CREB-binding proteins (CBP) as a transcriptional coactivator of GATA-2

Multi-faceted regulation of CREB family transcription factors

cAMP response element-binding protein (CREB) is a ubiquitously expressed nuclear transcription factor, which can be constitutively activated regardless of external stimuli or be inducibly activated by external factors such as stressors, hormones, neurotransmitters, and growth factors. However, CREB controls diverse biological processes including cell growth, differentiation, proliferation, survival, apoptosis in a cell-type-specific manner. The diverse functions of CREB appear to be due to CREB-mediated differential gene expression that depends on cAMP response elements and multi-faceted regulation of CREB activity. Indeed, the transcriptional activity of CREB is controlled at several levels including alternative splicing, post-translational modification, dimerization, specific transcriptional co-activators, non-coding small RNAs, and epigenetic regulation. In this review, we present versatile regulatory modes of CREB family transcription factors and discuss their functional consequences.

Quantitative and qualitative impairments in GATA2 and myeloid neoplasms

GATA2 is a key transcription factor critical for hematopoietic cell development. During the past decade, it became clear that heterozygous germline mutations in the GATA2 gene cause bone marrow failure and primary immunodeficiency syndrome, conditions that lead to a predisposition toward myeloid neoplasms, such as myelodysplastic syndrome, acute myeloid leukemia, and chronic myelomonocytic leukemia. Somatic mutations of the GATA2 gene are also involved in the pathogenesis of myeloid malignancies. Cases with GATA2 gene mutations are divided into two groups, resulting in either a quantitative deficiency or a qualitative defect in the GATA2 protein depending on the mutation position and type. In the former case, GATA2 mRNA expression from the mutant allele is markedly reduced or completely abrogated, and reduced GATA2 protein expression is involved in the pathogenesis. In the latter case, almost equal amounts of structurally abnormal and wildtype GATA2 proteins are predicted to be present and contribute to the pathogenesis. The development of mouse models of these human GATA2-related diseases has been undertaken, which naturally develop myeloid neoplasms.

Targeting pioneering factor and hormone receptor cooperative pathways to suppress tumor progression

Nuclear receptors and pioneer factors drive the development and progression of prostate cancer. In this disease, aggressive disease phenotypes and hormone therapy failures result from resurgent activity of androgen receptor (AR) and the upregulation of coactivator protein p300 and pioneer factors (e.g., GATA2 and FOXA1). Thus, a major emphasis in the field is to identify mechanisms by which castrate-resistant AR activity and pioneer factor function can be combinatorially suppressed. Here we show that the turmeric spice isoflavone curcumin suppresses p300 and CBP occupancy at sites of AR function. Curcumin reduced the association of histone acetylation and pioneer factors, thereby suppressing AR residence and downstream target gene expression. Histone deacetylase inhibitors reversed the effects of curcumin on AR activity, further underscoring the impact of curcumin on altering the chromatin landscape. These functions precluded pioneer factor occupancy, leading ultimately to a suppression of ligand-dependent and ligand-independent AR residence on chromatin. Moreover, these functions were conserved even in cells with heightened pioneer factor activity, thus identifying a potential strategy to manage this subclass of tumors. Biological relevance was further identified using in vivo xenograft models mimicking disease progression. Curcumin cooperated in vivo with androgen deprivation as indicated by a reduction in tumor growth and delay to the onset of castrate-resistant disease. Together, our results show the combinatorial impact of targeting AR and histone modification in prostate cancer, thus setting the stage for further development of curcumin as a novel agent to target AR signaling.

Targeting pioneering factor and hormone receptor cooperative pathways to suppress tumor progression

Nuclear receptors and pioneer factors drive the development and progression of prostate cancer. In this disease, aggressive disease phenotypes and hormone therapy failures result from resurgent activity of androgen receptor (AR) and the upregulation of coactivator protein p300 and pioneer factors (e.g., GATA2 and FOXA1). Thus, a major emphasis in the field is to identify mechanisms by which castrate-resistant AR activity and pioneer factor function can be combinatorially suppressed. Here we show that the turmeric spice isoflavone curcumin suppresses p300 and CBP occupancy at sites of AR function. Curcumin reduced the association of histone acetylation and pioneer factors, thereby suppressing AR residence and downstream target gene expression. Histone deacetylase inhibitors reversed the effects of curcumin on AR activity, further underscoring the impact of curcumin on altering the chromatin landscape. These functions precluded pioneer factor occupancy, leading ultimately to a suppression of ligand-dependent and ligand-independent AR residence on chromatin. Moreover, these functions were conserved even in cells with heightened pioneer factor activity, thus identifying a potential strategy to manage this subclass of tumors. Biological relevance was further identified using in vivo xenograft models mimicking disease progression. Curcumin cooperated in vivo with androgen deprivation as indicated by a reduction in tumor growth and delay to the onset of castrate-resistant disease. Together, our results show the combinatorial impact of targeting AR and histone modification in prostate cancer, thus setting the stage for further development of curcumin as a novel agent to target AR signaling.

GATA transcription factors regulate LHβ gene expression

The GATA family of transcription factors are critical determinants of cell differentiation as well as regulation of adult gene expression throughout the reproductive axis. Within the anterior pituitary gland, GATA factors have been shown to increase glycoprotein α-subunit gene promoter activity; however, nothing has been known about the impact of these factors on expression of the gonadotropin β-subunits. In this study, we demonstrate expression of both GATA2 and GATA4 in primary mouse gonadotropes and the gonadotrope cell line, LβT2. Based on the transient transfection in fibroblast cells, GATA factors increase LH β-subunit gene (LHβ) promoter activity alone and in synergy with the orphan nuclear receptors steroidogenic factor-1 (SF-1) and liver receptor homologue-1 (LRH-1). The GATA response was localized to a DNA regulatory region at position -101 in the rat LHβ gene promoter which overlaps with a previously described cis-element for pituitary homeobox-1 (Pitx1) and is flanked by two SF-1/LRH-1 regulatory sites. As determined by gel shift, GATA and Pitx1 can compete for binding to this element. Furthermore, mutation analysis revealed a requirement for both the GATA/Pitx1 and the SF-1/LRH-1 cis-elements in order to achieve synergy. These studies identify a novel role for GATA transcription factors in the pituitary and reveal additional molecular mechanisms by which precise modulation of LHβ gene expression can be achieved.

The exceptional properties of 9-methyl-beta-carboline: stimulation, protection and regeneration of dopaminergic neurons coupled with anti-inflammatory effects

Beta-carbolines (BCs) are potential endogenous and exogenous neurotoxins that may contribute to the pathogenesis of Parkinson's disease. However, we recently demonstrated protective and stimulatory effects of 9-methyl-BC (9-me-BC) in primary dopaminergic culture. In the present study, treatment with 9-me-BC unmasked a unique tetrad of effects. First, tyrosine hydroxylase (TH) expression was stimulated in pre-existing dopa decarboxylase immunoreactive neurons and several TH-relevant transcription factors (Gata2, Gata3, Creb1, Crebbp) were up-regulated. Neurite outgrowth of TH immunoreactive (THir) neurons was likewise stimulated. The interaction with tyrosine kinases (protein kinase A and C, epidermal growth factor-receptor, fibroblast growth factor-receptor and neural cell adhesion molecule) turned out to be decisive for these observed effects. Second, 9-me-BC protected in acute toxicity models THir neurons against lipopolysaccharide and 2,9-dime-BC(+) toxicity. Third, in a chronic toxicity model when cells were treated with 9-me-BC after chronic rotenone administration, a pronounced regeneration of THir neurons was observed. Fourth, 9-me-BC inhibited the proliferation of microglia induced by toxin treatment and installed an anti-inflammatory environment by decreasing the expression of inflammatory cytokines and receptors. Finally, 9-me-BC lowered the content of alpha-synuclein protein in the cultures. The presented results warrant the exploration of 9-me-BC as a novel potential anti-parkinsonian medication, as 9-me-BC interferes with several known pathogenic factors in Parkinson's disease as outlined above. Further investigations are currently under way.