The endoplasmic reticulum and the unfolded protein response

The endoplasmic reticulum (ER) is the site where proteins enter the secretory pathway. Proteins are translocated into the ER lumen in an unfolded state and require protein chaperones and catalysts of protein folding to attain their final appropriate conformation. A sensitive surveillance mechanism exists to prevent misfolded proteins from transiting the secretory pathway and ensures that persistently misfolded proteins are directed towards a degradative pathway. In addition, those processes that prevent accumulation of unfolded proteins in the ER lumen are highly regulated by an intracellular signaling pathway known as the unfolded protein response (UPR). The UPR provides a mechanism by which cells can rapidly adapt to alterations in client protein-folding load in the ER lumen by expanding the capacity for protein folding. In addition, a variety of insults that disrupt protein folding in the ER lumen also activate the UPR. These include changes in intralumenal calcium, altered glycosylation, nutrient deprivation, pathogen infection, expression of folding-defective proteins, and changes in redox status. Persistent protein misfolding initiates apoptotic cascades that are now known to play fundamental roles in the pathogenesis of multiple human diseases including diabetes, atherosclerosis and neurodegenerative diseases.     

Some problems of regressive evolution

The concept of morphophysiological regress as one of the main ways to biological progress, as well as its major factors (the sedentary and parasitic modes of life), are discussed. Some notions of regressive evolution are critically reviewed. Special attention is paid to evolutionary transformations of the nervous system, one of the main integrating factors in the body. All theories of evolutionary progress based on sedentary organisms are demonstrated to be untenable. The entire progressive evolution of Metazoa has been related to mobile life. Since regressive trends are common in the evolution, the phylogenetic tree of Metazoa requires serious revision.     

Role played by P2X and P2Y receptors in evoking the muscle chemoreflex.

The role played by purinergic 2Y receptors in evoking the muscle chemoreflex is not well defined. To shed light on this issue, we compared the pressor responses with popliteal arterial injection of UTP (1 mg/kg), a selective P2Y agonist, with those to popliteal arterial injection of ATP (1 mg/kg), a P2X and P2Y agonist, and to alpha,beta-methylene ATP (50 mug/kg), a selective P2X1 and P2X3 agonist, in decerebrate unanesthetized cats. We found that injection of ATP and alpha,beta-methylene ATP increased mean arterial pressure by 19 +/- 2 and 15 +/- 4 mmHg, whereas UTP had no affect on arterial pressure. In addition, the pressor responses to injection of ATP and alpha,beta-methylene ATP were abolished by section of the sciatic nerve, demonstrating that they were reflex in origin. We conclude that P2Y receptors on thin fiber muscle afferents play no role in evoking the muscle chemoreflex.     

Responses of group III and IV muscle afferents to dynamic exercise

Adreani, Christine M., Janeen M. Hill, and Marc P. Kaufman.Responses of group III and IV muscle afferents to dynamic exercise. J. Appl. Physiol. 82(6):1811-1817, 1997.Tetanic contraction of hindlimb skeletal muscle,induced by electrical stimulation of either ventral roots or peripheralnerves, is well known to activate group III and IV afferents.Nevertheless, the effect of dynamic exercise on the discharge of thesethin fiber afferents is unknown. To shed some light on this question,we recorded in decerebrate cats the discharge of 24 group III and 10 group IV afferents while the mesencephalic locomotor region (MLR) wasstimulated electrically. Each of the 34 afferents had their receptivefields in the triceps surae muscles. Stimulation of the MLR for 1 min caused the triceps surae muscles to contract rhythmically, an effectinduced by an -motoneuron discharge pattern and recruitment orderalmost identical to that occurring during dynamic exercise. Eighteen ofthe 24 group III and 8 of the 10 group IV muscle afferents werestimulated by MLR stimulation. The oxygen consumption of thedynamically exercising triceps surae muscles was increased by 2.5-foldover their resting levels. We conclude that low levels of dynamicexercise stimulate group III and IV muscle afferents.

     

G-protein-coupled receptor 1, G-protein Galpha-subunit 1, and prephenate dehydratase 1 are required for blue light-induced production of phenylalanine in etiolated Arabidopsis

Different classes of plant hormones and different wavelengths of light act through specific signal transduction mechanisms to coordinate higher plant development. A specific prephenate dehydratase protein (PD1) was discovered to have a strong interaction with the sole canonical G-protein Galpha-subunit (GPA1) in Arabidopsis (Arabidopsis thaliana). PD1 is a protein located in the cytosol, present in etiolated seedlings, with a specific role in blue light-mediated synthesis of phenylpyruvate and subsequently of phenylalanine (Phe). Insertion mutagenesis confirms that GPA1 and the sole canonical G-protein-coupled receptor (GCR1) in Arabidopsis also have a role in this blue light-mediated event. In vitro analyses indicate that the increase in PD1 activity is the direct and specific consequence of its interaction with activated GPA1. Because of their shared role in the light-mediated synthesis of phenylpyruvate and Phe, because they are iteratively interactive, and because activated GPA1 is directly responsible for the activation of PD1; GCR1, GPA1, and PD1 form all of or part of a signal transduction mechanism responsible for the light-mediated synthesis of phenylpyruvate, Phe, and those metabolites that derive from that Phe. Data are also presented to confirm that abscisic acid can act through the same pathway. An additional outcome of the work is the confirmation that phenylpyruvate acts as the intermediate in the synthesis of Phe in etiolated plants, as it commonly does in bacteria and fungi.     

Effects of Neostigmine and Atropine on Motor Activity of Ileum,Colon, and Rectum of Anaesthetized Subjects

In unanaesthetized patients atropine and neostigmine in doses normally used by anaesthetists to reverse muscle relaxants produced a pronounced increase in bowel activity. This response occurred whether atropine was given before or simultaneously with neostigmine.The response still occurred in 38% of patients anaesthetized without halothane, and possibly this increase in motility might endanger a recently constructed anastomosis. The ileum appeared particularly prone to neostigmine stimulation, and anastomoses involving ileum would seem especially at risk. When halothane was used during anaesthesia the response was completely inhibited during the period studied.     

Cyclooxygenase blockade attenuates responses of group III and IV muscle afferents to dynamic exercise in cats

Cyclooxygenase products accumulate in statically contracting muscles to stimulate group III and IV afferents. The role played by these products in stimulating thin fiber muscle afferents during dynamic exercise is unknown. Therefore, in decerebrated cats, we recorded the responses of 17 group III and 12 group IV triceps surae muscle afferents to dynamic exercise, evoked by stimulation of the mesencephalic locomotor region. Each afferent was tested while the muscles were freely perfused and while the circulation to the muscles was occluded. The increases in group III and IV afferent activity during dynamic exercise while the circulation to the muscles was occluded were greater than those during exercise while the muscles were freely perfused (P < 0.01). Indomethacin (5 mg/kg iv), a cyclooxygenase blocker, reduced the responses to dynamic exercise of the group III afferents by 42% when the circulation to the triceps surae muscles was occluded (P < 0.001) and by 29% when the circulation was not occluded (P = 0.004). Likewise, indomethacin reduced the responses to dynamic exercise of group IV afferents by 34% when the circulation was occluded (P < 0.001) and by 18% when the circulation was not occluded (P = 0.026). Before indomethacin, the activity of the group IV, but not group III, afferents was significantly higher during postexercise circulatory occlusion than during rest (P < 0.05). After indomethacin, however, group IV activity during postexercise circulatory occlusion was not significantly different from group IV activity during rest. Our data suggest that cyclooxygenase products play a role both in sensitizing group III and IV afferents during exercise and in stimulating group IV afferents during postexercise circulatory occlusion.     

Polysubstituted Isochroman Derivatives with Plant Growth Regulating Properties on Wheat (Triticum aestivum L. cv Klein Escorpion)

The synthesis of isochroman derivatives 4–9 from α-hydroxylactone 3 is reported. These heterocycles, carrying different substituents on C-3, C-4, and C-8, exhibited different degrees of inhibition of the vegetative growth of wheat (Triticum aestivum cv Klein Escorpion) plants, whereas plant developmental patterns such as their protein profile, carotenes/chlorophylls ratio, and weight/length relationship were not significantly affected. Microscopic observation of transverse sections of shoots and roots showed morphological changes in the treated plants, consistent with delayed development. The results suggest that among these isochromans the C-3 carbonyl moiety of the lactone and the C-4 free hydroxyl group are important but not essential for activity, and that a short side chain appended to C-3 is tolerated. However, cleavage of the C-8 methyl ether group to the related free phenol causes a drastic reduction in the growth inhibitory activity.     

Expression and characterization of human antithrombin III synthesized in mammalian cells

Antithrombin III (ATIII) has been expressed in transiently transfected COS-1 monkey cells and in stably transformed Chinese hamster ovary cells, and the resultant protein has been characterized for biological activity. Both cell types efficiently secrete high levels of heterogeneous molecular weight forms of ATIII antigen. The heterogeneity results from differences in post-translational modifications. However, only a small percentage (5-10%) of the total antigen expressed is biologically active. The fraction of biologically active ATIII has been purified from total ATIII by affinity fractionation on heparin-Sepharose. This fractionation indicates that the differences in the active and inactive forms of expressed ATIII result from differences in their ability to bind heparin. Purified ATIII has a specific activity very similar to that of plasma-derived ATIII and exhibits typical heparin-accelerated ATIII activity. The biologically active fraction of ATIII appears to represent the higher molecular weight forms of the ATIII expressed and is likely not a result of altered asparagine-linked glycosylation; however, the nature of the post-translational modification required for ATIII activity remains unclear. The ability to express biologically active ATIII at such high levels should allow further investigations of the structural requirements for ATIII activity.