Rin1 is a negative regulator of the IL3 receptor signal transduction pathways

Cytokines interact with cell-surface receptors, initiating signaling cascades that promote cell growth while inhibiting the pathways of apoptotic cells. Rin1 is a multifunctional protein that has been shown to regulate EGF receptor signaling and endocytosis. To examine the role of Rin1 in IL3 receptor signaling pathways, Rin1 and deletion mutants were expressed in cells using a retrovirus system. In this study, the overexpression of Rin1 molecules was shown to selectively block IL-3 activation of the Ras-Erk1/2 and PI3K/Akt pathways and the IL-3-stimulated incorporation of [3H] thymidine into DNA without a significant effect on the activity of the JNK and p38K pathways. Moreover, the depletion of Rin1 by RNA interference induced cell growth. In addition, Rin1 was also required as a downstream effector of BCR/ABL-induced cell proliferation. Interestingly, the expression of Rin1 selectively blocked the activation of Erk1/2 induced by the BCR/ABL oncogene. These results demonstrate that Rin1 plays an essential and selective role in both IL3- and BCR/ABL-induced cell proliferation and highlight a new function for Rin1 in leukemic cells.

Rin1 regulates insulin receptor signal transduction pathways

Rin1 is a multifunctional protein containing several domains, including Ras binding and Rab5 GEF domains. The role of Rin1 in insulin receptor internalization and signaling was examined by expressing Rin1 and deletion mutants in cells utilizing a retrovirus system. Here, we show that insulin-receptor-mediated endocystosis and fluid phase insulin-stimulated endocytosis are enhanced in cells expressing the Rin1:wild type and the Rin1:C deletion mutant, which contain both the Rab5-GEF and GTP-bound Ras binding domains. However, the Rin1:N deletion mutant, which contains both the SH2 and proline-rich domains, blocked insulin-stimulated receptor-mediated and insulin-stimulated fluid phase endocytosis. In addition, the expression of Rin1:delta (429-490), a natural occurring splice variant, also blocked both receptor-mediated and fluid phase endocystosis. Furthermore, association of the Rin1 SH2 domain with the insulin receptor was dependent on tyrosine phosphorylation of the insulin receptor. Morphological analysis indicates that Rin1 co-localizes with insulin receptor both at the cell surface and in endosomes upon insulin stimulation. Interestingly, the expression of Rin1:wild type and both deletion mutants blocks the activation of Erk1/2 and Akt1 kinase activities without affecting either JN or p38 kinase activities. DNA synthesis and Elk-1 activation are also altered by the expression of Rin1:wild type and the Rin1:C deletion mutant. In contrast, the expression of Rin1:delta stimulates both Erk1/2 and Akt1 activation, DNA synthesis and Elk-1 activation. These results demonstrate that Rin1 plays an important role in both insulin receptor membrane trafficking and signaling.

Rab5-activating protein 6, a novel endosomal protein with a role in endocytosis

Rab GTPases are regulators of membrane trafficking that cycle between active (GTP-bound) and inactive (GDP-bound) states. In this study, we report the identification of a new human Rab5 guanine nucleotide exchange factor (GEF), which we have named RAP6 (Rab5-activating protein 6). RAP6 contains a Rab5 GEF and a Ras GAP domain. We show that the Vps9 domain is sufficient for the interaction of RAP6 with GDP-bound Rab5 and that RAP6 stimulates Rab5 guanine nucleotide exchange. We also find that the Ras GAP domain of RAP6 shows GAP activity for Ras. Immunofluorescence experiments reveal that RAP6 is associated with plasma membrane and small intracellular vesicles that also contain Rab5. Additionally, the overexpression of RAP6 affects both fluid phase and receptor-mediated endocytosis. This study is the first to show that RAP6 is a novel regulator of endocytosis that exhibits GEF activity specific for Rab5 and GAP activity specific for Ras.

Risk factors for intrauterine growth restriction: a comparison between two Brazilian cities

In Brazil, similar intrauterine growth restriction (IUGR) rates were observed between cities with distinct levels of socioeconomic development, challenging the current knowledge that higher rates of IUGR would necessarily be observed in poorer areas than in wealthier ones. Ribeirão Preto, a city located in the most developed area in Brazil, showed an IUGR rate of 18% in 1994, whereas this rate was 18.5% in 1997/1998 in São Luis, located in one of the poorest areas in the country. The objective of this study was to compare risk factors for IUGR in these two cities and to identify factors that are responsible for this unexpected lack of difference between the rates. Using data from two birth cohorts, including 2839 neonates who were from Ribeirão Preto and born in 1994 and 2439 neonates who were from São Luis and born in 1997/1998, a multivariable analysis was conducted to assess changes in the risk for IUGR in the poorer city compared with the wealthier one in a combined model, adjusting for some risk factors for IUGR. The wealthier city showed higher rates of maternal smoking, attendance in the private sector, and obstetric interventions than the less developed one. Differences in maternal smoking and obstetric interventions were possibly responsible for the similarity of the rates between cities. It seems that early detection of IUGR followed by cesarean section in the wealthier city is associated with increased low birth weight and IUGR rates but reduced stillbirth and infant mortality rates.

Low dose remifentanyl infusion for analgesia and sedation in ventilated newborns

AIM

The aim of this study was to evaluate the analgesic effects of remifentanyl on mechanically ventilated newborns.

METHODS

Eighteen newborns, mechanically ventilated, were submitted to continuous infusion of R. A pain scale was used to evaluate comfort during mechanical ventilation. Data were collected at T0, T1, Tn, T ext, T post-ext; statistical analysis was performed by Student's t test and Pearson coefficient.

RESULTS

Mean R infusion time was 66.94+/-22.24 h, with mean dose of R 0.146+/-0.038 gamma/kg/min. Mean time to reach comfort was 20+/-13.11 h with a mean infusion of R equal to 0.173+/-0.146 gamma/kg/min; R was 0.18+/-0.039 gamma/kg/min on pressure controlled ventilation and R was 0.09+/- 0.045 gamma/kg/min on assisted ventilation. Statistically significant was considered the decrease in HR as well as the increase of SpO2 at T0 vs 30 min after infusion.

CONCLUSION

No adverse effects were observed during and after infusion.

INCREASING PRE-TERM AND LOW-BIRTH- WEIGHT RATES OVER TIME AND THEIR IMPACT ON INFANT MORTALITY IN SOUTH-EAST BRAZIL

This study investigates the possible effects of pre-term births and low birth weight on infant mortality rates (IMRs) over a 15-year period in Ribeirão Preto, Brazil, based on surveys carried out in 1978/79 and 1994. The 1978/79 survey included 6750 births over a 12-month period and the 1994 survey 2846 births over a 4-month period. Infant deaths were retrieved monthly from the city register. Infant mortality rate decreased from 36·6 to 16·9 deaths per 1000 over 15 years. The decrease in IMR was larger in the 2500–2999 g group than in any other group. The observed falls in IMR were attributable to decreases in birth-weight-specific mortality rates. Likewise, there was a general decrease in IMR in mild, moderate and severe pre-term births. The incidence rate ratio of infant mortality between surveys was 0·46 (95% CI 0·34–0·63); it increased to 0·57 (95% CI 0·35–0·75) when adjusted for birth weight and other factors in the model and rose to 0·69 (95% CI 0·49–0·97) when adjusted for length of gestation and other variables. The increase in pre-term births and low birth weight may have had, at most, a marginal effect on the IMR. Progress in the care of newborns may have decreased the mortality risk, but even mild pre-term birth still has an impact on infant mortality. There is room for further improvement in IMR by tackling the high rates of pre-term birth.

Receptor tyrosine kinase signaling and trafficking--paradigms revisited

The recognition of growth factors and other cell signaling agents by their cognate cell surface receptors triggers a cascade of signal transducing events. Ligand binding and subsequent activation of many signal transducing receptors increases their rate of internalization. Endocytosis of the receptor has always been viewed as primarily a mechanism for signal attenuation and receptor degradation, but recent evidence suggests that internalization may result in the formation of specialized signaling platforms on intracellular vesicles. Thus, understanding how interactions between receptors and intracellular signaling molecules, such as adaptors, GTPases, and kinases, are regulated will undoubtedly provide insight into the ways that cells sense and adapt to the extracellular milieu.

Monitoring of intrathoracic volemia and cardiac output in critically ill children

AIM

Hemodynamic monitoring is an important step in the management of critically ill children despite the difficulty in measuring preload indices continuously. The aim of the study was to analyze cardiac output parameters and preload indices after acute changes in mean airway pressure and volemia.

METHODS

Twenty-three children treated at our unit were enrolled in a prospective non randomized cohort study. Respiration was supported by controlled mechanical ventilation with positive expiratory-end pressure (PEEP), peak inspiratory pressure <20 cm H(2)O and mean airway pressure <10 cm H(2)O, and hemodynamic monitoring using the PiCCO system. Hemodynamic parameters were measured at T0 (base line), T(1) (after an increase in PEEP of 5 cm H(2)O for 10 min), and T(2) (after fluid challenge). The statistical analysis (BMPD New System software package) comprised comparison of changes at T(0) vs T(1), T(1) vs T(2) and T(0) vs T(2), construction of 3 correlation matrices and multiple linear regression analysis.

RESULTS

Sixty-nine hemodynamic parameters were measured in the 23 patients. A comparison between T(0) and T(1) showed no significant changes; differences between T(0) and T(2) were found for cardiac index (CI), (p=0.003); between T(0) and T(2) significant differences were found for CI (p=0.0015), intrathoracic blood volume index (ITBVI) (p=0.04) and stroke volume index (SVI) (p=0.06). The analysis of the correlation matrices yielded ITBVI with CI (p=0.0006), ITBVI with SVI (p=1 x 10(-5)), CI with SVI (p=0.002); a significant correlation between CI and extravascular lung water index (EVLWI) was found only at T(1). Multiple linear regression analysis showed that ITBVI and SVI were predictive for variance of CI at each time point.

CONCLUSION

ITBVI measured by a volumetric monitoring system such as the PiCCO may be considered a sensitive preload indicator also in critically ill children.

Lipid kinases play crucial and multiple roles in membrane trafficking and signaling

Phosphotidylinositols (PIs) are known to play an essential role in membrane trafficking and signaling transduction. PIs serve multiple functions, such as recruitment of cytosolic proteins with PI phosphate (PIP) binding domains and modification of the physical properties of the membranes in which they reside. As substrates for phosphoinositide-specific lipases they function as a switch point in phosphoinositide metabolism. Recent work with epidermal growth factor receptor (EGFR) and colony stimulating factor-1 receptor (CSFR) has identified a possible connection between endocytosis of activated receptors and type-1 phosphatidylinositol-4-phosphate-5-kinase. Furthermore, serine/tyrosine phosphorylation of phosphatidylinositol-4-phosphate-5-kinase seems to be essential for its activities. Indeed, one of the products of the phosphatidylinositol-4-phosphate-5-kinases, PIP2, has been shown to be involved in multiple steps of endocytosis, including the assembly of the clathrin coat, regulation of adaptor proteins, and production of endocytic vesicles via the regulation of dynamin. The discussion in this review focuses primarily on receptors with intrinsic enzymatic activity, specifically on receptor tyrosine kinases (RTKs). We will discuss their structure; mechanism of action and potential role in membrane trafficking and/or signaling through the regulation of phosphatidylinositol phosphate kinases.

The relative strength of weight and length at birth in contrast to social factors as determinants of height at 18 years in Brazil

BACKGROUND

There is scarce information on the relative importance of measurements at birth and social factors in determining adult height.

AIM

To assess the relative contribution of length and weight at birth, and social factors to height at 18 years.

METHODS

A total of 3470 boys born in Ribeirão Preto, Brazil, in 1978/1979 were reassessed at the time of military conscription. Anthropometric, demographic and social variables were collected concurrently and used in a multiple regression analysis.

RESULTS

A total of 2029 (61.3%) of the target population were assessed at 18 years. In the adjusted analysis, birth length, birth weight, social class, neighbourhood wealth of subject, maternal age and birth order were highly associated with height at 18 years. The results were similar when birth weight and length at birth were included as continuous or categorical variables. The differences in height due to length at birth were greater than those due to social factors.

CONCLUSIONS

This study has demonstrated the lasting and greater effect of length and weight at birth on height in comparison to social factors, but social factors are still meaningful in their effects on height. Birth length has a marginal greater effect on final height than birth weight.

Narrowing inequalities in infant mortality in Southern Brazil

OBJECTIVE

To determine the trends of infant mortality from 1995 to 1999 according to a geographic area-based measure of maternal education in Porto Alegre, Brazil.

METHODS

A registry-based study was carried out and a municipal database created in 1994 was used. All live births (n=119,170) and infant deaths (n=1,934) were considered. Five different geographic areas were defined according to quintiles of the percentage of low maternal educational level (<8 years of schooling): high, medium high, medium, medium low, and low [corrected]. The chi-square test for trend was used to compare rates between years. Incidence rate ratio was calculated using Poisson regression to identify excess infant mortality in poorer areas compared to higher schooling areas.

RESULTS

The infant mortality rate (IMR) decreased steadily from 18.38 deaths per 1,000 live births in 1995 to 12.21 in 1999 (chi-square for trend p<0.001). Both neonatal and post-neonatal mortality rates decreased although the drop seemed to be steeper for the post-neonatal component. The higher decline was seen in poorer areas.

CONCLUSION

Inequalities in IMR seem to have decreased due to a steeper reduction in both neonatal and post-neonatal components of infant mortality in lower maternal schooling area.

Regulation of Trypanosoma cruzi invasion of nonphagocytic cells by the endocytically active GTPases dynamin, Rab5, and Rab7

During invasion of nonphagocytic cells by Trypanosoma cruzi (T. cruzi), host cell lysosomes are recruited to the plasma membrane attachment site followed by lysosomal enzyme secretion. The membrane trafficking events involved in invasion have not been delineated. We demonstrate here that T. cruzi invasion of nonphagocytic cells was completely abolished by overexpression of a dominant negative mutant of dynamin. Likewise, overexpression of a dominant negative mutant of Rab5, the rate-limiting GTPase for endocytosis, resulted in reduced infection rates compared with cells expressing Rab5 wild-type. Moreover, cells expressing the activated mutant of Rab5 experienced higher infection rates. A similar pattern was also observed when Rab7-transfected cells were examined. Confocal microscopy experiments showed that parasites colocalized with green fluorescent protein-Rab5-positive early endosomes after 5 min of invasion. These data clearly indicate that newly forming T. cruzi phagosomes first interact with an early endosomal compartment and subsequently with other late component markers before lysosomal interaction occurs.

Phosphatidylinositol-4-phosphate 5-kinase-1beta is essential for epidermal growth factor receptor-mediated endocytosis

Phosphatidylinositol-4,5-bisphosphate (PIP(2)) is known to play an important role in signal transduction and membrane trafficking. We show that one enzyme responsible for PIP(2) production, phosphatidylinositol-4-phosphate 5-kinase type 1beta (PIPKbeta), is essential for epidermal growth factor receptor (EGFR)-mediated endocytosis. Expression of murine PIPKbeta in NR6 cells expressing EGFR strikingly increased receptor internalization. Moreover, the kinase was shown to form an immunoprecipitable complex with EGFR. Expression of either a truncated kinase or a kinase dead mutant inhibited EGFR endocytosis and also blocked the membrane recruitment of PIPKbeta and both clathrin light chain and dynamin. Our results delineate a novel mechanism by which PIPKbeta regulates receptor-mediated endocytosis and receptor tyrosine kinase membrane traffic.

Perinatal health and mother-child health care in the municipality of São Luís, Maranhão State, Brazil

The purpose of this article was to evaluate socioeconomic and demographic indicators, reproductive health, use of prenatal, childbirth, and neonatal services, and anthropometric data for mothers and infants. The authors performed a cross-sectional analysis of a systematic sample of 2,831 hospital births in São Luís, Maranhão State, from March 1997 to February 1998 at ten public and private maternity hospitals. The sample was stratified proportionally according to the number of births in each maternity hospital. Mothers answered a standard questionnaire. Of the total, 97.9% were live births and 98% were singletons. Prenatal coverage was 89.5%, and prevalence of cesarean sections was 33.8%. A physician provided prenatal care in 75.7% of cases and performed 73.8% of the deliveries. The Unified Health System covered the costs of 76.4% of the prenatal visits and 89.7% of the deliveries. A pediatrician was present in the delivery room in 50.2% of cases. The low birth weight rate was 9.6% and the preterm birth rate 13.9%. Reasons for concern included a high percentage of adolescent mothers, single mothers (or without partners), the high cesarean rate, and the high percentage of births attended by unqualified personnel.

Use of purified protein derivative to assess the risk of infection in children in close contact with adults with tuberculosis in a population with high Calmette-Guérin bacillus coverage

SETTING

Household contacts <15 years of age of adults with tuberculosis (TB) attending a reference center in Aracaju, Sergipe, Northeast Brazil.

OBJECTIVE

To assess the use of purified protein derivative (PPD) and frequency of infection in children with high Calmette-Guérin bacillus (BCG) coverage who were recently exposed to TB.

DESIGN

Cross-sectional study of 141 exposed household contacts <15 years of age and 506 nonexposed neighborhood controls. Children were examined and assessed for degree of exposure to index cases, BCG vaccination and scar and were tested with PPD.

RESULTS

Exposed children were younger and less up to date in their vaccination schedule than controls (P < 0.05). BCG had been given to 95.6% of exposed children and 97.4% of controls, but only 80.9% of exposed vs. 88.5% of controls had a scar (P < 0.05). Scar sizes of exposed children were smaller (medians, 4.5 and 7 mm, respectively; P < 0.05). Children had lower weight for age z scores and height than the National Center for Health Statistics standards. Exposed children had lower weight for age z scores than controls (P < 0.05). Sixty-seven (47.5%) exposed children and 18 (3.6%) controls had PPD readings of >10 mm. Positivity and induration sizes increased with age, although this was significant only in the controls. The presence of a BCG scar was not associated with having a positive PPD. The degree of exposure was an important factor for PPD positivity; 66 (60.6%) of the 109 children with close exposure were positive compared with 1 (3.1%) of 32 with less intimate exposure. PPD indurations among close contacts were also larger than those with restricted exposure and controls (16.3, 11 and 9.4 mm, respectively; P < 0.05). PPD positivity was associated with the quantification of acid-fast bacilli in the adult; 38.5% of contacts with adults with sputum with (+) were positive, compared with 42.3% of those with (++) and 58.4% with (+++) (P < 0.05).

CONCLUSION

PPD is a useful test to identify children infected with TB independently of whether they had received BCG or not. Children exposed to adults with TB are at high risk of infection. The risk of infection is associated with the intimacy of contact and the number of bacilli expectorated in sputum.

Drosophila rab GDI mutants disrupt development but have normal Rab membrane extraction

Rab GTPases are essential for vesicular transport. Rab GDP dissociation inhibitor (GDI) binds to GDP-bound rabs, removes rabs from acceptor membranes and delivers rabs to donor membranes. We isolated lethal GDI mutations in Drosophila and analyzed their developmental phenotypes. To learn how these mutations affect GDI structure, the crystal structure of Drosophila GDI was determined by molecular replacement to a resolution of 3.0 A. Two hypomorphic, missense mutations are located in domain II of GDI at highly conserved positions, but not in previously identified sequence conserved regions. The mutant GDIs were tested for ability to extract rabs from membranes and showed wild-type levels of rab membrane extraction. The two missense alleles showed intragenic complementation, indicating that domain II of GDI may have two separable functions. This study indicates that GDI function is essential for development of a complex, multicellular organism and that puparium formation and pole cell formation are especially dependent on GDI function.

Risk factors for low birthweight in north-east Brazil: the role of caesarean section

Caesarean section (CS) delivery is associated with low birthweight (LBW) in south-east Brazil. A hospital-based study was conducted on singleton infants from mothers residing in São Luís, to assess if an association between CS and LBW was found in the northern part of the country, where the CS rate is lower than in the south-east. A standardised questionnaire was administered to a sample of 2541 mothers in 10 hospitals, representing 94% of all deliveries, from March 1997 to February 1998. In a logistic model, type of delivery was the independent variable, the other variables were treated as confounders, and interaction terms were added between type of delivery and all other factors. LBW was associated with low maternal height, maternal smoking, primiparity, previous LBW, public insurance, preterm birth and CS. The CS rate was 33.7%. The risk of CS was higher for primiparous and married mothers, those with high level of schooling and attended by the same physician during prenatal and delivery care, deliveries held in private hospitals, daylight hours or evenings, and for those mothers who had adequate prenatal care. Because it appears unlikely that only medical reasons are operative, it is a possibility that CS could cause LBW, reflecting abusive indications for elective CS.

Ras-activated endocytosis is mediated by the Rab5 guanine nucleotide exchange activity of RIN1

RIN1 was originally identified by its ability to inhibit activated Ras and likely participates in multiple signaling pathways because it binds c-ABL and 14-3-3 proteins, in addition to Ras. RIN1 also contains a region homologous to the catalytic domain of Vps9p-like Rab guanine nucleotide exchange factors (GEFs). Here, we show that this region is necessary and sufficient for RIN1 interaction with the GDP-bound Rabs, Vps21p, and Rab5A. RIN1 is also shown to stimulate Rab5 guanine nucleotide exchange, Rab5A-dependent endosome fusion, and EGF receptor-mediated endocytosis. The stimulatory effect of RIN1 on all three of these processes is potentiated by activated Ras. We conclude that Ras-activated endocytosis is facilitated, in part, by the ability of Ras to directly regulate the Rab5 nucleotide exchange activity of RIN1.

Infant mortality rates according to socioeconomic status in a Brazilian city

OBJECTIVE

Data from municipal databases can be used to plan interventions aimed at reducing inequities in health care. The objective of the study was to determine the distribution of infant mortality according to an urban geoeconomic classification using routinely collected municipal data.

METHODS

All live births (total of 42,381) and infant deaths (total of 731) that occurred between 1994 and 1998 in Ribeirão Preto, Brazil, were considered. Four different geoeconomic areas were defined according to the family head's income in each administrative urban zone.

RESULTS

The trends for infant mortality rate and its different components, neonatal mortality rate and post-neonatal mortality rate, decreased in Ribeirão Preto from 1994 to 1998 (chi-square for trend, p<0.05). These rates were inversely correlated with the distribution of lower salaries in the geoeconomic areas (less than 5 minimum wages per family head), in particular the post-neonatal mortality rate (chi-square for trend, p<0.05). Finally, the poor area showed a steady increase in excess infant mortality.

CONCLUSIONS

The results indicate that infant mortality rates are associated with social inequality and can be monitored using municipal databases. The findings also suggest an increase in the impact of social inequality on infant health in Ribeirão Preto, especially in the poor area. The monitoring of health inequalities using municipal databases may be an increasingly more useful tool given the continuous decentralization of health management at the municipal level in Brazil.

Trypanosoma cruzi: phosphatidylinositol 3-kinase and protein kinase B activation is associated with parasite invasion

Multiple signal transduction events are triggered in the host cell during invasion by the protozoan parasite Trypanosoma cruzi. Here, we report the regulation of host cell phosphatydilinositol 3-kinase (PI3K) and protein kinase B (PKB/Akt) activities by T. cruzi during parasite-host cell interaction. Treatment of nonphagocytic cells (Vero, L(6)E(9), and NIH 3T3) and phagocytic cells (human and J774 murine macrophages) with the selective PI3K inhibitors Wortmannin and LY294002 significantly impaired parasite invasion in a dose-dependent fashion. A strong activation of PI3K and PKB/Akt activities in Vero cells was detected when these cells were incubated with trypomastigotes or their isolated membranes. Consistently, we were unable to detect activation of PI3K or PKB/Akt activities in host cells during epimastigote (noninfective) membrane-host cell interaction. Infection of transiently transfected cells containing an inactive mutant PKB showed a significant inhibition of invasion compared with the active mutant-transfected cells. T. cruzi PI3K-like activity was also required in host cell invasion since treatment of trypomastigotes with PI3K inhibitors prior to infection reduced parasite entry. Taken together, these results indicate that PI3K and PKB/Akt activation in parasites, as in host cells induced by T. cruzi, is an early invasion signal required for successful trypomastigote internalization.