Mechanisms of Cross-Talk between Intracellular Protein Degradation Pathways

Tight spatial and temporal regulation of protein turnover is essential to ensure maintenance of cellular health and survival. Cells employ several degradative mechanisms to execute the clearance of damaged or superfluous proteins, as well as of other cellular components including lipids and entire organelles. Autophagy is the umbrella term under which three distinct modes of lysosome-dependent protein degradation occur, namely macroautophagy, microautophagy and chaperone-mediated autophagy. In addition to autophagy, another major protein degradation mechanism is the ubiquitin-proteasome system whereby selectively targeted proteins are degraded into their constitutive peptides and amino acids aided by catalytic activities of a macromolecular complex named proteasome. Degradation of intracellular components through these catabolic pathways allows deliberation of basic building blocks required to maintain cellular energy and homeostasis. The extent to which different protein degradation pathways interact, collaborate or antagonize each other is under intense research scrutiny. Human pathologies arising from perturbed protein turnover, including aging, neurodegeneration and cancer, make further understanding of cross-talk between these homeostasis regulators an important research avenue medically, socially and economically.