Naive CD4 t cell proliferation is controlled by mammalian target of rapamycin regulation of GRAIL expression

Area of Science:

• Immunology
• Molecular Biology
• Cell Biology

Background:

• Naive CD4 T cells require specific signals for proliferation.
• The E3 ubiquitin ligase gene related to anergy in lymphocytes (GRAIL) is implicated in T cell anergy.
• The Akt-mammalian target of rapamycin (mTOR) pathway regulates cellular processes including translation.

Purpose of the Study:

• To elucidate the role of GRAIL in naive CD4 T cell proliferation.
• To investigate the signaling pathway linking T cell activation to GRAIL regulation.
• To understand the mechanism of action for biotherapeutics affecting T cell proliferation.

Main Methods:

• Analysis of GRAIL expression in quiescent and activated naive mouse and human CD4 T cells.
• Investigating the role of the Akt-mammalian target of rapamycin (mTOR) pathway in regulating GRAIL.
• Assessing the impact of CTLA4-Ig, rapamycin, and anti-IL-2 treatments on T cell proliferation.

Main Results:

• GRAIL is expressed in quiescent naive CD4 T cells and inhibits their proliferation.
• CD28 costimulation and IL-2 signaling activate the mTOR pathway.
• mTOR activation leads to Otubain-1 (Otub1) expression, which degrades GRAIL, enabling T cell proliferation.
• CTLA4-Ig, rapamycin, and anti-IL-2 treatments inhibit T cell proliferation by blocking mTOR-dependent Otub1 expression and maintaining GRAIL levels.

Conclusions:

• A mechanistic pathway links CD28 costimulation, IL-2R signaling, and mTOR activation to naive CD4 T cell proliferation via Otub1 and GRAIL regulation.
• GRAIL's function extends beyond anergy induction to regulating general naive CD4 T cell proliferation.
• Understanding this pathway provides insights into the action of immunomodulatory biotherapeutics.