The heterotrimeric G-protein alpha-subunit Galphaq regulates TCR-mediated immune responses through an Lck-dependent pathway.
Here, we examined the functional involvement of heterotrimeric G-proteins in TCR-induced immune responses. TCR/CD3 crosslinking resulted in activation of both Galphaq and Galphas, but not Galphai-2. Targeting of Galphas, Galphai-2 and Galphaq using siRNA demonstrated a specific role of Galphaq in TCR signaling. Jurkat TAg T cells with Galphaq knockdown displayed reduced activation of Lck and LAT phosphorylation, but paradoxically showed sustained ERK1/2 phosphorylation and increased NFAT-AP-1-reporter activity implicating Galphaq in the negative control of downstream signaling and IL-2-promoter activity. Primary T cells isolated from Galphaq-deficient mice had a similar TCR signaling response with reduced proximal LAT phosphorylation, sustained ERK1/2 phosphorylation and augmented immune responses including increased secretion of IL-2, IL-5, IL-12 and TNF-alpha. The effects on NFAT-AP-1-reporter activity were sensitive to the Src family kinase inhibitor PP2 and were reversed by transient expression of constitutively active Lck. Furthermore, expression of constitutively active Galphaq Q209L elevated Lck activity and Zap-70 phosphorylation. Together these data argue for a role of Galphaq in the fine-tuning of proximal TCR signals at the level of Lck and a negative regulatory role of Galphaq in transcriptional activation of cytokine responses.
Ngai
Jacob
J
The Biotechnology Centre of Oslo, Nordic EMBL Partnership, University of Oslo, Oslo, Norway.
Methi
Trond
T
Andressen
Kjetil Wessel
KW
Levy
Finn Olav
FO
Torgersen
Knut Martin
KM
Vang
Torkel
T
Wettschureck
Nina
N
Taskén
Kjetil
K
D016207:Cytokines / Q000096:biosynthesis; D043802:GTP-Binding Protein alpha Subunits, Gq-G11 / Q000502:physiology*; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000502:physiology; D006801:Humans; D019169:Jurkat Cells; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck) / Q000502:physiology*; D050778:NFATC Transcription Factors / Q000502:physiology; D011948:Receptors, Antigen, T-Cell / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*; D013601:T-Lymphocytes / Q000502:physiology; D018808:Transcription Factor AP-1 / Q000502:physiology
D016207:Cytokines; D050778:NFATC Transcription Factors; D011948:Receptors, Antigen, T-Cell; D018808:Transcription Factor AP-1; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D019205:GTP-Binding Protein alpha Subunits, Gs