Local protein synthesis in neuronal dendrites is critical for synaptic plasticity. However, the signaling cascades that couple synaptic activation to dendritic protein synthesis remain elusive. The purpose of this study is to determine the role of glutamate receptors and the mammalian target of rapamycin (mTOR) signaling in regulating dendritic protein synthesis in live neurons. We first characterized the involvement of various subtypes of glutamate receptors and the mTOR kinase in regulating dendritic synthesis of a green fluorescent protein (GFP) reporter controlled by ␣CaMKII 5 and 3 untranslated regions in cultured hippocampal neurons. Specific antagonists of N-methyl-D-aspartic acid (NMDA), ␣-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), and metabotropic glutamate receptors abolished glutamate-induced dendritic GFP synthesis, whereas agonists of NMDA and metabotropic but not AMPA glutamate receptors activated GFP synthesis in dendrites. Inhibitions of the mTOR signaling, as well as its upstream activators, phosphatidylinositol 3-kinase and AKT, blocked NMDA receptor-dependent dendritic GFP synthesis. Conversely, activation of mTOR signaling stimulated dendritic GFP synthesis. In addition, we also found that inhibition of the mTOR kinase blocked dendritic synthesis of the endogenous ␣CaMKII and MAP2 proteins induced by tetanic stimulations in hippocampal slices. These results identify critical roles of NMDA receptors and the mTOR signaling pathway for control of synaptic activity-induced dendritic protein synthesis in hippocampal neurons.

Gene transcription is required for establishing and maintaining the enduring form of long term potentiation (LTP). However, the transcriptome and its associated molecular programs that support LTP are not well understood. The purpose of this study was to identify activity-regulated genes (ARGs) and their molecular pathways that are modulated by LTP induction and to investigate the genomic mechanism for coordinating the transcription of ARGs. We performed time course DNA microarray analyses on the mouse dentate gyrus to determine the temporal genomic expression profiles of ARGs in response to LTP-inducing tetanic stimulation. Our studies uncovered ARGs that regulate various cellular processes, including the structure and function of the synapse, and offered an overview of the dynamic molecular programs that are probably important for LTP. Surprisingly, we found that ARGs are clustered on chromosomes, and ARG clusters are conserved during evolution. Although ARGs in the same cluster have apparently different molecular properties, they are functionally correlated by regulating LTP. In addition, ARGs in specific clusters are co-regulated by the cAMP-response element-binding protein. We propose that chromosomal clustering provides a genomic mechanism for coordinating the transcription of ARGs involved in LTP.

Growth-arrest and DNA-damage inducible (GADD) genes and Myeloid differentiation primary response (MyD) genes represent a family of genes that play a key role in negative control of cell growth. In the present study, following clone and location of human GADD45 gamma (MyDL) gene, we have found that its mRNA expression level was down-regulated in 15/23 cases of clinic hepatocellular carcinoma (HCC) by comparing the northern hybridization results between the tumor tissues and adjacent normal tissues. Transient transfection of GADD45 gamma cDNA with intact open reading frame sequence into the human hepatoma cells Hep-G2 resulted in dramatic growth suppression in colony formation assays. Furthermore, flow cytometry analysis indicated that GADD45 y caused cell cycle arrest at G2/M transition when transfected into Hep-G2 cells. Therefore, the possible role of GADD45 gamma in cell growth control was further confirmed in this paper.

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The expression of long-lasting synaptic plasticity requires synthesis of new proteins. A critical locus for protein synthesis to support synaptic plasticity is the dendrites. Previous studies demonstrate that synaptic activity activates dendritic protein synthesis. The mechanism by which synaptic activity stimulates protein synthesis in dendrites is, however, poorly understood. This study is to determine the role of the mitogen-activated protein kinase signaling pathway in activity-dependent dendritic protein synthesis. Using a green fluorescent protein reporter with CaMKII 5' and 3'untranslated regions, we show that dendritic synthesis of the green fluorescent protein induced by N-methyl-D-aspartate stimulation is abolished by U0126, a specific inhibitor of mitogen-activated protein kinase signaling. Our results suggest an important role of the mitogen-activated protein kinase signaling in dendritic protein synthesis induced by N-methyl-D-aspartate receptor activation.