The retinoblastoma gene and its product are targeted by ICBP90: a key mechanism in the G1/S transition during the cell cycle

UHRF1 poly-auto-ubiquitination induced by the anti-cancer drug, thymoquinone, is involved in the DNA repair machinery recruitment

DNA methylation is one of the most important epigenetic mark involved in many physiologic cellular processes and pathologies. During mitosis, the transmission of DNA methylation patterns from a mother to the daughter cells is ensured through the action of the Ubiquitin-like, containing PHD and RING domains, 1/DNA methyltransferase 1 (UHRF1/DNMT1) tandem. UHRF1 is involved in the silencing of many tumor suppressor genes (TSGs) via mechanisms that remain largely to be deciphered. The present study investigated the role and the regulation of UHRF1 poly-ubiquitination induced by thymoquinone, a natural anti-cancer drug, known to enhance or re-activate the expression of TSGs. We found that the auto-ubiquitination of UHRF1, induced by TQ, is mediated by reactive oxygen species, and occurs following DNA damage. We demonstrated that the poly-ubiquitinated form of UHRF1 is K63-linked and can still silence the tumor suppressor gene p16INK4A/CDKN2A. We further showed that TQ-induced auto-ubiquitination is mediated via the activity of Tip60. Since this latter is known as a nuclear receptor co-factor, we investigated if the glucocorticoid receptor (GR) might be involved in the regulation of UHRF1 ubiquitination. Activation of the GR, with dexamethasone, did not influence auto-ubiquitination of UHRF1. However, we could observe that TQ induced a K48-linked poly-ubiquitination of GR, probably involved in the proteosomal degradation pathway. Mass-spectrometry analysis of FLAG-HA-tagged UHRF1 identified UHRF1 partners involved in DNA repair and showed that TQ increased their association with UHRF1, suggesting that poly-ubiquitination of UHRF1 is involved in the DNA repair process. We propose that poly-ubiquitination of UHRF1 serves as a scaffold to recruit the DNA repair machinery at DNA damage sites.

Alterations of UHRF family Expression and was regulated by High Risk Type HPV16 in Uterine Cervical Cancer

The altered protein expression of inverted CCAAT box-binding protein of 90 kDa/ubiquitin-like with PHD and RING finger domains 1 (ICBP90/UHRF1), and Np95-like ring finger protein (NIRF)/UHRF2, which belong to the ubiquitin-like with PHD and RING finger domains (UHRF) family, is linked to tumor malignancy and the progression of various cancers. In this study, we analyzed the UHRF family expression in cervical cancers, and it's regulation by human papillomavirus (HPV). Western blotting was performed to analyze protein expression in cervical cancer cell lines. Immunohistochemical analysis were used to investigate the expression of UHRF family and MIB-1 in cervical cancer tissues. Transfection were done for analyze the relationship between UHRF family and HPVs. We showed that NIRF expression was decreased and ICBP90 expression was increased in cervical cancers compared to normal counterparts. Western blotting also showed that NIRF expression was quite low levels, but ICBP90 was high in human cervical cancer cell lines. Interestingly, ICBP90 was up regulated by high risk type HPV16 E6 and E7, but not low-risk type HPV11. On the other hand, NIRF was down regulated by high risk type HPV16 E6 but not by E7. Low risk type HPV11 E6 did not affect the NIRF expression at all. We propose that ICBP90 overexpression, and reduced NIRF expression, found in cervical cancers, is an important event of a cervical carcinogenesis, and especially ICBP90 may offer a proliferating marker and therapeutic target for treating uterine cervical cancers.

UHRF1 promotes spindle assembly and chromosome congression by catalyzing EG5 polyubiquitination

UHRF1 is an epigenetic coordinator bridging DNA methylation and histone modifications. Additionally, UHRF1 regulates DNA replication and cell cycle, and its deletion induces G1/S or G2/M cell cycle arrest. The roles of UHRF1 in the regulation of G2/M transition remain poorly understood. UHRF1 depletion caused chromosome misalignment, thereby inducing cell cycle arrest at mitotic metaphase, and these cells exhibited the defects of spindle geometry, prominently manifested as shorter spindles. Mechanistically, UHRF1 protein directly interacts with EG5, a kinesin motor protein, during mitosis. Furthermore, UHRF1 induced EG5 polyubiquitination at the site of K1034 and further promoted the interaction of EG5 with spindle assembly factor TPX2, thereby ensuring accurate EG5 distribution to the spindles during metaphase. Our study clarifies a novel UHRF1 function as a nuclear protein catalyzing EG5 polyubiquitination for proper spindle architecture and faithful genomic transmission, which is independent of its roles in epigenetic regulation and DNA damage repair inside the nucleus. These findings revealed a previously unknown mechanism of UHRF1 in controlling mitotic spindle architecture and chromosome behavior and provided mechanistic evidence for UHRF1 deletion-mediated G2/M arrest.

Inhibitors of UHRF1 base flipping activity showing cytotoxicity against cancer cells

Ubiquitin-like containing PHD and RING finger domain 1 (UHRF1) is a nuclear multi-domain protein overexpressed in numerous human cancer types. We previously disclosed the anthraquinone derivative UM63 that inhibits UHRF1-SRA domain base-flipping activity, although having DNA intercalating properties. Herein, based on the UM63 structure, new UHRF1-SRA inhibitors were identified through a multidisciplinary approach, combining molecular modelling, biophysical assays, molecular and cell biology experiments. We identified AMSA2 and MPB7, that inhibit UHRF1-SRA mediated base flipping at low micromolar concentrations, but do not intercalate into DNA, which is a key advantage over UM63. These molecules prevent UHRF1/DNMT1 interaction at replication forks and decrease the overall DNA methylation in cells. Moreover, both compounds specifically induce cell death in numerous cancer cell lines, displaying marginal effect on non-cancer cells, as they preferentially affect cells with high level of UHRF1. Overall, these two compounds are promising leads for the development of anti-cancer drugs targeting UHRF1.

Seasonal variation in the morphokinetics of in-vitro-derived bovine embryos is associated with the blastocyst developmental competence and gene expression

Summer heat stress is a major cause of reduced development of preimplantation embryos. Nevertheless, seasonal effects on embryo morphokinetics have been less studied. We used a non-invasive time-lapse system that allows continuous monitoring of embryos to study the seasonal impact on embryo morphokinetics. The experiments were performed during the cold and the hot seasons. Cumulus-oocyte complexes were aspirated from ovaries, in-vitro-matured, and fertilized. Putative zygotes were cultured in an incubator equipped with a time-lapse system. The cleavage and blastocyst formation rates were lower in the hot vs. the cold season (p < 0.01). The kinetics of the embryos differed between seasons, reflected by a delay in the second cleavage in the hot vs. the cold season (p < 0.03). The distribution of the embryos into different morphological grades (good, fair, and poor) throughout the first three cleavages differed between seasons, with a higher proportion of good-grade embryos in the hot season (p < 0.03). Cleaved embryos were categorized as either normal or abnormal, based on their first cleavage pattern. Normal cleavage was defined as when the first cleavage resulted in two equal blastomeres and further classified as either synchronous or asynchronous, according to their subsequent cleavages. Abnormal cleavage was defined as when the embryo directly cleaved into more than two blastomeres, it cleaved unequally into two unevenly sized blastomeres, or when the fusion of already divided blastomeres occurred. The proportion of abnormally cleaved embryos was higher in the hot season vs. the cold one (p < 0.01), reflected by a higher proportion of unequally cleaved embryos (p < 0.02). In the cold season, abnormally cleaved embryos had a lower potential to develop into blastocysts relative to their normally cleaved counterparts (p < 0.001). Blastocysts that developed in the cold and the hot seasons differed in the expression of genes that related to the cell cycle (STAT1; p < 0.01), stress (HSF1; p < 0.03), and embryo development (ZP3; p < 0.05). A higher expression level was recorded for the STAT1 and UHRF1 genes in blastocysts that developed from unequally vs. the synchronously cleaved embryos (p < 0.04). We provide the first evidence for a seasonal effect on embryo morphokinetics, which might explain the reduced embryo development during the hot season.

UHRF1 overexpression promotes osteosarcoma metastasis through altered exosome production and AMPK/SEMA3E suppression

Loss-of-function mutations at the retinoblastoma (RB1) gene are associated with increased mortality, metastasis, and poor therapeutic outcome in several cancers, including osteosarcoma. However, the mechanism(s) through which RB1 loss worsens clinical outcome remains understudied. Ubiquitin-like with PHD and Ring Finger domains 1 (UHRF1) has been identified as a critical downstream effector of the RB/E2F signaling pathway that is overexpressed in various cancers. Here, we determined the role and regulatory mechanisms of UHRF1 in rendering osteosarcoma cells more aggressive. Higher UHRF1 expression correlated with malignancy in osteosarcoma cell lines, clinical samples, and genetically engineered mouse models. Gain- and loss-of-function assays revealed that UHRF1 has cell-intrinsic and extrinsic functions promoting cell proliferation, migration, invasion, angiogenesis, and metastasis. UHRF1 overexpression induced angiogenesis by suppressing AMPK activation and Semaphorin 3E (SEMA3E) expression. Further, UHRF1-mediated migration and metastasis resulted, at least in part, through altered expression of extracellular vesicles and their cargo, including urokinase-type plasminogen activator (uPA). Novel osteosarcoma genetically engineered mouse models confirmed that knocking out Uhrf1 considerably decreased metastasis and reversed the poorer survival associated with Rb1 loss. This presents a new mechanistic insight into RB1 loss-associated poor prognosis and novel oncogenic roles of UHRF1 in the regulation of angiogenesis and exosome secretion, both critical for osteosarcoma metastasis. This provides substantial support for targeting UHRF1 or its downstream effectors as novel therapeutic options to improve current treatment for osteosarcoma.

UHRF2 regulates cell cycle, epigenetics and gene expression to control the timing of retinal progenitor and ganglion cell differentiation

Ubiquitin-like, containing PHD and RING finger domains 2 (UHRF2) regulates cell cycle and binds 5-hydroxymethylcytosine (5hmC) to promote completion of DNA demethylation. Uhrf2-/- mice are without gross phenotypic defects; however, the cell cycle and epigenetic regulatory functions of Uhrf2 during retinal tissue development are unclear. Retinal progenitor cells (RPCs) produce all retinal neurons and Müller glia in a predictable sequence controlled by the complex interplay between extrinsic signaling, cell cycle, epigenetic changes and cell-specific transcription factor activation. In this study, we find that UHRF2 accumulates in RPCs, and its conditional deletion from mouse RPCs reduced 5hmC, altered gene expressions and disrupted retinal cell proliferation and differentiation. Retinal ganglion cells were overproduced in Uhrf2-deficient retinae at the expense of VSX2+ RPCs. Most other cell types were transiently delayed in differentiation. Expression of each member of the Tet3/Uhrf2/Tdg active demethylation pathway was reduced in Uhrf2-deficient retinae, consistent with locally reduced 5hmC in their gene bodies. This study highlights a novel role of UHRF2 in controlling the transition from RPCs to differentiated cell by regulating cell cycle, epigenetic and gene expression decisions.

Dihydroartemisinin induces cell apoptosis through repression of UHRF1 in prostate cancer cells

Prostate cancer (PCa) seriously jeopardizes men's health worldwide. Dihydroartemisinin, which is an effective antimalarial agent, has shown potential anticancer effects in various human cancer cell lines, including PCa cells. However, the mechanisms underlying the anticancer activity of dihydroartemisinin are not fully understood. Ubiquitin-like with plant homeodomain and ring finger domain 1 (UHRF1) is highly expressed in a variety of tumors and is negatively correlated with the prognosis of various tumors. We reported previously that UHRF1 is downregulated during apoptosis induced by dihydroartemisinin in PC-3 PCa cells. In this study, we transfected PC-3 cells with lentiviruses containing UHRF1 or shRNA-UHRF1. Then, the cells were treated with dihydroartemisinin at different concentrations. Our data showed that overexpression of UHRF1 promoted cell proliferation and migration in PC-3 cells, inhibited cell apoptosis, increased cell proportion in G2 phase, increased DNA methyltransferase 1 and decreased p16INK4A expression at mRNA and protein levels. Downregulation of UHRF1 produces the opposite results. Moreover, the phenomena caused by overexpression of UHRF1 were inhibited after dihydroartemisinin treatment. Compared with control cells, cells overexpressing UHRF1 can resist the proapoptotic and antiproliferative effects of dihydroartemisinin to a certain extent. The effects of UHRF1 knockdown were further aggravated by dihydroartemisinin treatment, but no statistically significant effect was observed with increasing drug concentration. Our results suggested that dihydroartemisinin decreases proliferation and migration but enhances apoptosis of PCa cells, likely by downregulating UHRF1 and upregulating p16INK4A.

TIP60 governs the auto‑ubiquitination of UHRF1 through USP7 dissociation from the UHRF1/USP7 complex

Tat interactive protein, 60 kDa (TIP60) is an important partner of ubiquitin-like, containing PHD and RING finger domains 1 (UHRF1), ensuring various cellular processes through its acetyltransferase activity. TIP60 is believed to play a tumor suppressive role, partly explained by its downregulated expression in a number of cancers. The aim of the present study was to investigate the role and mechanisms of action of TIP60 in the regulation of UHRF1 expression. The results revealed that TIP60 overexpression downregulated the UHRF1 and DNA methyltransferase 1 (DNMT1) expression levels. TIP60 interfered with USP7-UHRF1 association and induced the degradation of UHRF1 in an auto-ubiquitination-dependent manner. Moreover, TIP60 activated the p73-mediated apoptotic pathway. Taken together, the data of the present study suggest that the tumor suppressor role of TIP60 is mediated by its regulation to UHRF1.

Thymoquinone Is a Multitarget Single Epidrug That Inhibits the UHRF1 Protein Complex

Silencing of tumor suppressor genes (TSGs) through epigenetic mechanisms, mainly via abnormal promoter DNA methylation, is considered a main mechanism of tumorigenesis. The abnormal DNA methylation profiles are transmitted from the cancer mother cell to the daughter cells through the involvement of a macromolecular complex in which the ubiquitin-like containing plant homeodomain (PHD), and an interesting new gene (RING) finger domains 1 (UHRF1), play the role of conductor. Indeed, UHRF1 interacts with epigenetic writers, such as DNA methyltransferase 1 (DNMT1), histone methyltransferase G9a, erasers like histone deacetylase 1 (HDAC1), and functions as a hub protein. Thus, targeting UHRF1 and/or its partners is a promising strategy for epigenetic cancer therapy. The natural compound thymoquinone (TQ) exhibits anticancer activities by targeting several cellular signaling pathways, including those involving UHRF1. In this review, we highlight TQ as a potential multitarget single epidrug that functions by targeting the UHRF1/DNMT1/HDAC1/G9a complex. We also speculate on the possibility that TQ might specifically target UHRF1, with subsequent regulatory effects on other partners.

Niacin stimulates EPH4EV mammary epithelial cell proliferation and mammary gland development in pubertal mice through activation of AKT/mTOR and ERK1/2 signaling pathways

Previous studies have shown the effects of vitamins on the development of the mammary gland. However, the role of niacin in this process has not been reported. Therefore, the aim of this study is to investigate the effects of niacin on mammary gland development in pubertal mice and to use a mouse mammary epithelial cell line to study the underlying mechanism. The results showed that niacin could activate the AKT/mTOR and ERK signaling pathways and increase phosphorylation of 4EBP1 to promote the synthesis of cell proliferation markers, leading to the dissociation of the Rb-E2F1 complex in mMECs. In addition, 0.5% niacin promoted mammary duct development, increased the expression of cyclin D1/D3 and PCNA and activated Akt/mTOR and ERK1/2 in the mammary glands of pubertal mice. These results strongly suggest that niacin stimulates mammary gland development in pubertal mice through the Akt/mTOR and ERK1/2 signaling pathways.

Retinoblastoma Tumor Suppressor Protein Roles in Epigenetic Regulation

Simple Summary

Loss of function of the retinoblastoma gene (RB1) is the rate-limiting step in the initiation of both the hereditary and sporadic forms of retinoblastoma tumor. Furthermore, loss of function of the retinoblastoma tumor suppressor protein (pRB) is frequently found in most human cancers. In retinoblastoma, tumor progression is driven by epigenetic changes following pRB loss. This review focuses on the diverse functions of pRB in epigenetic regulation.

Abstract

Mutations that result in the loss of function of pRB were first identified in retinoblastoma and since then have been associated with the propagation of various forms of cancer. pRB is best known for its key role as a transcriptional regulator during cell cycle exit. Beyond the ability of pRB to regulate transcription of cell cycle progression genes, pRB can remodel chromatin to exert several of its other biological roles. In this review, we discuss the diverse functions of pRB in epigenetic regulation including nucleosome mobilization, histone modifications, DNA methylation and non-coding RNAs.

Alternative splicing and allosteric regulation modulate the chromatin binding of UHRF1

UHRF1 is an important epigenetic regulator associated with apoptosis and tumour development. It is a multidomain protein that integrates readout of different histone modification states and DNA methylation with enzymatic histone ubiquitylation activity. Emerging evidence indicates that the chromatin-binding and enzymatic modules of UHRF1 do not act in isolation but interplay in a coordinated and regulated manner. Here, we compared two splicing variants (V1, V2) of murine UHRF1 (mUHRF1) with human UHRF1 (hUHRF1). We show that insertion of nine amino acids in a linker region connecting the different TTD and PHD histone modification-binding domains causes distinct H3K9me3-binding behaviour of mUHRF1 V1. Structural analysis suggests that in mUHRF1 V1, in contrast to V2 and hUHRF1, the linker is anchored in a surface groove of the TTD domain, resulting in creation of a coupled TTD-PHD module. This establishes multivalent, synergistic H3-tail binding causing distinct cellular localization and enhanced H3K9me3-nucleosome ubiquitylation activity. In contrast to hUHRF1, H3K9me3-binding of the murine proteins is not allosterically regulated by phosphatidylinositol 5-phosphate that interacts with a separate less-conserved polybasic linker region of the protein. Our results highlight the importance of flexible linkers in regulating multidomain chromatin binding proteins and point to divergent evolution of their regulation.

Aneuploidy and DNA Methylation as Mirrored Features of Early Human Embryo Development

Genome stability is an integral feature of all living organisms. Aneuploidy is the most common cause of fetal death in humans. The timing of bursts in increased aneuploidy frequency coincides with the waves of global epigenetic reprogramming in mammals. During gametogenesis and early embryogenesis, parental genomes undergo two waves of DNA methylation reprogramming. Failure of these processes can critically affect genome stability, including chromosome segregation during cell division. Abnormal methylation due to errors in the reprogramming process can potentially lead to aneuploidy. On the other hand, the presence of an entire additional chromosome, or chromosome loss, can affect the global genome methylation level. The associations of these two phenomena are well studied in the context of carcinogenesis, but here, we consider the relationship of DNA methylation and aneuploidy in early human and mammalian ontogenesis. In this review, we link these two phenomena and highlight the critical ontogenesis periods and genome regions that play a significant role in human reproduction and in the formation of pathological phenotypes in newborns with chromosomal aneuploidy.

UHRF1 Promotes Proliferation of Human Adipose-Derived Stem Cells and Suppresses Adipogenesis via Inhibiting Peroxisome Proliferator-Activated Receptor γ

Once the adipose tissue is enlarged for the purpose of saving excess energy intake, obesity may be observed. Ubiquitin-like with PHD and RING Finger domains 1 (UHRF1) is helpful in repairing damaged DNA as it increases the resistance of cancer cells against cytocidal drugs. Peroxisome proliferator-activated receptor γ (PPARγ), an important nucleus transcription factor participating in adipogenesis, has been extensively reported. To date, no study has indicated whether UHRF1 can regulate proliferation and differentiation of human adipose-derived stem cells (hADSCs). Hence, this study aimed to utilize overexpression or downregulation of UHRF1 to explore the possible mechanism of proliferation and differentiation of hADSCs. We here used lentivirus, containing UHRF1 (LV-UHRF1) and siRNA-UHRF1 to transfect hADSCs, on which Cell Counting Kit-8 (CCK-8), cell growth curve, colony formation assay, and EdU proliferation assay were applied to evaluate proliferation of hADSCs, cells cycle was investigated by flow cytometry, and adipogenesis was detected by Oil Red O staining and Western blotting. Our results showed that UHRF1 can promote proliferation of hADSCs after overexpression of UHRF1, while proliferation of hADSCs was reduced through downregulation of UHRF1, and UHRF1 can control proliferation of hADSCs through transition from G1-phase to S-phase; besides, we found that UHRF1 negatively regulates adipogenesis of hADSCs via PPARγ. In summary, the results may provide a new insight regarding the role of UHRF1 on regulating proliferation and differentiation of hADSCs.

DNA Methylation Readers and Cancer: Mechanistic and Therapeutic Applications

DNA methylation is a major epigenetic process that regulates chromatin structure which causes transcriptional activation or repression of genes in a context-dependent manner. In general, DNA methylation takes place when methyl groups are added to the appropriate bases on the genome by the action of "writer" molecules known as DNA methyltransferases. How these methylation marks are read and interpreted into different functionalities represents one of the main mechanisms through which the genes are switched "ON" or "OFF" and typically involves different types of "reader" proteins that can recognize and bind to the methylated regions. A tightly balanced regulation exists between the "writers" and "readers" in order to mediate normal cellular functions. However, alterations in normal methylation pattern is a typical hallmark of cancer which alters the way methylation marks are written, read and interpreted in different disease states. This unique characteristic of DNA methylation "readers" has identified them as attractive therapeutic targets. In this review, we describe the current state of knowledge on the different classes of DNA methylation "readers" identified thus far along with their normal biological functions, describe how they are dysregulated in cancer, and discuss the various anti-cancer therapies that are currently being developed and evaluated for targeting these proteins.

UHRF1 depletion and HDAC inhibition reactivate epigenetically silenced genes in colorectal cancer cells

BACKGROUND

Ubiquitin-like protein containing PHD and RING finger domains 1 (UHRF1) is a major regulator of epigenetic mechanisms and is overexpressed in various human malignancies. In this study, we examined the involvement of UHRF1 in aberrant DNA methylation and gene silencing in colorectal cancer (CRC).

RESULTS

CRC cell lines were transiently transfected with siRNAs targeting UHRF1, after which DNA methylation was analyzed using dot blots, bisulfite pyrosequencing, and Infinium HumanMethylation450 BeadChip assays. Gene expression was analyzed using RT-PCR and gene expression microarrays. Depletion of UHRF1 rapidly induced genome-wide DNA demethylation in CRC cells. Infinium BeadChip assays and bisulfite pyrosequencing revealed significant demethylation across entire genomic regions, including CpG islands, gene bodies, intergenic regions, and repetitive elements. Despite the substantial demethylation, however, UHRF1 depletion only minimally reversed CpG island hypermethylation-associated gene silencing. By contrast, the combination of UHRF1 depletion and histone deacetylase (HDAC) inhibition reactivated the silenced genes and strongly suppressed CRC cell proliferation. The combination of UHRF1 depletion and HDAC inhibition also induced marked changes in the gene expression profiles such that cell cycle-related genes were strikingly downregulated.

CONCLUSIONS

Our results suggest that (i) maintenance of DNA methylation in CRC cells is highly dependent on UHRF1; (ii) UHRF1 depletion rapidly induces DNA demethylation, though it is insufficient to fully reactivate the silenced genes; and (iii) dual targeting of UHRF1 and HDAC may be an effective new therapeutic strategy.

Deletion of maternal UHRF1 severely reduces mouse oocyte quality and causes developmental defects in preimplantation embryos

The ubiquitin-like, containing PHD and RING finger domains, 1 (UHRF1) protein recognizes DNA methylation and histone modification and plays a critical role in epigenetic regulation. Recently, UHRF1 was shown to have a role in DNA methylation in oocytes and early embryos. Here, we reveal that maternal UHRF1 determines the quality of mouse oocytes. We generated oocyte-specific Uhrf1-knockout mice and found that females were sterile, and few maternal UHRF1-null embryos developed into blastocysts. The UHRF1-null oocytes had an increased incidence of aneuploidy and DNA damage. In addition to defective DNA methylation, histone modification was affected during oogenesis, with UHRF1-null germinal vesicle and metaphase II-stage oocytes exhibiting reduced global histone H3 lysine 9 dimethylation levels and elevated acetylation of histone H4 lysine 12. Taken together, our results suggest that UHRF1 plays an important role in determining oocyte quality and affects epigenetic regulation of oocyte maturation as a maternal protein, which is crucial for embryo developmental potential. Further exploration of the biologic function and underlying mechanisms of maternal UHRF1 will enhance our understanding of the maternal control of the oocyte and early embryonic development.-Cao, Y., Li, M., Liu, F., Ni, X., Wang, S., Zhang, H., Sui, X., Huo, R. Deletion of maternal UHRF1 severely reduces mouse oocyte quality and causes developmental defects in preimplantation embryos.

Activated MEK/ERK Pathway Drives Widespread and Coordinated Overexpression of UHRF1 and DNMT1 in Cancer cells

The UHRF1-DNMT1 axis plays a key role in DNA maintenance methylation in mammals. Accumulative studies demonstrate that UHRF1 is broadly overexpressed in cancers, which contributes to cancer cell proliferation and tumorigenesis. Interestingly, a proteasome-dependent downregulation of UHRF1 has been observed in pluripotent ground state mouse embryonic stem cells (mESCs) cultured in the presence of two kinase (MEK1/MEK2 and GSK3β) inhibitors (termed 2i), raising the question whether UHRF1 is similarly regulated in cancer cells. Here we present evidence that while addition of 2i broadly downregulates UHRF1 and DNMT1 in various cancer cells, distinct underlying mechanisms are involved. In contrast to mESCs, 2i-induced downregulation of UHRF1 and DNMT1 in cancer cells cannot be rescued by proteasome inhibitor and occurs primarily at the level of transcription. Furthermore, downregulation of UHRF1 and DNMT1 by 2i is due to inhibition of MEK1/MEK2, but not GSK3β activity. Data mining reveals a marked co-expression of UHRF1 and DNMT1 in normal tissues as well as cancers. We provide evidence that multiple transcription factors including E2F1 and SP1 mediate the transcriptional activation of UHRF1 and DNMT1 by the activated MEK/ERK pathway. Together our study reveals distinct regulation of UHRF1/DNMT1 in mESCs and cancer cells and identifies activated MEK/ERK pathway as a driving force for coordinated and aberrant over-expression of UHRF1 and DNMT1 in cancers.

UHRF1 Licensed Self-Renewal of Active Adult Neural Stem Cells

Adult neurogenesis in the brain continuously seeds new neurons throughout life, but how homeostasis of adult neural stem cells (NSCs) is maintained is incompletely understood. Here, we demonstrate that the DNA methylation adapter ubiquitin-like, containing PHD and RING finger domains-1 (UHRF1) is expressed in, and regulates proliferation of, the active but not quiescent pool of adult neural progenitor cells. Mice with a neural stem cell-specific deficiency in UHRF1 exhibit a massive depletion of neurogenesis resulting in a collapse of formation of new neurons. In the absence of UHRF1, NSCs unexpectedly remain in the cell cycle but with a 17-fold increased cell cycle length due to a failure of replication phase entry caused by promoter demethylation and derepression of Cdkn1a, which encodes the cyclin-dependent kinase inhibitor p21. UHRF1 does not affect the proportion progenitor cells active within the cell cycle but among these cells, UHRF1 is critical for licensing replication re-entry. Therefore, this study shows that a UHRF1-Cdkn1a axis is essential for the control of stem cell self-renewal and neurogenesis in the adult brain. Stem Cells 2018;36:1736-1751.

Thymoquinone challenges UHRF1 to commit auto-ubiquitination: a key event for apoptosis induction in cancer cells

Down-regulation of UHRF1 (Ubiquitin-like containing PHD and Ring Finger 1) in Jurkat cells, induced by natural anticancer compounds such as thymoquinone, allows re-expression of tumor suppressor genes such as p73 and p16^INK4A . In order to decipher the mechanisms of UHRF1 down-regulation, we investigated the kinetic of expression of HAUSP (herpes virus-associated ubiquitin-specific protease), UHRF1, cleaved caspase-3 and p73 in Jurkat cells treated with thymoquinone. We found that thymoquinone induced degradation of UHRF1, correlated with a sharp decrease in HAUSP and an increase in cleaved caspase-3 and p73. UHRF1 concomitantly underwent a rapid ubiquitination in response to thymoquinone and this effect was not observed in the cells expressing mutant UHRF1 RING domain, suggesting that UHRF1 commits an auto-ubiquitination through its RING domain in response to thymoquinone treatment. Exposure of cells to Z-DEVD, an inhibitor of caspase-3 markedly reduced the thymoquinone-induced down-regulation of UHRF1, while proteosomal inhibitor MG132 had no such effect. The present findings indicate that thymoquinone induces in cancer cells a fast UHRF1 auto-ubiquitination through its RING domain associated with HAUSP down-regulation. They further suggest that thymoquinone-induced UHRF1 auto-ubiquitination followed by its degradation is a key event in inducing apoptosis through a proteasome-independent mechanism.

Np95/Uhrf1 regulates tumor suppressor gene expression of neural stem/precursor cells, contributing to neurogenesis in the adult mouse brain

Adult neurogenesis is a process of generating new neurons from neural stem/precursor cells (NS/PCs) in restricted adult brain regions throughout life. It is now generally known that adult neurogenesis in the hippocampal dentate gyrus (DG) and subventricular zone participates in various higher brain functions, such as learning and memory formation, olfactory discrimination and repair after brain injury. However, the mechanisms underlying adult neurogenesis remain to be fully understood. Here, we show that Nuclear protein 95 KDa (Np95, also known as UHRF1 or ICBP90), which is an essential protein for maintaining DNA methylation during cell division, is involved in multiple processes of adult neurogenesis. Specific ablation of Np95 in adult NS/PCs (aNS/PCs) led to a decrease in their proliferation and an impairment of neuronal differentiation and to suppression of neuronal maturation associated with the impairment of dendritic formation in the hippocampal DG. We also found that deficiency of Np95 in NS/PCs increased the expression of tumor suppressor genes p16 and p53, and confirmed that expression of these genes in NS/PCs recapitulates the phenotype of Np95-deficient NS/PCs. Taken together, our findings suggest that Np95 plays an essential role in proliferation and differentiation of aNS/PCs through the regulation of tumor suppressor gene expression in adult neurogenesis.

Long noncoding RNA UPAT promoted cell proliferation via increasing UHRF1 expression in non-small cell lung cancer

Evidence indicates that long non-coding RNAs (lncRNAs) serve a critical role in the regulation of non-small cell lung cancer (NSCLC) progression. LncRNA Ubiquitin-like with PHD and RING finger domains 1 (UHRF1) protein associated transcript (UPAT) has been identified to be overexpressed in a variety of types of cancer. The present study demonstrated that lncRNA UPAT expression was upregulated in NSCLC tissues and significantly associated with tumor size and Tumor-Node-Metastasis stage. Additionally, UPAT promoted NSCLC cell proliferation and G1-S phase transition in vitro. Furthermore, UPAT promoted NSCLC cell proliferation, partly via increasing UHRF1 expression and consequently epigenetically silencing RASSF1 and CDH13 transcription. In addition, the knockdown of UHRF1 partially decreased the promotion of cell growth and G1-S phase transition caused by UPAT overexpression. In conclusion, these data suggest that the lncRNA UPAT promotes the NSCLC cell proliferation and may be a potential therapeutic target of NSCLC.

Targeting the SET and RING-associated (SRA) domain of ubiquitin-like, PHD and ring finger-containing 1 (UHRF1) for anti-cancer drug development

Ubiquitin-like containing PHD Ring Finger 1 (UHRF1) is a multi-domain protein with a methyl-DNA binding SRA (SET and RING-associated) domain, required for maintenance DNA methylation mediated by DNMT1. Primarily expressed in proliferating cells, UHRF1 is a cell-cycle regulated protein that is required for S phase entry. Furthermore, UHRF1 participates in transcriptional gene regulation by connecting DNA methylation to histone modifications. Upregulation of UHRF1 may serve as a biomarker for a variety of cancers; including breast, gastric, prostate, lung and colorectal carcinoma. To this end, overexpression of UHRF1 promotes cancer metastasis by triggering aberrant patterns of DNA methylation, and subsequently, silencing tumor suppressor genes. Various small molecule effectors of UHRF1 have been reported in the literature, although the mechanism of action may not be fully characterized. Small molecules that potentially bind to the SRA domain may affect the ability of UHRF1 to bind hemimethylated DNA; thereby reducing aberrant DNA methylation. Therefore, in a subset of cancers, small molecule UHRF1 inhibitors may restore normal gene expression and serve as useful anti-cancer therapeutics.

Paf15 expression correlates with rectal cancer prognosis, cell proliferation and radiation response

Paf15, which participates in DNA repair, is overexpressed in numerous solid tumors. Blocking of Paf15 inhibits the growth of many types of cancer cells; while simultaneously enhancing cellular sensitivity to UV radiation. However, its expression and function in rectal cancer (RC) remain unknown. The current study was undertaken to assess the association of Paf15 expression with RC prognosis, as well as to explore the participation of Paf15 in the response of RC cells to irradiation. Increased Paf15 expression was observed in RC tissues and associated with pTNM stage and poor survival. In vitro, Paf15 induced increased RC cell proliferation while accelerating cell cycle progression, inhibiting cell death, and protecting against gamma radiation-induced DNA damage in RC cells. In conclusion, increased Paf15 expression is associated with increased RC proliferation, decreased patient survival, and a worse radiotherapeutic response.

Interaction of the epigenetic integrator UHRF1 with the MYST domain of TIP60 inside the cell

Background

The nuclear epigenetic integrator UHRF1 is known to play a key role with DNMT1 in maintaining the DNA methylation patterns during cell division. Among UHRF1 partners, TIP60 takes part in epigenetic regulations through its acetyltransferase activity. Both proteins are involved in multiple cellular functions such as chromatin remodeling, DNA damage repair and regulation of stability and activity of other proteins. The aim of this work was to investigate the interaction between UHRF1 and TIP60 in order to elucidate the dialogue between these two proteins.

Methods

Biochemical (immunoprecipitation and pull-down assays) and microscopic (confocal and fluorescence lifetime imaging microscopy; FLIM) techniques were used to analyze the interaction between TIP60 and UHRF1 in vitro and in vivo. Global methylation levels were assessed by using a specific kit. The results were statistically analyzed using Graphpad prism and Origin.

Results

Our study shows that UHRF1, TIP60 and DNMT1 were found in the same epigenetic macro-molecular complex. In vitro pull-down assay showed that deletion of either the zinc finger in MYST domain or deletion of whole MYST domain from TIP60 significantly reduced its interaction with UHRF1. Confocal and FLIM microscopy showed that UHRF1 co-localized with TIP60 in the nucleus and confirmed that both proteins interacted together through the MYST domain of TIP60. Moreover, overexpression of TIP60 reduced the DNA methylation levels in HeLa cells along with downregulation of UHRF1 and DNMT1.

Conclusion

Our data demonstrate for the first time that TIP60 through its MYST domain directly interacts with UHRF1 which might be of high interest for the development of novel oncogenic inhibitors targeting this interaction.

The epigenetic integrator UHRF1: on the road to become a universal biomarker for cancer

Cancer is one of the deadliest diseases in the world causing record number of mortalities in both developed and undeveloped countries. Despite a lot of advances and breakthroughs in the field of oncology still, it is very hard to diagnose and treat the cancers at early stages. Here in this review we analyze the potential of Ubiquitin-like containing PHD and Ring Finger domain 1 (UHRF1) as a universal biomarker for cancers. UHRF1 is an important epigenetic regulator maintaining DNA methylation and histone code in the cell. It is highly expressed in a variety of cancers and is a well-known oncogene that can disrupt the epigenetic code and override the senescence machinery. Many studies have validated UHRF1 as a powerful diagnostic and prognostic tool to differentially diagnose cancer, predict the therapeutic response and assess the risk of tumor progression and recurrence. Highly sensitive, non-invasive and cost effective approaches are therefore needed to assess the level of UHRF1 in patients, which can be deployed in diagnostic laboratories to detect cancer and monitor disease progression.

SENP8 limits aberrant neddylation of NEDD8 pathway components to promote cullin-RING ubiquitin ligase function

NEDD8 is a ubiquitin-like modifier most well-studied for its role in activating the largest family of ubiquitin E3 ligases, the cullin-RING ligases (CRLs). While many non-cullin neddylation substrates have been proposed over the years, validation of true NEDD8 targets has been challenging, as overexpression of exogenous NEDD8 can trigger NEDD8 conjugation through the ubiquitylation machinery. Here, we developed a deconjugation-resistant form of NEDD8 to stabilize the neddylated form of cullins and other non-cullin substrates. Using this strategy, we identified Ubc12, a NEDD8-specific E2 conjugating enzyme, as a substrate for auto-neddylation. Furthermore, we characterized SENP8/DEN1 as the protease that counteracts Ubc12 auto-neddylation, and observed aberrant neddylation of Ubc12 and other NEDD8 conjugation pathway components in SENP8-deficient cells. Importantly, loss of SENP8 function contributes to accumulation of CRL substrates and defective cell cycle progression. Thus, our study highlights the importance of SENP8 in maintaining proper neddylation levels for CRL-dependent proteostasis.

Plasma methionine depletion and pharmacokinetic properties in mice of methionine γ-lyase from Citrobacter freundii, Clostridium tetani and Clostridium sporogenes

PK studies were carried out after a single i.v. administration of 500 and 1000 U/kg by measuring of MGL activity in plasma samples. L-methionine concentration was measured by mass spectrometry. After single i.v. injection of 500U/kg the circulating T_1/2 of enzymes in mice varies from 73 to 123min. The AUC_0-tinf values determined for MGL 500U/kg from C. freundii, C. tetani and C. sporogenes are 8.21±0.28, 9.04±0.33 and 13.88±0.39U/(ml×h), respectively. Comparison of PK parameters of three MGL sources in the dose of 500U/kg indicated the MGL C. sporogenes to have better PK parameters: clearance 0.83(95%CI: 0.779-0.871) - was lower than C. tetanii 1.27(95%CI: 1.18-1.36) and C. freundii 1.39(95%CI: 1.30-1.49). Mice plasma methionine decreased to undetectable level 10min after MGL 1000 U/kg injection. After MGL C. sporogenes 500U/kg injection plasma methionine level completely omitted after 10min till 6h, assuming the sustainability of negligible levels of methionine (<5μM) in plasma of mice for about 6h. The recovery of methionine concentration showed the advantageous efficiency of MGL from C. sporogenes: 95% 0.010-0.022 vs 0.023-0.061 for MGL C. freundii and 0.036-0.056 for MGL C. tetani. There are no significant differences between methionine cleavage after MGL C. tetani and MGL C. sporogenes i.v. injection at all doses. MGL from C. sporogenes may be considered as promising enzyme for further investigation as potential anticancer agent.

Uhrf1 controls the self-renewal versus differentiation of hematopoietic stem cells by epigenetically regulating the cell-division modes

Hematopoietic stem cells (HSCs) are able to both self-renew and differentiate. However, how individual HSC makes the decision between self-renewal and differentiation remains largely unknown. Here we report that ablation of the key epigenetic regulator Uhrf1 in the hematopoietic system depletes the HSC pool, leading to hematopoietic failure and lethality. Uhrf1-deficient HSCs display normal survival and proliferation, yet undergo erythroid-biased differentiation at the expense of self-renewal capacity. Notably, Uhrf1 is required for the establishment of DNA methylation patterns of erythroid-specific genes during HSC division. The expression of these genes is enhanced in the absence of Uhrf1, which disrupts the HSC-division modes by promoting the symmetric differentiation and suppressing the symmetric self-renewal. Moreover, overexpression of one of the up-regulated genes, Gata1, in HSCs is sufficient to phenocopy Uhrf1-deficient HSCs, which show impaired HSC symmetric self-renewal and increased differentiation commitment. Taken together, our findings suggest that Uhrf1 controls the self-renewal versus differentiation of HSC through epigenetically regulating the cell-division modes, thus providing unique insights into the relationship among Uhrf1-mediated DNA methylation, cell-division mode, and HSC fate decision.

Signalling pathways in UHRF1-dependent regulation of tumor suppressor genes in cancer

Epigenetic silencing of tumor suppressor genes (TSGs) through DNA methylation and histone changes is a main hallmark of cancer. Ubiquitin-like with PHD and RING Finger domains 1 (UHRF1) is a potent oncogene overexpressed in various solid and haematological tumors and its high expression levels are associated with decreased expression of several TSGs including p16^INK4A, BRCA1, PPARG and KiSS1. Using its several functional domains, UHRF1 creates a strong coordinated dialogue between DNA methylation and histone post-translation modification changes causing the epigenetic silencing of TSGs which allows cancer cells to escape apoptosis. To ensure the silencing of TSGs during cell division, UHRF1 recruits several enzymes including histone deacetylase 1 (HDAC1), DNA methyltransferase 1 (DNMT1) and histone lysine methyltransferases G9a and Suv39H1 to the right place at the right moment. Several in vitro and in vivo works have reported the direct implication of the epigenetic player UHRF1 in tumorigenesis through the repression of TSGs expression and suggested UHRF1 as a promising target for cancer treatment. This review describes the molecular mechanisms underlying UHRF1 regulation in cancer and discusses its importance as a therapeutic target to induce the reactivation of TSGs and subsequent apoptosis.

Loss of Uhrf1 in neural stem cells leads to activation of retroviral elements and delayed neurodegeneration

In order to understand whether early epigenetic mechanisms instruct the long-term behavior of neural stem cells (NSCs) and their progeny, we examined Uhrf1 (ubiquitin-like PHD ring finger-1; also known as Np95), as it is highly expressed in NSCs of the developing brain and rapidly down-regulated upon differentiation. Conditional deletion of Uhrf1 in the developing cerebral cortex resulted in rather normal proliferation and neurogenesis but severe postnatal neurodegeneration. During development, deletion of Uhrf1 lead to global DNA hypomethylation with a strong activation of the intracisternal A particle (IAP) family of endogenous retroviral elements, accompanied by an increase in 5-hydroxymethylcytosine. Down-regulation of Tet enzymes rescued the IAP activation in Uhrf1 conditional knockout (cKO) cells, suggesting an antagonistic interplay between Uhrf1 and Tet on IAP regulation. As IAP up-regulation persists into postnatal stages in the Uhrf1 cKO mice, our data show the lack of means to repress IAPs in differentiating neurons that normally never express Uhrf1 The high load of viral proteins and other transcriptional deregulation ultimately led to postnatal neurodegeneration. Taken together, these data show that early developmental NSC factors can have long-term effects in neuronal differentiation and survival. Moreover, they highlight how specific the consequences of widespread changes in DNA methylation are for certain classes of retroviral elements.

UHRF1 suppression promotes cell differentiation and reduces inflammatory reaction in anaplastic thyroid cancer

Anaplastic thyroid cancer (ATC), an undifferentiated subtype of thyroid cancer, is one of the most malignant endocrine cancer with low survival rate, and resistant to chemotherapy and radiation therapy. Here we found that UHRF1 was highly expressed in human ATC compared with normal tissue and papillary thyroid cancer (PTC). Knockdown of UHRF1 inhibited proliferation of ATC in vitro and in vivo. Consistently, overexpression of UHRF1 promoted the proliferation of thyroid cancer cells. Moreover, UHRF1 suppression induced differentiation of three-dimensional (3D) cultured ATC cells and down-regulated the expression of dedifferentiation marker (CD97). The stem cell markers (Sox2, Oct4 and Nanog) were suppressed simultaneously. In addition, UHRF1 knockdown reduced the transcription of cytokines (IL-8, TGF-α and TNF-α), which might relieve the inflammatory reaction in ATC patients. This study demonstrated a role of UHRF1 in ATC proliferation, dedifferentiation and inflammatory reaction, presenting UHRF1 as a potential target in ATC therapy.

Cortical neurons gradually attain a post-mitotic state

Once generated, neurons are thought to permanently exit the cell cycle and become irreversibly differentiated. However, neither the precise point at which this post-mitotic state is attained nor the extent of its irreversibility is clearly defined. Here we report that newly born neurons from the upper layers of the mouse cortex, despite initiating axon and dendrite elongation, continue to drive gene expression from the neural progenitor tubulin α1 promoter (Tα1p). These observations suggest an ambiguous post-mitotic neuronal state. Whole transcriptome analysis of sorted upper cortical neurons further revealed that neurons continue to express genes related to cell cycle progression long after mitotic exit until at least post-natal day 3 (P3). These genes are however down-regulated thereafter, associated with a concomitant up-regulation of tumor suppressors at P5. Interestingly, newly born neurons located in the cortical plate (CP) at embryonic day 18-19 (E18-E19) and P3 challenged with calcium influx are found in S/G2/M phases of the cell cycle, and still able to undergo division at E18-E19 but not at P3. At P5 however, calcium influx becomes neurotoxic and leads instead to neuronal loss. Our data delineate an unexpected flexibility of cell cycle control in early born neurons, and describe how neurons transit to a post-mitotic state.

Hemi-methylated DNA opens a closed conformation of UHRF1 to facilitate its histone recognition

UHRF1 is an important epigenetic regulator for maintenance DNA methylation. UHRF1 recognizes hemi-methylated DNA (hm-DNA) and trimethylation of histone H3K9 (H3K9me3), but the regulatory mechanism remains unknown. Here we show that UHRF1 adopts a closed conformation, in which a C-terminal region (Spacer) binds to the tandem Tudor domain (TTD) and inhibits H3K9me3 recognition, whereas the SET-and-RING-associated (SRA) domain binds to the plant homeodomain (PHD) and inhibits H3R2 recognition. Hm-DNA impairs the intramolecular interactions and promotes H3K9me3 recognition by TTD–PHD. The Spacer also facilitates UHRF1–DNMT1 interaction and enhances hm-DNA-binding affinity of the SRA. When TTD–PHD binds to H3K9me3, SRA-Spacer may exist in a dynamic equilibrium: either recognizes hm-DNA or recruits DNMT1 to chromatin. Our study reveals the mechanism for regulation of H3K9me3 and hm-DNA recognition by URHF1.

UHRF1 is involved in the maintenance of DNA methylation, but the regulatory mechanism of this epigenetic regulator is unclear. Here, the authors show that it has a closed conformation and are able to make conclusions about the mechanism of recognition of epigenetic marks.

Conserved linker regions and their regulation determine multiple chromatin-binding modes of UHRF1

Ubiquitin-like with PHD and RING Finger domains 1 (UHRF1) is an important nuclear protein that is mutated and aberrantly expressed in many tumors. The protein integrates different chromatin modifications and is essential for their maintenance throughout the cell cycle. Separate chromatin-binding modules of UHRF1 have been studied on a functional and structural level. The unmodified N-terminus of histone H3 is recognized by a PHD domain, while a TTD domain specifically interacts with histone H3 Lysine 9 trimethylation. A SRA region binds hemimethylatd DNA. Emerging evidence indicates that the modules of UHRF1 do not act independently of each other but establish complex modes of interaction with patterns of chromatin modifications. This multivalent readout is regulated by allosteric binding of phosphatidylinositol 5-phosphate to a region outside the PHD, TTD and SRA domains as well as by phosphorylation of one of the linker regions connecting these modules. Here, we summarize the current knowledge on UHRF1 chromatin interaction and introduce a novel model of conformational transitions of the protein that are directed by the flexible and highly charged linker regions. We propose that these are essential in setting up defined structural states of the protein where different domains or combinations thereof are available for binding chromatin modifications or are prevented from doing so. Lastly, we suggest that controlled tuning of intramolecular linker interactions by ligands and posttranslational modifications establishes a rational framework for comprehending UHRF1 regulation and putatively the working mode of other chromatin factors in different physiological contexts.

UHRF1 promotes human osteosarcoma cell invasion by downregulating the expression of E‑cadherin in an Rb1‑dependent manner

Ubiquitin‑like with plant homeodomain (PHD) and RING‑finger domain 1 (UHRF1) maintains methylation patterns following DNA replication and is expressed at high levels in various types of human cancer. UHRF1 has been identified as a novel oncogene involved in the pathogenesis of hepatocellular carcinoma. Previous studies have demonstrated that inhibition of the expression of UHRF1 suppresses the proliferation of cancer cells. However, the role of UHRF1 in human osteosarcoma has not been investigated. The present study examined the expression levels of UHRF1 and retinoblastoma 1 (Rb1) in human osteosarcoma cell lines by western blot analysis. Stable overexpression of UHRF1 or knockdown of Rb1 was achieved by lentiviral transfection. Subsequently, a Cell Counting Kit-8 assay and a cell invasion assay were performed to detect the biological functions of UHRF1 in vitro. The results of the present study demonstrated that UHRF1 promoted the proliferation of human osteosarcoma cells. The present study also reported that UHRF1 was able to enhance the invasion of osteosarcoma cells in a retinoblastoma 1 (Rb1)‑dependent manner. UHRF1 promoted invasion in Rb1‑positive osteosarcoma cells, but not in Saos‑2 cells with homozygous loss of Rb1. Similarly, knockdown of Rb1 in Rb1‑positive osteosarcoma cells enhanced levels of invasion and eliminated the regulation of invasion by UHRF1. UHRF1 was found to inhibit the mRNA and protein expression levels of Rb1. Furthermore, deletion of Rb1 was found to suppress the expression of E‑cadherin and promote epithelial‑to‑mesenchymal transition (EMT). In addition, the overexpression of UHRF1 inhibited the expression of E‑cadherin and promoted EMT via the suppression of Rb1. These data demonstrated that UHRF1 promotes osteosarcoma cell invasion by downregulating the expression of E‑cadherin and increasing EMT in an Rb1‑dependent manner.

UHRF1 promotes proliferation of gastric cancer via mediating tumor suppressor gene hypermethylation

Epigenetic changes play significant roles in cancer development. UHRF1, an epigenetic regulator, has been shown to be overexpressed and to coordinate tumor suppressor gene (TSG) silencing in several cancers. In a previous study, we found that UHRF1 promoted gastric cancer (GC) invasion and metastasis. However, the role and underlying mechanism of UHRF1 in GC carcinogenesis remain largely unknown. In the present study, we investigated UHRF1 expression and function in GC proliferation and explored its downstream regulatory mechanism. The results demonstrated that UHRF1 overexpression was an independent and significant predictor of GC prognosis. Downregulation of UHRF1 suppressed GC proliferation and growth in vitro and in vivo, and UHRF1 upregulation showed opposite effects. Furthermore, downregulation of UHRF1 reactivated 7 TSGs, including CDX2, CDKN2A, RUNX3, FOXO4, PPARG, BRCA1 and PML, via promoter demethylation. These results provide insight into the GC proliferation process, and suggest that targeting UHRF1 represents a new therapeutic approach to block GC development.

Ubiquitin E3 ligase UHRF1 regulates p53 ubiquitination and p53-dependent cell apoptosis in clear cell Renal Cell Carcinoma

Ubiquitin-like with PHD and RING finger domain 1 (UHRF1) is a multi-domain ubiquitin E3 ligase that plays critical roles in regulation of DNA methylation and histone ubiquitination. In this study, we found UHRF1 is frequently overexpressed in human clear cell Renal Cell Carcinoma (ccRCC) tissues both at mRNA and protein levels. We showed that UHRF1 directly interacts with p53 both in vivo and in vitro. A new domain (PD) in UHRF1 was required for interaction with p53. We found that UHRF1 down-regulates p53 transactivation activity which was depends on the ubiquitin E3 ligase function. UHRF1 can promote non-degradative ubiquitination of p53, suppress p53 pathway activation and p53-dependent apoptosis in ccRCC cells. Together, our study suggests that UHRF1, which overexpressed ccRCC, may act as a p53 regulator, suppress p53 pathway activation and help ccRCC cells to escape from p53-dependent apoptosis.

Digging deep into "dirty" drugs - modulation of the methylation machinery

DNA methylation and histone modification are epigenetic mechanisms that result in altered gene expression and cellular phenotype. The exact role of methylation in myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML) remains unclear. However, aberrations (e.g. loss-/gain-of-function or up-/down-regulation) in components of epigenetic transcriptional regulation in general, and of the methylation machinery in particular, have been implicated in the pathogenesis of these diseases. In addition, many of these components have been identified as therapeutic targets for patients with MDS/AML, and are also being assessed as potential biomarkers of response or resistance to hypomethylating agents (HMAs). The HMAs 5-azacitidine (AZA) and 2'-deoxy-5-azacitidine (decitabine, DAC) inhibit DNA methylation and have shown significant clinical benefits in patients with myeloid malignancies. Despite being viewed as mechanistically similar drugs, AZA and DAC have differing mechanisms of action. DAC is incorporated 100% into DNA, whereas AZA is incorporated into RNA (80-90%) as well as DNA (10-20%). As such, both drugs inhibit DNA methyltransferases (DNMTs; dependently or independently of DNA replication) resulting in the re-expression of tumor-suppressor genes; however, AZA also has an impact on mRNA and protein metabolism via its inhibition of ribonucleotide reductase, resulting in apoptosis. Herein, we first give an overview of transcriptional regulation, including DNA methylation, post-translational histone-tail modifications, the role of micro-RNA and long-range epigenetic gene silencing. We place special emphasis on epigenetic transcriptional regulation and discuss the implication of various components in the pathogenesis of MDS/AML, their potential as therapeutic targets, and their therapeutic modulation by HMAs and other substances (if known). The main focus of this review is laid on dissecting the rapidly evolving knowledge of AZA and DAC with a special focus on their differing mechanisms of action, and the effect of HMAs on transcriptional regulation.

Up-regulation of UHRF1 by oncogenic Ras promoted the growth, migration, and metastasis of pancreatic cancer cells

Ubiquitin-like with PHD and ring finger domains 1 (UHRF1) has been reported as a marker for the differential diagnosis of pancreatic cancer and chronic pancreatitis. However, the expression pattern and biological functions of UHRF1 in the progression of pancreatic cancer are not fully understood. In this study, it was found that the expression of UHRF1 was significantly up-regulated in pancreatic cancer samples compared to their adjacent normal tissues. Meanwhile, the expression of UHRF1 was inversely correlated with the survival of pancreatic cancer patients. Moreover, in the biological function studies, UHRF1 was shown to promote the growth, migration, and metastasis of pancreatic cancer cells in vitro and in vivo. Mechanistically, the expression of UHRF1 was induced by oncogenic Ras in both pancreatic cancer mouse model and cultured cells. Taken together, our study demonstrated that UHRF1 played an oncogenic role in the progression of pancreatic cancer, and UHRF1 might be a promising target for the treatment of pancreatic cancer.

Characterization of Np95 expression in mouse brain from embryo to adult: A novel marker for proliferating neural stem/precursor cells

Nuclear protein 95 KDa (Np95, also known as UHRF1 or ICBP90) plays an important role in maintaining DNA methylation of newly synthesized DNA strands by recruiting DNA methyltransferase 1 (DNMT1) during cell division. In addition, Np95 participates in chromatin remodeling by interacting with histone modification enzymes such as histone deacetylases. However, its expression pattern and function in the brain have not been analyzed extensively. We here investigated the expression pattern of Np95 in the mouse brain, from developmental to adult stages. In the fetal brain, Np95 is abundantly expressed at the midgestational stage, when a large number of neural stem/precursor cells (NS/PCs) exist. Interestingly, Np95 is expressed specifically in NS/PCs but not in differentiated cells such as neurons or glial cells. Furthermore, we demonstrate that Np95 is preferentially expressed in type 2a cells, which are highly proliferative NS/PCs in the dentate gyrus of the adult hippocampus. Moreover, the number of Np95-expressing cells increases in response to kainic acid administration or to voluntary running, which are known to enhance the proliferation of adult NS/PCs. These results suggest that Np95 participates in the process of proliferation and differentiation of NS/PCs, and that it should be a useful novel marker for proliferating NS/PCs, facilitating the analysis of the complex behavior of NS/PCs in the brain.

Upregulated UHRF1 promotes bladder cancer cell invasion by epigenetic silencing of KiSS1

Ubiquitin-like with PHD and RING finger domains 1 (UHRF1), as an epigenetic regulator, plays important roles in the tumorigenesis and cancer progression. KiSS1 functions as a metastasis suppressor in various cancers, and epigenetic silencing of KiSS1 increases the metastatic potential of cancer cells. We therefore investigated whether UHRF1 promotes bladder cancer cell invasion by inhibiting KiSS1. The expression levels of UHRF1 and KiSS1 were examined by quantitative real-time PCR assay in vitro and in vivo. The role of UHRF1 in regulating bladder cancer metastasis was evaluated in bladder cancer cell. We found that UHRF1 levels are upregulated in most clinical specimens of bladder cancer when compared with paired normal tissues, and UHRF1 expression levels are significantly increased in primary tumors that subsequently metastasized compared with non-metastatic tumors. Forced expression of UHRF1 promotes bladder cancer cell invasion, whereas UHRF1 knockdown decreases cell invasion. Overexpression of UHRF1 increases the methylation of CpG nucleotides and reduces the expression of KiSS1. UHRF1 and KiSS1 expression level is negatively correlated in vivo and in vitro. Knockdown of KiSS1 promotes bladder cancer cell invasion. Importantly, forced expression of KiSS1 partly abrogates UHRF1-induced cell invasion. These data demonstrated that upregulated UHRF1 increases bladder cancer cell invasion by epigenetic silencing of KiSS1.

L-methionase: a therapeutic enzyme to treat malignancies

Cancer is an increasing cause of mortality and morbidity throughout the world. L-methionase has potential application against many types of cancers. L-Methionase is an intracellular enzyme in bacterial species, an extracellular enzyme in fungi, and absent in mammals. L-Methionase producing bacterial strain(s) can be isolated by 5,5′-dithio-bis-(2-nitrobenzoic acid) as a screening dye. L-Methionine plays an important role in tumour cells. These cells become methionine dependent and eventually follow apoptosis due to methionine limitation in cancer cells. L-Methionine also plays an indispensable role in gene activation and inactivation due to hypermethylation and/or hypomethylation. Membrane transporters such as GLUT1 and ion channels like Na²⁺, Ca²⁺, K⁺, and Cl⁻ become overexpressed. Further, the α-subunit of ATP synthase plays a role in cancer cells growth and development by providing them enhanced nutritional requirements. Currently, selenomethionine is also used as a prodrug in cancer therapy along with enzyme methionase that converts prodrug into active toxic chemical(s) that causes death of cancerous cells/tissue. More recently, fusion protein (FP) consisting of L-methionase linked to annexin-V has been used in cancer therapy. The fusion proteins have advantage that they have specificity only for cancer cells and do not harm the normal cells.

Proteome analysis of a hepatocyte-specific BIRC5 (survivin)-knockout mouse model during liver regeneration

The Baculoviral IAP repeat-containing protein 5 (BIRC5), also known as inhibitor of apoptosis protein survivin, is a member of the chromosomal passenger complex and a key player in mitosis. To investigate the function of BIRC5 in liver regeneration, we analyzed a hepatocyte-specific BIRC5-knockout mouse model using a quantitative label-free proteomics approach. Here, we present the analyses of the proteome changes in hepatocyte-specific BIRC5-knockout mice compared to wildtype mice, as well as proteome changes during liver regeneration induced by partial hepatectomy in wildtype mice and mice lacking hepatic BIRC5, respectively. The BIRC5-knockout mice showed an extensive overexpression of proteins related to cellular maintenance, organization and protein synthesis. Key regulators of cell growth, transcription and translation MTOR and STAT1/STAT2 were found to be overexpressed. During liver regeneration proteome changes representing a response to the mitotic stimulus were detected in wildtype mice. Mainly proteins corresponding to proliferation, cell cycle and cytokinesis were up-regulated. The hepatocyte-specific BIRC5-knockout mice showed impaired liver regeneration, which had severe consequences on the proteome level. However, several proteins with function in mitosis were found to be up-regulated upon the proliferative stimulus. Our results show that the E3 ubiquitin-protein ligase UHRF1 is strongly up-regulated during liver regeneration independently of BIRC5.

Increasing role of UHRF1 in the reading and inheritance of the epigenetic code as well as in tumorogenesis

Epigenetic mechanisms such as DNA methylation and histone posttranslational modifications, allow cells to maintain the phenotype throughout successive mitosis. UHRF1 plays a major role in the inheritance of some epigenetic marks from mother cells to daughter cells due to its particular structural domains. The originality of UHRF1 lies in the fact that it can read epigenetic marks and recruit the enzymes that catalyze the same epigenetic mark. The SRA domain senses the presence of a methylated cytosine on one DNA strand allowing the recruitment of DNMT1, which methylates the cytosine on the newly synthesized DNA. The recently identified tudor domain of UHRF1 senses the presence of methylated histone H3 conducting UHRF1 to recruit histone methyltransferases. Recent studies deciphering the relationships between some of the structural domains of UHRF1 provides new insights on the reading of the epigenetic code over a larger portion of histone tail than usually expected. Furthermore, latest developments highlights that UHRF1 is one of the proteins which is able to directly connect DNA methylation to histone epigenetic marks. This paper reviews the principles how UHRF1 acts as an epigenetic reader and discusses the properties of UHRF1 to be a biomarker as well as a therapeutic target.