Cell surface antigen CD109 is a novel member of the α2 macroglobulin/C3, C4, C5 family of thioester-containing proteins

Abstract

Cell surface antigen CD109 is a glycosylphosphatidylinositol (GPI)-linked glycoprotein of approximately 170 kd found on a subset of hematopoietic stem and progenitor cells and on activated platelets and T cells. Although it has been suggested that T-cell CD109 may play a role in antibodyinducing T-helper function and it is known that platelet CD109 carries the Gov alloantigen system, the role of CD109 in hematopoietic cells remains largely unknown. As a first step toward elucidating the function of CD109, we have isolated and characterized a human CD109 cDNA from KG1a and endothelial cells. The isolated cDNA comprises a 4335 bp open-reading frame encoding a 1445 amino acid (aa) protein of approximately 162 kd that contains a 21 aa Nterminal leader peptide, 17 potential Nlinked glycosylation sites, and a C-terminal GPI anchor cleavage-addition site. We report that CD109 is a novel member of the ␣2 macroglobulin (␣2M)/C3, C4, C5 family of thioester-containing proteins, and we demonstrate that native CD109 does indeed contain an intact thioester. Analysis of the CD109 aa sequence suggests that CD109 is likely activated by proteolytic cleavage and thereby becomes capable of thioester-mediated covalent binding to adjacent molecules or cells. In addition, the predicted chemical reactivity of the activated CD109 thioester is complementlike rather than resembling that of ␣2M proteins. Thus, not only is CD109 potentially capable of covalent binding to carbohydrate and protein targets, but the t ½ of its activated thioester is likely extremely short, indicating that CD109 action is highly restricted spatially to the site of its activation. IntroductionTo identify new surface antigens expressed by primitive hematopoietic stem and progenitor cells, we raised a series of monoclonal antibodies (mAbs) against the primitive CD34 ϩ acute myeloid leukemia cell line, KG1a. 1-3 Four of these mAbs-8A3, 7D1, 8A1, and 7C5-recognized a novel glycoprotein of approximately 170 kd that was expressed in a restricted pattern in the hematopoietic compartment and by endothelial cells. 4 Subsequently found to be identified by a number of additional mAbs, this antigen was designated CDw109 in 1993 5 and CD109 in 1996. 6 Antibodies to CD109 recognize monomeric polypeptides of about 170 kd and 150 kd in lysates of KG1a cells, T-cell lines, and activated T lymphoblasts, endothelial cells, and activated platelets. 3,[7][8][9][10][11] Peptide mapping and amino acid (aa) analysis indicate that the 150-kd form is likely derived proteolytically from the 170-kd form. 3,10 An additional band of about 120 kd that is occasionally observed arises through calcium-dependent proteolysis of the larger forms. 3,10 CD109 contains several N-linked endoglycosidase H-sensitive hybrid-type glycans but no O-linked glycans. 3,10 Consistent with this finding, ABH blood group antigens have recently been shown to be carried by platelet CD109. 12 KG1a CD109 is susceptible to cleavage with phosphatidylinositolspecific phospholipase C (PI-PLC), indicating that CD109 is bo...

A sodium dodecyl sulfate–polyacrylamide gel electrophoresis–liquid chromatography tandem mass spectrometry analysis of bovine cartilage tissue response to mechanical compression injury and the inflammatory cytokines tumor necrosis factor α and interleukin‐1β

“…CD109 is a 170-kd glucose-6-phosphate isomerase-linked protein that was recently identified as a member of the ␣ 2 -macroglobulin and the complement C3, C4, and C5 gene family, which are proteins that contain activated thioesters (28). The similarity of CD109 to ␣ 2 -macroglobulin suggests that it may serve as a protease inhibitor in cartilage or may possibly play a role in complement activity.…”

Signaling Receptors for TGF-β Family Members

“…The GPI-anchored protein CD109 belongs to the a 2 -macroglobulin family (Lin et al 2002) and binds TGF-b1 with high affinity and other TGF-b isoforms with lower affinity (Tam et al 1998). It also forms a complex with TGF-b signaling receptors and negatively regulates TGF-b signaling (Finnson et al 2006).…”

Expression of CD109 in human cancer

“…In addition, a sequence for the thioester bond (CGEQ) was found (amino acids 923-926 in Figure 1c) (Hofmann et al, 1999). After completing the sequence, it turned out that this cDNA encoded a mouse orthologue of the human CD109 gene, a member of the a 2 -macroglobulin/C3, C4, C5 family that was recently reported (Lin et al, 2002).…”

“…Lin et al (2002) recently reported the cloning of human CD109 gene that encodes a novel member of the a 2 -macroglobulin/C3, C4, C5 family, including a 2 -macroglobulin-like protease inhibitors and complement proteins. The amino-acid identity between human and mouse genes was approximately 69%.…”