A CDE/CHR-like element mediates repression of transcription of the mouse RB2 (p130) gene

Investigating the genetic basis of attention to facial expressions: the role of the norepinephrine transporter gene

OBJECTIVE

Levels of norepinephrine (NE) in the brain are related to attention ability in animals and risk of attention-deficit hyperactivity disorder in humans. Given the modulation of the norepinephrine transporter (NET) on NE levels in the brain and the link between NE and attention impairment of attention-deficit hyperactivity disorder, it was possible that the NET gene underpinned individual differences in attention processes in healthy populations.

METHODS

To investigate to what extent NET could modulate one's attention orientation to facial expressions, we categorized individuals according to the genotypes of the -182 T/C (rs2242446) polymorphism and measured individuals' attention orientation with the spatial cueing task.

RESULTS

Our results indicated that the -182 T/C polymorphism significantly modulated attention orientation to facial expressions, of which the CC genotype facilitated attention reorientation to the locations where cued faces were previously presented. However, this polymorphism showed no significant effects on the regulations of emotional cues on attention orientation.

CONCLUSION

Our findings suggest that the NET gene modulates the individual difference in attention to facial expressions, which provides new insights into the roles of NE in social interactions.

E2 Ubiquitin-conjugating Enzyme, UBE2C Gene, Is Reciprocally Regulated by Wild-type and Gain-of-Function Mutant p53

Spindle assembly checkpoint governs proper chromosomal segregation during mitosis to ensure genomic stability. At the cellular level, this event is tightly regulated by UBE2C, an E2 ubiquitin-conjugating enzyme that donates ubiquitin to the anaphase-promoting complex/cyclosome. This, in turn, facilitates anaphase-onset by ubiquitin-mediated degradation of mitotic substrates. UBE2C is an important marker of chromosomal instability and has been associated with malignant growth. However, the mechanism of its regulation is largely unexplored. In this study, we report that UBE2C is transcriptionally activated by the gain-of-function (GOF) mutant p53, although it is transcriptionally repressed by wild-type p53. We showed that wild-type p53-mediated inhibition of UBE2C is p21-E2F4-dependent and GOF mutant p53-mediated transactivation of UBE2C is NF-Y-dependent. We further explored that DNA damage-induced wild-type p53 leads to spindle assembly checkpoint arrest by repressing UBE2C, whereas mutant p53 causes premature anaphase exit by increasing UBE2C expression in the presence of 5-fluorouracil. Identification of UBE2C as a target of wild-type and GOF mutant p53 further highlights the contribution of p53 in regulation of spindle assembly checkpoint.

Association between major depressive disorder and the norepinephrine transporter polymorphisms T-182C and G1287A: a meta-analysis

BACKGROUND

Previous studies have implicated norepinephrine transporter (NET) gene polymorphisms in the etiology of major depressive disorder (MDD). Recently, two single nucleotide NET polymorphisms, T-182C (rs2242446) in the promoter region and G1287A (rs5569) in exon 9, were found to be associated with MDD in different populations. However, inconsistent and inconclusive results have also been obtained.

METHODS

In this study, we examined whether rs2242446 and rs5569 genetic variants are related to the etiology of MDD using a meta-analysis. Relevant case-control studies were retrieved by database searching and selected according to established inclusion criteria.

RESULTS

Eight articles were identified that tested the relationship between the NET T-182C and/or G1287A polymorphism and MDD. Statistical analyses revealed no significant association between these polymorphisms and MDD (OR=1.23, 95% CI=0.77-1.97, P=0.38 for T-182C; OR=1.00, 95% CI=0.78-1.29, P=0.99 for G1287A).

LIMITATIONS

The results must be treated with caution because of the small sample sizes of several included studies.

CONCLUSIONS

Our findings suggest that the NET T-182C and G1287A polymorphisms are not susceptibility factors for MDD.

The norepinephrine transporter gene is a candidate gene for panic disorder

Panic disorder (PD) is an anxiety disorder characterized by recurrent panic attacks with a lifetime prevalence of 4.7%. Genetic factors are known to contribute to the development of the disorder. Several lines of evidence point towards a major role of the norepinephrine system in the pathogenesis of PD. The SLC6A2 gene is located on chromosome 16q12.2 and encodes the norepinephrine transporter (NET), responsible for the reuptake of norepinephrine into presynaptic nerve terminals. The aim of the present study was to analyze genetic variants located within the NET gene for association with PD. The case-control sample consisted of 449 patients with PD and 279 ethnically matched controls. All cases fulfilled the ICD-10 diagnostic criteria for PD. Genotyping was performed using the Sequenom platform (Sequenom, Inc, San Diego, USA). To test for allelic and haplotypic association, the PLINK software was used, and COMBASSOC was applied to test for gene-wise association. After quality control 29 single nucleotide polymorphisms (SNPs) spanning the gene-region were successfully analyzed. Seven SNPs located within the 5' end of the gene were significantly associated with PD. Furthermore, the NET gene showed overall evidence for association with the disease (P = 0.000035). In conclusion, the present study indicates that NET could be a susceptibility gene for PD.

Function of the A-type cyclins during gametogenesis and early embryogenesis

The cyclins and their cyclin-dependent kinase partners, the Cdks, are the basic components of the machinery that regulates the passage of cells through the cell cycle. Among the cyclins, those known as the A-type cyclins are unique in that in somatic cells, they appear to function at two stages of the cell cycle, at the G1-S transition and again as the cells prepare to enter M-phase. Higher vertebrate organisms have two A-type cyclins, cyclin A1 and cyclin A2, both of which are expressed in the germ line and/or early embryo, following highly specialized patterns that suggest functions in both mitosis and meiosis. Insight into their in vivo functions has been obtained from gene targeting experiments in the mouse model. Loss of cyclin A1 results in disruption of spermatogenesis and male sterility due to cell arrest in the late diplotene stage of the meiotic cell cycle. In contrast, cyclin A2-deficiency is marked by early embryonic lethality; thus, understanding the function of cyclin A2 in the adult germ line awaits conditional mutagenesis or other approaches to knock down its expression.

Regulation of cyclin B2 expression and cell cycle G2/m transition by menin

Multiple endocrine neoplasia type 1 (MEN1) results from mutations in tumor suppressor gene Men1, which encodes nuclear protein menin. Menin up-regulates certain cyclin-dependent kinase inhibitors through increasing histone H3 lysine 4 (H3K4) methylation and inhibits G(0)/G(1) to S phase transition. However, little is known as to whether menin controls G(2)/M-phase transition, another important cell cycle checkpoint. Here, we show that menin expression delays G(2)/M phase transition and reduces expression of Ccnb2 (encoding cyclin B2). Menin associates with the promoter of Ccnb2 and reduces histone H3 acetylation, a positive chromatin marker for gene transcription, at the Ccnb2 locus. Moreover, Men1 ablation leads to an increase in cyclin B2 expression, histone H3 acetylation at the Ccnb2 locus, and G(2)/M transition. In contrast, knockdown of cyclin B2 diminishes the number of cells at M phase and reduces cell proliferation. Furthermore, menin interferes with binding of certain positive transcriptional regulators, such as nuclear factor Y (NF-Y), E2 factors (E2Fs), and histone acetyltransferase CREB (cAMP-response element-binding protein)-binding protein (CBP) to the Ccnb2 locus. Notably, MEN1 disease-related mutations, A242V and L22R, abrogate the ability of menin to repress cyclin B2 expression and G(2)/M transition. Both of the mutants fail to reduce the acetylated level of the Ccnb2 locus. Together, these results suggest that menin-mediated repression of cyclin B2 is crucial for inhibiting G(2)/M transition and cell proliferation through a previously unrecognized molecular mechanism for menin-induced suppression of MEN1 tumorigenesis.

The central role of CDE/CHR promoter elements in the regulation of cell cycle-dependent gene transcription

The cell cycle-dependent element (CDE) and the cell cycle genes homology region (CHR) control the transcription of genes with maximum expression in G(2) phase and in mitosis. Promoters of these genes are repressed by proteins binding to CDE/CHR elements in G(0) and G(1) phases. Relief from repression begins in S phase and continues into G(2) phase and mitosis. Generally, CDE sites are located four nucleotides upstream of CHR elements in TATA-less promoters of genes such as Cdc25C, Cdc2 and cyclin A. However, expression of some other genes, such as human cyclin B1 and cyclin B2, has been shown to be controlled only by a CHR lacking a functional CDE. To date, it is not fully understood which proteins bind to and control CDE/CHR-containing promoters. Recently, components of the DREAM complex were shown to be involved in CDE/CHR-dependent transcriptional regulation. In addition, the expression of genes regulated by CDE/CHR elements is mostly achieved through CCAAT-boxes, which bind heterotrimeric NF-Y proteins as well as the histone acetyltransferase p300. Importantly, many CDE/CHR promoters are downregulated by the tumor suppressor p53. In this review, we define criteria for CDE/CHR-regulated promoters and propose to distinguish two classes of CDE/CHR-regulated genes. The regulation through transcription factors potentially binding to the CDE/CHR is discussed, and recently discovered links to central pathways regulated by E2F, the pRB family and p53 are highlighted.

Identification and functional analysis of a CDE/CHR element in the POLD1 promoter

DNA polymerase delta is encoded by the POLD1 gene, the transcription of which is strictly cell cycle-dependent. However, the means by which POLD1 transcription is regulated by the cell cycle mechanism is currently unknown. We discovered a novel element in the POLD1 promoter known as a CDE(cell cycle-dependent element)/CHR(cell cycle gene homology region) element. A series of luciferase reporter constructs containing various POLD1 promoter mutations were used to investigate the role of the CDE/CHR element in POLD1 transcription. When the CDE/CHR element was mutated, the promoter activity was up-regulated, and the cell-cycle related factors E2F1 and p21 stopped regulating the promoter. Furthermore, cell cycle-dependent changes in the promoter activity required the integrative CDE/CHR element. Electrophoretic mobility shift assay (EMSA) revealed the presence of at least three types of DNA/protein complexes binding to the CDE/CHR element. Our findings provide strong evidence that the CDE/CHR-like sequence is an active functional element in the POLD1 promoter, which is important for the cell cycle regulation of the POLD1 gene.

p53 plays a role in mesenchymal differentiation programs, in a cell fate dependent manner

Background

The tumor suppressor p53 is an important regulator that controls various cellular networks, including cell differentiation. Interestingly, some studies suggest that p53 facilitates cell differentiation, whereas others claim that it suppresses differentiation. Therefore, it is critical to evaluate whether this inconsistency represents an authentic differential p53 activity manifested in the various differentiation programs.

Methodology/Principal Findings

To clarify this important issue, we conducted a comparative study of several mesenchymal differentiation programs. The effects of p53 knockdown or enhanced activity were analyzed in mouse and human mesenchymal cells, representing various stages of several differentiation programs. We found that p53 down-regulated the expression of master differentiation-inducing transcription factors, thereby inhibiting osteogenic, adipogenic and smooth muscle differentiation of multiple mesenchymal cell types. In contrast, p53 is essential for skeletal muscle differentiation and osteogenic re-programming of skeletal muscle committed cells.

Conclusions

These comparative studies suggest that, depending on the specific cell type and the specific differentiation program, p53 may exert a positive or a negative effect, and thus can be referred as a “guardian of differentiation” at large.

Transcription of the human cell cycle regulated BUB1B gene requires hStaf/ZNF143

BubR1 is a key protein mediating spindle checkpoint activation. Loss of this checkpoint control results in chromosomal instability and aneuploidy. The transcriptional regulation of the cell cycle regulated human BUB1B gene, which encodes BubR1, was investigated in this report. A minimal BUB1B gene promoter containing 464 bp upstream from the translation initiation codon was sufficient for cell cycle regulated promoter activity. A pivotal role for transcription factor hStaf/ZNF143 in the expression of the BUB1B gene was demonstrated through gel retardation assays, transient expression of mutant BUB1B promoter–reporter gene constructs and chromatin immunoprecipitation assay. Two phylogenetically conserved hStaf/ZNF143-binding sites (SBS) were identified which are indispensable for BUB1B promoter activity. In addition, we found that the domain covering the transcription start sites contains conserved boxes homologous to initiator (Inr), cell cycle dependent (CDE) and cell cycle genes homology regions (CHR) elements. Mutations within the CDE and CHR elements led to diminished cell cycle regulation of BUB1B transcription. These results demonstrate that BUB1B gene transcription is positively regulated by hStaf/ZNF143, a ubiquitously expressed factor, and that the CDE-CHR tandem element was essential for G2/M-specific transcription of the BUB1B gene.

Role for Brm in Cell Growth Control

Recently, we have shown implication of Brm, the catalytic subunit of the SWI/SNF chromatin remodeling complex, in repression of cyclin A expression in quiescent cells. Here, we have examined the fate of cells lacking Brm throughout the cycle. We find that despite elevated levels of cyclins A and E, these cells can respond to serum starvation, however, without reaching a canonical G(0) phase as they continue to express high levels of c-Myc and have an abnormally large average size. The response to serum starvation can be correlated with increased levels of Rb proteins p130 and p107 as well as increased association of p27 with the cyclin-dependent kinases, possibly compensating for the higher levels of G(1) cyclins by reducing their associated kinase activity. After serum stimulation, reentry into the cycle occurs normally, but the S phase is delayed and shorter. In addition, the M phase has an increased duration, and we observed frequent faulty chromosome segregation events in anaphase. Altogether, our data suggest that cells can partially overcome the absence of Brm by activating several compensatory mechanisms to control the cell cycle. However, they remain profoundly affected, unable to enter a canonical quiescent state, presenting a shorter S phase, and finally unable to perform correct chromosome segregation.

Footprinting the 'essential regulatory region' of the retinoblastoma gene promoter in intact human cells

The retinoblastoma tumour suppressor protein is a key cell cycle regulator. Protein-DNA interactions at the retinoblastoma (RB1) promoter, including the 'essential regulatory region', were investigated using novel DNA-targeted nitrogen mustards in intact human cells. The footprinting experiments were carried out in two different environments: in intact HeLa and K562 cells where the access of DNA-targeted probes to chromatin is affected by cellular protein-DNA interactions associated with gene regulation; and in purified DNA where their access is unencumbered by protein-DNA interactions. Using the ligation-mediated PCR (LMPCR) technique, the sites of damage were determined at base pair resolution on DNA sequencing gels. Our results demonstrate that, in intact cells, footprints were observed at the E2F, ATF and RBF1/Sp1 DNA binding motifs in the RB1 promoter. In addition, a novel footprint was observed at a previously unidentified cycle homology region (CHR) and at four uncharacterised protein-DNA binding sites. In further experiments, nitrogen mustard-treated cells were FACS sorted into G1, S and G2/M phases of the cell cycle prior to LMPCR analysis. Expression of the RB1 gene is cell cycle-regulated and footprinting studies of the promoter in FACS-sorted cells indicated that transcription factor binding at the GC box, CHR binding motif and the 'essential regulatory region' are cell cycle dependent.

p130/p107/p105Rb-dependent transcriptional repression during DNA-damage-induced cell-cycle exit at G2

The progression of normal cells from G2 into mitosis is stably blocked when their DNA is damaged. Tumor cells lacking p53 arrest only transiently in G2, but eventually enter mitosis. We show that an important component of the stable G2 arrest in normal cells is the transcriptional repression of more than 20 genes encoding proteins needed to enter into and progress through mitosis. Studies from a number of labs including our own have shown that, by inducing p53 and p21/WAF1, DNA damage can trigger RB-family-dependent transcriptional repression. Our studies reported here show that p130 and p107 play a key role in transcriptional repression of genes required for G2 and M in response to DNA damage. For plk1, repression is partially abrogated by loss of p130 and p107, and is completely abrogated by loss of all three RB-family proteins. Mouse cells lacking RB-family proteins do not accumulate with a 4N content of DNA when exposed to adriamycin, suggesting that all three RB-family proteins contribute to G2 arrest in response to DNA damage. Stable arrest in the presence of functional p53-to-RB signaling is probably due to the ability of cells to exit the cell cycle from G2, a conclusion supported by our observation that KI67, a marker of cell-cycle entry, is downregulated in both G1 and G2 in a p53-dependent manner.

Norepinephrine transporter (NET) promoter and 5'-UTR polymorphisms: association analysis in panic disorder

Several biochemical and pharmacological studies suggest that the catecholaminergic system involving the norepinephrine transporter (NET) is relevant for the pathogenesis of panic disorder. Three single nucleotide polymorphisms in the promoter or untranslated 5' region of the NET gene were investigated by means of RFLP analysis in a sample of 115 German patients with panic disorder and 115 matched controls. Statistical analysis failed to show association with the overall diagnosis of panic disorder. In the subgroup of patients with panic disorder without agoraphobia, however, two polymorphisms were found to be associated with the disease (G/C (rs2397771): p < 0.05; T/C (rs2242446): p < 0.01). While our data do not support a major function of the NET gene in the development of panic disorder, it may play a role in the subgroup of panic disorder without agoraphobia.

Distinct Regions of the Mouse Cyclin A1 Gene, Ccna1, Confer Male Germ-Cell Specific Expression and Enhancer Function1

The gene encoding mouse cyclin A1, Ccna1, is expressed at highest levels in late pachytene-diplotene spermatocytes, where it is required for meiotic cell division. To begin to understand the mechanisms responsible for its highly restricted pattern of expression, transgenic mouse lines carrying constructs consisting of the cyclin A1 regulatory region fused with the reporter gene lacZ were generated. Analysis of tissue-specific and testicular cell-type-specific transgene expression indicated that sequences within -1.3 kilobases (kb) of the cyclin A1 putative transcriptional start site were sufficient to direct transgene expression uniquely to late spermatocytes while maintaining repression in other tissues. However, sequences located between -4.8 kb and -1.3 kb of the putative transcriptional start site were apparently required to transcribe the reporter at levels needed for consistent X-gal staining. Comparison of the mouse, rat, and human proximal promoters revealed regions of high sequence conservation and consensus sequences both for known transcription factors, some of which are coexpressed with Ccna1, such as A-myb and Hsf2, and for elements that control expression of genes in somatic cell cycles, such as CDE, CHR, and CCAAT elements. Thus, the promoter region within 1.3 kb upstream of the putative Ccna1 transcriptional start can direct expression of lacZ to spermatocytes, while sequences located between -4.8 kb and -1.3 kb of the putative transcriptional start site may enhance expression of lacZ.

A Mutation Found in the Promoter Region of the HumanSurvivinGene is Correlated to Overexpression of Survivin in Cancer Cells

Survivin, a unique antiapoptotic factor, plays an important role in cell cycle regulation. Numerous clinical studies have shown that survivin is markedly overexpressed in most common types of cancer, suggesting that transcriptional deregulation is a major mechanism involved in aberrant expression of survivin in cancers. In this study, we have identified several polymorphisms in the survivin gene promoter. One of these polymorphisms is located at CDE/CHR repressor elements and appears to be a common mutation with high frequency among cancer cell lines compared to normal cell line controls. The presence of the mutation was correlated in these cell lines with increased survivin expression at the both mRNA and protein levels. Furthermore, gel mobility shift analysis and transcriptional analysis showed the mutation changed cell cycle-dependent transcription by modifying the binding motif of the CDE/CHR repressor. These results indicate that the high level of survivin in some cancers is, at least in part, due to a genetic defect in the promoter region of the human survivin gene, which causes derepression of survivin transcription apparently due to the mutated CDE/CHR repressor binding motifs.

Reduced transcription of the RB2/p130 gene in human lung cancer

Reduced expression of the retinoblastoma gene (RB)2/p130 protein, as well as mutation of exons 19, 20, 21, and 22 of the same gene, has been reported in primary lung cancer. However, it has been suggested by other investigators that mutational inactivation and loss of the RB2/p130 gene and protein, respectively, are rare events in lung cancer. In order to determine the contribution and mechanisms of RB2/p130 gene inactivation to lung cancer development and progression, we quantified RB2/p130 mRNA expression levels in a range of human lung cancer cell lines (n = 13) by real-time reverse transcription (RT)-polymerase chain reaction (PCR) analysis. In comparison to normal lung tissue, reduced transcription of the RB2/p130 gene was found in all small cell lung cancer cell lines examined, along with six out of the eight nonsmall cell lung cancers tested, most of which had inactivation of RB/p16 pathway. On the basis of Western blot analysis, the expression of RB2/p130 protein was consistent with RNA expression levels in all lung cancer cell lines examined. In addition, the mutational status of the RB2/p130 gene (specifically, exons 19, 20, 21, and 22) was determined in 30 primary lung cancers (from patients with distant metastasis) and 30 lung cancer cell lines by PCR-single strand conformation polymorphism (SSCP) analysis and direct DNA sequencing. There was no evidence of somatic mutations within the RB2/p130 gene in the 60 lung cancer samples (both cell lines and tumors) assessed, including the 11 lung cancer cell lines that displayed reduced expression of the gene. Furthermore, hypermethylation of the RB2/p130 promoter was not found in any of the above-mentioned 11 cell lines, as determined by a DNA methylation assay, combined bisulfite restriction analysis (COBRA). The results of the present study suggest that the reduced RB2/p130 expression seen in lung cancer may be in part transcriptionally mediated, albeit not likely via a mechanism involving hypermethylation of the RB2/p130 promoter. The observed reduction in RB2/p130 gene expression may be due to histone deacetylation, altered mRNA stability, and/or other forms of transcriptional regulation.

The pRb-related protein p130 is regulated by phosphorylation-dependent proteolysis via the protein-ubiquitin ligase SCF(Skp2)

p130 is a tumor suppressor of the pocket protein family whose expression is posttranscriptionally regulated and largely G0 restricted. The mechanism of down-regulation of p130 expression in proliferating cells was investigated. Our results indicate that the decline of p130 expression as G0 cells reenter the cell cycle is due to a decrease in protein stability. The enhancement of p130 turnover in late G1 and S phase compared with G0 and early G1 phase was dependent on Cdk4/6-specific phosphorylation of p130 on Serine 672, and independent of Cdk2 activity. The activity of the ubiquitin ligase complex Skp1-Cul1/Cdc53-F-box protein Skp2 (SCF(Skp2)) and the proteasome were necessary for p130 degradation. In vitro, recombinant Skp2 was able to bind hyperphosphorylated but not dephosphorylated p130. Furthermore, in vitro polyubiquitination of p130 by SCF(Skp2) was specifically dependent on phosphorylation of p130 on Serine 672. Thus, like the Cdk inhibitor p27(Kip1), p130 turnover is regulated by Cdk-dependent G1 phosphorylation leading to ubiquitin-dependent proteolysis.

A single cell cycle genes homology region (CHR) controls cell cycle-dependent transcription of the cdc25C phosphatase gene and is able to cooperate with E2F or Sp1/3 sites

The cdc25C phosphatase participates in regulating transition from the G2 phase of the cell cycle to mitosis by dephosphorylating cyclin-dependent kinase 1. The tumor suppressor p53 down-regulates expression of cdc25C as part of G2/M checkpoint control. Transcription of cdc25C oscillates during the cell cycle with no expression in resting cells and maximum transcription in G2. We had identified earlier a new mechanism of cell cycle-dependent transcription that is regulated by a cell cycle-dependent element (CDE) in conjunction with a cell cycle genes homology region (CHR). The human cdc25C gene was the first example. CDE/CHR tandem elements have since been found in promoters of many cell cycle genes. Here we show that the mouse cdc25C gene is regulated by a CHR but does not hold a CDE. Therefore, it is the first identified gene with CHR-dependent transcriptional regulation during the cell cycle not relying on a CDE located upstream of it. The CHR leads to repression of cdc25C transcription early in the cell cycle and directs a release of this repression in G2. Furthermore, we find that this CHR can cooperate in cell cycle-dependent transcription with elements placed directly upstream of it binding E2F, Sp1 or Sp3 transcription factors.

Cell-cycle-dependent regulation of human aurora A transcription is mediated by periodic repression of E4TF1

Human aurora A is a serine-threonine kinase that controls various mitotic events. The transcription of aurora A mRNA varies throughout the cell cycle and peaks during G(2)/M. To clarify the transcriptional mechanism, we first cloned the 1.8-kb 5'-flanking region of aurora A including the first exon. Transient expression of aurora A promoter-luciferase constructs containing a series of 5'-truncated sequences or site-directed mutations identified a 7-bp sequence (CTTCCGG) from -85 to -79 as a positive regulatory element. Electromobility shift assays identified the binding of positive regulatory proteins to the CTTCCGG element. Anti-E4TF1-60 antibody generated a supershifted complex. Furthermore, coexpression of E4TF1-60 and E4TF1-53 markedly increased aurora A promoter activity. Synchronized cells transfected with the aurora A promoter-luciferase constructs revealed that the promoter activity of aurora A increased in the S phase and peaked at G(2)/M. In addition, we identified a tandem repressor element, CDE/CHR, just downstream of the CTTCCGG element, and mutation within this element led to a loss of cell cycle regulation. We conclude that the transcription of aurora A is positively regulated by E4TF1, a ubiquitously expressed ETS family protein, and that the CDE/CHR element was essential for the G(2)/M-specific transcription of aurora A.

The periodic down regulation of Cyclin E gene expression from exit of mitosis to end of G(1) is controlled by a deacetylase- and E2F-associated bipartite repressor element

The expression of cyclin E and that of a few other bona fide cell cycle regulatory genes periodically oscillates every cycle in proliferating cells. Although numerous experiments have documented the role of E2F sites and E2F activities in the control of these genes as cells exit from G(0) to move through the initial G(1)/S phase transition, almost nothing is known on the role of E2Fs during the subsequent cell cycles. Here we show that a variant E2F-site that is part of the Cyclin E Repressor Module (CERM) (Le Cam et al., 1999b) accounts for the periodic down regulation of the cyclin E promoter observed between the exit from mitosis until the mid/late G(1) phase in exponentially cycling cells. This cell cycle-dependent repression correlates with the periodic binding of an atypical G(1)-specific high molecular weight p107-E2F complex (Cyclin E Repressor Complex: CERC2) that differs in both size and DNA binding behaviors from known p107-E2F complexes. Notably, affinity purified CERC2 displays a TSA-sensitive histone deacetylase activity and, consistent with this, derepression of the cyclin E promoter by trichostatin A depends on the CERM element. Altogether, this shows that the cell cycle-dependent control of cyclin E promoter in cycling cells is embroiled in acetylation pathways via the CERM-like E2F element.

Transactivation of murine cyclin A by polyomavirus large and small T antigens

Polyomavirus large and small T antigens cooperate in the induction of S phase in serum-deprived Swiss 3T3 cells. While the large T antigen is able to induce S phase-specific enzymes, we have recently shown that both T antigens contribute to the production of the cyclins E and A and that the small T antigen is essential for the induction of cyclin A-dependent cdk2 activity (S. Schüchner and E. Wintersberger, J. Virol. 73:9266-9273, 1999). Here we present our attempts to elucidate the mechanisms by which the large and the small T antigens transactivate the murine cyclin A gene. Using Swiss 3T3 cells carrying the T antigens and various mutants thereof under the hormone-inducible mouse mammary tumor virus promoter, as well as transient-cotransfection experiments with the T antigens and cyclin A promoter-luciferase reporter constructs, we found the following. The large T antigen activates the cyclin A promoter via two transcription factor binding sites, a cyclic AMP responsive element (CRE), and the major negative regulatory site called CDE-CHR. While an intact binding site for pocket proteins is required for the function of this T antigen at the CDE-CHR, its activity at the CRE is largely independent thereof. In contrast, an intact J domain and an intact zinc finger are required at both sites. The small T antigen also appears to have an influence on the cyclin A promoter through the CRE as well as the CDE-CHR. For this an interaction with protein phosphatase 2A is essential; mutation of the J domain does not totally eliminate but greatly reduces the transactivating ability.

The retinoblastoma-related Rb2/p130 gene is an effector downstream of AP-2 during neural differentiation

Rb2/p130, a member of the Retinoblastoma family of growth and tumour suppressor genes, is extensively implicated in the control of cell cycle and differentiation. The minimal promoter region of Rb2/p130 in T98G human glioblastoma cells was identified and its analysis revealed the presence of a KER1 palindromic sequence able to bind the transcription factor AP-2, a regulatory protein that plays a crucial role in ectodermal differentiation. This KER1 site interacted in vitro with AP-2, and AP-2 overexpression increased Rb2/p130 transcription and translation. We also found that rat PC12 pheochromocytoma cells, when induced to differentiate by NGF, displayed an increase of AP-2 protein levels and of Rb2/p130 transcription and protein levels. AP-2-transfected PC12 cells displayed enhanced transcription and translation of Rb2/p130 and of the cdk inhibitor p21(WAF1/CIP1), a gene known to be under the control of AP-2, but unable by itself to elicit PC12 differentiation. Overexpression of either AP-2 or Rb2/p130 elicited per se cell differentiation in the absence of NGF, while coexpression of AP-2B, a negative regulator of AP-2 transcriptional activity, inhibited only AP-2-induced differentiation. Altogether, these results indicate that Rb2/p130 is a critical effector of AP-2 in sustaining ectodermal differentiation.

Expression of the E2F and retinoblastoma families of proteins during neural differentiation

Development of the brain is determined by a strictly orchestrated program of proliferation, migration, apoptosis, differentiation, synaptogenesis, tract formation, and myelination. The E2F family of transcription factors, whose activity and functions are regulated in large part through interactions with the retinoblastoma (Rb) family of tumor suppressor proteins, has been implicated as a key regulator of proliferation, differentiation, and apoptosis in a variety of tissues. We have examined levels of the E2F and Rb families of proteins during both brain development and neural differentiation of P19 cells, and found the expression profiles during these two processes of neural development and maturation to be quite similar, i.e., strong up-regulation of p130, pronounced down-regulation of p107, moderate up-regulation of pRb, and significant down-regulation of most species of E2F and dimerization protein (DP). However, several specific isoforms, namely a 30 kDa form of DP-2, a 57 kDa species of E2F-3, a 59 kDa form of E2F-5 and the isoforms of E2F-1 recognized by the E2F-1 (KH-95) antibody were up-regulated suggesting that these particular isoforms of E2F and DP play a tissue-specific function in differentiation and maturation of nervous tissue. The potential role of the E2F/DP family of transcription factors in aspects of neural development and differentiation are considered.

A CDE/CHR tandem element regulates cell cycle-dependent repression of cyclin B2 transcription

Cyclin B is an important regulator of progression through the cell division cycle. The oscillating appearance of cyclin B1 and B2 proteins during the cell cycle is in part due to fluctuating mRNA levels. We had identified earlier a tandem promoter element named cell cycle-dependent element (CDE) and cell cycle genes homology region (CHR) which regulates cell cycle-dependent transcription of cdc25C, cyclin A and cdc2. Here we describe that cyclin B2 transcription is repressed through a novel CDE/CHR element in resting and G(1) cells. By relief of this repression in S and G(2) oscillating expression of cyclin B2 mRNA is achieved during the cell cycle.