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Identification of three alternatively spliced variants of human CD28 mRNA
G Magistrelli1, P Jeannin, G Elson
1Centre d'Immunologie Pierre Fabre, Saint Julien en Genevois, France.
Abstract:
CD28, expressed by T cells, plays a central role in providing costimulatory signals to T cells. The cd28 gene is organized into 4 exons. An alternatively spliced CD28 mRNA lacking most of the exon 2 has been previously evidenced. We report here that non stimulated human T cells express three additional alternatively spliced variants of CD28 mRNA (CD28a-c) in. The CD28a variant, expressed at similar levels to that of the full length CD28 mRNA encoding for the membrane form, lacks exon 3. This deletion introduces (i) a frame shift resulting in the addition of two extra amino acids and a premature stop codon and, (ii) induces the loss of the transmembrane region, suggesting that it could encodes for a soluble monomeric molecule which conserves the binding sites of CD28. The CD28b and CD28c variants, expressed at a low level compared with CD28a, are generated by deletion of most of the 3' end of exon 2 plus exon 3 and exon 2 plus exon 3, respectively. Activated T cells express only the membrane CD28 mRNA. These results suggest that resting human T cells may constitutively express both membrane and soluble CD28 which can differentially regulate the outcome of the T cell response.
Insights
Resting human T cells express soluble CD28 variants, alongside the membrane form, which may influence T cell responses. Activated T cells exclusively express the membrane CD28 mRNA.
Area of Science:
- Immunology
- Molecular Biology
- Cell Biology
Background:
- CD28 is crucial for T cell costimulation, with its gene organized into four exons.
- Previous research identified a CD28 mRNA splice variant lacking most of exon 2.
- The role of alternative splicing in CD28 expression in human T cells requires further investigation.
Purpose of the Study:
- To identify and characterize novel alternatively spliced CD28 mRNA variants in non-stimulated human T cells.
- To investigate the structural and potential functional implications of these variants.
- To determine the expression patterns of CD28 variants in resting versus activated T cells.
Main Methods:
- Analysis of alternatively spliced CD28 mRNA variants in human T cells using molecular techniques.
- Sequencing and structural analysis of identified CD28 mRNA variants.
- Comparison of CD28 mRNA expression in resting and activated T cells.
Main Results:
- Three new alternatively spliced CD28 mRNA variants (CD28a-c) were identified in non-stimulated human T cells.
- CD28a variant, similar in expression to full-length CD28, lacks exon 3, leading to a frameshift and loss of the transmembrane region, suggesting a soluble form.
- CD28b and CD28c variants, expressed at lower levels, result from deletions involving exon 2 and exon 3.
- Activated T cells exclusively express the membrane-bound CD28 mRNA.
Conclusions:
- Resting human T cells constitutively express both membrane and soluble forms of CD28.
- These soluble CD28 variants may play a distinct role in regulating T cell responses.
- Differential expression of CD28 isoforms in resting and activated T cells highlights complex regulatory mechanisms in T cell activation.