A particle-associated ATP-dependent proteolytic activity in erythroleukemia cells

Degradation of oxidized proteins in K562 human hematopoietic cells by proteasome

Exposure to various forms of oxidative stress (H2O2 and O2.-) significantly increased the intracellular degradation of both "short-lived" and "long-lived" cellular proteins in the human hematopoietic cell line K562. Oxidatively modified hemoglobin and superoxide dismutase used as purified proteolytic substrates were also selectively degraded by K562 cell lysates, but exposure of these protein substrates to very high hydrogen peroxide concentrations actually decreased their proteolytic susceptibility. Our studies found little or no change in the overall capacity of cells and cell lysates to degrade "foreign" oxidized proteins after treatment of K562 cells with hydrogen peroxide or paraquat, a finding supported by proteasome Western blots and unchanged capacity of cell lysates to degrade the fluorogenic peptide succinyl-leucine-leucine-valine-tyrosine-4-methylcoumarin-7-amide. Six days of daily treatment of K562 cells with an antisense oligodeoxynucleotide directed against the initiation codon region of the human proteasome C2 subunit gene dramatically depressed hydrogen peroxide-induced degradation of metabolically radiolabeled intracellular proteins. The actual amount of proteasome in antisense-treated K562 cells was also severely depressed, as revealed by Western blots and by measurements of the degradation of the fluorogenic peptide succinyl-leucine-leucine-valine-tyrosine-4-methylcoumarin-7-amide. The degradation of oxidatively modified foreign protein substrates was also markedly depressed in lysates prepared from K562 cells treated with the proteasome C2 antisense dideoxynucleotide. The inhibitor profile for the degradation of H2O2-modified hemoglobin by K562 cell lysates was consistent with a major role for the ATP-independent 20 S "core" proteasome complex. We conclude that proteasome, probably the 20 S core proteasome complex, is primarily responsible for the selective degradation of oxidatively damaged proteins in human hematopoietic cells. Since "oxidative marking" of cellular proteins by lipoxygenase has been proposed as an important step in red blood cell maturation, it is important to determine which protease or proteases could recognize and degrade such modified substrates. Our results provide evidence that proteasome can, indeed, conduct such selective degradation and appears to be the major cellular protease capable of fulfilling such a role in maturation.

Analysis by cell hybridization of mechanisms that regulate beta-adrenergic responses in reticulocytes and in differentiating erythroid cells

In intact reticulocytes, but not in fragmented membranes, the loss of adenylate cyclase activity during cell maturation followed a biphasic time course. A rapid phase (t1/2 approximately 2 h) during which the initial activity was reduced by 40-50% was followed by a slow phase with t1/2 close to 3 days. The fast decay seemed to occur on the adenylate cyclase level since (-)isoprenaline- or forskolin-stimulated activities behaved similarly and bacterial toxin-monitored Gs and Gi proteins remained stable. The mechanism of the initial decrease in hormonal responsiveness was further analysed in hybrid cells prepared by fusing reticulocytes with Friend erythroleukemia (MEL) cells. The hybrids contained reticulocyte-derived beta-adrenoceptors and MEL cell-derived adenylate cyclase and G proteins. Fusion of reticulocytes to native MEL cells caused adenylate cyclase activity to drop by 30% at 2 h and 45% at 18 h after fusion. By contrast, hybrids prepared after dimethylsulfoxide-induced differentiation of MEL cells showed stable or increasing rates of receptor-coupled cAMP formation between 2 and 18 h after fusion, concomitant with the enhanced activity of the Gs protein in these cells. A cyclase-stimulating factor present in the cytosol of MEL cells and of reticulocytes appeared not to be involved in short-term regulation of hormonal responsiveness. We conclude that the strength of beta-adrenergic responses in erythroid progenitor cells is primarily regulated by modulating G protein-mediated receptor cyclase coupling while reticulocytes, during early maturation, seem to rely on direct inactivation of adenylate cyclase, probably via a cytosolic proteolytic pathway.

Induction of the ATP-dependent proteolytic system in guinea pig reticulocyte lysates by triiodothyronine

The mechanism involved in the decreased numbers of several trans-membrane proteins such as sodium pump sites, sodium-lithium countertransport, sodium potassium cotransport proteins, proteins mediating the passive efflux of sodium and insulin receptors in erythrocytes from patients with hyperthyroidism is not known. The ATP-dependent proteolytic system which is involved in the loss of trans-membrane proteins during the maturation of the reticulocyte may be involved in the accelerated loss of these membrane proteins. Therefore, the effect of thyroid hormones on the ATP-dependent proteolytic activity of reticulocyte lysates was examined in this study. Reticulocytosis was induced in 14 guinea pigs by phenylhydrazine hydrochloride injections for 5 consecutive days followed by 2 days of rest. T3 (10 micrograms/100 g body weight) was injected into 7 animals on day 4 and day 6. Reticulocyte-rich blood was withdrawn on day 8. Oxygen consumption determined 24 hours after injection of T3 was 25% higher (p less than 0.01) and T3 treated animals had a 2.5 fold higher (p less than 0.01) weight loss than control animals. The ATP-dependent proteolytic activity measured in reticulocyte lysates using 125I labelled lysozyme was 3.6 fold higher in the T3 than in the control group of guinea pigs (p less than 0.01). We conclude that thyroid hormones induce the ATP-dependent proteolytic activity of reticulocyte lysates which may be responsible for the reduced number of several trans-membrane proteins found in erythrocytes from patients with hyperthyroidism.

The presence of ATP + ubiquitin-dependent proteinase and multicatalytic proteinase complex in bovine brain

The presence of two distinct high-molecular-weight proteases with similar pH optima in the weakly alkaline region was shown in cytosol of the bovine brain cortex. They were separated by ammonium sulfate fractionation and each was further purified by DEAE-Sephacel, Sephacryl S-300, DEAE-Cibacron Blue 3GA-agarose, heparin-agarose, and Sepharose 6B chromatography. The larger enzyme (Mr 1,400 kDa), which precipitates at 0-38% ammonium sulfate saturation, seems to be active in ATP + ubiquitin (Ub)-dependent proteolysis; it has low basal caseinolytic activity that is stimulated 3-fold by ATP, and when Ub is present ATP causes a 4.5-fold stimulation. A second proteinase was also found to be present (Mr 700 kDa) that precipitates at 38-80% ammonium sulfate saturation, is composed of multiple subunits ranging in Mr from 18 to 30 kDa, and degrades both protein and peptide substrates, demonstrating trypsin-, chymotrypsin- and cucumisin-like activities. Catalytic, biochemical, and immunological characteristics of this proteinase indicate that it is a multicatalytic proteinase complex (MPC), whose enzyme activity, in contrast to that of MPC from bovine pituitaries (1-3), is stimulated 1.7-fold by addition of ATP in the absence of ubiquitin at the early steps of purification; this property is lost during the course of further purification. Both proteinases are present in the nerve cells, since the primary chicken embryonic telencephalon neuronal cell culture extracts contain both ATP + Ub-dependent proteinase and MPC activities.

Stabilization of ornithine decarboxylase in erythroleukemia cells depleted of ATP

Ornithine decarboxylase activity in Friend erythroleukemia cells decayed with a half-life of 50 minutes after addition of cycloheximide and at a faster rate after addition of spermidine. Incubation with a medium containing dinitrophenol and 2-deoxy-glucose in place of glucose caused ATP depletion and blocked the turnover of ornithine decarboxylase, even after addition of spermidine. Dinitrophenol in the presence of glucose was able to provoke only a slight increase of the half-life of the enzyme. These results suggest that degradation of ornithine decarboxylase in erythroleukemia cells is ATP-dependent.

ATP-dependent peptide release from mitochondria of reticulocytes

ATP-dependent release of TCA-precipitable peptides from mitochondria-containing stroma (MCS) is described. The process is independent of ubiquitin, but is sensitive to hemin and to heat treatment. Neither chloramphenicol nor EGTA inhibit. 50% of the activity is dependent on charged tRNA. The peptides released from MCS possess a molecular mass of about 1-5 kDa and are degraded to TCA-soluble compounds by a cytosolic protease system (fraction II) without ubiquitin.

Murine erythroleukemia cells possess an active ubiquitin- and ATP-dependent proteolytic pathway

The ubiquitin (Ub)-dependent proteolytic pathway may function in selective elimination of cellular proteins during erythroid differentiation. Murine erythroleukemia (MEL) cells, which can be induced to differentiate to reticulocytes in culture, may provide a convenient system for studying the role of Ub-dependent proteolysis in erythroid differentiation. The following observations indicate that MEL cells possess an active Ub-dependent proteolytic pathway. (i) Addition of purified Ub to MEL cell fraction II (Ub-depleted lysate) stimulated ATP-dependent degradation of radioiodinated proteins. (ii) Covalent conjugation of carboxyl termini of Ub molecules to substrate protein amino groups is a necessary step in Ub-dependent degradation. Des-glygly-Ub (Ub lacking its carboxyl-terminal glygly moiety) did not stimulate protein degradation in MEL cell fraction II. (iii) The Ub-dependent component of protein degradation in MEL cell fraction II was specifically inhibited by amino acid derivatives that are inhibitors of Ub-protein ligase. (iv) MEL cell fraction II contained apparent homologs of all of the rabbit reticulocyte Ub carrier proteins (E2's) except E2(20K) and E2(230K). Ub-dependent proteolysis was seen only in MEL cell lysates prepared in the presence of leupeptin; an enzyme of the proteolytic pathway was inactivated if leupeptin was omitted.

ATP-stimulated proteolysis in soluble extracts of BHK 21/C13 cells. Evidence for multiple pathways and a role for an enzyme related to the high-molecular-weight protease, macropain

Soluble extracts of cultured cells (BHK 21/C13) degraded a variety of exogenous proteins to acid-soluble peptides at pH 8.0. ATP stimulated this proteolytic activity up to 10-fold. The ATP effect was dependent on Mg2+ and was not elicited by nonhydrolyzable analogs of ATP. After the extract was fractionated on DEAE-cellulose, ATP-stimulated protease activity was in the fraction that bound to the resin and eluted in buffer containing 0.4 M NaCl. This activity had characteristics that were indistinguishable from those of the unfractionated extract but the degree of ATP stimulation was two- to three-fold lower. Although no protease activity was detected in the unbound fraction, reconstitution of this material with the bound fraction enhanced the ATP stimulation up to twofold. The component responsible for the enhancement of the ATP stimulation had properties similar to ubiquitin and purified ubiquitin enhanced the ATP-stimulated protease activity in the fractionated extract. Substrates whose amino groups were almost completely blocked by various chemical modifications were still degraded in an ATP-stimulated fashion, but the degradation of these substrates was not affected by ubiquitin. The protease activity isolated by ion-exchange chromatography was fractionated further by gel filtration chromatography on Sephacryl S-300. ATP-stimulated protease activity eluted with an apparent molecular weight of 750,000. Protease activity was enhanced up to eightfold by Mg2+-ATP but was not increased further by ubiquitin. An activity that hydrolyzed the synthetic peptide Z-Val-Leu-Arg-MNA coeluted with ATP-stimulated protease activity, but peptide hydrolysis was not affected by ATP. These and other catalytic and biochemical characteristics suggested that the protease might be related to the high-molecular-weight protease, macropain, recently purified by us from human erythrocytes (M. J. McGuire and G. N. DeMartino Biochim. Biophys. Acta (1986) 873, 279-289). Antibodies raised against macropain specifically reacted with proteins characteristic of macropain in the column fractions containing ATP-stimulated protease activity. These antibodies also specifically immunoprecipitated 70-100% of the ATP-stimulated protease activity as well as Z-Val-Leu-Arg-MNA hydrolyzing activity. Thus BHK cell extracts appear to contain both ubiquitin-mediated and ubiquitin-independent pathways for the ATP-stimulated degradation of proteins. Furthermore, at least one of these pathways appears to involve a high-molecular-weight, ATP-stimulated protease related to macropain.

An ATP-dependent system specific for degradation of long-lived proteins in permeabilized cells

We have characterized a digitonin-permeabilized cell system for the ATP-dependent degradation of endogenous long-lived proteins. Proteolysis requires Mg2+ and ATP hydrolysis. Other nucleotide triphosphates (CTP, UTP) can partially replace the ATP requirement. The enhanced rate of degradation of long-lived proteins in response to serum starvation is maintained in the permeabilized cell system and can be partially inhibited by lysosomal inhibitors. The maintenance of intracellular architecture and ease of manipulation of soluble components make the permeabilized cell system ideal for studying the proteolysis of both endogenous and exogenous substrates.