PLCγ1 promotes phase separation of T cell signaling components

Area of Science:

• Immunology
• Cell Signaling
• Biophysics

Background:

• The T cell receptor (TCR) pathway is vital for adaptive immunity, initiating T cell activation upon encountering pathogenic antigens.
• While key TCR pathway components are known, understanding their precise cooperation in signal transduction remains incomplete.
• Phase separation, a biophysical phenomenon, is increasingly recognized for its role in organizing cellular signaling events into dynamic condensates.

Purpose of the Study:

• To investigate the role of phospholipase Cγ1 (PLCγ1) in the spatial organization and signal transduction of the TCR pathway.
• To elucidate the mechanism by which PLCγ1 influences the behavior of the LAT adaptor protein within the TCR signaling complex.
• To explore the impact of PLCγ1-mediated phase separation on downstream T cell activation events.

Main Methods:

• Biochemical assays to determine direct interactions between PLCγ1 and the LAT protein.
• Analysis of LAT protein stability and phosphorylation status in the presence and absence of PLCγ1.
• Computational modeling using patchy particle simulations to understand protein composition effects on cluster formation.

Main Results:

• Phospholipase Cγ1 (PLCγ1) directly cross-links LAT, promoting its phase separation into liquid-like condensates.
• PLCγ1 protects LAT from dephosphorylation by CD45, enhances LAT-dependent ERK activation, and promotes SLP76 phosphorylation.
• A non-monotonic relationship between PLCγ1 concentration and LAT clustering was observed, with simulations explaining regulation by protein composition.

Conclusions:

• PLCγ1 plays a critical role in initiating and regulating LAT phase separation within the TCR signaling pathway.
• This PLCγ1-driven phase separation is a key mechanism for efficient TCR signal transduction and T cell activation.
• The findings reveal a novel biophysical principle governing TCR signaling complex organization and function.