A role for Follistatin-like protein 1 (FSTL1) in colorectal cancer

Abstract

Follistatin-like protein 1 [FSTL1, alternative names: TGFβ-induced clone 36 (TSC36) or Follistatin-Related Protein (FRP)] is a glycosylated 308 amino-acid secreted protein expressed in various human tissues (1). It plays various roles in vertebrate development including the dorso-ventral axis establishment and skeletal, lung and ureter development (2). In mice, disruption of the fstl1 gene results in neonatal mortality hours after birth with respiratory distress (3). In human adult tissues FSTL1 mRNA is most abundantly expressed in adipose tissue, urinary bladder, prostate and endometrium (4). FSTL1 belongs to the SPARC (Secreted Protein Acid and Rich in Cysteine) family of proteins together with SPARC, FSTL4, FSTL5, SMOC1, SMOC2, hevin and testican-1, -2 and -3. Similar to other members of the family, FSTL1 possesses a follistatin domain and an extracellular calcium-binding (EC) domain. In human FSTL1 these domains occupy a position from amino acids 31 to 98 and from 113 to 232 respectively (3). More amino-terminal (amino acids 1–20), FSTL1 possesses a signal domain required for secretion of the protein. Carboxyterminal to EC domain, from amino acids 232 to 271 of the protein, a von Willebrand C type domain is present, which functions in protein-protein interactions.