Murine NKG2D ligands: “Double, double toil and trouble”

doi:10.1016/j.molimm.2008.09.035

Molecular Immunology

Volume 46, Issue 6, March 2009, Pages 1011-1019

https://doi.org/10.1016/j.molimm.2008.09.035 Get rights and content

Abstract

Unlike T and B cells, NK cells lack variable, clonotypic receptors that recognize foreign antigens. Instead, NK cells depend on conserved receptors such as NKG2D. NKG2D recognizes a variety of inducible self-proteins that belong to the non-classical MHC class I family. They include ULBP (1-3), MIC (A & B) in human and H60 (a, b & c), Rae-1 (α-ɛ) and Mult1 in mice. These self-proteins are expressed due to pathological stimuli, share limited amino acid homology and form the molecular basis for NKG2D-mediated activation. Recent studies have vastly improved our understanding of NKG2D receptor-mediated activation, signaling and function. However, a detailed knowledge on the immunobiology of its ligands is lacking. How many is too many? Is NKG2D the only receptor for these ligands? Where are these ligands expressed? What are the molecular mechanisms that regulate their expression? Do normal cells express these ligands? Does the communication between NKG2D receptor and its ligands travel through a two way road? If so, what do the ‘target’ cells get in turn, only death? How efficient are these ligands as molecular targets for NK cell-mediated tumor immunotherapy?

Section snippets

Background

NK cells are the major effector lymphocytes of innate immune system that defend against many forms of viral infections and tumor growth (Karre, 2002). NK cells are granular, bone marrow derived lymphocytes capable of executing ‘natural cytotoxicity’ of target cells without prior sensitizations (Moretta et al., 2001). NK cells also bridge innate and adoptive immune responses through the secretion of a variety of cytokines and chemokines (Biron et al., 1999, Farag et al., 2003, Moser and

Genomic organization of murine NKG2D ligands

Murine NKG2D ligands are located in chromosome 10 (Fig. 1A). Based on their genomic and protein homology, we classify them into three families, H60, Rae-1 and Mult1. H60 family has three members (a, b and c) and the first identified member, Histocompatibility antigen 60a (H60a), is a minor histocompatibility antigen (Malarkannan et al., 1998, Takada et al., 2008). Retinoic acid induced early transcript (Rae-1) family was identified as responders to retinoic acid (Zou et al., 1996, Nomura et

Evolution of murine NKG2D ligands

Organization and sequence homology of NKG2D ligand family indicate that they are generated by multiple rounds of gene duplication and divergence from an ancestral prototypic gene. To compare non-synonymous to synonymous substitutions in their genomic sequences, we generated internal sequence identity plots using PAML program (Yang, 2007). Since the genomic sequences of NKG2D ligands are distributed over multiple giga bases, we selected portions of contigs that represent the intron/exon

Protein structure and affinity of murine NKG2D ligands

NKG2D ligand family has distant structural homology to the classical MHC class I proteins. Murine NKG2D ligands vary in their length and amino acid sequence (Fig. 3). NKG2D ligands H60, Rae-1, Mult1 and the ULBPs have only the α1 and α2 MHC domains. MIC-A and MIC-B contain α1, α2, and α3 MHC domains. Interestingly, none of these ligands are able to bind to the β-2 microglobulin to form the classical MHC class I heterodimeric complexes (Bauer et al., 1998). The α1 and α2 helices of NKG2D ligands

Expression of NKG2D ligands in tumor cells

Clinically, NKG2D ligands can be used as potential molecular targets in NK cell-mediated immunotherapies to cure malignancies. However, past studies including from our laboratory have exclusively used model tumor cells that have been stably transfected to express the NKG2D ligands (Diefenbach et al., 2000, Cerwenka et al., 2000, Regunathan et al., 2005). Therefore, it becomes important to determine the expression of these ligands on naturally occurring tumor cells. Towards this we selected an

NKG2D ligands can be induced in normal cells

Although the expression and function of NKG2D ligands is well documented in tumor cells, their immunological relevance in normal cells is not clear. In BALB mice, H60a mRNA could be detected in multiple tissues including cardiac and skeletal muscles, spleen, thymus and skin, while H60b mRNA is restricted to the cardiac and skeletal muscles. H60c is unique in that its basal transcription was largely limited to the skin (Takada et al., 2008). Although in C57BL/6 strain, H60a gene is not

Molecular mechanisms that regulate the expression of NKG2D ligands

Recent studies have demonstrated that multiple cellular stresses could activate the expression of NKG2D ligands. Therefore, a tightly controlled regulation of NKG2D ligand expression is essential for preventing NK cell recognition of normal cells and their adverse effector functions. In Fig. 6, we have summarized multiple stimuli that have the ability to induce the expression of NKG2D ligands in normal and transformed cells. Transcription of human MIC-A and MIC-B can be induced by heat shock;

Concluding remarks

NKG2D plays a significant role as an activating receptor for NK, NKT and γδ-T cells and co-stimulating for αβ-T. Tremendous progress has been made in identifying and characterizing multiple ligands for NKG2D receptor. These ligands differ in their genomic organization, amino acid sequence, affinity to NKG2D and more importantly in their expression patterns. A rational explanation for the existence of multiple ligands for a single activating receptor, NKG2D, is still lacking. Future studies

References (41)

A. Cerwenka et al.
Retinoic acid early inducible genes define a ligand family for the activating NKG2D receptor in mice
Immunity
(2000)
D. Cosman et al.
ULBPs, novel MHC class I-related molecules, bind to CMV glycoprotein UL16 and stimulate NK cytotoxicity through the NKG2D receptor
Immunity
(2001)
A.V. Furano et al.
L1 (LINE-1) retrotransposon diversity differs dramatically between mammals and fish
Trends. Genet.
(2004)
L. Moretta et al.
Immunobiology of human NK cells
Transplant. Proc.
(2001)
C.A. O’Callaghan et al.
Molecular competition for NKG2D: H60 and RAE1 compete unequally for NKG2D with dominance of H60
Immunity
(2001)
J. Regunathan et al.
NKG2D receptor-mediated NK cell function is regulated by inhibitory Ly49 receptors
Blood
(2005)
A.A. Aravin et al.
The Piwi-piRNA pathway provides an adaptive defense in the transposon arms race
Science
(2007)
S. Bauer et al.
Activation of NK cells and T cells by NKG2D, a receptor for stress-inducible MICA
Science
(1999)
S. Bauer et al.
Expression, purification, crystallization and crystallographic characterization of the human MHC class I related protein MICA
Acta Crystallogr. D. Biol. Crystallogr.
(1998)
C.A. Biron et al.
Natural killer cells in antiviral defense: function and regulation by innate cytokines 31
Annu. Rev. Immunol.
(1999)

S. Boissinot et al.

Adaptive evolution in LINE-1 retrotransposons

Mol. Biol. Evol.

(2001)

L.N. Carayannopoulos et al.

Cutting edge: murine UL16-binding protein-like transcript 1: a newly described transcript encoding a high-affinity ligand for murine NKG2D

J. Immunol.

(2002)

L.N. Carayannopoulos et al.

Ligands for murine NKG2D display heterogeneous binding behavior

Eur. J. Immunol.

(2002)

A. Diefenbach et al.

A novel ligand for the NKG2D receptor activates NK cells and macrophages and induces tumor immunity

Eur. J. Immunol.

(2003)

A. Diefenbach et al.

Ligands for the murine NKG2D receptor: expression by tumor cells and activation of NK cells and macrophages

Nat. Immunol.

(2000)

S.S. Farag et al.

Biology and clinical impact of human natural killer cells 1

Int. J. Hematol.

(2003)

S. Gasser et al.

The DNA damage pathway regulates innate immune system ligands of the NKG2D receptor

Nature

(2005)

M. Girardi et al.

Regulation of cutaneous malignancy by gammadelta T cells

Science

(2001)

V. Groh et al.

Cell stress-regulated human major histocompatibility complex class I gene expressed in gastrointestinal epithelium

Proc. Natl. Acad. Sci. U. S. A

(1996)

V. Groh et al.

Costimulation of CD8alphabeta T cells by NKG2D via engagement by MIC induced on virus-infected cells

Nat. Immunol.

(2001)

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NKG2D recognizes a variety of self-inducible proteins that belongs to the nonclassical MHC class I family, which include (but is not limited to) ULBP (1–6) and MIC (A & B) in humans and H60 (a–c), Rae-1 (α-ε) and Mult-1 in mice. The murine binding affinity to NKG2D differs, with Mult-1 showing the greatest affinity (Samarakoon et al., 2009). IDO is the rate-limiting enzyme that catalyses the first step of the “kynurenine (KYN) pathway”, which quickly exhausts tryptophan (Trp) and leads to an accumulation of KYN metabolites.
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^☆: Quote in the title is from ‘Macbeth’, William Shakespeare.

^☆☆: This work was supported in part by ACS Scholar grant RSG-02-172-LIB; ROTRF grant # 111662730; and NIH grants R01 A1064826-01, U19 AI062627-01, NO1-HHSN26600500032C to S.M.

¹: S.M. is a recipient of ASBMT Young Investigator Award.

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ReviewMurine NKG2D ligands: “Double, double toil and trouble”☆,☆☆

Abstract

Section snippets

Background

Genomic organization of murine NKG2D ligands

Evolution of murine NKG2D ligands

Protein structure and affinity of murine NKG2D ligands

Expression of NKG2D ligands in tumor cells

NKG2D ligands can be induced in normal cells

Molecular mechanisms that regulate the expression of NKG2D ligands

Concluding remarks

Immunity

Immunity

Trends. Genet.

Transplant. Proc.

Immunity

Blood

The Piwi-piRNA pathway provides an adaptive defense in the transposon arms race

Science

Activation of NK cells and T cells by NKG2D, a receptor for stress-inducible MICA

Science

Expression, purification, crystallization and crystallographic characterization of the human MHC class I related protein MICA

Acta Crystallogr. D. Biol. Crystallogr.

Natural killer cells in antiviral defense: function and regulation by innate cytokines 31

Annu. Rev. Immunol.

Adaptive evolution in LINE-1 retrotransposons

Mol. Biol. Evol.

Cutting edge: murine UL16-binding protein-like transcript 1: a newly described transcript encoding a high-affinity ligand for murine NKG2D

J. Immunol.

Ligands for murine NKG2D display heterogeneous binding behavior

Eur. J. Immunol.

A novel ligand for the NKG2D receptor activates NK cells and macrophages and induces tumor immunity

Eur. J. Immunol.

Ligands for the murine NKG2D receptor: expression by tumor cells and activation of NK cells and macrophages

Nat. Immunol.

Biology and clinical impact of human natural killer cells 1

Int. J. Hematol.

The DNA damage pathway regulates innate immune system ligands of the NKG2D receptor

Nature

Regulation of cutaneous malignancy by gammadelta T cells

Science

Cell stress-regulated human major histocompatibility complex class I gene expressed in gastrointestinal epithelium

Proc. Natl. Acad. Sci. U. S. A

Costimulation of CD8alphabeta T cells by NKG2D via engagement by MIC induced on virus-infected cells

Nat. Immunol.

Review
Murine NKG2D ligands: “Double, double toil and trouble”☆,☆☆