The intracellular fragment of ERBB4, ERBB4s80 (E4ICD), binds to the promoter region of the SPARC gene. The ERBB4s80 binding site overlaps with binding elements for BRACH, ATF6, ATF and XBP1 transcription factors (Wali et al. 2014).
The intracellular fragment of ERBB4, ERBB4s80 (E4ICD) stimulates transcription of the SPARC gene, encoding Basement-membrane protein 40 (BM-40) (Wali et al. 2014).
Secreted protein acidic and rich in cysteine (SPARC), also known as osteonectin or BM-40, binds Collagen type I, hydroxyapatite and Ca2+, suggesting a role in the mineralization of bone and cartilage (Termine et al. 1981). It is expressed by osteoblasts, odontoblasts, and many other cell types (Romanowski et al. 1990, Mundlos et al. 1992, Papagerakis et al. 2002). SPARC expression has been used to follow the progression of osteoblast cytodifferentiation.
The long splice version of the PDGF-A chain as well as the COOH-terminal part of the PDGF-B precursor contain C-terminal protein motifs that confer retention of the secreted factors. In both the PDGF A- and B-chains, exon 6 encodes a basic sequence that mediates interaction with components of the extracellular matrix. PDGF binds to various types of collagens, thrombospondin and osteopontin; however, the major component of the matrix involved in PDGF binding is likely to be haparan sulphate. The negatively charged sulfate groups on the disaccharide building blocks of heparan sulfate (HS) polysaccharide chains provide binding sites for positively charged amino acid sequence motifs. The precursor of the B-chain may be retained in the matrix; after maturation when the COOH-terminal retention sequence has been cleaved off, the molecule may become more diffusible.
Compartment:
plasma membrane,
extracellular region
STAB1 (FEEL-1) binds acetylated low density lipoprotein (LDL) (Adachi & Tsujimoto 2002, Palani et al. 2011), phosphatidylserine (exposed when cells are lysed) (Park et al. 2009), advanced glycation end products (AGE) (Tamura et al. 2003, Hansen et al. 2005), and Osteonectin (SPARC) (Kzhyshkowska et al. 2006).