Adaptation of the Recreovía During COVID-19 Lockdowns: Making Physical Activity Accessible to Older Adults in Bogotá, Colombia

The community restrictions during the coronavirus disease 2019 pandemic adversely impacted older adults' physical activity levels. This convergent mixed-method study assessed the adaptation of the Recreovía, a community-based physical activity program in Bogotá, and characterized physical activity levels among older adult participants. Our results showed how the Recreovía adapted during the pandemic to continue promoting physical activity, through indoor and outdoor strategies, including virtual physical activity sessions and safety protocols. During this time, 72%-79% of the older adults attending the adapted program were physically active. A greater proportion of park users (84.2%) and more people involved in vigorous physical activity were observed during Recreovía days. Older adults had positive experiences and perceptions of the Recreovía program related to their health and social well-being. Even though the older adults prefer being outdoors, the adapted program allowed participants to continue with their physical activity routines as much as possible during the pandemic.

The impact of mutations affecting highly conserved amino acids in the simian immunodeficiency virus nucleocapsid protein on virion assembly, genomic RNA packaging and viral infectivity

The nucleocapsid (NC) domain of the retroviral Gag polyproteins mediates the incorporation of the viral genomic RNA into virions. Although SIV is widely used as a model for human immunodeficiency virus type 1 (HIV-1) infections, the SIV NC has been the subject of few studies which have provided discrepant data on the relative contribution of the two NC zinc finger motifs to genomic RNA encapsidation. Here, we demonstrate that mutations affecting the first cysteine in the distal zinc finger motif (C33S) or the N-terminal NC basic domain (R7A/K8A) drastically impair virion assembly and viral RNA binding. By contrast, amino acid substitutions targeting the first cysteine of the proximal zinc finger (C12S) or the basic region connecting both zinc fingers (R29A/R30A) allow substantial particle production and genomic RNA encapsidation. Our results help define the relative contribution of the SIV NC zinc finger motifs and basic regions to the NC biological properties.

Prevalence and Associated Factors of Excessive Recreational Screen Time Among Colombian Children and Adolescents

Objectives: Excessive recreational screen time (RST) is associated with detrimental effects for physical, psychological and cognitive development. This article aims to describe the prevalence of excessive RST among Colombian preschoolers, children and adolescents and explore its factors associated.

Methods: We analyzed data from the National Survey of Nutrition 2015. The sample included 4,503 preschoolers, 5,333 school-aged children and 6,623 adolescents. Poisson regression models with robust variance were conducted to estimate prevalence ratios and determine associated factors of excessive RST.

Results: Fifty percent of preschoolers, 61% of school-aged children and 73% of adolescents in Colombia had excessive RST. Positive associations were observed with the availability of TV in the child’s bedroom, the availability of video games at home, and eating while using screens. A negative association with rural area was observed for all age groups.

Conclusion: The majority of Colombian children and adolescents have excessive RST. Younger preschoolers, older school-aged children, wealthiest children and those from urban areas should be targeted by interventions to decrease RST. These interventions should promote limiting the availability of electronic devices in children’s bedrooms and not eating in front of screens.

Gender differences in physical activity and sedentary behavior: Results from over 200,000 Latin-American children and adolescents

More physical activity and less sedentary behavior is beneficial for children and adolescents. Worldwide, gender differences are >8% favorable for men and the Latin-American region presents an even higher level of insufficient physical activity among women, with a lack of information in young population. Thus, the aim of the current study was to describe the gender differences in physical activity and recreational sedentary behavior in children and adolescents from Latin-American countries. The targeted age range was 5 to 17 years and included 219,803 participants (106,698 boys and 113,105 girls) from 33 out of 47 Latin-American countries identified. Physical activity guidelines from the World Health Organization (≥60 minutes of moderate-to-vigorous physical activity seven days of the week) and <3 hours recreational sedentary behavior daily were the references. In general, boys showed a higher prevalence of meeting physical activity guidelines in comparison with girls. A higher proportion of girls met the <3 hours recreational sedentary behavior cut-point in only ten countries. Thirty percent of the identified countries had no available data. The majority had data from the Global School-based Student Health Survey with data principally on adolescents and only 11/33 countries reported data in the last 5-year period. In conclusion, gender differences in the compliance with physical activity guidelines and the <3 hours recreational sedentary behavior cut-point are evident among children and adolescents from Latin-American countries, with boys being more active than girls.

Global prevalence of physical activity for children and adolescents; inconsistencies, research gaps, and recommendations: a narrative review

BACKGROUND

One of the strategic actions identified in the Global Action Plan on Physical Activity (PA) 2018-2030 is the enhancement of data systems and capabilities at national levels to support regular population surveillance of PA. Although national and international standardized surveillance of PA among children and adolescents has increased in recent years, challenges for the global surveillance of PA persist. The aims of this paper were to: (i) review, compare, and discuss the methodological inconsistencies in children and adolescents' physical activity prevalence estimates from intercontinental physical activity surveillance initiatives; (ii) identify methodological limitations, surveillance and research gaps.

METHODS

Intercontinental physical activity surveillance initiatives for children and adolescents were identified by experts and through non-systematic literature searches. Prevalence of meeting PA guidelines by country, gender, and age were extracted when available. A tool was created to assess the quality of the included initiatives. Methods and PA prevalence were compared across data/studies and against the methodological/validity/translation differences.

RESULTS

Eight intercontinental initiatives were identified as meeting the selection criteria. Methods and PA definition inconsistencies across and within included initiatives were observed, resulting in different estimated national prevalence of PA, and initiatives contradicting each other's cross-country comparisons. Three findings were consistent across all eight initiatives: insufficient level of PA of children and adolescents across the world; lower levels of PA among girls; and attenuation of PA levels with age. Resource-limited countries, younger children, children and adolescents not attending school, with disability or chronic conditions, and from rural areas were generally under/not represented.

CONCLUSIONS

There are substantial inconsistencies across/within included initiatives, resulting in varying estimates of the PA situation of children and adolescents at the global, regional and national levels. The development of a new PA measurement instrument that would be globally accepted and harmonized is a global health priority to help improve the accuracy and reliability of global surveillance.

Community-Based Approaches to Reducing Health Inequities and Fostering Environmental Justice through Global Youth-Engaged Citizen Science

Growing socioeconomic and structural disparities within and between nations have created unprecedented health inequities that have been felt most keenly among the world's youth. While policy approaches can help to mitigate such inequities, they are often challenging to enact in under-resourced and marginalized communities. Community-engaged participatory action research provides an alternative or complementary means for addressing the physical and social environmental contexts that can impact health inequities. The purpose of this article is to describe the application of a particular form of technology-enabled participatory action research, called the Our Voice citizen science research model, with youth. An overview of 20 Our Voice studies occurring across five continents indicates that youth and young adults from varied backgrounds and with interests in diverse issues affecting their communities can participate successfully in multiple contributory research processes, including those representing the full scientific endeavor. These activities can, in turn, lead to changes in physical and social environments of relevance to health, wellbeing, and, at times, climate stabilization. The article ends with future directions for the advancement of this type of community-engaged citizen science among young people across the socioeconomic spectrum.

In vitro inhibitory effect of maraviroc on the association of the simian immunodeficiency virus envelope glycoprotein with CCR5

Asian macaques infected with simian immunodeficiency viruses (SIVs) isolated from African non-human primates develop a disease similar to human AIDS. SIV enters its target cells by binding to CD4 and a coreceptor, typically CCR5. Maraviroc is an entry inhibitor of human immunodeficiency virus type 1 (HIV-1) that prevents the interaction between CCR5 and the surface subunit gp120 of the viral envelope glycoprotein (Env). Thus far, the activity of maraviroc on SIV entry has been poorly studied. Here, we determined in vitro pharmacological parameters of the effect of maraviroc on the SIV Env association with CCR5. Cell-to-cell fusion inhibition assays were used to compare the susceptibility to maraviroc of the SIVsmmPBj Env-CCR5 interaction with that of HIV-1BaL Env. Analysis of dose-response curves and determination of IC₅₀ values demonstrate that increasing concentrations of maraviroc inhibit the membrane fusion activity of SIVsmmPBj Env in a manner and to an extent similar to that of HIV-1BaL Env.

Niveles de actividad física y adiposidad en adultos de hogares colombianos con inseguridad alimentaria

Introducción: La promoción de hábitos saludables y la reducción de la inseguridad alimentaria y nutricional (INSAN) son metas de políticas públicas nacionales en Colombia. Sin embargo, estudios que evalúen los niveles de actividad física e indicadores de adiposidad en hogares con INSAN son limitados. Objetivo: Evaluar el cumplimiento de las recomendaciones de actividad física e indicadores de adiposidad en relación con la inseguridad alimentaria y nutricional (INSAN) y con la participación de miembros del hogar en programas sociales de ayuda alimentaria, en la población adulta colombiana. Métodos: Se utilizaron encuestas nacionales de Colombia, ENSIN y ENDS 2010, y se estimaron razones de prevalencia a partir de modelos de regresión binomial negativa. Resultados: Los adultos de hogares con INSAN presentaron mayor cumplimiento de las recomendaciones de actividad física montando en bicicleta y caminando como medios de transporte (PR=1,23; IC95% 1,03-1,47; PR=1,10; IC95% 1,03-1,17), y los adultos de hogares con beneficiarios de programas de ayuda alimentaria presentaron un mayor cumplimiento de las recomendaciones de actividad al montar en bicicleta como medio de transporte (PR=1,33; IC95% 1,10-1,62). Los adultos de hogares con INSAN presentaron menor sobrepeso (PR=0,92; IC95% 0,86-0,97) y menor obesidad abdominal (PR=0,94; IC95% 0,90-0,98). Conclusiones: El estudio identificó los niveles del cumplimiento de las recomendaciones de actividad física y los niveles de adiposidad entre adultos pertenecientes a hogares con inseguridad alimentaria y hogares con miembros que participan en programas nacionales de seguridad alimentaria. Esta situación representa una oportunidad para acciones gubernamentales destinadas a mejorar las condiciones de estos hogares vulnerables a través de programas integrales que promuevan hábitos saludables.

Profiles of Active Transportation among Children and Adolescents in the Global Matrix 3.0 Initiative: A 49-Country Comparison

This article aims to compare the prevalence of active transportation among children and adolescents from 49 countries at different levels of development. The data was extracted from the Report Cards on Physical Activity for Children and Youth from the 49 countries that participated in the Global Matrix 3.0 initiative. Descriptive statistics and a latent profile analysis with active transportation, Human Development Index and Gini index as latent variables were conducted. The global average grade was a "C", indicating that countries are succeeding with about half of children and youth (47-53%). There is wide variability in the prevalence and in the definition of active transportation globally. Three different profiles of countries were identified based on active transportation grades, Human Development Index (HDI) and income inequalities. The first profile grouped very high HDI countries with low prevalence of active transport and low inequalities. The second profile grouped low and middle HDI countries with high prevalence of active transportation and higher inequalities. And the third profile was characterized by the relatively high prevalence of active transportation and more variability in the socioeconomic variables. Promising policies from countries under each profile were identified. A unified definition of active transportation and contextualized methods for its assessment are needed to advance in surveillance and practice.

Active School Transport among Children from Canada, Colombia, Finland, South Africa, and the United States: A Tale of Two Journeys

Walking and biking to school represent a source of regular daily physical activity (PA). The objectives of this paper are to determine the associations of distance to school, crime safety, and socioeconomic variables with active school transport (AST) among children from five culturally and socioeconomically different country sites and to describe the main policies related to AST in those country sites. The analytical sample included 2845 children aged 9-11 years from the International Study of Childhood Obesity, Lifestyle and the Environment. Multilevel generalized linear mixed models were used to estimate the associations between distance, safety and socioeconomic variables, and the odds of engaging in AST. Greater distance to school and vehicle ownership were associated with a lower likelihood of engaging in AST in sites in upper-middle- and high-income countries. Crime perception was negatively associated to AST only in sites in high-income countries. Our results suggest that distance to school is a consistent correlate of AST in different contexts. Our findings regarding crime perception support a need vs. choice framework, indicating that AST may be the only commuting choice for many children from the study sites in upper-middle-income countries, despite the high perception of crime.

[Association between autonomic disorders and subclinical atherosclerosis]

INTRODUCTION AND OBJECTIVES

Alterations of the sympathetic and parasympathetic nervous system have been proposed as precursors of the genesis and perpetuation of atherosclerosis for a long time. The objective of this study is to determine if there is an association between the presence of carotid atherosclerosis and the reduction in heart rate variability.

METHODS

Using a prospective case-control design, the heart rate variability and the presence of carotid atherosclerosis was investigated in 54 patients, divided into 2groups according to the presence or absence of carotid atherosclerosis. An analysis was made of the heart rate variability variables of the frequency (spectral) domain in high frequency band, low frequency band, parasympathetic autonomic balance, and the total spectral band.

RESULTS

Of the 54 individuals evaluated without previous cardiovascular disease consecutively, 26 of them (48%) presented with subclinical carotid atherosclerosis (ATE+). A reduction in heart rate variability was observed in the ATE+group represented by the low frequency (LF) spectrum (P<.0001). The parasympathetic activity specifically represented in the high frequency (HF) band was also lower in the ATE+group in the univariate analysis (P<.0001), same as the total spectral power (P<.0001), an index of integral autonomic regulation. No significant differences were found in the LF/HF analysis (P=.1598). After analysing variables with significant differences in the univariate analysis with a logistic regression model, only systolic blood preassure and the total spectral power were shown to be independent predictors of ATE+.

CONCLUSION

A reduction in heart rate variability was found in subjects with carotid atherosclerosis. Some spectral components of heart rate variability, like low frequency or total spectral power, were better predictors of carotid atherosclerosis than the parasympathetic autonomic balance. In this study it seems that total spectral power is an adequate measurement for analysing autonomic function.

Active streets for children: The case of the Bogotá Ciclovía

Introduction

The Ciclovía is a worldwide program in which streets are temporarily closed to motorized transport to create a space for recreation and outdoor play among children and adults. The aim of this study was to assess the associations between physical activity (PA), sedentary time (SED), body mass index and Ciclovía participation among children aged 9 to 13 years.

Methods

All students in the 4^th and 5^th grades from the selected schools were invited to participate in the study. The study included 923 children. PA and SED were measured using waist-worn accelerometers, and height and weight were measured using standardized procedures. Ciclovía participation was self-reported. The analyses included multilevel linear, generalized mixed and generalized additive models.

Results

The mean age of the sample was 10.1±0.7 years, and 49.5% were boys. In the last year, 46% of the children participated in the Ciclovía, and 34% reported participating frequently (at least once per month). No differences were found in the mean minutes of moderate-to-vigorous PA on weekdays between frequent Ciclovía users and sporadic and non-Ciclovía users (72 vs 69; p = 0.09). In contrast, frequent Ciclovía users had higher moderate-to-vigorous PA on Sundays than sporadic and non-Ciclovía users (65.6 vs 59.2; p = 0.01), specifically between the hours of 12:00 and 16:00. In addition, frequent Ciclovía users did not differ from the sporadic and non-Ciclovía users in SED (515.3 vs 521.3; p = 0.19). Frequent Ciclovía users had lower SED on Sundays than the sporadic and non-Ciclovía users (437.7 vs 456.5; p = 0.005). Additionally, frequent Ciclovía users were more likely to be overweight (28.3% vs 20.4% p = 0.01). We did not find differences in participation by sex, and low-to-middle income children were more likely to participate.

Conclusions

The Ciclovías offer an innovative, inclusive recreational space and consequently provide opportunities to increase moderate-to-vigorous PA and reduce SED among children.

School Food Environment, Food Consumption, and Indicators of Adiposity Among Students 7-14 Years in Bogotá, Colombia

BACKGROUND

In Colombia, the prevalence of overweight/obesity in children has increased by 26% in the past 5 years. School food environment may be an important contributor and offers opportunities for effective intervention.

METHODS

We conducted a cross-sectional study among 7- to 14-year-old schoolchildren from 10 schools in Bogotá, Colombia. We examined the school food environment and the relationship of individual-level consumption, and physical activity with overweight/obesity, measured by body mass index and percentage body fat.

RESULTS

Schools with a restaurant/store were characterized as having excessive unhealthy foods. In the sample of 714 schoolchildren, 17.5% were overweight and 10.5% were obese. In multivariate models, boys had significantly increased odds of being overweight/obese (odds ratio [OR]: 1.53; p = .01) as compared to girls. Schoolchildren who consumed a greater number of energy drinks (OR = 1.82; p = .04), and those who spent more than 3 hours per schoolday watching TV (OR = 1.53; p < .01) had increased odds of being overweight/obese.

CONCLUSIONS

Approximately 1 in 4 schoolchildren were overweight/obese, with boys, energy drink consumers, and those with low physical activity having increased risk. School-based interventions focused on improving food options and providing health behavior education may be effective to reduce overweight among children in Bogotá and similar settings.

Effects of a strategy for the promotion of physical activity in students from Bogotá

OBJECTIVE

To examine the effect of the promotion of physical activity during recess on the levels of physical activity, sedentary behaviors, and adiposity of Colombian students.

METHODS

Three schools were randomly selected by an intervention group in Bogotá, Colombia, in 2013: Intervention (Active Module of Active Recess – MARA) + Text Messages (SMS) (MARA+SMS group), intervention (MARA group), control (control group). Intervention was implemented for ten weeks. The duration and intensity of physical activity and sedentary behaviors were measured objectively using accelerometers Actigraph-GT3X+. Adiposity was measured by body mass index and fat percentage. We measured at baseline (T0) and during the tenth week of intervention (T1). We evaluated the effect of the intervention using a difference-in-difference analysis (DID).

RESULTS

We included 120 students (57.5% girls; mean age = 10.5 years; standard deviation [SD] = 0.64). There was a significant increase in the mean daily minutes of moderate to vigorous physical activity in the MARA group (Difference T1-T0 = 6.1 minutes, standard error [SE] = 3.49, p = 0.005) in relation to the control group. There were no significant changes in the minutes of moderate to vigorous physical activity in the MARA+SMS group (Difference T1-T0 = -1.0 minute; SE = 3.06; p = 0.363). The minutes decreased in the control group (Difference T1-T0 = -7.7 minutes; SE = 3.15; p = 0.011). The minutes of sedentary behaviors decreased in the MARA and MARA+SMS groups and increased in the control group (MARA Difference T1-T0 = -15.8 minutes; SE = 10.05; p= 0.279; MARA+SMS Difference T1-T0 = -11.5 minutes; SE = 8.80; p= 0.869; Control Difference T1-T0 = 10.9 minutes; SE = 9.07; p = 0.407). There was a higher participation in the MARA group in relation to the MARA+SMS group (MARA group = 34.4%; MARA+SMS group = 12.1%). There were no significant changes in adiposity at 10 weeks according to difference-in-differences analysis (body mass index p: ΔMARA+SMS group versus Δcontrol group = 0.945, ΔMARA group versus Δcontrol group = 0.847, ΔMARA+SMS group versus ΔMARA group = 0.990; FP p ΔMARA+SMS group versus Δcontrol group = 0.788, ΔMARA group versus Δcontrol group = 0.915, ΔMARA+SMS group versus ΔMARA group = 0.975).

CONCLUSIONS

The Active Module of Active Recess is a promising strategy to increase physical activity levels and decrease sedentary behavior in students. The addition of Text Messages was not associated with increased moderate to vigorous physical activity or changes in adiposity.

The reliability and validity of a short food frequency questionnaire among 9-11-year olds: a multinational study on three middle-income and high-income countries

OBJECTIVE

The main aim of this study was to assess the reliability and validity of a food frequency questionnaire with 23 food groups (I-FFQ) among a sample of 9-11-year-old children from three different countries that differ on economical development and income distribution, and to assess differences between country sites. Furthermore, we assessed factors associated with I-FFQ's performance.

METHODS

This was an ancillary study of the International Study of Childhood Obesity, Lifestyle and the Environment. Reliability (n=321) and validity (n=282) components of this study had the same participants. Participation rates were 95% and 70%, respectively. Participants completed two I-FFQs with a mean interval of 4.9 weeks to assess reliability. A 3-day pre-coded food diary (PFD) was used as the reference method in the validity analyses. Wilcoxon signed-rank tests, intraclass correlation coefficients and cross-classifications were used to assess the reliability of I-FFQ. Spearman correlation coefficients, percentage difference and cross-classifications were used to assess the validity of I-FFQ. A logistic regression model was used to assess the relation of selected variables with the estimate of validity. Analyses based on information in the PFDs were performed to assess how participants interpreted food groups.

RESULTS

Reliability correlation coefficients ranged from 0.37 to 0.78 and gross misclassification for all food groups was <5%. Validity correlation coefficients were below 0.5 for 22/23 food groups, and they differed among country sites. For validity, gross misclassification was <5% for 22/23 food groups. Over- or underestimation did not appear for 19/23 food groups. Logistic regression showed that country of participation and parental education were associated (P⩽0.05) with the validity of I-FFQ. Analyses of children's interpretation of food groups suggested that the meaning of most food groups was understood by the children.

CONCLUSION

I-FFQ is a moderately reliable method and its validity ranged from low to moderate, depending on food group and country site.

Lentiviral Gag assembly analyzed through the functional characterization of chimeric simian immunodeficiency viruses expressing different domains of the feline immunodeficiency virus capsid protein

To gain insight into the functional relationship between the capsid (CA) domains of the Gag polyproteins of simian and feline immunodeficiency viruses (SIV and FIV, respectively), we constructed chimeric SIVs in which the CA-coding region was partially or totally replaced by the equivalent region of the FIV CA. The phenotypic characterization of the chimeras allowed us to group them into three categories: the chimeric viruses that, while being assembly-competent, exhibit a virion-associated unstable FIV CA; a second group represented only by the chimeric SIV carrying the N-terminal domain (NTD) of the FIV CA which proved to be assembly-defective; and a third group constituted by the chimeric viruses that produce virions exhibiting a mature and stable FIV CA protein, and which incorporate the envelope glycoprotein and contain wild-type levels of viral genome RNA and reverse transcriptase. Further analysis of the latter group of chimeric SIVs demonstrated that they are non-infectious due to a post-entry impairment, such as uncoating of the viral core, reverse transcription or nuclear import of the preintegration complex. Furthermore, we show here that the carboxyl-terminus domain (CTD) of the FIV CA has an intrinsic ability to dimerize in vitro and form high-molecular-weight oligomers, which, together with our finding that the FIV CA-CTD is sufficient to confer assembly competence to the resulting chimeric SIV Gag polyprotein, provides evidence that the CA-CTD exhibits more functional plasticity than the CA-NTD. Taken together, our results provide relevant information on the biological relationship between the CA proteins of primate and nonprimate lentiviruses.

The dual burden of malnutrition in Colombia

BACKGROUND

Almost all nutrition policies in Colombia currently focus on either undernutrition or obesity, with the predominant emphasis on undernutrition. It is crucial to assess the prevalence of the dual burden of malnutrition in Colombia to better target programs and policies.

OBJECTIVE

The aim was to estimate the national prevalence of the dual burden of malnutrition in Colombia at the individual and household levels in children aged <5 y, school-age children, adolescents, and adults.

DESIGN

This was a cross-sectional analysis from the 2010 Colombian Demographic and Health Survey and the National Nutritional Survey that included 17,696 children aged <5 y, 25,508 school-aged children, 28,328 adolescents, 89,164 adults, and 10,487 households with mothers and children aged <5 y. The dual burden of malnutrition was defined as the coexistence of overweight and stunting or anemia in the same person or household.

RESULTS

In Colombia, low to high prevalences of overweight and obesity (3.4-51.2%) coexist with moderate to high prevalences of anemia (8.1-27.5%) and stunting (13.2%). The observed prevalence of the dual burden was lower than expected. Approximately 5% of households had at least one stunted child aged <5 y and an overweight mother compared with an expected prevalence of 6.9% (P < 0.001). Among school-aged children, 0.1% were classified as stunted and obese and 1.4% were both anemic and overweight compared with expected prevalences of 0.5% (P < 0.001) and 1.5% (P = 0.037), respectively. Among 13- to 49-y-old women, 3.4% had anemia and were overweight compared with an expected prevalence of 3.5% (P = 0.038).

CONCLUSIONS

National estimates of the dual burden of malnutrition in Colombia are lower than expected. Despite the independence of the occurrence of these conditions, the fact that the dual burden coexists at the national, household, and intraindividual levels suggests that public policies should address both conditions through multiple strategies. It is imperative to evaluate the current nutrition policies to inform malnutrition prevention efforts in Colombia and to share lessons with other countries at a similar stage of nutritional transition.

Replacement of the V3 domain in the surface subunit of the feline immunodeficiency virus envelope glycoprotein with the equivalent region of a T cell-tropic human immunodeficiency virus type 1 results in a chimeric surface protein that efficiently binds to CXCR4

Feline immunodeficiency virus (FIV) and the T cell-tropic strains of human immunodeficiency virus type 1 (HIV-1) share the use of the chemokine receptor CXCR4 for cell entry. To study this process further we developed a cell surface binding assay based on the expression of a soluble version of the FIV SU C-terminally tagged with the influenza virus hemagglutinin epitope (HA). The specificity of the assay was demonstrated by the following evidence: (1) the SU-HA protein bound to HeLa cells that express CXCR4 but not to MDCK cells that lack this chemokine receptor; and (2) binding of the SU-HA to HeLa cells was blocked by incubation with the CXCR4 antagonist AMD3100 as well as with the anti-CXCR4 monoclonal antibody (MAb) 12G5. Deletion of the V3 region from the FIV SU glycoprotein abolished its ability to bind CXCR4-expressing cells. Remarkably, substitution of the V3 domain of the FIV SU by the equivalent region of the HIV-1 NL4-3 isolate resulted in efficient cell surface binding of the chimeric SU protein to CXCR4. Moreover, transfection of MDCK cells with a plasmid encoding human CXCR4 allowed the association of the chimeric SU-HA glycoprotein to the transfected cells. Interestingly, while cell binding of the chimeric FIV-HIV SU was inhibited by an anti-HIV-1 V3 MAb, its association with CXCR4 was found to be resistant to AMD3100. Of note, the chimeric FIV-HIV Env glycoprotein was capable of promoting CXCR4-dependent cell-to-cell fusion.

Understanding the process of envelope glycoprotein incorporation into virions in simian and feline immunodeficiency viruses

The lentiviral envelope glycoproteins (Env) mediate virus entry by interacting with specific receptors present at the cell surface, thereby determining viral tropism and pathogenesis. Therefore, Env incorporation into the virions formed by assembly of the viral Gag polyprotein at the plasma membrane of the infected cells is a key step in the replication cycle of lentiviruses. Besides being useful models of human immunodeficiency virus (HIV) infections in humans and valuable tools for developing AIDS therapies and vaccines, simian and feline immunodeficiency viruses (SIV and FIV, respectively) are relevant animal retroviruses; the study of which provides important information on how lentiviral replication strategies have evolved. In this review, we discuss the molecular mechanisms underlying the incorporation of the SIV and FIV Env glycoproteins into viral particles.

Palmitoylation of the feline immunodeficiency virus envelope glycoprotein and its effect on fusion activity and envelope incorporation into virions

The feline immunodeficiency virus (FIV) envelope glycoprotein (Env) possesses a short cytoplasmic domain of 53 amino acids containing four highly conserved cysteines at Env positions 804, 811, 815 and 848. Since palmitoylation of transmembrane proteins occurs at or near the membrane anchor, we investigated whether cysteines 804, 811 and 815 are acylated and analyzed the relevance of these residues for Env functions. Replacement of cysteines 804, 811 and 815 individually or in combination by serine residues resulted in Env glycoproteins that were efficiently expressed and processed. However, mutations C804S and C811S reduced Env fusogenicity by 93% and 84%, respectively, compared with wild-type Env. By contrast, mutant C815S exhibited a fusogenic capacity representing 50% of the wild-type value. Remarkably, the double mutation C804S/C811S abrogated both Env fusion activity and Env incorporation into virions. Finally, by means of Click chemistry assays we demonstrated that the four FIV Env cytoplasmic cysteines are palmitoylated.

Mapping of the self-interaction domains in the simian immunodeficiency virus Gag polyprotein

To gain a better understanding of the assembly process in simian immunodeficiency virus (SIV), we first established the conditions under which recombinant SIV Gag lacking the C-terminal p6 domain (SIV GagΔp6) assembled in vitro into spherical particles. Based on the full multimerization capacity of SIV GagΔp6, and to identify the Gag sequences involved in homotypic interactions, we next developed a pull-down assay in which a panel of histidine-tagged SIV Gag truncation mutants was tested for its ability to associate in vitro with GST-SIVGagΔp6. Removal of the nucleocapsid (NC) domain from Gag impaired its ability to interact with GST-SIVGagΔp6. However, this Gag mutant consisting of the matrix (MA) and capsid (CA) domains still retained 50% of the wild-type binding activity. Truncation of SIV Gag from its N-terminus yielded markedly different results. The Gag region consisting of the CA and NC was significantly more efficient than wild-type Gag at interacting in vitro with GST-SIVGagΔp6. Notably, a small Gag subdomain containing the C-terminal third of the CA and the entire NC not only bound to GST-SIVGagΔp6 in vitro at wild-type levels, but also associated in vivo with full-length Gag and was recruited into extracellular particles. Interestingly, when the mature Gag products were analyzed, the MA and NC interacted with GST-SIVGagΔp6 with efficiencies representing 20% and 40%, respectively, of the wild-type value, whereas the CA failed to bind to GST-SIVGagΔp6, despite being capable of self-associating into multimeric complexes.

In vitro binding of simian immunodeficiency virus matrix protein to the cytoplasmic domain of the envelope glycoprotein

Incorporation of the envelope (Env) glycoprotein into budding virions is a key step in the replication cycle of lentiviruses. Previously, we provided genetic and biochemical evidence indicating that Env packaging into simian immunodeficiency virus (SIV) particles is mediated by the association of the Env cytoplasmic domain (CD) with the matrix (MA) domain of Gag. In this study, we developed an in vitro binding assay that, based on recombinant proteins expressed in bacteria, allowed us to demonstrate the physical interaction between the SIV Env CD and the MA in the absence of other viral or cellular proteins. We show that this association is blocked by mutations in each of the interacting domains that have been reported to interfere in vivo with the incorporation of Env into SIV virions. Moreover, we determined that the binding of SIV MA to the Env CD is saturable with a dissociation constant of 7x10(-7) M. Interestingly, the SIV MA is capable of specifically interacting in vitro with the human immunodeficiency virus type 1 Env CD, but not with that of the distantly related feline immunodeficiency virus. Our results strongly support the notion that the association between the SIV MA and Env CD plays a central role in the process of SIV Env incorporation into Gag-made particles.

Importance of the short cytoplasmic domain of the feline immunodeficiency virus transmembrane glycoprotein for fusion activity and envelope glycoprotein incorporation into virions

The mature form of the envelope (Env) glycoprotein of lentiviruses is a heterodimer composed of the surface (SU) and transmembrane (TM) subunits. Feline immunodeficiency virus (FIV) possesses a TM glycoprotein with a cytoplasmic tail of approximately 53 amino acids which is unusually short compared with that of the other lentiviral glycoproteins (more than 100 residues). To investigate the relevance of the FIV TM cytoplasmic domain to Env-mediated viral functions, we characterized the biological properties of a series of Env glycoproteins progressively shortened from the carboxyl terminus. All the mutant Env proteins were efficiently expressed in feline cells and processed into the SU and TM subunits. Deletion of 5 or 11 amino acids from the TM C-terminus did not significantly affect Env surface expression, fusogenic activity or Env incorporation into virions, whereas removal of 17 or 23 residues impaired Env-mediated cell-to-cell fusion. Further truncation of the FIV TM by 29 residues resulted in an Env glycoprotein that was poorly expressed at the cell surface, exhibited only 20% of the wild-type Env fusogenic capacity and was inefficiently incorporated into virions. Remarkably, deletion of the TM C-terminal 35 or 41 amino acids restored or even enhanced Env biological functions. Indeed, these mutant Env glycoproteins bearing cytoplasmic domains of 18 or 12 amino acids were found to be significantly more fusogenic than the wild-type Env and were efficiently incorporated into virions. Interestingly, truncation of the TM cytoplasmic domain to only 6 amino acids did not affect Env incorporation into virions but abrogated Env fusogenicity. Finally, removal of the entire TM cytoplasmic tail or deletion of as many as 6 amino acids into the membrane-spanning domain led to a complete loss of Env functions. Our results demonstrate that despite its relatively short length, the FIV TM cytoplasmic domain plays an important role in modulating Env-mediated viral functions.

Mutations at the C-terminus of the simian immunodeficiency virus envelope glycoprotein affect gp120-gp41 stability on virions

The transmembrane (TM) subunit of the envelope (Env) glycoprotein of the simian immunodeficiency virus (SIV) contains an unusually long cytoplasmic domain of 164 amino acids. Previously, we identified domains in the SIV TM cytoplasmic tail that are necessary for Env incorporation into virions and viral infectivity. In this study, we investigated the relevance to Env function of the highly conserved sequence comprising the immediate C-terminal 19 residues of TM. To this end, small in-frame deletions as well as a premature stop codon mutation were introduced into the coding region for the SIV TM C-terminus. All the mutant Env glycoproteins were expressed, processed and transported to the cell surface in an essentially wild-type manner. Moreover, the ability of the mutant Env proteins to mediate cell-to-cell fusion was similar to or slightly lower than that of the wild-type Env. However, viruses expressing the mutant Env glycoproteins were found to be poorly infectious in single-cycle infectivity assays. Further characterization of the TM mutant viruses revealed that while exhibiting wild-type levels of the TM protein, they contained significantly lower levels of the Env surface (SU) subunit, which is consistent with increased SU shedding from virions after Env incorporation. This phenotype was independent of Gag processing, since genetic inactivation of the viral protease did not increase SU retention by the resulting immature particles. Our findings indicate that deletions at the C-terminus of the SIV Env promote the instability of the SU-TM association on the virion surface and point to an important role for the TM cytoplasmic domain in modulating Env structure.

[Determination of colonic transit time in healthy subjects in Mexico City. Prospective study]

Colonic transit time (CTT) is determined by multiple factors; currently, normal values for the Mexican population are not available. In order to get an estimate one must look at the values reported in the international literature, but cultural, ethnical, nutritional and economic differences may lead to different values.

OBJECTIVE

To determine the normal values of colonic transit time in healthy people in Mexico City by the use of radiopaque markers.

PATIENTS AND METHODS

Prospective, longitudinal and observational study, which included healthy patients ranging from 18 to 60 years old; excluding pregnant women. The whole group of patients was given before breakfast a gelatin capsule which had 20 radiopaque markers inside -the markers were each 2mm long, and were made by the researcher-. After that, they were taken a simple abdominal X-ray film every 24 hours until they totally eliminated the markers. Their eating and defecation habits were evaluated and also the total amount of liquid they consumed. Inferential statistics were used; data was validated with both parametric and non-parametric tests, considering a significance of p < 0.05.

RESULTS

A hundred patients were included in the sample in which 48% were female and 52% male, they were divided in three groups: group A (31%)from 18 to 25 years, group B (37%)from 26 to 40 and group C (32%)from 41 to 60 years; there were no important differences in their water consumption, which was in average of 1.87 lts. in 24 hours; also, there were no considerable differences regarding to their meat, vegetables and fruits' consumption, which was in average of 4.4 times a week; the whole group eliminated the markers according to X-rays which was in 54% after 72 hrs, 45% after 48 hrs and 1% after 24 hrs. We can observe an increase of the CTT related to age: in group C 94% eliminated the markers after 72 hrs and there was no significant difference (statistically) with regards to the other groups. A tendency of an increase of CTT with regards to age was observed: in group A, 80% eliminated the markers after 48 hrs, in group B 49% eliminated them after 48 hrs and 51% after 72 hrs and, in group C, 94% eliminated them after 72 hrs without any statistically significant differences among the study groups.

CONCLUSION

The CTT in healthy patients is in a 100% of the cases studied lower or equal to 72 hrs with a tendency to increase in relation to age.

Functional relationship between the matrix proteins of feline and simian immunodeficiency viruses

To investigate the functional relationship between the matrix (MA) proteins of feline and simian immunodeficiency viruses (FIV and SIV, respectively), we generated chimeric proviruses in which the MA-coding region of an SIV infectious molecular clone was partially or fully replaced by its FIV counterpart. Chimeric SIV proviruses containing the amino-terminal 36 residues or the central and carboxy-terminal regions of the FIV MA assembled into virions as efficiently as wild-type SIV. However, the resulting virions were noninfectious in single-cycle infectivity assays. Furthermore, a chimeric SIV provirus containing the entire FIV MA was found to be severely impaired in virion production due to inefficient membrane binding of the chimeric Gag polyprotein. Interestingly, the assembly defective phenotype of this chimeric Gag precursor could be reversed either by introducing the G31K/G33K double amino acid substitution in the FIV-derived MA domain or by coexpression with wild-type SIV Gag. Of note, a chimeric FIV provirus expressing the SIV MA not only assembled into particles as efficiently as wild-type FIV, but also replicated in feline T cells with wild-type kinetics. Our results thus provide novel information about the functional homology between the MA proteins of distantly related lentiviruses.

Functional domains in the feline immunodeficiency virus nucleocapsid protein

Retroviral nucleocapsid (NC) proteins are small Gag-derived products containing one or two zinc finger motifs that mediate genomic RNA packaging into virions. In this study, we addressed the role of the feline immunodeficiency virus (FIV) NC protein in the late stages of virus replication by analyzing the assembly phenotype of FIV NC mutant viruses and the RNA binding activity of a panel of recombinant FIV NC mutant proteins. Substitution of serine for the first cysteine residue in the NC proximal zinc finger was sufficient to impair both virion assembly and genomic RNA binding. A similar defective phenotype with respect to particle formation and RNA binding was observed when the basic residues Lys28 and Lys29 in the region connecting both zinc fingers were replaced by alanine. In contrast, mutation of the first cysteine residue in the distal zinc finger had no effect on virion production and allowed substantial RNA binding activity of the mutant NC protein. Moreover, this NC mutant virus exhibited wild-type replication kinetics in the feline MYA-1 T-cell line. Interestingly, amino acid substitutions disrupting the highly conserved PSAP and LLDL motifs present in the C-terminus of the FIV NC abrogated virion formation without affecting the NC RNA binding activity. Our results indicate that the proximal zinc finger of the FIV NC is more important for virion production and genomic RNA binding than the distal motif. In addition, this study suggests that assembly domains in the FIV NC C-terminus may be functionally equivalent to those present in the p6 domain of the Gag polyprotein of primate lentiviruses.

Second-site revertants of a simian immunodeficiency virus gp41 mutant defective in envelope glycoprotein incorporation

We previously characterized a series of small in-frame deletions within the C-terminal third of the simian immunodeficiency virus (SIV) gp41 cytoplasmic domain that significantly impair the incorporation of the envelope (Env) glycoprotein into particles and Env-mediated virus entry. Among these mutations, removal of Env residues 832-837 caused the most drastic defective phenotype. In the present study, we introduced the Delta832-837 deletion into the PBj1.9 molecular clone and investigated the effect of this env mutation on virus replication in the CEMx174 cell line. This in-frame deletion was found to severely compromise virus replication. Interestingly, long-term culture of the PBjEnvDelta832-837 mutant led to the emergence of two independent populations of revertant viruses that, while differing in the time point at which they appear, encode truncated gp41 cytoplasmic tails of similar lengths. The first emergent virus population contained a premature stop codon mutation at Env residue 778, whereas the late-appearing population harbored a stop codon mutation at Env residue 774, which results in the truncation of the gp41 cytoplasmic tail to 52 and 48 amino acids, respectively. Analysis of derivatives of PBjEnvDelta832-837 containing either the Tyr778stop or the Trp774stop mutations demonstrated that these second-site changes were sufficient to reverse the Env incorporation and infectivity defects imposed by the original Delta832-837 deletion, as well as to confer to the Env double mutants essentially wild-type replication kinetics. Our results thus provide further insight into the mechanisms underlying SIV adaptation to novel selective forces.

Positive and negative modulation of virus infectivity and envelope glycoprotein incorporation into virions by amino acid substitutions at the N terminus of the simian immunodeficiency virus matrix protein

The matrix (MA) protein of the simian immunodeficiency viruses (SIVs) is encoded by the amino-terminal region of the Gag precursor and is the component of the viral capsid that lines the inner surface of the virus envelope. Previously, we identified domains in the SIV MA that are involved in the transport of Gag to the plasma membrane and in particle assembly. In this study, we characterized the role in the SIV life cycle of highly conserved residues within the SIV MA region spanning the two N-terminal alpha-helices H1 and H2. Our analyses identified two classes of MA mutants: (i) viruses encoding amino acid substitutions within alpha-helices H1 or H2 that were defective in envelope (Env) glycoprotein incorporation and exhibited impaired infectivity and (ii) viruses harboring mutations in the beta-turn connecting helices H1 and H2 that were more infectious than the wild-type virus and displayed an enhanced ability to incorporate the Env glycoprotein. Remarkably, among the latter group of MA mutants, the R22L/G24L double amino acid substitution increased virus infectivity eightfold relative to the wild-type virus in single-cycle infectivity assays, an effect that correlated with a similar increase in Env incorporation. Furthermore, the R22L/G24L MA mutation partially or fully complemented single-point MA mutations that severely impair or block Env incorporation and virus infectivity. Our finding that the incorporation of the Env glycoprotein into virions can be upregulated by specific mutations within the SIV MA amino terminus strongly supports the notion that the SIV MA domain mediates Gag-Env association during particle formation.

Presenilin 1 overexpressions in Chinese hamster ovary (CHO) cells decreases the phosphorylation of retinoblastoma protein: relevance for neurodegeneration

Mutations in the presenilin 1 (PS1) gene have been associated to familial Alzheimer disease although the exact pathogenic mechanism is unclear. We report that stable overexpression of wild type PS1 led to a decrease in cyclin-dependent kinase 4 (CDK 4) activity and retinoblastoma tumor suppressor protein (pRb) phosphorylation that correlated with decreased levels of beta-catenin and cyclin D1. PS1 mutant D385A also precipitated a similar effect suggesting that gamma-secretase cleavage is not essential for PS1-mediated CDK 4 inhibition. We postulate that PS1 overexpression may balance the hyperphosphorylation of pRb associated with death of post mitotic neurons after injury.

Small variations in the length of the cytoplasmic domain of the simian immunodeficiency virus transmembrane protein drastically affect envelope incorporation and virus entry

Simian immunodeficiency viruses (SIVs) have an envelope (Env) glycoprotein with an unusually long cytoplasmic domain of 164 amino acids. In this article, we have characterized a series of SIV Env truncation mutants in which the cytoplasmic domain was progressively shortened from its carboxyl terminus by 20 amino acids. Expression by means of the vaccinia virus system showed that all of the SIV Env mutants were expressed and processed into the surface and transmembrane (TM) subunits. When the ability of the Env mutants to associate with SIV Gag particles was examined, we found that deletion of 20 to 80 residues from the carboxyl terminus of the SIV TM cytoplasmic tail abrogated the incorporation of the Env glycoprotein into particles. By contrast, further truncation of the SIV TM protein by 100 to 140 amino acids restored the ability of the Env protein to associate with Gag particles. Interestingly, mutants bearing a 44- or 24-amino acid cytoplasmic domain were incorporated at levels significantly higher than those of the wild-type Env. Single-cycle infectivity assays showed that Env mutants bearing cytoplasmic tails of 144 to 64 amino acids were highly inefficient at mediating virus entry. By contrast, truncation of the cytoplasmic domain to 44 or 24 amino acids drastically enhanced virus infectivity with respect to that conferred by the full-length Env protein. Our results demonstrate that small variations in the length of the SIV Env cytoplasmic domain dramatically influence Env-mediated viral functions.

Mutational analysis of the feline immunodeficiency virus matrix protein

To study the process of feline immunodeficiency virus (FIV) assembly, we examined the suitability of the vaccinia vector system to reproduce FIV particle formation. To this end, we constructed a recombinant vaccinia virus carrying the FIV gag gene. Biochemical and electron microscopy analyses of cells infected with this recombinant virus showed that the FIV Gag polyprotein self-assembled into lentivirus-like particles that were released into the culture medium. As a first step in the identification of molecular determinants in FIV Gag that are involved in virus assembly, we performed a site-directed mutagenesis analysis of the N-terminal matrix (MA) domain of the FIV Gag precursor. To this end, a series of amino acid substitutions and small in-frame deletions were introduced into the FIV MA and the mutated FIV gag gene constructs were expressed by means of the vaccinia system. Characterization of the assembly phenotype of these FIV Gag mutants led to the identification of amino acidic regions within the MA domain that are necessary for efficient transport of the Gag precursor to the plasma membrane and particle assembly. Our results reveal the role that the FIV MA plays in virus morphogenesis and contribute to the understanding of the assembly process in non-primate lentiviruses.

Domains in the simian immunodeficiency virus gp41 cytoplasmic tail required for envelope incorporation into particles

The mechanism by which lentivirus envelope (Env) glycoproteins are packaged into budding virions is poorly understood. Simian immunodeficiency virus (SIV) contains an Env protein with an unusually long cytoplasmic tail. To investigate the role of this domain in the incorporation of the SIV Env into virions, we generated a series of SIV Env mutants carrying small in-frame deletions within the cytoplasmic domain. The effects of these mutations on Env synthesis, processing, and association with Gag particles were analyzed by means of the vaccinia virus expression system. All of the mutant Env glycoproteins were synthesized and processed in a manner similar to that of the wild-type Env. However, deletions affecting domains C-terminal to residue 832 in the SIV Env protein significantly impaired Env incorporation into particles. Cell surface biotinylation assays showed that this phenotype could not be attributed to inefficient cell surface expression of the Env mutants. Furthermore, when the Env deletion mutants were tested for their ability to mediate virus entry in single-cycle infectivity assays, those mutations that impaired Env incorporation also caused a severe defect in virus infectivity. Our results suggest that domains in the C-terminal third of the SIV Env protein are required for Env incorporation into particles and Env-mediated virus entry.

Substitution of leucine 8 in the simian immunodeficiency virus matrix protein impairs particle formation without affecting N-myristylation of the Gag precursor

In the late stages of replication of the simian immunodeficiency viruses (SIV), the matrix protein (MA) plays a central role in the transport of Pr55gag to the plasma membrane, assembly of virus particles, and incorporation of the envelope glycoprotein into particles. Targeting of Pr55gag to the plasma membrane is mediated by two motifs within the MA protein: the N-terminal myristate and a cluster of positively charged amino acids. In this report, we characterized the assembly phenotype of an SIV Gag mutant (L8Q) carrying the single amino acid substitution of glutamine for leucine at position 8 in the MA domain. The hydropathic profile of the mutated MA protein indicated that the L8Q amino acid change disrupts the hydrophobic character of the region comprising the first 10 residues of the protein. Expression of mutant L8Q Gag protein in CV-1 cells, by means of the vaccinia virus vector system, resulted in efficient synthesis and N-myristylation of Pr55gag. However, this mutation severely impaired particle production, as inferred from both biochemical and electron microscopy analyses. Cellular fractionation assays revealed that in cells expressing mutant L8Q, the proportion of cytosol-associated Pr55gag was significantly increased compared to that observed upon expression of wild-type Gag. Furthermore, mutant L8Q Gag partitioned onto cytosol and membrane fractions in a manner similar to nonmyristylated Gag polyprotein. Taken together, these results indicate that the L8Q mutation reduces the membrane-binding capacity of the Gag precursor. It is therefore likely that in the SIV MA, in addition to the N-myristate group, the hydrophobicity of the neighboring region is important for efficient association of Pr55gag with the plasma membrane.

Deletion mapping of functional domains in the rotavirus capsid protein VP6

VP6, the major capsid protein of rotavirus, oligomerizes into trimers that constitute the intermediate shell of the virions. In order to map functional domains in this protein, we introduced seven internal in-frame deletions within the coding region of gene 6 of human rotavirus strain Wa. Regions of homology among the VP6 proteins of group A and group C rotaviruses were targeted for deletion mutagenesis. The mutant VP6 proteins were expressed in mammalian cells using the recombinant vaccinia virus system and were examined for their ability to oligomerize into trimers as well as to assemble into double-layered virus-like particles upon coexpression with the rotavirus core protein VP2. Deletions that abolished trimerization defined a domain (residues 246 to 314) that maps within a larger region previously found to be critical for oligomerization (amino acids 105 to 328). When the capacity of each mutant to assemble into double-layered virus-like particles was analysed, three different assembly phenotypes were observed. Phenotype I was represented by two deletion mutants lacking residues 246 to 250 and 308 to 314 that produced particles with efficiencies similar to that of wild-type VP6. Phenotype II, characterized by a moderate decrease in the efficiency of particle assembly with respect to that of wild-type VP6, included two mutants with deletions at the C terminus of the protein. Phenotype III was exhibited by three mutants whose abilities to assemble into double-layered virus-like particles were drastically impaired. Two of these mutants define a previously unidentified assembly domain (amino acids 122 to 147) at the N terminus of rotavirus VP6.

Identification of domains in the simian immunodeficiency virus matrix protein essential for assembly and envelope glycoprotein incorporation

The matrix domain (MA) of the simian immunodeficiency virus (SIV) is encoded by the amino-terminal region of the Gag polyprotein precursor and is the component of the viral capsid that lines the inner surface of the virus envelope. To define domains of the SIV MA protein that are involved in virus morphogenesis, deletion and substitution mutations were introduced in this protein in the context of a gag-protease construct and expressed in the vaccinia virus vector system. The MA mutants were characterized with respect to synthesis and processing of the Gag precursor, assembly and release of virus-like particles, and incorporation of the envelope (Env) glycoprotein into particles. We have identified two regions of the SIV MA which are critical for particle formation. Both domains are located in a central hydrophobic alpha-helix of the SIV MA, according to data on the structure of this protein. In addition, we have characterized a domain whose mutation impairs the incorporation of SIV Env glycoproteins with long transmembrane cytoplasmic tails into particles. Interestingly, these mutant particles retained the ability to associate with SIV Env proteins with short cytoplasmic tails.

Assembly of double-layered virus-like particles in mammalian cells by coexpression of human rotavirus VP2 and VP6

Development in mammalian cells of a recombinant expression system that mimics the rotavirus capsid assembly process would be advantageous for studying the structural requirements for particle formation. To this end, we investigated the ability of a recombinant vaccinia virus system to produce double-layered virus-like particles. The genes coding for VP2 and VP6 proteins of the human rotavirus strain Wa were cloned and used to generate recombinant vaccinia viruses. Metabolic labelling of CV-1 cells infected with these recombinant viruses followed by immunoprecipitation with a polyclonal antiserum directed to Wa virus showed that VP2 and VP6 were efficiently expressed. The recombinant proteins were similar in size and immunoreactivity to authentic rotavirus proteins. Biochemical and electron microscopy analyses demonstrated that simultaneous expression of VP2 and VP6 in mammalian cells resulted in the formation of intracellular spherical particles resembling double-layered rotavirus particles.

Mutational analysis of the conserved cysteine residues in the simian immunodeficiency virus matrix protein

The matrix protein (MA) of human and simian immunodeficiency viruses (HIV and SIV) is encoded by the amino-terminal region of the Gag precursor and has been suggested to be involved in different processes during the early and late stages of the virus life cycle. The MA protein of SIV contains three cysteine residues at positions 57, 83, and 87, which are also highly conserved among HIV-2 isolates. In order to study the functional significance of these residues in virus morphogenesis, a series of mutations affecting the cysteines of SIV MA were introduced into a gag-protease construct and expressed in the vaccinia vector system. The MA mutants were assayed for their ability to synthesize and process the Gag polyprotein precursor as well as to release particles into the culture medium. In addition, the incorporation of the envelope glycoprotein (Env) into the Gag-made particles was investigated. Substitution of alanine for cysteine 87 had little effect on particle release and Env glycoprotein association. By contrast, the individual replacement of cysteines 57 or 83 by alanine, as well as the simultaneous mutation of cysteines 83 and 87, significantly reduced the ability of Gag polypeptides to produce extracellular particles. Assembly into particles appeared to be also affected, albeit to a lesser extent, when both cysteines 57 and 83 were replaced by alanine. Furthermore, substitution of cysteine 83 in the SIV MA domain was found to be detrimental to Gag polyprotein processing. Analysis of the Env glycoprotein association with recombinant particles revealed that this process was moderately affected in the case of the double mutants lacking cysteines 57 and 83, or cysteines 57 and 87, and the cysteine-minus triple mutant. Our results suggest that the conserved cysteines 57 and 83 in the MA domain are important for efficient SIV Gag particle production.

VP6 from porcine rotavirus strain CN86: amino acid sequence divergence with conservation of subgroup II specificity

A porcine rotavirus strain, CN86, originally isolated from rotavirus-infected piglets in Argentina, has been shown to possess unique characteristics. It was the first animal strain described to be antigenically related to human serotype G1 and the standard counterpart of another porcine strain showing rearrangement of genome segment 11. Owing to these features, molecular characterization of this virus seemed relevant. The gene encoding the major inner capsid protein, VP6, was cloned and its nucleotide sequence was determined. Comparative analysis of the deduced amino acid sequence of CN86 VP6 with those representing the four different subgroups showed that it is more closely related to subgroup II human Wa and porcine Gottfried strains, albeit to a lesser extent than they are to each other. Despite exhibiting sequence divergence, CN86 VP6 has 12 out of the 14 residues expected to be conserved in strains bearing subgroup II specificity. Interestingly, CN86 VP6 shows a high degree of homology with VP6 of porcine strain YM rotavirus which, although being closely related to subgroup II strains, has been serologically characterized as subgroup I. Subgroup II reactivity of CN86 strain, predicted by sequence analysis, was confirmed by ELISA with subgroup-specific monoclonal antibodies. Taken together, our results provide evidence for the existence of a human-pig lineage for rotavirus gene 6.

Expression of biologically active envelope glycoprotein from the acutely pathogenic simian immunodeficiency virus SIVsmmPBj

The full-length envelope (env) gene from the most acutely pathogenic primate lentivirus described so far, the simian immunodeficiency virus SIVsmmPBj14 was expressed by a recombinant vaccinia virus vector (vv-env4) and was completely characterized as a previous step for its use as an immunogen in vaccination trials. Radioimmunoprecipitation and Western blot experiments indicated that SIVsmmPBj gp160 precursor was processed into gp120 and gp41 subunits, and that gp120 was released into the medium. Flow cytometry analysis showed that recombinant SIVsmmPBj was transported to and expressed on the surface of vvenv4-infected cells. Biochemical analysis of virus-like particles produced by coinfection of cells with recombinant vaccinia viruses expressing SIVsmmPBj Env (vv-env4) and Gag (vv-wtgag) proteins revealed that the Env glycoprotein was incorporated into core-like particles. Furthermore, cells expressing SIVsmmPBj env gene products were found to undergo fusion with the same CD4+ cell lines in which the whole provirus has been shown to form syncytia.

Isolation of a mitotic-like cyclin homologue from the protozoan Trypanosoma brucei

Activation of the p34cdc2 protein kinase (PK) at different stages of the eukaryotic cell cycle is controlled by interaction with regulatory proteins known as cyclins (CYCs). Using a probe obtained by PCR amplification, we have isolated from the protozoan, Trypanosoma brucei, a cDNA clone encoding a CYC homologue. The amino acid sequence deduced for this gene (CYC1) shares structural homology with A- and B-type CYCs of other organisms, including a motif, the destruction box, which has been related to the rapid turnover of these CYC proteins in mitosis. When expressed in fission yeast, CYC1 is able to rescue the defect of a temperature-sensitive cdc13 mutant, demonstrating that it is functional as a cell-cycle regulator. In trypanosome cells, CYC1 associates with a 34-kDa protein that cross-reacts with a monoclonal antibody against the conserved 'PSTAIR' epitope of p34cdc2, and the complex displays histone H1 PK activity. Furthermore, when trypanosome cells are synchronized by hydroxyurea treatment, CYC1 accumulates as cells progress towards mitosis. These observations, taken together, suggest that CYC1 is a component of the active PK complex required for the control of trypanosome mitosis.

Assembly of the matrix protein of simian immunodeficiency virus into virus-like particles

To obtain a better understanding of the processes of assembly and morphogenesis of simian immunodeficiency virus (SIV), recombinant vaccinia viruses containing regions of the gag-pol open reading frame were constructed and their intracellular expression as well as the ability of the Gag polypeptides to be released into the culture medium as constituents of virus-like particles were studied. Biochemical and electron microscopy analyses of cells infected with a recombinant expressing only the SIV matrix (MA) domain of the Gag polyprotein (v-p17 gag) showed that this protein self-assembles into 100-nm virus-like particles which are released into the culture medium. Interestingly, coexpression of SIV MA and Env proteins resulted in incorporation of gp120 and gp41 proteins into the recombinant p17-made particles. In addition when a positively charged domain of SIV MA (residues 26-33), which is highly conserved among all HIV and SIV MA proteins, was mutated into an acidic region, particle release was abolished without affecting protein expression, processing, or stability. Further characterization of the phenotype of this mutant by electron microscopy indicated that this mutant was blocked at the stage of assembly. These results suggest that SIV MA protein, along with its function in myristic acid-mediated membrane targeting, has intrinsic information for self-assembly as well as incorporation of viral Env glycoproteins into particles.

Rotavirus NS26 is modified by addition of single O-linked residues of N-acetylglucosamine

We studied the post-translational modification of NS26, the protein product of rotavirus gene 11 segment. Based on the presence of a putative N-glycosylation site and the high content of serine and threonine residues in gene 11 amino acid sequence we investigated whether NS26 is modified by carbohydrate addition. Specific antibodies raised against the gene 11 product expressed in Escherichia coli recognized in infected cells two polypeptides with apparent molecular weight of 26,000 (26-kDa polypeptide) and 28,000 (28-kDa polypeptide). Pulse-chase experiments demonstrated that the 26-kDa product was processed to the 28-kDa polypeptide. Both polypeptides were metabolically labeled with [3H]glucosamine, indicating the presence of a carbohydrate moiety on the protein. NS26 was found to be resistant to endo-beta-N-acetylglucosaminidase H and endo-beta-N-acetylglucosaminidase F/peptide:N-glycosidase F treatment, but sensitive to removal by alkali-induced beta-elimination, suggesting that the saccharide chain was attached to the protein via an O-glycosidic linkage. Chromatographic analysis of total acid hydrolysates of [3H]glucosamine-labeled NS26-bound carbohydrate indicated the presence of N-acetylglucosamine. In addition, mild alkaline treatment of NS26 in the presence of NaB3H4 identified the O-linked carbohydrate moiety as N-acetylglucosamine. Taken together, these data demonstrate that NS26 is processed to a 28-kDa polypeptide by addition of O-linked monosaccharide residues of N-acetylglucosamine.

Structure of rearranged genome segment 11 in two different rotavirus strains generated by a similar mechanism

The structures of the rearranged genomic segment 11 of two spontaneous swine rotavirus strains were determined. We found that the rearrangements involved the duplication of normal segment 11 in a head-to-tail orientation, and partial deletions in both monomers. The open reading frame for VP11, the protein encoded by normal segment 11, was maintained. We also showed that the two rearranged genes were transcribed into RNA molecules of the same length as their corresponding genomic segments.

Rearrangement of genomic segment 11 in two swine rotavirus strains

We have recently reported the isolation of two group A swine rotaviruses each lacking normal genomic RNA segment 11 and showing instead one extra segment that migrated abnormally on gel electrophoresis. Hybridization studies performed with segment-specific probes and with a purified abnormal RNA segment showed that the extra bands had sequence homology to normal segment 11. Analysis of protein profiles of normal and rearranged strains showed that the gene product of segment 11 had no apparent change in its relative electrophoretic migration, suggesting that the rearranged genes remained functional.