Related Experiment Video

Updated: Jan 5, 2026

Author Spotlight: A Selective Luciferase-Based Assay for Monitoring ATG4B 27 Activity in Cells
09:51

Author Spotlight: A Selective Luciferase-Based Assay for Monitoring ATG4B 27 Activity in Cells

Published on: June 30, 2023

1.4K

Ochratoxin A Sequentially Activates Autophagy and the Ubiquitin-Proteasome System

Hafize Aysin Akpinar1, Hilal Kahraman2, Ibrahim Yaman3,4

  • 1Molecular Toxicology and Cancer Research Laboratory, Department of Molecular Biology and Genetics, Bogazici University, Bebek-Istanbul 34342, Turkey. aysindemirkol@gmail.com.

Toxins
|October 27, 2019
PubMed

Insights

Ochratoxin A (OTA) exposure activates autophagy and the ubiquitin-proteasome system (UPS), leading to cell death and sustained signaling pathway activation. Autophagy initially promotes cell death but later enables UPS activation, regulating phosphatases involved in OTA toxicity.

Area of Science:

  • Biochemistry
  • Cell Biology
  • Toxicology

Background:

  • Ochratoxin A (OTA) is a carcinogenic mycotoxin found in food and feed.
  • OTA is known to activate PI3K/AKT and MAPK/ERK1-2 signaling pathways.
  • The relationship between signaling pathways and protein stability suggests a role for proteolytic systems in OTA toxicity.

Purpose of the Study:

  • To investigate the impact of OTA on cellular proteolytic systems, specifically autophagy and the ubiquitin-proteasome system (UPS).
  • To determine the role of these proteolytic systems in OTA-induced cell death and sustained signaling pathway activation.

Main Methods:

  • Exposure of human kidney proximal tubule HK-2 and mouse embryonic fibroblast (MEF) cells to OTA.
  • Assessment of autophagic activity and UPS activity.
  • Analysis of cell death in wild-type and autophagy-deficient (Atg5-deficient) MEF cells.
  • Measurement of proteasomal activities (chymotrypsin-, caspase-, and trypsin-like) using purified and cellular proteasomes.
  • Evaluation of phosphatase levels (VHR/DUSP3, DUSP4, PHLPP).

Main Results:

  • OTA exposure activated both autophagy and UPS in HK-2 and MEF cells.
  • Autophagy was transient, peaking early and subsiding after 6 hours.
  • OTA induced cell death in wild-type MEF cells, but not in Atg5-deficient cells, indicating autophagy's pro-death role.
  • Prolonged OTA exposure increased proteasomal activity and decreased ubiquitinated protein levels.
  • Enhanced 26S proteasome activity was observed in the presence of OTA, dependent on prior autophagy induction.
  • Autophagy and subsequent UPS activation regulated levels of phosphatases VHR/DUSP3, DUSP4, and PHLPP.

Conclusions:

  • Autophagy and UPS activation are key cellular responses to OTA exposure.
  • Autophagy plays a dual role, initially promoting cell death and subsequently facilitating UPS activation.
  • The interplay between autophagy and UPS contributes to sustained PI3K/AKT and MAPK/ERK1-2 signaling, influencing OTA toxicity and carcinogenicity.
Keywords:
MAPK/ERK1-2PI3K/AKTautophagyochratoxin Aproteolytic pathwaysubiquitin-proteasome system

More Related Videos

The Lactate Dehydrogenase Sequestration Assay — A Simple and Reliable Method to Determine Bulk Autophagic Sequestration Activity in Mammalian Cells09:34

The Lactate Dehydrogenase Sequestration Assay — A Simple and Reliable Method to Determine Bulk Autophagic Sequestration Activity in Mammalian Cells

Published on: July 27, 2018

18.6K
Evaluation of LC3-II Release via Extracellular Vesicles in Relation to the Accumulation of Intracellular LC3-positive Vesicles06:58

Evaluation of LC3-II Release via Extracellular Vesicles in Relation to the Accumulation of Intracellular LC3-positive Vesicles

Published on: October 18, 2024

1.1K

Related Concept Videos

Autophagic Cell Death01:18

Autophagic Cell Death

Christian de Duve discovered “autophagy,” a process in which cellular components are engulfed by membrane-bound organelles called autophagosomes. The autophagosomes then fuse with lysosomes to digest the enclosed contents. Autophagy is generally activated in cells to prevent cell death. However, cell death is triggered when the damage is beyond repair.
Autophagy and Apoptosis
Autophagy can activate apoptosis. In normal conditions, the autophagy activating protein Beclin-1 and...
4.3K
Autophagy01:27

Autophagy

Autophagy is a self-digesting process by which a cell protects itself from threats both within and outside the cell, ranging from abnormal proteins to invading bacteria. In this process, obsolete components of the cell and invading microbes are degraded by hydrolytic enzymes active in an acidic environment of the lysosomal lumen.
An autophagic pathway consists of a series of signaling events activated in response to diverse stress and physiological conditions such as food deprivation,...
5.6K
The Proteasome01:13

The Proteasome

Eukaryotic cells can degrade proteins through several pathways. One of the most important among these is the ubiquitin-proteasome pathway. It helps the cell eliminate the misfolded, damaged, or unwarranted cytoplasmic proteins in a highly specific manner.
In this pathway, the target proteins are first tagged with small proteins called ubiquitin. This involves participation of a series of enzymes including— E1 (ubiquitin-activating enzyme), E2 (ubiquitin-conjugating enzyme), and E3...
1.5K
The Proteasome02:18

The Proteasome

Eukaryotic cells can degrade proteins through several pathways. One of the most important amongst these is the ubiquitin-proteasome pathway. It helps the cell eliminate the misfolded, damaged, or unwarranted cytoplasmic proteins in a highly specific manner.
In this pathway, the target proteins are first tagged with small proteins called ubiquitin. A series of enzymes carry out the ubiquitination of the target proteins - E1 (ubiquitin-activating enzyme), E2 (ubiquitin-conjugating enzyme), and E3...
10.0K
Delivery Pathways to the Lysosome01:36

Delivery Pathways to the Lysosome

Eukaryotic cells use different mechanisms to eliminate toxic waste obsolete and worn-out substances. Lysosomes play a pivotal role in this, and hence, these substances are carried to the lysosome from other parts of the cell and extracellular space through different pathways. The most elaborately studied pathways to the lysosome are the endocytic pathways.
Endocytosis
In endocytosis, the cell membrane takes up macromolecules and particles from the surrounding medium. Clathrin-mediated...
8.7K
The Intrinsic Apoptotic Pathway01:31

The Intrinsic Apoptotic Pathway

Internal cellular stress, such as cellular injury or hypoxia, triggers intrinsic apoptosis. The B-cell lymphoma 2 (Bcl-2) family of proteins are the primary regulators of the intrinsic apoptotic pathway. For example, during DNA damage, checkpoint proteins, such as Ataxia Telangiectasia Mutated (ATM protein) and Checkpoints Factor-2 (Chk2) proteins, are activated. These proteins phosphorylate p53 which further activates pro-apoptotic proteins, such as Bax, Bak, PUMA, and Noxa, and inhibits...
8.1K