PTPN22/Lyp: A novel regulator of integrin signalling and function in T lymphocytes

Abstract

Integrins are large heterodimeric surface receptors that, when engaged, are able to transduce information from the extracellular environment leading to a diverse set of cellular programmes including migratory responses. Despite a wealth of literature describing how integrins on T cells are activated such that they can bind to their ligand, the nature and regulation of the signal transduced via the integrin cytoplasmic tails once the integrin engages its counter-ligand is not yet clear. Here, we report that in primary human and mouse T cells, PTPN22, a cytoplasmic protein tyrosine phosphatase expressed only in immune cells, negatively regulates signal transduction downstream of LFA-1 engagement.

Loss of PTPN22/Lyp expression enhances integrin-mediated adhesion and migration in vitro and in vivo, while overexpression of wild type Lyp-R620 decreased migration. The catalytic activity of PTPN22 was required in order to regulate T cell migration. Co-immunoprecipitation experiments demonstrated that PTPN22 associated with Lck, ZAP-70, Vav and LFA-1 in migrating T blasts. In performing shear flow experiments and biophysical investigations, human individuals homozygous for the disease associated R620W mutation functionally recapitulated the phenotype of PTPN22 knockout mouse cells in that they were more adherent and demonstrated hyperphosphorylation of signalling intermediates downstream of LFA-1 engagement.

Super resolution microscopy revealed that in non-signalling T cells, PTPN22 formed large clusters that appeared to de-cluster following LFA-1 engagement. Suprisingly, the R620W mutation did not appear to impact clustering, but instead lead to less Lyp monomers being retained at the membrane outside of clusters in signalling T cells. A correlate between less Lyp monomers and increased LFA-1 clustering at the leading edge of migrating T cells is demonstrated, with an inverse relationship existing between number of Lyp monomers present at the plasma membrane and LFA-1 clustering.

These studies place PTPN22 as a novel negative regulator downstream of LFA-1 signalling, with a disease predisposing R620W mutation lending itself to a loss-of-function allele that might impact the development of autoimmune disease through dysregulation of integrin function

Date of Award	2015
Original language	English
Awarding Institution	King's College London
Supervisor	Andrew Cope (Supervisor)