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A protease-independent function for SPPL3 in NFAT activation
Stefanie L Makowski1, Zhaoquan Wang1, Joel L Pomerantz2
1Department of Biological Chemistry, Institute for Cell Engineering, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
Molecular and Cellular Biology
|November 12, 2014
Summary
Signal peptide peptidase-like 3 (SPPL3) activates NFAT signaling in lymphocytes, crucial for immune cell function. Surprisingly, its proteolytic activity is not required for this immune-related role.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- Signal peptide peptidase (SPP)-related intramembrane aspartyl proteases are involved in immunity.
- Signal peptide peptidase-like 3 (SPPL3) is an ER-localized protease with uncharacterized substrates.
- NFAT (nuclear factor of activated T-cells) is a transcription factor vital for lymphocyte development and function.
Purpose of the Study:
- To identify the cellular function of SPPL3.
- To investigate SPPL3's role in lymphocyte signaling pathways.
- To determine the mechanism by which SPPL3 influences NFAT activation.
Main Methods:
- SPPL3 was identified in a screen for NFAT activators.
- Assays were performed to measure Ca(2+) influx and NFAT activation in lymphocytes.
- Protein association studies (e.g., co-immunoprecipitation) were used to investigate interactions between SPPL3, STIM1, and Orai1.
Main Results:
- SPPL3 is required for maximal Ca(2+) influx and NFAT activation downstream of T cell receptor engagement.
- SPPL3's proteolytic activity is not essential for its function in this pathway.
- SPPL3 enhances the association of STIM1 (stromal interaction molecule 1) and Orai1, crucial components of store-operated calcium entry.
- SPPL3 interacts with STIM1 via its transmembrane region and CRAC activation domain (CAD), promoting STIM1 CAD association with Orai1.
Conclusions:
- SPPL3 plays a significant role in lymphocyte signaling, independent of its protease activity.
- This study reveals a non-proteolytic function for SPPL3 in regulating calcium signaling and NFAT activation.
- The findings highlight the expanding roles of intramembrane aspartyl proteases beyond proteolysis in cellular processes.
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