The recombinant third domain of human alpha-fetoprotein retains the antiestrotrophic activity found in the full-length molecule

Previous studies have shown that alpha-fetoprotein (AFP) interferes with es trogen (E-2)-stimulated growth, including E-2-stimulated breast cancer grow th. In an effort to localize the antiestrophic portion of the molecule, the C-terminal one-third (200 amino acids) of human AFP, known as Domain III, was produced in a baculovirus expression system as a fusion protein contain ing an amino terminal histidine tag. The histidine tag was included to faci litate purification by metal ion affinity chromatography. The purified reco mbinant Domain III fusion protein was functionally similar to full-length n atural AFP isolated from human cord sera or from cultured human hepatoma ce lls (HepG2) in that they all produced significant and quantitatively simila r inhibition of E-2-stimulated growth of immature mouse uterus, Furthermore , the dose-response profiles of the recombinant Domain III AFP and natural full-length AFP were similar. Preincubation of either protein in a molar ex cess of E-2 lowered the minimally effective antiestrotrophic dose and produ ced a difference spectrum consistent with a change in conformation. These f indings indicate that the antiestrotrophic activity of AFP is contained wit hin the third domain of the molecule, and they have obvious implications fo r the production of biologically active peptides derived from this portion of the AFP molecule. (C) 1999 Elsevier Science B.V, All rights reserved.