Epidermal growth factor receptor controls glycogen phosphorylase in T cells through small GTPases of the RAS family

Area of Science:

• Immunology
• Cell Signaling
• Biochemistry

Background:

• The muscle isoform of glycogen phosphorylase (PYGM) is involved in regulating T cell immune function.
• Signaling pathways in lymphoid cells are complex and often involve crosstalk between various proteins.
• Understanding these pathways is crucial for comprehending cellular responses and developing targeted therapies.

Purpose of the Study:

• To elucidate the regulatory pathway of glycogen phosphorylase (PYG) in human T cells.
• To investigate the role of small GTPases RAS and RAP1A, and their regulation by EGFR.
• To identify key components and mechanisms involved in PYG activation.

Main Methods:

• Enzymatic assays
• Pulldown assays
• Immunoprecipitation assays in human Kit 225 lymphoid cells

Main Results:

• Described signaling crosstalk between RAS and RAP1A, regulated by EGFR.
• Demonstrated that adenylyl cyclase type 6 (ADCY6) is essential for PYG activation.
• Showed PYG activation requires EPAC2 and RAP1 stimulation via RAS and ADCY6 phosphorylation (RAF1-mediated).
• Confirmed EGFR-dependency and potential initiation by constitutively active RAS.
• Identified specific inhibitors blocking PYG activation in T cells.

Conclusions:

• Established a novel paradigm for PYG activation dependent on receptor type.
• Highlighted the critical role of the RAS-EPAC2-RAP1-ADCY6-RAF1 axis in PYG regulation.
• Demonstrated EGFR's role in initiating this signaling cascade within T cells.
• Provided potential targets (RAS, EPAC, RAP1, RAF1, ADCY6, PKA) for modulating T cell immune function.