Insulin-like growth factor II (IGF-II) also known as multiplication stimulating activity (MSA), shows virtually identical bioactivities as IGF-I. Expression of IGF-II is highest in fetal tissues, where it is believed to play a major role in overall growth and development. After birth IGF-II expression decreases to much lower levels in a variety of tissues. IGF-II is produced also in several tumors. IGF-II binds to IGF-II receptor (IGF-IIR), to IGF-IR and weakly to the insulin receptor (IR). All IGF-II bioactivities in adult tissues are generally attributed to its interaction with IGF-IR. However, during embryogenesis the roles of both IGF-IIR and IR may be significant in promoting normal growth.
