RECONSTITUTION OF MAMMARY-GLAND DEVELOPMENT IN-VITRO - REQUIREMENT OFC-MET AND C-ERBB2 SIGNALING FOR BRANCHING AND ALVEOLAR MORPHOGENESIS

We have established a cell culture system that reproduces morphogenic processes in the developing mammary gland. EpH4 mouse mammary epitheli al cells cultured in matrigel form branched tubules in the presence of hepatocyte growth factor/scatter factor (HGF/SF), the ligand of the c -met tyrosine kinase receptor. In contrast, alveolar structures are fo rmed in the presence of neuregulin, a ligand of c-erbB tyrosine kinase receptors. These distinct morphogenic responses can also be observed with selected human mammary carcinoma tissue in explant culture. HGF/S F-induced branching was abrogated by the PI3 kinase inhibitors wortman nin and LY294002. In contrast, neuregulin-induced alveolar morphogenes is was inhibited by the MAPK kinase inhibitor PD98059, The c-met-media ted response could also be evoked by transfection of a c-met specific substrate, Gab1, which can activate the PI3 kinase pathway. An activat ed hybrid receptor that contained the intracellular domain of c-erbB2 receptor suffices to induce alveolar morphogenesis, and was observed i n the presence of tyrosine residues Y1028, Y1144, Y1201, and Y1226/27 in the substrate-binding domain of c-erbB2. Our data demonstrate that c-met and c-erbB2 signaling elicit distinct morphogenic programs in ma mmary epithelial cells: formation of branched tubules relies on a path way involving PI3 kinase, whereas alveolar morphogenesis requires MAPK kinase.