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Sequence variation of a novel heptahelical leucocyte receptor through alternative transcript formation
L Barella1, M Loetscher, A Tobler
1Theodor-Kocher Institute, University of Bern, Switzerland.
The Biochemical Journal
|August 1, 1995
Summary
Researchers identified a novel G-protein-coupled receptor, monocyte-derived receptor 15 (MDR15), which is an alternative form of BLR1. Despite structural similarity to chemokine receptors, MDR15 and BLR1 do not bind known chemokines, suggesting undiscovered ligands.
Area of Science:
- Immunology and Molecular Biology
- G-protein-coupled receptor (GPCR) research
- Leukocyte and chemokine signaling
Background:
- Leukocyte activation by chemoattractants (chemokines) occurs via G-protein-coupled receptors.
- Interleukin 8 (IL-8) is a key chemokine involved in leukocyte activation.
- Seven-transmembrane-domain receptors mediate chemokine signaling pathways.
Purpose of the Study:
- To isolate and characterize novel G-protein-coupled receptors involved in leukocyte function.
- To investigate the relationship between a newly identified receptor (MDR15) and known receptors (BLR1).
- To determine the ligand-binding properties and expression patterns of MDR15 and BLR1.
Main Methods:
- cDNA library screening of human blood monocytes to isolate novel receptor genes.
- Southern and Northern blot analyses to study gene structure and mRNA expression.
- Reverse transcription-PCR (RT-PCR) for transcript-specific analysis.
- Ligand-binding assays using radiolabeled chemokines and receptor-expressing cell lines.
Main Results:
- Isolation of a novel 327-amino acid receptor, monocyte-derived receptor 15 (MDR15), from human monocytes.
- MDR15 identified as an alternative transcript of the Burkitt's lymphoma receptor 1 (BLR1), encoded by the same gene.
- High expression of MDR15 and BLR1 transcripts observed in chronic B-lymphoid leukaemia, non-Hodgkin's lymphoma, monocytes, and lymphocytes.
- Despite structural similarity to IL-8 receptors, neither MDR15 nor BLR1 bound to a panel of known chemokines or other ligands.
Conclusions:
- MDR15 and BLR1 represent alternatively spliced transcripts of the same gene, expressed on leukocytes.
- The lack of binding to known chemokines suggests the existence of unidentified chemokine ligands for these receptors.
- Alternative transcript formation, particularly in the 5' coding region, may modulate ligand-binding selectivity of chemokine receptors.