A point mutation in the human CD45 gene associated with defective splicing of exon A

Abstract

CD45 is a receptor-type protein tyrosine phosphatase involved in the regulation of lymphocyte activation. Different CD45 isoforms are generated by alternative splicing of three variable exons (A, B and C). The pattern of CD45 splicing depends upon cell type and state of activation. CD45RA isoforms (containing exon A-encoded sequences) can usually be found on a subset of resting T cells, but not on activated T cells. We have recently described a variant pattern of CD45RA expression which is characterized by continuous expression of CD45RA molecules on activated and memory T cells. Here, we demonstrate that this phenotype is associated with heterozygosity for a point mutation at nucleotide position 77 of exon A, leading to a C-->G transition. This mutation does not change the protein sequence of the CD45RA isoform. We conclude that position 77 is part of a motif necessary for splicing of exon A, which supports the hypothesis that sequences within exons have significant effects on alternative splicing. The mutation of this motif might prevent binding of a transacting splice factor. In the heterozygous state, this mutation is not associated with impaired T cell reactivity. Functional consequences of the homozygous state remain to be elucidated.

The 77C→G Mutation in the Human CD45 (PTPRC) Gene Leads to Increased Intensity of TCR Signaling in T Cell Lines from Healthy Individuals and Patients with Multiple Sclerosis

“…The molecular basis for the aberrant expression of CD45RA is a point mutation at position 77 in exon A (77C3 G) (8,9). The mutation does not change the encoded amino acids but disrupts an exon-splicing silencer that normally represses the use of the 5Ј splice site of exon A (10).…”

The Exon A (C77G) Mutation Is a Common Cause of Abnormal CD45 Splicing in Humans

“…A C to G transversion at position 77 in exon A in the gene encoding CD45 has been shown to be responsible for the retention of CD45RA on T cells in individuals with variant CD45RA splicing (17,18). The transversion changes the sequence of exon A from CCCG to CCGG, which can be detected by restriction digestion with MspI that cuts only the mutant allele into two bands of 72 and 83 bp.…”

“…RT-PCR and immunoprecipitation revealed that only the 205-kDa (AB) isoform of CD45 lacks proper regulation, whereas expression of the 220-kDa (ABC) isoform follows the normal pattern (16). More recently a point mutation in the fourth or A exon of the gene encoding CD45, a C to G transversion at position 77 (C77G), has been shown to prevent the normal splicing of this exon in the affected individuals (17,18). Family studies revealed that the inheritance of the variant CD45RA pattern is that of a single autosomal dominant gene (19) and although these heterozygous individuals are apparently normal, a recent paper has described an association of exon A (C77G) and abnormal CD45 splicing with the development of multiple sclerosis in some families (20).…”

77 C/G mutation in the tyrosine phosphatase CD45 gene and autoimmune hepatitis: evidence for a genetic link

“…12 Changes in CD45 expression may alter immune responses in those patients by affecting activation, adhesion and migration of immune cells. 13 This splice variant was found to be associated with a C-G transition at nucleotide position 77 of exon A in the CD45 gene, 14 and subsequently it was shown that an exonic splicing silencer is disrupted by the mutation. 15 Splice variants of CD45 have been implicated in autoimmunity of humans and mice.…”