Peer Reviewed Evaluation of Registered End-Points of Randomised Trials (the PRE-REPORT study): a stepped wedge, cluster-randomised trial

OBJECTIVE

To test whether providing relevant clinical trial registry information to peer reviewers evaluating trial manuscripts decreases discrepancies between registered and published trial outcomes.

DESIGN

Stepped wedge, cluster-randomised trial, with clusters comprised of eligible manuscripts submitted to each participating journal between 1 November 2018 and 31 October 2019.

SETTING

Thirteen medical journals.

PARTICIPANTS

Manuscripts were eligible for inclusion if they were submitted to a participating journal during the study period, presented results from the primary analysis of a clinical trial, and were peer reviewed.

INTERVENTIONS

During the control phase, there were no changes to pre-existing peer review practices. After journals crossed over into the intervention phase, peer reviewers received a data sheet describing whether trials were registered, the initial registration and enrolment dates, and the registered primary outcome(s) when enrolment began.

MAIN OUTCOME MEASURE

The presence of a clearly defined, prospectively registered primary outcome consistent with the primary outcome in the published trial manuscript, as determined by two independent outcome assessors.

RESULTS

We included 419 manuscripts (243 control and 176 intervention). Participating journals published 43% of control-phase manuscripts and 39% of intervention-phase manuscripts (model-estimated percentage difference between intervention and control trials = -10%, 95% CI -25% to 4%). Among the 173 accepted trials, published primary outcomes were consistent with clearly defined, prospectively registered primary outcomes in 40 of 105 (38%) control-phase trials and 27 of 68 (40%) intervention-phase trials. A linear mixed model did not show evidence of a statistically significant primary outcome effect from the intervention (estimated difference between intervention and control=-6% (90% CI -27% to 15%); one-sided p value=0.68).

CONCLUSIONS

These results do not support use of the tested intervention as implemented here to increase agreement between prospectively registered and published trial outcomes. Other approaches are needed to improve the quality of outcome reporting of clinical trials.

TRIAL REGISTRATION NUMBER

ISRCTN41225307.

Electronic Health Record Adoption among Obstetrician/Gynecologists in the United States: Physician Practices and Satisfaction

Implementation of electronic health records (EHRs) has historically been lower among obstetrician-gynecologists (ob-gyns) than many physician groups. This study described ob-gyns' adoption and use of EHR systems in practice, as well as barriers and benefits to implementation. Surveys asking about the physicians' use of EHR, satisfaction with systems, and what features they found most or least helpful were mailed to 1,200 ob-gyns. An overall response rate of 57.4% was achieved, with 559 returning completed surveys. Over three-quarters of responders reported that they used an EHR system or planned to implement one. Physicians without EHR tended to be older, were more likely to be male, have a solo practice, and describe themselves as Asian/Pacific Islander. Over 63% of those physicians who use EHR reported being satisfied with their system, while 30.8% were not satisfied. Ob-gyns who reported satisfaction had a younger mean age (M = 52.98, SD = 8.87) than those not satisfied (M = 56.30, SD = 8.59; p = .002). Use of EHR systems among ob-gyns has increased in recent years and overall satisfaction with these systems is high. In spite of this, barriers to implementation are still present and increased outreach to certain groups of ob-gyns, including older practitioners and those in solo practices, is needed.

Child Maltreatment and Risky Sexual Behavior

Risky sexual behavior is a serious public health problem. Child sexual abuse is an established risk factor, but other forms of maltreatment appear to elevate risky behavior. The mechanisms by which child maltreatment influence risk are not well understood. This study used data from 859 high-risk youth, followed through age 18. Official reports of each form of maltreatment were coded. At age 16, potential mediators (trauma symptoms and substance use) were assessed. At age 18, risky sexual behavior (more than four partners, unprotected sex, unassertiveness in sexual refusal) was assessed. Neglect significantly predicted unprotected sex. Substance use predicted unprotected sex and four or more partners but did not mediate the effects of maltreatment. Trauma symptoms predicted unprotected sex and mediated effects of emotional maltreatment on unprotected sex and on assertiveness in sexual refusal and the effects of sexual abuse on unprotected sex. Both neglect and emotional maltreatment emerged as important factors in risky sexual behavior. Trauma symptoms appear to be an important pathway by which maltreatment confers risk for risky sexual behavior. Interventions to reduce risky sexual behavior should include assessment and treatment for trauma symptoms and for history of child maltreatment in all its forms.

Variations in Mental Health Diagnosis and Prescribing Across Pediatric Primary Care Practices

BACKGROUND

Primary care pediatricians increasingly care for children's mental health problems, but little is known about practice-level variation in diagnosis and psychotropic medication prescribing practices.

METHODS

This retrospective review of electronic heath records from 43 US primary care practices included children aged 4 to 18 years with ≥1 office visit from January 1, 2009, to June 30, 2014. We examined variability in diagnosis and psychotropic prescribing across practices using logistic regression with practice fixed effects and evaluated associations of the availability of colocated or community-based mental health providers or the proportion of children in foster care with diagnosis and prescribing using generalized linear mixed models.

RESULTS

Among 294 748 children, 40 932 (15%) received a mental health diagnosis and 39 695 (14%) were prescribed psychotropic medication. Attention deficit/hyperactivity disorder was most commonly diagnosed (1%-16% per practice). The proportion of children receiving any psychotropic medication (4%-26%) and the proportion receiving ≥2 medication classes (1%-12%) varied across practices. Prescribing of specific medication classes also varied (stimulants, 3%-18%; antidepressants, 1%-12%; α-agonists, 0%-8%; second-generation antipsychotics, 0%-5%). Variability was partially explained by community availability of psychiatrists (significantly higher odds of a diagnosis or prescription when not available) but not by colocation of mental health professionals or percentage of children in foster care.

CONCLUSIONS

The prevalence of mental health diagnosis and psychotropic medication prescribing varies substantially across practices and is only partially explained by psychiatrist availability. Research is needed to better define the causes of variable practice-level diagnosis and prescribing and implications for child mental health outcomes.

Adolescent Vaccination Performance in South Carolina Compared to the United States

National data on vaccine up-to-date (UTD) suggest that insufficient numbers of adolescents receive needed vaccines. This study analyzed public use data of the National Immunization Survey-Teen (NIS-Teen) from 2010 through 2013 for South Carolina (SC) adolescents and compared immunization rates to those of United States (US) adolescents. We also examined trends for each vaccine recommended for adolescents for both SC and US adolescents. UTD rates in SC adolescents for the quadrivalent meningococcal conjugate vaccine (MCV4) and the tetanus- diphtheria, acellular pertussis (Tdap) vaccine lag those of US adolescents, despite demonstrating a trend of improvement in SC adolescents from 45% to 69% for MCV and from 48% to 72% for Tdap. Human papillomavirus (HPV) vaccine UTD rates for SC adolescents demonstrated improvement over a 4 year period. HPV vaccination for SC girls improved when compared to the US, however UTD rates for both the SC and US were still well below the Healthy People 2020 goal of 80%. For all three vaccines, parental recall for a provider recommendation to vaccinate their adolescent was around or below 50%, except for HPV in females where it reached 65% in SC and 69% in the US. Differences between state and national rates may help SC providers focus on specific interventions needed to improve UTD rates.

Vaccination Rates among Adolescents in Minnesota as Compared with the United States: Not "Above Average"

Because adolescents make relatively few visits to clinics for preventive care, their vaccination rates suffer. We examined rates among Minnesota youths to see how they compared with those among teens throughout the United States. We used National Immunization Survey-Teen (NIS-Teen) data to estimate vaccination rates for 13- to 17-year-olds in Minnesota from 2008 through 2013 and compared them to national rates for MCV4, Tdap and HPV vaccines. We also examined rates of provider recommendation for each of the three vaccines and rates of parental intention to vaccinate against HPV. We found rates for all three vaccinations increased between 2008 and 2013, but they continue to be low for both MCV4 (69%) and HPV (38% of females and 9% of males completed the three-dose series in 2013). Fortunately, the percentage of Minnesota clinicians recommending those vaccines is increasing (the percentage recommending HPV vaccination for females increased from 55% in 2008 to 74% in 2013; however, only 44% recommended it for males in 2013). The percentage of parents in Minnesota reporting intent to vaccinate their female children against HPV rose from 52% in 2008 to 58% in 2013; the percentage intending to vaccinate their male children rose from 16% in 2010 to 47% in 2013. Clinicians and public health officials must address how we can improve HPV vaccination rates among adolescents.

Changing patterns of alpha agonist medication use in children and adolescents 2009-2011

OBJECTIVES

The purpose of this study was to describe rates and patterns of long- and short-acting alpha agonist use for behavioral problems in a primary care population following Food and Drug Administration (FDA) approval of the long-acting alpha agonists guanfacine and clonidine.

METHODS

Children and adolescents 4-18 years of age, who received an alpha agonist prescription between 2009 and 2011, were identified from a sample of 45 United States primary care practices in two electronic health record-based research networks. Alpha agonist receipt was identified using National Drug Codes and medication names. The proportion of subjects receiving long- and short-acting prescriptions in each year was calculated and examined with respect to reported mental health diagnoses, and whether indications for use were on-label, had evidence from clinical trials, or had no trial evidence.

RESULTS

In a cohort of 282,875 subjects, 27,671 (10%) received any psychotropic medication and only 4,227 subjects (1.5%) received at least one prescription for an alpha agonist, most commonly a short-acting formulation (83%). Only 20% of alpha agonist use was on-label (use of long-acting formulations for attention-deficit/hyperactivity disorder [ADHD]). Most subjects (68%) received alpha agonists for indications with evidence of efficacy from clinical trials but no FDA approval, primarily short-acting formulations for ADHD and autism; 12% received alpha agonists for diagnoses lacking randomized clinical trial evidence in children, including sleep disorders and anxiety, or for which there was no documented mental health diagnosis. Rates of long-acting alpha agonist use increased more than 20-fold from 0.2% to 4%, whereas rates of short-acting alpha agonist use grew only slightly between 2009 and 2011 from 10.6% to 11.3%.

CONCLUSIONS

Alpha agonist use was uncommon in this population, and most subjects received short-acting forms for conditions that were off-label, but with clinical trial evidence. The safety and efficacy of use for conditions, including sleep disorders and anxiety, lacking evidence from randomized trials, warrant further investigation.

Obstetrician/gynecologists' experiences with electronic health record systems: a narrative study

OBJECTIVE

To explore the experiences of obstetrician/gynecologists (ob/gyns) with regard to the use of electronic health record (EHR) systems in practice.

STUDY DESIGN

Surveys were mailed to 1,200 ob/gyns, with an overall response rate of 57.2%, 402 of whom currently use an EHR system. The survey included questions about the physicians' use of EHR systems as well as what features they found most or least helpful. In addition, a focus group of 6 practicing ob/gyns at a university-based hospital was conducted in which they were encouraged to give free responses about their experiences working with EHR systems. Responses from surveys and the focus group were analyzed for frequency by the investigators.

RESULTS

The majority of ob/gyns who used an EHR reported being satisfied with that system (61.4%). The most commonly reported impediments to EHR use were time needed, ineffective templates, note quality, interference with patient interactions, and expense. The most commonly cited positives were electronic medication prescription (e-scribing) capabilities, efficiency, and ease of access to notes, including legibility.

CONCLUSION

In spite of increased adoption of EHR systems, more work is needed to improve ob/gyn satisfaction with EHR systems.

Adolescent vaccination in Oklahoma: a work in progress

BACKGROUND

Nationally, uptake of adolescent vaccines is variable.

OBJECTIVE

To compare adolescent immunization rates and clinician recommendation for adolescent vaccines over time in Oklahoma with the U.S.

METHODS

We analyzed the 2010-2012 National Immunization Survey of Teens (NIS-Teen).

RESULTS

MCV4 and Tdap are consistently lower in Oklahoma compared to the U.S. HPV rates have been comparable. Parents report that health care providers in Oklahoma are less likely to recommend adolescent vaccines compared to the national average. Intention to not receive HPV in the next 12 months is distressingly high both in Oklahoma and across the nation with both improving.

CONCLUSION

Over the three years, Oklahoma's immunization rates consistently underperform national estimates for MCV4 and Tdap but not for HPV. We recommend Oklahoma health care providers improve their vaccination rates through making clear their vaccine recommendations to the parent and patient in the clinical encounter.

Prevalence of tuberculosis symptoms and latent tuberculous infection among prisoners in northeastern Malaysia

SETTING

There are currently no routine screening procedures for active tuberculosis (TB) or latent tuberculous infection (LTBI) in Malaysian prisons.

OBJECTIVE

To determine the prevalence and correlates of LTBI and active TB symptoms among Malaysian prisoners with and without human immunodeficiency virus (HIV) infection using the tuberculin skin test (TST) and the World Health Organization TB symptom-based screening instrument.

DESIGN

A cross-sectional survey of 266 prisoners was performed in Kelantan, Malaysia. Consenting participants underwent two-step TST and were screened for active TB symptoms. Standardized cut-offs of respectively ≥5 and ≥10 mm were used to define reactive TST among prisoners with and without HIV. Clinical and behavioral data were assessed and HIV-infected prisoners were stratified by CD4 status.

RESULTS

Overall LTBI prevalence was 87.6%, with significantly lower TST reactivity among HIV-infected than non-HIV-infected prisoners (83.6% vs. 91.5%, P < 0.05); however, TB symptoms were similar (16.9% vs. 10.1%, P = 0.105). On multivariate analysis, previous incarceration (aOR 4.61, 95%CI 1.76-12.1) was the only significant correlate of LTBI. Increasing age (aOR 1.07, 95%CI 1.01-1.13), lower body mass index (aOR 0.82, 95%CI 0.70-0.96) and TST-reactive status (aOR 3.46, 95%CI 1.20-9.97) were correlated with TB symptoms.

CONCLUSION

LTBI is highly prevalent, associated with previous incarceration, and suggests the need for routine TB screening on entry to Malaysian prisons.

Youth self-report of physical and sexual abuse: a latent class analysis

OBJECTIVE

To determine if meaningful groups of at-risk pre-adolescent youth could be identified based on their self-report of physical and sexual abuse histories.

METHODS

Youth participating in a consortium of ongoing longitudinal studies were interviewed using an audio-computer assisted self-interview (A-CASI) when they were approximately 12 years of age to obtain information about their perceived experiences of physical (18 items) and sexual (12 items) abuse. In addition, Child Protective Service records were reviewed and the taxonomy developed for defining maltreatment characteristics (Barnett, Manly, & Cicchetti, 1993) was applied. A total of 795 youth completed the age 12 interview and had their records reviewed during the period from birth to the time of their age 12 interview. A latent variable modeling approach, specifically latent class analysis (LCA), was used to generate profiles of youth based on their endorsements of the physical and sexual abuse items. These profiles were then compared to CPS reports of physical or sexual abuse to determine their validity.

RESULTS

The LCA identified 4 interpretable classes or groups of pre-adolescent youth. Based on the pattern of responses to specific items the classes were identified as follows: (1) no physical or sexual abuse; (2) high physical abuse/low sexual abuse; (3) no physical abuse/moderate sexual abuse; and (4) high physical and sexual abuse. Follow-up analyses indicated that the odds of a CPS report for Classes 2, 3, and 4 compared to Class 1 were significantly greater (2.21, 2.55, and 5.10, respectively).

CONCLUSION

The latent variable modeling approach allowed for the identification of meaningful groups of youth that accounted for both the occurrence of multiple types of abuse as well as differing severities associated with each type. It is suggested that this methodological approach may be most useful in future efforts to identify the antecedents and consequences of maltreatment.

PRACTICE IMPLICATIONS

The results of the present study not only have implications for future research efforts, but also suggest that in practice, youth at-risk for maltreatment may be reliable and valid reporters of their physical and sexual abuse experiences.

Importance of early neglect for childhood aggression

OBJECTIVE

The goal was to examine the association between early childhood neglect (birth to age 2 years) and later childhood aggression at ages 4, 6, and 8 years, compared with aggression's associations with early childhood abuse and later abuse and neglect.

METHODS

A prospective cohort of 1318 predominantly at-risk children, recruited from 4 US cities and 1 southern state, were monitored from birth to 8 years of age. Maltreatment was determined through review of local child protective services records. A hierarchical, linear model approach, a special case of general, linear, mixed modeling, was used to predict aggressive behavior scores, as reported by the child's primary caregiver at ages 4, 6, and 8 years.

RESULTS

Only early neglect significantly predicted aggression scores. Early abuse, later abuse, and later neglect were not significantly predictive in a controlled model with all 4 predictors.

CONCLUSION

This longitudinal study suggests that child neglect in the first 2 years of life may be a more-important precursor of childhood aggression than later neglect or physical abuse at any age.

The transcription factor snail represses Crumbs3 expression and disrupts apico-basal polarity complexes

In epithelial cells, the tight junction divides the plasma membrane into distinct apical and basolateral domains. Polarization is essential for epithelial cell function, and apico-basal cell polarity is lost during the epithelial to mesenchymal transition (EMT), a program of events characterized not only by loss of cell polarity, but also by enhanced cell motility and increased cell invasion. Among several apically localized protein complexes, the Crumbs and Par protein complexes have pivotal roles in control of epithelial polarity and apical membrane formation. Here, we demonstrate that the Snail transcriptional repressor antagonizes expression of the Crumbs polarity complex. We show that Snail abolishes localization of the Crumbs and Par complexes to the tight junction, decreases Crumbs complex protein levels and suppresses Crumbs3 transcription. Evidence that Snail acts directly to antagonize Crumbs3 promoter activity is presented. Strikingly, we note that reexpression of exogenous Crumbs3 in Snail-expressing Madin-Darby Canine Kidney cells partially restores cell-cell junctions. Moreover, we find that the EMT inducer transforming growth factor-beta elicits transcriptional repression of Crumbs3 and results in a measurable loss of Crumbs3 protein. Our findings provide new insights into the links between the transcriptional repression function of Snail and its role in antagonizing key apico-basal polarity factors during EMT.

Apical junctional complexes and cell polarity

Recent studies have greatly expanded our knowledge of initial events that lead to epithelial cell polarity. Epithelial polarity is defined, in part, by apical cell-cell tight junctions that separate the plasma membrane into the apical domain and the basolateral domain, as well as the zonula adherens that mediate intercellular adhesion. The process of epithelial polarization is closely coupled to the biogenesis of these junctions. Studies in mammalian epithelial cells and lower organisms have identified two evolutionarily conserved junctional complexes as important epithelia polarity regulators: the Crumbs complex and the partitioning defective complex. Disruption of the components of the two complexes leads to a disorder of epithelial cell polarity and defects in junction formation or maintenance. Recent discoveries have revealed more details of how the two junctional polarity complexes function to establish epithelial polarity. They also raised the question about the relationship between polarity and adhesion. Although it is widely accepted that cell-cell adhesion provides a landmark from which polarity can proceed, there are results pointing to the possibility that polarity complexes can regulate cell-cell adhesion. It seems likely that proteins that control cell adhesion and cell polarity work intimately together to establish final epithelial polarity.

Lenercept (p55 tumor necrosis factor receptor fusion protein) in severe sepsis and early septic shock: a randomized, double-blind, placebo-controlled, multicenter phase III trial with 1,342 patients

OBJECTIVE

Phase III study to confirm a trend observed in a previous phase II study showing that a single dose of lenercept, human recombinant p55 tumor necrosis factor receptor-immunoglobulin G1 (TNFR55-IgG1) fusion protein, decreased mortality in patients with severe sepsis or early septic shock.

DESIGN

Multicenter, double-blind, phase III, placebo-controlled, randomized study.

SETTING

A total of 108 community and university-affiliated hospitals in the United States (60), Canada (6) and Europe (42).

PATIENTS

A total of 1,342 patients were recruited who fulfilled the entry criteria within the 12-hr period preceding the study drug administration.

INTERVENTION

After randomization, an intravenous dose of 0.125 mg/kg lenercept or placebo was given. The patient was monitored for up to 28 days, during which standard diagnostic, supportive, and therapeutic care was provided.

MEASUREMENTS AND MAIN RESULTS

The primary outcome measure was 28-day all-cause mortality. Baseline characteristics were as follows: a total of 1,342 patients were randomized; 662 received lenercept and 680 received placebo. The mean age was 60.5 yrs (range, 17-96 yrs); 39% were female; 65% had medical admissions, 8% had scheduled surgical admissions, and 27% had unscheduled surgical admissions; 73% had severe sepsis without shock, and 27% had severe sepsis with early septic shock. Lenercept and placebo groups were similar at baseline with respect to demographic characteristics, simplified acute physiology score II-predicted mortality, profiles of clinical site of infection and microbiological documentation, number of dysfunctioning organs, and interleukin-6 (IL-6) plasma concentration. Lenercept pharmacokinetics were similar in severe sepsis and early septic shock patients. Tumor necrosis factor was bound in a stable manner to lenercept as reflected by the accumulation of total serum tumor necrosis factor alpha concentrations. There were 369 deaths, 177 on lenercept (27% mortality) and 192 on placebo (28% mortality). A one-sided Cochran-Armitage test, stratified by geographic region and baseline, predicted 28-day all-cause mortality (simplified acute physiology score II), gave a p value of .141 (one-sided). Lenercept treatment had no effect on incidence or resolution of organ dysfunctions. There was no evidence that lenercept was detrimental in the overall population.

CONCLUSION

Lenercept had no significant effect on mortality in the study population.

Interaction with mLin-7 alters the targeting of endocytosed transmembrane proteins in mammalian epithelial cells

To investigate the targeting mechanism for proteins bound to the mammalian Lin-7 (mLin-7) PDZ domain, we created receptor protein chimeras composed of the carboxyl-terminal amino acids of LET-23 fused to truncated nerve growth factor receptor/P75. mLin-7 bound to the chimera with a wild-type LET-23 carboxyl-terminal tail (P75t-Let23WT), but not a mutant tail (P75t-Let23MUT). In Madin-Darby canine kidney (MDCK) cells, P75t-Let23WT localized to the basolateral plasma membrane domain, whereas P75t-Let23MUT remained apical. Furthermore, mutant mLin-7 constructs acted as dominant interfering proteins and inhibited the basolateral localization of P75t-Let23WT. The mechanisms for this differential localization were examined further, and, initially, we found that P75t-Let23WT and P75t-Let23MUT were delivered equally to the apical and basolateral plasma membrane domains. Although basolateral retention of P75t-Let23WT, but not P75t-Let23MUT, was observed, the greatest difference in receptor localization was seen in the rapid trafficking of P75t-Let23WT to the basolateral plasma membrane domain after endocytosis, whereas P75t-Let23MUT was degraded in lysosomes, indicating that mLin-7 binding can alter the fate of endocytosed proteins. Altogether, these data support a model for basolateral protein targeting in mammalian epithelial cells dependent on protein-protein interactions with mLin-7, and also suggest a dynamic role for mLin-7 in endosomal sorting.

Cargo of kinesin identified as JIP scaffolding proteins and associated signaling molecules

The cargo that the molecular motor kinesin moves along microtubules has been elusive. We searched for binding partners of the COOH terminus of kinesin light chain, which contains tetratricopeptide repeat (TPR) motifs. Three proteins were found, the c-jun NH(2)-terminal kinase (JNK)-interacting proteins (JIPs) JIP-1, JIP-2, and JIP-3, which are scaffolding proteins for the JNK signaling pathway. Concentration of JIPs in nerve terminals requires kinesin, as evident from the analysis of JIP COOH-terminal mutants and dominant negative kinesin constructs. Coprecipitation experiments suggest that kinesin carries the JIP scaffolds preloaded with cytoplasmic (dual leucine zipper-bearing kinase) and transmembrane signaling molecules (the Reelin receptor, ApoER2). These results demonstrate a direct interaction between conventional kinesin and a cargo, indicate that motor proteins are linked to their membranous cargo via scaffolding proteins, and support a role for motor proteins in spatial regulation of signal transduction pathways.

Positive versus negative signaling of LET-23: regulation through the adaptor protein, SEM-5

Worby and Margolis highlight advances in our understanding of signaling from growth factor receptors using the worm Caenorhabditis elegans as a model organism. ARK-1, a cytoplasmic tyrosine kinase, appears to be a negative regulator of multiple pathways in C. elegans. The authors discuss several models for how this negative regulation may occur. The adaptor protein (Grb2 in mammals or SEM-5 in C. elegans) may serve as a regulated scaffold for the binding of other signaling proteins that include both positive (Ras) and negative (ACK) regulators. Thus, Grb2 may function in a cellular decision point for transducing the incoming signals.

Modulation of amyloid precursor protein metabolism by X11alpha /Mint-1. A deletion analysis of protein-protein interaction domains

Modulation of amyloid precursor protein (APP) metabolism plays a pivotal role in the pathogenesis of Alzheimer's disease. The phosphotyrosine-binding/protein interaction (PTB/PI) domain of X11alpha, a neuronal cytosolic adaptor protein, binds to the YENPTY sequence in the cytoplasmic carboxyl terminus of APP. This interaction prolongs the half-life of APP and inhibits Abeta40 and Abeta42 secretion. X11alpha/Mint-1 has multiple protein-protein interaction domains, a Munc-18 interaction domain (MID), a Cask/Lin-2 interaction domain (CID), a PTB/PI domain, and two PDZ domains. These X11alpha protein interaction domains may modulate its effect on APP processing. To test this hypothesis, we performed a deletion analysis of X11alpha effects on metabolism of APP(695) Swedish (K595N/M596L) (APP(sw)) by transient cotransfection of HEK 293 cells with: 1) X11alpha (X11alpha-wt, N-MID-CID-PTB-PDZ-PDZ-C), 2) amino-terminal deletion (X11alpha-DeltaN, PTB-PDZ-PDZ), 3) carboxyl-terminal deletion (X11alpha-DeltaPDZ, MID-CID-PTB), or 4) deletion of both termini (PTB domain only, PTB). The carboxyl terminus of X11alpha was required for stabilization of APP(sw) in cells. In contrast, the amino terminus of X11alpha was required to stimulate APPs secretion. X11alpha, X11alpha-DeltaN, and X11alpha-PTB, but not X11alpha-DeltaPDZ, were effective inhibitors of Abeta40 and Abeta42 secretion. These results suggest that additional protein interaction domains of X11alpha modulate various aspects of APP metabolism.

ERBIN: a basolateral PDZ protein that interacts with the mammalian ERBB2/HER2 receptor

The ERBB receptors have a crucial role in morphogenesis and oncogenesis. We have identified a new PDZ protein we named ERBIN (ERBB2 interacting protein) that acts as an adaptor for the receptor ERBB2/HER2 in epithelia. ERBIN contains 16 leucine-rich repeats (LRRs) in its amino terminus and a PDZ (PSD-95/DLG/ZO-1) domain at its carboxy terminus, and belongs to a new PDZ protein family. The PDZ domain directly and specifically interacts with ERBB2/HER2. ERBIN and ERBB2/HER2 colocalize to the lateral membrane of human intestinal epithelial cells. The ERBIN-binding site in ERBB2/HER2 has a critical role in restricting this receptor to the basolateral membrane of epithelial cells, as mutation of the ERBIN-binding site leads to the mislocalization of the receptor in these cells. We suggest that ERBIN acts in the localization and signalling of ERBB2/HER2 in epithelia.

Molecular events implicated in brain tumor angiogenesis and invasion

We have conducted studies designed to help elucidate the molecular mechanisms involved in brain tumor invasion and angiogenesis, which are critical in the growth of malignant tumors of the central nervous system. A variety of molecular factors have been implicated in these processes. Here we focus on three that are of particular importance in the progression of brain tumors. Angiopoietins are involved in the regulation of vascular development. Hypoxia inducible factor-1 is a transcription factor that up-regulates genes, including genes encoding vascular endothelial growth factor under hypoxic conditions. Focal adhesion kinase is associated with infiltration of tumor cells and angiogenesis.

Molecular cloning and characterization of Pals, proteins associated with mLin-7

In Caenorhabditis elegans, three PDZ domain proteins, Lin-2, Lin-7, and Lin-10, are necessary for the proper targeting of the Let-23 growth factor receptor to the basolateral surface of epithelial cells. It has been demonstrated that homologues of Lin-2, Lin-7, and Lin-10 form a heterotrimeric complex in mammalian brain. Using Far Western overlay assay, we have identified additional proteins that can bind to the amino terminus of mLin-7 and cloned the genes encoding these proteins using bacterial expression cloning. We call these proteins Pals, for proteins associated with Lin-7. These proteins, which include mammalian Lin-2, contain a conserved mLin-7 binding domain in addition to guanylate kinase, PDZ (postsynaptic density 95/discs large/zona occludens-1), and Src homology 3 domains. Using site-directed mutagenesis, we have identified the conserved residues among these proteins crucial for mLin-7 binding. Two of these proteins, Pals1 and Pals2, are newly described. Pals1 consists of 675 amino acids and maps to mouse chromosome 12. Pals2 was found to exist in two splice forms of 539 and 553 amino acids and maps to mouse chromosome 6. Like mLin-2, Pals1 and Pals2 localize to the lateral membrane in Madin-Darby canine kidney cells. Pals proteins represent a new subfamily of membrane-associated guanylate kinases that allow for multiple targeting complexes containing mLin-7.

mLin-7 is localized to the basolateral surface of renal epithelia via its NH(2) terminus

In Caenorhabditis elegans, the basolateral localization of the Let-23 growth factor receptor tyrosine kinase requires the expression of three genes: lin-2, lin-7, and lin-10. Mammalian homologs of these three genes have been identified, and a complex of their protein products exists in mammalian neurons. In this paper, we examine the interaction of these mammalian proteins in renal epithelia. Coprecipitation experiments demonstrated that mLin-2/CASK binds to mLin-7, and immunofluorescent labeling showed that these proteins colocalized at the basolateral surface of Madin-Darby canine kidney cells and renal epithelia. Although labeling intensity varied markedly among different renal epithelial cells, those cells strongly expressing mLin-7 also showed intense mLin-2/CASK labeling. We have also demonstrated that mLin-2/CASK binding requires amino acids 12-32 of mLin-7 and have shown that this region of mLin-7 is also necessary for the targeting of mLin-7 to the basolateral surface. Furthermore, the overexpression of mLin-2/CASK mutants in Madin-Darby canine kidney cells caused endogenous mLin-7 to mislocalize. In summary, the NH(2) terminus of mLin-7 is crucial for its basolateral localization, likely through its interaction with mLin-2/CASK.

Interaction of c-Jun amino-terminal kinase interacting protein-1 with p190 rhoGEF and its localization in differentiated neurons

c-Jun amino-terminal kinase (JNK) interacting protein-1 (JIP-1) was originally identified as a cytoplasmic inhibitor of JNK. More recently, JIP-1 was proposed to function as a scaffold protein by complexing specific components of the JNK signaling pathway, namely JNK, mitogen-activated protein kinase kinase 7, and mixed lineage kinase 3. We have identified the human homologue of JIP-1 that contains a phosphotyrosine binding (PTB) domain in addition to a JNK binding domain and an Src homology 3 domain. To identify binding targets for the hJIP-1 PTB domain, a mouse embryo cDNA library was screened using the yeast two-hybrid system. One clone encoded a 191-amino acid region of the neuronal protein rhoGEF, an exchange factor for rhoA. Overexpression of rhoGEF promotes cytoskeletal rearrangement and cell rounding in NIE-115 neuronal cells. The interaction of JIP-1 with rhoGEF was confirmed by coimmunoprecipitation of these proteins from lysates of transiently transfected HEK 293 cells. Using glutathione S-transferase rhoGEF fusion proteins containing deletion or point mutations, we identified a putative PTB binding site within rhoGEF. This binding site does not contain tyrosine, indicating that the JIP PTB domain, like that of Xll alpha and Numb, binds independently of phosphotyrosine. Several forms of endogenous JIP-1 protein can be detected in neuronal cell lines. Indirect immunofluorescence analysis localized endogenous JIP-1 to the tip of the neurites in differentiated NIE-115 and PC12 cells. The interaction of JIP-1 with rhoGEF and its subcellular localization suggests that JIP-1 may function to specifically localize a signaling complex in neuronal cells.

The function of PTB domain proteins

Phosphotyrosine binding (PTB) domains have been identified in a large number of proteins. In proteins like Shc and IRS-1, the PTB domain binds in a phosphotyrosine-dependent fashion to peptides that form a b turn. In these proteins, PTB domains play an important role in signal transduction by growth factor receptors. However, in several other proteins, the PTB domains have been found to participate in phosphotyrosine-independent interactions. The X11 family of proteins contains a PTB domain that binds peptides in a phosphotyrosine-independent fashion. The homologue of X11 in C. elegans is the lin-10 gene, a gene crucial for receptor targeting to the basolateral surface of body wall epithelia. The X11/Lin-10 proteins are found in a complex with two other proteins, Lin-2 and Lin-7, which have also been implicated in basolateral targeting in worm epithelia. This protein complex is also likely to be important in the targeting of cell surface proteins in mammalian neurons and epithelia. The ability of the PTB domain to bind peptides in a phosphotyrosine-dependent and -independent fashion allows this domain to be involved in diverse cellular functions.

Asterriquinones produced by Aspergillus candidus inhibit binding of the Grb-2 adapter to phosphorylated EGF receptor tyrosine kinase

Five new asterriquinone analogs (2-4, 6, 7), together with previously identified neoasterriquinone (1) and isoasterriquinone (5), were isolated from a fermentation broth of the fungus Aspergillus candidus and purified by HSCCC (high speed counter current chromatography) followed by HPLC. The structures were determined by 1D and 2D NMR and MS/MS techniques. All seven showed inhibitory activity against the binding of a recombinant protein containing the SH2 protein domain of Grb-2 to the tyrosine phosphorylated form of the EGF receptor tyrosine kinase. Some of these asterriquinones exhibited specific inhibition of Grb-2 binding compared to Grb-7 and PLC-gamma.

Molecular analysis of the X11-mLin-2/CASK complex in brain

A heterotrimeric complex containing Lin-10/X11alpha, Lin-2/CASK, and Lin-7 is evolutionarily conserved from worms to mammals. In Caenorhabditis elegans, it localizes Let-23, a receptor tyrosine kinase, to the basolateral side of vulval epithelium, a step crucial for proper vulva development. In mammals, the complex may also participate in receptor targeting in neurons. Accordingly, phosphotyrosine binding (PTB) and postsynaptic density-95/Discs large/Zona Occludens-1 domains found in X11alpha and mLin-2/CASK bind to cell-surface proteins, including amyloid precursor protein, neurexins, and syndecans. In this paper, we have further analyzed the X11alpha-mLin-2/CASK association that is mediated by a novel protein-protein interaction. We show that the mLin-2/CASK calmodulin kinase II (CKII) domain directly binds to a 63 amino acids peptide located between the Munc-18-1 binding site and the PTB domain in X11alpha. Ca2+/calmodulin association with mLin-2/CASK does not modify the X11alpha-mLin-2 interaction. A region containing the mLin-2/CASK guanylate kinase domain also interacts with X11alpha but with a lower affinity than the CKII domain. Immunostaining of X11alpha in the brain shows that the protein is expressed in areas shown previously to be positive for mLin-2/CASK staining. Together, our data demonstrate that the X11alpha-mLin-2 complex contacts many partners, creating a macrocomplex suitable for receptor targeting at the neuronal plasma membrane.

Role of tyrosine residues and protein interaction domains of SHC adaptor in VEGF receptor 3 signaling

The VEGFR3/FLT4 receptor, which is involved in vasculogenesis and angiogenesis, binds and phosphorylates SHC proteins on tyrosine residues. SHC contains two phosphotyrosine interaction domains: a PTB (Phosphotyrosine Binding) and a SH2 (Src Homology 2) domain. Previous studies have shown that SHC proteins are phosphorylated on Y239/Y240 and Y313 (Y317 in humans) by tyrosine kinases such as the EGF and IL3 receptors. We have investigated which of the SHC tyrosine residues are targeted by the VEGFR3/ FLT4 kinase and the role of the SHC PTB and SH2 domains in this process. Our results show that Y239/ Y240 and Y313 are simultaneously phosphorylated by the kinase, creating GRB2 binding sites. Mutation of SHC PTB, but not SH2, domain interferes with the SHC phosphorylation by VEGFR3/FLT4. Soft agar assay experiments revealed that the VEGFR3/FLT4 transforming capacity is increased by the mutation of Y239/Y240 to phenylalanines in SHC, suggesting that these two residues mediate an inhibitory signal for cell growth. Mutation of the two phosphorylation sites increases this effect, suggesting that they have a synergistic role.

Insulin receptor substrate 2 and Shc play different roles in insulin-like growth factor I signaling

The major substrates for the type I insulin-like growth factor (IGF-I) receptor are Shc and insulin receptor substrate (IRS) proteins. In the current study, we report that IGF-I induces a sustained tyrosine phosphorylation of Shc and its association with Grb2 in SH-SY5Y human neuroblastoma cells. The time course of Shc tyrosine phosphorylation parallels the time course of IGF-I-stimulated activation of extracellular signal-regulated kinase (ERK). Transfection of SH-SY5Y cells with a p52 Shc mutant decreases Shc tyrosine phosphorylation and Shc-Grb2 association. This results in the inhibition of IGF-I-mediated ERK tyrosine phosphorylation and neurite outgrowth. In contrast, IGF-I induces a transient tyrosine phosphorylation of IRS-2 and an association of IRS-2 with Grb2. The time course of IRS-2 tyrosine phosphorylation and IRS-2-Grb2 and IRS-2-p85 association closely resembles the time course of IGF-I-mediated membrane ruffling. Treating cells with the phosphatidylinositol 3'-kinase inhibitors wortmannin and LY294002 blocks IGF-I-induced membrane ruffling. The ERK kinase inhibitor PD98059, as well as transfection with the p52 Shc mutant, has no effect on IGF-I-mediated membrane ruffling. Immunolocalization studies show IRS-2 and Grb2, but not Shc, concentrated at the tip of the extending growth cone where membrane ruffling is most active. Collectively, these results suggest that the association of Shc with Grb2 is essential for IGF-I-mediated neurite outgrowth, whereas the IRS-2-Grb2-phosphatidylinositol 3'-kinase complex may regulate growth cone extension and membrane ruffling.

Interaction of cytosolic adaptor proteins with neuronal apolipoprotein E receptors and the amyloid precursor protein

Apolipoprotein E, alpha2-macroglobulin, and amyloid precursor protein (APP) are involved in the development of Alzheimer's disease. All three proteins are ligands for the low density lipoprotein (LDL) receptor-related protein (LRP), an abundant neuronal surface receptor that has also been genetically linked to Alzheimer's disease. The cytoplasmic tails of LRP and other members of the LDL receptor gene family contain NPxY motifs that are required for receptor endocytosis. To investigate whether these receptors may have functions that go beyond ligand internalization, e.g. possible roles in cellular signaling, we searched for proteins that might interact with the cytoplasmic tails of the receptors. A family of adaptor proteins containing protein interaction domains that can interact with NPxY motifs has previously been described. Using yeast 2-hybrid and protein coprecipitation approaches in vitro, we show that the neuronal adaptor proteins FE65 and mammalian Disabled bind to the cytoplasmic tails of LRP, LDL receptor, and APP, where they can potentially serve as molecular scaffolds for the assembly of cytosolic multiprotein complexes. FE65 contains two distinct protein interaction domains that interact with LRP and APP, respectively, raising the possibility that LRP can modulate the intracellular trafficking of APP. Tyrosine-phosphorylated mammalian Disabled can recruit nonreceptor tyrosine kinases, such as src and abl, to the cytoplasmic tails of the receptors to which it binds, suggesting a molecular pathway by which receptor/ligand interaction on the cell surface could generate an intracellular signal.

Identification of an evolutionarily conserved heterotrimeric protein complex involved in protein targeting

In Caenorhabditis elegans, lin-2, lin-7, and lin-10 genetically interact to control the trafficking of the Let-23 growth factor receptor to the basolateral surface of body epithelia. The human homologue of the lin-10 gene has recently been identified as a member of the X11 gene family. The X11 proteins contain one phosphotyrosine binding (PTB) and two PSD-95.Dlg.ZO-1 (PDZ) domains as well as an extended amino terminus. We have previously shown that the PTB domain of X11alpha (also known as Mint1) can bind to the amyloid precursor protein (APP) in a phosphotyrosine-independent fashion and can markedly inhibit the processing of APP to the amyloid beta (Abeta) peptide. Here, we report that X11alpha directly binds to the mammalian homologue of Lin-2 (mLin-2), also known as CASK. This binding is mediated by direct interaction between the Calmodulin Kinase II (CKII)-like domain of mLin-2 and the amino terminus of X11alpha. Furthermore, we can detect direct interactions between mLin-2 and mammalian Lin-7 (mLin-7). In mouse brain, we have identified a heterotrimeric complex that contains mLin-2, mLin-7, and X11alpha and that is likely important for the localization of proteins in polarized cells. This complex may play an important role in the trafficking and processing of APP in neurons.

The X11alpha protein slows cellular amyloid precursor protein processing and reduces Abeta40 and Abeta42 secretion

Constitutive amyloid precursor protein (APP) metabolism results in the generation of soluble APP (APPs) and Abeta peptides, including Abeta40 and Abeta42-the major component of amyloid plaques in Alzheimer's disease brain. The phosphotyrosine binding (PTB) domain of X11 binds to a peptide containing a YENPTY motif found in the carboxyl terminus of APP. We have cloned the full-length X11 gene now referred to as X11alpha. Coexpression of X11alpha with APP results in comparatively greater levels of cellular APP and less APPs, Abeta40, and Abeta42 recovered in conditioned medium of transiently transfected HEK 293 cells. These effects are impaired by a single missense mutation of either APP (Y682G within the YENPTY motif) or X11alpha (F608V within the PTB domain), which diminishes their interaction, thus demonstrating specificity. The inhibitory effect of X11alpha on Abeta40 and Abeta42 secretion is amplified by coexpression with the Swedish mutation of APP (K595N/M596L), which promotes its amyloidogenic processing. Pulse-chase analysis demonstrates that X11alpha prolongs the half-life of APP from approximately 2 h to approximately 4 h. The effects of X11alpha on cellular APP and APPs recovery were confirmed in a 293 cell line stably transfected with APP. The specific binding of the PTB domain of X11alpha to the YENPTY motif-containing peptide of APP appears to slow cellular APP processing and thus reduces recovery of its soluble fragments APPs, Abeta40, and Abeta42 in conditioned medium of transfected HEK 293 cells. X11alpha may be involved in APP trafficking and metabolism in neurons and thus may be implicated in amyloidogenesis in normal aging and Alzheimer's disease brain.

Functional analysis of the Numb phosphotyrosine-binding domain using site-directed mutagenesis

The Numb protein is involved in cell fate determination during Drosophila neural development. Numb has a protein domain homologous to the phosphotyrosine-binding domain (PTB) in the adaptor protein Shc. In Shc, this domain interacts with specific phosphotyrosine containing motifs on receptor tyrosine kinases and other signaling molecules. Residues N-terminal to the phosphotyrosine are also crucial for phosphopeptide binding to the Shc PTB domain. Several amino acid residues in Shc have been implicated by site-directed mutagenesis to be critical for Shc binding to receptor tyrosine kinases. We have generated homologous mutations in Numb to test whether, in vivo, these changes affect Numb function during Drosophila sensory organ development. Two independent amino acid changes that interfere with Shc binding to phosphotyrosine residues do not affect Numb activity in vivo. In contrast, a mutation shown to abrogate the ability of the Shc PTB domain to bind residues upstream of the phosphotyrosine virtually eliminates Numb function. Similar results were observed in vitro by examining the binding of the Numb PTB domain to proteins from Schneider S2 cells. Our data confirm the importance of the PTB domain for Numb function but strongly suggest that the Numb PTB domain is not involved in phosphotyrosine-dependent interactions.

The 66-kDa Shc isoform is a negative regulator of the epidermal growth factor-stimulated mitogen-activated protein kinase pathway

In addition to tyrosine phosphorylation of the 66-, 52-, and 46-kDa Shc isoforms, epidermal growth factor (EGF) treatment of Chinese hamster ovary cells expressing the human EGF receptor also resulted in the serine/threonine phosphorylation of approximately 50% of the 66-kDa Shc proteins. The serine/threonine phosphorylation occurred subsequent to tyrosine phosphorylation and was prevented by pretreatment of the cells with the MEK-specific inhibitor PD98059. Surprisingly, only the gel-shifted 66-kDa Shc isoform (serine/threonine phosphorylated) was tyrosine phosphorylated and associated with Grb2. In contrast, only the non-serine/threonine-phosphorylated fraction of 66-kDa Shc was associated with the EGF receptor. To assess the relationship between the three Shc isoforms in EGF-stimulated signaling, the cDNA encoding the 66-kDa Shc species was cloned from a 16-day-old mouse embryo library. Sequence alignment confirmed that the 66-kDa Shc cDNA resulted from alternative splicing of the primary Shc transcript generating a 110-amino acid extension at the amino terminus. Co-immunoprecipitation of Shc and Grb2 from cells overexpressing the 52/46-kDa Shc isoforms versus the 66-kDa Shc species directly demonstrated a competition of binding for a limited pool of Grb2 proteins. Furthermore, expression of the 66-kDa Shc isoform markedly accelerated the inactivation of ERK following EGF stimulation. Together, these data indicate that the serine/threonine phosphorylation of 66-kDa Shc impairs its ability to associate with the tyrosine-phosphorylated EGF receptor and can function in a dominant-interfering manner by inhibiting EGF receptor downstream signaling pathways.

Sequence-specific recognition of the internalization motif of the Alzheimer's amyloid precursor protein by the X11 PTB domain

The crystal structure of the phosphotyrosine-binding domain (PTB) of the X11 protein has been determined, in complex with unphosphorylated peptides corresponding to a region of beta-amyloid precursor protein (betaAPP) that is required for receptor internalization. The mode of binding to X11 of the unphosphorylated peptides, which contain an NPxY motif, resembles that of phosphorylated peptides bound to the Shc and IRS-1 PTB domains. Eight peptide residues make specific contacts with the X11 PTB domain, and they collectively achieve high affinity (KD = 0.32 microM) and specificity. These results suggest that, in contrast to the SH2 domains, the PTB domains are primarily peptide-binding domains that have, in some cases, acquired specificity for phosphorylated tyrosines.

Wiskott-Aldrich syndrome protein is associated with the adapter protein Grb2 and the epidermal growth factor receptor in living cells

Src homology domains [i.e., Src homology domain 2 (SH2) and Src homology domain 3 (SH3)] play a critical role in linking receptor tyrosine kinases to downstream signaling networks. A well-defined function of the SH3-SH2-SH3 adapter Grb2 is to link receptor tyrosine kinases, such as the epidermal growth factor receptor (EGFR), to the p21ras-signaling pathway. Grb2 has also been implicated to play a role in growth factor-regulated actin assembly and receptor endocytosis, although the underlying mechanisms remain unclear. In this study, we show that Grb2 interacts through its SH3 domains with the human Wiskott-Aldrich syndrome protein (WASp), which plays a role in regulation of the actin cytoskeleton. We find that WASp is expressed in a variety of cell types and is exclusively cytoplasmic. Although the N-terminal SH3 domain of Grb2 binds significantly stronger than the C-terminal SH3 domain to WASp, full-length Grb2 shows the strongest binding. Both phosphorylation of WASp and its interaction with Grb2, as well as with another adapter protein Nck, remain constitutive in serum-starved or epidermal growth factor-stimulated cells. WASp coimmunoprecipitates with the activated EGFR after epidermal growth factor stimulation. Purified glutathione S-transferase-full-length-Grb2 fusion protein, but not the individual domains of Grb2, enhances the association of WASp with the EGFR, suggesting that Grb2 mediates the association of WASp with EGFR. This study suggests that Grb2 translocates WASp from the cytoplasm to the plasma membrane and the Grb2-WASp complex may play a role in linking receptor tyrosine kinases to the actin cytoskeleton.

The role of the Shc phosphotyrosine interaction/phosphotyrosine binding domain and tyrosine phosphorylation sites in polyoma middle T antigen-mediated cell transformation

The phosphotyrosine interaction (PI)/phosphotyrosine binding (PTB) domain of Shc binds specific tyrosine-phosphorylated motifs found on activated growth factor receptors and proteins such as polyoma virus middle T antigen (MT). Phenylalanine 198 (Phe198) has been identified as a crucial residue involved in the interaction of the Shc PI/PTB with phosphopeptides. In NIH 3T3 cells expressing MT, p52 Shc carrying the F198V mutation is weakly phosphorylated and does not bind MT or Grb2. Overexpression of the PI/PTB domain alone as Shc amino acids 1-238 acted in a dominant interfering fashion blocking MT-induced transformation. However, expression of a slightly longer construct, Shc 1-260, which encompasses Tyr239/Tyr240, a novel Shc tyrosine phosphorylation site, did not block transformation. This was found to be due to the ability of Shc 1-260 to become tyrosine-phosphorylated and bind Grb2. Furthermore, full-length Shc in which Tyr239/Tyr240 had been mutated to phenylalanine did not become tyrosine-phosphorylated or bind Grb2 but did inhibit colony formation in soft agar. Conversely, p52 Shc carrying a mutation in the other tyrosine phosphorylation site, Tyr317, became heavily tyrosine-phosphorylated, bound Grb2, and gave rise to colonies in soft agar.

C. elegans cell migration gene mig-10 shares similarities with a family of SH2 domain proteins and acts cell nonautonomously in excretory canal development

The mig-10 gene of Caenorhabditis elegans is required for the long-range anteroposterior migration of embryonic neurons CAN, ALM, and HSN and proper development of the excretory canals. Here, we report the cloning and initial molecular characterization of mig-10. The predicted MIG-10 proteins share a large region of similarity with a recently identified family of mammalian SH2 domain proteins, Grb7 and Grb10. We call this region of similarity the GM region (for Grb and Mig). MIG-10 proteins do not contain an SH2 domain, but share with the Grbs a pleckstrin homology (PH) domain and proline-rich regions, features commonly found in signal transduction proteins. The functions of Grb7 and Grb10 are unknown, but Grb7 is overexpressed in certain breast cancers, where it is bound to the growth factor receptor HER2, while Grb10 has been implicated in insulin signaling. We also report the isolation of a new mig-10(e2527) allele, as well as the molecular characterization of e2527 (splice acceptor mutation) and the canonical ct41 (amber) allele. Finally, we report the results of a genetic mosaic analysis which reveal that mig-10 acts cell nonautonomously in the development of the excretory canals and suggest a possible focus for mig-10 activity within descendants of the AB cell lineage. Elucidation of the role of mig-10 in C. elegans development should lead to a better understanding of cell migration and may shed light on the function of a family of SH2 domain proteins apparently involved in signal transduction and cancer.

Grb7 is a downstream signaling component of platelet-derived growth factor alpha- and beta-receptors

Ligand stimulation of the platelet-derived growth factor (PDGF) alpha- or beta-receptors leads to activation of their intrinsic tyrosine kinases and autophosphorylation of tyrosine residues. Grb7 is an SH2 and PH domain-containing molecule that is known to be overexpressed in some breast cancer tissues and cell lines. Here we show that the SH2 domain of Grb7 can directly bind to the autophosphorylated PDGF beta-receptor in vitro. Grb7 association to the PDGF beta-receptor was dramatically reduced by replacement of tyrosine residues 716 or 775 with phenylalanine residues. Synthetic phosphorylated peptides containing Tyr-716 or Tyr-775 inhibited binding of the Grb7 SH2 domain to the autophosphorylated PDGF beta-receptor in a manner similar to but distinct from the binding of the Grb2 SH2 domain. Grb7 associated with activated PDGF beta-receptors in vivo, and the association was dramatically reduced by substitution of Tyr-716 or Tyr-775 with a phenylalanine residue. Furthermore, complex formation between Shc and Grb7 was observed after ligand stimulation of PDGF alpha- or beta-receptors in cells transfected with Grb7 cDNA or in the breast cancer cell line BT-474. Thus, Grb7 is implicated in PDGF signaling pathways in certain cell types by binding to the receptor directly or indirectly via Shc.

The phosphotyrosine interaction domains of X11 and FE65 bind to distinct sites on the YENPTY motif of amyloid precursor protein

The phosphotyrosine interaction (PI) domains (also known as the PTB, or phosphotyrosine binding, domains) of Shc and IRS-1 are recently described domains that bind peptides phosphorylated on tyrosine residues. The PI/PTB domains differ from Src homology 2 (SH2) domains in that their binding specificity is determined by residues that lie amino terminal and not carboxy terminal to the phosphotyrosine. Recently, it has been appreciated that other cytoplasmic proteins also contain PI domains. We now show that the PI domain of X11 and one of the PI domains of FE65, two neuronal proteins, bind to the cytoplasmic domain of the amyloid precursor protein ((beta)APP). (beta)APP is an integral transmembrane glycoprotein whose cellular function is unknown. One of the processing pathways of (beta)APP leads to the secretion of A(beta), the major constituent of the amyloid deposited in the brain parenchyma and vessel walls of Alzheimer's disease patients. We have found that the X11 PI domain binds a YENPTY motif in the intracellular domain of (beta)APP that is strikingly similar to the NPXY motifs that bind the Shc and IRS-1 PI/PTB domains. However, unlike the case for binding of the Shc PI/PTB domain, tyrosine phosphorylation of the YENPTY motif is not required for the binding of (beta)APP to X11 or FE65. The binding site of the FE65 PI domain appears to be different from that of X11, as mutations within the YENPTY motif differentially affect the binding of X11 and FE65. Using site-directed mutagenesis, we have identified a crucial residue within the PI domain involved in X11 and FE65 binding to (beta)APP. The binding of X11 or FE65 PI domains to residues of the YENPTY motif of (beta)APP identifies PI domains as general protein interaction domains and may have important implications for the processing of (beta)APP.

The PI/PTB domain: a new protein interaction domain involved in growth factor receptor signaling

In summary, a new domain called the PI/PTB domain has been identified in the Shc adapter protein. This motif binds the NPXpY motif that is found in a large number of signal transduction molecules. The presence in Shc of both a PI/PTB domain and an SH2 domain presumably gives Shc the ability to interact with a large number of tyrosine-phosphorylated proteins. The structure of the PI/PTB domain has been solved and is very similar to the PH domain. Highly related in binding specificity is the PTB domain of IRS-1 and IRS-2, which also binds an NPXpY motif. Several other PI domains have been identified that may also have binding specificity for the NPXY motif. The terminology used at present to define these domains is unclear. The original terms PI and PTB domain stood for phosphotyrosine interaction and phosphotyrosine binding domain, respectively. The name may be inappropriate for some members of this family in which phosphotyrosine may not be essential for binding. Furthermore, these domains are structurally related to the previously named PH domains. At present we feel the use of the name PTB domain should be reserved for Shc and IRS-1/IRS-2, where phosphotyrosine binding has been demonstrated. We place the other proteins we have identified in the PI domain family, with PI now representing the protein interaction rather than the phosphotyrosine interaction domain. The role of several of the PI domains in other proteins is beginning to be studied. It seems clear that our understanding of these domains and their function in cell biology will rapidly expand over the next several years.

Grb10: A new substrate of the insulin-like growth factor I receptor

Using the yeast two-hybrid system, we have isolated a new substrate of the insulin-like growth factor I receptor (IGF-IR), identified as Grb10, a member of the family of SH2 domain proteins. With the help of several mutants of the IGF-IR, we have mapped the binding site of Grb10 between amino acids 1229 and 1245 of the receptor, a sequence that is dispensable for the mitogenic activity of the IGF-IR. Grb10 coprecipitates with the IGF-IR in cell lysates and is probably involved in the regulation of its activity.