Human alpha-fetoprotein contains potential heterodimerization motifs capable of interaction with nuclear receptors and transcription/growth factors.

Alpha-fetoprotein (AFP) serum levels in man have long been utilized as a tumor marker and as a birth defect screening agent in the clinical laboratory. Although the physiological role of AFP has remained obscure, the stereotypic carrier/transport function of a fetal counterpart to albumin has been attributed to this oncofetal protein. However, reports from a multitude of investigators in the last decade have provided a rationale to reconsider and extend the biological role of AFP to include cell growth modulation during development. Previously, a leucine zipper-like (heptad) motif, which mimicked that found in the steroid/thyroid receptor superfamily, was postulated for portions of the third domain of AFP. The present report proposes the presence of additional potential heterodimerization sites for the nuclear receptor superfamily members and other growth factors in the second and third domains of human AFP.