Recombinant Human Follistatin-like 4 Protein, CF

Follistatin-like 4 (FSTL4) is a presumably secreted member of the follistatin domain-containing protein family (1). Follistatin itself is a potent inhibitor of the TGF-beta superfamily member, activin (1, 2), and this activity is reflected in several other proteins of this family that contain varying numbers of the cysteine-rich follistatin domain. Many of these are matrix proteins such as SPARC and testican for which TGF-beta superfamily inhibition status is presumed but unknown (2, 3). R&D Systems recombinant human FSTL4 inhibits the ability of a TGF-beta superfamily member, BMP-6, to induce osteoblast differentiation of a mouse fibroblast cell line. Human FSTL4 cDNA encodes an 842 amino acid (aa) protein containing a 22 aa signal sequence, a follistatin (EGF- and kazal-like) domain, an EF‑hand calcium-binding motif, and two Ig-like cell adhesion molecule-type (IgCAM) domains (1, 4). The second IgCAM domain contains a consensus sequence for FGF/FGF receptor interaction (4). Mature human FSTL4 shares 84%, 82% and 82% aa identity with mouse, rat and bovine FSTL4, respectively. Identity with other follistatin-like family members is mainly within consensus residues of the follistatin domain. Of two reported human FSTL4 isoforms, one is missing the follistatin and EF‑hand domains, while the other contains all recognized domains, but is truncated after aa 600 (4).