Tissue-specific and allelic expression of the complement regulator CD46 is controlled by alternative splicing

Area of Science:

• Immunology
• Molecular Biology
• Genetics

Background:

• CD46 (membrane cofactor protein) is a cell surface glycoprotein involved in complement regulation.
• CD46 protein exhibits heterogeneity, appearing as 66 and 56 kDa bands in lymphocytes.
• CD46 structure includes extracellular domains, a transmembrane region, and a cytoplasmic tail.

Purpose of the Study:

• To investigate the molecular mechanisms underlying CD46 protein heterogeneity.
• To identify the role of alternative mRNA splicing in CD46 isoform generation.

Main Methods:

• Analysis of CD46 mRNA variants using differential splicing of 5 exons.
• Correlation of RNA transcript distribution with protein isoform sizes via SDS-PAGE.
• Investigation of tissue-specific, allelic, and malignancy-related regulatory factors.

Main Results:

• At least 14 CD46 mRNA variants are generated through differential splicing.
• Specific exons (7, 8, 9, 12, 13) are differentially included or excluded, creating distinct isoforms.
• Leukemic cells and EBV-transformed B cells produce a larger 74 kDa CD46 isoform.
• Allelic differences in lymphocytes correlate with inclusion/exclusion of exon 8.
• Placenta and spermatozoa exhibit unique splicing patterns, deleting specific exons.
• All tissues show differential splicing of exon 13, leading to alternative cytoplasmic tails.
• Observed RNA transcript patterns correlate with predicted protein isoform sizes.

Conclusions:

• Alternative mRNA splicing is the primary driver of CD46 glycoprotein heterogeneity.
• Differential splicing generates diverse CD46 isoforms with potentially distinct functions.
• Expression of CD46 isoforms is tightly regulated by various biological factors.