Modulation of natural killer cell functions by interactions between 2B4 and CD48 in cis and in trans.

Maren Claus,Carsten Watzl,Sabine Wingert

doi:10.1098/rsob.160010

Abstract

SLAM-related receptors (SRRs) are important modulators of immune cell function. While most SRRs are homophilic, 2B4 (CD244) interacts with CD48, a GPI-anchored protein expressed on many haematopoietic cells. Here we show that natural killer (NK) cell-expressed 2B4 not only binds in trans to CD48 on neighbouring cells but also interacts in cis with CD48 on the same cell. 2B4 uses the same binding site to interact with CD48 in cis and in trans and structural flexibility of 2B4 is necessary for the cis interaction. Furthermore, the cis interaction is sufficient to induce basal phosphorylation of 2B4. However, cis interaction reduces the ability of 2B4 to bind CD48 in trans. As a consequence, stimulation-dependent phosphorylation of 2B4 upon binding to CD48 positive target cells is reduced. Interfering with the cis interaction therefore enhanced the lysis of CD48-expressing tumour cells. These data show that the density of 2B4 and CD48 on both the NK cell and the potential target cell modulates NK cell activity.

Highlights

Natural killer (NK) cells are innate lymphoid cells and are important for effective early immune responses against viral infections and tumour formation
To study the impact of this interaction on NK cell function, we investigated the binding of soluble CD48-ILZ fusion protein to 2B4 on primary NK cells and the NK cell line NK92.C1
We assumed that a possible cis interaction between 2B4 and CD48 on the same NK cell might interfere with the binding of soluble CD48-ILZ fusion protein (sCD48) in trans

Summary

Introduction

Natural killer (NK) cells are innate lymphoid cells and are important for effective early immune responses against viral infections and tumour formation. Through the engagement of activating receptors, NK cells are able to recognize and selectively kill transformed or virally infected cells [1] They can secrete various cytokines and chemokines and are involved in modulating adaptive immune responses [2]. Binding of CD48 to 2B4 induces the phosphorylation of four immunoreceptor tyrosinebased switch motifs (ITSMs) in its cytoplasmic tail and recruitment of small adapter proteins SAP and EAT-2 [7]. This in turn activates signalling cascades resulting in NK cell cytotoxicity and production of cytokines such as IFNg and TNF-a. While SAP can bind to all four phosphorylated ITSMs, the third ITSM can recruit the phosphatases SHP-1, SHP-2, SHIP and the inhibitory kinase Csk [7,8]

Methods

Results

Conclusion