Stabilized β-Catenin Functions through TCF/LEF Proteins and the Notch/RBP-Jκ Complex To Promote Proliferation and Suppress Differentiation of Neural Precursor Cells

Abstract

The proliferation and differentiation of neural precursor cells are mutually exclusive during brain development. Despite its importance for precursor cell self renewal, the molecular linkage between these two events has remained unclear. Fibroblast growth factor 2 (FGF2) promotes neural precursor cell proliferation and concurrently inhibits their differentiation, suggesting a cross talk between proliferation and differentiation signaling pathways downstream of the FGF receptor. We demonstrate that FGF2 signaling through phosphatidylinositol 3 kinase activation inactivates glycogen synthase kinase 3β (GSK3β) and leads to the accumulation of β-catenin in a manner different from that in the Wnt canonical pathway. The nuclear accumulated β-catenin leads to cell proliferation by activating LEF/TCF transcription factors and concurrently inhibits neuronal differentiation by potentiating the Notch1-RBP-Jκ signaling pathway. β-Catenin and the Notch1 intracellular domain form a molecular complex with the promoter region of the antineurogenic hes1 gene, allowing its expression. This signaling interplay is especially essential for neural stem cell maintenance, since the misexpression of dominant-active GSK3β completely inhibits the self renewal of neurosphere-forming stem cells and prompts their neuronal differentiation. Thus, the GSK3β/β-catenin signaling axis regulated by FGF and Wnt signals plays a pivotal role in the maintenance of neural stem/precursor cells by linking the cell proliferation to the inhibition of differentiation.

ACKNOWLEDGMENTS

We greatly thank Morris J. Birnbaum (University of Pennsylvania) for the gift of GSK3β-S9A cDNA, Hans Clevers (The Netherlands Institute of Developmental Biology) for the gift of pcDNA3.1-ΔNTCF4, Makoto Hijikata (Kyoto University) for the gift of the original 7×TCF-Luc plasmid, Akira Nagafuchi (Kumamoto University) for the gift of stabilized β-catenin and pEF-mβH cDNA, Brian A. Hemmings (Friedrich Miescher Institute, Basel, Switzerland) for the gift of dnAkt cDNA (pCMV5-AktAAA), and Atsuko Sakurai (National Cardio Vascular Center) for useful information on the anti-β-catenin antibody. We also thank Kinichi Nakashima (Nara Institute of Science and Technology) and Yutaka Yoshinaga (Kumamoto University) for helpful discussions. We thank Yuko Saiki, Kaori Kaneko, and Sayomi Iwaki for their technical assistance. We also thank Michiko Teramoto for her secretarial assistance.

This work was supported by a grant-in-aid for 21st Century COE research from the Ministry of Education, Culture, Sports, Science and Technology Cell Fate Regulation Research and Education Unit, the Naito Foundation (T.S.); grants-in-aid 16047223 and 18053018 for Scientific Research on Priority Areas on the elucidation of glia-neuron network mediated information processing systems (T.K.), grants-in-aid for scientific research on priority areas on molecular brain science (T.T.), and grants-in-aid for scientific research on priority areas on self-renewal and pluripotency of the stem cells (T.T.) from the Ministry of Education, Culture, Sports, Science and Technology; grant-in-aid 18700365 for Scientific Research for Young Scientist (T.S.), grants-in-aid 17500255 for scientific research (C) (T.K.), and grants-in-aid for scientific research (B) (T.T.) from the Japan Society for the Promotion of Sciences, NCNP, and CREST.