V Domain of Human SLAM (CDw150) Is Essential for Its Function as a Measles Virus Receptor

Abstract

Measles virus (MV), a member of the Morbillivirus genus in the Paramyxoviridae family, causes an acute childhood disease which still claims roughly 1 million lives a year. MV is a nonsegmented negative-strand RNA virus with two envelope glycoproteins, the hemagglutinin (H) and fusion (F) proteins (10). CD46 has been shown to be a cellular receptor for vaccine strains of MV such as the Edmonston and Halle strains (9, 25). These strains are capable of infecting all CD46-positive primate cell lines. However, recent clinical isolates of MV, which were usually isolated in the marmoset B-cell line B95a or human B-cell lines, were found to grow only in some primate B-and T-cell lines and human dendritic cells (11,12,14,16,32,33,37,38). By using vesicular stomatitis virus (VSV) pseudotypes bearing MV envelope proteins, we showed that virus entry is a major determinant of cell tropism of the Edmonston and B95a-isolated MV strains (38).Recently, expression cloning, combined with the VSV pseudotype system, allowed us to identify signaling lymphocytic activation molecule (SLAM; also known as CDw150) as a cellular receptor for MV (39). We showed that the cell surface expression of human SLAM (hSLAM) rendered rodent cells susceptible to all MV strains examined, including the Edmonston strain, B95a-isolated strains, peripheral blood mononuclear cell-isolated strains, and MV present in throat swabs from measles patients (39). SLAM, an important costimulatory molecule in lymphocyte activation, is expressed on some T and B cells (2,3,7,22,30,31,34), consistent with MV tropism and pathology including lymphopenia and immunosuppression (10). SLAM contains two highly glycosylated immunoglobulin (Ig) superfamily domains and has structural features placing it within the CD2 family, which includes CD2, CD48, CD58, 2B4, and Ly-9 (8). Like other members of the CD2 family, SLAM comprises an N-terminal membrane-distal V-set domain and a membrane-proximal C2-set domain, followed by the transmembrane segment (TM) and cytoplasmic tail (CY). A recent study showed that mouse SLAM (mSLAM) also shares molecular and functional characteristics with the human counterpart, with its predicted amino acid sequence exhibiting 58% similarity to that of hSLAM (6).In this study, we first examined whether mSLAM can act as a cellular receptor for MV, in an attempt to explain MV's inability to infect mice. We then defined the region of hSLAM that interacts with MV, by constructing various chimeric molecules. We also examined the interaction between MV envelope proteins and recombinant soluble forms of SLAM. The results indicated that the V domain of hSLAM, which binds the MV H protein, is essential for its function as an MV receptor. MATERIALS AND METHODS Cells and viruses.Derivations and culture conditions of cell lines used have been described elsewhere (38). The Edmonston (American Type Culture Collection) and KA (37) strains of MV were grown and titrated on Vero and B95a cells, respectively. Pseudotype viruses (VSV⌬G‫,ء‬ VSV⌬G‫-ء‬EdHF, VSV⌬G‫-ء‬ KAHF, and V...

Crystal structure of measles virus hemagglutinin provides insight into effective vaccines

“…3A). Our previous studies have determined that the putative MV-H-binding site on SLAM includes I60, H61, and V63 on the N-terminal variable domain (25,26). From the structural model for SLAM built based on the crystal structure of the closely related molecule NTB-A (27) (data not shown), these residues plausibly exist in the area extending from one face of the ␤-sheet to membrane-distant loops.…”

“…In addition to currently available live vaccines, antiviral drugs are desirable for the treatment of MV patients. Our study clearly shows that the negatively charged SLAMbinding site, which seems to electrostatically complement the MV-H-binding site on SLAM (25,26), serves as the main target for drugs/antibodies that block MV entry. Our model (SI Fig.…”

Distinct Kinetics for Binding of the CD46 and SLAM Receptors to Overlapping Sites in the Measles Virus Hemagglutinin Protein

“…The low kinetic association rate of the SLAM molecule suggests binding of the receptor molecule to the relatively inaccessible inner cavity of the ␤-propeller, where sialic acid binds to the NDV neuraminidase. The N-terminal domain of SLAM is the MV-binding domain (30). Therefore, as shown for binding of ICAM-1 to rhinoviruses (29), we predicted that the loops in the tip of the MV-binding domain of SLAM would penetrate into the cavity of the propeller, as illustrated in Fig.…”

Morbilliviruses and human disease

“…There is still some controversy about the usage of different receptors by different MV strains. If wild-type viruses exclusively use CD150 [38,40], which is not expressed on epithelial cells, this means that they cannot be infected by the inhaled virus. In that case, initial replication of the virus can only take place in tissue resident lymphocytes, macrophages or dendritic cells that express SLAM.…”