Re-establishment of gap junctional intercellular communication (GJIC) between human endometrial carcinomas by prostaglandin E(2).

Reduced intercellular communication via gap junctions is correlated with carcinogenesis. Gap junctional intercellular communication (GJIC), between normal human endometrial epithelial cells is enhanced when endometrial stromal cells were present in culture. This enhancement of GJIC between normal epithelial cells also occurs when they are cultured in medium conditioned by stromal cells. This observation indicated that a soluble compound (or compounds) produced and secreted by stromal cells mediates GJIC in epithelial cells. Previous studies have shown that endometrial stromal cells release prostaglandin E(2) (PGE(2)) and prostaglandin F(2α) (PGF(2α)) under physiological conditions. When we evaluated the response of normal endometrial epithelial cells to various concentrations of PGE(2,) we found enhanced GJIC with 1nM PGE(2). This is a smaller increase in GJIC than that induced by medium conditioned by stromal cells. When the extracellular concentration of PGE(2) was measured after incubation with stromal cells, it was found to be similar to the concentrations showing maximal GJIC between the normal epithelial cells. When indomethacin was used to inhibit prostaglandin synthesis by stromal cells, GJIC was reduced but not eliminated between normal endometrial epithelial cells. These observations suggest that although PGE(2) secreted by stromal cells is an important mediator of GJIC between the epithelial cells, it is not the sole mediator. Transformed endometrial epithelial cells did not demonstrate GJIC even in the presence of stromal cells. However, we were able to re-establish GJIC in transformed epithelial cells when we added PGE(2) to the cells. Our findings show that PGE(2) may serve as an intercellular mediator between stromal and epithelial cells that regulates GJIC in normal and malignant epithelial cells. This suggests that maintenance of GJIC by preserving or replacing PGE(2) secretion by endometrial stromal cells may have the potential to suppress carcinogenesis in endometrial epithelial cells.

BRG1 co-localizes with DNA replication factors and is required for efficient replication fork progression.

For DNA replication to occur, chromatin must be remodeled. Yet, we know very little about which proteins alter nucleosome occupancy at origins and replication forks and for what aspects of replication they are required. Here, we demonstrate that the BRG1 catalytic subunit of mammalian SWI/SNF-related complexes co-localizes with origin recognition complexes, GINS complexes, and proliferating cell nuclear antigen at sites of DNA replication on extended chromatin fibers. The specific pattern of BRG1 occupancy suggests it does not participate in origin selection but is involved in the firing of origins and the process of replication elongation. This latter function is confirmed by the fact that Brg1 mutant mouse embryos and RNAi knockdown cells exhibit a 50% reduction in replication fork progression rates, which is associated with decreased cell proliferation. This novel function of BRG1 is consistent with its requirement during embryogenesis and its role as a tumor suppressor to maintain genome stability and prevent cancer.

Beyond the Syndrome: Extensive Congenital Abnormalities in an Infant With Trisomy 21.

Herein we discuss the clinical course and subsequent autopsy of a female infant with trisomy 21 with balanced Rastelli Type "C" complete atrioventricular septal defect (AVSD), tetralogy of Fallot and right aortic arch with mirror image branching pattern who underwent a palliative right modified Blalock-Taussig-Thomas shunt (mBTTS) for hypoxemia from progressive right ventricular outflow tract obstruction. The baby was found to have multiple concomitant pathologic findings not typically seen with this constellation of cardiac anatomy. Autopsy revealed significant abdominal adhesions with near-complete stenosis of the transverse colon. In addition, the infant was found to have significantly elongated villi within the small and large bowel and a relatively large collagenous polyp in the small bowel. The decedent also had an abnormal tracheal bronchus, characterized by an additional superior right-sided bronchus, which is an extremely rare abnormality. Her clinical course was complicated by severe pulmonary hypertensive arteriolar changes out of proportion to what would be typical for her age, trisomy 21 status, and degree of left to right intracardiac shunting. Furthermore, she had refractory anasarca and recurrent chylous pleural effusions without gross lymphatic abnormalities that may have been secondary to systemic capillary leak syndrome (SCLS) versus severe pulmonary hypertension. Due to the aforementioned findings, the family elected for comfort care and the baby expired shortly after extubation. Overall, the infant had multiple, rare coexisting congenital abnormalities that likely represents an extreme phenotype of trisomy 21 that has not been described in the literature to date.

Abasic sites preferentially form at regions undergoing DNA replication.

We investigated whether apurinic/apyrimidinic (AP/abasic) sites were more frequent in regions of DNA replication in cells and whether their number increased during oxidative stress. DNA fiber spreading and fluorescent immunostaining were used to detect areas of DNA replication and sites of AP lesions in extended DNA fibers. The distribution of AP sites was determined in DNA fibers from vertebrate cells maintained under normal culture conditions or stressed with exogenous H(2)O(2). AP lesions per unit length were enumerated in bulk DNA or at replication sites. The background density of AP sites in DNA fibers was 5.4 AP sites/10(6) nt, while newly replicated DNA contained 12.9 AP sites/10(6) nt. In cells exposed to 20 µM H(2)O(2), AP sites in newly replicated DNA increased to 20.8/10(6) nt. Determinations of AP site density in bulk DNA by fiber analysis or standard slot blot assays agreed to within 10%. Our findings show that the fiber assay not only accurately determines the frequency of AP sites but also shows their distribution. They also reveal that there is increased susceptibility to oxidative damage in DNA regions undergoing replication, which may explain the previously observed clustering of AP sites.

Genistein effects on stromal cells determines epithelial proliferation in endometrial co-cultures.

BACKGROUND: Estrogen is the leading etiologic factor for endometrial cancer. Estrogen-induced proliferation of endometrial epithelial cells normally requires paracrine growth factors produced by stromal cells. Epidemiologic evidence indicates that dietary soy prevents endometrial cancer, and implicates the phytoestrogen genistein in this effect. However, results from previous studies are conflicting regarding the effects of genistein on hormone responsive cancers. METHODS: The effects of estrogen and genistein on proliferation of Ishikawa (IK) endometrial adenocarcinoma cells were examined in co-cultures of IK cells with endometrial stromal cells, recapitulating the heterotypic cell-to-cell interactions observed in vivo. The roles of estrogen receptor (ER)α and ERß were evaluated using ERα and ERß specific agonists. ER activation and cell proliferation in the IK epithelial cells were determined by alkaline phosphatase assay and Coulter counter enumeration, respectively. RESULTS: Both estrogen and genistein increased estrogen receptor-induced gene activity in IK cells over a range of concentrations. Estrogen alone but not genistein increased IK proliferation in co-cultures. When primed by estrogen treatment, increasing concentrations of genistein produced a biphasic effect on IK proliferation: nM concentrations inhibited estrogen-induced proliferation while µM concentrations increased proliferation. Studies with an ERß-specific agonist produced similar results. Genistein did not influence the effects of estrogen on IK proliferation in monoculture. CONCLUSIONS: Our study indicates that nutritionally relevant concentrations (nM) of genistein inhibit the proliferative effects of estrogen on endometrial adenocarcinoma cells presumably through activation of stromal cell ERß. We believe that sub-micromolar concentrations of genistein may represent a novel adjuvant for endometrial cancer treatment and prevention.

Accumulation of true single strand breaks and AP sites in base excision repair deficient cells.

Single strand breaks (SSBs) are one of the most frequent DNA lesions caused by endogenous and exogenous agents. The most utilized alkaline-based assays for SSB detection frequently give false positive results due to the presence of alkali-labile sites that are converted to SSBs. Methoxyamine, an acidic O-hydroxylamine, has been utilized to measure DNA damage in cells. However, the neutralization of methoxyamine is required prior to usage. Here we developed a convenient, specific SSB assay using alkaline gel electrophoresis (AGE) coupled with a neutral O-hydroxylamine, O-(tetrahydro-2H-pyran-2-yl)hydroxylamine (OTX). OTX stabilizes abasic sites (AP sites) to prevent their alkaline incision while still allowing for strong alkaline DNA denaturation. DNA from DT40 and isogenic polymerase ß null cells exposed to methyl methanesulfonate were applied to the OTX-coupled AGE (OTX-AGE) assay. Time-dependent increases in SSBs were detected in each cell line with more extensive SSB formation in the null cells. These findings were supported by an assay that indirectly detects SSBs through measuring NAD(P)H depletion. An ARP-slot blot assay demonstrated a significant time-dependent increase in AP sites in both cell lines by 1mM MMS compared to control. Furthermore, the Pol ß-null cells displayed greater AP site formation than the parental DT40 cells. OTX use represents a facile approach for assessing SSB formation, whose benefits can also be applied to other established SSB assays.

Genome-wide sequence and functional analysis of early replicating DNA in normal human fibroblasts.

BACKGROUND: The replication of mammalian genomic DNA during the S phase is a highly coordinated process that occurs in a programmed manner. Recent studies have begun to elucidate the pattern of replication timing on a genomic scale. Using a combination of experimental and computational techniques, we identified a genome-wide set of the earliest replicating sequences. This was accomplished by first creating a cosmid library containing DNA enriched in sequences that replicate early in the S phase of normal human fibroblasts. Clone ends were then sequenced and aligned to the human genome. RESULTS: By clustering adjacent or overlapping early replicating clones, we identified 1759 "islands" averaging 100 kb in length, allowing us to perform the most detailed analysis to date of DNA characteristics and genes contained within early replicating DNA. Islands are enriched in open chromatin, transcription related elements, and Alu repetitive elements, with an underrepresentation of LINE elements. In addition, we found a paucity of LTR retroposons, DNA transposon sequences, and an enrichment in all classes of tandem repeats, except for dinucleotides. CONCLUSION: An analysis of genes associated with islands revealed that nearly half of all genes in the WNT family, and a number of genes in the base excision repair pathway, including four of ten DNA glycosylases, were associated with island sequences. Also, we found an overrepresentation of members of apoptosis-associated genes in very early replicating sequences from both fibroblast and lymphoblastoid cells. These data suggest that there is a temporal pattern of replication for some functionally related genes.

Effect of normal endometrial stroma on growth and differentiation in Ishikawa endometrial adenocarcinoma cells.

Endometrial cancer is characterized by alterations in the stromal cells and the supporting extracellular matrix in addition to the intrinsic alterations of the malignant epithelial cells. We have developed a cell culture model that demonstrates the role of stromal cells in the regulation of proliferation, hormone responsiveness, and differentiation of an endometrial adenocarcinoma cell line (Ishikawa). Conditioned medium (CM) was collected from normal primary human endometrial stromal cells grown on plastic or within the basement membrane extract, Matrigel. The CM produced by stromal cells cultured in contact with Matrigel markedly inhibited Ishikawa cell proliferation compared with CM from stromal cells cultured on plastic. Ishikawa cell proliferation varied with steroid hormone treatment in the presence of CM from stromal cells embedded in Matrigel. When the Ishikawa cells were placed in coculture in contact with stromal cells in Matrigel, production of a differentiated epithelial secretory product, glycodelin, was induced. Gene expression of stromal cell hormone receptors, growth factors, and integrins was analyzed by reverse transcription-PCR in the presence of Matrigel to determine the potential factors involved in stromal regulatory function. These combined studies imply that the phenotype of the Ishikawa cells can be induced to differentiate to more closely resemble normal endometrial epithelium by reintroduction of stromal factors and appropriate extracellular matrix. Additionally, the study shows that basement membrane proteins influence the regulatory function of stromal cells as they mediate epithelial cell growth.

Decidual differentiation of stromal cells promotes Proprotein Convertase 5/6 expression and lefty processing.

Lefty/Ebaf polypeptides, novel members of the TGF-beta superfamily, are involved in endometrial differentiation and embryo implantation. Recently, we showed that, during undisturbed estrous cycle, lefty is present in mouse uterine horn primarily in a precursor form. Here, we show that decidual differentiation of endometrial stroma leads to increased lefty (approximately 3.1- to 3.6-fold in vivo and 5- to 8-fold in vitro) and processing of its precursor primarily to its long form. This event occurs on d 5 of pregnancy, and is paralleled by proprotein convertase (PC)5/6 up-regulation (approximately 6-fold increase for PC5A and 3-fold increase for PC5B) in decidualized uterine horn, independent of embryo implantation. Among the known convertases, only PC5/6A processes lefty to its long form. Taken together, the findings show that decidualized differentiation of stroma, which is a prerequisite for embryo implantation, leads to processing of lefty by PC5/6A.

SWI/SNF complexes are required for full activation of the DNA-damage response.

SWI/SNF complexes utilize BRG1 (also known as SMARCA4) or BRM (also known as SMARCA2) as alternative catalytic subunits with ATPase activity to remodel chromatin. These chromatin-remodeling complexes are required for mammalian development and are mutated in ~20% of all human primary tumors. Yet our knowledge of their tumor-suppressor mechanism is limited. To investigate the role of SWI/SNF complexes in the DNA-damage response (DDR), we used shRNAs to deplete BRG1 and BRM and then exposed these cells to a panel of 6 genotoxic agents. Compared to controls, the shRNA knockdown cells were hypersensitive to certain genotoxic agents that cause double-strand breaks (DSBs) associated with stalled/collapsed replication forks but not to ionizing radiation-induced DSBs that arise independently of DNA replication. These findings were supported by our analysis of DDR kinases, which demonstrated a more prominent role for SWI/SNF in the activation of the ATR-Chk1 pathway than the ATM-Chk2 pathway. Surprisingly, γH2AX induction was attenuated in shRNA knockdown cells exposed to a topoisomerase II inhibitor (etoposide) but not to other genotoxic agents including IR. However, this finding is compatible with recent studies linking SWI/SNF with TOP2A and TOP2BP1. Depletion of BRG1 and BRM did not result in genomic instability in a tumor-derived cell line but did result in nucleoplasmic bridges in normal human fibroblasts. Taken together, these results suggest that SWI/SNF tumor-suppressor activity involves a role in the DDR to attenuate replicative stress and genomic instability. These results may also help to inform the selection of chemotherapeutics for tumors deficient for SWI/SNF function.

Temporal and functional analysis of DNA replicated in early S phase.

In summary, recently developed technologies have begun to draw back the curtain of mystery that obscures some of the basic mechanisms of DNA replication at multiple levels. Studies using extended DNA and chromatin fiber techniques have proven valuable for identifying the location of origins of replication at specific genomic sites and determining their temporal order of replication, for identifying and quantifying sites of DNA damage and localizing chromatin proteins in relation to sites of DNA replication. The future potential of these methods include further discoveries in functional genomics and contributions to the elucidation of the histone code. Such studies could prove very valuable in studies of the mechanisms of cancer development, aging, and other processes of disordered genomic functioning.

FEN1 functions in long patch base excision repair under conditions of oxidative stress in vertebrate cells.

From in vitro studies, flap endonuclease 1 (FEN1) has been proposed to play a role in the long patch (LP) base excision repair (BER) subpathway. Yet the role of FEN1 in BER in the context of the living vertebrate cell has not been thoroughly explored. In the present study, we cloned a DT40 chicken cell line with a deletion in the FEN1 gene and found that these FEN1-deficient cells exhibited hypersensitivity to H(2)O(2). This oxidant produces genotoxic lesions that are repaired by BER, suggesting that the cells have a deficiency in BER affecting survival. In experiments with extracts from the isogenic FEN1 null and wild-type cell lines, the LP-BER activity of FEN1 null cells was deficient, whereas repair by the single-nucleotide BER subpathway was normal. Other consequences of the FEN1 deficiency were also evaluated. These results illustrate that FEN1 plays a role in LP-BER in higher eukaryotes, presumably by processing the flap-containing intermediates of BER.

Temporal differences in DNA replication during the S phase using single fiber analysis of normal human fibroblasts and glioblastoma T98G cells.

We have recently shown that replication forks pause near origins in normal human fibroblasts (NHF1-hTERT) but not glioblastoma T98G cells. This observation led us to question whether other differences in the replication program may exist between these cell types that may relate to their genetic integrity. To identify differences, we detected immunoflourescently the sequential incorporation of the nucleotide analogs IdU and CldU into replicating DNA at the start of every hour of a synchronized S phase. We then characterized the patterns of labeled replicating DNA tracks and quantified the percentages and lengths of the tracks found at these hourly intervals. From the directionality of labeling in single extended replicating DNA fibers, tracks were categorized as single bidirectional origins, unidirectional elongations, clusters of origins firing in tandem, or merging forks (terminations). Our analysis showed that the start of S phase is enriched in single bidirectional origins in NHF1-hTERT cells, followed by an increase in clustering during mid S phase and an increase in merging forks during late S phase. Early S phase in T98G cells also largely consisted of single bidirectional origin initiations; however, an increase in clustering was delayed until an hour later, and clusters were shorter in mid/late S phase than in NHF1-hTERT cells. The spike in merging forks also did not occur until an hour later in T98G cells. Our observations suggest models to explain the temporal replication of single and clustered origins, and suggest differences in the replication program in a normal and cancer cell line.

DNA replication and the GINS complex: localization on extended chromatin fibers.

BACKGROUND: The GINS complex is thought to be essential for the processes of initiation and elongation of DNA replication. This complex contains four subunits, one of which (Psf1) is proposed to bind to both chromatin and DNA replication-associated proteins. To date there have been no microscopic analyses to evaluate the chromatin distribution of this complex. Here, we show the organization of GINS complexes on extended chromatin fibers in relation to sites of DNA replication and replication-associated proteins. RESULTS: Using immunofluorescence microscopy we were able to visualize ORC1, ORC2, PCNA, and GINS complex proteins Psf1 and Psf2 bound to extended chromatin fibers. We were also able to detect these proteins concurrently with the visualization of tracks of recently replicated DNA where EdU, a thymidine analog, was incorporated. This allowed us to assess the chromatin association of proteins of interest in relation to the process of DNA replication. ORC and GINS proteins were found on chromatin fibers before replication could be detected. These proteins were also associated with newly replicated DNA in bead-like structures. Additionally, GINS proteins co-localized with PCNA at sites of active replication. CONCLUSION: In agreement with its proposed role in the initiation of DNA replication, GINS proteins associated with chromatin near sites of ORC binding that were devoid of EdU (absence of DNA replication). The association of GINS proteins with PCNA was consistent with a role in the process of elongation. Additionally, the large size of our chromatin fibers (up to approximately 7 Mb) allowed for a more expansive analysis of the distance between active replicons than previously reported.

Effects of tibolone metabolites on human endometrial cell lines in co-culture.

In human endometrium, cell proliferation is regulated by ovarian steroids through heterotypic interactions between stromal and epithelial cells populating this tissue. The authors test the proliferative effects of tibolone and its metabolites using endometrial co-cultures that mimic the normal proliferative response to hormones. They found that both the Delta(4)-tibolone metabolite and the pure progestin ORG2058 counteract estradiol-driven epithelial cell proliferation. Surprisingly, the estrogen receptor binding 3-hydroxyl-metabolites of tibolone also counteracted estradiol-driven proliferation. Inhibition of proliferation by 3beta-OH-tibolone was abrogated by low doses of the progesterone receptor antagonist mifepristone. This suggests that 3beta-OH-tibolone is converted to a progestagenic metabolite. The authors found that the stromal cells used in the co-cultures express high levels of the ketosteroid dehydrogenase AKR1C2, which is able to oxidize 3beta-OH-tibolone back to tibolone. Thus, the unexpected progestagenic effect of 3beta-OH-tibolone in these co-cultures may be due to metabolic activity present in the stromal cells of the co-cultures.

DNA replication in early S phase pauses near newly activated origins.

During the S phase of the cell cycle, the entire genome is replicated. There is a high level of orderliness to this process through the temporally and topologically coordinated activation of many replication origins situated along chromosomes. We investigated the program of replication from origins initiating in early S phase by labeling synchronized normal human fibroblasts (NHF1) with nucleotide analogs for various pulse times and measuring labeled tracks in combed DNA fibers. Our analysis showed that replication forks progress 9-35 kilobases from newly initiated origins, followed by a pause in synthesis before replication resumes. Pausing was not observed near origins that initiated in the middle of S phase. No evidence for pausing near origins was found at the beginning of the S phase in glioblastoma T98G cells. Treatment with the S phase checkpoint inhibitor caffeine abrogated pausing in NHF1 cells in early S phase. This suggests that pausing may comprise a novel aspect of the intra-S phase checkpoint pathway or a related new early S checkpoint. Further, it is possible that the loss of this regulatory process in cancer cells such as T98G could be a contributing factor in the genetic instability that typifies cancers.

Early replication and the apoptotic pathway.

In higher eukaryotes there is a link between time of replication and transcription. It is generally accepted that genes that are actively transcribed are replicated in the first half of S phase while inactive genes replicate in the second half of S phase. We have recently reported that in normal human fibroblasts there are some functionally related genes that replicate at the same time in S phase. This had been previously reported for functionally related genes that are located in clusters, for example the alpha- and beta-globin complexes. We have shown, however, that this also occurs with some functionally related genes that are not organized in a cluster, but rather are distributed throughout the genome. For example, using GOstat analysis of data from our and other groups, we found an overrepresentation of genes involved in the apoptotic process among sequences that are replicated very early (approximately in the first hour of S phase) in both fibroblasts and lymphoblastoid cells. This finding leads us to question how and why the replication of genes in the apoptotic pathway is temporally organized in this manner. Here we discuss the possible explanations and implications of this observation.

Mapping of an origin of DNA replication in the promoter of fragile X gene FMR1.

An origin of bidirectional DNA replication was mapped to the promoter of the FMR1 gene in human chromosome Xq27.3, which has been linked to the fragile X syndrome. This origin is adjacent to a CpG island and overlaps the site of expansion of the triplet repeat (CGG) at the fragile X instability site, FRAXA. The promoter region of FMR2 in the FRAXE site (approximately 600 kb away, in chromosome band Xq28) also includes an origin of replication, as previously described [Chastain II, P.D., Cohen, S.M., Brylawski, B.P., Cordeiro-Stone, M., Kaufman, D.G., 2006. A late origin of DNA replication in the trinucleotide repeat region of the human FMR2 gene. Cell Cycle 5, 869-872]. FMR1 transcripts were detected in foreskin and male fetal lung fibroblasts, while FMR2 transcripts were not. However, both FMR1 and FMR2 were found to replicate late in S phase (approximately 6 h into the S phase of normal human fibroblasts). The position of the origin of replication relative to the CGG repeat, and perhaps the late replication of these genes, might be important factors in the susceptibility to triplet repeat amplification at the FRAXA and FRAXE sites.