Invariant TCR-triggered protein kinase D activation mediates NKT cell development.

Area of Science:

• Immunology
• Cell Biology
• Molecular Biology

Background:

• Invariant natural killer T (iNKT) cell development in the thymus depends on invariant T cell receptor (iTCR) and CD1d interactions.
• These interactions induce the transcription factor promyelocytic leukemia zinc finger (PLZF), but the upstream signaling pathway is not fully understood.

Purpose of the Study:

• To elucidate the signaling pathway connecting iTCR engagement to PLZF induction during iNKT cell development.
• To identify key molecular players involved in this critical immune cell differentiation process.

Main Methods:

• Utilized T cell-specific protein kinase D (PKD)-deficient mice (Prkd2/3∆CD4) to assess PKD's role.
• Employed knock-in mice with phosphorylation-defective Ikaros (Ikzf1S267/275A) and mice lacking the Ikaros-binding site in the PLZF gene (Zbtb16∆IBS).
• Analyzed PLZF induction, iNKT cell generation, and Ikaros's transcriptional activity on the PLZF gene.

Main Results:

• PKD deficiency severely impaired PLZF induction and iNKT cell generation, which could be rescued by PLZF transgene expression.
• PKD was identified as a kinase phosphorylating Ikaros upon iTCR stimulation.
• Phosphorylation-defective Ikaros mutants and mice lacking the Ikaros-binding site on the PLZF gene showed impaired iNKT cell development, while conventional T cells remained unaffected.

Conclusions:

• Protein kinase D (PKD) acts as a critical link between iTCR signaling and PLZF induction in iNKT cells.
• PKD mediates iNKT cell development by phosphorylating Ikaros, which subsequently drives PLZF transcription.