An alternative exon 1 of the CD5 gene regulates CD5 expression in human B lymphocytes.
T lymphocytes and a subpopulation of B lymphocytes express the CD5 coreceptor. Its functional importance is evident from the multiple levels and developmental stages of the regulation of its expression. We here report the discovery of a novel regulatory exon upstream of the noncoding region of the CD5 gene in humans. This alternate exon 1 is designated E1B (with the conventional exon 1 renamed E1A) and was shown to regulate the expression of CD5. E1B-containing transcripts existed exclusively in B lymphocytes and encoded a protein that was truncated and retained intracellularly. As a consequence, the amount of E1A-containing transcripts was down-regulated and the membrane CD5 expression was diminished in the presence of E1B-containing transcripts. High levels of E1A transcripts were found in chronic lymphocytic leukemia, and there were no E1A transcripts in 697 pre-B cells, which have no membrane CD5. Introduction of E1B into Jurkat cells reduced their membrane expression of CD5, and sequence analysis revealed that the E1B motif is a defective human endogenous retrovirus. A balance between the 2 alternative exons 1 might be central to the regulation of membrane CD5 in human B cells, and, through CD5-associated SH2-containing phosphatase 1, to the modulation of B-cell antigen receptor-transduced signals.
Laboratory of Immunology, Brest University Medical School, BP824, F29609 Brest Cedex, France.
Yves
Y
Renaudineau
Sophie
S
Hillion
Alain
A
Saraux
Rizgar A
RA
Mageed
Pierre
P
Youinou
D017398:Alternative Splicing / Q000235:genetics*; D001402:B-Lymphocytes / Q000378:metabolism*; D001483:Base Sequence; D018956:CD5 Antigens / Q000235:genetics* / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D030541:Databases, Genetic; D005091:Exons / Q000235:genetics*; D006801:Humans; D042541:Intracellular Space / Q000378:metabolism; D008969:Molecular Sequence Data; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013601:T-Lymphocytes / Q000378:metabolism; D024363:Transcription Initiation Site; D014158:Transcription, Genetic / Q000235:genetics
D018956:CD5 Antigens; D020033:Protein Isoforms; D012333:RNA, Messenger