Protein Kinase PKR Mediates the Apoptosis Induction and Growth Restriction Phenotypes of C Protein-Deficient Measles Virus

The measles virus (MV) accessory proteins V and C play important roles in MV replication and pathogenesis. Infection with recombinant MV lacking either V or C causes more cell death than infection with the parental vaccine-equivalent virus (MVvac), and C-deficient virus grows poorly relative to the parental virus. Here, we show that a major effector of the C phenotype is the RNA-dependent protein kinase PKR. Using human HeLa cells stably deficient in PKR as a result of RNA interference-mediated knockdown (PKR^kd cells), we demonstrated that a reduction in PKR partially rescued the growth defect of C knockout (C^ko) virus but had no effect on the growth of either wild-type (WT) or V knockout (V^ko) virus. Increased growth of the C^ko virus in PKR^kd cells correlated with increased viral protein expression, while defective growth and decreased protein expression in PKR-sufficient cells correlated with increased phosphorylation of PKR and the α subunit of eukaryotic initiation factor 2. Furthermore, infection with WT, V^ko, or especially C^ko virus caused significantly less apoptosis in PKR^kd cells than in PKR-sufficient cells. Although apoptosis induced by C^ko virus infection in PKR-sufficient cells was blocked by a caspase antagonist, the growth of C^ko virus was not restored to the WT level by treatment with this pharmacologic inhibitor. Taken together, these results indicate that PKR plays an important antiviral role during MV infection but that the virus growth restriction by PKR is not dependent upon the induction of apoptosis. Furthermore, the results establish that a principal function of the MV C protein is to antagonize the proapoptotic and antiviral activities of PKR.     

Photoaffinity spin-labeling of the Ca2+ ATPase in sarcoplasmic reticulum : Evidence for oligomeric structure

A spin labeled fatty acid (16-doxylstearic acid) was linked to a photochemical reacting group (azido derivative). When the molecule is introduced, at a low concentration, into rabbit sarcoplasmic reticulum membranes, the spectrum before illumination is identical to the spectrum obtained with the corresponding spin labeled fatty acid. After illumination, a large immobilized components is seen. It corresponds to about 70% of the ESR signal of the effectively bound label, at room temperature. The fraction of immobilized component varies with temperature, from 100% at 0°C to 50% at 35°C. Addition of a small amount of detergent (dodecyl octaethylene glycol monoether), under non solubilizing conditions, decreases the fraction of signal due to a strongly immobilized probe. A possible interpretation is that the immobilized signal reflects protein bound spin labels trapped in Ca²⁺ ATPase oligomers, which are partially dissociated by detergent addition or temperature increase.     

Weak interaction of spectrin with phosphatidylcholine-phosphatidylserine multilayers: a 2H and 31P NMR study

Spectrin from human erythrocytes binds to bilayer dispersions of both DMPC and DMPS:DMPC (1:1, w/w). However, no effect of bound spectrin on the conformation of the lipid head groups, as measured from the deuterium quadrupolar splittings of DMPC or DMPS specifically deuterated in the polar head groups, was detected in 1:1 mixtures of the two lipids containing either deuterated DMPC or DMPS. Neither the phase transition of the DMPS:DMPC mixtures, nor the spin-lattice relaxation time (T1) of the deuterated DMPS head group, was affected by spectrin. These results argue against any strong interaction of spectrin with phosphatidylserine and rule out the possibility that spectrin is responsible for the maintenance of PS in the inner monolayer of the erythrocyte membrane during the whole life-span of this cell.     

Phospholipid flippases

Protein mediated phospholipid translocation through membranes has been observed in rat liver endoplasmic reticulum and in the plasma membrane of erythrocytes as well as in a few other cell membranes. Lipid translocation in plasma membranes is ATP dependent and selectively accumulates aminophospholipids on the inner monolayers.     

Thyroid function and trisomy 21. TSH increase and rT3 deficiency

An excess of thyrotropin (TSH) with normal levels of tetraiodothyronine (T4) and of 3,5,3'-triiodothyronine (T3) was confirmed in the serum of 78 trisomy 21 children. A severe deficiency of 3,3',5'-triiodo-thyronine (rT3 or reverse T3) was observed and the decrease of the rT3/TSH ratio was highly significant. These new facts suggest that the rT3 deficiency plays a peculiar role in trisomy 21 (maybe through the regulation of one or few steps of monocarbons' metabolism). A systematic control of thyroid function (including the patient's rT3 level) is mandatory for the follow-up of every trisomy 21 patient.     

Asymmetric distribution of phospholipids in spectrin-poor erythrocyte vesicles

We have investigated by electron spin resonance, at 37 degrees C, the outside-inside passage and the equilibrium distribution of spin-labeled phospholipids, respectively, in ATP-containing ghosts, in heat-treated erythrocytes, and in heat-induced vesicles. The heat-treated vesicles were spectrin depleted to approximately 25% of the original content and had lost almost 100% of the other cytoskeletal proteins. Yet the vesicles, as long as they contained ATP, were capable of translocating the aminophospholipids with the same efficiency as the heat-treated erythrocytes, and almost with the same efficiency as ATP-containing ghosts. In the vesicles, sphingomyelin and phosphatidylcholine analogues underwent a very slow transverse diffusion as in native cells. We conclude that spectrin and other cytoskeleton proteins are not major factors for the establishment and maintenance of phospholipid asymmetry in human erythrocytes, which may be chiefly due to the aminophospholipid translocase activity.