Possible involvement of the 90-kDa heat shock protein in the regulation of protein synthesis

The heme-sensitive eukaryotic initiation factor (eIF)-2 alpha kinase regulates translational activity in reticulocytes by phosphorylation of the smallest subunit of eukaryotic peptide initiation factor 2, eIF-2. Highly purified preparations of the kinase contain an abundant 90-kDa polypeptide which appears to modulate the activity of the enzyme. The physical properties and structural characteristics of the reticulocyte 90-kDa peptide are similar to those of the 90-kDa heat shock protein (hsp 90) from HeLa and other mammalian cells. The reticulocyte and HeLa cell proteins are shown to be immunologically cross-reactive. A direct comparison of the two proteins by one-dimensional peptide mapping of large peptides generated by limited proteolysis and by reversed-phase high performance liquid chromatography analysis of tryptic peptides indicates that they represent the same protein species. Like the 90-kDa reticulocyte protein, HeLa cell hsp 90 causes increased eIF-2 alpha phosphorylation by the heme-sensitive kinase and is a potent inhibitor of protein synthesis in the reticulocyte lysate system. A potential mechanism for the latter inhibition is inferred. These results implicate hsp 90 in the regulation of protein synthesis via its interaction with and perhaps regulation of the heme-sensitive kinase and phosphorylation of eIF-2 alpha.

A type 1 phosphoprotein phosphatase active with phosphorylated Mr = 68,000 initiation factor 2 kinase

A type 1 protein phosphatase from reticulocytes is shown to efficiently dephosphorylate the Mr = 68,000 phosphopeptide of the double-stranded RNA-dependent kinase that phosphorylates the alpha subunit of eukaryotic peptide initiation factor 2, eIF-2. The kinase, activated in the presence of double-stranded RNA with concomitant phosphorylation of the Mr = 68,000 peptide, causes inhibition of peptide initiation and thereby effects translational control of protein synthesis. The Mn2+-dependent phosphatase is classified as a type 1 enzyme in that it is inhibited by inhibitor 2 in nanomolar concentrations and appears to have a Mr = 35,000 catalytic subunit. Dephosphorylation of the Mr = 68,000 peptide by the phosphatase is directly associated with a loss in kinase activity which can be restored by incubation with double-stranded RNA in the presence of ATP. The results demonstrate that the eIF-2 alpha kinase can undergo cyclic activation-inactivation that appears to be directly related to the phosphorylation state of the Mr = 68,000 peptide. They strongly support the previous conclusion that double-stranded RNA is required only for activation of the kinase and phosphorylation of the Mr = 68,000 peptide.

Internalized myofiber capillaries: observations on their origin and clinical features

Internalized capillaries limited to type 1 muscle fibers were noted in seven patients. They occurred in each case in association with a similar admixture of neurogenic and myopathic features that included atrophic and hypertrophic fibers, internal nuclei, fiber splitting, and endomyseal and perimyseal fibrosis. Internalized capillaries in enlarged type 1 fibers arose from fiber splits on step section study of four patients. They occurred in the gastrocnemius, quadriceps, and soleus muscles from patients with a variety of disorders that included Becker dystrophy, diabetes mellitus and strenuous leg activities, Achilles tendon rupture, and myotonic dystrophy. Exercise-induced myalgias were noted in the four patients with the most plentiful intramuscular capillaries, and in three of these muscle hypertrophy was present. The concurrence of internalized myofiber capillaries and exercise-induced myalgias may represent an associated biochemical/pathological defect.

The phosphorylation state of the reticulocyte 90-kDa heat shock protein affects its ability to increase phosphorylation of peptide initiation factor 2 alpha subunit by the heme-sensitive kinase

The rabbit reticulocyte Mr 90,000 protein associated with the heme-sensitive eIF-2 alpha kinase has been identified previously as the mammalian heat shock protein of this size class (hsp 90). Purified reticulocyte hsp 90 when added exogenously to the kinase increases its activity. This stimulatory effect is abolished after incubation of hsp 90 with a highly purified type 1 phosphoprotein phosphatase isolated from reticulocytes. Phosphorylation of dephosphorylated hsp 90 by casein kinase II but not by cAMP-dependent protein kinase restores the biological activity of hsp 90 to stimulate eIF-2 alpha phosphorylation.

Quantification and characterization of regulin, a Mr-230,000 highly elongated protein of rabbit reticulocytes

Procedures are described by which regulin in rabbit reticulocytes was quantified and isolated in relatively large amounts. In these cells the protein occurs at a ratio of about 1.1-1.6 regulin monomers/spectrin tetramer, corresponding to 80,000-100,000 molecules of Mr-230,000 regulin/cell. Erythrocytes contain less than 12% of the amount of regulin in reticulocytes and the protein has not been detected in non-erythroid cells. Regulin was found primarily in the cytosolic fraction of lysed reticulocytes. It appears to be unusually sensitive to proteolysis by Ca2+-activated thiol proteases. Isolation of Mr-230,000 undegraded regulin was accomplished by the use of protease inhibitors including N-ethylmaleimide. A striking characteristic of regulin is its tendency to aggregate in neutral solution of low ionic strength. Physical studies of the isolated protein indicate that it has a highly elongated form in solution. The protein has no known enzymatic activity but was shown previously to interact with and increase the enzymatic activity of a protein phosphatase. The properties of regulin suggest that it may have a structural function but it appears to be physically and immunologically distinct from known proteins. It is suggested that regulin may contribute to a gel matrix within the cytoplasm of reticulocytes.

The 90-kilodalton peptide of the heme-regulated eIF-2 alpha kinase has sequence similarity with the 90-kilodalton heat shock protein

Highly purified preparations of the heme-controlled eIF-2 alpha (eukaryotic peptide initiation factor 2 alpha subunit) kinase of rabbit reticulocytes contain an abundant 90-kilodalton (kDa) peptide that is immunologically cross-reactive with spectrin and that modulates the activity of the enzyme [Kudlicki, W., Fullilove, S., Read, R., Kramer, G., & Hardesty, B. (1987) J. Biol. Chem. 262, 9695-9701]. The amino-terminal sequence of the 90-kDa protein has a high degree of similarity with the known amino-terminal sequences of the Drosophila 83-kDa heat shock protein (20 out of 22 residues) and with other related heat shock proteins. The amino acid sequence of a tryptic phosphopeptide isolated by high-performance liquid chromatography from the eIF-2 alpha kinase associated 90-kDa protein after phosphorylation by casein kinase II is shown to be identical with a 14 amino acid segment of the known sequence of the Drosophila 83-kDa heat shock protein. Results of hydrodynamic studies indicate a highly elongated structure for the reticulocyte protein, characteristic of a structural protein. Additional structural similarities between the eukaryotic heat shock proteins, the reticulocyte eIF-2 alpha kinase associated 90-kDa peptide, and spectrin are discussed.

Identification of spectrin-related peptides associated with the reticulocyte heme-controlled alpha subunit of eukaryotic translational initiation factor 2 kinase and of Mr 95,000 peptide that appears to be the catalytic subunit

An isolation procedure for the reticulocyte heme-controlled alpha subunit of eukaryotic translational initiation factor 2 (eIF-2 alpha) kinase is described which yields different fractions with kinase activity. Each is associated with a different spectrin-related peptide as identified by anti-spectrin monoclonal antibodies. The most abundant of these peptides is the Mr 90,000 species characterized previously (Kudlicki, W., Fullilove, S., Kramer, G., and Hardesty, B. (1985) Proc. Natl. Acad. Sci. U.S.A. 82, 5332-5336). Association with the spectrin-related peptides appears to account for the heterogeneity of the enzyme during its isolation and for its highly asymmetric structure. Isolated alpha or beta spectrin subunits as well as the separated homogeneous Mr 90,000 peptide cause an increase in the initial rate of eIF-2 alpha phosphorylation that is related to a decrease in Km with little or no effect on Vmax for the phosphorylation reaction. Fractionation of highly purified eIF-2 alpha kinase preparations using affinity chromatography on monoclonal anti-spectrin antibodies has separated eIF-2 alpha kinase activity from the Mr 100,000 phosphopeptide which copurifies with the kinase during all other purification steps. A Mr 95,000 peptide, detectable only by photoaffinity labeling with 8-azido-[alpha 32P]ATP, is shown to be distinct from the Mr 100,000 phosphopeptide and appears to be the catalytic subunit of the eIF-2 alpha kinase.

[An unusual cause of subcutaneous postsacral swelling]

A subcutaneous sacrococcygeal located myxopapillary ependymoma is a rare presentation of this malignancy. It has a tendency to metastasize, even after a long latent period. This is a report of such a case together with proposals for treatment and follow-up.

Is plasma GABA of peripheral origin?

Plasma levels of gamma-aminobutyric acid (GABA) appear to be altered in affective disorders and alcoholism. Plasma levels of GABA were not affected by menstrual cycle, exercise, gender, gut flora, nor by cholinergic stimulation by bethanechol. An obvious peripheral source for plasma GABA could not be demonstrated.

Evidence for a second phosphorylation site on eIF-2 alpha from rabbit reticulocytes

Ser 51 in the NH2-terminal sequence of the alpha-subunit of eukaryotic peptide initiation factor 2 (eIF-2) has been identified as a second phosphorylation site for the heme-controlled eIF-2 alpha kinase from rabbit reticulocytes. Increased phosphorylation of this serine relative to the previously described phosphorylation site (Ser 48) is observed when the kinase reaction is carried out in the presence of the alpha-subunit of spectrin. A synthetic peptide corresponding to eIF-2 alpha (41-54) is phosphorylated only in Ser 51 by the eIF-2 alpha kinase.

The NH2-terminal sequence of the alpha and gamma subunits of eukaryotic initiation factor 2 and the phosphorylation site for the heme-regulated eIF-2 alpha kinase

Rabbit reticulocyte eukaryotic initiation factor 2 was phosphorylated with the heme-regulated alpha subunit of eukaryotic initiation factor 2 kinase, and then the individual subunits were resolved by reversed-phase high performance liquid chromatography. Phosphorylated and unphosphorylated forms of the alpha subunit also were well resolved. The NH2-terminal sequences of intact alpha and gamma subunits were determined. No sequence was obtained from the beta subunit, suggesting that it may have a blocked NH2-terminus. Overlapping tryptic and chymotryptic phosphopeptides from the NH2-terminal sequence of the alpha subunit of eukaryotic initiation factor 2 were used to establish the order of amino acids 1-52 and localized the phosphorylation site within the sequence: -Leu-Leu-Ser48-Glu-Leu-Ser51-. Subdigestion of a tryptic fragment with chymotrypsin generated only phosphopeptides that appeared to terminate at leucine 50, indicating phosphorylation at serine 48.

Etiology of the pulmonary pathophysiology associated with inhalation injury

This study describes an experimental model of smoke inhalation injury in sheep in which the same pathophysiologic alterations occur as with clinical inhalation injury in man. Diffuse pulmonary mucosal sloughing with atelectasis and emphysema with concomitant development of pulmonary edema results in a decrease in arterial oxygen and progressive pulmonary deterioration which results in a substantial mortality. Increased pulmonary edema fluid is shown to be caused by an increased microvascular permeability to protein with pulmonary lymph and tracheobronchial fluid, a filtrate of plasma. Concomitant with this increase in microvascular permeability is an influx of neutrophils, release of proteolytic enzymes and an identified presence of the metabolite of the prostanoid thromboxane A2 which are postulated as contributors to the progressive pulmonary dysfunction post inhalation injury.

Interaction of the 56,000-dalton phosphoprotein phosphatase from reticulocytes with regulin and inhibitor 2

The interaction of divalent metal ions with a homogeneous 56,000-dalton phosphoprotein phosphatase isolated from rabbit reticulocytes was studied. The effects of the ions on enzymatic activity and on fluorescence from a 3-(4-maleimidylphenyl)-4-methyl-7-(diethylamino)coumarin derivative of the protein were compared. Enzymatic activity is dependent on Mn2+. The apparent association constant for Mn2+ is about 0.5 mM-1 as judged from enzymatic activity and from changes in fluorescence caused by binding of the metal ion; Ca2+ and Mg2+ do not affect enzymatic activity and appear not to bind tightly to the enzyme; however, Co2+, Fe2+, and Zn2+ bind to the protein and inhibit the Mn2+-activated enzyme. The 56,000-dalton phosphoprotein phosphatase was found to interact with regulin, a spectrin-associated protein also isolated from reticulocytes, and with skeletal muscle phosphatase inhibitor 2. The interaction was followed by changes in the enzymatic activity and by quenching of fluorescence from the coumarin derivative of the phosphatase. Homogeneous regulin (Mr approximately 230,000) increases the activity of the enzyme severalfold; this stimulation is Mn2+-dependent. Inhibitor 2 decreases enzyme activity but only if the two proteins are preincubated in the absence of Mn2+. Comparable differences in the effect of Mn2+ were also observed in parallel experiments in which changes in fluorescence from the coumarin-labeled 56,000-dalton phosphatase were measured. In these experiments, it was shown that Mn2+ enhances the interaction between regulin and the 56,000-dalton phosphatase, but inhibits the interaction between the phosphatase and inhibitor 2.

Inhibition of protein synthesis by the beta-subunit of spectrin

The 220 kDa beta-subunit of erythroid cell spectrin is a potent inhibitor of protein synthesis in lysates from rabbit reticulocytes. On the basis of weight of protein added to a lysate reaction mixture, it has about half the inhibitory activity of highly purified heme-regulated eIF-2 alpha kinase. Inhibition appears to be at the level of peptide initiation but does not involve a kinase that phosphorylates eIF-2 on its alpha-subunit.

Electrostatic effect of trypsin binding on the hydrogen exchange rate of bovine pancreatic trypsin inhibitor beta-sheet NH's

The changes of H-D exchange rates upon protein-protein interactions are generally interpreted as a result of the changes of the dynamic properties of the proteins. The effect of trypsin binding on the H-D exchange kinetics of some trypsin inhibitor amide H's was reported (Simon et al., 1984). In this paper the electrostatic potential originating from the trypsin molecule is calculated at the positions of the studied amide H's in the trypsin-trypsin inhibitor complex. We conclude that the observed decrease of the exchange rates is mainly due to the electrostatic field of the trypsin molecule.