Enhancement of p53-dependent gene activation by the transcriptional coactivator Zac1

PLAGL1 overexpression induces cytoplasmic DNA accumulation that triggers cGAS/STING activation

Pancreatic β-cell damage mediated by apoptosis is believed to be a main trigger of type 1 diabetes mellitus (T1DM), which is proposed as an organ-specific autoimmune disease mediated by T cells. Nonetheless, the fundamental origins of T1DM remain uncertain. Here, we illustrate that an increase in PLAGL1 expression induces β-cell apoptosis, as evidenced by mitochondrial membrane impairment and nucleolar degradation. The gene expression levels from cDNA samples were determined using qRT-PCR method. Western blot and Co-immunoprecipitation were applied for protein expression and interactions, respectively. Flow cytometry and TUNEL assay were used to detect pancreatic β cell apoptosis. Female NOD/LtJ mice with recent-onset T1DM has been used in in vivo studies. Glucose-stimulated insulin secretion (GSIS) and glucose tolerance test (GTT) method is used for islet function assessment. Haematoxylin and Eosin (H&E) and Immunohistochemistry (IHC) were performed to evalute histological improvement of islet beta. Subsequent cytoplasmic DNA accumulation triggers DNA senser, the cyclic guanosine monophosphate-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway. STING activation further stimulates downstream IRF3 and NF-kB pathways, thus boost type-I interferon signalling and NF-kB mediated inflammation. These findings elucidate a molecular mechanism linking PLAGL1 induced cell apoptosis to type-I interferon signalling and suggest a potential benefit for targeting cGAS/STING in T1DM treatment.

Targeting Viral Transcription for HIV Cure Strategies

Combination antiretroviral therapy (ART) suppresses viral replication to undetectable levels, reduces mortality and morbidity, and improves the quality of life of people living with HIV (PWH). However, ART cannot cure HIV infection because it is unable to eliminate latently infected cells. HIV latency may be regulated by different HIV transcription mechanisms, such as blocks to initiation, elongation, and post-transcriptional processes. Several latency-reversing (LRA) and -promoting agents (LPA) have been investigated in clinical trials aiming to eliminate or reduce the HIV reservoir. However, none of these trials has shown a conclusive impact on the HIV reservoir. Here, we review the cellular and viral factors that regulate HIV-1 transcription, the potential pharmacological targets and genetic and epigenetic editing techniques that have been or might be evaluated to disrupt HIV-1 latency, the role of miRNA in post-transcriptional regulation of HIV-1, and the differences between the mechanisms regulating HIV-1 and HIV-2 expression.

PLAGL1 is associated with prognosis and cell proliferation in pancreatic adenocarcinoma

BACKGROUND

Emerging evidence has shown the crucial roles of pleomorphic adenoma gene (PLAG) family genes in multiple cancers. However, their functions and mechanisms in pancreatic adenocarcinoma (PAAD) remain poorly understood.

METHODS

We analyzed the expression levels of PLAG family genes in both The Cancer Genome Atlas (TCGA) database and a Gene Expression Omnibus (GEO) database, and confirmed the results in our three independent cohorts of 382 PAAD tissues and 362 adjacent nontumor pancreatic tissues. Integrated analyses were carried out to explore the function, mechanism and prognostic value of the selected PLAG family gene in PAAD patients.

RESULTS

By analyzing the TCGA and GEO databases, PLAGL1 was identified to be downregulated in PAAD tissues, and its decreasing levels of both mRNA and protein were verified in our three independent PAAD cohorts. PLAGL1 expression was inversely correlated with clinicopathological factors including the Ki67⁺ cell rate and pathologic stage. Further GSEA of the TCGA-PAAD cohort demonstrated that multiple signaling pathways implicated in cell proliferation were enriched in the lower PLAGL1 expressing PAAD group. Moreover, we demonstrated that PLAGL1 expression was obviously negatively associated with patients' overall survival outcome in both the TCGA-PAAD cohort and our verification cohorts. Additionally, through MTS and BrdU assays, we further demonstrated in vitro that PLAGL1 had the impact of preventing the proliferation of pancreatic cancer cells.

CONCLUSIONS

Our present study suggested that downregulated PLAGL1 might act as a biomarker in predicts poor prognosis and one of important factors in increasing cell proliferation in PAAD. This study provides us with a novel prognostic marker and therapeutic strategy for PAAD, which deserves further study.

DNA Repair Inhibition Leads to Active Export of Repetitive Sequences to the Cytoplasm Triggering an Inflammatory Response

Adult-onset neurodegenerative diseases are often accompanied by evidence of a chronic inflammation that includes activation of microglial cells and altered levels of brain cytokines. Aspects of this response are likely secondary reactions to neurodegeneration, but for many illnesses the inflammation may itself be an early and even causative disease event. In such cases, the inflammation is referred to as "sterile" as it occurs in the absence of an actual bacterial or viral pathogen. A potent trigger of sterile inflammation in CNS microglia has been shown to be the presence of DNA in the cytoplasm (cytoDNA) induced either by direct DNA damage or by inhibited DNA repair. We have shown that cytoDNA comes from the cell nucleus as a result of insufficient DNA damage repair. Using wild-type and Atm ^-/- mouse microglia, we extend these observations here by showing that its genomic origins are not random, but rather are heavily biased toward transcriptionally inactive, intergenic regions, in particular repetitive elements and AT-rich sequences. Once released from the genome, in both males and females, we show that cytoDNA is actively exported to the cytoplasm by a CRM1-dependent mechanism. In the cytoplasm, it is degraded either by a cytosolic exonuclease, Trex1, or an autophagy pathway that ends with degradation in the lysosome. Blocking the accumulation of cytoDNA prevents the emergence of the sterile inflammation reaction. These findings offer new insights into the emergence of sterile inflammation and offer novel approaches that may be of use in combatting a wide range of neurodegenerative conditions.SIGNIFICANCE STATEMENT Sterile inflammation describes a state where the defenses of the immune system are activated in the absence of a true pathogen. A potent trigger of this unorthodox response is the presence of DNA in the cytoplasm, which immune cells interpret as an invading virus or pathogen. We show that when DNA damage increases, fragments of the cell's own genome are actively exported to the cytoplasm where they are normally degraded. If this degradation is incomplete an immune reaction is triggered. Both age and stress increase DNA damage, and as age-related neurodegenerative diseases are frequently accompanied by a chronic low-level inflammation, strategies that reduce the induction of cytoplasmic DNA or speed its clearance become attractive therapeutic targets.

Genomic Imprinting at the Porcine PLAGL1 Locus and the Orthologous Locus in the Human

Implementation of genomic imprinting in mammals often results in cis-acting silencing of a gene cluster and monoallelic expression, which are important for mammalian growth and function. Compared with widely documented imprinting status in humans and mice, current understanding of genomic imprinting in pigs is relatively limited. The objectives of this study were to identify DNA methylation status and allelic expression of alternative spliced isoforms at the porcine PLAGL1 locus and assess the conservation of the locus compared to the orthologous human locus. DNA methylome and transcriptome were constructed using porcine parthenogenetic or biparental control embryos. Using methylome, differentially methylated regions between those embryos were identified. Alternative splicing was identified by differential splicing analysis, and monoallelic expression was examined using single nucleotide polymorphism sites. Moreover, topological boundary regions were identified by analyzing CTCF binding sites and compared with the boundary of human orthologous locus. As a result, it was revealed that the monoallelic expression of the PLAGL1 gene in porcine embryos via genomic imprinting was maintained in the adult stage. The porcine PLAGL1 locus was largely conserved in regard to maternal hypermethylation, tissue distribution of mRNA expression, monoallelic expression, and biallelic CTCF-binding, with exceptions on transcript isoforms produced by alternative splicing instead of alternative promoter usage. These findings laid the groundwork for comparative studies on the imprinted PLAGL1 gene and related regulatory mechanisms across species.

Molecular mechanisms of β-cell dysfunction and death in monogenic forms of diabetes

Monogenetic forms of diabetes represent 1%-5% of all diabetes cases and are caused by mutations in a single gene. These mutations, that affect genes involved in pancreatic β-cell development, function and survival, or insulin regulation, may be dominant or recessive, inherited or de novo. Most patients with monogenic diabetes are very commonly misdiagnosed as having type 1 or type 2 diabetes. The severity of their symptoms depends on the nature of the mutation, the function of the affected gene and, in some cases, the influence of additional genetic or environmental factors that modulate severity and penetrance. In some patients, diabetes is accompanied by other syndromic features such as deafness, blindness, microcephaly, liver and intestinal defects, among others. The age of diabetes onset may also vary from neonatal until early adulthood manifestations. Since the different mutations result in diverse clinical presentations, patients usually need different treatments that range from just diet and exercise, to the requirement of exogenous insulin or other hypoglycemic drugs, e.g., sulfonylureas or glucagon-like peptide 1 analogs to control their glycemia. As a consequence, awareness and correct diagnosis are crucial for the proper management and treatment of monogenic diabetes patients. In this chapter, we describe mutations causing different monogenic forms of diabetes associated with inadequate pancreas development or impaired β-cell function and survival, and discuss the molecular mechanisms involved in β-cell demise.

A functional screen identifies transcriptional networks that regulate HIV-1 and HIV-2

The molecular networks involved in the regulation of HIV replication, transcription, and latency remain incompletely defined. To expand our understanding of these networks, we performed an unbiased high-throughput yeast one-hybrid screen, which identified 42 human transcription factors and 85 total protein-DNA interactions with HIV-1 and HIV-2 long terminal repeats. We investigated a subset of these transcription factors for transcriptional activity in cell-based models of infection. KLF2 and KLF3 repressed HIV-1 and HIV-2 transcription in CD4+ T cells, whereas PLAGL1 activated transcription of HIV-2 through direct protein-DNA interactions. Using computational modeling with interacting proteins, we leveraged the results from our screen to identify putative pathways that define intrinsic transcriptional networks. Overall, we used a high-throughput functional screen, computational modeling, and biochemical assays to identify and confirm several candidate transcription factors and biochemical processes that influence HIV-1 and HIV-2 transcription and latency.

Gene expression profiling identifies the role of Zac1 in cervical cancer metastasis

The zinc-finger protein which regulates apoptosis and cell cycle arrest 1 (Zac1), encoded by Plagl1 gene, is a seven-zinc-finger containing transcription factor belonging to the imprinted genome and is expressed in diverse types of embryonic and adult human tissues. Zac1 is postulated to be a tumor suppressor by inducing cell cycle arrest and apoptosis through interacting and modulating transcriptional activity of p53 as it was named. Correspondingly, the reduction or loss of Zac1 expression is associated with the incidence and progression of several human tumors, including cervical cancer, breast cancer, ovarian cancer, pituitary tumors, and basal cell carcinoma, implying the rationality of utilizing Zac1 expression as novel a biomarker for the evaluation of cervical cancer prognosis. However, to date, it has not been elucidated whether Zac1 expression is related to the prognosis of patients in clinical cervical cancer tumor samples. To address the questions outlined above, we report here a comprehensive investigation of Zac1 expression in biopsies of clinical cervical carcinoma. By analyzing Zac1 expression in various gene expression profiling of cervical cancer databases, we show the association between high Zac1 expression and poor prognosis of cervical cancer. Functional enrichment analysis showed that high Zac1 expression was associated with epithelial-mesenchymal transition (EMT), which was further observed in clinical characteristics and metastatic carcinoma samples using immunohistochemical staining. Correspondingly, hypomethylation of CpG island on Zac1 promoter was observed in samples with high Zac1 expression in cervical carcinoma. Finally, overexpression of Zac1 in a variety of cervical cancer cell lines increase their mesenchymal biomarker expression and migration, strengthening the correlation between cervical cancers with high Zac1 expression and metastasis in clinical. In summary, this research firstly revealed that identifying Zac1 expression or the methylation status of CpG site on Zac1 promoter may provide us with novel indicators for the evaluation of cervical cancer metastasis.

Proteomics reveals the alleviation of zinc towards aflatoxin B1-induced cytotoxicity in human hepatocyes (HepG2 cells)

Aflatoxin B1 (AFB1) is a known carcinogen found in contaminated food and designated by the World Health Organization as a class I carcinogenic substance. AFB1 presents with carcinogenicity, teratogenicity, and mutagenicity, and the liver is the human organ most susceptible to AFB1. Zinc (Zn), which is one of the essential nutrient elements that could protect the cells from biological toxins, heavy metals, hydrogen peroxide, metal chelators and radiation, is assessed in this study for its potential to alleviate AFB1-induced cytotoxicity. Samples were divided into three groups, namely CK, AFB1, and AFB1+Zn. Protein expressions were analyzed by two-way electrophoresis combined with flight mass spectrometry, with 41 differentially expressed proteins identified in the results, mainly related to oxidative stress, cell apoptosis, DNA damage, and energy metabolism. Zn was found to regulate the expression of peroxidases (peroxiredoxin-1, peroxiredoxin-5, peroxiredoxin-6) to relieve AFB1-induced oxidative stress. Moreover, Zn could decrease the expression of pro-apoptotic genes (cleaved-caspase-3, caspase-9, and Bax) and increase the expression of anti-apoptotic genes (Bcl-2 and Bcl-xl) to alleviate the cell apoptosis induced by AFB1. In addition, AFB1 reduced intracellular ATP levels, whereas Zn supplementation boosted ATP levels and maintained homeostasis and a steady state of cellular energy metabolism by modulating AMPK-ACC phosphorylation levels, while many zinc finger proteins changed after AFB1 treatment. These results, therefore, indicate that Zn could alleviate AFB1-induced cytotoxicity by changing the expressions of zinc finger proteins in liver hepatocellular carcinoma (HepG2 cells).

Genome-wide Analysis of the Alternative Splicing Profiles Revealed Novel Prognostic Index for Kidney Renal Cell Clear Cell Carcinoma

Alternative splicing (AS) is a major mechanism that greatly enhanced the diversity of proteome. Mounting evidence demonstrated that aberration of AS are important steps for the initiation and progression of human cancers. Here, we comprehensively investigated the association between whole landscape of AS profiles and the survival outcome of renal cell carcinoma (RCC) patients using RNA-seq data from TCGA SpliceSeq. Because of the limited number size of deaths in kidney chromophobe renal cell carcinoma (KICH) and papillary renal cell carcinoma (KIRP) TCGA cohorts, we only conducted survival analysis in kidney clear renal cell carcinoma (KIRC). We further constructed prognostic index (PI) based on prognosis-related AS events and built correlation network for splicing factors and prognosis-related AS events. According to the results, a total of 5351 AS events in 3522 genes were significantly correlated with the overall survival (OS) of kidney clear cell renal cell carcinoma (KIRC) patients. Seven of the PI models exhibited preferable prognosis-predicting capacity for KIRC with PI-ALL reaching the highest area under curve value of 0.875. The splicing regulatory network between splicing factors and prognosis-related AS events depicted a tangled web of relationships between them. One of the splicing factors: KHDRBS3 was validated by immunohistochemistry to be down-regulated in KIRC tissues. In conclusion, the powerful efficiency of risk stratification of PI models indicated the potential of AS signature as promising prognostic markers for KIRC and the splicing regulation network provided possible genetic mechanism of KIRC.

SNAP reverses temozolomide resistance in human glioblastoma multiforme cells through down-regulation of MGMT

Glioblastoma multiforme (GBM) is the most frequently occurring and gravest primary tumor of the CNS in adults. The development of chemoresistance to temozolomide (TMZ), the first-line chemotherapy for GBM, is an important factor contributing to poor treatment outcomes. Down-regulation of O-6-methylguanine-DNA methyltransferase (MGMT) expression in GBM cells is an attractive strategy for overcoming TMZ resistance and improving outcomes. This study revealed that the nitric oxide (NO) donor S-nitroso-N-acetylpenicillamine (SNAP) exerts antitumorigenic effects on TMZ-sensitive and TMZ-resistant (TMZ-R) glioma cells. Pretreatment with SNAP not only induced apoptosis, mitochondrial dysfunction, and hypoxia-inducing factor 1, but also resensitized TMZ-R GBM cells to TMZ through down-regulation of MGMT expression. SNAP acted principally through post-translational modification of p53, phosphorylated N-myc downstream regulated gene 1, and MGMT protein stability in TMZ-R GBM cells. Additionally, when applied together, SNAP and TMZ enhanced the inhibition of tumor growth in vitro and in vivo. This study sheds new light on a potential strategy to overcome TMZ resistance in GBM and thus possesses the potential for prolonging survival of patients with GBM.-Tsai, C.-K., Huang, L.-C., Wu, Y.-P., Kan, I.-Y., Hueng, D.-Y. SNAP reverses temozolomide resistance in human glioblastoma multiforme cells through down-regulation of MGMT.

The antitumor properties of metformin and phenformin reflect their ability to inhibit the actions of differentiated embryo chondrocyte 1

Background

Differentiated embryo chondrocyte 1 (DEC1) is a helix-loop-helix transcription factor that directly binds to the class B E-box in target genes. DEC1 exerts both pro-survival and pro-apoptotic effects in a cell- and tissue-dependent manner. Its actions play role the progression of cancer remains unclear.

Methods

We first examined the functional roles of DEC1 using the transient promoter reporter assay. Then, the knockdown of DEC1 expression was performed with the short hairpin RNA strategy in HeLa and A2058 cancer cell lines to check the cell cycle and mitochondrial function profile using the flow cytometry and Seahorse assays. We later clarified the role of DEC1 in the tumorigenesis using the colony formation, anchorage-independent growth assay, and cellular proliferation analysis.

Results

In the present study, we tested two guanide-containing drugs, metformin and phenformin, and found that both exhibit cytotoxicity against HeLa cervical carcinoma and A2058 melanoma cells. This effect was mediated, at least in part, through activation of the AMPK pathway; degradation of important cellular proteins, such as DEC1 and p53; and suppression of mitochondrial function, colony formation, and anchorage-independent cell proliferation. Our results further suggest that the cytotoxicity of metformin and phenformin reflect the impact of the repressive actions of DEC1 on gene expression, including DEC1 itself. This in turn suppresses both anchorage-independent growth and cell proliferation.

Conclusion

These findings provide several lines of evidence suggesting that DEC1 activity contributes to tumorigenicity and that the antitumor properties of biguanides reflect their ability to inhibit DEC1 functions.

Plag1 and Plagl2 have overlapping and distinct functions in telencephalic development

The Plag gene family has three members; Plagl1/Zac1, which is a tumor suppressor gene, and Plag1 and Plagl2, which are proto-oncogenes. All three genes are known to be expressed in embryonic neural progenitors, and Zac1 regulates proliferation, neuronal differentiation and migration in the developing neocortex. Here we examined the functions of Plag1 and Plagl2 in neocortical development. We first attempted, and were unable to generate, E12.5 Plag1;Plagl2 double mutants, indicating that at least one Plag1 or Plagl2 gene copy is required for embryonic survival. We therefore focused on single mutants, revealing a telencephalic patterning defect in E12.5 Plagl2 mutants and a proliferation/differentiation defect in Plag1 mutant neocortices. Specifically, the ventral pallium, a dorsal telencephalic territory, expands into the ventral telencephalon in Plagl2 mutants. In contrast, Plag1 mutants develop normal regional territories, but neocortical progenitors proliferate less and instead produce more neurons. Finally, in gain-of-function studies, both Plag1 and Plagl2 reduce neurogenesis and increase BrdU-uptake, indicative of enhanced proliferation, but while Plagl2 effects on proliferation are more immediate, Plag1 effects are delayed. Taken together, we found that the Plag proto-oncogenes genes are essential regulators of neocortical development and although Plag1 and Plagl2 functions are similar, they do not entirely overlap. This article has an associated First Person interview with the first author of the paper.

Metformin causes cancer cell death through downregulation of p53-dependent differentiated embryo chondrocyte 1

Background

Metformin is the most commonly used first-line medicine for type II diabetes mellitus. Acting via AMP-activated protein kinase, it has been used for more than 60 years and has an outstanding safety record. Metformin also offers protection against cancer, but its precise mechanisms remain unclear.

Methods

We first examined the cytotoxic effects of metformin in the HeLa human cervical carcinoma and ZR-75-1 breast cancer cell lines using assays of cell viability, cleaved poly-ADP-ribose polymerase, and Annexin V-fluorescein isothiocyanate apoptosis, as well as flow cytometric analyses of the cell cycle profile and reactive oxygen species (ROS). We later clarified the effect of metformin on p53 protein stability using transient transfection and cycloheximide chase analyses.

Results

We observed that metformin represses cell cycle progression, thereby inducing subG1 populations, and had induced apoptosis through downregulation of p53 protein and a target gene, differentiated embryo chondrocyte 1 (DEC1). In addition, metformin increased intracellular ROS levels, but N-acetyl cysteine, a ROS scavenger, failed to suppress metformin-induced apoptosis. Further results showed that metformin disrupted the electron transport chain and collapsed the mitochondrial membrane potential, which may be the cause of the elevated ROS levels. Examination of the mechanisms underlying metformin-induced HeLa cell death revealed that reduced stability of p53 in metformin-treated cells leads to decreases in DEC1 and induction of apoptosis.

Conclusion

The involvement of DEC1 provides new insight into the positive or negative functional roles of p53 in the metformin-induced cytotoxicity in tumor cells.

PLAGL1 gene function during hepatoma cells proliferation

Hepatocellular carcinoma develops as a multistep process, in which cell cycle deregulation is a central feature, resulting in unscheduled proliferation. The PLAGL1 gene encodes a homonym zinc finger protein that is involved in cell-proliferation control. We determined the genomic profile and the transcription and expression level of PLAGL1, simultaneously with that of its molecular partners p53, PPARγ and p21, in cell-lines derived from patients with liver cancer, during in vitro cell growth. Our investigations revealed that genomic and epigenetic changes of PLAGL1 are also present in hepatoma cell-lines. Transcription of PLAGL1 in tumor cells is significantly lower than in normal fibroblasts, but no significant differences in terms of protein expression were detected between these two cell-types, indicating that there is not a direct relationship between the gene transcriptional activity and protein expression. RT-PCR analyses on normal fibroblasts, used as control, also showed that PLAGL1 and p53 genes transcription occurs as an apparent orchestrated process during normal cells proliferation, which gets disturbed in cancer cells. Furthermore, abnormal trafficking of the PLAGL1 protein may occur in hepatocarcinogenesis.

Zac1 regulates IL-11 expression in osteoarthritis

Interleukin (IL)-11, a member of the IL-6 family of cytokines, exerts pleiotropic effects under normal and various disease conditions. We assessed IL-11 expression regulation and the IL-11/IL-6 ratio in osteoarthritis (OA) to better guide clinical therapeutic decision-making. Our findings suggest that Zac1, a zinc finger protein that regulates apoptosis and cell cycle arrest, is a transcription factor regulating IL-11 expression. Zac1 overexpression or knockdown respectively induced or suppressed IL-11 expression in HeLa cells. Zac1 acted synergistically with AP-1, human papillomavirus E2, and hypoxia inducible factor 1 alpha (HIF1α). IL-11 expression under various conditions, including hypoxia or treatment with phorbol 12-myristate 13-acetate or copper sulfate. Recombinant IL-11-induced phosphorylation of signal transducer and activator of transcription 3 at tyrosine 705 was reduced in a dose-dependent manner in HeLa cells. Cross-talk between Zac1, IL-11, p53, and suppressor of cytokine signaling 3 was differentially affected by copper sulfate, digoxin, and caffeine. Finally, aggressive vs. conventional treatment of OA patients was primarily determined by IL-6 levels. However, we suggest that OA patients with higher IL-11 levels may respond well to conventional treatments, even in the presence of high IL-6.

The cytotoxic mechanism of epigallocatechin gallate on proliferative HaCaT keratinocytes

BACKGROUND

Epigallocatechin gallate (EGCG) is the major ingredient of sinecatechins ointment, approved for the treatment of external genital and perianal warts. However, the molecular mechanism for EGCG's effect on warts resulting from the human papillomavirus (HPV) infection of keratinocytes is not well understood. HPV may survive in proliferative keratinocytes and may be involved in cell cycle regulation and progression. The objective of this study was to investigate the mechanism underlying EGCG's treatment on external genital warts of HPV infection through the cultured keratinocyte cells from the HaCaT cell line.

METHODS

MTT and flow cytometry assays were used to measure cell viability and the cell cycle profile, with and without EGCG treatment, for HaCaT keratinocyte cells cultured in a calcium-free medium and 1.8 mM calcium which induced proliferative and differentiated keratinocytes, respectively, for 24 h. The expression levels of cytotoxic proteins and factors were evaluated with the RT-PCR and western blotting analysis.

RESULTS

EGCG influenced the proliferation stage but not the differentiation stage of keratinocytes. We suggest that apoptosis and autophagy might be the possible mechanism for the EGCG's effect on the proliferative HaCaT cells. Furthermore, we found that EGCG reduced the protein levels of cyclin D1 and Zac1 (a zinc-finger protein which regulates apoptosis and cell cycle arrest 1) dose-dependently in proliferative as compared to differentiated keratinocytes. It also induced the expression of p21 and DEC1 (differentiated embryo-chondrocyte expressed gene 1), and promoted G1 arrest of cell cycle in proliferative keratinocytes.

CONCLUSIONS

These results help clarify the mechanisms of EGCG treatment of HPV-infected keratinocytes and may contribute to new targets, such as Zac1 and DEC1 for external genital and perianal warts.

Transcriptional analysis of the conidiation pattern shift of the entomopathogenic fungus Metarhizium acridum in response to different nutrients

Background

Most fungi, including entomopathogenic fungi, have two different conidiation patterns, normal and microcycle conidiation, under different culture conditions, eg, in media containing different nutrients. However, the mechanisms underlying the conidiation pattern shift are poorly understood.

Results

In this study, Metarhizium acridum undergoing microcycle conidiation on sucrose yeast extract agar (SYA) medium shifted to normal conidiation when the medium was supplemented with sucrose, nitrate, or phosphate. By linking changes in nutrients with the conidiation pattern shift and transcriptional changes, we obtained conidiation pattern shift libraries by Solexa/Illumina deep-sequencing technology. A comparative analysis demonstrated that the expression of 137 genes was up-regulated during the shift to normal conidiation, while the expression of 436 genes was up-regulated at the microcycle conidiation stage. A comparison of subtractive libraries revealed that 83, 216, and 168 genes were related to sucrose-induced, nitrate-induced, and phosphate-induced conidiation pattern shifts, respectively. The expression of 217 genes whose expression was specific to microcycle conidiation was further analyzed by the gene expression profiling via multigene concatemers method using mRNA isolated from M. acridum grown on SYA and the four normal conidiation media. The expression of 142 genes was confirmed to be up-regulated on standard SYA medium. Of these 142 genes, 101 encode hypothetical proteins or proteins of unknown function, and only 41 genes encode proteins with putative functions. Of these 41 genes, 18 are related to cell growth, 10 are related to cell proliferation, three are related to the cell cycle, three are related to cell differentiation, two are related to cell wall synthesis, two are related to cell division, and seven have other functions. These results indicate that the conidiation pattern shift in M. acridum mainly results from changes in cell growth and proliferation.

Conclusions

The results indicate that M. acridum shifts conidiation pattern from microcycle conidiation to normal conidiation when there is increased sucrose, nitrate, or phosphate in the medium during microcycle conidiation. The regulation of conidiation patterning is a complex process involving the cell cycle and metabolism of M. acridum. This study provides essential information about the molecular mechanism of the induction of the conidiation pattern shift by single nutrients.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2971-0) contains supplementary material, which is available to authorized users.

PLAGL1: an important player in diverse pathological processes

The PLAGL1 gene encodes a homonymous zinc finger protein that promotes cell cycle arrest and apoptosis through multiple pathways. The protein has been implicated in metabolic, genetic, and neoplastic illnesses, but the molecular mechanisms by which the protein PLAGL1 participates in such diverse processes remains to be elucidated. In this review, we focus mainly on the molecular biology of PLAGL1 and the relevance of its abnormalities to several pathological processes.

Role of ZAC1 in transient neonatal diabetes mellitus and glucose metabolism

Transient neonatal diabetes mellitus 1 (TNDM1) is a rare genetic disorder representing with severe neonatal hyperglycaemia followed by remission within one and a half year and adolescent relapse with type 2 diabetes in half of the patients. Genetic defects in TNDM1 comprise uniparental isodisomy of chromosome 6, duplication of the minimal TNDM1 locus at 6q24, or relaxation of genomically imprinted ZAC1/HYMAI. Whereas the function of HYMAI, a non-coding mRNA, is still unidentified, biochemical and molecular studies show that zinc finger protein 1 regulating apoptosis and cell cycle arrest (ZAC1) behaves as a factor with versatile transcriptional functions dependent on binding to specific GC-rich DNA motives and interconnected regulation of recruited coactivator activities. Genome-wide expression profiling enabled the isolation of a number of Zac1 target genes known to regulate different aspects of β-cell function and peripheral insulin sensitivity. Among these, upregulation of Pparγ and Tcf4 impairs insulin-secretion and β-cell proliferation. Similarly, Zac1-mediated upregulation of Socs3 may attenuate β-cell proliferation and survival by inhibition of growth factor signalling. Additionally, Zac1 directly represses Pac1 and Rasgrf1 with roles in insulin secretion and β-cell proliferation. Collectively, concerted dysregulation of these target genes could contribute to the onset and course of TNDM1. Interestingly, Zac1 overexpression in β-cells spares the effects of stimulatory G-protein signaling on insulin secretion and raises the prospect for tailored treatments in relapsed TNDM1 patients. Overall, these results suggest that progress on the molecular and cellular foundations of monogenetic forms of diabetes can advance personalized therapy in addition to deepening the understanding of insulin and glucose metabolism in general.

The inhibitory mechanism by curcumin on the Zac1-enhanced cyclin D1 expression in human keratinocytes

BACKGROUND

ZAC, a zinc finger protein regulating cell cycle arrest and apoptosis, mRNA was found highly expressed in the hyper-proliferative epidermal compartment of psoriatic skin. On the other hand, curcumin has been tried for treatment of psoriasis partly due to its anti-proliferative property.

OBJECTIVES

Since cyclin D1 is a positive regulator for cell-cycle progression and its expression can be inhibited by curcumin, we would like to test whether the expression of cyclin D1 can be affected by Zac1. The cross-talk between curcumin and Zac1 upon the regulation of cyclin D1 expression will also be explored in the HaCaT cell line.

METHODS

Cyclin D1 promoter luciferase reporter was used to measure the transcriptional activity of Zac1 in the absence or presence of curcumin treatment for HaCaT cells. Likewise, RT-PCR, western blotting and flow cytometry were employed to evaluate the expression of Zac1, cyclin D1 and other negative regulators of S phase entry in cell-cycle.

RESULTS

Zac1 enhances the expression of cyclin D1, but curcumin decreases both the expression of Zac1 and cyclin D1. Interestingly, Zac1-induced cyclin D1 promoter activity is abolished by curcumin. Supportively, curcumin indeed exhibits an inhibitory effect to prevent cultured keratinocytes from entry into S phase in the cell cycle.

CONCLUSIONS

These findings revealed that Zac1 modulates not only cell differentiation and apoptosis but also cell proliferation. The experimental results implied that curcumin may inhibit the expression of ZAC, consequently down-regulate the cyclin D1 expression and decelerate cell-cycle progression of psoriatic keratinocytes.

Imprinted Zac1 in neural stem cells

Neural stem cells (NSCs) and imprinted genes play an important role in brain development. On historical grounds, these two determinants have been largely studied independently of each other. Recent evidence suggests, however, that NSCs can reset select genomic imprints to prevent precocious depletion of the stem cell reservoir. Moreover, imprinted genes like the transcriptional regulator Zac1 can fine tune neuronal vs astroglial differentiation of NSCs. Zac1 binds in a sequence-specific manner to pro-neuronal and imprinted genes to confer transcriptional regulation and furthermore coregulates members of the p53-family in NSCs. At the genome scale, Zac1 is a central hub of an imprinted gene network comprising genes with an important role for NSC quiescence, proliferation and differentiation. Overall, transcriptional, epigenomic, and genomic mechanisms seem to coordinate the functional relationships of NSCs and imprinted genes from development to maturation, and possibly aging.

The p53 co-activator Zac1 neither induces cell cycle arrest nor apoptosis in chicken Lim1 horizontal progenitor cells

Chicken horizontal progenitor cells are able to enter their final mitosis even in the presence of DNA damage despite having a functional p53-p21 system. This suggests that they are resistant to DNA damage and that the regulation of the final cell cycle of horizontal progenitor cells is independent of the p53-p21 system. The activity of p53 is regulated by positive and negative modulators, including the zinc finger containing transcription factor Zac1 (zinc finger protein that regulates apoptosis and cell cycle arrest). Zac1 interacts with and enhances the activity of p53, thereby inducing cell cycle arrest and apoptosis. In this work, we use a gain-of-function assay in which mouse Zac1 (mZac1) is overexpressed in chicken retinal progenitor cells to study the effect on the final cell cycle of horizontal progenitor cells. The results showed that overexpression of mZac1 induced expression of p21 in a p53-dependent way and arrested the cell cycle as well as triggered apoptosis in chicken non-horizontal retinal progenitor cells. The negative regulation of the cell cycle by mZac1 is consistent with its proposed role as a tumour-suppressor gene. However, the horizontal cells were not affected by mZac1 overexpression. They progressed into S- and late G2/M-phase despite overexpression of mZac1. The inability of mZac1 to arrest the cell cycle in horizontal progenitor cells support the notion that the horizontal cells are less sensitive to events that triggers the p53 system during their terminal and neurogenic cell cycle, compared with other retinal cells. These properties are associated with a cell that has a propensity to become neoplastic and thus with a cell that may develop retinoblastoma.

Both gene deletion and promoter hyper-methylation contribute to the down-regulation of ZAC/PLAGL1 gene in gastric adenocarcinomas: a case control study

BACKGROUND AND OBJECTIVE

Pleiomorphic adenoma gene-like 1 (PLAGL1, also known as LOT1 and ZAC) is a zinc-finger nuclear transcription factor, which possesses antiproliferative effects and is frequently epigenetically silenced during tumorigenesis. PLAGL1 gene is located on 6q24-25, a chromosomal region that is frequently deleted in various kinds of cancers. Both promoter hyper-methylation and loss of heterozygosity may lead to the down-regulation of PLAGL1 in human somatic cancers. Here we aimed to investigate the abnormalities of PLAGL1 in gastric cancers.

METHODS

We collected 153 case-matched gastric adenocarcinoma (GAC) cases. Quantitative real-time PCR method was applied to evaluate the expression levels as well as gene copy numbers of PLAGL1 in the collected samples. Methylation-specific PCR (MSP) assay was performed to analyze the methylation status of PLAGL1 P1 promoter.

RESULTS

Decreased expression of PLAGL1 mRNA was observed in GAC tissues, especially in advanced GACs. Copy number decrease of PLAGL1 gene in GACs was observed in 9.15% (19 out of 153) of the GAC samples and was closely correlated with gene expression. Methylation status of PLAGL1 promoter in GAC tissues was higher than in normal controls, which was inversely correlated with the expression levels of PLAGL1 mRNA.

CONCLUSION

DNA deletion and promoter hyper-methylation both contribute to the down-regulation of PLAGL1 in GACs.

Imprinted genes and the environment: links to the toxic metals arsenic, cadmium, lead and mercury

Imprinted genes defy rules of Mendelian genetics with their expression tied to the parent from whom each allele was inherited. They are known to play a role in various diseases/disorders including fetal growth disruption, lower birth weight, obesity, and cancer. There is increasing interest in understanding their influence on environmentally-induced disease. The environment can be thought of broadly as including chemicals present in air, water and soil, as well as food. According to the Agency for Toxic Substances and Disease Registry (ATSDR), some of the highest ranking environmental chemicals of concern include metals/metalloids such as arsenic, cadmium, lead and mercury. The complex relationships between toxic metal exposure, imprinted gene regulation/expression and health outcomes are understudied. Herein we examine trends in imprinted gene biology, including an assessment of the imprinted genes and their known functional roles in the cell, particularly as they relate to toxic metals exposure and disease. The data highlight that many of the imprinted genes have known associations to developmental diseases and are enriched for their role in the TP53 and AhR pathways. Assessment of the promoter regions of the imprinted genes resulted in the identification of an enrichment of binding sites for two transcription factor families, namely the zinc finger family II and PLAG transcription factors. Taken together these data contribute insight into the complex relationships between toxic metals in the environment and imprinted gene biology.

Characterization of a new mouse p53 variant: loss-of-function and gain-of-function

Background

p53 is a major tumor suppressor that is inactivated in over 50% of human cancer types through either mutation or inactivating interactions with viral or cellular proteins. The uncertainties around the link between p53 status, therapeutic response, and outcome in cancer suggest that additional factors may be involved. p53 isoforms that are generated via the alternative splicing pathway may be promising candidates for further investigation.

Result

In this study, we report one new p53 protein with two internally deleted regions, resulting in one deleted amino acid fragment (from amino acid residues 42 to 89) and one reading frame-shift region (from amino acid residues 90-120) compared to wild-type p53. The functional status of the new p53 protein, which has a defect in its proline-rich and N-terminal DNA-binding domains, was characterized as possessing an intact conformation, exhibiting no transactivation activity, exerting a dominant-negative effect and an interacting with a coactivator with an arginine methyltransferase activity.

Conclusion

Taken together, our findings provide valuable information about the structure and function of p53 for the regulation of transactivation activity and cellular protein-protein interactions. Furthermore, natural p53 isoforms will help us understand the functional roles of the p53 family and potential therapeutics for p53-dependent cancers.

Genetic and epigenetic mutations of tumor suppressive genes in sporadic pituitary adenoma

Human pituitary adenomas are the most common intracranial neoplasms. Approximately 5% of them are familial adenomas. Patients with familial tumors carry germline mutations in predisposition genes, including AIP, MEN1 and PRKAR1A. These mutations are extremely rare in sporadic pituitary adenomas, which therefore are caused by different mechanisms. Multiple tumor suppressive genes linked to sporadic tumors have been identified. Their inactivation is caused by epigenetic mechanisms, mainly promoter hypermethylation, and can be placed into two groups based on their functional interaction with tumor suppressors RB or p53. The RB group includes CDKN2A, CDKN2B, CDKN2C, RB1, BMP4, CDH1, CDH13, GADD45B and GADD45G; AIP and MEN1 genes also belong to this group. The p53 group includes MEG3, MGMT, PLAGL1, RASSF1, RASSF3 and SOCS1. We propose that the tumor suppression function of these genes is mainly mediated by the RB and p53 pathways. We also discuss possible tumor suppression mechanisms for individual genes.

Down-regulation of Zac1 gene expression in rat white adipose tissue by androgens

ZAC1 is a zinc-finger protein transcription factor, a transcriptional cofactor for nuclear receptors, and a co-activator of nuclear receptors, which interacts with multiple signaling pathways affecting apoptosis, cell cycle arrest, and metabolism. Some data suggest that ZAC1 regulates the expression of genes associated with function of adipose tissue. Since there is no information about the levels of Zac1 gene expression in white adipose tissue (WAT), and the expression of several genes associated with metabolic function of WAT is significantly lower in male than female animals, we have examined: (a) the relative ZAC1 mRNA levels in some organs/tissues, including three main depots of WAT, in 3-month-old male rats; (b) the relative ZAC1 mRNA levels in WAT of male and female rats; (c) the effect of orchidectomy and orchidectomy with concomitant testosterone treatment on ZAC1 mRNA and protein levels; (d) the effect of ovariectomy and ovariectomy with concomitant 17β-estradiol treatment on ZAC1 mRNA levels; (e) the effect of dihydrotestosterone on ZAC1 mRNA levels in isolated adipocytes. Our results indicate that: (a) ZAC1 mRNA levels are relatively high in WAT in comparison with other organs/tissues; (b) ZAC1 mRNA levels in subcutaneous WAT are approximately 2-fold lower than in epididymal and retroperitoneal adipose tissue; (c) ZAC1 mRNA levels in WAT of adult female rats are approximately 2-fold higher than in male rats; (d) testosterone is inversely related to ZAC1 mRNA and protein levels in WAT of male rats; and (e) dihydrotestosterone decreases the ZAC1 mRNA levels in adipocytes in dose dependent manner. In conclusion, Zac1 gene is highly expressed in white adipose tissue of adult rats. Androgens could play an important role in down-regulation of the ZAC1 mRNA and protein levels in rats.

Expression of Clu and Tgfb1 during murine tooth development: effects of in-vivo transfection with anti-miR-214

Expression of clusterin (Clu) in the murine first molar tooth germ was markedly increased at postnatal developmental stages. The time-course of expression of this gene paralleled those of other genes encoding proteins involved during the secretory phase of odontogenesis, as described previously. Immunohistochemical studies of clusterin in murine molar tooth germs suggested this protein to be located in outer enamel epithelium, regressing enamel organ, secretory ameloblasts, and the dental epithelium connecting the tooth to the oral epithelium at an early eruptive stage. Immunolabelling of transforming growth factor beta-1 (TGF-β1) revealed it to be located close to clusterin. The levels of expression of Clu and Tgfb1 were markedly decreased following in-vivo transfection with anti-miR-214. In contrast, the expression of several genes associated with regulation of growth and development were increased by this treatment. We suggest that clusterin has functions during secretory odontogenesis and the early eruptive phase. Bioinformatic analysis after treatment with anti-miR-214 suggested that, whilst cellular activities associated with tooth mineralization and eruption were inhibited, activities associated with an alternative developmental activity (i.e. biosynthesis of contractile proteins) appeared to be stimulated. These changes probably occur through regulation mediated by a common cluster of transcription factors and support suggestions that microRNAs (miRNAs) are highly significant as regulators of differentiation during odontogenesis.

Grail as a molecular determinant for the functions of the tumor suppressor p53 in tumorigenesis

The transcription factor p53 is a multifunctional tumor suppressor that arrests the cell cycle in response to stress and modulates the DNA repair process or induces apoptosis. The cellular level and activity of p53 are tightly controlled to maintain proper functioning. This study identified a novel p53-binding glycoprotein, gene related to anergy in lymphocytes (Grail), which formed a negative feedback loop (similar to that of Mdm2). Grail physically and functionally interacted with the N-terminus of p53 to target its degradation and modulate its transactivation activity. Grail also senses and regulates cellular p53 levels, modulates a panel of p53-targeted promoters, and has a role in p53-induced apoptosis in cultured cells. Overexpression of Grail inhibited p53-induced apoptosis by increasing p53 degradation. However, cells not expressing Grail failed to undergo p53-dependent apoptosis, resulting in p21-dependent G1 arrest. Thus, Grail may provide a novel regulatory route for controlling p53 activity under stress conditions.

Transient neonatal diabetes mellitus gene Zac1 impairs insulin secretion in mice through Rasgrf1

The biallelic expression of the imprinted gene ZAC1/PLAGL1 underlies ≈ 60% of all cases of transient neonatal diabetes mellitus (TNDM) that present with low perinatal insulin secretion. Molecular targets of ZAC1 misexpression in pancreatic β cells are unknown. Here, we identified the guanine nucleotide exchange factor Rasgrf1 as a direct Zac1/Plagl1 target gene in murine β cells. Doubling Zac1 expression reduced Rasgrf1 expression, the stimulus-induced activation of mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K) pathways, and, ultimately, insulin secretion. Normalizing Rasgrf1 expression reversed this phenotype. Moreover, the transplantation of Zac1-overexpressing β cells failed to reinstate euglycemia in experimental diabetic mice. In contrast, Zac1 expression did not interfere with the signaling of the glucagon-like peptide 1 receptor (GLP-1R), and the GLP-1 analog liraglutide improved hyperglycemia in transplanted experimental diabetic mice. This study unravels a mechanism contributing to insufficient perinatal insulin secretion in TNDM and raises new prospects for therapy.

Specific changes in the expression of imprinted genes in prostate cancer--implications for cancer progression and epigenetic regulation

Epigenetic dysregulation comprising DNA hypermethylation and hypomethylation, enhancer of zeste homologue 2 (EZH2) overexpression and altered patterns of histone modifications is associated with the progression of prostate cancer. DNA methylation, EZH2 and histone modifications also ensure the parental-specific monoallelic expression of at least 62 imprinted genes. Although it is therefore tempting to speculate that epigenetic dysregulation may extend to imprinted genes, expression changes in cancerous prostates are only well documented for insulin-like growth factor 2 (IGF2). A literature and database survey on imprinted genes in prostate cancer suggests that the expression of most imprinted genes remains unchanged despite global disturbances in epigenetic mechanisms. Instead, selective genetic and epigenetic changes appear to lead to the inactivation of a sub-network of imprinted genes, which might function in the prostate to limit cell growth induced via the PI3K/Akt pathway, modulate androgen responses and regulate differentiation. Whereas dysregulation of IGF2 may constitute an early change in prostate carcinogenesis, inactivation of this imprinted gene network is rather associated with cancer progression.

A non-covalent interaction between small ubiquitin-like modifier-1 and Zac1 regulates Zac1 cellular functions

Zac1, a zinc-finger protein that regulates apoptosis and cell cycle arrest 1, such as p53, can induce cell-cycle arrest and apoptosis. The transactivation and coactivation functions of Zac1 may occur at non-promyelocytic leukemia nuclear body (PML-NB) sites in the presence of other PML-NB components, including ubiquitin-conjugating 9 (Ubc9). It is unclear whether post-translational modification of Zac1 by the small ubiquitin-like modifier SUMO plays a role in the coactivation functions of Zac1 for the regulation of the p21 gene. Mutagenesis experiments revealed that the two SUMO-binding lysine residues of Zac1, K237 and K424, repress the transactivation activity of Zac1. Studies using a SUMO-1 C-terminal di-glycine motif mutant that is deficient in the ability to form covalent bonds with lysines, SUMO-1 (GA), and a dominant-negative Ubc9 construct (C93S) indicated that SUMO-1 might regulate Zac1 transactivation and coactivation via a non-covalent interaction. Unlike the wild-type Zac1, which induced apoptosis, the Zac1 (K237/424R) double mutant had the ability to induce autophagy. The functional role of p21 remains to be investigated. SUMO-1 selectively suppressed the induction of the p21 gene and protein by wild-type Zac1 but not by the Zac1 (K237/424R) double mutant. Moreover, wild-type Ubc9 but not Ubc9 (C93S) further potentiated the suppression of SUMO-1 in all Zac1-induced p21 promoter activities. Our data reveal that p21 may be an important factor for the prevention of Zac1-induced apoptosis without affecting autophagosome formation. This work indicates that Zac1 functions are regulated, at least in part, via non-covalent interactions with SUMO-1 for the induction of p21, which is important for the modulation of apoptosis.

Imprinted genes that regulate early mammalian growth are coexpressed in somatic stem cells

Lifelong, many somatic tissues are replenished by specialized adult stem cells. These stem cells are generally rare, infrequently dividing, occupy a unique niche, and can rapidly respond to injury to maintain a steady tissue size. Despite these commonalities, few shared regulatory mechanisms have been identified. Here, we scrutinized data comparing genes expressed in murine long-term hematopoietic stem cells with their differentiated counterparts and observed that a disproportionate number were members of the developmentally-important, monoallelically expressed imprinted genes. Studying a subset, which are members of a purported imprinted gene network (IGN), we found their expression in HSCs rapidly altered upon hematopoietic perturbations. These imprinted genes were also predominantly expressed in stem/progenitor cells of the adult epidermis and skeletal muscle in mice, relative to their differentiated counterparts. The parallel down-regulation of these genes postnatally in response to proliferation and differentiation suggests that the IGN could play a mechanistic role in both cell growth and tissue homeostasis.

Different roles of p53 in the regulation of DNA damage caused by 1,2-heteroannelated anthraquinones and doxorubicin

The anthracyclin antibiotic agent doxorubicin (DXR) has been widely used as a chemotherapeutic drug for more than 40 years, but its clinical use has been limited by its cardiotoxicity. The mechanism of action of DXR remains uncertain and controversial. A series of 1,2-heteroannelated anthraquinones and anthra[1,2-d]imidazole-6,11-dione compounds were synthesized and their cytotoxicity profiles were analyzed using the National Cancer Institute 60 (NCI 60) platform and human telomerase inhibition assays. In the current study, three of the 1,2-heteroannelated anthraquinones, NSC745795, NSC745885 and NSC745887, were found to differ from each other with respect to their effects on cell cycle regulation, apoptosis, autophagy, senescence and their abilities to induce DNA damage. The differences depended on the presence or absence of a heterocyclic moiety, which suggested that the differences were due, at least in part, to differential effects on specific cellular targets, such as p53. In contrast to DXR, which induced p53 expression, treatment with NSC745885 resulted in the degradation of several proteins, including p53, via proteasome-dependent and -independent pathways in HeLa cells. These results provide insights into the molecular mechanisms governing cell inhibition by 1,2-heteroannelated anthraquinone derivatives and suggest that these mechanisms could serve as the basis for new structure-based drug designs.

Zac1 plays a key role in the development of specific neuronal subsets in the mouse cerebellum

BACKGROUND

The cerebellum is composed of a diverse array of neuronal subtypes. Here we have used a candidate approach to identify Zac1, a tumor suppressor gene encoding a zinc finger transcription factor, as a new player in the transcriptional network required for the development of a specific subset of cerebellar nuclei and a population of Golgi cells in the cerebellar cortex.

RESULTS

We found that Zac1 has a complex expression profile in the developing cerebellum, including in two proliferating progenitor populations; the cerebellar ventricular zone and the external granular layer overlying posterior cerebellar lobules IX and X. Zac1 is also expressed in some postmitotic cerebellar neurons, including a subset of GABAergic interneurons in the medial cerebellar nuclei. Notably, GABAergic interneurons in the cerebellar nuclei are derived from the cerebellar ventricular zone, where Zac1 is also expressed, consistent with a lineage relationship between these two Zac1+ populations. Zac1 is also expressed in a small subset of cells in the posterior vermis, including some neurogranin-immunoreactive (NG+) Golgi cells, which, based on short-term birthdating, are derived from the EGL, where Zac1 is also expressed. However, Zac1+ cells and NG+ Golgi cells in the cerebellar cortex also display unique properties, as they are generated within different, albeit overlapping, time windows. Finally, consistent with the expression profile of Zac1, two conspicuous abnormalities were found in the cerebellum of Zac1 null mice: the medial cerebellar nuclei, and not the others, were significantly reduced in size; and the number of Golgi cells in cerebellar lobule IX was reduced by approximately 60% compared to wild-type littermates.

CONCLUSIONS

The data presented here indicate that the tumor suppressor gene Zac1 is expressed in a complex fashion in the developing cerebellum, including in two dividing progenitor populations and in specific subsets of postmitotic neurons, including Golgi cells and GABAergic neurons in the medial nuclei, which require Zac1 for their differentiation. We thus conclude that Zac1 is a critical regulator of normal cerebellar development, adding a new transcriptional regulator to the growing list of factors involved in generating neuronal diversity in the developing cerebellum.

Zac1 plays a key role in the development of specific neuronal subsets in the mouse cerebellum

Background

The cerebellum is composed of a diverse array of neuronal subtypes. Here we have used a candidate approach to identify Zac1, a tumor suppressor gene encoding a zinc finger transcription factor, as a new player in the transcriptional network required for the development of a specific subset of cerebellar nuclei and a population of Golgi cells in the cerebellar cortex.

Results

We found that Zac1 has a complex expression profile in the developing cerebellum, including in two proliferating progenitor populations; the cerebellar ventricular zone and the external granular layer overlying posterior cerebellar lobules IX and X. Zac1 is also expressed in some postmitotic cerebellar neurons, including a subset of GABAergic interneurons in the medial cerebellar nuclei. Notably, GABAergic interneurons in the cerebellar nuclei are derived from the cerebellar ventricular zone, where Zac1 is also expressed, consistent with a lineage relationship between these two Zac1⁺ populations. Zac1 is also expressed in a small subset of cells in the posterior vermis, including some neurogranin-immunoreactive (NG⁺) Golgi cells, which, based on short-term birthdating, are derived from the EGL, where Zac1 is also expressed. However, Zac1⁺ cells and NG⁺ Golgi cells in the cerebellar cortex also display unique properties, as they are generated within different, albeit overlapping, time windows. Finally, consistent with the expression profile of Zac1, two conspicuous abnormalities were found in the cerebellum of Zac1 null mice: the medial cerebellar nuclei, and not the others, were significantly reduced in size; and the number of Golgi cells in cerebellar lobule IX was reduced by approximately 60% compared to wild-type littermates.

Conclusions

The data presented here indicate that the tumor suppressor gene Zac1 is expressed in a complex fashion in the developing cerebellum, including in two dividing progenitor populations and in specific subsets of postmitotic neurons, including Golgi cells and GABAergic neurons in the medial nuclei, which require Zac1 for their differentiation. We thus conclude that Zac1 is a critical regulator of normal cerebellar development, adding a new transcriptional regulator to the growing list of factors involved in generating neuronal diversity in the developing cerebellum.

Zac1 is a histone acetylation-regulated NF-κB suppressor that mediates histone deacetylase inhibitor-induced apoptosis

Histone deacetylase (HDAC) inhibitors are a class of promising anticancer reagents. They are able to induce apoptosis in embryonic carcinoma (EC) cells. However, the underlying mechanism remains poorly understood. Here we show that increased expression of zinc-finger protein regulator of apoptosis and cell-cycle arrest (Zac1) is implicated in HDAC inhibitor-induced apoptosis in F9 and P19 EC cells. By chromatin immunoprecipitation analysis we identified that increased Zac1 expression is mediated by histone acetylation of the Zac1 promoter region. Knockdown of Zac1 inhibited HDAC inhibitor-induced cell apoptosis. Moreover, HDAC inhibitors repressed nuclear factor-κB (NF-κB) activity, and this effect is abrogated by Zac1 knockdown. Consistently, Zac1 overexpression suppressed cellular NF-κB activity. Further investigation showed that Zac1 inhibits NF-κB activity by interacting with the C-terminus of the p65 subunit, which suppresses the phosphorylation of p65 at Ser468 and Ser536 residues. These results indicate that Zac1 is a histone acetylation-regulated suppressor of NF-κB, which is induced and implicated in HDAC inhibitor-mediated EC cell apoptosis.

Regulated recruitment of tumor suppressor BRCA1 to the p21 gene by coactivator methylation

Tumor suppression by p53 and BRCA1 involves regulation of cell cycle, apoptosis, and DNA repair and is influenced by transcriptional coactivators and post-translational modifications. Here we show that coactivator-associated arginine methyltransferase 1 (CARM1) methylates Arg 754 in the KIX region of coactivator p300. Methylated p300 and p300 protein fragments are preferentially recognized by BRCT domains of BRCA1, identifying the BRCT domain as a novel methylarginine-binding module. CARM1 and p300 cooperate with BRCA1 and p53 to induce expression of the critical cell cycle and proliferation regulator p21(WAF1/CIP1) in response to DNA damage. This induction was severely attenuated by elimination of CARM1 or its methyltransferase activity, or by mutation of Arg 754 of p300. Absence of CARM1 methyltransferase activity led to failure of cells to arrest in the G1 phase of the cell cycle in response to DNA damage. CARM1 methyltransferase activity was required for induction of some p53 target genes (p21 and Gadd45) but not others (Bax) by DNA damage. Recruitment of BRCA1 to the p53-binding region of the p21 promoter in response to DNA damage required methylation of Arg 754 of p300 by CARM1. Thus, coactivator methylation may be crucial for fine-tuning the tumor suppressor function of BRCA1 and other BRCT domain proteins.

The novel metastasis promoter Merm1/Wbscr22 enhances tumor cell survival in the vasculature by suppressing Zac1/p53-dependent apoptosis

Understanding metastasis is integral to curative cancer treatments. Using a mouse genetic screening model, we identified Merm1/Wbscr22 as a novel metastasis promoter that includes a methyltransferase fold in its structure. Merm1 showed high levels of expression in invasive breast cancer. Ectopic expression of Merm1 in nonmetastatic cells enhanced metastasis formation without affecting cell growth and motility. The intact methyltransferase fold of Merm1 was required for metastasis formation. Interestingly, Merm1 expression promoted cell survival after entrapment in the lung microvasculature. Consistent with these results, knockdown of endogenous Merm1 in tumor cells reduced lung retention and metastasis formation. On the basis of comparative transcriptome analysis, Merm1 expression was negatively correlated with the expression of tumor suppressor Zac1. We confirmed that Merm1 suppressed Zac1 expression with histone H3 methylation at Lys(9) in the Zac1 promoter region. Zac1 can induce apoptosis through its ability to transcriptionally coactivate p53, which regulates apoptosis in the vasculature and is often downregulated in metastasis. We found that Zac1 knockdown reduced the p53-dependent apoptosis that was enhanced by Merm1 knockdown, thereby increasing lung retention of metastatic cells. Our findings show that Merm1 enhances cancer cell survival in the vasculature by suppressing Zac1/p53-dependent apoptosis, thereby enhancing metastasis.

Transient neonatal diabetes mellitus type 1

Transient neonatal diabetes mellitus type 1 (TNDM1) is a rare but remarkable form of diabetes which presents in infancy, resolves in the first months of life, but then frequently recurs in later life. It is caused by overexpression of the imprinted genes PLAGL1 and HYMAI on human chromosome 6q24. The expression of these genes is normally restricted to the paternal allele as a result of maternal DNA methylation. TNDM1 is not associated with mutation of PLAGL1 or HYMAI, but rather with their overexpression via uniparental disomy, chromosome duplication, or relaxation of imprinting. Study of patients with TNDM1 has provided valuable insights into the causes of imprinting disorders. Over half of patients with maternal hypomethylation at the TNDM1 locus have additional hypomethylation of other maternally methylated imprinted genes throughout the genome, and the majority of these patients have mutations in the transcription factor ZFP57. TNDM1 with maternal hypomethylation has also been observed in patients conceived by assisted reproduction, and in discordant monozygotic twins. The variable clinical features of TNDM1 may be associated with variation in the nature of the underlying epigenetic and genetic mutations, and future study of this disorder is likely to yield further insights not only into the biological mechanisms of imprinting, but also into the contribution of epigenetics to diabetes.

Interaction between the transactivation domain of p53 and PC4 exemplifies acidic activation domains as single-stranded DNA mimics

The tumor suppressor p53 regulates cell cycle arrest and apoptosis by transactivating several genes that are critical for these processes. The transcriptional activity of p53 is often regulated by post-translational modifications and its interactions with various transcriptional coactivators. Here we report a physical interaction between the N-terminal transactivation domain (TAD) of p53 and the C-terminal DNA-binding domain of positive cofactor 4 (PC4(CTD)). Using NMR spectroscopy, we showed that residues 35-57 (TAD2) interact with PC4. (15)N,(1)H HSQC and fluorescence competition experiments indicated that TAD binds to the DNA-binding site of PC4. Hepta-phosphorylation of the TAD peptide increased its binding affinity. Computer modeling of the p53N-PC4 complex revealed several important interactions that are reminiscent of those in the single-stranded DNA-PC4 complex. The ubiquitous nature of the acidic transactivation domain of p53 in mediating interactions with several transcription cofactors is also manifested as a DNA mimetic.

Spatial link between nucleoli and expression of the Zac1 gene

Eukaryotic genomes are highly organized within the cell nucleus. Genome organization not only implies the preferential positioning of genetic elements in the interphase nucleus but also the topographic distribution of biological processes. We have investigated the relationship between spatial organization and genome function in single cells. Myc, c-Met, Igf2r, Asb4, and Zac1 genes have the same radial distribution, but they are not positioned in close proximity with respect to each other. Three-dimensional mapping of their transcription sites uncovered a gene-specific pattern of relative positioning with respect to the nucleolus. We found that the Zac1 gene transcription preferentially occurs juxtaposed to the nucleolus, and that its mRNA accumulates at this site of transcription. Nucleoli isolation followed by qRT-PCR provided evidence for a physical interaction between Zac1 mRNA and the nucleolus. Actinomycin-D treatment induced disassembly of the nucleolus, loss of the RNA-FISH signal, and dramatic increase of the ZAC protein level. However, inhibition of RNA polymerase II had no effect over the Zac1 FISH signal and the protein expression. Induction of cell cycle arrest, which involves participation of the ZAC protein, provoked mRNA release from its retention site and protein synthesis. Our data demonstrate that Zac1 mRNA preferentially accumulates in close proximity to nucleoli within the cell nucleus. In addition, our results suggest a functional link between such spatial distribution and protein expression.

ZAC1 is up-regulated by hypertonicity and decreases sorbitol dehydrogenase expression, allowing accumulation of sorbitol in kidney cells

Affymetrix GeneChip technology was employed to detect differentially expressed genes in inner medullary collecting duct (IMCD3) cells grown under isotonic and hypertonic conditions. A marked up-regulation was found for the zinc-finger protein ZAC1 under hypertonic stress (219-fold, p < 0.001). Changes in expression for ZAC1 were verified by quantitative PCR for message and Western blotting for protein. In mouse and human kidney tissues, ZAC1 expression was substantial in the papilla and was absent in the cortex. Furthermore, ZAC1 expression significantly increased in the papilla of mice following 36 h of fluid restriction and decreased in polyuric mice consuming sucrose in water. Because ZAC1 has been described to be a potential negative regulator of sorbitol dehydrogenase (SDH) in hippocampal cells, we examined whether this relationship also occurs in kidney cells under hypertonic stress. We found that stable IMCD3 clones silenced for ZAC1 to varying levels demonstrated an inverse effect on SDH expression. ZAC1 binds to a consensus repression site within the promoter of SDH, pointing to a mechanism whereby ZAC1 acts by repressing SDH transcriptional activity during hypertonic conditions. Taken together, these data strongly suggest that ZAC1 is up-regulated under hypertonic stress and negatively regulates expression of SDH, allowing for accumulation of sorbitol as a compatible organic osmolyte.