Figure 1.

p25/cdk5 activation inhibits GSK3β through the NRG receptor pathway. A, Representative immunoblots of cdk5, p35/p25, pGSK3β–S9, GSK3β, β-catenin, and pβ-catenin on brain extracts from Ntg (n = 7) and p25 (n = 7) mice at postnatal day 4. pGSK3β–S9 levels normalized to GSK3β total protein were significantly increased in p25 mice compared with Ntg mice (p < 0.01). Four different sets of animals were examined with similar results; the most representative set is shown. p25 mice showed significantly increased levels of β-catenin and significantly decreased levels of the GSK3β target pβ-catenin. B, Representative immunoblots showing levels of neuregulin signaling components, pAkt-S473, Akt, pPI3K–Y199 (p55 subunit), and pErbB2–Y877. β-Tubulin was used for loading control; there was a significant increase of pAkt–S473 (p < 0.05), pPI3K–Y199 (p < 0.05), and pErbB2–Y877(p < 0.05) in p25 mice compared with Ntg mice. C, Correlation analysis of pErbB2 and pGSK3β–S9 in Ntg and p25 mice showed a significant correlation between pErbB2–Y877 and pGSK3β–S9 (p < 0.01).