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Volume 96, number 1 FEBS LETTERS December 1978

BINDING SPECIFICITY OF ESTROGENS AND NORANDROGENS TO RAT a-FETOPROTEIN (AFP)

Vera VERSGE and AndrC 0. BAREL Algemene en Biologische Scheikunde. Vrije Universiteit Brussel, 65 Paardenstraat, B-l 640 Sint Genesius Rode. Belgium

Received 28 September 1978

1. Introduction obtain binding with AFP. A strong binding (binding constant 107-lo8 M-l) of some 19-norandrogens to Most of the recent binding experiments AFP was also observed. with rat oc-fetoprotein (AFP) were considered and realized in relation with the well-known microhetero- geneity of this protein. Some differences were found 2. Materials and methods [l] in binding capacity of the various forms, while essentially identical binding properties for the iso 2.1. Chemicals cY-fetoproteins were reported [2- 41. There are only [2,4,6,7-jH] was purchased from the scant reports concerning the binding of this fetal Radiochemical Center, Amersham. Unlabelled protein with non- ligands. The presence of fatty were periodically tested for purity by thin-layer acids on human AFP has been shown [5], a bilirubin chromatography.Steroidsnumber 1,4,5.9,11,12,14,15 binding site on AFP revealed [6] and interaction and 17 (see table 1 for a complete list of steroids) between aflatoxin B1 and AFP reported [7]. were obtained from Sigma Chemical Co., St Louis. Binding specificity studies of AFP with various Steroids number 3,6,7.8,16 and 18 were kindly steroids are necessary since they provide a better provided by Dr Zeelen, Organon, Oss. Steroids insight in the biological role of this carcino-fetal number 2 and 10 were kindly provided by Dr Pons, globulin [8,9] particularly in comparison with the rat University of Montpellier. Finally steroid number 13 uterus estradiol receptor [lo]. Up to now very few was a gift of Dr Leclercq, University of Brussels. Blue quantitative data have been collected for non-estrogen Sepharose was purchased from Pharmacia, Uppsala. steroids [2,11,12]. A large number of steroids has All the other reagents were reagent grade. been investigated [ 131 by studying the diminution of the fluorescence of a dye bound to the protein 2.2. Pwifica tion (1 -aniline-naphthalene-8-sulfonate). However, this Rat AFP was isolated from the amniotic fluid and last method implies that competition exists between the fetal serum of Wistar rats by preparative slab gel the dye and the steroid for the same site. electrophoresis on polyacrylamide as in [2]. Before We describe here the displacement experiments of electrophoresis, the crude AFP solution was passed bound radiolabelled estradiol with 18 steroids through a Blue Sepharose C 1-6B column in order to (estrogens and non-estrogens). The displacement data selectively remove most of the albumin fraction. were examined using a simple linear analysis in order to obtain binding constants between AFP and the 2.3. Binding Experiments considered steroids. The obtained results provide sub- The association constant for the estradiol-AFP stantial evidence that the steroid does not necessarily interaction was obtained by equilibrium dialysis with have to contain the estratriene skeleton in order to Sephadex G-25, at pH 8.5 and 25”C, in a batchwise

Elsevier/North-Holland Biomedical Press 155 Volume 96. number 1 I.EBS LETTERS December 1978 fashion as in [1-,141 using radiolabelled estradiol. In order to determine the interactions of unlabelled steroids with AFP, displacement experimentsof bound radiolabelled estradiol were carried out. A constant 10 amount of [3H]estradiol (10 or 50 pmol) and AFP ( 150 pmol) was added to each tube containing a con- stant weight of Sephadex G-25 in buffer, pH 8.5. Various quantities of unlabelled steroid were added (from 50 7000 pmol) in order to displace the bound [3H]estradiol. From the radioactivity of the external volume, the amount of labelled estradiol bound to AFP was calculated as in [ 151. The residual binding 5 10 was plotted against the total amount of added steroid. (FIBIES The quantity of steroid necessary to obtain, for Fig.1 Competition for the estradlol bmdmg site of ArP. DIS- example, 10% displacement was then graphically placement of bound [ ‘fl]estrad~ol with 3-acetylestronc (, ‘- ) determined. As a result of the mass law, the equilibrium and 1 la-hpdroxyestrone (0-o). Data are presented accordmg relationship between estradiol and the steroid for a to the equation in section 2.3. The free/bound for the steroid single binding site is given by the following equation: (F/B)* IS plotted agamst the free/bound for eatradlol (F/B)l:S,

3.2. Bimhg data with the other steroids In order to determine the interactions between AFP and several other ligands. experunents of dls- where B = bound, F = free, K = association constant. placement of tritiated estradiol were cal-ried out. The subscripts A and ES refer to steroid and radio- Table 1 summarizes the interference of 18 derivatives labelled estradiol, respectively. The ratio of the with respect to estradiol. For convenience, the ligands intrinsic association constants, KA/KES may be con- were classified as: sidered as an index of cotnpetition. If K,, is known, (i) Compounds which compete successfully with the value of K, can be readily calculated from the estradiol; slope of the linear plot, when (F/B)* is plotted in (ii) Compounds which compete very poorly; function of (F/BjEs. The advantage of this equation (iii) Those which have no significant displacement is to obtain in a very convenient graphical analysis capacity. the ratio of the binding constants. As an example of However, for the last two types of compounds, a 50% this plot, fig.1 illustrates the displacement of bound inhibition was not reached at saturating concentra- [“Hlestradiol b y 3- acetylestrone and 1 la-hydroxy- tions and therefore no competition index could be . calculated. First the identification of the determinant regions of the 2stratriene skeleton for binding with AFP was considered. As essential factors for estrogen binding 3. Results and discussion we pointed out that addition of a hydroxyl group at position C ,(, (derivatives 11 and 12) or alkylation of 3.1 Binditzg data bclithestradiol the 17/3hydroxyl group (derivative 10) or a change in As described [2], rat AFP binds 17P-estradiol orientation of the C I’ hydroxyl group (derivative 14) maximally at pH 8.5 with an association constant of result in an extensive decrease m affinity for AFP. 5 * 1 X 10’ M-l. The Scatchard plots always gave On the other hand modification at position C3 (alkyla- straight lines suggesting that AFP displays only a tion of the hydroxyl group. derivative 2) or mtroduc- single class of binding sites (stoichlometry of tion of a hydroxyl group at position C,, (comparison binding 0.9 If 0.1). between estrone and 1 la-hydroxyestrone. derivative 3)

156 Volume 96, number 1 FEBS LETTERS December 1978

Table 1 Competition between tritiated estradiol and various steroids for binding on AFP

Steroid Number of Steroid, pmol added in order Competition Binding derivative to obtain 20% displacement index KAjK~s constant (M-l)

(i) Compounds which compete - 17p-Estradiol ref. 127 1 .oo 5 x 10’ Estrone 1 107 1.85 9x 10’ 3-Acetylestrone 2 129 0.95 5 x lo7 1 lol-Hydroxyestrone 3 213 0.33 2x lo7 Equiline 4 606 0.08 4x lo6 17~ 5 940 0.05 3x lo6 19-NorandrostGene-17p-01 6 92 5.55 3x lo8 19-Norandrost+ene-17~01 7 775 0.06 3 x 10” 19-Norpregn4-ene-20S-ol 8 125 1.04 5 x lo7 19-Nortestosterone 9 1306 0.04 2x lob

(ii) Compounds which compete poorly

17p-Acetylestradiol 10 2000 160,17P- 11 3500 16p,l’I@ 12 3500 _ _ 17p-Estradiol-6-one(Ocarboxy- methyl)oxime 13 4360 0.01 6 x lo5 17~Estradiol 14 7000 _ _

(iii) Compounds which do not compete

17P- 15 _ 17ol-Testosterone 16 _ Androstadiene-3,17-dione 17 _ Androstd-ene-17p-01 18 _

does not modify extensively its binding with this fetal succinateesepharose gel would be a more efficient protein. Finally, modification of the estratriene affinity adsorbent for the purification of AFP as the skeleton at position C, (addition of a ketoxime group, 7&derivative of estradiol used in [ 18,191. derivative 13) or introduction of a C7 -Cs double According to the well-known estrogenic binding bond (comparison between estrone and equiline, properties of AFP, the importance of an aromatic derivatives 1 and 4) result in an important decrease in A ring among the factors intervening in steroid affinity. However, these steroids still show some dis- recognition was emphasized [ 131. We observed a placement capacity. Therefore, a major factor in the virtual lack of displacement capacity for all the chosen AFP-estradiol interactions resides in the integrity of with a Cr,, methyl group (derivatives the /3-hydroxyl configuration (change of configuration number 15-l 8). On the other hand the nor-derivatives or alkylation). This hypothesis does not agree with of testosterone and androst4-ene-17/3-01 (derivatives [ 131 where it was concluded that AFP was very little number 6-9) are very effective in displacing bound influenced by modification of the estrogens at C r7. estradiol. Particularly striking is the comparison The synthesis of appropriate specific affinity labels between androst-4-ene-17/l-01 which has no displace- for AFP should preferentially involve modifications ment capacity and its 19-nor derivative which is of the estratriene skeleton at positions C3 or C rr. For characterized by an inhibition constant of 3 X 1 OS M-', example, the synthesis of an estrone-3-monohemi- greater than that of estradiol. It may also be noted,

157 Volume 96, number 1 FEBS LETTERS December 1978

similarly to that observed for the 170(- and p-isomers [3] Aussel,C. and Masseyeff, R. (1977) FEBS Lett. 81. of estradiol, that the /3-enantiomer of 19norandrost- 363-365. 4-ene-17-01 is much more strongly bound to AFP than [4] Aussel. C., Kerckaert, J. P. and Bnyard, B. (1978) Blochim. Biophys. Acta 533, 504-510. the oc-enantiomer. [S] Parmelee, D. C., Evenson. $1. A. and Deutsch. H. F. This study clearly shows the high affinity of some (1978) J. Biol. Chem. 253, 2114 -2119. 19-norsteroids for the estradiol binding site of AFP. L61 Versie, V. C. and Barel. A. 0. (1978) Fed. Proc. Fed. The addition of a C1, methyl group prevents the Am. Sot. Exp. Biol. 37, 1620. abstr. no. 1928. binding of the . In disagreement with the [71 Evrain, C., Cittanova, N. and Jnyle, M. F. ( 1978) Biochim. Biophys. Acta 533,408-414. hypothesis defended [ 131, it is suggested here that ISI McEwen. B. S., Plapinger, L.. Chaptal, C.. Gerlack, J. AFP interacts strongly with 19-norandrogens where and Waliach, G. (1975) Brain Res. 96,400 -406. the A ring is no longer aromatic. As a consequence [91 Keller, R. H.. Calvanico, N. J. and Tomasi, T. B. jr it would be of interest to devise affinity labels start- (1976) in: Once-Developmental Gene Expression ing from the skeleton of 19+orandrogens, since these (Fishman, W. H. and Sell, S. eds) pp. 287-295. Radanyi. C., Mercier-Bodard, C.. Secco-Millet, C., compounds are generally much more soluble in water llO1 Baulieu. E.-M and Richard-Foy, H. (1977) Proc. than estrogens. Natl. Acad. Sci. USA 74, 2269-2272. 1111 Liang-Tang, L. K. and Soloff. M. S. (1972) Biochim. Biophys. Acta 263, 753-763. Acknowledgements [I21 Payne, D. W. and Katzenellenbogen. J. A. (1978) Fed. Proc. Fed. Am, Sot. Exp. Biol. 37, 1663 (abstr. no. 2168) This work was financially supported by the [I31 Laurent. C., de Lanzon. S., Cittanova, N., Nunez, E. and Jayle. M. F. (1975) Biochem. J. 151,513-518. Programmatie van Wetenschapsbeleid, conventie [I41Pearlman, W. H. and Crkpy. 0. (1967) J. Blol. Chem. nr, 77/81-119. The authors thank Mrs M. Gesquiere 242,182-189. and I. Peeters for expert technical assistance. [ 151 Goertz, G. R., G&in, M. R., Crdpy, 0. C.. Longchampt, J. E. and Jayle. M. F. (1973) EurlJ. Biochem. 35, 311-317. References 1161 Cheng, Y. and Prusoff, W. H. (1973) Blochem. Pharma- col. 22,3099-3108. [l] Benassayag, C., Vallette, G., Cittnnova, N., Nunez, E. 1171 Scatchard, G. (1949) Ann. NY Acad. Scl. 51,660-672. and Jayle. M. F. ( 1975) Biochim. Biophys. Acta 4 12. [I81 Amon. R., Teicher, E., Bustin, M. and Sela, M. (1973) 295-305. FEBS Lett. 32, 335-338. [2] Verske. V. and Barel. A. 0. (1978) Biochem. J. 173. 1191 Uriel. J., Boudlon, D. and Dupiers, M. (1975) FEBS 73-81. Lett. 53, 305.-308.

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