Inhibitor of Apoptosis (IAP)-like Protein Lacks a Baculovirus IAP Repeat (BIR) Domain and Attenuates Cell Death in Plant and Animal Systems

Abstract

A novel Arabidopsis thaliana inhibitor of apoptosis was identified by sequence homology to other known inhibitor of apoptosis (IAP) proteins. Arabidopsis IAP-like protein (AtILP) contained a C-terminal RING finger domain but lacked a baculovirus IAP repeat (BIR) domain, which is essential for antiapoptotic activity in other IAP family members. The expression of AtILP in HeLa cells conferred resistance against tumor necrosis factor (TNF)-␣/ActD-induced apoptosis through the inactivation of caspase activity. In contrast to the C-terminal RING domain of AtILP, which did not inhibit the activity of caspase-3, the N-terminal region, despite displaying no homology to known BIR domains, potently inhibited the activity of caspase-3 in vitro and blocked TNF-␣/ActD-induced apoptosis. The antiapoptotic activity of the AtILP N-terminal domain observed in plants was reproduced in an animal system. Transgenic Arabidopsis lines overexpressing AtILP exhibited anti-apoptotic activity when challenged with the fungal toxin fumonisin B1, an agent that induces apoptosis-like cell death in plants. In AtIPL transgenic plants, suppression of cell death was accompanied by inhibition of caspase activation and DNA fragmentation. Overexpression of AtILP also attenuated effector protein-induced cell death and increased the growth of an avirulent bacterial pathogen. The current results demonstrated the existence of a novel plant IAP-like protein that prevents caspase activation in Arabidopsis and showed that a plant anti-apoptosis gene functions similarly in plant and animal systems.All living organisms use a process of cell suicide to achieve and maintain homeostasis during normal development as well as in response to environmental stress or during pathogen challenge (1). This functionally conserved process, known as programmed cell death (PCD) 5 or apoptosis, is genetically regulated and associated with distinct morphological and biochemical characteristics. Extensive study over the past decade has illuminated the biological and molecular mechanisms of the regulation of apoptosis in animal systems (2-7). Apoptosis is triggered by the sequential activation of cysteine proteases known as caspases, which results in protein cleavage and the breakdown of DNA molecules. This apoptotic cascade is regulated by both initiators and inhibitors and can be activated by diverse stimuli. Caspases are synthesized as zymogens that are activated by proteolytic cleavage at specific aspartic acid residues in the P1 position (8). Compartmentalization of caspases and their cofactors suggests that two major apoptotic pathways exist. One pathway of apoptosis, observed in animal systems, can be induced by the deprivation of serum from tissue culture cells, leading to the release of cytochrome c from mitochondria. Apoptosis activating factor-1 (Apaf1) and cytochrome c form a complex with procaspase-9, which is then activated. Active caspase-9 triggers the common caspase cascade by cleaving procaspase-3 (9 -11). Caspase-3 is responsible either wholly or in part fo...

In silico study on Arabidopsis BAG gene expression in response to environmental stresses

“…The BAG family is a multifunctional group of proteins that act as co-chaperones that regulate cell signaling, growth, and development and are involved in environmental stress responses (Doukhanina et al 2006; Kim et al 2011). Thus, it is important to know their expression in response to different biotic and abiotic stresses and regulatory mechanisms.…”

“…As in animals, PCD has been characterized in plants during normal growth and development, as well as in response to various types of stress, including abiotic stress conditions such as heat, cold, salt, and UV radiation and biotic stress conditions such as the hypersensitivity response (HR) to pathogens (Nawkar et al 2013; Williams and Dickman 2008). Plants share a conserved mechanism of PCD with animal systems, which includes proteins like Bax inhibitor-1 (BI-1), Arabidopsis IAP-like protein (AtILP), and BAG family proteins (Ishikawa et al 2011; Kabbage and Dickman 2008; Kim et al 2011; Takayama and Reed 2001; Yan et al 2003). …”

A Phytophthora capsici Effector Targets ACD11 Binding Partners that Regulate ROS-Mediated Defense Response in Arabidopsis

“…Indeed, RBOHD gene was up regulated in bpl2, bpl3, bpl4, and RxLR207-transgenic plants while CAT2 gene was down regulated (Supplemental Figure 7C). Second, we selected four marker genes involved in the response to ROS/cell death, including two positive regulators, FMO1 and MSL10, and two negative regulators, FAH1 and ATILP Kim et al, 2011;Maruta et al, 2014;Veley et al, 2014). The expression levels of FMO1 increased to 7.8-to 37.2-fold in bpl2, bpl3, bpl4, and RxLR207-transgenic lines, and the expression levels of MSL10 increased to 2.4-to 3.9-fold (Supplemental Figure 7C).…”

The Life and Death of a Plant Cell

“…Although no homology to a BIR domain has been discovered, simple Basic Local Alignment Search Tool (BLAST) searches revealed Arabidopsis proteins with RING domains exhibiting some similarity to those from human and D. melanogaster IAPs. Validation of functionality came with the discovery that Arabidopsis thaliana IAP-LIKE PROTEIN (AtILP) inhibits tumor necrosis factor alpha (TNFα)-induced cell death in HeLa cells and suppresses caspase and caspase-like activity in HeLa cells and Arabidopsis upon treatment with FB1 (94). Overexpression of AtILP also inhibits HR-PCD.…”