[Poisonous substances and geographical distribution of poisoning in hospitalized children based on data from 25 hospitals in China from 2016 to 2020].

Objective: To investigate the poisonous substances and geographical distribution of poisoning in children in China. Methods: A cross-sectional study. The clinical data of 8 385 hospitalized children from January 2016 to December 2020 were extracted from the FUTang Updating Medical Records database. These children aged 0 to 18 years and were admitted due to poisoning. They were grouped according to age (newborns and infants, toddlers, preschoolers, school-age children, adolescents), place of residence (Northeast China, North China, Central China, East China, South China, Southwest China, Northwest China), and mode of discharge (discharge under medical advice, transfer to another hospital under medical advice, discharge without medical advice, death, other). The poisonous substance and causes of poisoning in different groups were analyzed. Results: Among these 8 385 children, 4 734 (56.5%) were male and 3 651 (43.5%) female, with a male-to-female ratio of 1.3∶1. The age was 3 (2, 7) years. The prevalence of poisoning was 51.8% (4 343/8 385) in toddlers, 16.5% (1 380/8 385) in adolescents, 14.8% (1 242/8 385) in preschoolers, 14.4% (1 206/8 385) in school-age children, and 2.5% (214/8 385) in newborns and infants. Drug poisoning accounted for 43.5% (3 649/8 385) and pesticide accounted for 26.8% (2 249/8 385). Drug poisoning was more common in adolescents (684/1 380, 49.6%) and toddlers (2 041/4 343, 47.0%); non-drug poisoning was more common in school-age children (891/1 206, 73.9%), of which carbon monoxide was mainly in newborns and infants (41/214, 19.2%) and food poisoning in children of school age (241/1 206, 20.0%). Regarding regional characteristics, drug poisoning was more frequent in South China (188/246, 64.2%) and non-drug poisoning was more frequent in Southwest China (815/1 123, 72.5%). For drugs, anti-epileptic drugs, sedative-hypnotic drugs and anti-Parkinson's disease drugs had a higher proportion of poisoning in North China (138/1 034, 13.0%) than that in other regions. For non-drug poisoning, pesticides (375/1 123, 33.3%), food poisoning (209/1 123, 18.6%) and contact with poisonous animals (86/1 123, 7.7%) were more common in Southwest China than in other regions; carbon monoxide poisoning was more common in North China (81/1 034, 7.6%) and Northwest China (65/1 064, 6.3%). In Central China, poisoning happened more in toddlers (792/1 295, 61.2%) and less in adolescents (115/1 295, 8.8%) than in other regions. Regarding different age groups, poisoning in adolescent happened more in Northeast China (121/457, 26.5%), North China (240/1 034, 23.2%), and Northwest China (245/1 064, 23.0%). The rate of discharge under medical advice, discharge without medical advice, and mortality rate within the 5 years were 77.0% (6 458/8 385), 20.8% (1 743/8 385), 0.5% (40/8 385), respectively. Conclusions: Poisoning is more common in male and toddlers. Poisonous substances show a regional characteristic and vary in different age groups, with drugs and insecticides as the most common substances.

[Clinical and prognostic characteristics of REM sleep related obstructive sleep apnea in children].

Objective: To analyze the clinical and prognostic characteristics of rapid eye movement sleep related obstructive sleep apnea (REM-OSA) in children. Methods: A retrospective analysis was performed on the clinical data of 62 children aged from 2 to 14 years who were admitted to Beijing Children's Hospital, Capital Medical University from December 2017 to April 2021, diagnosed with moderate to severe OSA by polysomnography monitoring (PSG), underwent adenoid tonsillectomy, and completed follow-up 6 months after surgery. There were 45 males (72.6%) and 17 females (27.4%). The age range was 2.0-12.3 years. All children completed the clinical data collection, PSG, OSA-18 quality of life questionnaire and Children's Sleep questionnaire-sleep related breathing disorder subscale at baseline. PSG and OSA-18 quality of life questionnaire were reexamined at 6 months after surgery. Children were divided into REM-OSA group (33 cases) and non-REM-OSA group (29 cases) according to whether the obstructive apnea-hypopnea index (OAHI) during rapid eye movement sleep and OAHI during non-rapid eye movement sleep ratio was≥2. Baseline PSG parameters and scale scores, 6-month postoperative cure rate and OSA-18 quality of life questionnaire scores of the 2 groups were compared, and statistical analysis was performed using SPSS 23.0 software. Results: There were no significant differences in age, sex, body mass index, neck circumference/height ratio, overweight or obesity, history of disease, tonsil and adenoid size between the two groups (all P>0.05). Compared with non-REM-OSA group, REM-OSA group had higher oxygen desaturation index and proportion of SpO2<90% of total sleep time (Z=-2.723, P=0.006;Z=-3.414; P=0.001 respectively), and lower SpO2 nadir (Z=-3.957, P<0.001). The proportion of obstructive apnea in total respiratory events (related to anatomical factors) in REM-OSA group was higher than that in non-REM-OSA group (t=2.840, P=0.006). However, the proportion of central apnea in total respiratory events and arousal index (related to functional factors) in REM-OSA group was lower than that in non-REM-OSA group (t=-2.597, P=0.012;Z=-2.956, P=0.003), and there were no significant differences in other PSG parameters between the two groups (all P>0.05). There was an interaction effect between the two groups in the change trend of OSA cure rate at 6 months after surgery under different baseline OAHI (χ2=4.282, P=0.039). Conclusions: The weight of anatomic factors and functional factors in the etiology of children with REM-OSA and non-REM OSA was different, and the postoperative OSA cure rate of children with different baseline OAHI changed in reverse trend.

[Mortality of drowning and road traffic injury among children aged 5-14 in China from 2008 to 2019].

Objective: To analyze the trajectory of drowning and road traffic injury mortality among children aged 5-14 years in China from 2008 to 2019. Methods: Mortality data of unintentional injuries were from the Mortality Surveillance Data Set of National Disease Surveillance System from 2009 to 2018 and grouped by regions, urban and rural areas, genders, and age groups. The trajectory model was used to analyze the trend of drowning and road traffic injury mortality with years. Results: The mortality of drowning and road traffic injury showed a similar trend. In the trajectory model of drowning mortality, east, middle and west rural boys and western urban boys of all ages belonged to the high mortality group. The moderate mortality group included eastern urban boys and western girls aged 5-9 years and also contained eastern and middle urban boys and western urban girls aged 10-14 years. The other combinations belonged to the low mortality group. In the trajectory model of road traffic injury mortality, western urban boys, all rural boys and western rural girls aged 5-9 years, middle and western rural boys and western urban boys aged 10-14 years belonged to the high mortality group. Eastern urban girls aged 5-9 years and 10-14 years belonged to the low mortality group. The other combinations belonged to the moderate mortality group. Conclusion: There are different groups in the trajectory model of drowning and road traffic injury mortality among children in China. Identifying the trajectory of injury mortality is helpful to carry out more targeted prevention in China.

[Statistical methods for repeated measurement data in scientific research].

Repeated measurement data is a common type of data in medicine, whichcan not be simply compared at each time point, and a professional statistical analysis method should be used to analysis this kind of data. Three common statistical methods were introduced for repeated measurement data, including repeated measurement analysis of variance, generalized estimation equations and multilevel models.The implementation of specific software and related results for the three methods based on some cases were also explainedin the article. Additionally, we compared the actual application of the three methods, in order to help clinical researchers to analyze repeated measurement data correctly and to improve their efficiency of data analysis.

[Endothelial dysfunction in children with obstructive sleep apnea syndrome].

Objective: To evaluate the endothelial function in obstructive sleep apnea syndrome(OSAS) children and to identify related factors of endothelial dysfunction. Methods: This was a cross-sectional study. Children with habitual snoring (snoring ≥3 nights per week) admitted to the ward of otolaryngology, head and neck surgery, Beijing Children's Hospital were recruited to this study between 1(st) June 2015 and 1(st) March 2016. All children aged 3 to 11 years and of them 245 were boys and 110 were girls. All subjects underwent an overnight polysomnography (PSG), as well as endothelial function testing. All subjects were grouped into primary snoring (PS) and OSAS group according to the obstructive apnea hypopnea index (OAHI). T test or Wilcoxon test were used to compare the differences in PSG results between the two groups, and univariate and multivariate correlation analyses were used to explore the relevant factors affecting the endothelial function. Results: A total of 355 subjects were enrolled and 248 had OSAS, and 107 had PS. There were no significant differences in age, gender and body mass index (BMI) Z-score between the two groups (all P>0.05). OSAS group had higher OAHI, oxgen desaturation index and respiratory related arousal index (5.2 (2.2, 13.2) vs. 0.4 (0.1, 0.7), 4.1 (2.0, 13.1) vs. 0.5 (0.1, 1.0), 2.5 (1.0, 4.8) vs. 0.4 (0.1, 0.9), Z=-14.957, -11.790, -10.378, all P<0.01), and lower minimum oxygen saturation and reactive hyperemia index (RHI) than those of PS (0.89 (0.85, 0.92) vs. 0.94 (0.91, 0.95), 1.2±0.2 vs. 1.1±0.1, Z=-9.337, t=5.354, P<0.01). Univariate regression analysis showed that RHI was linearly correlated with age (parameter estimate=0.017, P<0.01), gender (parameter estimate=0.065, P<0.01), OAHI (parameter estimate=-0.023, P<0.01), oxygen desaturation index (parameter estimate=-0.019, P<0.01), respiratory related arousal index (parameter estimate=-0.031, P<0.01), and oxygen saturation nadir (parameter estimate=0.067, P=0.045). The relationship between BMI Z-score and RHI was quadratic. Multivariate regression analysis showed that age (parameter estimate=0.015, P<0.01), BMI Z-score (parameter estimate=0.040, P<0.01), BMI Z-score quadratic form (parameter estimate=-0.010, P<0.01), respiratory related arousal index (parameter estimate=-0.020, P<0.01) were independently correlated with RHI. Conclusions: Children with OSAS have significant endothelial dysfunction compared with PS. Frequent arousals due to obstructive respiratory events during sleep may be a candidate risk factor for endothelial dysfunction in children with OSAS.

[The prevalence of snoring and its related family factors of children from 3 to 14 years old in Beijing].

Objective: To investigate the snoring status and related family factors of children from 3 to 14 years old in Beijing. Methods: From May to July, 2015, data of children from 3 to 14 years old were obtained from a status survey from 7 districts(Xicheng, Chaoyang, Changping, Shunyi, Fangshan, Huairou and Mentougou) in Beijing. A total of 11 420 children from 25 primary and middle schools were randomly selected. Pediatric Sleep Questionnaire (PSQ) and a self-administered questionnaire were carried out for the adopted children. Self-administered questionnaire included the snoring related family factors. Logistic regression was used to estimate the odd ratio(OR) with 95% confidence intervals for variables. Results: A total of 9 198 children meet the inclusion criteria and are analyzed in the study, of whom 901 (9.80%) were found with snoring behavior. The incidence of boys is higher than girls. Obese children take higher risk of snoring. Compared with younger children (≤6 years old), older children (≥12 years old) have a significantly lower risk of snoring (OR=0.464, 95%CI 0.368-0.585). There is no statistical association between full-term infants, infant feeding pattern, parental cigarette smoking and child snoring.The children with family history of snoring have a significantly higher risk of snoring occurrence. The educational background of mother is statistically related to children snoring (OR=1.241, 95%CI 1.058-1.457). Conclusions: The incidence of children snoring in Beijing is 9.80%, male gender, obesity, and young age are all risk factors for children snoring. There is a significantly statistical relationship between snoring and related family factors, such as family snoring history and education experience.

[Logistic regression analysis in observational study].

Logistic regression has been recognized as a commonly used method in epidemiological studies. However, in practice, many people only consider 'data' rather than 'study design' as important issue when working on the analysis, which may easily lead to some misleading results and conclusions. Based on the purpose of observational research during the design of the study, this paper discusses the specific ideas in logistic regression analysis, and provides references for the practical application when logistic regression method is used.

[Analysis of sleep quality and related factors among children in Beijing].

Objective: To investigate the sleep quality of children in Beijing and to analyze the related factors. Methods: The data were collected from the survey of 3-14 years old children in 7 urban districts of Beijing in 2015. By using multi-stage stratified cluster random sampling method, 26 kindergartens and primary and secondary schools in 7 districts and counties, including Xicheng, Chaoyang, Changping, Shunyi, Fangshan, Huairou and Mentougou, were randomly selected, with a total of 11 420 children. Children's sleep status was investigated with Children's Sleep Questionnaire (PSQ), and the proportion of children with sleep quality problems when the PSQ score was greater than 7. Various sleep related factors were investigated with self-made questionnaire. A multilevel model was used to analyze the relationship between PSQ score and related factors. Results: The average PSQ score of the children was 3.60±2.69. The proportion of children with sleep quality problems was 8.87%(816/9 198). Multilevel model analysis showed that the younger the children, the higher the PSQ score (<6 years old vs. 6~12 years old vs. >12 years old: 3.94±2.58 vs. 3.58±2.66 vs. 3.30±2.84, F=33.015, P<0.001); male PSQ score higher than female (3.89±2.75 vs. 3.30±2.60, t=10.560, P<0.001); and snoring, obesity, father/mother snoring, playing games before bed, surfing the internet, eating and other factors were statistically related to PSQ. Conclusions: Sleep quality of children in Beijing should not be neglected, especially preschool children with high PSQ scores. Parents should pay attention to children's snoring problems and try to reduce some pre-sleep behaviors that may affect sleep quality.

[Evaluation of polysomnographic diagnostic criteria for obstructive sleep apnea syndrome in children].

Objective: To determine the appropriate criteria of obstructive sleep apnea syndrome (OSAS) in children. Method: Children with snoring and healthy children were recruited from October 2014 to September 2015. Subjects were divided into four groups based on polysomnography(PSG). Group 1: children with obstructive apnea hypopnea index(OAHI)≥1 (the OSAS criteria of the International Classification of Sleep Disorders, ICSD) but their AHI≤5 or OAI ≤1 (under the OSAS criteria of AHI>5 or OAI>1 by the American Thoracic Society, ATS); Group 2: children with OAHI<1 (the primary snoring criteria of the ICSD); Group 3: children with AHI>5 or OAI>1; and Group 4: normal children as controls. Sleep disorder scales and polysomnography parameters were compared among the four groups. Results: A total of 1 115 children were included.There were 143, 345, 529 and 98 children in each group. After adjust for age, gender and body mass index(BMI), children in group 1 had higher total sleep disorder scale score (P<0.01), as well as sub-scores for severe snoring (P<0.01), daytime behavior problem (P<0.01) and sleep related nighttime abnormality (P<0.05) compared with normal controls, and they had longer mean and longest duration of obstructive apnea and hypopnea and lower minimum oxygen saturation compared with children with obstructive AHI<1 (all P<0.05 or <0.01). Conclusion: OAHI>1 should be defined as the criteria of OSAS in children.

[The validity and reliability of simplified Chinese version of the pediatric sleep questionnaire for screening children with obstructive sleep apnea syndrome in Beijing].

Objective: To evaluate the validity and reliability of the simplified Chinese version of pediatric sleep questionnaire (PSQ) used in screening obstructive sleep apnea syndrome (OSAS) of children in Beijing. Methods: Children with snoring who presented to the Sleep Center of Beijing Children's Hospital between August 2014 and July 2015 and healthy children were included in the study. All children underwent PSG and then were divided into OSAS group and control group based on the PSG and their guardians were asked to complete the simplified Chinese version of PSQ that was formed by both translation from PSQ and retroversion to PSQ. Structure validity evaluation included confirmatory factor analysis which used Amos structural equation model and exploratory factor analysis which used principal component analysis. Predictive validity were measured with Logistic regression model. Internal reliability and test-retest reliability were evaluated by Cronbach 's alpha coefficient and intra-class correlation coefficient (ICC), respectively. The screening efficiency was evaluated by the receiver operating characteristic curve (ROC). Results: The study included 235 children aged 3-16 years old, 145 children of them with the age of (5.8±2.1) in OSAS group and 90 children with the age of (7.7±3.3) in control group. Confirmatory factor analysis indicated most items belonging to individual factors with load coefficient ≥ 0.5. Predictive validity analysis revealed 13 items positively related to the diagnosis of OSAS (all OR>1, all P<0.05). Cronbach's alpha coefficients were respectively 0.703 (overall reliability), 0.767 (breathing factor), 0.849 (sleepiness factor) and 0.689 (behavior factor). The test-retest ICC reliability was 0.986 (PSQ), 0.991 (breathing factor), 0.727 (sleepiness factor), and 0.870 (behavior factor) with P<0.05. In receiver operating characteristic curve, the area under curve of simplified Chinese version PSQ score was 0.922 with P<0.05 and the cutoff value of PSQ score was 7 in 22 items with the sensitivity of 0.776, specificity of 0.867, positive predictive value of 0.868 and negative prediction value of 0.774. Conclusions: The simplified Chinese version of PSQ is suitable to the screen of OSAS for the children in Beijing area with good reliability and validity. It also has acceptable sensitivity and specificity for screening children with OSAS when the cutoff score is 7 points.

[The application of Hoffmann method in the establishment of children's reference intervals of erythrocyte count].

OBJECTIVE: To verify the reliability and feasibility of Hoffmann method in establishing pediatric reference intervals (RI) of erythrocyte count. METHODS: Three hundreds and ninty-two thousands of hospital-based data for erythrocyte count of children aged in 1 to 17, measured by the Sysmex Xs-800i, was collected from Beijing Children's Hospital during January to December 2014. Outliers were removed using the Dixon method, then Hoffmann method was conducted to establish the gender and age stratified pediatric RIs of erythrocyte count. The erythrocyte count of 2 217 healthy children, recruited from Beijing Children's Hospital and Liaocheng Children's Hospital in Shandong province, was conducted as normal reference to verify the reliability of Hoffmann method in establishing RIs and to compare with existing RIs. RESULTS: In 4 subgroups as following, male aging 1 to 12 years, male aging 13 to 17 years, female aging 1 to 12 years, female aging 13 to 17 years, the RIs of erythrocyte count established using Hoffmann method were (4.1-5.4)×10(12)/L, (4.4-5.7)×10(12)/L, (4.0-5.3)×10(12)/L, (4.0-5.3)×10(12)/L, respectively. The verification results in 2 217 healthy children showed that the proportions of out of range in four subgroups were 6.17%, 8.81%, 6.22%, 7.78%, respectively. CONCLUSION: Hoffmann method produce reliable RIs according with the actual situation in healthy children, which is also convenient and is worth popularizing in clinical practice.

The protein tyrosine phosphatase, Shp2, positively contributes to FLT3-ITD-induced hematopoietic progenitor hyperproliferation and malignant disease in vivo.

Internal tandem duplications (ITDs) in the fms-like tyrosine kinase receptor (FLT3-ITDs) confer a poor prognosis in acute myeloid leukemia (AML). We hypothesized that increased recruitment of the protein tyrosine phosphatase, Shp2, to FLT3-ITDs contributes to FLT3 ligand (FL)-independent hyperproliferation and STAT5 activation. Co-immunoprecipitation demonstrated constitutive association of Shp2 with the FLT3-ITD, N51-FLT3, as well as with STAT5. Knockdown of Shp2 in Baf3/N51-FLT3 cells significantly reduced proliferation while having little effect on WT-FLT3-expressing cells. Consistently, mutation of N51-FLT3 tyrosine 599 to phenylalanine or genetic disruption of Shp2 in N51-FLT3-expressing bone marrow low-density mononuclear cells reduced proliferation and STAT5 activation. In transplants, genetic disruption of Shp2 in vivo yielded increased latency to and reduced severity of FLT3-ITD-induced malignancy. Mechanistically, Shp2 co-localizes with nuclear phospho-STAT5, is present at functional interferon-γ activation sites (GAS) within the BCL2L1 promoter, and positively activates the human BCL2L1 promoter, suggesting that Shp2 works with STAT5 to promote pro-leukemogenic gene expression. Further, using a small molecule Shp2 inhibitor, the proliferation of N51-FLT3-expressing bone marrow progenitors and primary AML samples was reduced in a dose-dependent manner. These findings demonstrate that Shp2 positively contributes to FLT3-ITD-induced leukemia and suggest that Shp2 inhibition may provide a novel therapeutic approach to AML.

Cross-talk between endothelial cells and tumor via delta-like ligand 4/Notch/PTEN signaling inhibits lung cancer growth.

Lung cancer is a leading cause of cancer death in many countries. Notch signaling has been demonstrated to frequently participate in the process of lung carcinogenesis. Delta-like ligand 4 (Dll4) is a vascular-specific ligand of Notch, and has a critical role in the angiogenesis of numerous cancers. However, the role of Dll4 in the cross-talk between endothelial cells (ECs) and tumor cells remains obscure. Herein, our study revealed that Dll4-expressing ECs (EC-Dll4) significantly suppressed the proliferation of neighboring non-small cell lung cancer (NSCLC) cells and attenuated the growth of NSCLC xenograft in nude mice. On the contrary, silencing endothelial Dll4 by its specific interference RNA reversed these effects of Dll4 on NSCLC cell proliferation and tumor formation. Furthermore, activation of Notch1, but not Notch2 or Notch3, was enhanced in NSCLC cells cultured with EC-Dll4, as well as in xenografts induced by a mixture of NSCLC cells and EC-Dll4. Interference of Notch1 significantly attenuated Dll4-mediated suppression of NSCLC cell proliferations, indicating that Dll4/Notch1 signaling negatively modulates the NSCLC growth. Moreover, PTEN expression in NSCLC cells was increased by EC-Dll4 or rhDll4 (recombinant human-Dll4 protein), and the induction was impaired by Notch1 interference suggesting that Dll4 could upregulate PTEN expression by Notch1. Taken together, we conclude that the cross-talk between ECs and NSCLC cells by Dll4/Notch1/PTEN signaling pathway inhibits the growth of NSCLC.

Stat3 promotes the development of erythroleukemia by inducing Pu.1 expression and inhibiting erythroid differentiation.

Leukemogenesis requires two classes of mutations, one that promotes proliferation and one that blocks differentiation. The erythroleukemia induced by Friend virus is a multistage disease characterized by an early proliferative stage driven by the interaction of the viral glycoprotein, gp55, with Sf-Stk and the EpoR, and a late block to differentiation resulting from retroviral insertion in the Pu.1 locus. We demonstrate here that activation of Stat3 by Sf-Stk in the early stage of disease is essential for the progression of erythroleukemia in the presence of differentiation signals induced by the EpoR, but is dispensable in the late stages of the disease. Furthermore, we identify Pu.1 as a Stat3 target gene in the early stages of erythroleukemia development. Our results support a model whereby the activation of Stat3 in the early stage of disease plays a pivotal role in regulating differentiation through the upregulation of Pu.1, thus inhibiting differentiation and favoring the expansion of infected erythroblasts and enhancing the pool of progenitors available for the acquisition of additional mutations, including insertional activation of Pu.1, resulting in full leukemic transformation.

Role of Gab2 in mammary tumorigenesis and metastasis.

Overexpression of the adaptor/scaffolding protein Gab2 has been detected in primary human breast cancer cells and cell lines, although its functional significance in breast carcinogenesis is not fully understood. Here, we show a requirement for Gab2 in promoting mammary tumor metastasis. Although Gab2 expression levels were elevated in mammary tumors induced by the Neu (ErbB-2) oncogene, homozygous deletion of Gab2 in mice had only a modest effect on the initiation of Neu-induced mammary tumors. Notably, ablation of Gab2 severely suppressed lung metastasis. Gab2-deficient cancer cells displayed normal Akt activities, and their proliferative rate in vitro was similar to control cells. However, Gab2(-/-) cancer cells exhibited decreased migration and impaired Erk activation, and the defects were rescued by re-introduction of Gab2 into Gab2(-/-) cells. These findings suggest that although Gab2 overexpression may confer growth advantage to tumor cells, the functional requirement for Gab2 in mammary tumor initiation/growth may be dispensable, and that Gab2 may have a prominent role in promoting mammary tumor metastasis.

GRB2-mediated recruitment of GAB2, but not GAB1, to SF-STK supports the expansion of Friend virus-infected erythroid progenitor cells.

Friend virus induces the development of erythroleukemia in mice through the interaction of a viral glycoprotein, gp55, with a truncated form of the Stk receptor tyrosine kinase, short form-Stk (Sf-Stk), and the EpoR. We have shown previously that the ability of Sf-Stk to participate in the transformation of Friend virus-infected cells requires the kinase activity and Grb2-binding site of Sf-Stk. Here we show that Grb2 heterozygous mice exhibit decreased susceptibility to Friend erythroleukemia and that expansion of erythroid progenitors in response to infection requires the C-terminal SH3 domain of Grb2. A fusion protein in which the Grb2-binding site in Sf-Stk is replaced by Gab2, supports the growth of progenitors from mice lacking Sf-Stk, whereas a Sf-Stk/Gab1 fusion protein does not. Gab2 is expressed in spleens from Friend virus-infected mice, co-immunoprecipitates with Sf-Stk and is tyrosine phosphorylated in the presence of Sf-Stk. Mice with a targeted deletion in Gab2 are less susceptible to Friend erythroleukemia and the expansion of erythroid progenitor cells in response to infection can be rescued by expression of Gab2, but not Gab1. Taken together, these data indicate that a Sf-Stk/Grb2/Gab2 complex mediates the growth of primary erythroid progenitor cells in response to Friend virus.

Protein tyrosine phosphatases.

The molecular mechanisms of signal transduction have been at the focus of increasingly intense scientific research. As a result, our understanding of protein tyrosine kinase-mediated signaling has advanced at an unprecedented pace during the past decade. In contrast, the study of protein tyrosine phosphatases has lagged behind, but is now gathering momentum and is predicted to become a "hot topic" in the field within the next few years. This review summarizes the current state-of-the art in our understanding of the structure, regulation and role of protein tyrosine phosphatases with emphasis on the lymphocyte system.

The tyrosine phosphatase SHP-2 is required for mediating phosphatidylinositol 3-kinase/Akt activation by growth factors.

SHP-2 is a ubiquitously expressed non-transmembrane tyrosine phosphatase with two SH2 domains. Multiple reverse-genetic studies have indicated that SHP-2 is a required component for organ and animal development. SHP-2 wild-type and homozygous mutant mouse fibroblast cells in which the N-terminal SH2 domain was target-deleted were used to examine the function of SHP-2 in regulating Phosphatidylinositol 3-Kinase (PI3K) activation by growth factors. In addition, SHP-2 and various mutants were introduced into human glioblastoma cells as well as SHP-2(-/-) mouse fibroblasts. We found that EGF stimulation and EGFR oncoprotein (DeltaEGFR) expression independently induced the co-immunoprecipitation of the p85 subunit of PI3K with SHP-2. Targeted deletion of the N-terminal SH2 domain of SHP-2 severely impaired PDGF- and IGF-induced Akt phosphorylation. Ectopic expression of SHP-2 in U87MG gliobastoma cells elevated EGF-induced Akt phosphorylation, and the effect was abolished by mutation of its N-terminal SH2 domain. Likewise, the reconstitution of SHP-2 expression in the SHP-2(-/-) cells enhanced Akt phosphorylation induced by EGF while rescuing that induced by PDGF and IGF. Further lipid kinase activity assays confirmed that SHP-2 modulation of Akt phosphorylation correlated with its regulation of PI3K activation. Based on these results, we conclude that SHP-2 is required for mediating PI3K/Akt activation, and the N-terminal SH2 domain is critically important for a "positive" role of SHP-2 in regulating PI3K pathway activation.

Requirement of Shp-2 tyrosine phosphatase in lymphoid and hematopoietic cell development.

Shp-1 and Shp-2 are cytoplasmic phosphotyrosine phosphatases with similar structures. Mice deficient in Shp-2 die at midgestation with defects in mesodermal patterning, and a hypomorphic mutation at the Shp-1 locus results in the moth-eaten viable (me(v)) phenotype. Previously, a critical role of Shp-2 in mediating erythroid/myeloid cell development was demonstrated. By using the RAG-2-deficient blastocyst complementation, the role of Shp-2 in lymphopoiesis has been determined. Chimeric mice generated by injecting Shp-2(-/-) embryonic stem cells into Rag-2-deficient blastocysts had no detectable mature T and B cells, serum immunoglobulin M, or even Thy-1(+) and B220(+) precursor lymphocytes. Collectively, these results suggest a positive role of Shp-2 in the development of all blood cell lineages, in contrast to the negative effect of Shp-1 in this process. To determine whether Shp-1 and Shp-2 interact in hematopoiesis, Shp-2(-/-):me(v)/me(v) double-mutant embryos were generated and the hematopoietic cell development in the yolk sacs was examined. More hematopoietic stem/progenitor cells were detected in Shp-2(-/-):me(v)/me(v) embryos than in Shp-2(-/-) littermates. The partial rescue by Shp-1 deficiency of the defective hematopoiesis caused by the Shp-2 mutation suggests that Shp-1 and Shp-2 have antagonistic effects in hematopoiesis, possibly through a bidirectional modulation of the same signaling pathway(s).