| Secreted Frizzled Related Proteins (sFRPs) are a family of vertebrate proteins which contain homology to the ligand-binding domain of the Frizzled family of transmembrane receptors. sFRPs are ~30-35kD in size and are comprised of 3 domains: a signal sequence, a cysteine-rich domain (CRD) of about 110 amino acids (aa) with high degree of similarity to the Frizzled proteins, including 10 conserved cysteines, and a 175aa conserved hydrophilic carboxy terminal region. Because sFRPs contain a CRD very similar to the region responsible for binding Wnt ligands in Frizzleds, sFRPs are thought to act as soluble antagonists of Wnt signals, often postulated to act as tumor suppressor genes (1). sFRP-4, also known as DDC-4, FrpAP, frpHE and FrzB-2, is expressed in brain, kidney, lung, ovary, prostate, mammary gland, and endometrium (1,2). This protein shows complex functions with respect to cell survival: it is upregulated with apoptosis during ovulation (3), regulates apoptosis in chondrocytes (4), and promotes apoptosis in mammary glands when expressed in transgenic mice (5). On the other hand, sFRP-4 can also act to enhance growth as it is upregulated in endometrial and breast carcinomas (6,7). Since it is not detected in other carcinomas such as the ovary, colon, and pancreas, this suggest that its role in cancer is likely to be tissue dependent (6). In addition sFRP-4 is characterized as a circulating phosphaturic factor expressed by tumors associated with osteomalacia that antagonizes renal Wnt signaling (7). Of all the secreted frizzled related proteins, sFRP-4 is most closely related to sFRP-3 (1). Mouse and human sFRP-4 proteins share 92% amino acid identity. Source: A DNA sequence encoding amino acid residues Met1-Val 346 of human secreted Frizzled Related Protein-4 (sFRP-4) (Accession NP_003005, Rattner, A. et al., 1997, Proc. Natl. Acad. Sci. USA 94(7): 2859-2863) was expressed with a C-terminal 10X his tag in a mouse myeloma cell line, NS0. Molecular Mass: Mature recombinant human sFRP-4 is a monomeric protein. Based on N-terminal sequencing, it starts with Ala22 at its N-terminus. As a result of glycosylation, the recombinant protein migrates with an apparent molecular mass of ~55kD in SDS-PAGE under reducing conditions. Activity: Measured by its ability to inhibit Wnt-3As ability to induce alkaline phosphatase synthesis in the presence of BMP-2 by MC3T3E1 osteoblastic cells. The ED50 for this effect is typically 4-20ug/ml, in the presence of 20ng/ml of rmWnt-3a. Storage and Stability: Lyophilized powder may be stored at -20C. Reconstitute to nominal volume by adding sterile PBS, 0.1% HSA or BSA. Aliquot and store at -20C. Reconstituted product is stable for 12 months at -20C. For maximum recovery of product, centrifuge the original vial after thawing and prior to removing the cap. Further dilutions can be made in assay buffer. |
