CD109 is a gene of 132.53 kb comprising 33 exons and 32 introns. The 5 part of exon 1 and the 3 part of exon 33 are non-coding.

Three splice variants are known. The length of the longest variant is 9464 bp (CDS: 426-4763). mRNA is mainly expressed in skin and testis.

Not known.

CD109 is a GPI-anchored cell-surface glycoprotein and is a member of the alpha-2-macroglobulin/C3,C4,C5 family of thioester-containing proteins (Sutherland et al., 1991; Haregewoin et al., 1994; Smith et al., 1995; Lin et al., 2002). The CD109 protein was first identified as a cell-surface antigen detected by a monoclonal antibody raised against the primitive lymphoid/myeloid cell line KG1a (Sutherland et al., 1991). It was also shown that CD109 carries the biallelic platelet-specific alloantigen Gov (Kelton et al., 1990; Smith et al., 1995).

CD109 is expressed on a subset of fetal and adult CD34⁺ bone marrow mononuclear cells, mesenchymal stem cell subsets, phytohemagglutinin (PHA)-activated T lymphoblasts, thrombin-activated platelets, leukemic megakaryoblasts, endothelial cells, and some human tumor cell lines, but not on fresh peripheral leukocytes and normal bone marrow leukocytes (Kelton et al., 1990; Murray et al., 1999; Giesert et al., 2003).
In normal human tissues other than hematopoietic cells, CD109 is expressed in limited cells including the myoepithelial cells of the mammary, lacrimal, salivary and bronchial glands and the basal cells of the prostate and the bronchial epithelia (Hashimoto et al., 2004; Zhang et al., 2005; Sato et al., 2007; Hasegawa et al., 2007; Hasegawa et al., 2008).
Recently, it has been reported that CD109 is highly expressed in several types of human cancer tissues, in particular squamous cell carcinomas (Hashimoto et al., 2004; Zhang et al., 2005; Sato et al., 2007; Hasegawa et al., 2007; Hasegawa et al., 2008; Järvinen et al., 2008; Hagiwara et al., 2008; Ohshima et al., 2010; Hagikura et al., 2010).

Plasma membrane.

CD109 negatively regulates TGF-beta signaling in keratinocytes by directly modulating TGF-beta receptor activity in vitro (Finnson et al., 2006).

Orthologs: mouse CD109, rat CD109, cow CD109, dog CD109, chicken CD109, hagfish CD109, nematode CD109.
Paralogs: alpha-2-macroglobulin, alpha-2-macroglobulin-like-1, C3, C4, C5, PZP, CPAMD8.

A Tyr703Ser polymorphism of CD109 is associated with Gov^a and Gov^b alloantigenic determination (Schuh et al., 2002).