Characterization of human FCRLA isoforms

Area of Science:

• Immunology
• Molecular Biology
• Cell Biology

Background:

• Fc receptor-like protein A (FCRLA) is a B-cell specific, ER-resident protein with an unclear function.
• Human FCRLA interacts with immunoglobulins M, G, and A.
• ER retention is mediated by FCRLA's N-terminal domain.

Purpose of the Study:

• To investigate the functional impact of alternative splicing in human FCRLA.
• To determine how variations in the signal peptide length affect FCRLA processing and localization.
• To characterize novel FCRLA transcripts encoding proteins with longer signal peptides.

Main Methods:

• Analysis of human tissue transcripts for alternative FCRLA splicing.
• Transfection experiments to express different FCRLA isoforms.
• Assessment of protein topology, molecular mass, processing, glycosylation, and secretion.

Main Results:

• Human tissues express FCRLA transcripts with an additional exon, resulting in a longer signal peptide (LSP).
• The LSP had no effect on the topology or mass of the four-domain FCRLA.
• In two-domain FCRLA isoforms (FCRLAd2), the SSP-FCRLAd2 accumulated in the ER due to uncleaved signal peptide, while LSP-FCRLAd2 was processed, O-glycosylated, and secreted.
• The secreted LSP-FCRLAd2 isoform did not bind IgG or IgM.

Conclusions:

• Signal peptide length is a critical determinant for the processing and cellular fate of specific FCRLA isoforms.
• Alternative splicing leading to LSP variants can alter FCRLA secretion and potentially its function.
• The secreted FCRLAd2 isoform's lack of immunoglobulin binding suggests distinct roles for different FCRLA variants.