title: The human CD8β M-4 isoform dominant in effector memory T cells has distinct cytoplasmic motifs that confer unique properties.
abstract: The CD8 co-receptor influences T cell recognition and responses in both anti-tumor and anti-viral immunity. During evolution in the ancestor of humans and chimpanzees, the CD8B gene acquired two additional exons. As a result, in humans, there are four CD8β splice variants (M1 to M4) that differ in their cytoplasmic tails. The M-1 isoform which is the equivalent of murine CD8β, is predominantly expressed in naïve T cells, whereas, the M-4 isoform is predominantly expressed in effector memory T cells. The characteristics of the M-4 isoform conferred by its unique 36 amino acid cytoplasmic tail are not known. In this study, we identified a dihydrophobic leucine-based receptor internalization motif in the cytoplasmic tail of M-4 that regulated its cell surface expression and downregulation after activation. Further the M-4 cytoplasmic tail was able to associate with ubiquitinated targets in 293T cells and mutations in the amino acids NPW, a potential EH domain binding site, either enhanced or inhibited the interaction. In addition, the M-4 tail was itself mono-ubiquitinated on a lysine residue in both 293T cells and a human T cell line. When peripheral blood human T cells expressed CD8αβ M-4, the frequency of MIP-1β secreting cells responding to antigen presenting cells was two-fold higher as compared to CD8αβ M-1 expressing T cells. Thus, the cytoplasmic tail of the CD8β M-4 isoform has unique characteristics, which likely contributed to its selective expression and function in human effector memory T cells.
authors.affiliation: Department of Laboratory Medicine, Yale University School of Medicine, New Haven, Connecticut, United States of America.
authors.forename: Deepshi
authors.initials: D
authors.lastname: Thakral
authors.forename: Maria M
authors.initials: MM
authors.lastname: Coman
authors.forename: Arunima
authors.initials: A
authors.lastname: Bandyopadhyay
authors.forename: Sunil
authors.initials: S
authors.lastname: Martin
authors.forename: James L
authors.initials: JL
authors.lastname: Riley
authors.forename: Paula B
authors.initials: PB
authors.lastname: Kavathas
mesh_terms: D015153:Blotting, Western; D016827:CD8 Antigens / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002478:Cells, Cultured; D054407:Chemokine CCL4 / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism*; D005434:Flow Cytometry; D006801:Humans; D047468:Immunoprecipitation; D016297:Mutagenesis, Site-Directed; D020033:Protein Isoforms / Q000737:chemistry* / Q000378:metabolism*; D017434:Protein Structure, Tertiary
chemical_list: D016827:CD8 Antigens; D054407:Chemokine CCL4; D020033:Protein Isoforms