Convergence of mammalian RQC and C-end rule proteolytic pathways via alanine tailing

Sarcopenia could result from the inability of an older individual to recover muscle lost during catabolic periods. To test this hypothesis, we compared the capacity of 5-day-refed 12- and 24-mo-old rats to recover muscle mass lost after 10 days without food. We measured gastrocnemius and liver protein synthesis with the flooding-dose method and also measured nitrogen balance, 3-methylhistidine excretion, and the gene expression of components of proteolytic pathways in muscle comparing fed, starved, and refed rats at each age. We show that 24-mo-old rats had an altered capacity to recover muscle proteins. Muscle protein synthesis, inhibited during starvation, returned to control values during refeeding in both age groups. The lower recovery in 24-mo-old rats was related to a lack of inhibition of muscle proteolysis during refeeding. The level of gene expression of components of the proteolytic pathways did not account for the variations in muscle proteolysis at both ages. In conclusion, this study highlights the role of muscle proteolysis in the lower recovery of muscle protein mass lost during catabolic periods.

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Exercise Reduces the Resumption of Tumor Growth and Proteolytic Pathways in the Skeletal Muscle of Mice Following Chemotherapy

Cancers ◽

10.3390/cancers12113466 ◽

2020 ◽

Vol 12 (11) ◽

pp. 3466

Author(s):

Edson Alves de Lima ◽

Alexandre Abilio de Souza Teixeira ◽

Luana Amorim Biondo ◽

Tiego Aparecido Diniz ◽

Loreana Sanches Silveira ◽

...

Keyword(s):

Tumor Growth ◽

Muscle Atrophy ◽

Endurance Exercise ◽

Premature Death ◽

Tumor Growth Rate ◽

Beneficial Effects ◽

Lung Carcinoma Cells ◽

Doxorubicin Toxicity ◽

Lewis Lung Carcinoma Cells ◽

Proteolytic Pathways

The pathogenesis of muscle atrophy plays a central role in cancer cachexia, and chemotherapy contributes to this condition. Therefore, the present study aimed to evaluate the effects of endurance exercise on time-dependent muscle atrophy caused by doxorubicin. For this, C57 BL/6 mice were subcutaneously inoculated with Lewis lung carcinoma cells (LLC group). One week after the tumor establishment, a group of these animals initiated the doxorubicin chemotherapy alone (LLC + DOX group) or combined with endurance exercise (LLC + DOX + EXER group). One group of animals was euthanized after the chemotherapy cycle, whereas the remaining animals were euthanized one week after the last administration of doxorubicin. The practice of exercise combined with chemotherapy showed beneficial effects such as a decrease in tumor growth rate after chemotherapy interruption and amelioration of premature death due to doxorubicin toxicity. Moreover, the protein degradation levels in mice undergoing exercise returned to basal levels after chemotherapy; in contrast, the mice treated with doxorubicin alone experienced an increase in the mRNA expression levels of the proteolytic pathways in gastrocnemius muscle (Trim63, Fbxo32, Myostatin, FoxO). Collectively, our results suggest that endurance exercise could be utilized during and after chemotherapy for mitigating muscle atrophy promoted by doxorubicin and avoid the resumption of tumor growth.

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Activators of Inactive Renin (‘Prorenin’) in Human Plasma: Their Connection with Kinin Formation, Coagulation and Fibrinolysis

Clinical Science ◽

10.1042/cs057089s ◽

1979 ◽

Vol 57 (s5) ◽

pp. 89s-92s ◽

Cited By ~ 6

Author(s):

F. H. M. Derkx ◽

B. N. Bouma ◽

H. L. Tan-Tjiong ◽

M. A. D. H. Schalekamp

Keyword(s):

Human Plasma ◽

Hageman Factor ◽

Active Renin ◽

Normal Plasma ◽

Inactive Renin ◽

Fletcher Factor ◽

Free Plasma ◽

Renin Activation ◽

Dependent Pathway ◽

Proteolytic Pathways

1. Human plasma was treated at 4°C with acid, trypsin, plasmin, streptokinase, urokinase, active Hageman factor fragment (β-XIIa) and β-XIIa-activated plasma prekallikrein (Fletcher factor). The conversion of inactive into active renin (activation) was studied in normal plasma (n = 10), Hageman factor-deficient plasma (n = 2), Fletcher factor-deficient plasma (n = 1) and plasminogen-free plasma (n = 4). 2. In normal plasma inactive renin was activated at pH 7·5 after treatment at pH < 4·0; at pH 3·3 the results were the same as with trypsin. This was also the case in plasminogen-free plasma. In Hageman factor-deficient plasma and in Fletcher factor-deficient plasma, however, the quantities of renin that were activated after acidification were much smaller than with trypsin. The addition of physiological amounts of active kallikrein to pH 3·3-pretreated Hageman factor-deficient plasma caused complete activation of renin. In contrast, the addition of active Hageman factor fragment to pH 3·3-pretreated Fletcher factor-deficient plasma had little or no effect. 3. Plasmin, streptokinase-activated plasminogen and urokinase-activated plasminogen activated inactive renin in pH 4·0-pretreated normal plasma as well as in pH 4·0-pretreated Hageman factor-deficient plasma and Fletcher factor-deficient plasma. 4. It is concluded that inactive renin is activated by two separate proteolytic pathways: one pathway depends on both Hageman factor and plasma prekallikrein, and the other pathway depends on plasminogen. In the Hageman factor-dependent pathway plasma kallikrein and not Hageman factor is the major activator of inactive renin. It is assumed that pH 3·3-treatment of plasma destroys the major inhibitors of kallikrein and that pH 4·0-treatment destroys the major inhibitor of plasmin.

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Ubiquilins in the crosstalk among proteolytic pathways

Biological Chemistry ◽

10.1515/hsz-2012-0120 ◽

2012 ◽

Vol 393 (6) ◽

pp. 441-447 ◽

Cited By ~ 31

Author(s):

Dong Yun Lee ◽

Eric J. Brown

Keyword(s):

Protein Degradation ◽

Binding Proteins ◽

Major Protein ◽

Degradation Pathways ◽

Cytosolic Proteins ◽

Sequestosome 1 ◽

Ubiquitin Binding ◽

Proteolytic Pathways

Abstract Protein degradation occurs through several distinct proteolytic pathways for membrane and cytosolic proteins. There is evidence that these processes are linked and that crosstalk among these major protein degradation pathways occurs. Ubiquilins, a family of ubiquitin-binding proteins, are involved in all protein degradation pathways. This minireview provides an overview of ubiquilin function in protein degradation and contrasts it with sequestosome-1 (p62), a protein that also has been implicated in multiple proteolytic pathways.

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Tim54p connects inner membrane assembly and proteolytic pathways in the mitochondrion

The Journal of Cell Biology ◽

10.1083/jcb.200706195 ◽

2007 ◽

Vol 178 (7) ◽

pp. 1161-1175 ◽

Cited By ~ 37

Author(s):

David K. Hwang ◽

Steven M. Claypool ◽

Danielle Leuenberger ◽

Heather L. Tienson ◽

Carla M. Koehler

Keyword(s):

Protein Import ◽

Mitochondrial Morphology ◽

Inner Membrane ◽

Active Complex ◽

Membrane Complex ◽

Independent Functions ◽

F1fo Atpase ◽

Negative Phenotype ◽

Proteolytic Pathways ◽

Strain Background

Tim54p, a component of the inner membrane TIM22 complex, does not directly mediate the import of inner membrane substrates but is required for assembly/stability of the 300-kD TIM22 complex. In addition, Δtim54 yeast exhibit a petite-negative phenotype (also observed in yeast harboring mutations in the F1Fo ATPase, the ADP/ATP carrier, mitochondrial morphology components, or the i–AAA protease, Yme1p). Interestingly, other import mutants in our strain background are not petite-negative. We report that Tim54p is not involved in maintenance of mitochondrial DNA or mitochondrial morphology. Rather, Tim54p mediates assembly of an active Yme1p complex, after Yme1p is imported via the TIM23 pathway. Defective Yme1p assembly is likely the major contributing factor for the petite-negativity in strains lacking functional Tim54p. Thus, Tim54p has two independent functions: scaffolding/stability for the TIM22 membrane complex and assembly of Yme1p into a proteolytically active complex. As such, Tim54p links protein import, assembly, and turnover pathways in the mitochondrion.

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Secondary Bortezomib-Resistance Is Characterized by Upregulation of Proteasomal Subunits and Their Insufficient Inhibition by Bortezomib, Which Can Be Overcome by Alternative Proteasome Inhibitors Combined with Induction of the ER Stress Response.

Blood ◽

10.1182/blood.v108.11.2583.2583 ◽

2006 ◽

Vol 108 (11) ◽

pp. 2583-2583

Author(s):

Thomas Ruckrich ◽

Jeannette Gogel ◽

Marianne Kraus ◽

Huib Ovaa ◽

Christoph Driessen

Keyword(s):

Stress Response ◽

Er Stress ◽

Proteasome Inhibitors ◽

Cytotoxic Drugs ◽

Proteasome Activity ◽

Intact Cells ◽

Secondary Resistance ◽

Er Stress Response ◽

Proteolytic Pathways

Abstract Resistance towards proteasome inhibition by Bortezomib (Velcade®) represents a challenge for myeloma therapy. Its biology has not yet been characterized in detail. We have demonstrated that Bortezomib-sensitive malignant haematopoetic cells can acquire secondary resistance to Bortezomib in vitro. We here present the first analysis of proteasome biology and activity, alternative proteolytic pathways, ubiquitin-specific proteases (USP) and the ER stress response (unfolded protein response, UPR) upstream of the proteasome, as well as in vitro cytotoxicity of conventional cytotoxic drugs, alternative proteasome inhibitors and agents that target the UPR in Bortezomib-resistant (BR) cells, compared to wild type (WT) controls. BR cells had higher activities of all subunits of the constitutive and the immunoproteasome, as deferred from turnover of fluorogenic substrates as well as affinity-labelling of active proteasome subunits in intact cells. This was mirrored by increased levels of proteasomal β1 and β2, but especially β5 polypeptides, implicating a homeostatic system that senses and corrects low proteasome activity in cells chronically exposed to Bortezomib. While the vinylsulfone-type proteasome inhibitor NLVS abrogated detectable proteasome activity in both BR and WT cells, Bortezomib at therapeutic concentrations eliminated proteasomal β1 and β5-type activity only in WT cells, while BR cells retained residual activity. These changes in proteasome biology appear to be the molecular hallmark of required Bortezomib resistance, since no changes were observed between WT and BR cells in alternative cytosolic or lysosomal proteolytic pathways, UPR activity as well as the gross activity pattern of USP. As expected, this translated into sensitivity against cytotoxic drugs in vitro: BR cells were less sensitive towards alternative proteasome inhibitors. However, while the IC50 for pan-proteasome inhibitors was only roughly doubled in BR cells, it was nearly tenfold elevated for the β5-preferring vinylsulfone inhibitor NLVS. By contrast, sensitivity towards anthracyclines or cytotoxicity induced by ER stressors as well as the synergy between proteasome inhibitors and UPR-activators remained unaffected in BR cells. Based on our data, proteasome inhibitors with activity profiles different from that of Bortezomib, alone or in combination with induction of the UPR, may represent an appropriate concept to overcome secondary Bortezomib resistance.

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