoding green fluorescent protein (GFP) fused to the N terminus of Stat5B and performed site-directed mutagenesis. When co-expressed with growth hormone (GH) receptor in COS-7 cells, GFP-Stat5B is tyrosyl-phosphorylated, forms dimers, and binds DNA in response to GH in a manner indistinguishable from untagged Stat5B. In multiple cell types, laser scanning confocal imaging of GFP-Stat5B co-expressed with GH receptor shows that GFP-Stat5B undergoes a rapid, dramatic accumulation in the nucleus upon GH stimulation. We introduced alanine substitutions in several regions of Stat5B and assayed for GH-dependent nuclear localization. Only the mutation that prevented binding to DNA (466VVVI469) abrogated GH-stimulated nuclear localization. This mutant fusion protein is tyrosyl-phosphorylated and dimerizes in response to GH. These results suggest that either high affinity binding to DNA contributes to nuclear accumulation of Stat5B or that this region is crucial for two functions, namely accumulation of Stat5B in the nucleus and DNA binding. Thus, we have identified a mutant Stat5 defective in nuclear localization despite its ability to be tyrosyl-phosphorylated and to dimerize.

Heat shock protein 90-dependent (geldanamycin-inhibited) movement of the glucocorticoid receptor through the cytoplasm to the nucleus requires intact cytoskeleton

We use here a chimera of the green fluorescent protein (GFP) and the glucocorticoid receptor (GR) to test the notion that the protein chaperone heat shock protein-90 (hsp90) is required for steroid-dependent translocation of the receptor through the cytoplasm along cytoskeletal tracks. The GFP-GR fusion protein undergoes steroid-mediated translocation from the cytoplasm to the nucleus, where it is transcriptionally active. Treatment of 3T3 cells containing steroid-bound GFP-GR with geldanamycin, a benzoquinone ansamycin that binds to hsp90 and disrupts its function, inhibits dexamethasone-dependent translocation from the cytoplasm to the nucleus. The t1/2 for translocation in the absence of geldanamycin is approximately 5 min, and the t1/2 in the presence of geldanamycin is approximately 45 min. In cells treated for 1 h with the cytoskeletal disrupting agents colcemid, cytochalasin D, and beta,beta'-iminodipropionitrile to completely disrupt the microtubule, microfilament, and intermediate filament networks, respectively, the GFP-GR still translocates rapidly to the nucleus in a strictly dexamethasone-dependent manner but translocation is no longer affected by geldanamycin. After withdrawal of the cytoskeletal disrupting agents for 3 h, normal cytoskeletal architecture is restored, and geldanamycin inhibition of dexamethasone-dependent GFP-GR translocation is restored. We suggest that in cells without an intact cytoskeletal system, the GFP-GR moves through the cytoplasm by diffusion. However, under physiological conditions in which the cytoskeleton is intact, diffusion is limited, and the GFP-GR utilizes a movement machinery that is dependent upon hsp90 chaperone activity. In contrast to the GR, GFP-STAT5B, a signaling protein that is not complexed with hsp90, undergoes GH-dependent translocation to the nucleus in a manner that is not dependent upon hsp90 chaperone activity.

Mitochondrial participation in the intracellular Ca2+ network

Calcium can activate mitochondrial metabolism, and the possibility that mitochondrial Ca2+ uptake and extrusion modulate free cytosolic [Ca2+] (Cac) now has renewed interest. We use whole-cell and perforated patch clamp methods together with rapid local perfusion to introduce probes and inhibitors to rat chromaffin cells, to evoke Ca2+ entry, and to monitor Ca2+-activated currents that report near-surface [Ca2+]. We show that rapid recovery from elevations of Cac requires both the mitochondrial Ca2+ uniporter and the mitochondrial energization that drives Ca2+ uptake through it. Applying imaging and single-cell photometric methods, we find that the probe rhod-2 selectively localizes to mitochondria and uses its responses to quantify mitochondrial free [Ca2+] (Cam). The indicated resting Cam of 100-200 nM is similar to the resting Cac reported by the probes indo-1 and Calcium Green, or its dextran conjugate in the cytoplasm. Simultaneous monitoring of Cam and Cac at high temporal resolution shows that, although Cam increases less than Cac, mitochondrial sequestration of Ca2+ is fast and has high capacity. We find that mitochondrial Ca2+ uptake limits the rise and underlies the rapid decay of Cac excursions produced by Ca2+ entry or by mobilization of reticular stores. We also find that subsequent export of Ca2+ from mitochondria, seen as declining Cam, prolongs complete Cac recovery and that suppressing export of Ca2+, by inhibition of the mitochondrial Na+/ Ca2+ exchanger, reversibly hastens final recovery of Cac. We conclude that mitochondria are active participants in cellular Ca2+ signaling, whose unique role is determined by their ability to rapidly accumulate and then release large quantities of Ca2+.

Hyperkalemia associated with cyclosporine (CsA) use in bone marrow transplantation

Two adult leukemia patients underwent allogeneic bone marrow transplantation and received cyclosporine (CsA) as part of their immunosuppressive therapy. Despite adequate kidney function, both patients developed hyperkalemia. Cyclosporine was the only pharmaceutical agent to which this electrolyte abnormality could be attributed. Although the mechanism of the hyperkalemia is unclear, it seems to be related to an aldosterone-resistant state. Cyclosporine-induced hyperkalemia is a relatively common occurrence; however, there is only a single 'case report' addressing this phenomenon in bone marrow transplantation patients. We propose both mechanisms and methods of managing CsA-associated hyperkalemia in allogeneic transplantation patients.

Ca2+ clearance mechanisms in isolated rat adrenal chromaffin cells

1. Intracellular Ca2+ clearance mechanisms were studied in rat adrenal chromaffin cells, by measuring slow tail currents through small-conductance Ca(2+)-activated K+ channels and using indo-1 photometry following depolarization-induced Ca2+ loading. 2. Following several-hundred millisecond depolarizations, [Ca2+]i decayed in three phases. An initial fast decay was followed by a long-lasting, low plateau, then [Ca2+]i returned to the resting level slowly. 3. Replacement of external Na+ moderately slowed [Ca2+]i decay, indicating a contribution of plasma membrane Na(+)-Ca2+ exchange. 4. Raising external pH or application of extracellular Eosin of La3+ prolonged slow tail currents, indicating a contribution of plasma membrane Ca(2+)-ATPase to Ca2+ clearance. 5. Ca(2+)-induced Ca2+ release from caffeine-sensitive stores occurred during depolarization. 6. Inhibition of endoplasmic reticulum Ca(2+)-ATPase had little effect on Ca2+ clearance. 7. Slow tail currents and [Ca2+]i decay following 0.2 - 2 s depolarizations were much prolonged by mitochondrial inhibition with carbonyl cyanide m-chlorophenylhydrazone (CCCP) or Ruthenium Red, which abolished the initial rapid decay and plateau of [Ca2+]i. 8. In conclusion, mitochondrial Ca2+ uptake plays a major role in Ca2+ clearance by rapidly and reversibly sequestering Ca2+ during depolarization-evoked Ca2+ loads.

Dominant role of mitochondria in clearance of large Ca2+ loads from rat adrenal chromaffin cells

Cytosolic Ca2+ (Ca2+c) clearance from adrenal chromaffin cells was studied by whole-cell patch clamp and indo-1 Ca2+ photometry after influx of Ca2+ through voltage-dependent Ca2+ channels. We isolated the rates of Ca2+c clearance by several mechanisms using combinations of the following agents (with their expected targets): Li+ or TEA substituted for Na+ (Na(+)-Ca2+ exchange), 1 mM La3+ applied after the depolarization (Na(+)-Ca2+ exchange and plasma membrane Ca(2+)-ATPase), 1 microM thapsigargin (pumping into reticular stores), and 2 microM carbonyl cyanide m-chlorophenylhydrazone (uptake into mitochondria). Remarkably, whenever [Ca2+]c rose above approximately 500 nM, Ca2+c clearance by mitochondria exceeded clearance by either Na(+)-Ca2+ exchange or the Ca2+ pumps of the plasma and reticular membranes. As [Ca2+]c fell again, Ca2+ reemerged from mitochondria, prolonging the final return to basal levels.

Sphingosine: a mediator of acute renal tubular injury and subsequent cytoresistance

The goal of this study was to determine whether sphingosine and ceramide, second messengers derived from sphingolipid breakdown, alter kidney proximal tubular cell viability and their adaptive responses to further damage. Adult human kidney proximal tubular (HK-2) cells were cultured for 0-20 hr in the presence or absence of sphingosine, sphingosine metabolites (sphingosine 1-phosphate, dimethylsphingosine), or C2, C8, or C16 ceramide. Acute cell injury was assessed by vital dye exclusion and tetrazolium dye transport. Their subsequent impact on superimposed ATP depletion/Ca2+ ionophore-induced damage was also assessed. Sphingosine (> or = 10 microM), sphingosine 1-phosphate, dimethylsphingosine, and selected ceramides (C2 and C8, but not C16) each induced rapid, dose-dependent cytotoxicity. This occurred in the absence of DNA laddering or morphologic changes of apoptosis, suggesting a necrotic form of cell death. Prolonged exposure (20 hr) to subtoxic sphingosine doses (< or = 7.5 microM) induced substantial cytoresistance to superimposed ATP depletion/Ca2+ ionophore-mediated damage. Conversely, neither short-term sphingosine treatment (< or = 8.5 hr) nor 20-hr exposures to any of the above sphingosine/ceramide derivatives/metabolites or various free fatty acids reproduced this effect. Sphingosine-induced cytoresistance was dissociated from the extent of cytosolic Ca2+ loading (indo-1 fluorescence), indicating a direct increase in cell resistance to attack. We conclude that sphingosine can exert dual effects on proximal renal tubular viability: in high concentrations it induces cell necrosis, whereas in low doses it initiates a cytoresistant state. These results could be reproduced in human foreskin fibroblasts, suggesting broad-based relevance to the area of acute cell injury and repair.

The suppression of Ca(2+)- and voltage-dependent outward K+ current during mAChR activation in rat adrenal chromaffin cells

1. The mechanism by which muscarine, ionomycin or caffeine results in suppression of Ca(2+)- and voltage-dependent outward current in rat adrenal chromaffin cells was evaluated using both whole-cell voltage clamp and single channel recording. 2. The whole-cell current activated following the elevation of the cytosolic calcium concentration ([Ca2+]i) by muscarine inactivates with a time course comparable to that of single Ca(2+)- and voltage-dependent potassium (BK) channels. 3. The whole-cell inactivating current is pharmacologically similar to BK current. 4. The voltage dependence of inactivation and rate of recovery from inactivation are qualitatively similar for both whole-cell current and ensemble averages of single BK channels. Furthermore, changes in the rate of whole-cell current inactivation track expected changes in submembrane [Ca2+]. 5. The suppression of outward current can be accounted for solely by inactivation of BK channels and does not depend on the means by which [Ca2+]i is elevated. 6. Muscarinic acetylcholine receptor (mAChR) activation, changes in holding potential (-50 to -20 mV), and step depolarizations of different amplitude and duration were tested for their ability to elevate [Ca2+]i and thereby regulate the availability of BK current for activation. 7. Following muscarine-induced elevation of [Ca2+]i at holding potentials positive to -40 mV, the availability of BK current for activation was typically reduced by more than 50%. 8. Holding potentials in the range of -50 to -20 mV produced only slight alterations in the availability of BK current for activation. 9. Step depolarizations that cause maximal rates of Ca2+ influx (0 to +10 mV) must exceed 200 ms to reduce the availability of BK current by approximately 50%. 10. The results show that the muscarine-induced elevation of [Ca2+]i produces a profound reduction in the availability of BK channels for activation at membrane potentials likely to be physiologically meaningful. Although depolarization- induced Ca2+ influx can inactivate BK current, we propose that short duration depolarizations that occur during normal electrical activity will not significantly alter BK channel availability.

Protein synthesis inhibition induces cytoresistance in cultured human proximal tubular (HK-2) cells

After sublethal injury, proximal tubular cells acquire resistance to further attack. This study evaluated whether this could be a possible consequence of decreased protein synthesis, a potential correlate of cell damage. To this end, cultured human proximal tubular cells (HK-2) were subjected to 0-24 h of protein synthesis inhibition (> 98%), either by adding protein synthesis inhibitors [cycloheximide (CH) or verrucarin A] or by inducing sublethal ATP depletion (antimycin A + 2-deoxyglucose). After 24 h of these treatments, significant resistance to Ca2+ ionophore/ATP depletion-induced attack was noted (assessed by vital dye exclusion, compared with normal cells). That < or = 6 h of protein synthesis inhibition caused no cytoresistance implied the importance of evolving protein depletion rather than nonspecific drug effects or protein synthesis inhibition per se. CH plus ATP depletion did not induce additive benefits, suggesting a common mechanism. Cytoresistance was dissociated from the extent of free Ca2+ loading and ATP depletion but was associated with a decrease in membrane deacylation. CH removal promptly restored protein synthesis and cytoresistance was lost; conversely, ATP recovery did not restore protein synthesis and cytoresistance persisted. The emergence of cytoresistance correlated with the disappearance/dephosphorylation of an unidentified 130-kDa tyrosine-phosphorylated protein/protein complex (denoted pp-130). The functional significance of this change was suggested by the fact that tyrosine phosphatase inhibition with orthovanadate maintained pp-130 expression and prevented the cytoresistant state. We conclude that protein synthesis inhibition in HK-2 cells can induce a cytoresistant state. Suppression in phospholipase activity and altered tyrosine phosphorylation events may have functional significance in this regard.

Severe illness in African children with diarrhoea: implications for case management strategies

To identify clinical disorders associated with severe illness in African children with diarrhoea, we studied a group of under-5-year-olds with diarrhoea who had been brought to a large public hospital in central Cote d'Ivoire. The general condition of children with diarrhoea was assessed and classified according to criteria recommended by WHO, and then used as a nonspecific indicator of severity. Of the 264 children with diarrhoea who were enrolled in the study, 196 had nonsevere illness and 68 severe illness. Children with severe illness were significantly more likely than those with nonsevere illness to be dehydrated (45% versus 11%), moderate-to-severely wasted (47% versus 29%), bacteraemic (26% versus 9%), severely anaemic (haemoglobin level <6 g/dl; 15% versus 6%), have Plasmodium falciparum parasitaemia (27% versus 14%), and have two or more of these five conditions (60% versus 14%). Nontyphoidal Salmonella spp. were present in 68% of the blood isolates but were not associated with seropositivity to human immunodeficiency virus (HIV). The study demonstrates the need for a more comprehensive approach to assessment and management of children with diarrhoea that ensures prompt recognition of bacteraemia, anaemia, wasting and malaria, as well as dehydration. Simple nonspecific observational criteria, such as those recommended by WHO for assessing and classifying general condition, are useful for identifying children with diarrhoea who are at high risk of having life-threatening clinical disorders, and can readily be used by health workers whose clinical training and access to diagnostic laboratory facilities are both limited.

Growth hormone-releasing hexapeptide elevates intracellular calcium in rat somatotropes by two mechanisms

The actions of GH-releasing hexapeptide (His-D-Trp-Ala-Trp-D-Phe-Lys-NH2 or GHRP-6) on single rat somatotropes were studied using whole cell patch clamp electrophysiology and indo-1 Ca2+ photometry. GHRP-6 elevated intracellular free Ca2+ ([Ca2+]i) in two phases: a rapid transient phase, followed by a persistent phase. Based on its insensitivity to treatments that block Ca2+ entry [removal of external Ca2+, addition of the dihydropyridine Ca2+ channel blocker nitrendipine (1 microM), and the hyperpolarizing action of zero external Na+ or 100 nM somatostatin], the transient elevation is the result of release of Ca2+ from intracellular stores. The half-maximal concentration for the peak [Ca2+]i rise during Ca2+ release was 49 nM GHRP-6. Prior treatment of cells with caffeine (10 mM) or ryanodine (50 microM) abolished or partially occluded GHRP-6-induced Ca2+ release. Simultaneous measurement of [Ca2+]i and membrane current or potential revealed that the transient release of Ca2+ by GHRP-6 activates a voltage-independent Ca(2+)-activated K+ conductance, which transiently hyperpolarizes the somatotrope. The GHRP-6-induced persistent [Ca2+]i elevation is abolished by removal of external Ca2+ or external Na+ or the addition of 1 microM nitrendipine or 100 nM somatostatin, consistent with Ca2+ entry through voltage-dependent Ca2+ channels. In nondialyzed cells (perforated patch recording), we have identified a long-lasting GHRP-6-induced depolarization which may be responsible for the persistent [Ca2+]i elevation.

Multiple components of voltage-dependent potassium current in normal rat anterior pituitary cells

1. Voltage-dependent K+ currents were studied in normal rat anterior pituitary cells using the patch-clamp technique. To obtain cultures enriched for lactotrophs, density gradient centrifugation was performed on pituitary cells isolated from lactating rats. 2. Depolarizations to about -30 mV from a holding potential of -80 mV activate a rapidly inactivating [time constant (tau) approximately 15-20 ms at -20 mV]K+ current. This transient current activated at low voltages (termed IA) is abolished by 5 mM external 4-aminopyridine (4-AP) but is largely resistant to external tetraethylammonium (TEA) (< or = 30 mM). 3. Recovery from inactivation of IA is fast, with a tau of 100-200 ms at -80 mV. Deactivation is also fast (tau approximately 2.2 ms at -50 mV). The voltage of half-activation of IA is approximately -20 mV. The current is completely inactivated at a holding potential of -40 mV. 4. Voltage-dependent K+ current activated by depolarizations from a holding potential of -40 mV was first detectable at about -20 mV (high voltage-activated) and had a time course that varied among cells. 5. Deactivation of high voltage-activated K+ current was best described by the sum of two exponentials, with tau of about 3.7 and 30 ms at -50 mV. Both components reversed close to the equilibrium potential for K+. 6. The amplitudes of the two tail currents were independent of each other when variable-duration commands were used to activate current. The amplitude of the fast component was largest with 10- to 20-ms commands to +40 mV and was reduced (< or = 50%) with 136-ms commands. The slow component amplitude reached a peak by 40 ms and remained constant for commands < or = 136 ms at +40 mV. 7. The contribution of each component to the total high voltage-activated tail current was variable among cells, with the amount of fast component correlating with the amount of inactivation produced by commands to +40 mV. 8. The two components of tail current activated by depolarizations from the -40 mV holding potential were abolished by external TEA (10 mM). 4-AP (5 mM externally) selectively abolished the fast component of high voltage-activated tail current while only partially reducing the slow component. 9. These results suggest that normal rat anterior pituitary cells possess at least three distinct types of voltage-dependent K+ current: a low voltage-activated, transient current (IA) and two high voltage-activated currents.(ABSTRACT TRUNCATED AT 400 WORDS)

Actions of growth-hormone-releasing hormone on rat pituitary cells: intracellular calcium and ionic currents

Actions of growth-hormone-releasing hormone (GHRH) on single rat anterior pituitary cells were studied using indo-1 fluorescence to monitor changes in intracellular calcium, [Ca2+]i, and perforated-patch recording to measure changes in membrane potential and ionic currents. GHRH elevated [Ca2+]i in non-voltage-clamped cells by a mechanism that was dependent upon extracellular Na+ and Ca2+ and was blocked by the dihydropyridine Ca(2+)-channel blocker, nitrendipine. Resting cells had a fluctuating membrane potential whose a mean value depolarized by 9 mV in response to GHRH. The membrane-permeant cAMP analogue, 8-(4-chlorophenylthio)cAMP, mimicked the action of GHRH on membrane potential. Under voltage clamping, GHRH activated a small inward current (1-5 pA). Two types of response could be distinguished. The type I response had an inward current that was largest at more negative potentials (-90 mV), and the type II response had inward current that was larger at more positive potentials (-40 to -70 mV). Both types of response were reversible and blocked by removal of extracellular Na+. These results suggest that the rise in [Ca2+]i produced by GHRH in non-voltage-clamped cells results from the activation via cAMP of a Na(+)-dependent conductance, which depolarizes the cell and increases the Ca2+ influx through voltage-gated Ca2+ channels.

Characteristics and regulation of a muscarinically activated K current in HSG-PA cells

Whole cell currents were measured in HSG-PA cells (a proposed model for salivary gland duct cells) after muscarinic receptor activation or exposure to known signaling agents. Exposure to carbachol or oxotremorine M produced large and often oscillatory increases in outward current whose reversal potentials indicated a K current. The current was sensitive to extracellular atropine, charybdotoxin, and quinine, but not apamin, and to 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid in the pipette. The response was prolonged or increased by guanosine 5'-O-(3-thiotriphosphate) and mimicked by D-myo-inositol 1,4,5-trisphosphate (IP3) or heparin in the pipette and by extracellular Ca ionophores. Tetraethylammonium indirectly inhibited the response via the muscarinic receptor. Fura 2 in cell suspensions showed that muscarinic agonists increased cytosolic Ca ion concentration ([Ca2+]i) five- to sevenfold, and measurements with indo 1 in individual cells showed that the oscillatory changes in outward current were tightly correlated with parallel changes in [Ca2+]i. The results indicate that muscarinic receptor stimulation of HSG-PA cells activates Ca(2+)-activated K channels through a signaling pathway involving a G protein, IP3 production, and increased [Ca2+]i levels. These findings are similar to those in salivary gland acinar cells.

Kinetic and pharmacological properties of low voltage-activated Ca2+ current in rat clonal (GH3) pituitary cells

1. Low voltage-activated (LVA) Ca2+ current in clonal (GH3) pituitary cells was studied with the use of the whole-cell recording technique. The use of internal fluoride to facilitate the rundown of high voltage-activated (HVA) Ca2+ current allowed the study of LVA current in virtual isolation. 2. In 10 mM [Ca2+]o, detectable LVA current begins to appear at about -50 mV, with half-maximal activation occurring at -33 mV. The time course of activation was best described by a Hodgkin-Huxley expression with n = 3, suggesting that at least three closed states must be traversed before channel opening. 3. Deactivation was found to vary exponentially with membrane potential between -60 and -160 mV, indicating that channel closing is rate-limited by a single, voltage-dependent transition. 4. Onset and removal of inactivation between -40 and -130 mV were best described by the sum of two exponentials. Between -80 and -130 mV, both components of removal of inactivation showed little voltage dependence, with time constants of approximately 200-300 ms and 1-2 s. At membrane potentials above -40 mV, a single component of inactivation onset was detected. This component was voltage independent between -20 and +20 mV (tau = 22 ms). Thus inactivation of LVA current is best described by multiple, voltage-in-dependent processes. 5. Significant inactivation of LVA current occurred at -65 mV without detectable macroscopic current. This suggests that inactivation is not strictly coupled to channel opening. 6. Peak LVA current increased with increasing [Ca2+]o, with saturation approximately 50 mM. The Ca(2+)-dependence of peak LVA current was reasonably well described by a single-site binding isotherm with half-maximal LVA current at approximately 7 mM. 7. LVA current in GH3 cells was largely resistant to blockade by Ni2+. The relative potency of inorganic cations in blocking GH3 LVA current was (concentrations which produced 50% block): La3+ (2.4 microM) greater than Cd2+ (188 microM) greater than Ni2+ (777 microM). 8. Several organic agents, including putative LVA blockers, HVA current blockers and various anesthetic agents, were tested for their ability to block LVA current. The concentrations that produced 50% block are as follows: nifedipine (approximately 50 microM), D600 (51 microM), diltiazem (131 microM), octanol (244 microM), pentobarbital (985 microM), methoxyflurane (1.41 mM), and amiloride (1.55 mM). Phenytoin and ethosuximide produced 36 and 10% block at 100 microM and 2.5 mM, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)