Monday, April 15, 2013

VPREB3 and Platelets

VPREB3 protein is the human homolog of the mouse VpreB3 (8HS20) protein, and is specifically expressed in cell lines representative of all stages of B-cell differentiation. It is also related to VPREB1 and other members of the immunoglobulin supergene family. This protein associates with membrane mu heavy chains early in the course of pre-B cell receptor biosynthesis. The precise function of the protein is not known, but it may contribute to mu chain transport in pre-B cells.

This protein doesn’t appear to be detectable in platelet proteome studies but its transcript is present in platelets (detected by both RNA-seq and microarray studies). Its role in platelet biology remains unclear. Even interesting is that the RNA-seq experiment found a much lower expression level than the microarray experiment (0.15 RPKM vs. 27250 MFI). Perhaps the level of gene expression is quite variable from person to person.

CD23 and Platelets

CD (Fc Epsilon Receptor II), has been shown to be present in platelets and may play a role in platelet aggregation. However, none of the publically available platelet proteome databases (Martens et al. Proteomics 2006; Burkhart et al, Blood 2012; Vaudel et al, Journal of Proteome Research 2012) have found this specific protein in platelets. When looking at transcriptome, CD23 RNA doesn’t appear to be present in megakaryocyte (using microarray). However, platelet RNA-seq analysis have found low levels of transcript in platelets (RPKM = 0.37).

While it is easy to speculate why there is such a discrepancy, it is possible that CD23 is induced in people with some allergy exposure and in individuals who are otherwise healthy (as were people in the studies that failed to find CD23), this transcript and its product may not be detectable.

It will be worthwhile to look at individuals with allergic responses (or parasitic infections) and examine whether they have higher expression of CD23 gene and protein. Comparing platelet aggregation in individuals with allergies and those without may also be illuminating.