The transcription factor myocyte-enhancer factor 2 (MEF2) has been shown to be required for the survival of different types of neurons. However, the death- or survival-inducing second messenger pathways that regulate MEF2 activity remain to be fully elucidated. Membrane depolarization by KCl induces neuronal survival that is dependent upon MEF2-mediated gene transactivation. Here we report that membrane depolarizationinduced activation of MEF2 requires the cAMP-protein kinase A (PKA) pathway. Inhibition of the activity of cAMP-PKA pathway attenuates membrane depolarization-induced activation of MEF2 activity and neuronal survival, whereas enhancing the activity of this pathway prevents KCl withdrawal-induced inhibition of MEF2 and neuronal apoptosis. Moreover, PKA directly phosphorylates MEF2 at Thr-20 in vitro to increase MEF2 DNA binding activity. A mutation of Thr-20 to Ala renders MEF2 resistant to PKA phosphorylation in vitro and reduces its DNA binding activity. Transfection of this T20A mutant blocks survival and induces apoptosis in cultured cortical and cerebellar granule neurons. This study identifies the transcription factor MEF2 as a target of cAMP-PKA pathway and demonstrates that PKA phosphorylation of MEF2 is a key step in modulating its DNA binding activity and ability to promote neuronal survival.

We explored the feasibility of studying nuclear matrix protein (NMP) expressions of the hepatocytes in normal and cirrhotic rat livers with liver regeneration after partial hepatectomy. Sixteen Wistar healthy rats were studied with experimental liver regeneration and/or liver cirrhosis. Two-dimensional (2-D) gel electrophoresis was used to generate these NMP compositions from these rat liver samples. Several antibodies against cytokeratin, vimentin, actin, B23, HNF4alpha, and heat shock protein 70 were used for identification by Western blot. Totally, 41 strongly stained protein spots were characterized on the 2-D gels. Thirty-four protein spots were detected in all of these rat livers, of which, cytokeratin, vimentin, actin, HNF4alpha, and heat shock protein 70 were identified. B23 was detected in the regenerated livers. Three protein spots (s33, s34, and s35) were detectable only inNMPpreparation extracted from the regenerating rat livers after hepatectomy. Another three protein spots (s36, s37, and s38) were detectable only in NMP preparation extracted from thioacetamide-induced cirrhotic rat livers. Under these conditions including experimental liver regeneration and/or liver cirrhosis, Over thirty higher abundance NMPs of hepatocytes were consistently expressed and considered as common and basic NMPs. Some of the NMPs are specific for liver regeneration and may play a critical role in cell proliferation and cell cycle, and some are specific for liver cirrhosis.

The neuroprotective properties of bis (7)-tacrine, a novel dimeric acetylcholinesterase (AChE) inhibitor, on glutamate-induced excitotoxicity were investigated in primary cultured cerebellar granule neurons (CGNs). Exposure of CGNs to 75