The expression of KLF11 (TIEG2), a monoamine oxidase B transcriptional activator in the prefrontal cortex of human alcohol dependence.

BACKGROUND: The biochemical pathways underlying alcohol abuse and dependence are not well understood, although brain cell loss and neurotoxicity have been reported in subjects with alcohol dependence. Monoamine oxidase B (MAO B; an enzyme that catabolizes neurotransmitters such as dopamine) is consistently increased in this psychiatric illness. MAO B has been implicated in the pathogenesis of alcohol dependence and alcohol-induced brain neurotoxicity. Recently, the cell growth inhibitor protein, Kruppel-like factor 11 (KLF11), has been reported to be an MAO transcriptional activator. KLF11 is also known as TIEG2 (transforming growth factor-beta-inducible early gene 2) and mediates apoptotic cell death. This study investigates the protein expression of KLF11 and its relationship with MAO B using human postmortem prefrontal cortex from subjects with alcohol dependence. METHODS: Twelve subjects with alcohol dependence and the respective psychiatrically normal control subjects were investigated. Expression of KLF11 and MAO B proteins in the prefrontal cortex was measured by Western blot analysis. Correlation studies involving KLF11 and MAO B protein expression were performed. Localization of KLF11 in the human prefrontal cortex was also determined by immunohistochemistry. RESULTS: Levels of KLF11 protein were significantly increased by 44% (p < 0.03) in the postmortem prefrontal cortex of subjects with alcohol dependence as compared to age- and gender-matched, psychiatrically normal control subjects. Furthermore, KLF11 levels were significantly and positively correlated with both the increased MAO B protein levels and blood alcohol content in alcohol-dependent subjects. In addition, KLF11 protein expression was visualized in both neuronal and glial cells. CONCLUSIONS: This novel study shows the important role of KLF11, an MAO transcriptional activator, in human alcohol dependence. It further supports that the KLF11-MAO B cell death cascade may contribute to chronic alcohol-induced brain damage. This argues a case for KLF11-MAO B inhibition as a novel therapeutic strategy that may impact this highly prevalent illness.

Mechanistic role for a novel glucocorticoid-KLF11 (TIEG2) protein pathway in stress-induced monoamine oxidase A expression.

Chronic stress is a risk factor for psychiatric illnesses, including depressive disorders, and is characterized by increased blood glucocorticoids and brain monoamine oxidase A (MAO A, which degrades monoamine neurotransmitters). This study elucidates the relationship between stress-induced MAO A and the transcription factor Kruppel-like factor 11 (KLF11, also called TIEG2, a member of the Sp/KLF- family), which inhibits cell growth. We report that 1) a glucocorticoid (dexamethasone) increases KLF11 mRNA and protein levels in cultured neuronal cells; 2) overexpressing KLF11 increases levels of MAO A mRNA and enzymatic activity, which is further enhanced by glucocorticoids; in contrast, siRNA-mediated KLF11 knockdown reduces glucocorticoid-induced MAO A expression in cultured neurons; 3) induction of KLF11 and translocation of KLF11 from the cytoplasm to the nucleus are key regulatory mechanisms leading to increased MAO A catalytic activity and mRNA levels because of direct activation of the MAO A promoter via Sp/KLF-binding sites; 4) KLF11 knockout mice show reduced MAO A mRNA and catalytic activity in the brain cortex compared with wild-type mice; and 5) exposure to chronic social defeat stress induces blood glucocorticoids and activates the KLF11 pathway in the rat brain, which results in increased MAO A mRNA and enzymatic activity. Thus, this study reveals for the first time that KLF11 is an MAO A regulator and is produced in response to neuronal stress, which transcriptionally activates MAO A. The novel glucocorticoid-KLF11-MAO A pathway may play a crucial role in modulating distinct pathophysiological steps in stress-related disorders.

The reduction of R1, a novel repressor protein for monoamine oxidase A, in major depressive disorder.

The novel transcriptional repressor protein, R1 (JPO2/CDCA7L/RAM2), inhibits monoamine oxidase A (MAO A) gene expression and influences cell proliferation and survival. MAO A is implicated in several neuropsychiatric illnesses and highly elevated in major depressive disorder (MDD); however, whether R1 is involved in these disorders is unknown. This study evaluates the role of R1 in depressed subjects either untreated or treated with antidepressant drugs. R1 protein levels were determined in the postmortem prefrontal cortex of 18 untreated MDD subjects and 12 medicated MDD subjects compared with 18 matched psychiatrically normal control subjects. Western blot analysis showed that R1 was significantly decreased by 37.5% (p<0.005) in untreated MDD subjects. The R1 level in medicated MDD subjects was also significantly lower (by 30%; p<0.05) compared with control subjects, but was not significantly different compared with untreated MDD subjects. Interestingly, the reduction in R1 was significantly correlated with an increase (approximately 40%; p<0.05) in MAO A protein levels within the MDD groups compared with controls. Consistent with the change in MAO A protein expression, the MAO A catalytic activity was significantly greater in both MDD groups compared with controls. These results suggest that reduced R1 may lead to elevated MAO A levels in untreated and treated MDD subjects; moreover, the reduction of R1 has been implicated in apoptotic cell death and apoptosis has also been observed in the brains of MDD subjects. Therefore, modulation of R1 levels may provide a new therapeutic target in the development of more effective strategies to treat MDD.

Ethanol increases TIEG2-MAO B cell death cascade in the prefrontal cortex of ethanol-preferring rats.

Brain cell loss has been reported in subjects with alcoholism. However, the molecular mechanisms are unclear. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and monoamine oxidase B (MAO B) reportedly play a role in cellular dysfunction with regards to ethanol exposure. We have recently reported that GAPDH protein expression was increased in the brains of rats fed with ethanol. Furthermore, GAPDH interacts with the transcriptional activator, transforming growth factor-beta-inducible early gene 2 (TIEG2), to augment TIEG2-mediated MAO B activation, resulting in neuronal cell damage due to ethanol exposure. The current study investigates whether the TIEG2-MAO B cascade is also active in the brains of rats fed with ethanol. Ten ethanol-preferring rats were fed with a liquid diet containing ethanol, with increasing amounts of ethanol up to a final concentration of 6.4% representing a final diet containing 36% of calories for 28 days. Ten control rats were fed the liquid diet without ethanol. The expression of TIEG2 protein, MAO B mRNA levels, MAO B catalytic activity, and the levels of anti-apoptotic protein Bcl 2 and apoptotic protein caspase 3 were determined in the prefrontal cortex of the rats. Ethanol significantly increased protein levels of TIEG2, active caspase 3, MAO B mRNA and enzyme activity, but significantly decreased Bcl 2 protein expression compared to control rats. In summary, ethanol increases the TIEG2-MAO B brain cell death cascade in rat brains, suggesting that the TIEG2-MAO B pathway is a novel pathway for brain cell damage resulting from ethanol exposure, and may contribute to chronic alcohol-induced brain damage.

Global gene expression analysis reveals specific and redundant roles for H1 variants, H1c and H1(0), in gene expression regulation.

In mammals, the functional significance of the presence of evolutionarily conserved, multiple non-allelic H1 variants remains unclear. We used a unique overproduction approach coupled with cell cycle synchronization and early time point assays to assess differential effects of H1 variants, H1c and H1(0), on global gene expression in the absence of compensatory events that may mask variant-specific effects. We found that H1c and H1(0) act primarily as specific rather than global regulators of gene expression. Many of the genes affected were uniquely targeted by either H1c or H1(0), affirming that H1 variants have some unique roles. We also identified genes that were affected by both variants, in which cases the expression of these genes was, for the most part, affected similarly by both the variants. This observation suggests that as well as having specific functions, the H1 variants share common roles in the organization of chromatin. We further noted that H1(0) repressed more genes than did H1c, which may underlie the prevailing notion that H1(0) is a stronger repressor of transcription.

Histone H1 variants differentially inhibit DNA replication through an affinity for chromatin mediated by their carboxyl-terminal domains.

Multiple forms of histone H1 are found in most mammalian tissues, and diversity in their temporal and spatial expression likely corresponds to diversity in function. Here, using Xenopus egg extracts, we show that while the somatic H1s significantly inhibit DNA replication in Xenopus sperm nuclei, little or no inhibition is seen in the case of the testes-specific variant, H1t. We suggest that differences in H1-chromatin interactions might explain some of the diversity in H1 function. To demonstrate this, we show that the somatic H1 variants preferentially assemble into chromatin relative to H1t. Differences in chromatin structure are seen depending on whether chromatin assembly occurs in the presence of somatic H1s or H1t. These data suggest that the mechanistic basis for some of the functional differences of H1 variants lies in their relative affinity for chromatin. Using a series of domain-switch mutants of H1(0) and H1t we identify the H1 carboxyl-terminal domains as the domains responsible for the differential affinity for chromatin and, concurrently, for the differential effects of H1 variants upon DNA replication.