Effect of antibody to the hemin-controlled translational repressor in rabbit reticulocyte lysate

Antinuclear Autoantibodies in Health: Autoimmunity Is Not a Synonym of Autoimmune Disease

The incidence of autoimmune diseases is increasing. Antinuclear antibody (ANA) testing is a critical tool for their diagnosis. However, ANA prevalence in healthy persons has increased over the last decades, especially among young people. ANA in health occurs in low concentrations, with a prevalence up to 50% in some populations, which demands a cutoff revision. This review deals with the origin and probable physiological or compensatory function of ANA in health, according to the concept of immunological clearance, theory of autoimmune regulation of cell functions, and the concept of functional autoantibodies. Considering ANA titers ≤1:320 as a serological marker of autoimmune diseases seems inappropriate. The role of anti-DFS70/LEDGFp75 autoantibodies is highlighted as a possible anti-risk biomarker for autoimmune rheumatic disorders. ANA prevalence in health is different in various regions due to several underlying causes discussed in the review, all influencing additive combinations according to the concept of the mosaic of autoimmunity. Not only are titers, but also HEp-2 IFA) staining patterns, such as AC-2, important. Accepting autoantibodies as a kind of bioregulator, not only the upper, but also the lower borders of their normal range should be determined; not only their excess, but also a lack of them or "autoimmunodeficiency" could be the reason for disorders.

Tissue distribution and immunoreactivity of heme-regulated eIF-2 alpha kinase determined by monoclonal antibodies

A highly purified preparation of heme-regulated inhibitor (HRI), an eIF-2 alpha kinase, from rabbit reticulocyte lysates has been used for generating monoclonal antibodies (mAB). Two hybridoma clones secreting HRI-specific antibodies (mAB A and mAB F) were obtained. Both antibodies immunoprecipitated biosynthetically labeled as well as phosphorylated HRI in reticulocyte lysates and also recognized denatured HRI in a Western blot. In in vitro protein kinase assays, preincubation of HRI with the antibodies significantly diminished both autokinase and eIF-2 alpha kinase activities. HRI from reticulocyte lysates could be quantitatively removed by immunoprecipitation with mAB F, and such HRI-depleted lysates were able to maintain protein synthesis under conditions of heme deficiency. With these monoclonal antibodies, HRI was detected only in the reticulocytes and bone marrow of anemic rabbits, among several rabbit tissues tested. The antibodies did not detect cross-reacting HRI in rat or human reticulocytes or in mouse erythroleukemic cells or human K562 cells even after induction of differentiation, although eIF-2 alpha kinase activity was detected in them. Polyclonal anti-rabbit HRI antibody detected HRI in rat reticulocytes. However, no cross-reacting HRI was detected by polyclonal antibody in human reticulocytes or other cell types tested. These findings suggest that HRI is not ubiquitous, and may be erythroid-specific, and that it is antigenically different in different species.

The phosphorylation of eukaryotic initiation factor 2: a principle of translational control in mammalian cells

In eukaryotic cells, protein biosynthesis is controlled at the level of polypeptide chain initiation. During the initiation process, eukaryotic initiation factor 2 (eIF-2) catalyzes the binding of Met-tRNAf and GTP to the 40S ribosomal subunit. In a later step, eIF-2 is released from the ribosomal initiation complex, most likely as an eIF-2.GDP complex, and another initiation factor termed eIF-2B is necessary to recycle eIF-2 by displacing GDP by GTP. In rabbit reticulocytes, inhibition of protein synthesis is accompanied by the phosphorylation of the alpha-subunit of eIF-2, a process that does not render eIF-2 inactive, but prevents it from being recycled by eIF-2B. First described in rabbit reticulocytes as inhibitors of translation, two distinct eIF-2 alpha kinases are known: the haemin-controlled kinase (termed HCI) and the double-stranded RNA-activated kinase (termed DAI). eIF-2 alpha phosphorylation appears to be a reversible control mechanism since corresponding phosphatases have been described. Recent reports indicate a correlation between eIF-2 alpha phosphorylation and the inhibition of protein synthesis in several mammalian cell types under a range of physiological conditions. In this review, the physical and functional features of the known eIF-2 alpha kinases are described with respect to their role in mammalian cells and the mode of activation by cellular signals. Furthermore, the possible impact of the eIF-2/eIF-2B ratio and of the subcellular compartmentation of these factors (and the eIF-2 alpha kinases) on mammalian protein synthesis is discussed.

The effect of ethanol on polypeptide chain initiation in reticulocyte lysates. Inhibition of recycling of initiation factor eIF-2

Using the reticulocyte cell-free system, we have investigated the mechanism by which ethanol inhibits the initiation of protein synthesis. Ethanol inhibited the formation of 40S-initiation complexes, and this effect correlated well with the inhibition by ethanol of overall peptide-chain initiation. Ethanol was a more potent inhibitor of translation at 37 degrees than at 30 degrees. The inhibition of peptide-chain initiation and 40S-initiation complex formation in reticulocyte lysates under other conditions is associated with increased phosphorylation of the alpha-subunit of protein synthesis initiation factor-2 (eIF-2 alpha) and the inhibition of recycling of this factor. Recycling of eIF-2 is mediated by another protein factor GEF (= guanine nucleotide-exchange factor). The addition of ethanol to reticulocyte lysates led to increased phosphorylation of eIF-2 alpha and to a decrease in the rate of exchange of guanine nucleotides bound to eIF-2. This second finding indicated that recycling of eIF-2 was impaired probably due to decreased availability of GEF. Using purified components it was found that ethanol inhibited the ability of GEF to stimulate eIF-2 and that this inhibition showed a similar temperature dependence to the effect of ethanol on overall protein synthesis. Taken together, these results suggest that ethanol leads to inhibition of peptide-chain initiation both through increased phosphorylation of eIF-2 alpha and by directly inhibiting the productive interaction of eIF-2 and GEF.