GTPase-activating protein (RASAL1) associates with ZAP-70 of the TCR and negatively regulates T-cell proliferation and anti-tumor immunity

• Published in: The Journal of immunology (1950) Vol. 202; no. 1_Supplement; pp. 184 - 184.4
• Main Authors: Rudd, Christopher E, Thaker, Youg Raj, Raab, Monika, Strebhardt, Klaus
• Format: Journal Article
• Language: English
• Published: 01.05.2019
• ISSN: 0022-1767; 1550-6606
• DOI: 10.4049/jimmunol.202.Supp.184.4

Abstract T-cell activation is needed for responses to antigen and controls responses to foreign antigen and cancer neo-antigens in immunotherapy. The full range of signaling events that inhibit T-cell activation and limit anti-tumor reactivity is unclear. Previous studies have identified the importance of phosphatases and E-3 ligases as inhibitors of activation. In this study, we show by a combination of tandem affinity chromatography, co-precipitation and proximity ligation analysis (PLA) that RASAL1, a novel GTPase-activating protein (GAP), binds to ZAP-70 of the TCR complex and inhibits anti-CD3 activation of ERKs and proliferation in T-cells. RASAL1 inhibited via two pathways where it binds and inhibits ZAP-70 activity, and acts as a GAP to inhibit the p21ras-ERK pathway. As a negative regulator, its expression is induced as a consequence of T-cell activation, where it reduced in vitro responses to anti-CD3 and to antigenic peptides presented by dendritic cells (DCs), while having no effect on T-cell dwell times. Further, we show that siRNA knock-down of RASAL1 expression increased in vivo CD4+ T-cell responses to peptide antigen while reducing the pulmonary metastasis of B16 melanoma and the growth of solid EL-4 lymphoma tumors. This anti-tumor effect was accompanied by a marked increase in CD8+ tumor-infiltrating T-cells (TILs) expressing effector molecules granzyme B (GZMB) and interferon γ-1 (IFNγ1). These findings identify RASAL1 as a new negative regulator of T-cell activation and tumor immunity.