Oestrogen receptor-alpha regulates non-canonical Hedgehog-signalling in the mammary gland

Mesenchymal dysplasia (mes) mice harbour a truncation in the C-terminal region of the Hh-ligand receptor, Patched-1 (mPtch1). While the mes variant of mPtch1 binds to Hh-ligands with an affinity similar to that of wild type mPtch1 and appears to normally regulate canonical Hh-signalling via smoothened, the mes mutation causes, among other non-lethal defects, a block to mammary ductal elongation at puberty. We demonstrated previously Hh-signalling induces the activation of Erk1/2 and c-src independently of its control of smo activity. Furthermore, mammary epithelial cell-directed expression of an activated allele of c-src rescued the block to ductal elongation in mes mice, albeit with delayed kinetics. Given that this rescue was accompanied by an induction in estrogen receptor-alpha (ER alpha) expression and that complex regulatory interactions between ER alpha and c-src are required for normal mammary gland development, it was hypothesized that expression of ERa would also overcome the block to mammary ductal elongation at puberty in the mes mouse. We demonstrate here that conditional expression of ER alpha in lumina] mammary epithelial cells on the mes background facilitates ductal morphogenesis with kinetics similar to that of the MMTV-c-src(Act) mice. We demonstrate further that Erk1/2 is activated in primary mammary epithelial cells by Shh-ligand and that this activation is blocked by the inhibitor of c-src, PP2, is partially blocked by the ERa inhibitor, ICI 182780 but is not blocked by the smo-inhibitor, SANT-1. These data reveal an apparent Hh-signalling cascade operating through c-src and ER alpha that is required for mammary gland morphogenesis at puberty. (C) 2014 Elsevier Inc. All rights reserved.