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1.  Roles and potential therapeutic targets of the ubiquitin proteasome system in muscle wasting 
BMC Biochemistry  2007;8(Suppl 1):S7.
Muscle wasting, characterized by the loss of protein mass in myofibers, is in most cases largely due to the activation of intracellular protein degradation by the ubiquitin proteasome system (UPS). During the last decade, mechanisms contributing to this activation have been unraveled and key mediators of this process identified. Even though much remains to be understood, the available information already suggests screens for new compounds inhibiting these mechanisms and highlights the potential for pharmaceutical drugs able to treat muscle wasting when it becomes deleterious. This review presents an overview of the main pathways contributing to UPS activation in muscle and describes the present state of efforts made to develop new strategies aimed at blocking or slowing muscle wasting.
Publication history: Republished from Current BioData's Targeted Proteins database (TPdb; ).
doi:10.1186/1471-2091-8-S1-S7
PMCID: PMC2106371  PMID: 18047744
2.  Multiple phosphorylation events control mitotic degradation of the muscle transcription factor Myf5 
BMC Biochemistry  2005;6:27.
Background
The two myogenic regulatory factors Myf5 and MyoD are basic helix-loop-helix muscle transcription factors undergoing differential cell cycle dependent proteolysis in proliferating myoblasts. This regulated degradation results in the striking expression of these two factors at distinct phases of the cell cycle, and suggests that their precise and alternated disappearance is an important feature of myoblasts, maybe connected to the maintenance of the proliferative status and/or commitment to the myogenic lineage of these cells. One way to understand the biological function(s) of the cyclic expression of these proteins is to specifically alter their degradation, and to analyze the effects of their stabilization on cells. To this aim, we undertook the biochemical analysis of the mechanisms governing Myf5 mitotic degradation, using heterologous systems.
Results
We show here that mitotic degradation of Myf5 is conserved in non-myogenic cells, and is thus strictly under the control of the cell cycle apparatus. Using Xenopus egg extracts as an in vitro system to dissect the main steps of Myf5 mitotic proteolysis, we show that (1) Myf5 stability is regulated by a complex interplay of phosphorylation/dephosphorylation, probably involving various kinases and phosphatases, (2) Myf5 is ubiquitylated in mitotic extracts, and this is a prerequisite to its degradation by the proteasome and (3) at least in the Xenopus system, the E3 responsible for its mitotic degradation is not the APC/C (the major E3 during mitosis).
Conclusion
Altogether, our data strongly suggest that the mitotic degradation of Myf5 by the ubiquitin-proteasome system is precisely controlled by multiple phosphorylation of the protein, and that the APC/C is not involved in this process.
doi:10.1186/1471-2091-6-27
PMCID: PMC1322219  PMID: 16321160

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