Fetuin-B, a second member of the fetuin family in mammals

A set of orthologous plasma proteins found in human, sheep, pig, cow and ro dents, now collectively designated fetuin-A, constitutes the fetuin family. Fetuin-A has been identified as a major protein during fetal life and is a lso involved in important functions such as inhibition of the insulin recep tor tyrosine kinase activity, protease inhibitory activities and developmen t-associated regulation of calcium metabolism and osteogenesis. Furthermore , fetuin-A is a key partner in the recovery phase of an acute inflammatory response. We now describe a second protein of the fetuin family, called fet uin-B, which is found at least in human and rodents. On grounds of domain h omology, overall conservation of cysteine residues and chromosomal assignme nts of the corresponding genes in these species, fetuin-B is unambiguously a paralogue of fetuin-A. Yet, fetuin-A and fetuin-B exhibit significant dif ferences at the amino acid sequence level, notably including variations wit h respect to the archetypal fetuin-specific signature. Differences and simi larities in terms of gene regulation were also observed. Indeed, studies pe rformed during development in rat and mouse showed for the first time high expression of a member of the fetuin family in adulthood, as shown with the fetuin-B mRNA in rat. However, like its fetuin-A counterpart, the fetuin-B mRNA level is down-regulated during the acute phase of experimentally indu ced inflammation in rat.