Apolipoproteins A-I,A-II and E are independently distributed among intracellular and newly secreted HDL of human hepatoma cells

Whereas hepatocytes secrete the major human plasma high density lipoproteins (HDL)-protein, apo A-I, as lipid-free and lipidated species, the biogenic itineraries of apo A-II and apo E are unknown. Human plasma and HepG2 cell-derived apo A-II and apo E occur as monomers, homodimers and heterodimers. Dimerization of apo A-II, which is more lipophilic than apo A-I, is catalyzed by lipid surfaces. Thus, we hypothesized that lipidation of intracellular and secreted apo A-II exceeds that of apo A-I, and once lipidated, apo A-II dimerizes. Fractionation of HepG2 cell lysate and media by size exclusion chromatography showed that intracellular apo A-II and apo E are fully lipidated and occur on nascent HDL and VLDL respectively, while only 45% of intracellular apo A-I is lipidated. Secreted apo A-II and apo E occur on small HDL and on LDL and large HDL respectively. HDL particles containing both apo A-II and apo A-I form only after secretion from both HepG2 and Huh7 hepatoma cells. Apo A-II dimerizes intracellularly while intracellular apo E is monomeric but after secretion associates with HDL and subsequently dimerizes. Thus, HDL apolipoproteins A-I, A-II and E have distinct intracellular and post-secretory pathways of hepatic lipidation and dimerization in the process of HDL formation. These early forms of HDL are expected to follow different apolipoprotein-specific pathways through plasma remodeling and reverse cholesterol transport.     

Effect of oral diazepam on feeding behavior and activity of Hawai’i ’amakihi (Hemignathus virens)

Feeding behavior and activity during captivity were studied in wild-caught Hawai’i ’amakihi, Hemignathus virens, to evaluate diazepam's hyperphagic and anxiolytic effects. Birds were captured in mist nets, given either oral diazepam (1 mg/kg) or an equivalent volume per weight of lactated Ringer's solution orally, and held in captivity for 6 h. Thirteen-minute focal animal samples were videotaped at the beginning of each hour. Feeding behaviors, grooming and picking events, changes in position, and body weights were recorded. Mean duration of feeding, percentage of time spent feeding, and number of feeding events were significantly higher for treatment birds than for controls, and significantly increased over time. Feeding duration was significantly correlated to weight change. Weight change was not significantly different between groups, but on average treatment birds lost less weight than control birds. No significant differences in grooming behaviors were found between the groups, but there was a session effect of increased grooming over time in both groups. Also, a significant session effect in movement events was apparent, with control birds becoming less active and treatment birds becoming more active over time. Results indicate diazepam increased feeding behaviors and movement in this passerine species during a short period of captivity.     

Application of a two-stage Syrian hamster embryo cell transformation assay to cigarette smoke particulate matter

The induction of transformation in Syrian hamster embryo (SHE) cells is a multifactorial process, in comparison to endpoints induced in in vitro genotoxicity assays such as Ames, mouse lymphoma and cytogenetics [Y. Berwald, L. Sachs, In vitro cell transformation with chemical carcinogens, Nature (London) 200 (1963) 1182-1184]. Furthermore, a number of non-genotoxic carcinogens and promoters such as clofibrate and diethylhexylphthalate, have been positively identified in this assay, while giving false negative results in traditional genotoxicity assays [H. Yamasaki, J. Ashby, M. Bignami, W. Jongen, K. Linnainmaa, R.F. Newbold, G. Nguyen-Ba, S. Parodi, E. Rivedal, D. Schiffmann, J.W.I.M. Simons, P. Vasseur, Nongenotoxic carcinogens: development of detection methods based on mechanisms: a European project, Mutat. Res. 353 (1996) 47-63]. A high concordance between results obtained in this assay when compared with rodent carcinogenesis bioassays has also been noted [R.J. Isfort, G.A. Kerckaert, R.A. LeBoeuf, Comparison of the standard and reduced pH Syrian hamster embryo (SHE) in vitro cell transformation assays to predict the carcinogenic potential of chemicals, Mutat. Res. 356 (1996) 11-63]. Carcinogenesis is known to be a multistage process, with agents potentially acting at each stage. Specifically, mouse skin painting experiments established that tumour induction could be mechanistically divided into two distinct phases, termed initiation and promotion. Initiation, is defined as the stage at which a normal cell is converted to a latent tumour cell, followed by promotion where the latent tumour cell progresses to a tumour [W.F. Friedwald, P. Rous, The initiating and promoting elements in tumour production: analysis of the effects of tar, benzpyrene and methylcholanthrene on rabbit skin, J. Exp. Med. 80 (1944) 101-125]. A protocol for the pH 6.7 SHE transformation assay has been developed which allows separation of cell transformation process into two phases, potentially analogous to initiation and promotion in vivo. This allows chemicals found to be positive in the traditional SHE cell transformation assay to be further classified as initiators or promoters. Following validation with known initiators, benzo(a)pyrene and N-methyl-N'-nitro-N-nitrosoguanidine and promoters, 12-O-tetradecanoyl-phorbol-13-acetate and phenobarbitone, the two-stage model was applied to cigarette smoke particulates which was found to act both at the initiation and promotion stage of cell transformation.     

Lysosomal chat maintains the balance

The original idea that each protein follows a particular proteolytic pathway for its degradation is no longer supported. Instead, different proteolytic systems can simultaneously contribute to the degradation of a particular protein, or they can alternate in this task depending, for the most part, on the cellular conditions. It is thus reasonable to expect that some level of communication exists among different proteolytic systems to orchestrate these coordinated activities. Direct cross-talk between two forms of autophagy, macroautophagy and chaperone-mediated autophagy (CMA) has been recently demonstrated. Cells respond to blockage of CMA by upregulating macroautophagy. Although macroautophagy cannot completely substitute for the lack of CMA, the partial redundancy between both pathways allows some level of compensation, enough to maintain protein degradation and preserve cell homeostasis. Understanding the cross-talk among different autophagic pathways and with other proteolytic systems is important to predict the type of compensatory mechanisms that could be elicited in response to failure of one of these systems, and to understand the consequences that manipulating one of these pathways for therapeutic purposes could have on the activity of the other pathways.