ABSTRACT
Galectin-3, a member of the galectin protein family, has been found to regulate cell proliferation, inhibit apoptosis and promote inflammatory responses. Galectin-3 is also expressed in the adult rat hippocampus, but its role in learning and memory function is not known. Here, we found that contextual fear-conditioning training, spatial training or injection of NMDA into the rat CA1 area each dramatically decreased the level of endogenous galectin-3 expression. Overexpression of galectin-3 impaired fear memory, whereas galectin-3 knockout (KO) enhanced fear retention, spatial memory and hippocampal long-term potentiation. Galectin-3 was further found to associate with integrin α3, an association that was decreased after fear-conditioning training. Transfection of the rat CA1 area with small interfering RNA against galectin-3 facilitated fear memory and increased phosphorylated focal adhesion kinase (FAK) levels, effects that were blocked by co-transfection of the FAK phosphorylation-defective mutant Flag-FAKY397F. Notably, levels of serine-phosphorylated galectin-3 were decreased by fear conditioning training. In addition, blockade of galectin-3 phosphorylation at Ser-6 facilitated fear memory, whereas constitutive activation of galectin-3 at Ser-6 impaired fear memory. Interestingly galectin-1 plays a role in fear-memory formation similar to that of galectin-3. Collectively, our data provide the first demonstration that galectin-3 is a novel negative regulator of memory formation that exerts its effects through both extracellular and intracellular mechanisms.
ABSTRACT
Amyloid-ß (Aß) produces neurotoxicity in the brain and causes neuronal death, but the endogenous defense mechanism that is activated on Aß insult is less well known. Here we found that acute Aß increases the expression of PIAS1 and Mcl-1 via activation of MAPK/ERK, and Aß induction of PIAS1 enhances HDAC1 SUMOylation in rat hippocampus. Knockdown of PIAS1 decreases endogenous HDAC1 SUMOylation and blocks Aß induction of Mcl-1. Sumoylated HDAC1 reduces it association with CREB, increases CREB binding to the Mcl-1 promoter and mediates Aß induction of Mcl-1 expression. Transduction of SUMO-modified lenti-HDAC1 vector to the hippocampus of APP/PS1 mice rescues spatial learning and memory deficit and long-term potentiation impairment in APP/PS1 mice. It also reduces the amount of amyloid plaque and the number of apoptotic cells in CA1 area of APP/PS1 mice. Meanwhile, HDAC1 SUMOylation decreases HDAC1 binding to the neprilysin promoter. These results together reveal an important role of HDAC1 SUMOylation as a naturally occurring defense mechanism protecting against Aß toxicity and provide an alternative therapeutic strategy against AD.
Subject(s)
Amyloid beta-Peptides/toxicity , Epigenesis, Genetic , Histone Deacetylase 1/metabolism , Neuroprotection/drug effects , Alzheimer Disease/metabolism , Alzheimer Disease/pathology , Animals , Apoptosis/drug effects , Butadienes/pharmacology , Disease Models, Animal , Gene Expression/drug effects , HEK293 Cells , Hippocampus/metabolism , Histone Deacetylase 1/genetics , Humans , Male , Mice , Mice, Transgenic , Nitriles/pharmacology , Protein Binding , Protein Inhibitors of Activated STAT/antagonists & inhibitors , Protein Inhibitors of Activated STAT/genetics , Protein Inhibitors of Activated STAT/metabolism , RNA Interference , Rats , Rats, Sprague-Dawley , SumoylationABSTRACT
BACKGROUND: Hairy and Enhancer of split 1 (Hes-1) is a transcriptional repressor that plays an important role in neuronal differentiation and development, but post-translational modifications of Hes-1 are much less known. In the present study, we aimed to investigate whether Hes-1 could be SUMO-modified and identify the candidate SUMO acceptors on Hes-1. We also wished to examine the role of the SUMO E3 ligase protein inhibitor of activated STAT1 (PIAS1) in SUMOylation of Hes-1 and the molecular mechanism of Hes-1 SUMOylation. Further, we aimed to identify the molecular target of Hes-1 and examine how Hes-1 SUMOylation affects its molecular target to affect cell survival. RESULTS: In this study, by using HEK293T cells, we have found that Hes-1 could be SUMO-modified and Hes-1 SUMOylation was greatly enhanced by the SUMO E3 ligase PIAS1 at Lys8, Lys27 and Lys39. Furthermore, Hes-1 SUMOylation stabilized the Hes-1 protein and increased the transcriptional suppressing activity of Hes-1 on growth arrest and DNA damage-inducible protein alpha (GADD45α) expression. Overexpression of GADD45α increased, whereas knockdown of GADD45αα expression decreased cell apoptosis. In addition, H2O2 treatment increased the association between PIAS1 and Hes-1 and enhanced the SUMOylation of Hes-1 for endogenous protection. Overexpression of Hes-1 decreased H2O2-induced cell death, but this effect was blocked by transfection of the Hes-1 triple sumo-mutant (Hes-1 3KR). Overexpression of PIAS1 further facilitated the anti-apoptotic effect of Hes-1. Moreover, Hes-1 SUMOylation was independent of Hes-1 phosphorylation and vice versa. CONCLUSIONS: The present results revealed, for the first time, that Hes-1 could be SUMO-modified by PIAS1 and GADD45α is a novel target of Hes-1. Further, Hes-1 SUMOylation mediates cell survival through enhanced suppression of GADD45α expression. These results revealed a novel role of Hes-1 in addition to its involvement in Notch signaling. They also implicate that SUMOylation could be an important posttranslational modification that regulates cell survival.
Subject(s)
Basic Helix-Loop-Helix Transcription Factors/biosynthesis , Cell Cycle Proteins/biosynthesis , Homeodomain Proteins/biosynthesis , Nuclear Proteins/biosynthesis , STAT1 Transcription Factor/biosynthesis , Sumoylation/genetics , Apoptosis/genetics , Basic Helix-Loop-Helix Transcription Factors/metabolism , Cell Cycle Proteins/metabolism , Cell Survival/genetics , Gene Expression Regulation/drug effects , HEK293 Cells , Homeodomain Proteins/metabolism , Humans , Hydrogen Peroxide/pharmacology , Nuclear Proteins/metabolism , Phosphorylation , STAT1 Transcription Factor/metabolism , Signal Transduction/drug effects , Transcription Factor HES-1 , Ubiquitin-Protein Ligases/metabolismABSTRACT
Signal transducer and activator of transcription-1 (STAT1) has an important role in inflammation and the innate immune response, but its role in the central nervous system is less well understood. Here, we examined the role of STAT1 in spatial learning and memory, and assessed the involvement of STAT1 in mediating the memory-impairing effect of amyloid-beta (Aß). We found that water maze training downregulated STAT1 expression in the rat hippocampal CA1 area, and spatial learning and memory function was enhanced in Stat1-knockout mice. Conversely, overexpression of STAT1 impaired water maze performance. STAT1 strongly upregulated the expression of the extracellular matrix protein laminin ß1 (LB1), which also impaired water maze performance in rats. Furthermore, Aß impaired spatial learning and memory in association with a dose-dependent increase in STAT1 and LB1 expression, but knockdown of STAT1 and LB1 both reversed this effect of Aß. This Aß-induced increase in STAT1 and LB1 expression was also associated with a decrease in the expression of the N-methyl-D-aspartate receptor (NMDAR) subunits, NR1, and NR2B. Overexpression of NR1 or NR2B or exogenous application of NMDA reversed Aß-induced learning and memory deficits as well as Aß-induced STAT1 and LB1 expression. Our results demonstrate that STAT1 negatively regulates spatial learning and memory through transcriptional regulation of LB1 expression. We also identified a novel mechanism for Aß pathogenesis through STAT1 induction. Notably, impairment of spatial learning and memory by this STAT1-mediated mechanism is independent of cAMP responsive element-binding protein signaling.
