Presence of estrogen receptor (ER)-like proteins and endogenous ligands for ER in solanaceae

Abstract

The synthesis of steroid hormones in different plant species and the possibility that these molecules could regulate cell growth, tissue differentiation and germination has been reported. However, the mechanism of action of these endogenous steroids in plant cells is still poorly understood. In the present work, binding experiments with [3H]17β-estradiol in the presence and absence of an excess of unlabeled 17β-estradiol showed that Solanum glaucophyllum and Lycopersicon esculentum organs contain estrogen-binding sites. Scatchard analysis detected saturable [ 3H]17β-estradiol-binding sites (Kd∼6.6nM; B max∼1140fmol/mg protein) in S. glaucophyllum callus tissue. Estrogen-like compounds were detected in lipid extracts from S. glaucophyllum and L. esculentum. Moreover, the lipid fraction was able to compete with [ 3H]17β-estradiol for binding to estrogen receptor (ER) from breast cancer MCF-7 cells as well as with estrogen-binding sites present in both plant species. Western blot analysis with monoclonal antibodies against different domains of the ER α, detected a ∼67kDa band in various organs of both plant species. These proteins were able to bind estradiol in ligand blot assays using 17β-estradiol macromolecular derivatives as ligands. Western and ligand blot experiments of subcellular fractions from callus tissues of S. glaucophyllum showed that the ER-like protein of ∼67kDa was most concentrated in the nuclear fraction. Reactive bands of lower molecular weight were also detected. Altogether these results provide evidence about the existence of estrogen-binding proteins and endogenous ligands in Solanaceae.