Stabilized beta-catenin functions through TCF/LEF proteins and the Notch/RBP-Jkappa 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 3beta (GSK3beta) and leads to the accumulation of beta-catenin in a manner different from that in the Wnt canonical pathway. The nuclear accumulated beta-catenin leads to cell proliferation by activating LEF/TCF transcription factors and concurrently inhibits neuronal differentiation by potentiating the Notch1-RBP-Jkappa signaling pathway. beta-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 GSK3beta completely inhibits the self renewal of neurosphere-forming stem cells and prompts their neuronal differentiation. Thus, the GSK3beta/beta-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.
Article: Suppression of glycogen synthase kinase activity is not sufficient for leukemia enhancer factor-1 activation.[show abstract] [hide abstract]
ABSTRACT: Glycogen synthase kinase-3 (GSK) can be regulated by different signaling pathways including those mediated by protein kinase Akt and Wnt proteins. Wnt proteins are believed to activate a transcription factor leukemia enhancer factor-1 (LEF-1) by inhibiting GSK, and Akt was shown to phosphorylate GSK and inhibit its kinase activity. We investigated the effect of an activated Akt on the accumulation of cytosolic beta-catenin and LEF-1-dependent transcription. Although the activated Akt, mAkt, clearly inhibited the kinase activity of GSK, mAkt alone did not induce accumulation of cytosolic beta-catenin or activate LEF-1-dependent transcription. On the contrary, coexpressed Wnt-1 and Frat activated LEF-1 but did not show significant inhibition of GSK-mediated phosphorylation of a peptide substrate. However, mAkt could act synergistically with Wnt-1 or Frat to activate LEF-1. In addition, the interaction of GSK for Axin appeared to decrease in the presence of mAkt, whereas the interaction for Frat remained unchanged. Consistently, a GSK mutant with substitution of a Phe residue for residue Tyr-216, which showed one-fifth of kinase activity of the wild-type GSK, exhibited a reduced association for Axin than the wild-type GSK. These results suggest that inhibition of GSK kinase activity is not sufficient for activation of LEF-1 but may facilitate the activation by reducing the interaction of GSK for Axin. The additional mechanism for LEF-1 activation may require dissociation of GSK from Axin as Frat facilitates the dissociation of GSK from Axin.Journal of Biological Chemistry 11/1999; 274(43):30419-23. · 4.77 Impact Factor
Article: STAT5 as a molecular regulator of proliferation, differentiation and apoptosis in hematopoietic cells.[show abstract] [hide abstract]
ABSTRACT: Signal transducers and activators of transcription (STATs) play key roles in growth factor-mediated intracellular signal transduction. In the present study using a constitutively active STAT5 mutant, we show that STAT5 has pleiotropic functions regulating cell proliferation, differentiation and apoptosis in an IL-3-dependent Ba/F3 cell line. The mutant STAT5 possessed constitutive tyrosine phosphorylation and DNA binding activity, induced expression of bcl-xL and pim-1 in the absence of IL-3 in Ba/F3 cells, and rendered Ba/F3 cells factor-independent. Unexpectedly, IL-3 treatment of the factor-independent Ba/F3 cells expressing the constitutively active STAT5 resulted in apoptosis within 24 h, or differentiation followed by cell death. In these cells, mRNA expression of growth inhibitory genes downstream of STAT5 such as CIS, JAB/SOCS-1/SSI-1, and p21(WAF1/Cip1) was highly induced, correlating with prolonged hyper-phosphorylation of the mutant STAT5 after IL-3 stimulation. Of the STAT5-regulated genes, we found that constitutive expression of JAB/SOCS-1/SSI-1 was sufficient to induce apoptosis of Ba/F3 cells, while p21(WAF1/Cip1) could induce differentiation of these cells. In contrast, constitutive expression of pim-1 was sufficient to induce IL-3-independent growth of Ba/F3 cells. These findings suggest that a single transcription factor regulates cell fate by varying the intensity and duration of the expression of a set of target genes.The EMBO Journal 10/1999; 18(17):4754-65. · 9.20 Impact Factor
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ABSTRACT: The signaling systems of Notch and bone morphogenetic protein (BMP) are highly conserved from flies to mammals and have been shown to be important in the development of multiple organs. For instance, in the fate determination of mouse neuroepithelial cells, Notch signaling plays a role in keeping the progenitors from differentiating into neurons. BMP is also known to inhibit neuronal differentiation. In this paper, we show that BMP2 enhances Notch-induced transcriptional activation of Hes-5 and Hesr-1 in mouse neuroepithelial cells. BMP2 stimulation, in addition to the introduction of the intracellular domain of Notch (NIC), resulted in enhanced activation of the Hes-5 gene promoter. RBP-Jkappa binding to its target sequence is important not only for Notch signaling, but also for BMP2 signaling, to activate the Hes-5 gene promoter. Smad1, a Smad species that is activated by BMP2, barely interacted with NIC, but did form a complex with NIC in the simultaneous presence of the coactivators P/CAF and p300. Recruitment of p300 to the NIC-containing complex was facilitated by activated Smad1, which is suggested to contribute to BMP2-mediated enhancement of Notch-induced Hes-5 expression. These data suggest a novel functional cooperation between Notch signaling and BMP signaling.Nucleic Acids Research 11/2003; 31(19):5723-31. · 8.03 Impact Factor