Protein kinase C overactivity impairs prefrontal cortical regulation of working memory.

The prefrontal cortex is a higher brain region that regulates thought, behavior, and emotion using representational knowledge, operations often referred to as working memory. We tested the influence of protein kinase C (PKC) intracellular signaling on prefrontal cortical cognitive function and showed that high levels of PKC activity in prefrontal cortex, as seen for example during stress exposure, markedly impair behavioral and electrophysiological measures of working memory. These data suggest that excessive PKC activation can disrupt prefrontal cortical regulation of behavior and thought, possibly contributing to signs of prefrontal cortical dysfunction such as distractibility, impaired judgment, impulsivity, and thought disorder.

The mood stabilizer valproic acid activates mitogen-activated protein kinases and promotes neurite growth.

The mood-stabilizing agents lithium and valproic acid (VPA) increase DNA binding activity and transactivation activity of AP-1 transcription factors, as well as the expression of genes regulated by AP-1, in cultured cells and brain regions involved in mood regulation. In the present study, we found that VPA activated extracellular signal-regulated kinase (ERK), a kinase known to regulate AP-1 function and utilized by neurotrophins to mediate their diverse effects, including neuronal differentiation, neuronal survival, long term neuroplasticity, and potentially learning and memory. VPA-induced activation of ERK was blocked by the mitogen-activated protein kinase/ERK kinase inhibitor PD098059 and dominant-negative Ras and Raf mutants but not by dominant-negative stress-activated protein kinase/ERK kinase and mitogen-activated protein kinase kinase 6 mutants. VPA also increased the expression of genes regulated by the ERK pathway, including growth cone-associated protein 43 and Bcl-2, promoted neurite growth and cell survival, and enhanced norepinephrine uptake and release. These data demonstrate that VPA is an ERK pathway activator and produces neurotrophic effects.

The mood-stabilizing agents lithium and valproate robustly increase the levels of the neuroprotective protein bcl-2 in the CNS.

Differential display of mRNA was used to identify concordant changes in gene expression induced by two mood-stabilizing agents, lithium and valproate (VPA). Both treatments, on chronic administration, increased mRNA levels of the transcription factor polyomavirus enhancer-binding protein (PEBP) 2beta in frontal cortex (FCx). Both treatments also increased the DNA binding activity of PEBP2 alphabeta and robustly increased the levels of bcl-2 (known to be transcriptionally regulated by PEBP2) in FCx. Immunohistochemical studies revealed a marked increase in the number of bcl-2-immunoreactive cells in layers 2 and 3 of FCx. These novel findings represent the first report of medication-induced increases in CNS bcl-2 levels and may have implications not only for mood disorders, but also for long-term treatment of various neurodegenerative disorders.

Valproate robustly enhances AP-1 mediated gene expression.

Valproic acid (VPA) is a potent broad spectrum anticonvulsant with demonstrated efficacy in the treatment of Bipolar Affective Disorder, but the biochemical basis for VPA's antimanic or mood-stabilizing actions have not been fully elucidated. It has been demonstrated that VPA, at therapeutically relevant concentrations, increases AP-1 DNA binding activity in cultured cells in vitro. These findings raise the possibility that VPA may produce its mood-stabilizing effects by regulating the expression of subsets of genes via its effects on the AP-1 family of transcription factors. To determine if VPA does, in fact, enhance AP-1 mediated gene expression, the effects of VPA on the expression of a luciferase reporter gene were studied in transiently transfected rat C6 glioma and human SH-SY5Y neuroblastoma cells using the pGL2-control vector. The luciferase gene in the vector is driven by an SV40 promoter which contains well characterized AP-1 sites. VPA produced a greater than doubling of luciferase activity in a time- and concentration-dependent manner in both cell lines. Furthermore, mutations of the AP-1 sites in the SV40 promoter markedly attenuated the VPA-induced increases in luciferase activity. These effects of VPA on AP-1 mediated gene expression are very similar to the effects observed with lithium, and suggest that the temporal regulation of AP-1 mediated gene expression in critical neuronal circuits may play a role in the long-term therapeutic efficacy of these agents.

Lithium stimulates gene expression through the AP-1 transcription factor pathway.

Lithium, a monovalent cation, is the mainstay in the treatment of manic-depressive (MDI) illness, but despite extensive research, its mechanism of action remains to be elucidated. Since lithium requires chronic administration for therapeutic efficacy, and because its beneficial effects last well beyond its discontinuation, it has been postulated that lithium may exert major effects at the genomic level. In the present study we found that lithium, at therapeutically relevant concentrations, increases AP-1 DNA binding activity in human SH-SY5Y cells and rat C6 glioma cells. Additionally, in both SY5Y and C6 cells transiently transfected with a reporter gene vector driven by an SV40 promoter, lithium increased the activity of the reporter gene in a time- and concentration-dependent manner. Furthermore, mutations in the AP-1 sites of the reporter gene promoter significantly attenuated lithium's effects. These data indicate that lithium stimulates gene expression through the AP-1 transcription factor pathway, effects which may play a role in its long-term mood-stabilizing effects.

Lithium increases tyrosine hydroxylase levels both in vivo and in vitro.

Lithium, a simple monovalent cation, is the mainstay in the treatment of manic-depressive illness, but despite extensive research, its mechanism of action remains to be elucidated. Because lithium requires chronic administration for therapeutic efficacy and because its beneficial effects last well beyond its discontinuation, it has been postulated that lithium may exert major effects at the genomic level. We have previously shown that lithium, at therapeutically relevant concentrations, increases gene expression through the activator protein-1 (AP-1) transcription factor pathway in vitro. In the present study, we have sought to determine if lithium also increases the expression of endogenous genes known to be regulated by AP-1 and have therefore investigated the effects of lithium on tyrosine hydroxylase (TH) levels. Male Wistar rats were treated with LiCl for 9 days (subacute) or 4 weeks (chronic), and TH levels were measured in frontal cortex, hippocampus, and striatum using immunoblotting. Chronic (but not subacute) lithium treatment resulted in significant increases in TH levels in rat frontal cortex, hippocampus, and striatum. Lithium (1 mM) also increased TH levels in human SH-SY5Y neuroblastoma cells in vitro, indicating that lithium increases TH levels in both rodent and human tissues, likely via a direct cellular effect. These effects are compatible with (but likely not exclusively due to) an effect on the DNA binding of the 12-O-tetradecanoylphorbol 13-acetate response element to the AP-1 family of transcription factors.

[Study of the infiltrating lymphocyte subsets and transferrin receptor in gastric and colorectal carcinomas].

Infiltrating mononuclear cell (MNC) subsets and transferrin receptor (TfR) expression at the localized lesions were studied in 28 cases of gastric carcinoma and 36 cases of colorectal carcinoma by immunohistochemical technique by using a panel of monoclonal antibodies. The results showed that the percentage of T4+ cells in the infiltrating MNCs decreased while that of T8+ cells increased relatively and the T4/T8 ratios declined along with the progression of the tumor. The TfR positive rates in gastric and colorectal carcinomas were 73.08% and 100% respectively. The expressing intensity of TfR in the tumors correlated with the density of local infiltrating MNC subsets. These findings indicated that the local immune response against tumor moves toward a tendency of developing a deeper inhibitory effect during the tumor progression.