FcRY, an Fc receptor related gene differentially expressed during B lymphocyte development and activation

A bioinformatics approach has lead to the identification of FcRY, a new Fc receptor related gene. FcRY is predicted to encode a protein with three immunoglobulin (Ig) domains followed by a mucin-like domain containing a proline-rich stalk and a C-terminal leucine rich region. The predicted protein lacks a hydrophobic domain for insertion into the plasma membrane, suggesting that FcRY is an intracellular or secreted protein. This feature is shared with the product of the FcRX/FCRL/FREB gene that is closely linked to FcRY in both human and mouse genomes. Fcry transcripts are first detectable among mouse B lineage cells at the pre-B cell stage. Splenic B cells of the newly formed, follicular, and marginal zone subsets express Fcry, as do germinal center B cells to a lesser extent. FcRY is also expressed in subpopulations of human B cells. A consistent characteristic of FcRY in both species is low level gene expression, which can be further downregulated in normal mouse B cells by signaling through the B cell receptor (BCR) or CD40, thereby suggesting a correlation between cell cycle entrance and diminished FcRY expression. Fcry is upregulated by short-term treatment with BAFF/BLyS, which promotes B cell survival rather than proliferation. LPS induces very rapid but transient enhancement. We observed a pronounced upregulation of Fcry expression in WEHI 231 cells induced by BCR crosslinking to undergo cell cycle arrest prior to apoptosis, consistent with the possible regulation of Fcry expression by cell cycle status.