PRR7 Is a Transmembrane Adaptor Protein Expressed in Activated T Cells Involved in Regulation of T Cell Receptor Signaling and Apoptosis

Matouš Hrdinka,Peter Dráber,Ondřej Štěpánek,Tereza Ormsby,Pavel Otáhal,Pavla Angelisová,Tomáš Brdička,Jan Pačes,Václav Hořejší,Karel Drbal

doi:10.1074/jbc.m110.175117

Abstract

Transmembrane adaptor proteins (TRAPs) are important organizers and regulators of immunoreceptor-mediated signaling. A bioinformatic search revealed several potential novel TRAPs, including a highly conserved protein, proline rich 7 (PRR7), previously described as a component of the PSD-95/N-methyl-d-aspartate receptor protein complex in postsynaptic densities (PSD) of rat neurons. Our data demonstrate that PRR7 is weakly expressed in other tissues but is readily up-regulated in activated human peripheral blood lymphocytes. Transient overexpression of PRR7 in Jurkat T cell line led to gradual apoptotic death dependent on the WW domain binding motif surrounding Tyr-166 in the intracellular part of PRR7. To circumvent the pro-apoptotic effect of PRR7, we generated Jurkat clones with inducible expression of PRR7 (J-iPRR7). In these cells acute induction of PRR7 expression had a dual effect. It resulted in up-regulation of the transcription factor c-Jun and the activation marker CD69 as well as enhanced production of IL-2 after phorbol 12-myristate 13-acetate (PMA) and ionomycin treatment. On the other hand, expression of PRR7 inhibited general tyrosine phosphorylation and calcium influx after T cell receptor cross-linking by antibodies. Moreover, we found PRR7 constitutively tyrosine-phosphorylated and associated with Src. Collectively, these data indicate that PRR7 is a potential regulator of signaling and apoptosis in activated T cells.

Highlights

LAT [2, 3], PAG [4, 5], NTAL [6, 7], and LIME [8, 9], whereas others (LAX, SIT, TRIM, GAPT) are present in non-raft membrane (10 –13)
N-terminal part of proline rich 7 (PRR7) as well as sequences surrounding tyrosines 153 and 166 form a putative domain identified in Pfam data base [26] as the WBP-1 domain (PF11669). This domain is present in WW domain-binding protein 1 (WBP-1) where it mediates the interaction with WW domains of Yes-associated protein (YAP) via tandem PPXY motifs in its C terminus [27]
We observed that in Jurkat clones with inducible expression of PRR7 (J-iPRR7) cells, apoptosis could be clearly detected within 24 h of induction by RSL1 and gradually increased with time (Fig. 3, B and C), suggesting that apoptosis induction was a direct consequence of PRR7 expression

Summary

Introduction

LAT [2, 3], PAG [4, 5], NTAL [6, 7], and LIME [8, 9], whereas others (LAX, SIT, TRIM, GAPT) are present in non-raft membrane (10 –13). Similar motifs encompass tyrosines 153 and 166 in PRR7, suggesting possible involvement of this region in an interaction with a WW domain containing protein (Fig. 1C). We observed that in J-iPRR7 cells, apoptosis could be clearly detected within 24 h of induction by RSL1 and gradually increased with time (Fig. 3, B and C), suggesting that apoptosis induction was a direct consequence of PRR7 expression.

Results

Conclusion