Collagen/β1 integrin signaling up-regulates the ABCC1/MRP-1 transporter in an ERK/MAPK-dependent manner

The mechanisms by which β1 integrins regulate chemoresistance of cancer cells are still poorly understood. In this study, we report that collagen/β1 integrin signaling inhibits doxorubicin-induced apoptosis of Jurkat and HSB2 leukemic T-cells by up-regulating the expression and function of the ATP-binding cassette C 1 (ABCC1) transporter, also known as multidrug resistance-associated protein 1. We find that collagen but not fibronectin reduces intracellular doxorubicin content and up-regulates the expression levels of ABCC1. Inhibition and knockdown studies show that up-regulation of ABCC1 is necessary for collagen-mediated reduction of intracellular doxorubicin content and collagen-mediated inhibition of doxorubicin-induced apoptosis. We also demonstrate that activation of the extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinase signaling pathway is involved in collagen-induced reduction of intracellular doxorubicin accumulation, collagen-induced up-regulation of ABCC1 expression levels, and collagen-mediated cell survival. Finally, collagen-mediated up-regulation of ABCC1 expression and function also requires actin polymerization. Taken together, our results indicate for the first time that collagen/β1 integrin/ERK signaling up-regulates the expression and function of ABCC1 and suggest that its activation could represent an important pathway in cancer chemoresistance. Thus simultaneous targeting of collagen/β1 integrin and ABCC1 may be more efficient in preventing drug resistance than targeting each pathway alone.     

Phylogeography and Sex-Biased Dispersal across Riverine Manatee Populations (Trichechus inunguis and Trichechus manatus) in South America

Phylogeographic patterns and sex-biased dispersal were studied in riverine populations of West Indian (Trichechus manatus) and Amazonian manatees (T. inunguis) in South America, using 410bp D-loop (Control Region, Mitochondrial DNA) sequences and 15 nuclear microsatellite loci. This multi-locus approach was key to disentangle complex patterns of gene flow among populations. D-loop analyses revealed population structuring among all Colombian rivers for T. manatus, while microsatellite data suggested no structure. Two main populations of T. inunguis separating the Colombian and Peruvian Amazon were supported by analysis of the D-loop and microsatellite data. Overall, we provide molecular evidence for differences in dispersal patterns between sexes, demonstrating male-biased gene flow dispersal in riverine manatees. These results are in contrast with previously reported levels of population structure shown by microsatellite data in marine manatee populations, revealing low habitat restrictions to gene flow in riverine habitats, and more significant dispersal limitations for males in marine environments.     

Population biology patterns of commercially important mollusks in México

The need to propose recommendations for the management of over 80 species of bivalves and gastropod mollusks exploited commercially in Mexico, led to look for trends on the population and reproductive biology in relation to prevailing environmental conditions of the habitats where they are exploited. The reproductive cycle, growth parameters for the von Bertalanffy equation, mortality and recruitment of 18 populations of 14 species from 13 localities are compared and related to ambient temperature, precipitation, evaporation, geomorphology, tides, and water salinity and temperature. Localities were classified as influenced by landmasses or with marine influence, with a desert or tropical humid climate. With restricted or continuous communication to oceanic waters and with or without freshwater runoff. The reproductive cycles were classified in four groups in relation to intensity and duration of the spawning season: 1) limited to one annual spawning, 2) two or more defined spawning periods, 3) two or more extended spawning periods, and 4) continuous low intensity spawning. And three groups in relation to gonad recovery, and duration and intensity of gametogenesis: 1) post spawn and rest stages absent or restricted, 2) fast gametogenesis and a clear mature stage. and 3) extended gametogenesis and limited maturity stages. The population parameters were classified in relation to age structure and number of cohorts, intensity and duration of recruitment, and growth rates as expressed by infinity and K. In relation to their life cycle four types were found: 1) population represented by only one cohort, at least during part of the year, 2) with two or more cohorts at any time, 3) longevity under five years, and 4) longevity over live years. In relation to recruitment: 1) one recruitment period restricted to a short season, 2) two or more recruitment periods, 3) constant recruitment with one or more peaks, and 4) constant recruitment without periods of dominance.     

High performance two-dimensional gel electrophoresis using a wetting agent Tergitol NP7

Two-dimensional electrophoresis is an efficient method for the analysis of a broad range of complex protein samples. Current two-dimensional gel techniques are not suited for analysis of the small amount of proteins from tissue samples in the presence of high concentration of salts. Here we describe an improved two-dimensional gel electrophoresis procedure based on the use of a nonionic wetting agent, Tergitol NP7, in rehydration solution combined with the application of a linear potential sweep during isoelectrofocusing. This experimental approach yields a dramatic increase in the resolution and focusing of proteins visualized on two-dimensional gels. This technique is less time-consuming and laborious than the current techniques and can be used for a variety of two-dimensional electrophoresis applications, including proteome analysis.     

Transport of cholesterol into mitochondria is rate-limiting for bile acid synthesis via the alternative pathway in primary rat hepatocytes

Bile acid synthesis occurs mainly via two pathways: the "classic" pathway, initiated by microsomal cholesterol 7alpha-hydroxylase (CYP7A1), and an "alternative" (acidic) pathway, initiated by sterol 27-hydroxylase (CYP27). CYP27 is located in the inner mitochondrial membrane, where cholesterol content is very low. We hypothesized that cholesterol transport into mitochondria may be rate-limiting for bile acid synthesis via the "alternative" pathway. Overexpression of the gene encoding steroidogenic acute regulatory (StAR) protein, a known mitochondrial cholesterol transport protein, led to a 5-fold increase in bile acid synthesis. An increase in StAR protein coincided with an increase in bile acid synthesis. CYP27 overexpression increased bile acid synthesis by <2-fold. The rates of bile acid synthesis following a combination of StAR plus CYP27 overexpression were similar to those obtained with StAR alone. TLC analysis of (14)C-labeled bile acids synthesized in cells overexpressing StAR showed a 5-fold increase in muricholic acid; in chloroform-extractable products, a dramatic increase was seen in bile acid biosynthesis intermediates (27- and 7,27-hydroxycholesterol). High-performance liquid chromatography analysis showed that 27-hydroxycholesterol accumulated in the mitochondria of StAR-overexpressing cells only. These findings suggest that cholesterol delivery to the inner mitochondrial membrane is the predominant rate-determining step for bile acid synthesis via the alternative pathway.     

Hepatitis C virus core protein uses triacylglycerols to fold onto the endoplasmic reticulum membrane

Lipid droplets (LDs) are involved in viral infections, but exactly how remains unclear. Here, we study the hepatitis C virus (HCV) whose core capsid protein binds to LDs but is also involved in the assembly of virions at the endoplasmic reticulum (ER) bilayer. We found that the amphipathic helix-containing domain of core, D2, senses triglycerides (TGs) rather than LDs per se. In the absence of LDs, D2 can bind to the ER membrane but only if TG molecules are present in the bilayer. Accordingly, the pharmacological inhibition of the diacylglycerol O-acyltransferase enzymes, mediating TG synthesis in the ER, inhibits D2 association with the bilayer. We found that TG molecules enable D2 to fold into alpha helices. Sequence analysis reveals that D2 resembles the apoE lipid-binding region. Our data support that TG in LDs promotes the folding of core, which subsequently relocalizes to contiguous ER regions. During this motion, core may carry TG molecules to these regions where HCV lipoviroparticles likely assemble. Consistent with this model, the inhibition of Arf1/COPI, which decreases LD surface accessibility to proteins and ER-LD material exchange, severely impedes the assembly of virions. Altogether, our data uncover a critical function of TG in the folding of core and HCV replication and reveals, more broadly, how TG accumulation in the ER may provoke the binding of soluble amphipathic helix-containing proteins to the ER bilayer.     

Multiple intraguild predators reduce mortality risk of a mutual agricultural pest prey in simple,but not in complex,experimental settings

Multiple predator species that coexist with each other and their mutual prey can have combined effects on prey mortality that are similar to the sum of each predator's individual impact (linear effects), greater than the sum of each predator's individual impact (risk enhancement), or less than the sum of each predator's individual impact (risk reduction). Understanding multiple predator effects is important to determine the impact of predators on pest prey in agroecosystems. If two predators share the same broad spatial domain and hunting mode and engage in intraguild predation, then their combination is expected to result in risk reduction for a mutual prey. We tested this hypothesis using both additive and replacement experimental designs on two species of generalist wolf spider predators (Tasmanicosa leuckartii and Hogna crispipes) that hunt in the same domain, and a mutual insect prey (cotton bollworm Helicoverpa armigera). We used two types of enclosures: a small simple laboratory enclosure, and a larger more complex cotton plant enclosure. We found that in the small simple laboratory enclosures, the presence of two spiders led to risk reduction of Helicoverpa larva mortality as expected, but in larger more complex cotton plant enclosures the presence of both species resulted in linear effects rather than risk reduction on Helicoverpa mortality. Furthermore, intraguild predation did not change multiple predator effects in laboratory or plant enclosures. This study has implications for managing arthropod predators in agroecosystems; contrary to predictions of ecological frameworks, coexistence of predators that share the same hunting mode and hunting domain may not lead to risk reduction on a mutual prey in more complex environments, where encounters among predators can be lower. Conservation of multiple predators of a single guild can play an essential role on biological control of insect pests.