Extracellular isoforms of CD6 generated by alternative splicing regulate targeting of CD6 to the immunological synapse.
The great majority of mammalian genes yield multiple transcripts arising from differential mRNA processing, but in very few instances have alternative forms been assigned distinct functional properties. We have cloned and characterized a new isoform of the accessory molecule CD6 that lacks the CD166 binding domain and is expressed in rat and human primary cells. The novel isoform, CD6Deltad3, results from exon 5 skipping and consequently lacks the third scavenger receptor cysteine-rich (SRCR) domain of CD6. Differential expression of the SRCR domain 3 resulted in a remarkable functional difference: whereas full-length CD6 targeted to the immunological synapse, CD6Deltad3 was unable to localize at the T cell:APC interface during Ag presentation. Analysis of expression of CD6 variants showed that, while being more frequent in coexpression with full-length CD6, the CD6Deltad3 isoform constituted the sole species in a small percentage of T cells. In the rat thymus, CD6Deltad3 is less represented in double-positive thymocytes but is detectable in nearly 50% of single-positive CD4 or CD8 thymocytes, suggesting that CD6 switching between full-length and Deltad3 isoforms may be involved in thymic selection. Strikingly, CD6Deltad3 is markedly up-regulated upon activation of T lymphocytes, partially substituting full-length CD6, as evaluated by RT-PCR analysis at the single-cell level, by immunoblotting, and by flow cytometry using Abs recognizing SRCR domains 1 and 3 of human CD6. This elegant mechanism controlling the expression of the CD166 binding domain may help regulate signaling delivered by CD6, through different types of extracellular engagement.
Castro
Mónica A A
MA
Group of Cell Activation and Gene Expression, Instituto de Biologia Molecular e Celular, Universidade do Porto, Porto, Portugal.
Oliveira
Marta I
MI
Nunes
Raquel J
RJ
Fabre
Stéphanie
S
Barbosa
Rita
R
Peixoto
António
A
Brown
Marion H
MH
Parnes
Jane R
JR
Bismuth
Georges
G
Moreira
Alexandra
A
Rocha
Benedita
B
Carmo
Alexandre M
AM
D020410:Activated-Leukocyte Cell Adhesion Molecule / Q000378:metabolism; D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D000938:Antigen-Presenting Cells / Q000737:chemistry / Q000276:immunology*; D015703:Antigens, CD / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D000945:Antigens, Differentiation, T-Lymphocyte / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008213:Lymphocyte Activation; D008969:Molecular Sequence Data; D020033:Protein Isoforms / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D051381:Rats; D051116:Receptors, Scavenger / Q000378:metabolism; D017384:Sequence Deletion; D013601:T-Lymphocytes / Q000737:chemistry / Q000276:immunology*; D013950:Thymus Gland / Q000276:immunology
D020410:Activated-Leukocyte Cell Adhesion Molecule; D015703:Antigens, CD; D000945:Antigens, Differentiation, T-Lymphocyte; C062279:CD6 antigen; D020033:Protein Isoforms; D051116:Receptors, Scavenger