A protease-independent function for SPPL3 in NFAT activation.
The signal peptide peptidase (SPP)-related intramembrane aspartyl proteases are a homologous group of polytopic membrane proteins, some of which function in innate or adaptive immunity by cleaving proteins involved in antigen presentation or intracellular signaling. Signal peptide peptidase-like 3 (SPPL3) is a poorly characterized endoplasmic reticulum (ER)-localized member of this family, with no validated cellular substrates. We report here the isolation of SPPL3 in a screen for activators of NFAT, a transcription factor that controls lymphocyte development and function. We find that SPPL3 is required downstream of T cell receptor engagement for maximal Ca(2+) influx and NFAT activation. Surprisingly, the proteolytic activity of SPPL3 is not required for its role in this pathway. SPPL3 enhances the signal-induced association of stromal interaction molecule 1 (STIM1) and Orai1 and is even required for the full activity of constitutively active STIM1 variants that bind Orai1 independently of ER Ca(2+) release. SPPL3 associates with STIM1 through at least two independent domains, the transmembrane region and the CRAC activation domain (CAD), and can promote the association of the STIM1 CAD with Orai1. Our results assign a function in lymphocyte signaling to SPPL3 and highlight the emerging importance of nonproteolytic functions for members of the intramembrane aspartyl protease family.
Department of Biological Chemistry, Institute for Cell Engineering, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
Stefanie L
SL
Makowski
Department of Biological Chemistry, Institute for Cell Engineering, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
Zhaoquan
Z
Wang
Department of Biological Chemistry, Institute for Cell Engineering, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA joel.pomerantz@jhmi.edu.
Joel L
JL
Pomerantz
D016282:Aspartic Acid Endopeptidases / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism*; D050778:NFATC Transcription Factors / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D000071737:Stromal Interaction Molecule 1
D015220:Calcium Channels; D008565:Membrane Proteins; D050778:NFATC Transcription Factors; D009363:Neoplasm Proteins; C103530:STIM1 protein, human; D000071737:Stromal Interaction Molecule 1; D016282:Aspartic Acid Endopeptidases; C513914:signal peptide peptidase like 3, human