The CCAAT/enhancer binding protein delta (CEBPD, C/EBPδ, NF-IL6β) is induced in many inflammation-related diseases, suggesting that CEBPD and its downstream targets may play central roles in these conditions. Neuropathological studies show that a neuroinflammatory response parallels the early stages of Alzheimer's disease (AD). However, the precise mechanistic correlation between inflammation and AD pathogenesis remains unclear. CEBPD is upregulated in the astrocytes of AD patients. Therefore, we asked if activation of astrocytic CEBPD could contribute to AD pathogenesis. In this report, a novel role of CEBPD in attenuating macrophage-mediated phagocytosis of damaged neuron cells was found. By global gene expression profiling, we identified the inflammatory marker pentraxin-3 (PTX3, TNFAIP5, TSG-14) as a CEBPD target in astrocytes. Furthermore, we demonstrate that PTX3 participates in the attenuation of macrophage-mediated phagocytosis of damaged neuron cells. This study provides the first demonstration of a role for astrocytic CEBPD and the CEBPD-regulated molecule PTX3 in the accumulation of damaged neurons, which is a hallmark of AD pathogenesis.

Neuropathological hallmarks of Alzheimer's disease are extracellular senile plaques and intracellular neurofibrillary lesions. The neurofibrillary lesions mainly consist of the hyperphosphorylated microtubule-associated protein Tau predominantly expressed in the axon of CNS neurons. Hyperphosphorylation of Tau negatively affects its binding to tubulin and decreases the capacity to promote microtubule assembly. Among a number of proline-directed kinases capable of phosphorylating paired helical filament-Tau, glycogen synthase kinase 3b (GSK3b) was first identified as a Tau protein kinase I and has been demonstrated to phosphorylate Tau both in vivo and in vitro. However, the phosphorylation mechanism of Tau by GSK3b remained unclear. In this study, we show that the T231 is the primary phosphorylation site for GSK3b and the Tau227-237 (AVVRTPPKSPS) derived from Tau containing T231P232 motif is identified as the GSK3b binding site with high affinity of a Kd value 0.82 ± 0.16 lmol/L. Our results suggest that direct binding and phosphorylation of T231P232 motif by GSK3b induces conformational change of Tau and consequentially alters the inhibitory activity of its N-terminus that allows the phosphorylation of C-terminus of Tau by GSK3b. Furthermore, hyperphosphorylation reduces Tau's ability to promote tubulin assembly and to form bundles in N18 cells. T231A mutant completely abolishes Tau phosphorylation by GSK3b and retains the ability to promote tubulin polymerization and bundle formation. Taken together, these results suggest that phosphorylation of T231 by GSK3b may play an important role in Tau's hyperphosphorylation and functional regulation. Keywords: Alzheimer's disease, glycogen synthase kinase 3b, hyperphosphorylation, Tau, Thr231. J. Neurochem. (2007) 103, 802-813. A diagnosis of Alzheimer's disease (AD) is made when a patient exhibits clinical evidence of progressive dementia and when a post-mortem examination of brain reveals the characteristic neuropathology consisting of extracellular senile plaques and intracellular neurofibrillary lesions (Goedert and Spillantini 2006). The neurofibrillary lesions mainly consist of the hyperphosphorylated microtubule (MT)-associated protein Tau (Avila 2006). Tau is a family of MTassociated proteins that are produced by alternative mRNA splicing of a single gene as six isoforms and express predominantly within neurites and axons in adult brain. The largest Tau found in the brain containing 441 amino acids contains two N-terminal inserts and four MT-binding repeats. However, the smallest isoform has no N-terminal insert and has three MT-binding repeats instead (Buee et al. 2000;Avila 2006). Interestingly, 4R-tau was easily phosphorylated by brain protein kinases and aggregated into filaments Received January 31, 2007; revised manuscript received April 25, 2007; accepted June 13, 2007. Address correspondence and reprint requests to Pei-Jung Lu, PhD, Department of Medical Education and Research, Kaohsiung Veterans General Hospital 386 Ta-Chung 1st Rd., Kaoh...

Purpose: Recent evidence indicates that a tumor suppressor gene CEBPD (CCAAT/enhancer-binding protein delta) is downregulated in many cancers including cervical cancer, which provides a therapeutic potential associated with its reactivation. However, little is known for CEBPD activators and the effect of reactivation of CEBPD transcription upon anticancer drug treatment. In this study, we identified a novel CEBPD activator, 1-(2-hydroxy-5-methylphenyl)-3-phenyl-1,3-propanedione (HMDB). The purpose of this study is to characterize the mechanism of HMDB-induced CEBPD activation and its potential effect in cancer therapy.Experimental Design: Methylation-specific PCR assay, reporter assay, and chromatin immunoprecipitation (ChIP) assay were performed to dissect the signaling pathway of HMDB-induced CEBPD transcription. Furthermore, a consequence of HMDB-induced CEBPD expression was linked with E2F1 and retinoblastoma (RB), which discloses the scenario of CEBPD, E2F1, and RB bindings and transcriptional regulation on the promoters of proapoptotic genes, PPARG2 and GADD153. Finally, the anticancer effect of HMDB was examined in xenograft mice.Results: We demonstrate that CEBPD plays an essential role in HMDB-mediated apoptosis of cancer cells. HMDB up-regulates CEBPD transcription through the p38/CREB pathway, thus leading to transcriptional activation of PPARG2 and GADD153. Furthermore, increased level of CEBPD attenuates E2F1-induced cancer cell proliferation and partially rescues RB/E2F1-mediated repression of PPARG2 and GADD153 transcription. Moreover, HMDB treatment attenuates the growth of A431 xenografts in severe combined immunodeficient mice mice.Conclusions: These results clearly demonstrate that HMDB kills cancer cells through activation of CEBPD pathways and suggest that HMDB can serve as a superior chemotherapeutic agent with limited potential for adverse side effects. Clin Cancer Res; 16(23); 5770-80. Ó2010 AACR.