Inactivation of Carbonyl-Detoxifying Enzymes by H2O2 Is a Trigger to Increase Carbonyl Load for Initiating Programmed Cell Death in Plants

Abstract

H2O2-induced programmed cell death (PCD) of tobacco Bright Yellow-2 (BY-2) cells is mediated by reactive carbonyl species (RCS), degradation products of lipid peroxides, which activate caspase-3-like protease (C3LP). Here, we investigated the mechanism of RCS accumulation in the H2O2-induced PCD of BY-2 cells. The following biochemical changes were observed in 10-min response to a lethal dose (1.0 mM) of H2O2, but they did not occur in a sublethal dose (0.5 mM) of H2O2. (1) The C3LP activity was increased twofold. (2) The intracellular levels of RCS, i.e., 4-hydroxy-(E)-hexenal and 4-hydroxy-(E)-nonenal (HNE), were increased 1.2–1.5-fold. (3) The activity of a reduced nicotinamide adenine dinucleotide phosphate (NADPH)-dependent carbonyl reductase, scavenging HNE, and n-hexanal was decreased. Specifically, these are the earliest events leading to PCD. The proteasome inhibitor MG132 suppressed the H2O2-induced PCD, indicating that the C3LP activity of the β1 subunit of the 20S proteasome was responsible for PCD. The addition of H2O2 to cell-free protein extract inactivated the carbonyl reductase. Taken together, these results suggest a PCD-triggering mechanism in which H2O2 first inactivates a carbonyl reductase(s), allowing RCS levels to rise, and eventually leads to the activation of the C3LP activity of 20S proteasome. The carbonyl reductase thus acts as an ROS sensor for triggering PCD.

Protein Carbonylation: Emerging Roles in Plant Redox Biology and Future Prospects

“…Wong et al proposed two major types of protein carbonylation, primary protein carbonylation and secondary protein carbonylation, to reflect how the modification occurs [ 92 ] ( Figure 3 ). Primary protein carbonylation involves metal-catalyzed oxidation (MCO) of the side chains of Lys, Pro, and Thr residues, leading to aldehyde or ketone formation [ 93 , 94 ]. Primary protein carbonylation may also occur, although to a much lesser extent, through α-amidation pathways or glutamyl side chains, which leads to the synthesis of peptides with the α-keto derivative at the N-terminal [ 13 , 95 ].…”

Tanned or Sunburned: How Excessive Light Triggers Plant Cell Death

“…Another vicious circle has been highlighted between RCS and H2O2 (Biswas et al, 2020). RCS can alter protein function by covalent modification (Colzani et al, 2013), and H2O2 scavenging enzymes (catalase and ascorbate peroxidase) were observed in a study as targets of RCS (Mano et al, 2014).…”

“…In addition, an animal catalase has been shown to form adducts with HNE, leading to inactivation of the enzyme and a compromised H2O2 scavenging (Bauer and Zarkovic, 2015;Biswas et al, 2020).…”

Oxidative Stress in Plants

“…Another interesting feature of this special issue focuses on investigating the other H 2 O 2 targets involved in programmed cell death. Dr. Mano’s group [ 8 ] studied the mechanism that increased the reactive carbonyl species in the H 2 O 2 -produced programmed cell death in tobacco Bright Yellow-2 cells. They suggested that H 2 O 2 initially inactivates a carbonyl reductase(s), which increases the reactive carbonyl species content, leading to the activation of the caspase-3-like protease of the 20S proteasome.…”