CXXC5 regulates differentiation of C2C12 myoblasts into myocytes

Effect of LncRNA LOC106505926 on myogenesis and Lipogenesis of porcine primary cells

BACKGROUND

Skeletal muscle development and fat deposition have important effects on meat quality. The study of regulating skeletal muscle development and fat deposition is of great significance in improving the quality of carcass and meat. In the present study, whole transcriptome sequencing (including RNA-Seq and miRNA-Seq) was performed on the longissimus dorsi muscle (LDM) of Jinfen White pigs at 1, 90, and 180 days of age.

RESULTS

The results showed that a total of 245 differentially expressed miRNAs were screened in any two comparisons, which may be involved in the regulation of myogenesis. Among them, compared with 1-day-old group, miR-22-5p was significantly up-regulated in 90-day-old group and 180-day-old group. Functional studies demonstrated that miR-22-5p inhibited the proliferation and differentiation of porcine skeletal muscle satellite cells (PSCs). Pearson correlation coefficient analysis showed that long non-coding RNA (lncRNA) LOC106505926 and CXXC5 gene had strong negative correlations with miR-22-5p. The LOC106505926 and CXXC5 were proven to promote the proliferation and differentiation of PSCs, as opposed to miR-22-5p. In terms of mechanism, LOC106505926 functions as a molecular sponge of miR-22-5p to modulate the expression of CXXC5, thereby inhibits the differentiation of PSCs. In addition, LOC106505926 regulates the differentiation of porcine preadipocytes through direct binding with FASN.

CONCLUSIONS

Collectively, our results highlight the multifaceted regulatory role of LOC106505926 in controlling skeletal muscle and adipose tissue development in pigs and provide new targets for improving the quality of livestock products by regulating skeletal muscle development and fat deposition.

Biomaterial Design Inspired by Regenerative Research Organisms

The efficacy of implanted biomaterials is largely dependent on the response of the host's immune and stromal cells. Severe foreign body response (FBR) can impede the integration of the implant into the host tissue and compromise the intended mechanical and biochemical function. Many features of FBR, including late-stage fibrotic encapsulation of implants, parallel the formation of fibrotic scar tissue after tissue injury. Regenerative organisms like zebrafish and salamanders can avoid fibrosis after injury entirely, but FBR in these research organisms is rarely investigated because their immune competence is much lower than humans. The recent characterization of a regenerative mammal, the spiny mouse (Acomys), has inspired us to take a closer look at cellular regulation in regenerative organisms across the animal kingdom for insights into avoiding FBR in humans. Here, we highlight how major features of regeneration, such as blastema formation, macrophage polarization, and matrix composition, can be modulated across a range of regenerative research organisms to elucidate common features that may be harnessed to minimize FBR. Leveraging a deeper understanding of regenerative biology for biomaterial design may help to reduce FBR and improve device integration and performance.

Idax and Rinf facilitate expression of Tet enzymes to promote neural and suppress trophectodermal programs during differentiation of embryonic stem cells

The Inhibitor of disheveled and axin (Idax) and its ortholog the Retinoid inducible nuclear factor (Rinf) are DNA binding proteins with nuclear and cytoplasmic functions. Rinf is expressed in embryonic stem cells (ESCs) where it regulates transcription of the Ten-eleven translocation (Tet) enzymes, promoting neural and suppressing mesendoderm/trophectoderm differentiation. Here, we find that Idax, which is not expressed in ESCs, is induced upon differentiation. Like Rinf, Idax facilitates neural and silences trophectodermal programs. Individual or combined loss of Idax and Rinf led to downregulation of neural and upregulation of trophectoderm markers during differentiation of ESCs to embryoid bodies as well as during directed differentiation of ESCs to neural progenitor cells (NPCs) and trophoblast-like cells. These defects resemble those of Tet-deficient ESCs. Consistently, Tet genes are direct targets of Idax and Rinf, and loss of Idax and Rinf led to downregulation of Tet enzymes during ESC differentiation to NPCs and trophoblast-like cells. While Idax and Rinf single and double knockout (DKO) mice were viable and overtly normal, DKO embryos had reduced expression of several NPC markers in embryonic forebrains and deregulated expression of selected trophoblast markers in placentas. NPCs derived from DKO forebrains had reduced self-renewal while DKO placentas had increased junctional zone and reduced labyrinth layers. Together, our findings establish Idax and Rinf as regulators of Tet enzymes for proper differentiation of ESCs.

Synergistic Effects of Multiple Factors Involved in COVID-19-dependent Muscle Loss

The COVID-19 pandemic caused by the novel SARS-CoV-2 coronavirus is an ongoing pandemic causing severe health crisis worldwide. Recovered COVID-19 patients go through several long-term side effects such as fatigue, headaches, dizziness, weight loss, and muscle loss among others. Our study sought to determine the molecular mechanisms behind muscle loss in COVID-19 patients. We hypothesized that multiple factors such as cytokine storm and therapeutic drugs (glucocorticoid and antiviral drugs) might be involved in muscle loss. Using the Gene Expression Omnibus database, we identified several studies that performed RNA sequencing on skeletal muscles with the treatment of cytokine, glucocorticoid, and antiviral drugs. Our study identified cytokines, such as IL-1b, and IL-6, associated with altered regulation of several genes involved in the myogenic processes, including Ttn, Cxxc5, Malat1, and Foxo1. We also observed that glucocorticoid altered the expression of Foxo1, Lcn2, Slc39a14, and Cdkn1a. Finally, we found out that the antiviral (RNA-dependent RNA polymerase inhibitor) drug regulates the expression of some of the muscle-related genes (Txnip, Ccnd1, Hdac9, and Fbxo32). Based on our findings, we hypothesize that the cytokine storm, glucocorticoids, and antiviral drugs might be synergistically involved in COVID-19-dependent muscle loss.

CHAF1A Blocks Neuronal Differentiation and Promotes Neuroblastoma Oncogenesis via Metabolic Reprogramming

Neuroblastoma (NB) arises from oncogenic disruption of neural crest (NC) differentiation. Treatment with retinoic acid (RA) to induce differentiation has improved survival in some NB patients, but not all patients respond, and most NBs eventually develop resistance to RA. Loss of the chromatin modifier chromatin assembly factor 1 subunit p150 (CHAF1A) promotes NB cell differentiation; however, the mechanism by which CHAF1A drives NB oncogenesis has remained unexplored. This study shows that CHAF1A gain-of-function supports cell malignancy, blocks neuronal differentiation in three models (zebrafish NC, human NC, and human NB), and promotes NB oncogenesis. Mechanistically, CHAF1A upregulates polyamine metabolism, which blocks neuronal differentiation and promotes cell cycle progression. Targeting polyamine synthesis promotes NB differentiation and enhances the anti-tumor activity of RA. The authors' results provide insight into the mechanisms that drive NB oncogenesis and suggest a rapidly translatable therapeutic approach (DFMO plus RA) to enhance the clinical efficacy of differentiation therapy in NB patients.

A prelude to the proximity interaction mapping of CXXC5

CXXC5 is a member of the zinc-finger CXXC family proteins that interact with unmodified CpG dinucleotides through a conserved ZF-CXXC domain. CXXC5 is involved in the modulation of gene expressions that lead to alterations in diverse cellular events. However, the underlying mechanism of CXXC5-modulated gene expressions remains unclear. Proteins perform their functions in a network of proteins whose identities and amounts change spatiotemporally in response to various stimuli in a lineage-specific manner. Since CXXC5 lacks an intrinsic transcription regulatory function or enzymatic activity but is a DNA binder, CXXC5 by interacting with proteins could act as a scaffold to establish a chromatin state restrictive or permissive for transcription. To initially address this, we utilized the proximity-dependent biotinylation approach. Proximity interaction partners of CXXC5 include DNA and chromatin modifiers, transcription factors/co-regulators, and RNA processors. Of these, CXXC5 through its CXXC domain interacted with EMD, MAZ, and MeCP2. Furthermore, an interplay between CXXC5 and MeCP2 was critical for a subset of CXXC5 target gene expressions. It appears that CXXC5 may act as a nucleation factor in modulating gene expressions. Providing a prelude for CXXC5 actions, our results could also contribute to a better understanding of CXXC5-mediated cellular processes in physiology and pathophysiology.

A CpG island promoter drives the CXXC5 gene expression

CXXC5 is a member of the zinc-finger CXXC family that binds to unmethylated CpG dinucleotides. CXXC5 modulates gene expressions resulting in diverse cellular events mediated by distinct signaling pathways. However, the mechanism responsible for CXXC5 expression remains largely unknown. We found here that of the 14 annotated CXXC5 transcripts with distinct 5' untranslated regions encoding the same protein, transcript variant 2 with the highest expression level among variants represents the main transcript in cell models. The DNA segment in and at the immediate 5'-sequences of the first exon of variant 2 contains a core promoter within which multiple transcription start sites are present. Residing in a region with high G-C nucleotide content and CpG repeats, the core promoter is unmethylated, deficient in nucleosomes, and associated with active RNA polymerase-II. These findings suggest that a CpG island promoter drives CXXC5 expression. Promoter pull-down revealed the association of various transcription factors (TFs) and transcription co-regulatory proteins, as well as proteins involved in histone/chromatin, DNA, and RNA processing with the core promoter. Of the TFs, we verified that ELF1 and MAZ contribute to CXXC5 expression. Moreover, the first exon of variant 2 may contain a G-quadruplex forming region that could modulate CXXC5 expression.

The epigenetic regulator RINF (CXXC5) maintains <i>SMAD7</i> expression in human immature erythroid cells and sustains red blood cells expansion

The gene CXXC5, encoding a retinoid-inducible nuclear factor (RINF), is located within a region at 5q31.2 commonly deleted in myelodysplastic syndrome and adult acute myeloid leukemia. RINF may act as an epigenetic regulator and has been proposed as a tumor suppressor in hematopoietic malignancies. However, functional studies in normal hematopoiesis are lacking, and its mechanism of action is unknown. Here, we evaluated the consequences of RINF silencing on cytokine-induced erythroid differentiation of human primary CD34⁺ progenitors. We found that RINF is expressed in immature erythroid cells and that RINF-knockdown accelerated erythropoietin-driven maturation, leading to a significant reduction (~45%) in the number of red blood cells, without affecting cell viability. The phenotype induced by RINF-silencing was dependent on tumor growth factor b (TGFb) and mediated by SMAD7, a TGFb-signaling inhibitor. RINF upregulates SMAD7 expression by direct binding to its promoter and we found a close correlation between RINF and SMAD7 mRNA levels both in CD34⁺ cells isolated from bone marrow of healthy donors and myelodysplastic syndrome patients with del(5q). Importantly, RINF knockdown attenuated SMAD7 expression in primary cells and ectopic SMAD7 expression was sufficient to prevent the RINF knockdown-dependent erythroid phenotype. Finally, RINF silencing affects 5’-hydroxymethylation of human erythroblasts, in agreement with its recently described role as a TET2-anchoring platform in mouse. Collectively, our data bring insight into how the epigenetic factor RINF, as a transcriptional regulator of SMAD7, may fine-tune cell sensitivity to TGFb superfamily cytokines and thus play an important role in both normal and pathological erythropoiesis.

Rinf Regulates Pluripotency Network Genes and Tet Enzymes in Embryonic Stem Cells

The Retinoid inducible nuclear factor (Rinf), also known as CXXC5, is a nuclear protein, but its functions in the context of the chromatin are poorly defined. We find that in mouse embryonic stem cells (mESCs), Rinf binds to the chromatin and is enriched at promoters and enhancers of Tet1, Tet2, and pluripotency genes. The Rinf-bound regions show significant overlapping occupancy of pluripotency factors Nanog, Oct4, and Sox2, as well as Tet1 and Tet2. We found that Rinf forms a complex with Nanog, Oct4, Tet1, and Tet2 and facilitates their proper recruitment to regulatory regions of pluripotency and Tet genes in ESCs to positively regulate their transcription. Rinf deficiency in ESCs reduces expression of Rinf target genes, including several pluripotency factors and Tet enzymes, and causes aberrant differentiation. Together, our findings establish Rinf as a regulator of the pluripotency network genes and Tet enzymes in ESCs.

Whole-genome sequencing association analysis reveals the genetic architecture of meat quality traits in Chinese Qingyu pigs

The Chinese Qingyu pig breed is an invaluable indigenous genetic resource. However, few studies have investigated the genetic architecture of meat quality traits in Qingyu pigs. Here, 30 purebred Qingyu pigs were subjected to whole-genome sequencing. After quality control, 18 436 759 SNPs were retained. Genome-wide association studies (GWAS) were then performed for meat pH and color at three postmortem time points (45 min, 24 h, and 48 h) using single-marker regression analysis. In total, 11 and 69 SNPs were associated with meat pH and color of the longissimus thoracis muscle (LTM), respectively, while 54 and 29 SNPs were associated with meat pH and color of the semimembranosus muscle (SM), respectively. Seven SNPs associated with pork pH were shared by all three postmortem time points. Several candidate genes for meat traits were identified, including four genes (CXXC5, RYR3, BNIP3, and MYCT1) related to skeletal muscle development, regulation of Ca²⁺ release in the muscle, and anaerobic respiration, which are promising candidates for selecting superior meat quality traits in Qingyu pigs. To our knowledge, this is the first study investigating the postmortem genetic architecture of pork pH and color in Qingyu pigs. Our findings further the current understanding of the genetic factors influencing meat quality.

CXXC5 as an unmethylated CpG dinucleotide binding protein contributes to estrogen-mediated cellular proliferation

Evidence suggests that the CXXC type zinc finger (ZF-CXXC) protein 5 (CXXC5) is a critical regulator/integrator of various signaling pathways that include the estrogen (E2)-estrogen receptor α (ERα). Due to its ZF-CXXC domain, CXXC5 is considered to be a member of the ZF-CXXC family, which binds to unmethylated CpG dinucleotides of DNA and through enzymatic activities for DNA methylation and/or chromatin modifications generates a chromatin state critical for gene expressions. Structural/functional features of CXXC5 remain largely unknown. CXXC5, suggested as transcription and/or epigenetic factor, participates in cellular proliferation, differentiation, and death. To explore the role of CXXC5 in E2-ERα mediated cellular events, we verified by generating a recombinant protein that CXXC5 is indeed an unmethylated CpG binder. We uncovered that CXXC5, although lacks a transcription activation/repression function, participates in E2-driven cellular proliferation by modulating the expression of distinct and mutual genes also regulated by E2. Furthermore, we found that the overexpression of CXXC5, which correlates with mRNA and protein levels of ERα, associates with poor prognosis in ER-positive breast cancer patients. Thus, CXXC5 as an unmethylated CpG binder contributes to E2-mediated gene expressions that result in the regulation of cellular proliferation and may contribute to ER-positive breast cancer progression.

CXXC5 Mediates P. gingivalis-suppressed Cementoblast Functions Partially via MAPK Signaling Network

Porphyromonas (P.) gingivalis associates tightly with periodontal diseases and it is also a dominant pathogen of periapical periodontitis. However, the influence of P. gingivalis on cementoblasts, root surface cells pivotal in the apical areas, and the possible involvement of other molecules remain largely elusive. CXXC5 is a nuclear protein that regulates gene expression as well as cell growth, differentiation, and apoptosis. In this study, P. gingivalis repressed the mineralization capacity of cementoblasts by inducing inflammatory reactions and inhibiting cell differentiation. Intriguingly, the expression of CXXC5 decreased in P. gingivalis-treated OCCM-30 cells and apical periodontitis models but gradually increased during mineralization. Furthermore, RNA interference of CXXC5 significantly inhibited cementoblast differentiation, represented by decline of bone-associated markers Osterix, osteocalcin (OCN), and alkaline phosphatase (ALP). CXXC5 overexpression facilitated differentiation, and therefore attenuated the P. gingivalis-repressed effects on OCCM-30 cells. In addition, Erk1/2, p38, and PI3K-Akt were inactivated by silencing CXXC5 and activated upon its overexpression, whereas Wnt/β-catenin exhibited an opposite trend. The employment of specific inhibitors revealed that the CXXC5-dependent promotions of cementoblast differentiation were partially abrogated by p38 and PI3K-Akt inhibitors but were exacerbated by inhibiting Erk1/2. Overall, our experiment demonstrated a novel function of CXXC5 in the regeneration of impaired cementum caused by P. gingivalis invasion and suggested that MAPK signaling network balances the facilitation effects of CXXC5 in cementoblast differentiation.

CXXC5: A novel regulator and coordinator of TGF-β, BMP and Wnt signaling

CXXC5 is a member of the CXXC-type zinc-finger protein family. Proteins in this family play a pivotal role in epigenetic regulation by binding to unmethylated CpG islands in gene promoters through their characteristic CXXC domain. CXXC5 is a short protein (322 amino acids in length) that does not have any catalytic domain, but is able to bind to DNA and act as a transcription factor and epigenetic factor through protein-protein interactions. Intriguingly, increasing evidence indicates that expression of the CXXC5 gene is controlled by multiple signaling pathways and a variety of transcription factors, positioning CXXC5 as an important signal integrator. In addition, CXXC5 is capable of regulating various signal transduction processes, including the TGF-β, Wnt and ATM-p53 pathways, thereby acting as a novel and crucial signaling coordinator. CXXC5 plays an important role in embryonic development and adult tissue homeostasis by regulating cell proliferation, differentiation and apoptosis. In keeping with these functions, aberrant expression or altered activity of CXXC5 has been shown to be involved in several human diseases including tumourigenesis. This review summarizes the current understanding of CXXC5 as a transcription factor and signaling regulator and coordinator.

Zinc-finger proteins in health and disease

Zinc-finger proteins (ZNFs) are one of the most abundant groups of proteins and have a wide range of molecular functions. Given the wide variety of zinc-finger domains, ZNFs are able to interact with DNA, RNA, PAR (poly-ADP-ribose) and other proteins. Thus, ZNFs are involved in the regulation of several cellular processes. In fact, ZNFs are implicated in transcriptional regulation, ubiquitin-mediated protein degradation, signal transduction, actin targeting, DNA repair, cell migration, and numerous other processes. The aim of this review is to provide a comprehensive summary of the current state of knowledge of this class of proteins. Firstly, we describe the actual classification of ZNFs, their structure and functions. Secondly, we focus on the biological role of ZNFs in the development of organisms under normal physiological and pathological conditions.

Estradiol-Estrogen Receptor α Mediates the Expression of the CXXC5 Gene through the Estrogen Response Element-Dependent Signaling Pathway

17β-estradiol (E2), the primary circulating estrogen hormone, mediates physiological and pathophysiological functions of breast tissue mainly through estrogen receptor α (ERα). Upon binding to E2, ERα modulates the expression of target genes involved in the regulation of cellular proliferation primarily through interactions with specific DNA sequences, estrogen response elements (EREs). Our previous microarray results suggested that E2-ERα modulates CXXC5 expression. Because of the presence of a zinc-finger CXXC domain (ZF-CXXC), CXXC5 is considered to be a member of the ZF-CXXC family, which binds to non-methylated CpG dinucleotides. Although studies are limited, CXXC5 appears to participate as a transcription factor, co-regulator and/or epigenetic factor in the regulation of cellular events induced by various signaling pathways. However, how signaling pathways mediate the expression of CXXC5 is yet unclear. Due to the importance of E2-ERα signaling in breast tissue, changes in the CXXC5 transcription/synthesis could participate in E2-mediated cellular events as well. To address these issues, we initially examined the mechanism whereby E2-ERα regulates CXXC5 expression. We show here that CXXC5 is an E2-ERα responsive gene regulated by the interaction of E2-ERα with an ERE present at a region upstream of the initial translation codon of the gene.