PubMed Health⌕ Search

Biomedical subjects

P O Seglen

Publications and source records attributed to P O Seglen.

At least 19 recordsLinked to original sources
PubMed1995

Inhibition of asialoglycoprotein endocytosis and degradation in rat hepatocytes by protein phosphatase inhibitors.

In isolated rat hepatocytes, a radiolabelled tyramine-cellobiose conjugate of asialo-orosomucoid, 125I-TC-AOM, was rapidly taken up by receptor-mediated endocytosis and proteolytically degraded in the lysosomes, where radioactive degradation products accumulated. Okadaic acid and other protein phosphatase inhibitors (microcystin-LR, calyculin A) strongly reduced the fraction of asialoglycoprotein (ASGP) receptors localized to the cell surface, and correspondingly inhibited the uptake of 125I-TC-AOM. In addition, the inhibitors suppressed 125I-TC-AOM degradation strongly (90% at 150 nM) and potently (half-maximal effect at 20 nM okadaic acid), indicating an involvement of protein phosphorylation, and of a protein phosphatase of type 2A, in the regulation of intracellular endocytic flux. The effects of okadaic acid on 125I-TC-AOM accumulation, as well as on degradation, could be eliminated by the protein kinase inhibitor genistein. Okadaic acid prevented the transfer of 125I-TC-AOM to a non-recycling endocytic compartment, causing its retention in a recycling compartment from which about one-third of the endocytosed 125I-TC-AOM could be returned to the cell surface and detached from its receptor in the presence of EGTA. ASGP receptors recycled extensively both in the presence and absence of okadaic acid, as indicated by a sustained uptake of 125I-TC-AOM. Sucrose density gradient analysis and sedimentation studies indicated that okadaic acid caused accumulation of 125I-TC-AOM in light endosomes (1.11 g/ml), preventing its transfer to dense endosomes (1.14 g/ml) and lysosomes (1.18 g/ml). The lysosomes could be identified in density gradients by their contents of lysosomal marker enzymes and acid-soluble radioactivity, and by their sensitivity towards the lysosome-disrupting agent glycyl-L-phenylalanine-2-naphthylamide. By using endocytosed AOM-gold particles as an ultrastructural endocytic marker, it could be shown that the light endosomes accumulating ASGP in the presence of okadaic acid had the morphological appearance of small endocytic vesicles/tubules and multivesicular endosomes. Whereas in control cells 4% of the AOM-gold was in small vesicles/tubules, 55% in multivesicular endosomes and 41% in lysosomes, the corresponding figures for okadaic acid-treated cells were 17%, 73% and 11%. Our results thus indicate that protein phosphatase inhibitors have two effects on ASGP endocytosis: (1) an early inhibition of ligand uptake, due to a reduction in the fraction of ASGP receptors at the cell surface, and (2) an inhibition of ASGP transfer from a recycling compartment consisting of light, small endocytic vesicles and multivesicular endosomes, to a non-recycling compartment consisting of dense multivesicular endosomes.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1995

Vanadate inhibition of hepatocytic autophagy. Calcium-modulated and osmolality-modulated antagonism by asparagine.

The phosphate analogue vanadate, at 10 mM, strongly (approximately 90%) inhibited the autophagic sequestration of endogenous lactate dehydrogenase in isolated rat hepatocytes. The effect of vanadate was markedly (approximately 80%) antagonized by asparagine (20 mM), and to a lesser extent by glutamine, glycine, and alanine. The antagonism was only observed in the presence of Ca2+ when an isotonic standard incubation medium was used, but by increasing the medium osmolality this Ca2+ requirement could be eliminated. Asparagine induced a cell swelling (17% at 20 mM) that might account for at least part of its vanadate antagonism, since hypotonic cell swelling by itself stimulated autophagy (with a maximal effect at approximately 200 mosM). Conversely, hypertonic media inhibited autophagy and were additive to vanadate. In a strongly hypotonic medium (less than 200 mosM), both asparagine and vanadate were inhibitory. However, since vanadate alone had no effect on cell volume, the vanadate-asparagine antagonism could not be exerted exclusively at the level of cell volume regulation. An additional mechanism might be a partial deamination of asparagine, generating ammonia, which was found to oppose the vanadate inhibition of autophagy while having no effect on cell volume. Other metabolizable amino acids, like alanine and glycine, were moderately vanadate-antagonistic while failing to induce cell swelling. These results are compatible with a vanadate-antagonistic effect of asparagine mediated partly through an unknown mechanism (possibly pH change) by its deamination product, ammonia, partly through cell swelling and a secondary Ca2+ influx that could compensate for a vanadate-induced depletion of intracellular calcium stores.

Adenosine Triphosphate↗
PubMed1995

Disruption of the cytokeratin cytoskeleton and inhibition of hepatocytic autophagy by okadaic acid.

To learn whether autophagy might be dependent on any of the major cytoskeletal elements, the effect of various cytoskeleton inhibitors on autophagy and cytoskeletal organization was studied in isolated rat hepatocytes. Autophagy, measured as the sequestration of endogenous lactate dehydrogenase, was completely inhibited in isolated rat hepatocytes by the protein phosphatase inhibitor okadaic acid (30 nM). Only small effects were seen with vinblastine (10 microM) or cytochalasin D (10 microM). Indirect immunofluorescence microscopy with antibody to a 55-kDa cytokeratin, corresponding to human cytokeratin 8 (CK8), revealed that whereas control cells contained a well-organized network of cytokeratin intermediate filaments, okadaic acid disrupted this network into small spherical aggregates. Treatment with cytochalasin D or vinblastine, which disrupt microfilaments and microtubules, respectively, had no detectable effect on the cytokeratin filament distribution. Neither the microtubule network (detected by indirect immunofluorescence with antibodies against alpha- and beta-tubulin) nor the actin microfilament network (detected by rhodamine-palloidin) was disrupted by okadaic acid. Naringin (100 microM), a putative protein kinase-inhibitory flavonoid, offered complete protection against the autophagy-inhibitory and cytokeratin-disruptive effects of okadaic acid. Two other flavonoids, genistein (100 microM) and prunin (100 microM), as well as KN-62 (10 microM), a specific inhibitor of Ca2+/calmodulin-dependent kinase II), likewise displayed a good ability to protect against the effect of okadaic acid upon cytokeratin organization, while no such protection was seen with H-89 (20 microM), an inhibitor of the cyclic nucleotide-dependent protein kinases, or with H-7 (100 microM), which in addition inhibits protein kinase C. The results suggest that the cytokeratin cytoskeleton of hepatocytes is subject to rapid control by phosphorylation and dephosphorylation and that cytokeratin filaments may somehow be involved in the autophagic process.

Animals↗
PubMed1995

Ultrastructural and immunocytochemical characterization of autophagic vacuoles in isolated hepatocytes: effects of vinblastine and asparagine on vacuole distributions.

The interactions between the autophagic and the endocytic degradation pathways were investigated by means of immunogold labeling of autophagic vacuoles (AVs) in ultrathin frozen sections from isolated rat hepatocytes. AVs were identified by their autophagocytosed contents of the degradation-resistant cytosolic enzyme CuZn-superoxide dismutase (SOD). Another cytosolic enzyme, carbonic anhydrase (CAIII), was rapidly degraded in the lysosomes, making the vacuolar CAIII/SOD ratio useful as a rough indicator of the progress of autophagic-lysosomal degradation. Lysosomes could be recognized by the presence of the lysosomal membrane glycoprotein lgp120, which was absent from hepatocytic endosomes. Endocytic inputs into the AVs were detected by the presence of gold-conjugated bovine serum albumin (BSA-gold), taken up by fluid-phase endocytosis. All vacuoles recognized morphologically as AVs were SOD-positive, as were essentially all of the lysosomes (96%). The majority (72%) of the lysosomes also labeled positively for BSA within 2 h of endocytosis. The data are thus compatible with the notion that all lysosomes can engage in both autophagic and endocytic degradation. Lgp120 appeared to distinguish well between lysosomes and nonlysosomal AVs: the lgp120-negative AVs (nonlysosomes) had a CAIII/SOD ratio identical to that of the cytosol, indicating that no degradation had occurred. In the lgp120-positive AVs (lysosomes), the ratio was only 43% of the cytosolic value, consistent with substantial CAIII degradation. Among the nonlysosomal AVs (about one-third of all AVs), one-half were BSA-positive, suggesting that early AVs (autophagosomes) and suggesting that early AVs (autophagosomes) and intermediary AVs (amphisomes) that had fused with endosomes were equally abundant. These morphological data thus support previous biochemical evidence for a prelysosomal meeting of the autophagic and endocytic pathways. The microtubule inhibitor vinblastine inhibited the autophagic influx to the lysosomes, causing an accumulation of autophagosomes and a reduction in average lysosomal size. Vinblastine also inhibited the endocytic flux, thereby precluding the formation of amphisomes and of BSA-positive lysosomes. High concentrations (20 mM) of asparagine induced swelling of amphisomes and of BSA-positive lysosomes, probably reflecting an acidotropic effect of ammonia generated by asparagine deamination. Asparagine also caused an accumulation of autophagosomes, amphisomes, and BSA-negative lysosomes, presumably as a result of impaired fusion with the swollen BSA-positive lysosomes. The two agents thus appear to perturb the autophagic-endocytic-lysosomal vacuole dynamics by different mechanisms, making them useful in the further study of these complex organelle interactions.

Animals↗
PubMed1994

Effect of 4-acetylaminofluorene and other tumour promoters on hepatocellular growth and binucleation.

The complete liver carcinogen 2-acetylaminofluorene (2-AAF) promoted the outgrowth of large neoplastic liver nodules and hepatocellular carcinomas in diethylnitrosamine-treated rats. 2-AAF did not alter the overall proliferative activity of normal hepatocytes, but suppressed binucleation and induced, on a long-term basis, an increase in proliferative activity and in the fraction of diploid hepatocytes relative to control animals. The analogue 4-acetylaminofluorene (4-AAF) was much less effective than 2-AAF as a promoter of large nodules and carcinomas, but promoted the outgrowth of medium-sized nodules (1 < 2.5 mm). While 2-AAF specifically stimulated the growth of cells in enzyme-altered foci, the cells responding to 4-AAF were more randomly distributed throughout the liver tissue. In contrast to 2-AAF, 4-AAF strongly stimulated the growth (DNA synthesis) of normal hepatocytes, but like 2-AAF it suppressed binucleation and caused a long-term increase in the proliferative activity and in the fraction of diploid hepatocytes. Other liver tumour promoters (cyproterone acetate, alpha-hexachlorocyclohexane, methylclofenapate) likewise stimulated the growth and suppressed the binucleation of normal hepatocytes. All hepatocellular ploidy classes were affected virtually equally by mitogenic stimulation, but at low proliferation rates the mononuclear cells were more proliferative than the binuclear cells. Since this difference could be eliminated by increasing the mitogen dose, it would seem that mononuclear cells may be somewhat more sensitive towards mitogens than binuclear cells. In contrast to previously reported results [Styles et al. (1990) Carcinogenesis, 11, 1149-1152], methylclofenapate was not found to specifically stimulate binuclear hepatocytes. Our results indicate that liver tumour promoters in general tend to induce a non-binucleating, non-polyploidizing hepatocellular growth pattern, similar to that observed during liver regeneration. 4-AAF is confirmed to be, at best, a very weak promoter of liver carcinogenesis, but appears to be an effective promoter of benign tumours.

2-Acetylaminofluorene↗
PubMed1992

Protein kinase-dependent effects of okadaic acid on hepatocytic autophagy and cytoskeletal integrity.

The protein phosphatase inhibitor okadaic acid suppressed autophagy completely in isolated rat hepatocytes, as measured by the sequestration of electroinjected [3H]raffinose into sedimentable autophagic vacuoles. Okadaic acid was effectively antagonized by the general protein kinase inhibitors K-252a and KT-5926, the calmodulin antagonist W-7, and by KN-62, a specific inhibitor of Ca2+/calmodulin-dependent protein kinase II (CaMK-II). These inhibitors also antagonized a cytoskeleton-disruptive effect of okadaic acid, manifested as the disintegration of cell corpses after breakage of the plasma membrane. CaMK-II, or a closely related enzyme, would thus seem to play a role in the control of autophagy as well as in the control of cytoskeletal organization.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1992

Prelysosomal and lysosomal connections between autophagy and endocytosis.

In isolated rat hepatocytes electroloaded with [14C]sucrose, autophaged sugar accumulated in lysosomes under control conditions, and in prelysosomal autophagic vacuoles (amphisomes) in the presence of asparagine, an inhibitor of autophagic-lysosomal fusion. Endocytic uptake of the sucrose-cleaving enzyme invertase resulted in rapid and complete degradation of autophaged sucrose in both amphisomes and lysosomes. Pre-accumulated sucrose was degraded equally well in both compartments, regardless of amphisomal-lysosomal flux inhibition by asparagine, suggesting that endocytic entry into the autophagic pathway can take place both at the lysosomal and at the amphisomal level. The completeness of sucrose degradation by endocytosed invertase furthermore indicates that all lysosomes involved in autophagy can also engage in endocytosis. Endocytosed invertase reached the amphisomes even when autophagy was blocked by 3-methyladenine, and autophaged sucrose reached this compartment even when endocytic influx was blocked by vinblastine, suggesting that amphisomes may exhibit some degree of permanence independently of either pathway.

Animals↗
PubMed1992

Proteases and proteolysis in the lysosome.

Proteins sequestered by a non-selective bulk process within the lysosomes turn over with an apparent half-life of about 8 minutes and this rapid lysosomal proteolysis is initiated by endopeptidases, in particular by the cathepsins D and L. We describe also the cathepsins B and H which show mainly exopeptidase and only low endopeptidase activity. Especially cathepsin H is most probably the only lysosomal aminopeptidase in many cell types. Additionally, the properties of other mammalian lysosomal endo- and exopeptidases are compared. Finally, we discuss some of the conditions for the action of lysosomal proteases as the low intralysosomal pH, the high part of lysosomal thiol groups and the absence of intralysosomal proteinase inhibitors.

Animals↗
PubMed1992

Autophagy and other vacuolar protein degradation mechanisms.

Autophagic degradation of cytoplasm (including protein, RNA etc.) is a non-selective bulk process, as indicated by ultrastructural evidence and by the similarity in autophagic sequestration rates of various cytosolic enzymes with different half-lives. The initial autophagic sequestration step, performed by a poorly-characterized organelle called a phagophore, is subject to feedback inhibition by purines and amino acids, the effect of the latter being potentiated by insulin and antagonized by glucagon. Epinephrine and other adrenergic agonists inhibit autophagic sequestration through a prazosin-sensitive alpha 1-adrenergic mechanism. The sequestration is also inhibited by cAMP and by protein phosphorylation as indicated by the effects of cyclic nucleotide analogues, phosphodiesterase inhibitors and okadaic acid. Asparagine specifically inhibits autophagic-lysosomal fusion without having any significant effects on autophagic sequestration, on intralysosomal degradation or on the endocytic pathway. Autophaged material that accumulates in prelysosomal vacuoles in the presence of asparagine is accessible to endocytosed enzymes, revealing the existence of an amphifunctional organelle, the amphisome. Evidence from several cell types suggests that endocytosis may be coupled to autophagy to a variable extent, and that the amphisome may play a central role as a collecting station for material destined for lysosomal degradation. Protein degradation can also take place in a 'salvage compartment' closely associated with the endoplasmic reticulum (ER). In this compartment unassembled protein chains are degraded by uncharacterized proteinases, while resident proteins return to the ER and assembled secretory and membrane proteins proceed through the Golgi apparatus. In the trans-Golgi network some proteins are proteolytically processed by Ca(2+)-dependent proteinases; furthermore, this compartment sorts proteins to lysosomes, various membrane domains, endosomes or secretory vesicles/granules. Processing of both endogenous and exogenous proteins can occur in endosomes, which may play a particularly important role in antigen processing and presentation. Proteins in endosomes or secretory compartments can either be exocytosed, or channeled to lysosomes for degradation. The switch mechanisms which decide between these options are subject to bioregulation by external agents (hormones and growth factors), and may play an important role in the control of protein uptake and secretion.

Animals↗
PubMed1992

Analytical methods for the study of liver cell proliferation.

Various cytometric methods for analysis of regenerating rat liver growth (DNA ploidy distributions, binucleation, and DNA synthesis by in vivo BrdUrd incorporation) were evaluated. The overall hepatocellular growth rate (labeling index), the binucleation rate, and separate indices for mononuclear and binuclear cells could be measured simply by microscope counting of collagenase-isolated hepatocytes immunostained for BrdUrd. Flow cytometry of cells stained for BrdUrd and DNA provided labeling indices for the various hepatocellular DNA ploidy classes as well as for nonparenchymal cells (identified by their size-dependent light scatter), but could not distinguish between mononuclear and binuclear hepatocytes. Image cytometry, using fluorescence or Feulgen staining, was inferior to flow cytometry in terms of speed and DNA resolution, but allowed a complete analysis of all hepatocellular DNA ploidy and nuclearity classes. It may therefore be the method of choice, particularly for analysis of liver cell cultures from which single cells are not easily obtained. Fluorescence staining would seem to be preferable to Feulgen staining, since the latter could not be used simultaneously with BrdUrd staining and therefore required a two-step analysis. A non-immunological method, based on the ability of incorporated BrdUrd to quench DNA staining by a Hoechst dye, could only be applied to isolated nuclei, thus giving no information about binucleation. The latter method may be useful for analysis of tumors which are difficult to dissociate to intact whole cells.

Animals↗
PubMed1992

Reduced proliferative activity of polyploid cells in primary hepatocellular carcinoma.

The proliferative activity of tumor cells differing in DNA content (ploidy) and nuclearity was investigated in primary hepatocellular carcinomas of the rat by flow cytometric analysis of collagenase-isolated cells immunostained after labelling with bromodeoxyuridine (BrdU) in vivo. The diploid cell fraction in these euploid tumours was higher than in normal liver, and the rate of binucleation as well as the proliferative activity of the binuclear cells was very low. The highest proliferative activity (BrdU labelling index) was found among the diploid tumour cells. The activity in mononuclear tetraploid and octoploid cells was reduced in inverse proportion to their increasing DNA content, possibly suggesting a loss of proliferative potential associated with polyploidization. There was a significant correlation between the proliferative activity of hepatocellular carcinoma cells and nonparenchymal liver cells in the different tumours, indicating that different cell types within a tumour may respond to common growth stimuli. Treatment of tumour-bearing rats with a promoting carcinogen (2-acetylaminofluorene) resulted in significant stimulation of tumour cell proliferation (all ploidy classes), whereas the proliferation of non-parenchymal (stromal) cells in the tumour was slightly inhibited.

2-Acetylaminofluorene↗
PubMed1991

Inhibition of autophagic-lysosomal delivery and autophagic lactolysis by asparagine.

Overall autophagy was measured in isolated hepatocytes as the sequestration and lysosomal hydrolysis of electroinjected [14C]lactose, using HPLC to separate the degradation product [14C]glucose from undegraded lactose. In addition, the sequestration step was measured separately as the transfer from cytosol to sedimentable cell structures of electroinjected [3H]raffinose or endogenous lactate dehydrogenase (LDH; in the presence of leupeptin to inhibit lysosomal proteolysis). Inhibitor effects at postsequestrational steps could be detected as the accumulation of autophaged lactose (which otherwise is degraded intralysosomally), or of LDH in the absence of leupeptin. Asparagine, previously shown to inhibit autophagic but not endocytic protein breakdown, strongly suppressed the autophagic hydrolysis of electroinjected lactose. Vinblastine, which inhibits both types of degradation, likewise suppressed lactose hydrolysis. Asparagine had little or no effect on sequestration, but caused an accumulation of autophaged LDH and lactose, indicating inhibition at a postsequestrational step. Neither asparagine nor vinblastine affected the degradation of intralysosomal lactose preaccumulated in the presence of the reversible lysosome inhibitor propylamine. However, if lactose was preaccumulated in the presence of asparagine, both asparagine and vinblastine suppressed its subsequent degradation. The data thus indicate that autophagic-lysosomal delivery, i.e., the transfer of autophaged material from prelysosomal vacuoles to lysosomes, is inhibited selectively by asparagine and non-selectively by vinblastine.

Animals↗
PubMed1991

Diploid growth pattern of hepatocellular tumours induced by various carcinogenic treatments.

Hepatocellular carcinomas from rats of different strains, subjected to a variety of carcinogenic treatment regimens in different laboratories (initiation by diethylnitrosamine or dimethylhydrazine, promotion by phenobarbital, 2-acetylaminofluorene, nafenopin, orotic acid or deoxycholic acid, growth stimulation by partial hepatectomy or necrogenic CCl4 treatment), were all found to be predominantly diploid by flow cytometric analysis, in contrast to normal liver tissue in which polyploid nuclei were predominant. A switch from polyploidization to diploid growth would thus seem to be a common property of malignant liver tumours. Benign neoplastic liver nodules were likewise predominantly diploid, with the exception of nodules induced by long-term deoxycholic acid treatment in Fischer rats. In addition to containing a majority of polyploid cells, the latter nodules failed to progress to the carcinoma stage.

Animals↗
PubMed1991

Hepatocytic autophagy.

Autophagy is a non-selective bulk process for degradation of cytoplasm, as indicated by ultrastructural evidence and by the similarity in autophagic sequestration rates of various cytosolic enzymes with different half-lifes. The initial autophagic sequestration step is subject to feedback inhibition by amino acids, an effect which is potentiated by insulin and antagonized by glucagon. Epinephrine and other adrenergic agonists inhibit autophagic sequestration through a prazosin-sensitive, alpha 1-adrenergic mechanism. The sequestration is also inhibited by cAMP and by protein phosphorylation as indicated by the effects of cyclic nucleotide analogues, phosphodiesterase inhibitors and okadaic acid. Asparagine specifically inhibits autophagic-lysosomal fusion without having any significant effects on autophagic sequestration, intralysosomal degradation or on the endocytic pathway. Autophaged material that accumulates in prelysosomal vacuoles in the presence of asparagine is accessible to endocytosed enzymes, revealing the existence of an amphifunctional organelle, the amphisome. Evidence from several cell types suggests that endocytosis may be coupled to autophagy in a differential (ligand-dependent) manner, and that amphisomes may play a central role as collecting stations for material destined for lysosomal degradation.

Amino Acids↗
PubMed1991

Role of cyclic nucleotides in the control of hepatic autophagy.

Using isolated hepatocytes as a model system we have investigated whether the cyclic nucleotides cAMP and cGMP are involved in the regulation of the autophagic process. The dibutyryl-cyclic nucleotide analogues db-cAMP and db-cGMP both inhibited autophagic sequestration, suggesting that cAMP and cGMP may be of significance for this step. The adenylate cyclase stimulator deacetyl-forskolin both raised the level of intracellular cAMP and reduced sequestration markedly. In contrast, the guanylate cyclase stimulating agent atriopeptin did not affect sequestration although, it effectively elevated, the level of cGMP. Several inhibitors of cyclic nucleotide phosphodiesterases strongly suppressed autophagy and elevated the level of both cAMP and cGMP. However, one inhibitor, milrinone, raised the cAMP level 3-4 x while having no significant effect on cGMP. These results suggest that cAMP may be involved in the control of hepatic autophagy, whereas the role of cGMP, if any, remains unclear.

Animals↗
PubMed1991

Effects of adrenergic agonists and antagonists on autophagic activity in isolated rat liver cells.

The effect of various adrenergic agonists on autophagic sequestration--measured as the transfer of electroinjected [3H]raffinose from cytosol to vacuoles of the autophagic pathway--was investigated. Epinephrine and other agonists with alpha-effects inhibited sequestration through a specific alpha 1-adrenergic, i.e. prazosin-sensitive, mechanism. The beta-adrenergic agonist isoproterenol also inhibited sequestration, but by a non-beta-specific (propranolol-insensitive) mechanism. All sequestration-inhibitory agents suppressed overall autophagic-lysosomal proteolysis. The inhibitory action of the adrenergic agonists on protein metabolism was not specific to the autophagic pathway since protein synthesis was suppressed as well. However, intracellular levels of ATP were not adversely affected, ruling out the possibility that the agonists might be generally cytotoxic.

Adenosine Triphosphate↗
PubMed1990

Both endocytic and endogenous protein degradation in fibroblasts is stimulated by serum/amino acid deprivation and inhibited by 3-methyladenine.

Incubation of BHK-21 hamster fibroblasts in a serum- and amino acid-deficient medium caused a 3-fold increase in the degradation of endogenous protein, a doubling of the degradation of endocytosed epidermal growth factor, and an eightfold increase in the degradation of endocytosed alpha 2-macroglobulin. 3-Methyladenine (3MA) inhibited the deprivation-induced lysosomal degradation of both endogenous and endocytosed protein, but had no effect on basal (non-induced) degradation. 3MA also inhibited deprivation-induced protein degradation in human IMR-90 fibroblasts. Some inhibition of protein synthesis and of endocytic uptake of alpha 2-macroglobulin was observed in 3MA-treated BHK-21 cells, whereas cellular ATP levels were unaffected. These results are different from those obtained with isolated hepatocytes, and suggest that in some cells both endogenous and endocytic protein degradation may be accelerated as part of a general deprivation response.

Adenine↗