Minireview: Mechanisms of protein turnover in cultured cells

Amenta, Joseph S.; Brocher, S C

doi:10.1016/0024-3205(81)90444-6

Cited by 107 publications

(56 citation statements)

References 55 publications

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“…Since there is good evidence (review [34]) that endogenous proteolysis in perfused liver or isolated hepatocytes is a lysosomal process, these results again suggest that lysosomes are involved in hepatic lipolysis.…”

Section: Lysosomal Triacylglycerol Lipase and Hepatic Lipolysismentioning

confidence: 75%

Lipolysis of hepatic triacylglycerol stores

et al. 1982

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Section: Lysosomal Triacylglycerol Lipase and Hepatic Lipolysismentioning

confidence: 75%

Lipolysis of hepatic triacylglycerol stores

et al. 1982

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“…For example, cytosolic ATP-dependent pathways of protein catabolism are responsible for the degradation of abnormal proteins (2, 3, 5, 6) and perhaps certain short-lived normal proteins (7,8), while lysosomes are responsible for most of the increased proteolysis in tissues of starved animals (9-12) and in cultured cells deprived of serum (1,13,14). Both lysosomal and nonlysosomal pathways probably contribute to the breakdown of intracellular proteins in optimally nourished tissues (2, 9-11) and in cultured cells supplemented with serum (1,14).Among the many advantages of erythrocyte-mediated microinjection (15-17) is the ability to modify proteins of interest prior to microinjection to probe effects of protein structure on rates and pathways of proteolysis. For example, several microinjection studies have addressed the role of ubiquitin in the rapid degradation of abnormal proteins by ATP-dependent pathways in the cytosol (6,(18)(19)(20).…”

mentioning

confidence: 99%

mentioning

confidence: 99%

“…Multiple pathways of intracellular protein degradation exist in mammalian cells (1)(2)(3)(4), and the current challenge is to define the roles of each pathway in contributing to overall proteolysis. For example, cytosolic ATP-dependent pathways of protein catabolism are responsible for the degradation of abnormal proteins (2,3,5,6) and perhaps certain short-lived normal proteins (7,8), while lysosomes are responsible for most of the increased proteolysis in tissues of starved animals (9)(10)(11)(12) and in cultured cells deprived of serum (1,13,14).…”

mentioning

confidence: 99%

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Covalent linkage of ribonuclease S-peptide to microinjected proteins causes their intracellular degradation to be enhanced during serum withdrawal.

Backer¹,

Dice²

1986

Proc. Natl. Acad. Sci. U.S.A.

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The amino-terminal 20 amino acids are required for micro' jected ribonuclease A (RNase A) to be taken up by lysosomes and degraded at an enhanced rate during serum withdrawal. We used water-soluble carbodlimides to covalently attach the RNase S-peptide (residues 1-20) to [3H]RNase S-protein (residues 21-124) at unspecified locations. We then measured catabolism of the [3H]S-protein-S-peptide conjugate after its microiujection into human diploid fibroblasts. The attached S-peptide caused the degradation of S-protein to be enhanced 2-fold in the absence of serum.Control experiments showed that degradation of [3H]RNase S-protein remained unresponsive to serum after conjugation with the inactive fragment, RNase S-peptide (residues 1-10). Covalent attachment of RNase S-peptide had a similar effect on the catabolism of two other proteins. Degradation rates of microiijected '5I-labeled lysozyme and '251-labeled insulin A chain are normally unresponsive to serum withdrawal. However, breakdown rates of micro'mjected "SI-labeled lysozyme-S-peptide and '251-labeled insulin A chain-S-peptide conjugates were increased 2-fold during serum deprivation. We suggest that RNase S-peptide acts as a "signal sequence" that directs cytosolic proteins to lysosomes through a pathway that is activated by deprivation conditions. Multiple pathways of intracellular protein degradation exist in mammalian cells (1-4), and the current challenge is to define the roles of each pathway in contributing to overall proteolysis. For example, cytosolic ATP-dependent pathways of protein catabolism are responsible for the degradation of abnormal proteins (2, 3, 5, 6) and perhaps certain short-lived normal proteins (7,8), while lysosomes are responsible for most of the increased proteolysis in tissues of starved animals (9-12) and in cultured cells deprived of serum (1,13,14). Both lysosomal and nonlysosomal pathways probably contribute to the breakdown of intracellular proteins in optimally nourished tissues (2, 9-11) and in cultured cells supplemented with serum (1,14).Among the many advantages of erythrocyte-mediated microinjection (15-17) is the ability to modify proteins of interest prior to microinjection to probe effects of protein structure on rates and pathways of proteolysis. For example, several microinjection studies have addressed the role of ubiquitin in the rapid degradation of abnormal proteins by ATP-dependent pathways in the cytosol (6,(18)(19)(20).We have concentrated on pathways of degradation of long-lived proteins whose catabolic rates are increased in cultured cells in response to serum withdrawal (21-24). Pancreatic ribonuclease A (RNase A) microinjected into human fibroblasts is degraded with a half-life of 80-100 hr. When serum is removed from the fibroblasts, its degradative rate is increased 2-fold (22). The S-peptide region (residues 1-20 of RNase A) contains the information required for recognition of the entire protein for enhanced catabolism during serum withdrawal. RNase S-protein (residues of RNase A) is degrade...

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“…Heterophagy and autophagy are the processes by which cells segregate and degrade exogenous and endogenous macromolecules respectively (2). These two processes can exist independently or interdependently (15).…”

mentioning

confidence: 99%

Lysosomophagy in macrophages after the endocytosis of colloidal gold-labeled Concanavalin A.

Wen¹,

Piao²,

Zhou³

et al. 1991

Acta Histochem. Cytochem

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We have investigated the lysosomophagy in mouse peritoneal macrophages after the endocytosis of colloidal gold-labeled Concanavalin A (ConA-Au). The mice were injected intraperitoneally with ConA-Au. At different intervals of time (5-120 min), peritoneal macrophages were isolated and observed under an electron microscope. Besides the active endocytosis of ConA, a large number of lysosomes appeared and were digested by other lysosomes after 20-30 min incubation (lysosomophagy, a kind of lysosomal wrapping mechanism).We concluded that an active heterophagy could induce excessive multiplication of lysosomes. In order to maintain the balance of lysosomal system, these excessive lysosomes were finally degraded by other lysosomes.Heterophagy and autophagy are the processes by which cells segregate and degrade exogenous and endogenous macromolecules respectively (2). These two processes can exist independently or interdependently (15). Both of them have a close relationship with lysosomes. One of the main functions of macrophages and mononuclear phagocytes is to engulf foreign materials and transfer them to lysosomes for degradation.After the endocytosis of numerous exogenous macromolecules, some reactive changes happen in the cells. The purpose of the present study is to investigate the morphological changes of lysosomes in macrophages after the receptor-mediated endocytosis of concanavalin A (ConA). The ConA was labeled with colloidal gold as a probe, then was injected into the peritoneal cavity of mouse. After different intervals of time, the glycogen-elicited peritoneal macrophages were isolated and observed under an electron microscope. MATERIALS AND METHODSColloidal gold-labeling of ConA 5 mg ConA (Sigma Chemical Company) was dissolved in 4 ml distilled water. In order to remove salts and polymers, the ConA solution (at PH 6.75) was dialysed for 30 hr and centrifuged at 33,000 rev/m for 1 hr. The sediments were discarded and the final concentration of ConA was regulated to 1 mg/ml. The reduction method with sodium citrate was used to prepare colloidal gold solution (at pH 6.9-7.0). The optimal quantity of ConA was 15 mg in 1 ml gold solution (tested by the visual method). 600 pl ConA was added into 40 ml colloidal gold solution, mixed, then 10% fetal bovine serum (FBS) was added with the final concentration of 1%. The suspension of ConA-gold complex (ConA-Au) was centrifuged at 1,500 rev/m for 20 min, and the supernatant was centrifuged again at 15,000 rev/m for 20 min. The supernatant was stored at 4°C . The stock solution was diluted 10 times when used. Preparation of peritoneal macrophages 12 male Kunming strain mice weighing 25-30 g were divided into group A and B . The mice were injected intraperitoneally with 2 ml of 2% sterile glycogen, once a day, for three days in succession. On the third day after the last injection, group A and group B animals were injected intraperitoneally with 1 ml pure colloidal gold solution (Au) and 1 ml colloidal gold-labeled ConA (ConA-Au), respectively. At intervals ranging fr...

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Minireview: Mechanisms of protein turnover in cultured cells

Cited by 107 publications

References 55 publications

Lipolysis of hepatic triacylglycerol stores

Lipolysis of hepatic triacylglycerol stores

Covalent linkage of ribonuclease S-peptide to microinjected proteins causes their intracellular degradation to be enhanced during serum withdrawal.

Lysosomophagy in macrophages after the endocytosis of colloidal gold-labeled Concanavalin A.

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