A/T Run Geometry of B-form DNA Is Independent of Bound Methyl-CpG Binding Domain, Cytosine Methylation and Flanking Sequence

Integrative Investigation of Flavonoids Targeting YBX1 Protein-Protein Interaction Network in Breast Cancer: From Computational Analysis to Experimental Validation

Y-box-binding protein 1 (YBX1) is a multifunctional oncoprotein with its nuclear localization contributing to chemo-resistance in breast cancer. Through its interactions with various proteins and lncRNAs, YBX1 promotes cancer cell migration, invasion, and metastasis. Despite its significant role in cancer progression, studies on YBX1's protein-protein interactions (PPIs) remain limited. Flavonoids are natural compounds with anticancer properties that inhibit metastasis, modulate immunity, and induce apoptosis, with minimal systemic toxicity, making them strong candidates for cancer therapy. Targeting PPIs offers a promising approach for cancer therapy and flavonoids, with their anticancer properties, may modulate these interactions. Our study focused on the YBX1 PPI network, specifically targeting HSPA1A, IGF2BP1, MECP2, G3BP1, EWSR1, PURA, and SYNCRIP. We selected four flavonoids Quercetin, Fisetin, Rutin, and Myricitrin based on literature and conducted 26 docking sessions. Further ADMET analysis indicated Quercetin and Fisetin as more favorable for drug-likeness parameters than Rutin and Myricitrin, which was underscored by MD simulation data. In vitro studies showed that Quercetin and Fisetin downregulated YBX1 expression in a dose-dependent manner (50 μM to 150 μM) in MCF-7 cells. Our study provides a preliminary understanding of YBX1 PPI and the potential of flavonoids to disrupt these interactions. This study investigates the potential of flavonoids to target YBX1 PPIs, providing insights into novel therapeutic strategies for YBX1-driven cancers.

The Molecular Basis of MeCP2 Function in the Brain

MeCP2 is a reader of the DNA methylome that occupies a large proportion of the genome due to its high abundance and the frequency of its target sites. It has been the subject of extensive study because of its link with 'MECP2-related disorders', of which Rett syndrome is the most prevalent. This review integrates evidence from patient mutation data with results of experimental studies using mouse models, cell lines and in vitro systems to critically evaluate our understanding of MeCP2 protein function. Recent evidence challenges the idea that MeCP2 is a multifunctional hub that integrates diverse processes to underpin neuronal function, suggesting instead that its primary role is to recruit the NCoR1/2 co-repressor complex to methylated sites in the genome, leading to dampening of gene expression.

Plasticity at the DNA recognition site of the MeCP2 mCG-binding domain

MeCP2 is an abundant protein, involved in transcriptional repression by binding to CG and non-CG methylated DNA. However, MeCP2 might also function as a transcription activator as MeCP2 is found bound to sparsely methylated promoters of actively expressed genes. Furthermore, Attachment Region Binding Protein (ARBP), the chicken ortholog of MeCP2, has been reported to bind to Matrix/scaffold attachment regions (MARs/SARs) DNA with an unmethylated 5'-CAC/GTG-3' consensus sequence. In our previous study, although we have systemically measured the binding abilities of MBDs to unmethylated CAC/GTG DNA and the complex structures reveal that the MBD2-MBD (MBD of MBD2) binds to the unmethylated CAC/GTG DNA by recognizing the complementary GTG trinucleotide, how the MeCP2-MBD (MBD of MeCP2) recognizes the unmethylated CAC/GTG DNA, especially the MARs DNA, is still unclear. In this study, we investigated the binding characteristics of MeCP2 in recognizing unmethylated 5'-CAC/GTG-3' motif containing DNA by binding and structural studies. We found that MeCP2-MBD binds to MARs DNA with a comparable binding affinity to mCG DNA, and the MeCP2-CAC/GTG complex structure revealed that MeCP2 residues R111 and R133 form base-specific interactions with the GTG motif. For comparison, we also determined crystal structures of the MeCP2-MBD bound to mCG and mCAC/GTG DNA, respectively. Together, these crystal structures illustrate the adaptability of the MeCP2-MBD toward the GTG motif as well as the mCG DNA, and also provide structural basis of a biological role of MeCP2 as a transcription activator and its disease implications in Rett syndrome.

Cytosine methylation of mitochondrial DNA at CpG sequences impacts transcription factor A DNA binding and transcription

In eukaryotes, cytosine methylation of nuclear DNA at CpG sequences (5mCpG) regulates epigenetic inheritance through alterations in chromatin structure. However, mitochondria lack nucleosomal chromatin, therefore the molecular mechanisms by which 5mCpG influences mitochondria must be different and are as yet unknown. Mitochondrial Transcription Factor A (TFAM) is both the primary DNA-compacting protein in the mitochondrial DNA (mtDNA) nucleoid and a transcription-initiation factor. TFAM must encounter hundreds of CpGs in mtDNA, so the occurrence of 5mCpG has the potential to impact TFAM-DNA recognition. We used biophysical approaches to determine whether 5mCpG alters any TFAM-dependent activities. 5mCpG in the heavy strand promoter (HSP1) increased the binding affinity of TFAM and induced TFAM multimerization with increased cooperativity compared to nonmethylated DNA. However, 5mCpG had no apparent effect on TFAM-dependent DNA compaction. Additionally, 5mCpG had a clear and context-dependent effect on transcription initiating from the three mitochondrial promoters. Taken together, our findings demonstrate that 5mCpG in the mitochondrial promoter region does impact TFAM-dependent activities in vitro.

An early seizure variant type of a male Rett syndrome patient with a MECP2 p.Arg133His missense mutation

BACKGROUND

The clinical spectrum of Rett syndrome (RTT; Mendelian Inheritance in Man [MIM] #312750) in males is considered to be wider than previously expected. Therefore, the existence of RTT with a normal male karyotype is still controversial. Here, we report the first case of a male patient presenting with an early seizure type of Rett-like phenotypes with a missense variant of MECP2.

METHOD

An 8-month-old male was admitted to the pediatric department due to an initial seizure event following aspiration pneumonia and was referred to our clinic for the evaluation of unexplained neuroregression. Genomic DNA was prepared from venous blood by standard procedures and was processed at the Yale Center for Genome Analysis (YCGA) for whole exome sequencing (WES). Processing of sequence data, variant calling, and the identification of de novo mutations were then performed. Direct Sanger sequencing was performed following PCR amplification.

RESULT

In this patient with a normal karyotype, WES analysis led to the identification of a novel, de novo missense variant of MECP2 (p.Arg133His) that is not observed in the normal population.

CONCLUSION

This rare case of an p.Arg133His hemizygous MECP2 missense mutation could guide future treatment and follow-up plans for RETT-like phenotypes.

Structural investigation of Rett-inducing MeCP2 mutations

X-ray structure of methyl-CpG binding domain (MBD) of MeCP2, an intrinsically disordered protein (IDP) involved in Rett syndrome, offers a rational basis for defining the spatial distribution for most of the sites where mutations responsible of Rett syndrome, RTT, occur. We have ascribed pathogenicity for mutations of amino acids bearing positively charged side chains, all located at the protein-DNA interface, as positive charge removal cause reduction of the MeCP2-DNA adduct lifetime. Pathogenicity of the frequent proline replacements, outside the DNA contact moiety of MBD, can be attributed to the role of this amino acid for maintaining both unfolded states for unbound MeCP2 and, at the same time, to favor some higher conformational order for stabilizing structural determinants required by protein activity. These hypotheses can be extended to transcription repressor domain, TRD, the other MeCP2-DNA interaction site and, in general, to all the IDP that interact with nucleic acids.

Structural Basis of MeCP2 Distribution on Non-CpG Methylated and Hydroxymethylated DNA

The Rett-syndrome-associated methyl-CpG-binding protein 2 (MeCP2) selectively binds methylated DNA to regulate transcription during the development of mature neurons. Like other members of the methyl-CpG-binding domain (MBD) family, MeCP2 functions through the recognition of symmetrical 5-methylcytosines in CpG (mCG) dinucleotides. Advances in base-level resolution epigenetic mapping techniques have revealed, however, that MeCP2 can bind asymmetrically methylated and hydroxymethylated CpA dinucleotides and that this alternative binding selectivity modifies gene expression in the developing mammalian brain. The structural determinants of binding to methylated CpA (mCA) and hydroxymethylated DNA have not been previously investigated. Here, we employ isothermal titration calorimetry and NMR spectroscopy to characterize MeCP2 binding to methylated and hydroxymethylated mCG and mCA DNA, examine the effects of Rett-syndrome-associated missense mutations, and make comparisons to the related and evolutionarily most ancient protein, MBD2. These analyses reveal that MeCP2 binds mCA with high affinity in a strand-specific and orientation-dependent manner. In contrast, MBD2 does not show high affinity or methyl-specific binding to mCA. The Rett-associated missense mutations (T158M, R106W, and P101S) destabilize the MeCP2 MBD and disrupt the recognition of mCG and mCA equally. Finally, hydroxymethylation of a high-affinity mCA site does not alter the binding properties, whereas hemi-hydroxylation of the equivalent cytosine in an mCG site decreases affinity and specificity. Based on these findings, we suggest that MeCP2 recognition of methylated/hydroxymethylated CpA dinucleotides functions as an epigenetic switch redistributing MeCP2 among mCG and mCA loci.