N-Terminal-Dependent Protein Degradation and Targeting Cancer Cells

: Intracellular protein degradation is mediated selectively by the Ubiquitin-Proteasome System (UPS) and autophagic-lysosomal system in mammalian cells. Many cellular and physiological processes, such as cell division, cell differentiation, and cellular demise, are fine-tuned via the UPS-mediated protein degradation. Notably, impairment of UPS contributes to human disorders, including cancer and neurodegeneration. The proteasome- dependent N-degron pathways mediate the degradation of proteins through their destabilizing aminoterminal residues. Recent advances unveiled that targeting N-degron proteolytic pathways can aid in sensitizing some cancer cells to chemotherapeutic agents. Furthermore, interestingly, exploiting the N-degron feature, the simplest degradation signal in mammals, and fusing it to a ligand specific for Estrogen-Related Receptor alpha (ERRa) has demonstrated its utility in ERRa knockdown, via N-terminal dependent degradation, and also its efficiency in the inhibition of growth of breast cancer cells. These recent advances uncover the therapeutic implications of targeting and exploiting N-degron proteolytic pathways to curb growth and migration of cancer cells.

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mTOR inhibition activates overall protein degradation by the ubiquitin proteasome system as well as by autophagy

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1521919112 ◽

2015 ◽

Vol 112 (52) ◽

pp. 15790-15797 ◽

Cited By ~ 185

Author(s):

Jinghui Zhao ◽

Bo Zhai ◽

Steven P. Gygi ◽

Alfred Lewis Goldberg

Keyword(s):

Amino Acids ◽

Protein Synthesis ◽

Protein Degradation ◽

Mammalian Cells ◽

Cholesterol Biosynthesis ◽

Mammalian Target Of Rapamycin ◽

Ubiquitin Proteasome System ◽

Mtor Inhibition ◽

Protein Ubiquitination ◽

Ubiquitin Proteasome

Growth factors and nutrients enhance protein synthesis and suppress overall protein degradation by activating the protein kinase mammalian target of rapamycin (mTOR). Conversely, nutrient or serum deprivation inhibits mTOR and stimulates protein breakdown by inducing autophagy, which provides the starved cells with amino acids for protein synthesis and energy production. However, it is unclear whether proteolysis by the ubiquitin proteasome system (UPS), which catalyzes most protein degradation in mammalian cells, also increases when mTOR activity decreases. Here we show that inhibiting mTOR with rapamycin or Torin1 rapidly increases the degradation of long-lived cell proteins, but not short-lived ones, by stimulating proteolysis by proteasomes, in addition to autophagy. This enhanced proteasomal degradation required protein ubiquitination, and within 30 min after mTOR inhibition, the cellular content of K48-linked ubiquitinated proteins increased without any change in proteasome content or activity. This rapid increase in UPS-mediated proteolysis continued for many hours and resulted primarily from inhibition of mTORC1 (not mTORC2), but did not require new protein synthesis or key mTOR targets: S6Ks, 4E-BPs, or Ulks. These findings do not support the recent report that mTORC1 inhibition reduces proteolysis by suppressing proteasome expression [Zhang Y, et al. (2014) Nature 513(7518):440–443]. Several growth-related proteins were identified that were ubiquitinated and degraded more rapidly after mTOR inhibition, including HMG-CoA synthase, whose enhanced degradation probably limits cholesterol biosynthesis upon insulin deficiency. Thus, mTOR inhibition coordinately activates the UPS and autophagy, which provide essential amino acids and, together with the enhanced ubiquitination of anabolic proteins, help slow growth.

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Intracellular Dynamics of the Ubiquitin-Proteasome-System

F1000Research ◽

10.12688/f1000research.6835.2 ◽

2015 ◽

Vol 4 ◽

pp. 367 ◽

Cited By ~ 4

Author(s):

Maisha Chowdhury ◽

Cordula Enenkel

Keyword(s):

Cell Cycle ◽

Protein Degradation ◽

Mammalian Cells ◽

Cell Cycle Progression ◽

Current Knowledge ◽

Ubiquitin Proteasome System ◽

Yeast Cells ◽

Ubiquitin Chain ◽

Dividing Cells ◽

Ubiquitin Proteasome

The ubiquitin-proteasome system is the major degradation pathway for short-lived proteins in eukaryotic cells. Targets of the ubiquitin-proteasome-system are proteins regulating a broad range of cellular processes including cell cycle progression, gene expression, the quality control of proteostasis and the response to geno- and proteotoxic stress. Prior to degradation, the proteasomal substrate is marked with a poly-ubiquitin chain. The key protease of the ubiquitin system is the proteasome. In dividing cells, proteasomes exist as holo-enzymes composed of regulatory and core particles. The regulatory complex confers ubiquitin-recognition and ATP dependence on proteasomal protein degradation. The catalytic sites are located in the proteasome core particle. Proteasome holo-enzymes are predominantly nuclear suggesting a major requirement for proteasomal proteolysis in the nucleus. In cell cycle arrested mammalian or quiescent yeast cells, proteasomes deplete from the nucleus and accumulate in granules at the nuclear envelope (NE) / endoplasmic reticulum ( ER) membranes. In prolonged quiescence, proteasome granules drop off the nuclear envelopeNE / ER membranes and migrate as droplet-like entitiesstable organelles throughout the cytoplasm, as thoroughly investigated in yeast. When quiescence yeast cells are allowed to resume growth, proteasome granules clear and proteasomes are rapidly imported into the nucleus.Here, we summarize our knowledge about the enigmatic structure of proteasome storage granules and the trafficking of proteasomes and their substrates between the cyto- and nucleoplasm.Most of our current knowledge is based on studies in yeast. Their translation to mammalian cells promises to provide keen insight into protein degradation in non-dividing cells, which comprise the majority of our body’s cells.

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Targeting Cancer Cells via N-degron-based PROTACs

Endocrinology ◽

10.1210/endocr/bqaa185 ◽

2020 ◽

Vol 161 (12) ◽

Author(s):

Mohamed A Eldeeb ◽

Cornelia E Zorca ◽

Richard P Fahlman

Keyword(s):

Protein Degradation ◽

Cancer Cells ◽

Substrate Recognition ◽

Ubiquitin Proteasome System ◽

Migration And Invasion ◽

Target Proteins ◽

Selective Degradation ◽

The Past ◽

Ubiquitin Proteasome ◽

Lysosomal System

Abstract In mammals, protein degradation is mediated selectively by the ubiquitin proteasome system (UPS) and the autophagic-lysosomal system. Over the past decades, N-degron pathways have been shown to be responsible for the selective degradation of proteins that harbor destabilizing N-terminal motifs. Recent studies have employed these pathways in the development of proteolysis targeting chimeras (PROTACs) composed of a degradation module linked to a substrate recognition domain to target proteins encoded by cancer-related genes for proteasomal destruction. Herein we provide an overview of PROTACs in the context of the N-degron concept and address the application of this technique to curb the migration and invasion of cancer cells, with a focus on the far-reaching potential of exploiting N-degron pathways for therapeutic purposes.

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Intracellular Dynamics of the Ubiquitin-Proteasome-System

F1000Research ◽

10.12688/f1000research.6835.1 ◽

2015 ◽

Vol 4 ◽

pp. 367 ◽

Cited By ~ 17

Author(s):

Maisha Chowdhury ◽

Cordula Enenkel

Keyword(s):

Cell Cycle ◽

Protein Degradation ◽

Mammalian Cells ◽

Cell Cycle Progression ◽

Current Knowledge ◽

Ubiquitin Proteasome System ◽

Yeast Cells ◽

Ubiquitin Chain ◽

Dividing Cells ◽

Ubiquitin Proteasome

The ubiquitin-proteasome system is the major degradation pathway for short-lived proteins in eukaryotic cells. Targets of the ubiquitin-proteasome-system are proteins regulating a broad range of cellular processes including cell cycle progression, gene expression, the quality control of proteostasis and the response to geno- and proteotoxic stress. Prior to degradation, the proteasomal substrate is marked with a poly-ubiquitin chain. The key protease of the ubiquitin system is the proteasome. In dividing cells, proteasomes exist as holo-enzymes composed of regulatory and core particles. The regulatory complex confers ubiquitin-recognition and ATP dependence on proteasomal protein degradation. The catalytic sites are located in the proteasome core particle. Proteasome holo-enzymes are predominantly nuclear suggesting a major requirement for proteasomal proteolysis in the nucleus. In cell cycle arrested mammalian or quiescent yeast cells, proteasomes deplete from the nucleus and accumulate in granules at the nuclear envelope (NE) / endoplasmic reticulum (ER) membranes. In prolonged quiescence, proteasome granules drop off the NE / ER membranes and migrate as stable organelles throughout the cytoplasm, as thoroughly investigated in yeast. When quiescence yeast cells are allowed to resume growth, proteasome granules clear and proteasomes are rapidly imported into the nucleus.Here, we summarize our knowledge about the enigmatic structure of proteasome storage granules and the trafficking of proteasomes and their substrates between the cyto- and nucleoplasm.Most of our current knowledge is based on studies in yeast. Their translation to mammalian cells promises to provide keen insight into protein degradation in non-dividing cells which comprise the majority of our body’s cells.

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Perspectives on the development of first-in-class protein degraders

Future Medicinal Chemistry ◽

10.4155/fmc-2021-0033 ◽

2021 ◽

Author(s):

Kalyn M Rambacher ◽

Matthew F Calabrese ◽

Masaya Yamaguchi

Keyword(s):

Protein Degradation ◽

E3 Ligase ◽

Ubiquitin Proteasome System ◽

26S Proteasome ◽

Target Protein ◽

Protein Homeostasis ◽

Recent Advances ◽

Subsequent Degradation ◽

Ubiquitin Proteasome

Targeted protein degradation is a broad and expanding field aimed at the modulation of protein homeostasis. A focus of this field has been directed toward molecules that hijack the ubiquitin proteasome system with heterobifunctional ligands that recruit a target protein to an E3 ligase to facilitate polyubiquitination and subsequent degradation by the 26S proteasome. Despite the success of these chimeras toward a number of clinically relevant targets, the ultimate breadth and scope of this approach remains uncertain. Here we highlight recent advances in assays and tools available to evaluate targeted protein degradation, including and beyond the study of E3-targeted chimeric ligands. We note several challenges associated with degrader development and discuss various approaches to expanding the protein homeostasis toolbox.

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Drug Development Targeting the Ubiquitin–Proteasome System (UPS) for the Treatment of Human Cancers

Cancers ◽

10.3390/cancers12040902 ◽

2020 ◽

Vol 12 (4) ◽

pp. 902 ◽

Cited By ~ 1

Author(s):

Xiaonan Zhang ◽

Stig Linder ◽

Martina Bazzaro

Keyword(s):

Cancer Cells ◽

Mammalian Cells ◽

Proteasome Inhibitors ◽

Cancer Therapeutics ◽

Ubiquitin Proteasome System ◽

Cancer Therapies ◽

Catalytic Core ◽

Essential Components ◽

Ubiquitin Proteasome ◽

Ubiquitin Conjugating Enzymes

Cancer cells are characterized by a higher rate of protein turnover and greater demand for protein homeostasis compared to normal cells. In this scenario, the ubiquitin–proteasome system (UPS), which is responsible for the degradation of over 80% of cellular proteins within mammalian cells, becomes vital to cancer cells, making the UPS a critical target for the discovery of novel cancer therapeutics. This review systematically categorizes all current reported small molecule inhibitors of the various essential components of the UPS, including ubiquitin-activating enzymes (E1s), ubiquitin-conjugating enzymes (E2s), ubiquitin ligases (E3s), the 20S proteasome catalytic core particle (20S CP) and the 19S proteasome regulatory particles (19S RP), as well as their mechanism/s of action and limitations. We also discuss the immunoproteasome which is considered as a prospective therapeutic target of the next generation of proteasome inhibitors in cancer therapies.

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