Responses to cholesterol depletion are often taken as evidence of a role for lipid rafts in cell function. Here, we show that depletion of cell cholesterol has global effects on cell and plasma membrane architecture and function. The lateral mobility of membrane proteins is reduced when cell cholesterol is chronically or acutely depleted. The change in mobility is a consequence of the reorganization of the cell actin. Binding of a GFP-tagged pleckstrin homology domain specific for phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] to the plasma membrane is reduced after cholesterol depletion. This result implies that the reorganization of cytoskeleton depends on the loss or redistribution of plasma membrane PI(4,5)P2. Consistent with this observation, agents that sequester plasma membrane PI(4,5)P2 mimic the effects of cholesterol depletion on actin organization and on lateral mobility.T here is a growing consensus that cell surface membranes are patchworks of domains, local concentrations of membrane proteins, and lipids quite different from the average for an entire membrane (1). Cholesterol is important in organizing some types of domains, usually termed lipid rafts (2, 3). These lipid rafts are thought to be required for cell functions, including directed mobility and capping of membrane proteins, receptor-mediated signaling, entry and exit of pathogens and membrane trafficking (reviewed in ref. 4). Lipid rafts are dispersed when cell cholesterol is extracted (3). Hence, an effect of cholesterol depletion on a particular function is usually assumed to show that lipid rafts are required for this function (5-11). This assumption neglects the way in which the effects of cholesterol depletion ramify beyond local membrane environments and so have global effects on membrane and cell properties.Our starting point for considering global effects of cholesterol depletion is recent work showing that the key regulatory phospholipid, phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] is concentrated in cholesterol-dependent domains in proximity to concentrations of F actin, and other components of membrane trafficking (12-16). The localization of PI(4,5)P2 is consistent with its regulated involvement in a wide variety of cell functions (17), particularly regulation of the cytoskeleton (18). Availability of PI(4,5)P2 modulates the cytoskeleton͞membrane interaction (19), the stability of cortical actin, and the turnover of cytoplasmic stress fibers (20).Here, we connect the requirement for cholesterol in organizing plasma membrane PI(4,5)P2 with the role of PI(4,5)P2 in organizing the cytoskeleton. We found that the lateral mobility of plasma membrane proteins was restricted after cholesterol depletion. This effect was reversed by cytochalasin D and was paralleled by changes in organization and turnover of cell actin. The level of PI(4,5)P2 in the plasma membrane was reduced after cholesterol depletion, and the effects of cholesterol depletion were mimicked by sequestering plasma membrane PI(4,5)P2. Thus, cholesterol depleti...

Despite speculation that peers’ alcohol-related content on social media sites (SMS) may influence the alcohol use behaviors of SMS frequenting college students, this relationship has not been investigated longitudinally. The current prospective study assesses the relationship between exposure to peers’ alcohol-related SMS content and later-drinking among first-year college students. Among 408 first-year students, total exposure to peers’ alcohol-related content on Facebook, Instagram, and Snapchat during the initial 6 weeks of college predicted alcohol consumption 6 months later. The rather robust relationship persisted even after students’ and close friends drinking were accounted for, indicating that alcohol references on SMS do not simply reflect alcohol use behaviors that would otherwise be observed in the absence of SMS and be predictive of later alcohol use. Findings also illuminate important gender differences in the degree to which peers’ alcohol-related SMS content influenced later drinking behavior as well as psychological mediators of this relationship. Among females, enhancement drinking motives and beliefs about the role of alcohol in the college experience fully mediated the relationship between SMS alcohol exposure and later drinking. Males, however, evidenced a much stronger predictive relationship between SMS alcohol exposure and second semester drinking, with this relationship only partially explained by perceptions of drinking norms, enhancement drinking motives, and beliefs about the role of alcohol in the college experience. Implications of these findings for college drinking prevention efforts and directions for future research are discussed.

The Epstein-Barr virus (EBV) nuclear protein BS-MLF1 (SM) is expressed early after entry of EBV into the lytic cycle. SM transactivates reporter gene constructs driven by a wide variety of promoters, but the mechanism of SM action is poorly understood. In this study, we demonstrate that the SM protein inhibits expression of intron-containing genes and activates expression of intron-less genes. We demonstrate that SM has the predicted inhibitory effect on expression of a spliced EBV gene but activates an unspliced early EBV gene. SM inhibited gene expression at the posttranscriptional level by preventing the accumulation of nuclear and cytoplasmic RNA transcripts. Conversely, SM led to increased accumulation of nuclear mRNA from intron-less genes without affecting the rate of transcription, indicating that SM enhances nuclear RNA stability. The ratio of cytoplasmic to nuclear polyadenylated mRNA was increased in the presence of SM, suggesting that SM also enhances nucleocytoplasmic mRNA transport. The degree of transactivation by SM was dependent on the sequence of the 3-untranslated region of the target mRNA. Finally, we demonstrate that the amino-terminal portion of SM fused to glutathione-Stransferase binds radioactively labeled RNA in vitro, indicating that SM is a single-stranded RNA binding protein. Importantly, the latent and immediate-early genes of EBV contain introns whereas many early and late genes do not. Thus, SM may down-regulate synthesis of host cell proteins and latent EBV proteins while simultaneously enhancing expression of specific lytic EBV genes by binding to mRNA and modulating its stability and transport.

The actin-binding proteins moesin and α-actinin-1 limit the lateral mobility and clustering of ICAM-1 in dendritic cells and thereby promote antigen-dependent conjugate formation and T cell priming.

The objective of this study was to identify physical, social, and intrapersonal cues that were associated with the consumption of sweetened beverages and sweet and salty snacks among adolescents from lower SES neighborhoods. Students were recruited from high schools with a minimum level of 25% free or reduced cost lunches. Using Ecological Momentary Assessment, participants (N=158) were trained to answer brief questionnaires on handheld PDA devices: (a) each time they ate or drank, (b) when prompted randomly, and (c) once each evening. Data were collected over 7 days for each participant. Participants reported their location (e.g., school grounds, home), mood, social environment, activities (e.g., watching TV, texting), cravings, food cues (e.g., saw a snack), and food choices. Results showed that having unhealthy snacks or sweet drinks among adolescents was associated with being at school, being with friends, feeling lonely or bored, craving a drink or snack, and being exposed to food cues. Surprisingly, sweet drink consumption was associated with exercising. Watching TV was associated with consuming sweet snacks but not with salty snacks or sweet drinks. These findings identify important environmental and intrapersonal cues to poor snacking choices that may be applied to interventions designed to disrupt these food-related, cue-behavior linked habits.

The assembly of class I MHC molecules and their export from the endoplasmic reticulum (ER) is governed by chaperones and accessory proteins. We present evidence that the putative cargo receptor protein Bap31 participates in the transport and the quality control of human class I molecules. Transfection of the human adenocarcinoma cell line HeLa with yellow fluorescent protein-Bap31 chimeras increased surface levels of class I in a dose-dependent manner, by as much as 3.7-fold. The increase in surface class I resulted from an increase in the rate of export of newly synthesized class I molecules to the cell surface and from an increase in the stability of the exported molecules. We propose that Bap31 performs quality control on class I molecules in two distinct phases: first, by exporting peptide-loaded class I molecules to the ER/Golgi intermediate compartment, and second, by retrieving class I molecules that have lost peptides in the acidic post-ER environment. This function of Bap31 is conditional or redundant, because we find that Bap31 deficiency does not reduce surface class I levels. Overexpression of the Bap31 homolog, Bap29, decreases surface class levels in HeLa, indicating that it does not substitute for Bap31.

Inhibitory control and sensitivity to reward are relevant to the food choices individuals make frequently. An imbalance of these systems can lead to deficits in decision-making that are relevant to food ingestion. This study evaluated the relationship between dietary behaviors – binge eating and consumption of sweetened beverages and snacks - and behavioral control processes, among 198 ethnically diverse adolescents, ranging in age from 14 to 17, in Southern California. Neurocognitive control processes were assessed with the Iowa Gambling Task, a generic Go/No-Go task, and a food-specific Go/No-Go task. The food-specific Go/No-Go task directly ties the task to food cues that trigger responses, addressing an integral link between cue-habit processes. Dietary measures were assessed with self-administered food frequency and binge eating questionnaires. Results of latent variable models revealed marked gender differences. Inhibitory problems on the food-specific and generic Go/No-Go tasks were significantly correlated with binge eating only in females, whereas inhibitory problems measured with these tasks were the strongest correlates of sweet snack consumption in males. Higher BMI percentile and sedentary behavior also predicted binge eating in females and sweet snack consumption in males. Inhibitory problems on the generic Go/No-Go, poorer affective decision-making, assessed with the Iowa Gambling Task, and sedentary behavior were associated with sweetened beverage consumption in males, but not females. The food-specific Go/No-Go was not predictive in models evaluating sweetened beverage consumption, providing some initial discriminant validity for the task, which consisted of sweet/fatty snacks as no-go signals and no sugar-sweetened beverage signals. This research extends other study findings, revealing gender differences in inhibitory function relevant to behavioral control. Further, the findings contribute to research implicating the relevance of cues in habitual behaviors and their relationship to snack food consumption in an understudied population of diverse adolescents not receiving treatment for obesity or eating disorders.

The sensors of the unfolded protein response react to endoplasmic reticulum (ER) stress by transient activation of their enzymatic activities, which initiate various signaling cascades. In addition, the sensor IRE1α exhibits stress‐induced clustering in a transient time frame similar to activation of its endoRNase activity. Previous work had suggested that the clustering response and RNase activity of IRE1α are functionally linked, but here we show that they are independent of each other and have different behaviors and modes of activation. Although both clustering and the RNase activity are responsive to luminal stress conditions and to depletion of the ER chaperone binding protein, RNase‐inactive IRE1α still clusters and, conversely, full RNase activity can be accomplished without clustering. The clusters formed by RNase‐inactive IRE1α are much larger and persist longer than those induced by ER stress. Clustering requires autophosphorylation, and an IRE1α mutant whose RNase domain is responsive to ligands that bind the kinase domain forms yet a third type of stress‐independent cluster, with distinct physical properties and half‐lives. These data suggest that IRE1α clustering can follow distinct pathways upon activation of the sensor.—Ricci, D., Marrocco, I., Blumenthal, D., Dibos, M., Eletto, D., Vargas, J., Boyle, S., Iwamoto, Y., Chomistek, S., Paton, J. C., Paton, A. W., Argon, Y. Clustering of IRE1α depends on sensing ER stress but not on its RNase activity. FASEB J. 33, 9811–9827 (2019). http://www.fasebj.org