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Cellular control of ubiquitin-proteasome-dependent proteolysis¹

Human Nutrition Research Center of Clermont-Ferrand and Institut National de la Recherche Agronomique, Nutrition and Protein Metabolism Unit, Theix, 63122 Ceyrat, France

² To whom correspondence should be addressed (phone: 33 4 73 62 42 11; fax: 33 4 73 62 47 55; E-mail: attaix{at}clermont.inra.fr).

Abstract

This review focuses on recent advances in our understanding of the ubiquitin-proteasome-dependent pathway, which plays a major role in skeletal muscle proteolysis and is involved in the control of many major biological functions. The ubiquitination/deubiquitination system is a complex machine responsible for the specific tagging and proofreading of substrates degraded by the 26S proteasome, but ubiquitination itself also serves other functions. The formation of a polyubiquitin degradation signal is usually required for proteasome-dependent proteolysis. Hierarchical families of enzymes, which may comprise dozens of members to achieve high selectivity, control this process. The substrates tagged by ubiquitin are then recognized by the 26S proteasome and degraded into peptides. However, the 26S proteasome also recognizes and degrades some non-ubiquitinated proteins, and several proteasome populations participate in protein breakdown. Thus, mammalian cells contain multiple ubiquitin-and(or) proteasome-dependent pathways. These systems can degrade single proteins by alternative mechanisms and may also interfere or cooperate with other proteolytic pathways.

¹ Studies in the laboratory of the authors are supported by the Association pour la Recherche contre le Cancer, the Conseil Reégional d'Auvergne, the Institut National de la Recherche Agronomique, the French Ministère de la Recherche, and Nestlé.