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Identification of Ipaf, a human caspase-1-activating protein related to Apaf-1
J L Poyet1, S M Srinivasula, M Tnani
1Center for Apoptosis Research and the Department of Microbiology and Immunology, Kimmel Cancer Institute, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.
Insights
Researchers identified Ipaf, a protein that directly activates procaspase-1. This discovery sheds light on caspase-1 activation pathways involved in inflammation and apoptosis.
Area of Science:
- Molecular Biology
- Cellular Signaling
- Immunology
Background:
- Procaspase-9 activation relies on its CARD domain interacting with Apaf-1.
- Procaspase-1 also possesses a CARD domain, hinting at a similar activation mechanism involving an Apaf-1-related molecule.
Purpose of the Study:
- To identify and characterize a human Apaf-1-related protein involved in procaspase-1 activation.
- To elucidate the interaction between the identified protein and procaspase-1.
Main Methods:
- Identification of a novel human Apaf-1-related protein, Ipaf.
- Analysis of Ipaf's domain structure (CARD, nucleotide-binding, LRR).
- Investigation of Ipaf's interaction with procaspase-1 using CARD-CARD interactions.
- Functional assays using a constitutively active Ipaf mutant in transfected cells.
Main Results:
- Ipaf was identified as a human Apaf-1-related protein with CARD, nucleotide-binding, and LRR domains.
- Ipaf directly and specifically binds to the CARD domain of procaspase-1.
- A truncated, constitutively active Ipaf induced procaspase-1 processing and caspase-1-dependent apoptosis.
Conclusions:
- Ipaf acts as a specific and direct activator of procaspase-1.
- Ipaf may play a role in caspase-1 activation in response to inflammatory and apoptotic signals.
Abstract:
Procaspase-9 contains an NH2-terminal caspase-associated recruitment domain (CARD), which is essential for direct association with Apaf-1 and activation. Procaspase-1 also contains an NH2-terminal CARD domain, suggesting that its mechanism of activation, like that of procaspase-9, involves association with an Apaf-1-related molecule. Here we describe the identification of a human Apaf-1-related protein, named Ipaf that contains an NH2-terminal CARD domain, a central nucleotide-binding domain, and a COOH-terminal regulatory leucine-rich repeat domain (LRR). Ipaf associates directly and specifically with the CARD domain of procaspase-1 through CARD-CARD interaction. A constitutively active Ipaf lacking its COOH-terminal LRR domain can induce autocatalytic processing and activation of procaspase-1 and caspase-1-dependent apoptosis in transfected cells. Our results suggest that Ipaf is a specific and direct activator of procaspase-1 and could be involved in activation of caspase-1 in response to pro-inflammatory and apoptotic stimuli.