Structure/Activity Relationships for GMEB-2: The Second Member of the Glucocorticoid Modulatory Element-Binding Complex

GMEB2 Promotes the Growth of Colorectal Cancer by Activating ADRM1 Transcription and NF-κB Signalling and Is Positively Regulated by the m6A Reader YTHDF1

Transcription factors are frequently aberrantly reactivated in various cancers, including colorectal cancer (CRC). However, as a transcription factor, the role of GMEB2 in cancer is still unclear, and further studies are needed. Here, we aimed to identify the function and mechanism of GMEB2 in regulating the malignant progression of CRC. GMEB2 was found to be highly expressed in online data analyses. We demonstrated that GMEB2 was markedly upregulated at both the mRNA and protein levels in CRC cells and tissues. GMEB2 knockdown inhibited CRC cell growth in vitro and in vivo. Mechanistically, as a transcription factor, GMEB2 transactivated the ADRM1 promoter to increase its transcription. Rescue experiments showed that ADRM1 downregulation partially reversed the promoting effects of GMEB2 on CRC growth in vitro. Moreover, the GMEB2/ADRM1 axis induced nuclear translocation of NF-κB, thus activating NF-κB signalling. Finally, we further revealed that YTHDF1 recognized and bound to the m⁶A site on GMEB2 mRNA, which enhanced its stability. Taken together, our findings reveal the crucial role and regulatory mechanism of GMEB2 in CRC for the first time and provide a novel potential therapeutic target for CRC therapy.

Genome-wide alterations in hippocampal 5-hydroxymethylcytosine links plasticity genes to acute stress

Environmental stress is among the most important contributors to increased susceptibility to develop psychiatric disorders, including anxiety and post-traumatic stress disorder. While even acute stress alters gene expression, the molecular mechanisms underlying these changes remain largely unknown. 5-hydroxymethylcytosine (5hmC) is a novel environmentally sensitive DNA modification that is highly enriched in post-mitotic neurons and is associated with active transcription of neuronal genes. Recently, we found a hippocampal increase of 5hmC in the glucocorticoid receptor gene (Nr3c1) following acute stress, warranting a deeper investigation of stress-related 5hmC levels. Here we used an established chemical labeling and affinity purification method coupled with high-throughput sequencing technology to generate the first genome-wide profile of hippocampal 5hmC following exposure to acute restraint stress and a one-hour recovery. This approach found a genome-wide disruption in 5hmC associated with acute stress response, primarily in genic regions, and identified known and potentially novel stress-related targets that have a significant enrichment for neuronal ontological functions. Integration of these data with hippocampal gene expression data from these same mice found stress-related hydroxymethylation correlated to altered transcript levels and sequence motif predictions indicated that 5hmC may function by mediating transcription factor binding to these transcripts. Together, these data reveal an environmental impact on this newly discovered epigenetic mark in the brain and represent a critical step toward understanding stress-related epigenetic mechanisms that alter gene expression and can lead to the development of psychiatric disorders.

A WW-like module in the RAG1 N-terminal domain contributes to previously unidentified protein-protein interactions

More than one-third of the RAG1 protein can be truncated from the N-terminus with only subtle effects on the products of V(D)J recombination in vitro or in a mouse. What, then, is the function of the N-terminal domain? We believe it to be regulatory. We determined, several years ago, that an included RING motif could function as an ubiquitin E3 ligase. Whether this activity is limited to automodification, or may alter other proteins in the cell, remains an open question. We revisited the issue of additional protein–protein interactions between RAG1 and other proteins by means of the yeast two-hybrid assay. We confirmed the interaction already described with KPNA2/RCH1/SRP1α and found two others—to the transcription factor GMEB1/PIF p96 and the splicing factor SF3A2/SF3a66. A luciferase reporter assay demonstrates that a protein complex containing RAG proteins and the transcription factor can assemble in cells. Further mapping identified a region within the N-terminal domain resembling a WW motif. Point mutation directed at residues conserved in WW motifs eliminated binding to one of the partners. Phylogenetic analysis shows the WW-like module to be highly conserved. The module contributes to protein–protein interactions that may also influence how RAG1 binds DNA targets.

Differential modulation of glucocorticoid and progesterone receptor transactivation

The determinants of the different biological activities of progesterone receptors (PRs) vs. glucocorticoid receptors (GRs), which bind to the same DNA sequences, remain poorly understood. The mechanisms by which differential expression of a common target gene can be achieved by PR and GR include unequal agonist steroid concentrations for half maximal induction (EC50) and dissimilar amounts of residual partial agonist activity for antisteroids in addition to the more common changes in total gene induction, or Vmax. Several factors are known to alter some or all of these three parameters for GR-regulated gene induction and some (i.e., the corepressors NCoR and SMRT) modulate the EC50 and partial agonist activity for GR and PR induction of the same gene in opposite directions. The current study demonstrates that other factors known to modulate GR properties (GME, GMEB-2, Ubc9, and STAMP) can also differentially interact with PRs or alter several of the above induction parameters under otherwise identical conditions. These results support the hypothesis that the modulation of EC50, partial agonist activity, and Vmax by a given factor is not limited to one receptor in a specific cell line. Furthermore, the number of factors that unequally modulate PR and GR induction parameters is now greatly expanded, thereby increasing the possible mechanisms for differential gene regulation by PRs vs. GRs.

Glucocorticoid Receptor Ligand Binding Domain Is Sufficient for the Modulation of Glucocorticoid Induction Properties by Homologous Receptors, Coactivator Transcription Intermediary Factor 2, and Ubc9

Several factors modulate the position of the dose-response curve of steroid receptor-agonist complexes and the partial agonist activity of antagonist complexes, thereby causing differential gene activation by circulating hormones and unequal gene repression during endocrine therapies with antisteroids. We now ask whether the modulatory activity of three factors (homologous receptor, coactivator transcription intermediary factor 2, and Ubc9) requires the same or different domains of glucocorticoid receptors (GRs). In all cases, we find that neither the amino terminal half of the receptor, which contains the activation function-1 activation domain, nor the DNA binding domain is required. This contrasts with the major role of activation function-1 in determining the amount of gene expression and partial agonist activity of antisteroids with most steroid receptors. However, the situation is more complicated with Ubc9, where GR N-terminal sequences prevent the actions of Ubc9, but not added GR or transcription intermediary factor 2, at low GR concentrations. Inhibition is relieved by deletion of these sequences or by replacement with the comparable region of progesterone receptors but not by overexpression of the repressive sequences. These results plus the binding of C-terminal GR sequences to the suppressive N-terminal domain implicate an intramolecular mechanism for the inhibition of Ubc9 actions at low GR concentrations. A shift from noncooperative to cooperative steroid binding at high GR concentrations suggests that conformational changes reposition the inhibitory N-terminal sequence to allow Ubc9 interaction with elements of the ligand binding domain. Collectively, these results indicate a dominant role of GR C-terminal sequences in the modulation of the dose-response curve and partial agonist activity of GR complexes. They also reveal mechanistic differences both among individual modulators and between the ability of the same factors to regulate the total amount of gene expression.

PCR expression mutagenesis: a high-throughput mutation assay applied to the glucocorticoid receptor ligand-binding domain

Glucocorticoid receptors (GRs) are extensively studied members of the steroid hormone receptor superfamily that regulate the transcription rates of numerous genes. Notwithstanding, the role of each GR amino acid in the various steps of transactivation is still unknown. A recent report shows that linear DNA has the same capacity as super-helical plasmid DNA for gene expression in transient transfection assays. Based on this observation, we describe a high-throughput assay to analyze a large set of alanine point mutations that are introduced by two rounds of PCR. The PCR products are then directly transfected into cells. This PCR expression mutagenesis (PEM) technique is used to identify several new residues of the GR ligand binding domain that influence ligand binding and/or transactivation. PEM thus provides a quick method for screening large quantities of mutant proteins. In combination with automation, PEM provides a more rapid and efficient tool for probing the role of each amino acid in the biological functions of a given protein.