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1.
J Infect Dis ; 2021 Jan 20.
Artigo em Inglês | MEDLINE | ID: mdl-33471124

RESUMO

CD4 expression identifies a subset of mature T-cells primarily assisting the germinal center reaction and contributing to CD8 +-T-cell and B-cell activation, functions and longevity. Herein, we present a family in which a novel variant disrupting the translation-initiation-codon of the CD4 gene resulted in complete loss of membrane and plasma soluble-CD4 in peripheral blood, lymph node, bone marrow, skin and ileum of a homozygous proband. This inherited CD4-knock-out disease illustrates the clinical and immunological features of a complete deficiency of any functional component of CD4 and its similarities and differences with other clinical models of primary or acquired loss of CD4 +-T-cells.

2.
Pediatr Res ; 2021 Jan 19.
Artigo em Inglês | MEDLINE | ID: mdl-33469179

RESUMO

The COVID-19 pandemic will leave an indelible mark on the careers of current medical trainees. Given the disruptions to medical education, economic impact on institutions, and the uncertainties around future job prospects, trainees are facing unprecedented challenges. This situation is especially concerning for futures of pediatric physician-scientist trainees, where concerns regarding maintaining the pipeline were well documented prior to the emergence of COVID-19. In this Perspectives article, we leverage the unique expertise of our workgroup to address concerns of physician-scientist trainees and to provide suggestions on how to navigate career trajectories in the post-COVID-19 era. We identified and addressed four major areas of concern: lack of in-person conferences and the associated decrease access to mentors and networking activities, decreased academic productivity, diminished job prospects, and mental health challenges. We also suggest actions for trainees, mentors and educational leaders, and institutions to help support trainees during the pandemic, with a goal of maintaining the pediatric physician-scientist pipeline.

3.
Clin Immunol ; 222: 108638, 2020 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-33276124

RESUMO

To assess how B cell phenotype analysis correlates with antigen responses in patients with class switch recombination defects (CSRD) we quantified memory B cells by flow-cytometry and immunized CSRD patients with the neoantigen bacteriophage phiX174 (phage). CSRD patients showed uniformly absent or markedly reduced switched memory B cells (IgM-IgD-CD27+). CD40L patients had reduced CD27+ memory B cells (both non-switched and switched). In NEMO patients, results varied depending on the IKKγ gene variant. Three of four AID patients had normal percentages of CD27+ memory B cells while CD27+IgM-IgD- switched memory B cells were markedly reduced in all AID patients. Antibody response to phage was remarkably decreased with lack of memory amplification and class-switching in immunized CD40L, UNG deficient, and NEMO patients. Distinct B-cell phenotype pattern correlated with abnormal antibody responses to a T-cell dependent neoantigen, representing a powerful tool to identify CSRD patients.

4.
JAMA Pediatr ; 2020 Oct 12.
Artigo em Inglês | MEDLINE | ID: mdl-33044493

RESUMO

Importance: Limited data on vertical and perinatal transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and health outcomes of neonates born to mothers with symptomatic or asymptomatic coronavirus disease 2019 (COVID-19) are available. Studies are needed to inform evidence-based infection prevention and control (IP&C) policies. Objective: To describe the outcomes of neonates born to mothers with perinatal SARS-CoV-2 infection and the IP&C practices associated with these outcomes. Design, Setting, and Participants: This retrospective cohort analysis reviewed the medical records for maternal and newborn data for all 101 neonates born to 100 mothers positive for or with suspected SARS-CoV-2 infection from March 13 to April 24, 2020. Testing for SARS-CoV-2 was performed using Cobas (Roche Diagnostics) or Xpert Xpress (Cepheid) assays. Newborns were admitted to well-baby nurseries (WBNs) (82 infants) and neonatal intensive care units (NICUs) (19 infants) in 2 affiliate hospitals at a large academic medical center in New York, New York. Newborns from the WBNs roomed-in with their mothers, who were required to wear masks. Direct breastfeeding after appropriate hygiene was encouraged. Exposures: Perinatal exposure to maternal asymptomatic/mild vs severe/critical COVID-19. Main Outcomes and Measures: The primary outcome was newborn SARS-CoV-2 testing results. Maternal COVID-19 status was classified as asymptomatic/mildly symptomatic vs severe/critical. Newborn characteristics and clinical courses were compared across maternal COVID-19 severity. Results: In total, 141 tests were obtained from 101 newborns (54 girls [53.5%]) on 0 to 25 days of life (DOL-0 to DOL-25) (median, DOL-1; interquartile range [IQR], DOL-1 to DOL-3). Two newborns had indeterminate test results, indicative of low viral load (2.0%; 95% CI, 0.2%-7.0%); 1 newborn never underwent retesting but remained well on follow-up, and the other had negative results on retesting. Maternal severe/critical COVID-19 was associated with newborns born approximately 1 week earlier (median gestational age, 37.9 [IQR, 37.1-38.4] vs 39.1 [IQR, 38.3-40.2] weeks; P = .02) and at increased risk of requiring phototherapy (3 of 10 [30.0%] vs 6 of 91 [7.0%]; P = .04) compared with newborns of mothers with asymptomatic/mild COVID-19. Fifty-five newborns were followed up in a new COVID-19 Newborn Follow-up Clinic at DOL-3 to DOL-10 and remained well. Twenty of these newborns plus 3 newborns followed up elsewhere had 32 nonroutine encounters documented at DOL-3 to DOL-25, and none had evidence of SARS-CoV-2 infection, including 6 with negative retesting results. Conclusions and Relevance: No clinical evidence of vertical transmission was identified in 101 newborns of mothers positive for or with suspected SARS-CoV-2 infection, despite most newborns rooming-in and direct breastfeeding practices.

5.
J Clin Invest ; 130(10): 5272-5286, 2020 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-32865517

RESUMO

Human natural killer cell deficiency (NKD) arises from inborn errors of immunity that lead to impaired NK cell development, function, or both. Through the understanding of the biological perturbations in individuals with NKD, requirements for the generation of terminally mature functional innate effector cells can be elucidated. Here, we report a cause of NKD resulting from compound heterozygous mutations in minichromosomal maintenance complex member 10 (MCM10) that impaired NK cell maturation in a child with fatal susceptibility to CMV. MCM10 has not been previously associated with monogenic disease and plays a critical role in the activation and function of the eukaryotic DNA replisome. Through evaluation of patient primary fibroblasts, modeling patient mutations in fibroblast cell lines, and MCM10 knockdown in human NK cell lines, we have shown that loss of MCM10 function leads to impaired cell cycle progression and induction of DNA damage-response pathways. By modeling MCM10 deficiency in primary NK cell precursors, including patient-derived induced pluripotent stem cells, we further demonstrated that MCM10 is required for NK cell terminal maturation and acquisition of immunological system function. Together, these data define MCM10 as an NKD gene and provide biological insight into the requirement for the DNA replisome in human NK cell maturation and function.

6.
J Clin Immunol ; 2020 Sep 19.
Artigo em Inglês | MEDLINE | ID: mdl-32949294

RESUMO

PURPOSE: DiGeorge syndrome has substantial heterogeneity with variable immune deficiency and dysregulation. Implicated immunopathology includes reduced thymic output and increased peripheral homeostatic proliferation with Th2 skewing and expansion of self-reactive cells. We hypothesized that T cell lymphopenia severity will be associated with higher odds of autoimmunity and/or asthma. METHODS: Using the US Immunodeficiency Network registry, we identified patients with 22q11.2 deletion (and/or TBX1). Initial absolute CD3+ T cell values were stratified: normal, 50-99% and below 50% of the lower limit of age-adjusted normal values. Patients with and without reported autoimmunity and asthma were compared using chi-square tests and multivariate logistic regression. RESULTS: Among 415 patients, autoimmunity was reported in 17 (4.1%), and asthma was reported in 28 (6.7%). Compared with those with no reported autoimmunity, patients with reported autoimmunity more frequently had low CD19+ B cells [3.3% (12/364) vs 28.6% (4/14); p = 0.002] and low IgG [6.2% (20/321) vs 29.4% (5/17); p = 0.005] levels. There were no statistically significant differences in other immune characteristics among those with and without reported asthma. Patients with absolute CD3 levels below 50% of age-adjusted normal values had higher odds of reported autoimmunity (n = 319, OR = 7.56, 95% CI = 1.58-36.17, p = 0.01) and reported asthma (n = 319, OR = 4.5, 95% CI = 1.06-18.93, p = 0.04) as compared with those with normal CD3 values, adjusted for age and low IgG. CONCLUSIONS: Absolute CD3+ T cell counts below 50% of age-adjusted normal values may be associated with higher odds of autoimmunity and/or asthma in patients with DiGeorge syndrome and be potentially useful to identify higher-risk patients.

7.
Expert Rev Clin Immunol ; 16(9): 897-909, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-32822560

RESUMO

INTRODUCTION: Genetic testing of patients with clinically diagnosed or suspected primary immunodeficiencies (PIDs) constitutes standard of care. Choice of testing modality and patient attributes can impact the likelihood of securing a diagnosis. AREAS COVERED: Published diagnostic rates for gene panel testing, exome sequencing (WES), and whole genome sequencing are compared among cohorts identified within PubMed. Performance of the testing platforms is reviewed in PIDs taken as a whole, followed by separate cohorts of patients with suspected PIDs, specific PIDs, and clinical phenotypes that can be associated with underlying PIDs. EXPERT OPINION: Massively parallel high-throughput sequencing clearly represents the most expedient method for diagnosis of PIDs. For patients from highly consanguineous backgrounds, WES and whole genome sequencing should be performed to obtain optimal diagnostic yield. For patients for whom familial consanguinity is unlikely, choice of platform depends upon the phenotype. In patients with suspected PIDs, assessment for copy number variants is important, whether as part of gene panel bioinformatic analyses or combined with WES. Diagnostic rates overall for massively parallel sequencing are high for clinically diagnosed and suspected PIDs. WES may have a slightly higher overall yield, but gene panel testing represents a cost-effective and efficient reasonable initial step.

8.
Semin Perinatol ; : 151286, 2020 Jul 23.
Artigo em Inglês | MEDLINE | ID: mdl-32826081

RESUMO

As the COVID-19 pandemic continues to spread worldwide, it is crucial that we determine populations that are at-risk and develop appropriate clinical care policies to protect them. While several respiratory illnesses are known to seriously impact pregnant women and newborns, preliminary data on the novel SARS-CoV-2 Coronavirus suggest that these groups are no more at-risk than the general population. Here, we review the available literature on newborns born to infected mothers and show that newborns of mothers with positive/suspected SARS-CoV-2 infection rarely acquire the disease or show adverse clinical outcomes. With this evidence in mind, it appears that strict postnatal care policies, including separating mothers and newborns, discouraging breastfeeding, and performing early bathing, may be more likely to adversely impact newborns than they are to reduce the low risk of maternal transmission of SARS-CoV-2 or the even lower risk of severe COVID-19 disease in otherwise healthy newborns.

9.
Immunity ; 53(3): 672-684.e11, 2020 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-32750333

RESUMO

Autoinflammatory disease can result from monogenic errors of immunity. We describe a patient with early-onset multi-organ immune dysregulation resulting from a mosaic, gain-of-function mutation (S703I) in JAK1, encoding a kinase essential for signaling downstream of >25 cytokines. By custom single-cell RNA sequencing, we examine mosaicism with single-cell resolution. We find that JAK1 transcription was predominantly restricted to a single allele across different cells, introducing the concept of a mutational "transcriptotype" that differs from the genotype. Functionally, the mutation increases JAK1 activity and transactivates partnering JAKs, independent of its catalytic domain. S703I JAK1 is not only hypermorphic for cytokine signaling but also neomorphic, as it enables signaling cascades not canonically mediated by JAK1. Given these results, the patient was treated with tofacitinib, a JAK inhibitor, leading to the rapid resolution of clinical disease. These findings offer a platform for personalized medicine with the concurrent discovery of fundamental biological principles.

10.
Blood Adv ; 4(16): 3990-4006, 2020 Aug 25.
Artigo em Inglês | MEDLINE | ID: mdl-32841340

RESUMO

Adaptive immune responses are acknowledged to evolve from innate immunity. However, limited information exists regarding whether encounters between innate cells direct the generation of specialized T-cell subsets. We aim to understand how natural killer (NK) cells modulate cell-mediated immunity in humans. We found that human CD14+CD16- monocytes that differentiate into inflammatory dendritic cells (DCs) are shaped at the early stages of differentiation by cell-to-cell interactions with NK cells. Although a fraction of monocytes is eliminated by NK-cell-mediated cytotoxicity, the polarization of interferon-γ (IFN-γ) at the NKp30-stabilized synapses triggers a stable IFN-γ signature in surviving monocytes that persists after their differentiation into DCs. Notably, NK-cell-instructed DCs drive the priming of type 17 CD8+ T cells (Tc17) with the capacity to produce IFN-γ and interleukin-17A. Compared with healthy donors, this cellular network is impaired in patients with classical NK-cell deficiency driven by mutations in the GATA2 gene. Our findings reveal a previously unrecognized connection by which Tc17-mediated immunity might be regulated by NK-cell-mediated tuning of antigen-presenting cells.

11.
Science ; 369(6500): 202-207, 2020 07 10.
Artigo em Inglês | MEDLINE | ID: mdl-32647003

RESUMO

Immunodeficiency often coincides with hyperactive immune disorders such as autoimmunity, lymphoproliferation, or atopy, but this coincidence is rarely understood on a molecular level. We describe five patients from four families with immunodeficiency coupled with atopy, lymphoproliferation, and cytokine overproduction harboring mutations in NCKAP1L, which encodes the hematopoietic-specific HEM1 protein. These mutations cause the loss of the HEM1 protein and the WAVE regulatory complex (WRC) or disrupt binding to the WRC regulator, Arf1, thereby impairing actin polymerization, synapse formation, and immune cell migration. Diminished cortical actin networks caused by WRC loss led to uncontrolled cytokine release and immune hyperresponsiveness. HEM1 loss also blocked mechanistic target of rapamycin complex 2 (mTORC2)-dependent AKT phosphorylation, T cell proliferation, and selected effector functions, leading to immunodeficiency. Thus, the evolutionarily conserved HEM1 protein simultaneously regulates filamentous actin (F-actin) and mTORC2 signaling to achieve equipoise in immune responses.


Assuntos
Actinas/metabolismo , Citocinas/biossíntese , Síndromes de Imunodeficiência/genética , Transtornos Linfoproliferativos/genética , Alvo Mecanístico do Complexo 2 de Rapamicina/metabolismo , Proteínas de Membrana/fisiologia , Fator 1 de Ribosilação do ADP/metabolismo , Linfócitos T CD4-Positivos/imunologia , Proliferação de Células , Humanos , Síndromes de Imunodeficiência/imunologia , Transtornos Linfoproliferativos/imunologia , Proteínas de Membrana/genética , Linhagem , Fosforilação , Família de Proteínas da Síndrome de Wiskott-Aldrich/química , Família de Proteínas da Síndrome de Wiskott-Aldrich/metabolismo
12.
Expert Rev Clin Immunol ; 16(7): 717-732, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32720819

RESUMO

INTRODUCTION: During the last 4 decades, registration of patients with primary immunodeficiencies (PID) has played an essential role in different aspects of these diseases worldwide including epidemiological indexes, policymaking, quality controls of care/life, facilitation of genetic studies and clinical trials as well as improving our understanding about the natural history of the disease and the immune system function. However, due to the limitation of sustainable resources supporting these registries, inconsistency in diagnostic criteria and lack of molecular diagnosis as well as difficulties in the documentation and designing any universal platform, the global perspective of these diseases remains unclear. AREAS COVERED: Published and unpublished studies from January 1981 to June 2020 were systematically reviewed on PubMed, Web of Science and Scopus. Additionally, the reference list of all studies was hand-searched for additional studies. This effort identified a total of 104614 registered patients and suggests identification of at least 10590 additional PID patients, mainly from countries located in Asia and Africa. Molecular defects in genes known to cause PID were identified and reported in 13852 (13.2% of all registered) patients. EXPERT OPINION: Although these data suggest some progress in the identification and documentation of PID patients worldwide, achieving the basic requirement for the global PID burden estimation and registration of undiagnosed patients will require more reinforcement of the progress, involving both improved diagnostic facilities and neonatal screening.

13.
JAMA Pediatr ; 174(10): e202430, 2020 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-32492092

RESUMO

Importance: Descriptions of the coronavirus disease 2019 (COVID-19) experience in pediatrics will help inform clinical practices and infection prevention and control for pediatric facilities. Objective: To describe the epidemiology, clinical, and laboratory features of patients with COVID-19 hospitalized at a children's hospital and to compare these parameters between patients hospitalized with and without severe disease. Design, Setting, and Participants: This retrospective review of electronic medical records from a tertiary care academically affiliated children's hospital in New York City, New York, included hospitalized children and adolescents (≤21 years) who were tested based on suspicion for COVID-19 between March 1 to April 15, 2020, and had positive results for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Exposures: Detection of SARS-CoV-2 from a nasopharyngeal specimen using a reverse transcription-polymerase chain reaction assay. Main Outcomes and Measures: Severe disease as defined by the requirement for mechanical ventilation. Results: Among 50 patients, 27 (54%) were boys and 25 (50%) were Hispanic. The median days from onset of symptoms to admission was 2 days (interquartile range, 1-5 days). Most patients (40 [80%]) had fever or respiratory symptoms (32 [64%]), but 3 patients (6%) with only gastrointestinal tract presentations were identified. Obesity (11 [22%]) was the most prevalent comorbidity. Respiratory support was required for 16 patients (32%), including 9 patients (18%) who required mechanical ventilation. One patient (2%) died. None of 14 infants and 1 of 8 immunocompromised patients had severe disease. Obesity was significantly associated with mechanical ventilation in children 2 years or older (6 of 9 [67%] vs 5 of 25 [20%]; P = .03). Lymphopenia was commonly observed at admission (36 [72%]) but did not differ significantly between those with and without severe disease. Those with severe disease had significantly higher C-reactive protein (median, 8.978 mg/dL [to convert to milligrams per liter, multiply by 10] vs 0.64 mg/dL) and procalcitonin levels (median, 0.31 ng/mL vs 0.17 ng/mL) at admission (P < .001), as well as elevated peak interleukin 6, ferritin, and D-dimer levels during hospitalization. Hydroxychloroquine was administered to 15 patients (30%) but could not be completed for 3. Prolonged test positivity (maximum of 27 days) was observed in 4 patients (8%). Conclusions and Relevance: In this case series study of children and adolescents hospitalized with COVID-19, the disease had diverse manifestations. Infants and immunocompromised patients were not at increased risk of severe disease. Obesity was significantly associated with disease severity. Elevated inflammatory markers were seen in those with severe disease.


Assuntos
Infecções por Coronavirus/diagnóstico , Infecções por Coronavirus/epidemiologia , Pneumonia Viral/diagnóstico , Pneumonia Viral/epidemiologia , Adolescente , Criança , Pré-Escolar , Feminino , Hospitalização , Hospitais Pediátricos , Humanos , Lactente , Recém-Nascido , Masculino , Cidade de Nova Iorque/epidemiologia , Pandemias , Estudos Retrospectivos , Índice de Gravidade de Doença , Adulto Jovem
14.
J Clin Invest ; 130(8): 4411-4422, 2020 Aug 03.
Artigo em Inglês | MEDLINE | ID: mdl-32484799

RESUMO

Patients with common variable immunodeficiency associated with autoimmune cytopenia (CVID+AIC) generate few isotype-switched B cells with severely decreased frequencies of somatic hypermutations (SHMs), but their underlying molecular defects remain poorly characterized. We identified a CVID+AIC patient who displays a rare homozygous missense M466V mutation in ß-catenin-like protein 1 (CTNNBL1). Because CTNNBL1 binds activation-induced cytidine deaminase (AID) that catalyzes SHM, we tested AID interactions with the CTNNBL1 M466V variant. We found that the M466V mutation interfered with the association of CTNNBL1 with AID, resulting in decreased AID in the nuclei of patient EBV-transformed B cell lines and of CTNNBL1 466V/V Ramos B cells engineered to express only CTNNBL1 M466V using CRISPR/Cas9 technology. As a consequence, the scarce IgG+ memory B cells from the CTNNBL1 466V/V patient showed a low SHM frequency that averaged 6.7 mutations compared with about 18 mutations per clone in healthy-donor counterparts. In addition, CTNNBL1 466V/V Ramos B cells displayed a decreased incidence of SHM that was reduced by half compared with parental WT Ramos B cells, demonstrating that the CTNNBL1 M466V mutation is responsible for defective SHM induction. We conclude that CTNNBL1 plays an important role in regulating AID-dependent antibody diversification in humans.

16.
J Clin Immunol ; 40(4): 551-553, 2020 05.
Artigo em Inglês | MEDLINE | ID: mdl-32417998

RESUMO

Several recent studies provide valuable new information that expands the spectrum of human disease associated with mutations in CDC42.

18.
Immunol Res ; 68(1): 48-53, 2020 02.
Artigo em Inglês | MEDLINE | ID: mdl-32128663

RESUMO

Severe combined immunodeficiency (SCID) is a group of syndromes resulting from genetic defects causing severe deficiency in T cell and B cell function. These conditions are life-threatening and result in susceptibility to serious infections. SCID is often fatal in the first year of life if not detected and properly treated. SCID and related T cell lymphopenias can be detected in newborns by a simple screening test, the T cell receptor excision circle (TREC) assay, using the same dried blood spot samples already collected from newborns to screen for other genetic disorders. The TREC assay facilitates the earliest possible identification of cases of SCID before opportunistic infections, irreversible organ damage, or death, thus allowing for the possibility of curative treatment through hematopoietic stem cell transplant and gene therapy. Infants receiving hematopoietic stem cell transplant in the first few months of life, after being identified through screening, have a high probability of survival (95-100%), along with lower morbidity. The TREC assay has proven to have outstanding specificity and sensitivity to accurately identify almost all infants with SCID (the primary targets) as well as additional infants having other select immunologic abnormalities (secondary targets). The TREC assay is inexpensive and has been effectively integrated into many public health programs. Without timely treatment, SCID is a fatal disease that causes accrual of exorbitant healthcare costs even in just 1 year of life. The cost of care for just one infant with SCID, not diagnosed through newborn screening, could be more than the cost of screening for an entire state or regional population. Continued implementation of TREC screening will undoubtedly enhance early diagnosis, application of treatment, and healthcare cost savings. The Jeffrey Modell Foundation helped initiate newborn screening for SCID in the USA in 2008 and continues its efforts to advocate for SCID screening worldwide. Today, all 50 states and Puerto Rico are screening for SCID and T cell lymphopenia, with 27 million newborns screened to date, and hundreds diagnosed and treated. Additionally, there are at least 20 countries around the world currently conducting screening for SCID at various stages. Newborn screening for SCID and related T cell lymphopenia is cost-effective, and most importantly, it is lifesaving and allows children with SCID the opportunity to live a healthy life.

19.
Blood ; 135(9): 629-637, 2020 02 27.
Artigo em Inglês | MEDLINE | ID: mdl-31945148

RESUMO

Natural killer cell deficiencies (NKDs) are an emerging phenotypic subtype of primary immune deficiency. NK cells provide a defense against virally infected cells using a variety of cytotoxic mechanisms, and patients who have defective NK cell development or function can present with atypical, recurrent, or severe herpesviral infections. The current pipeline for investigating NKDs involves the acquisition and clinical assessment of patients with a suspected NKD followed by subsequent in silico, in vitro, and in vivo laboratory research. Evaluation involves initially quantifying NK cells and measuring NK cell cytotoxicity and expression of certain NK cell receptors involved in NK cell development and function. Subsequent studies using genomic methods to identify the potential causative variant are conducted along with variant impact testing to make genotype-phenotype connections. Identification of novel genes contributing to the NKD phenotype can also be facilitated by applying the expanding knowledge of NK cell biology. In this review, we discuss how NKDs that affect NK cell cytotoxicity can be approached in the clinic and laboratory for the discovery of novel gene variants.


Assuntos
Citotoxicidade Imunológica/imunologia , Deficiência de GATA2/imunologia , Células Matadoras Naturais/imunologia , Doenças da Imunodeficiência Primária/imunologia , Animais , Humanos
20.
Biophys J ; 118(3): 586-599, 2020 02 04.
Artigo em Inglês | MEDLINE | ID: mdl-31952801

RESUMO

The coordination of lipid messenger signaling with cytoskeletal regulation is central to many organelle-specific regulatory processes. This coupling often depends on the function of multidomain scaffolds that orchestrate transient interactions among multiple signaling intermediates and regulatory proteins on organelles. The number of possible scaffold interaction partners and the ability for these interactions to occur at different timescales makes investigations of scaffold functions challenging. This work employs live cell imaging to probe how the multidomain scaffold IQ motif containing GTPase activating protein 1 (IQGAP1) coordinates the activities of proteins affecting local actin polymerization, membrane processing, and phosphoinositide signaling. Using endosomes that are confined by a local actin network as a model system, we demonstrate that IQGAP1 can transition between different actin and endosomal membrane tethered states. Fast scaffold binding/disassociation transitions are shown to be driven by interactions between C-terminal scaffold domains and Rho GTPases at the membrane. Fluctuations in these binding modes are linked to negative regulation of actin polymerization. Although this control governs core elements of IQGAP1 dynamics, actin binding by the N-terminal calponin homology domain of the scaffold is shown to help the scaffold track the temporal development of endosome membrane markers, implying actin associations bolster membrane and actin coordination. Importantly, these effects are not easily distilled purely through standard (static) co-localization analyses or traditional pathway perturbations methods and were resolved by performing dynamic correlation and multiple regression analyses of IQGAP1 scaffold mutants. Using these capabilities with pharmacological inhibition, we provide evidence that membrane tethering is dependent on the activities of the lipid kinase phosphoinositide 3-kinase in addition to the Rho GTPases Rac1 and Cdc42. Overall, these methods and results point to a scaffold tethering mechanism that allows IQGAP1 to help control the amplitude of phosphoinositide lipid messenger signaling by coordinating signaling intermediate activities with the development and disassembly of local actin cytoskeletal networks.

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