TRIM28 regulates transcriptional activity of methyl-DNA binding protein Kaiso by SUMOylation

A novel DNA binding protein encoded by circZNF131 inhibits the growth of gastric cancer by suppressing CTBP2 transcription

Circular RNAs (circRNAs) play critical roles in the occurrence of gastric cancer (GC). However, the roles of proteins encoded by circRNAs in GC remain largely unknown. This study aimed to investigate the role of ZNF131-354aa in GC. circZNF131 overexpression plasmids and short hairpin RNAs were used to overexpress and silence circZNF131 expression levels, respectively. Mass spectrometry, co-immunoprecipitation, and Western blotting were used to identify the circZNF131-encoded protein, named ZNF131-354aa. Chromatin immunoprecipitation assay was used to examine the DNA-binding activity of ZNF131-354aa. A subcutaneous tumor model was established in nude mice to examine the effects of ZNF131-354aa on GC growth. Overexpression of circZNF131 was found to inhibit the proliferation, migration and invasion of GC cells, while knockdown of circZNF131 had the opposite effect. Furthermore, immunoprecipitation and mass spectrometry verified that circZNF131 encoded a 40.5 kDa protein, ZNF131-354aa. ZNF131-354aa was shown to inhibit GC progression. ZNF131-354aa was found to be degraded by tripartite motif-containing 28 (TRIM28)-mediated ubiquitination. Moreover, ZNF131-354aa was found to promote E-cadherin and phosphatase and tensin homolog (PTEN) expression by interacting with the intron of the C-terminal binding protein 2 (CTBP2) gene and repressing its expression. In conclusion, ZNF131-354aa acts as a tumor suppressor in GC by inhibiting CTBP2 transcription.

Identifying the DNA methylation preference of transcription factors using ProtBERT and SVM

Transcription factors (TFs) can affect gene expression by binding to certain specific DNA sequences. This binding process of TFs may be modulated by DNA methylation. A subset of TFs that serve as methylation readers preferentially binds to certain methylated DNA and is defined as TFPM. The identification of TFPMs enhances our understanding of DNA methylation's role in gene regulation. However, their experimental identification is resource-demanding. In this study, we propose a novel two-step computational approach to classify TFs and TFPMs. First, we employed a fine-tuned ProtBERT model to differentiate between the classes of TFs and non-TFs. Second, we combined the Reduced Amino Acid Category (RAAC) with K-mer and SVM to predict the potential of TFs to bind to methylated DNA. Comparative experiments demonstrate that our proposed methods outperform all existing approaches and emphasize the efficiency of our computational framework in classifying TFs and TFPMs. Cross-species validation on an independent mouse dataset further demonstrates the generalizability of our proposed framework In addition, we conducted predictions on all human transcription factors and found that most of the top 20 proteins belong to the Krueppel C2H2-type Zinc-finger family. So far, some studies have demonstrated a partial correlation between this family and DNA methylation and confirmed the preference of some of its members, thereby showing the robustness of our approach.

SUMOylation of TRIM28 is positively modulated by the BTB/POZ domain of Kaiso

BACKGROUND

TRIM28 plays a crucial role in maintaining genomic stability and establishing imprinting, facilitated by the diversity of KRAB zinc finger proteins. The SUMOylation of TRIM28 is essential for its function and is enhanced in the presence of the KRAB domain. Previously, we demonstrated that Kaiso, another factor capable of interacting with TRIM28, can promote its SUMOylation. Here we investigate which structural elements of Kaiso are necessary for the hyper-SUMOylation of TRIM28.

METHODS AND RESULTS

We found that the SUMO-interacting motifs (SIMs) of Kaiso are not responsible for TRIM28 SUMOylation. The SUMOylation of individual TRIM28 domains in the presence of Kaiso was not observed, suggesting the importance of TRIM28's structural integrity for this process. The Kaiso BTB/POZ domain, but not its closest homolog ZBTB4, is sufficient for the effective hyper-SUMOylation of TRIM28. Also, using single-cell sequencing data of mouse embryos, we identified cells in which co-expression of Kaiso and TRIM28 occurs, including the immune system, nervous system and various epithelial cells.

CONCLUSIONS

BTB/POZ domain of Kaiso may function similarly to KRAB domains in its interaction with TRIM28 regulating its SUMOylation.

Dynamic BTB-domain filaments promote clustering of ZBTB proteins

The formation of dynamic protein filaments contributes to various biological functions by clustering individual molecules together and enhancing their binding to ligands. We report such a propensity for the BTB domains of certain proteins from the ZBTB family, a large eukaryotic transcription factor family implicated in differentiation and cancer. Working with Xenopus laevis and human proteins, we solved the crystal structures of filaments formed by dimers of the BTB domains of ZBTB8A and ZBTB18 and demonstrated concentration-dependent higher-order assemblies of these dimers in solution. In cells, the BTB-domain filamentation supports clustering of full-length human ZBTB8A and ZBTB18 into dynamic nuclear foci and contributes to the ZBTB18-mediated repression of a reporter gene. The BTB domains of up to 21 human ZBTB family members and two related proteins, NACC1 and NACC2, are predicted to behave in a similar manner. Our results suggest that filamentation is a more common feature of transcription factors than is currently appreciated.

Genomic Imprinting and Random Monoallelic Expression

The review discusses the mechanisms of monoallelic expression, such as genomic imprinting, in which gene transcription depends on the parental origin of the allele, and random monoallelic transcription. Data on the regulation of gene activity in the imprinted regions are summarized with a particular focus on the areas controlling imprinting and factors influencing the variability of the imprintome. The prospects of studies of the monoallelic expression are discussed.

The N-Terminal Part of Drosophila CP190 Is a Platform for Interaction with Multiple Architectural Proteins

CP190 is a co-factor in many Drosophila architectural proteins, being involved in the formation of active promoters and insulators. CP190 contains the N-terminal BTB/POZ (Broad-Complex, Tramtrack and Bric a brac/POxvirus and Zinc finger) domain and adjacent conserved regions involved in protein interactions. Here, we examined the functional roles of these domains of CP190 in vivo. The best-characterized architectural proteins with insulator functions, Pita, Su(Hw), and dCTCF, interacted predominantly with the BTB domain of CP190. Due to the difficulty of mutating the BTB domain, we obtained a transgenic line expressing a chimeric CP190 with the BTB domain of the human protein Kaiso. Another group of architectural proteins, M1BP, Opbp, and ZIPIC, interacted with one or both of the highly conserved regions in the N-terminal part of CP190. Transgenic lines of D. melanogaster expressing CP190 mutants with a deletion of each of these domains were obtained. The results showed that these mutant proteins only partially compensated for the functions of CP190, weakly binding to selective chromatin sites. Further analysis confirmed the essential role of these domains in recruitment to regulatory regions associated with architectural proteins. We also found that the N-terminal of CP190 was sufficient for recruiting Z4 and Chromator proteins and successfully achieving chromatin opening. Taken together, our results and the results of previous studies showed that the N-terminal region of CP190 is a platform for simultaneous interaction with various DNA-binding architectural proteins and transcription complexes.