Residues Y429 and Y463 of the human CD5 are targeted by protein tyrosine kinases

Abstract

The human CD5 lymphocyte cell surface co‐receptor modulates activation and differentiation responses mediated by the antigen‐specific receptor of T and B cells. CD5 is phosphorylated followinglymphocyte activation; however, the exact sites and kinases involved are yet to be determined. Jurkat T cell transfectants expressing tyrosine‐mutated CD5 molecules have been used to show that residues Y429 and Y463 are targeted in vivo by protein tyrosine kinases following cell stimulation with anti‐CD3 mAb or pervanadate. This is in agreement with data from direct in vitrokinase assays using purified recombinant Lck and Fyn protein tyrosine kinases. The analysis of Lck‐ and CD3‐deficient Jurkat cells shows that tyrosine phosphorylation of CD5 requires Lck activity. We propose that T cell activation mediates CD5 tyrosine phosphorylation at residues Y429 and Y463 mainly through the activation of Lck.

Functional requirement of tyrosine residue 429 within CD5 cytoplasmic domain for regulation of T cell activation and survival

“…This possibility is in agreement with the demonstration that Y441, unlike Y429 and Y463, is not phosphorylated by Lck upon TCR activation [4,5]. In this context, the pseudo-ITAM of CD5 is not encoded by a single exon as classical ITAMs are [4]. Moreover, when hemi-phosphorylated, some ITAM regions can behave as ITIM regions [33].…”

“…Indeed, the "pseudo ITAM" region of hCD5 was postulated to play a crucial role in RasGAPmediated TCR downregulation, through a mechanism that involves the inactivation of ERK [21]. This possibility is in agreement with the demonstration that Y441, unlike Y429 and Y463, is not phosphorylated by Lck upon TCR activation [4,5]. In this context, the pseudo-ITAM of CD5 is not encoded by a single exon as classical ITAMs are [4].…”

“…Briefly, 10 7 EL4 cells were transfected with 10 mg of Nde-I linearized wild-type and mutant CD5 constructs. The generation and cloning of human CD5 constructs (WT, Y429A, Y441A, Y463A and YYY/AAA) was done as previously reported [4]. Using G418 as a selection marker, clones were enriched; after this, the different mutants were selected for similar mCD3 hi and hCD5 hi expression using a FACSAria I Cell Sorter (BD Biosciences).…”

“…Three major signal transductionrelated motifs can be found within the cytoplasmic region of CD5. First, a "pseudo-ITAM" domain, comprising Y429 and Y441 residues; second, a Casein Kinase 2 (CK2) binding domain (S458eS461) (CK2-BD) near the carboxy-terminal region of CD5 [3] and finally a distal Y463 residue [4,5]. Upon TCR engagement, these domains become phosphorylated allowing the recruitment of several signaling proteins including p56lck, TCRz chain, PI3K, c-Cbl, RasGAP [6,7] and CK2 [8].…”

Greater frequency of CD5-negative CD8+ T cells against human immunodeficiency virus type 1 than other viruses is consistent with adaptation to antigenic variation

“…The group B cysteine-rich scavenger receptor CD5 modulates antigen-specific signaling on virtually all T cells in a ligand-independent manner [1-5]. When T cells form conjugates with antigen-presenting cells, CD5 colocalizes with TCRs engaging cognate MHC/peptide complexes within the immunological synapse and recruits SHP phosphatases to the area through its cytoplasmic tyrosine inhibitory motif (ITIM), [3,6]. Thus, localized antagonism of phosphorylation events by CD5 diminishes TCR-derived activation signals [7].…”