Elevating calcium in Th2 cells activates multiple pathways to induce IL-4 transcription and mRNA stabilization

Area of Science:

• Immunology
• Molecular Biology
• Cell Signaling

Background:

• T cell activation typically involves stimulation via the T cell receptor (TCR) and co-stimulatory signals.
• Phorbol 12-myristate 13-acetate (PMA) and ionomycin are commonly used to mimic T cell activation and induce cytokine production.
• The specific signaling pathways downstream of ionomycin stimulation in different T helper cell subsets remain incompletely understood.

Purpose of the Study:

• To elucidate the molecular mechanisms by which ionomycin alone induces cytokine production in T cells.
• To identify the key signaling molecules and transcription factors involved in ionomycin-mediated IL-4 and IFN-gamma production.
• To investigate the role of p38 and CaMKIV in T cell cytokine signaling.

Main Methods:

• In vitro and in vivo generation of murine Th1 and Th2 cells.
• Stimulation of T cells with ionomycin.
• Analysis of cytokine production (IL-4, IFN-gamma, IL-2) using relevant assays.
• Assessment of signaling pathway activation, including NFAT, p38 phosphorylation, and CaMKIV activity.
• Gene knockdown experiments (e.g., ASK1) to determine pathway requirements.
• Analysis of transcription factor activation (AP-1) and gene transcription (Il4).
• Investigation of mRNA stabilization mechanisms.

Main Results:

• Ionomycin alone induced Interleukin-4 (IL-4) and Interferon-gamma (IFN-gamma) production in both Th1 and Th2 cells, but not IL-2.
• Ionomycin-induced cytokine production was dependent on Nuclear Factor of Activated T cells (NFAT), p38, and Calmodulin-dependent Kinase IV (CaMKIV).
• Ionomycin triggered p38 phosphorylation via a calcium-dependent, cyclosporine A-sensitive pathway, involving ASK1.
• CaMKIV activation, along with p38, led to AP-1 induction, which cooperated with NFAT for IL-4 gene transcription.
• p38 also contributed to IL-4 production through mRNA stabilization.
• TCR stimulation also activated p38, which was essential for optimal IL-4 and IFN-gamma production.

Conclusions:

• Ionomycin is sufficient to induce specific T cell cytokine profiles (IL-4, IFN-gamma) through distinct signaling pathways.
• The interplay between NFAT, p38, CaMKIV, and AP-1 is critical for regulating T cell cytokine gene expression and production.
• p38 signaling plays a dual role in T cell activation, influencing both gene transcription and mRNA stability for cytokine production.