The SDCBP gene is comprised of 9 exons, spanning 2,96 kb on chromosome 8q12.
The SDCBP promoter region has not been functionally explored, although two studies (Lin et al., 1998; Stier et al., 2000) describe SDCBP as an interferon-gamma and TNF-alpha inducible gene. Among predicted transcription factor binding sites upstream the transcription start site of SDCBP there are: Nf-KappaB, Nf-KappaB1 and p53.

Five alternatively spliced transcript variants of SDCBP, each comprising 9 exons, have been described.

SDCBP gene codes for a syntenin protein of 298 amino acid residues with a predicted molecular mass of 33 kDa (Lin et al., 1998; Grootjans et al., 1997). Three isoforms are produced by alternative splicing: isoform 1 (NP_001007068.1) which represents the full-length protein of 298 aa; isoform 2 (NP_001007069) of 292 aa missing residues 12-17; isoform 3 (NP_001007070) of 297 aa missing residue 81. Syntenin is a scaffolding protein, endowed with several biological activities and involved in cancer metastases development (reviewed in Das et al., 2012a). The molecule has four domains: an N-terminal domain (aa 1-113) with no homology to known structural motifs, two PDZ domains (PDZ-1 aa 114-193 and PDZ-2 aa 198-273) and a COOH-terminal domain. The crystal structure of the two PDZ domains showed independent interaction of each domain with protein targets (Cierpicki et al., 2005; Kang et al., 2004).
Postranslational modifications: syntenin can be phosphorylated on tyrosine (Sulka et al., 2009) and serine residues (Rajesh et al., 2011).

SDCBP is expressed in fetal kidney, liver, lung and brain. In adult high expression is present in hearth and placenta (Lin et al., 1998; Zimmermann et al., 2001). It is also expressed in several human tumor cell lines. Several types of tumors express high levels of SDCBP such as gastric, colon and breast carcinomas (Koo et al., 2002), cutaneous (Helmke et al., 2004) and uveal melanoma (Gangemi et al., 2012).

SDCBP protein is localized to adherens junctions, focal adhesion plaques, inner side of the cell membrane, cytoplasm, endoplasmic reticulum, cytoskeleton (Zimmermann et al., 2001), nucleus (Gangemi et al., 2012) and melanosomes (Basrur et al., 2003). It is also present in cell-released exosomes (Baietti et al., 2012).

SDCBP was identified as melanoma differentiation-associated gene (MDA)-9 (Lin et al., 1998). The same gene was independently cloned and named syntenin, by yeast two hybrid screening. Syntenin interacts through its PDZ domains with the heparan-sulfates syndecans, which are involved in molecular recognition, signaling, and cell trafficking (Grootjans et al., 1997). Through its binding with syndecans and PIP2, syntenin mediates syndecan recycling through endosomal compartments (Zimmermann et al., 2002). This process modulates the surface availability of growth factor receptors such as FGFR, which follows syndecan in the recycling pathway (Zimmermann et al., 2005). Syntenin binds the C-terminal domain of the pro-transforming growth factor α (proTGFα) (Fernández-Larrea et al., 1999) and to the Delta1 ligand of Notch (Estrach et al., 2007), tethering them to the cell surface. In addition, syntenin directly interacts with the C-terminal of Frizzled 7 and supports non-canonical Wnt signaling (Wawrzak et al., 2009).
Syntenin binds to the cytoplasmic tail of the tetraspanin CD63 at the plasma membrane and is therefore part of the tetraspanin-enriched microdomains (Latysheva et al., 2006). The over-expression of syntenin can limit internalization of CD63, suggesting a role for syntenin as a regulator of endocytosis.
Syntenin is involved in the establishment and maintenance of synaptic structures through its interaction with several adhesion molecules, such as neurofascin (Koroll et al., 2001). Presynaptic development also depends upon the interaction of the syntenin PDZ domains with ephrin-B1 and ephrin-B2 (McClelland et al., 2009). SDCBP participates in the formation and maturation of synapses and colocalizes with Glutamate receptors at growth cones (Hirbec et al., 2005). Outgrowth of developing axon is also regulated by syntenin, which provides a scaffold for the serine/threonine kinase Unc51.1 and for Rab5 GTPase (Tomoda et al., 2004).
Syntenin participates in B cell development and differentiation by interacting with interleukin-5 (IL-5) receptor α and the transcription factor Sox4 and mediates IL-5-induced Sox4 activation (Geijsen et al., 2001). Proteosomal degradation of Sox4 is prevented by the binding of its c terminal domain with SDCBP, which contributes to its localization into the nucleus (Beekman et al., 2012).
Syntenin mediates the generation of functional asymmetry in T cells during the cellular response to polarized extracellular cues, through the generation of polarized actin structures (Sala-Valdés et al., 2012).
Syntenin interacts with Ubiquitin through is C- and N-terminal regions and facilitates the recruitment of ubiquitinated proteins to its transmembrane partners. The process is facilitated by syntenin dimerization and is inhibited by phosphorylation of its serin in the N terminal domain mediated by Ulk1 (Rajesh et al., 2011).
Syntenin has a key role in exosome formation through the binding of syndecan 1, syndecan 2, syndecan 3, syndecan 4 with the PDZ domains and ALIX with the N-terminal domain (Baietti et al., 2012).

The SDCBP gene is conserved in chimpanzee, Rhesus monkey, dog, cow, mouse, rat, chicken, zebrafish, and mosquito (NCBI).
Paralog: SDCBP2.
SDCBP is highly related to SDCBP2 at the amino acid level (70% over the PDZ domains) and in the domains organization (Koroll et al., 2001).

Not yet described. Genetic polymorphisms of SDCBP (561 SNPs) have been reported (NCBI) but their relationship to disease is unknown.