“…Smad3/4 has a prominent role in regulating the expression of proteins involved in neuronal survival/death, differentiation, and plasticity (reviewed in Sanyal et al, 2004;Gomes et al, 2005). One of the Smad3/4-regulated protein targets is plasminogen activator inhibitor type-1 (PAI-1, also referred to as Serp1), which binds and inactivates tissue-type plasminogen activator (tPA), a multifaceted protein implicated in neurite outgrowth (Krystosek and Seeds, 1981), neuronal migration (Moonen et al, 1982;Seeds et al, 1999), learning (Qian et al, 1993;Seeds et al, 1995), excitotoxicity (Tsirka et al, 1995), synaptic plasticity (Baranes et al, 1998;Fiumelli et al, 1999;Neuhoff et al, 1999), stress response , and pathogenesis of mood disorders (Eskandari et al, 2005;Tsai, 2006). Using small interfering RNA (siRNA) and dominant negative mutants specific to GSK-3α and GSK-3β, we recently reported that GSK-3α inhibition causes an upregulation of Smad3/4-dependent transactivation and PAI-1 protein levels, while inhibition of GSK-3β induces a downregulation of Smad3/4 transactivation and PAI-1 expression (Liang and Chuang, 2006).…”