No abstract

The homeostatic regulation of neuronal activity in glutamatergic and GABAergic synapses is critical for neural circuit development and synaptic plasticity. The induced expression of the transcription factor early growth response 1 (Egr-1) in neurons is tightly associated with many forms of neuronal activity, but the underlying target genes in the brain remained to be elucidated. This study uses a quantitative real-time PCR approach, in combination with in vivo chromatin immunoprecipitation, and reveals that GABA A receptor subunit, GABRA2 (a2), GABRA4 (a4), and GABRQ (h) genes, are transcriptional targets of Egr-1. Transfection of a construct that overexpresses Egr-1 in neuroblastoma (Neuro2A) cells up-regulates the a2, a4, and h subunits. Given that Egr-1 knockout mice display less GABRA2, GABRA4, and GRBRQ mRNA in the hippocampus, and that Egr-1 directly binds to their promoters and induces mRNA expression, the present findings support a role for Egr-1 as a major regulator for altered GABA A receptor composition in homeostatic plasticity, in a glutamatergic activity-dependent manner.

Taxol (paclitaxel) is a potent anticancer drug that has been found to be effective against several tumor types, including cervical cancer. However, the exact mechanism underlying the antitumor effects of paclitaxel is poorly understood. Here, paclitaxel induced the apoptosis of cervical cancer HeLa cells and correlated with the enhanced activation of caspase-3 and TAp73, which was strongly inhibited by TAp73β small interfering RNA (siRNA). In wild-type activating transcription factor 3 (ATF3)–overexpressed cells, paclitaxel enhanced apoptosis through increased α and β isoform expression of TAp73; however, these events were attenuated in cells containing inactive COOH-terminal–deleted ATF3 [ATF3(ΔC)] or ATF3 siRNA. In contrast, paclitaxel-induced ATF3 expression did not change in TAp73β -overexpressed or TAp73β siRNA–cotransfected cells. Furthermore, paclitaxel-induced ATF3 translocated into the nucleus where TAp73β is expressed, but not in ATF3 (ΔC) or TAp73β siRNA–transfected cells. As confirmed by the GST pull-down assay, ATF3 bound to the DNA-binding domain of p73, resulting in the activation of p21 or Bax transcription, a downstream target of p73. Overexpression of ATF3 prolonged the half-life of TAp73β by inhibiting its ubiquitination and thereby enhancing its transactivation and proapoptotic activities. Additionally, ATF3 induced by paclitaxel potentiated the stability of TAp73β, not its transcriptional level. Chromatin immunoprecipitation analyses show that TAp73β and ATF3 are recruited directly to the p21 and Bax promoter. Collectively, these results reveal that overexpression of ATF3 potentiates paclitaxel-induced apoptosis of HeLa cells, at least in part, by enhancing TAp73β's stability and its transcriptional activity. The investigation shows that ATF3 may function as a tumor-inhibiting factor through direct regulatory effects on TAp73β, suggesting a functional link between ATF3 and TAp73β.

In neuronal development, dendritic outgrowth and arborization are important for the establishment of neural circuit formation. A previous study reported that PSD-95-interacting regulator of spine morphogenesis (Preso) formed a complex with PAK-interacting exchange factor-beta (βPix) via PSD-95/Dlg/ZO-1 (PDZ) interaction. Here, we report that Preso and its binding protein, βPix, are localized in dendritic growth cones. Knockdown and dominant-negative inhibition of Preso in cultured neurons markedly reduced the dendritic outgrowth but not branching, and led to a decrease in the intensity of βPix and F-actin in neuronal dendritic tips. Moreover, phosphatidylinositol 4,5-bisphosphate (PIP(2) ) induced a conformational change in Preso toward the open PDZ domain and enhanced the interaction with βPix. In addition, the Preso band 4.1 protein, ezrin, radixin and moesin (FERM) domain mutant is unable to interact with PIP(2) and it did not rescue the Preso-knockdown effect. These results indicate that PIP(2) is a key signalling molecule that regulates dendritic outgrowth through activation of small GTPase signalling via interaction between Preso and βPix.