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CARD11 mediates factor-specific activation of NF-kappaB by the T cell receptor complex
Joel L Pomerantz1, Elissa M Denny, David Baltimore
1Division of Biology, California Institute of Technology, Pasadena, CA 91125, USA. jpomeran@caltech.edu
Insights
Researchers identified CARD11, a key protein, that activates NF-kappaB signaling in T cells following T cell receptor (TCR) stimulation. This discovery clarifies a crucial step in immune cell activation pathways.
Area of Science:
- Immunology
- Molecular Biology
- Cell Signaling
Background:
- Nuclear factor kappa B (NF-kappaB) is a critical signaling target downstream of the T cell receptor (TCR) complex.
- The precise mechanisms by which TCR signaling activates NF-kappaB remain incompletely understood.
- Identifying novel molecular players in this pathway is essential for understanding T cell activation.
Purpose of the Study:
- To identify novel molecules involved in T cell receptor (TCR) signaling pathways that activate Nuclear factor kappa B (NF-kappaB).
- To elucidate the specific role of identified molecules in NF-kappaB activation downstream of the TCR.
- To characterize the functional domains and signaling interactions of newly identified proteins.
Main Methods:
- Utilized an expression cloning strategy to screen a mouse thymus cDNA library.
- Employed a CARD-deleted variant of CARD11 and RNA interference (RNAi) for functional analysis.
- Conducted RNAi-rescue experiments to confirm the necessity of specific CARD11 domains.
Main Results:
- Identified CARD11, a membrane-associated guanylate kinase (MAGUK) protein, as a mediator of NF-kappaB activation.
- Demonstrated that CARD11 mediates NF-kappaB activation specifically in response to TCR stimulation (alphaCD3/alphaCD28) and PMA/ionomycin, but not TNFalpha or dsRNA.
- Showed that CARD11 functions upstream of the IkappaB-kinase (IKK) complex, cooperates with Bcl10 in a CARD domain-dependent manner, and is not required for TCR-mediated NFAT or AP-1 induction.
Conclusions:
- CARD11 plays a critical role in the factor-specific activation of NF-kappaB by the T cell receptor (TCR) complex.
- Established a role for a MAGUK family member, CARD11, in antigen receptor signaling pathways.
- These findings provide new insights into the molecular mechanisms governing T cell activation and immune responses.
Abstract:
NF-kappaB is a critical target of signaling downstream of the T cell receptor (TCR) complex, but how TCR signaling activates NF-kappaB is poorly understood. We have developed an expression cloning strategy that can identify catalytic and noncatalytic molecules that participate in different pathways of NF-kappaB activation. Screening of a mouse thymus cDNA library yielded CARD11, a membrane-associated guanylate kinase (MAGUK) family member containing CARD, PDZ, SH3 and GUK domains. Using a CARD-deleted variant of CARD11 and RNA interference (RNAi), we demonstrate that CARD11 mediates NF-kappaB activation by alphaCD3/alphaCD28 cross-linking and PMA/ionomycin treatment, but not by TNFalpha or dsRNA. CARD11 is not required for TCR-mediated induction of NFAT or AP-1. CARD11 functions upstream of the IkappaB-kinase (IKK) complex and cooperates with Bcl10 in a CARD domain-dependent manner. RNAi-rescue experiments suggest that the CARD, coiled-coil, SH3 and GUK domains of CARD11 are critical for its signaling function. These results implicate CARD11 in factor- specific activation of NF-kappaB by the TCR complex and establish a role for a MAGUK family member in antigen receptor signaling.