THE MURINE BP-3 GENE ENCODES A RELATIVE OF THE CD38 NAD GLYCOHYDROLASE FAMILY

The murine BP-3 antigen is a variably glycosylated glycosyl-phosphatidylinositol (GPI)-linked molecule that is selectively expressed by early B and T lineage cells and a discrete subpopulation of reticular cells in the peripheral lymphoid organs. It is also expressed on the brush border of intestinal epithelial cells, the lumenal surface of renal collecting tubules and mature myeloid cells. To further explore the nature of the BP-3 antigen, we purified the protein, obtained peptide sequences and used these to isolate cDNA clones. Two BP-3 cDNA clones were found to share the same open reading frame, but to utilize different polyadenylation sites. Expression of a full-length cDNA clone confirmed that it encodes the BP-3 antigen. Northern blot analysis with this cDNA probe revealed BP-3 transcripts of 1.3 and 2.3 kb in various tissues and cell lines representing myeloid, B and T cell lineages, while a probe containing the most 3' untranslated region of the longer cDNA clone hybridized only with the 2.3 kb RNA species. Analysis of the BP-3 cDNA sequence indicates that it represents a previously undescribed gene that shares significant homology with genes encoding nicotinamide adenine dinucleotide (NAD) glycohydrolase of Aplysia californica and the CD38 antigens in mouse and human. However, cells expressing the recombinant BP-3 protein did not exhibit NADase activity, suggesting that it may be a distant relative of NAD hydrolase with different function.