Extended life span of human endometrial stromal cells transfected with cloned origin-defective, temperature-sensitive simian virus 40

The single-cell atlas of cultured human endometrial stromal cells

OBJECTIVE

To systematically analyze the cell composition and transcriptome of primary human endometrial stromal cells (HESCs) and transformed human endometrial stromal cells (THESCs).

DESIGN

The primary HESCs from 3 different donors and 1 immortalized THESC were collected from the human endometrium at the midsecretory phase and cultured in vitro.

SETTING

Academic research laboratory.

PATIENT(S)

None.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Single-cell ribonucleic acid sequencing analysis.

RESULT(S)

We found the individual differences among the primary HESCs and bigger changes between the primary HESCs and THESCs. Cell clustering with or without integration identified cell clusters belonging to mature, proliferative, and active fibroblasts that were conserved across all samples at different stages of the cell cycles with intensive cell communication signals. All primary HESCs and THESCs can be correlated with some subpopulations of fibroblasts in the human endometrium.

CONCLUSION(S)

Our study indicated that the primary HESCs and THESCs displayed conserved cell characters and distinct cell clusters. Mature, proliferative, and active fibroblasts at different stages or cell cycles were detected across all samples and presented with a complex cell communication network. The cultured HESCs and THESCs retained the features of some subpopulations within the human endometrium.

Critical role of TRPC1-mediated Ca²⁺ entry in decidualization of human endometrial stromal cells

Decidualization is an ovarian steroid-induced remodeling/differentiation process of uterus essential for embryo implantation and placentation. Here, we investigated the possible involvement of enhanced Ca²⁺ dynamics in the decidualization process in human endometrial stromal cells (hESC) in its connection with a recently emerging nonvoltage-gated Ca²⁺ entry channel superfamily, the transient receptor potential (TRP) protein. Combined application of 17β-estradiol (E₂) (10 nM) and progesterone (P₄) (1 μM) for 7-14 d resulted in morphological changes of hESC characteristic of decidualization (i.e. cell size increase), whereas sole application of E₂ exerted little effects. A 7- to 14-d E₂/P₄ treatment greatly increased the expression level of decidualization markers IGF binding protein-1 (IGFBP-1) and prolactin and also up-regulated the expression of TRPC1, a canonical TRP subfamily member that has been implicated in store-operated Ca²⁺ influx (SOC) in other cell types. In parallel with this up-regulation, SOC activity in hESC, the nuclear translocation of phosphorylated cAMP responsive element binding protein (p-CREB) and the expression of Forkhead box protein 01 were enhanced significantly. Small interfering RNA knockdown of TRPC1 counteracted the E₂/P₄-induced up-regulation of IGFBP-1 and prolactin and enhancement of SOC activity together with the inhibition of hESC size increase, p-CREB nuclear translocation, and FOXO1 up-regulation. Coadministration of SOC inhibitors SK&F96365 or Gd³⁺ with E₂/P₄ also suppressed the up-regulation of IGFBP-1 and hESC size increase. Similar inhibitory effects were observed with extracellularly applied TRPC1 extracellular loop 3-directed antibody, which is known to bind a near-pore domain of TRPC1 channel and block its Ca²⁺ transporting activity. These results strongly suggest that up-regulation of TRPC1 protein and consequent enhancement of SOC-mediated Ca²⁺ influx may serve as a crucial step for the decidualization process of hESC probably via p-CREB-dependent transcriptional activity associated with FOXO1 activation.

Expression of Exogenous Human Telomerase in Cultures of Endometrial Stromal Cells Does Not Alter Their Hormone Responsiveness1

In the human endometrium, stromal cells mediate the proliferative response of epithelial cells to the steroid hormones estrogen and progesterone. These stromal-epithelial interactions are readily studied in vitro by coculture of both cell types. A major impediment to such studies is the rapid senescence of normal stromal cells. To circumvent this problem, we tested whether human endometrial stromal cells immortalized by expressing a transduced human telomerase reverse transcriptase (TERT) subunit retained the ability to mediate hormonal control of epithelial proliferation in the coculture assay. We found that the telomerized stromal cells were very similar to the parental strain from which they were derived according to criteria of proliferation, karyotype, cellular localization of cytoskeletal markers and nuclear staining, and basal gene expression based on microarray analysis. We also showed that expression of estrogen and progesterone receptors, as assessed by immunodetection, was similar in both telomerized and parental stromal cells. Importantly, the telomerized stromal cells were shown in coculture assay to be as effective as normal stromal cells in regulating the proliferation of endometrial epithelial cells in response to estrogen or progesterone. The availability of these long-lived stromal cells may advance studies addressing the mechanistic, regulatory, and cell structural basis of stromal-epithelial interactions and hormonal responses in normal, preneoplastic, and neoplastic human endometrial tissue.

Analysis of the guinea-pig estrogen-regulated gec1/GABARAPL1 gene promoter and identification of a functional ERE in the first exon

The gec1/GABARAPL1 (GABA(A)-receptor-associated protein like-1) gene has been identified as an early estrogen-regulated gene in guinea-pig cultured endometrial glandular epithelial cells (GEC). Guinea-pig and human gec1/GABARAPL1 proteins share 87% identity with GABARAP, which acts as a protein linker between microtubules and the GABA(A) receptor. To investigate the molecular mechanisms regulating gec1/GABARAPL1 gene expression, the 1.5-kbp region upstream of the translation initiation codon of the guinea-pig gec1/GABARAPL1 gene was cloned. A 300-bp fragment encompassing a pyrimidine-rich initiator element (INR) and the transcription start site (+1) was sufficient to initiate transcription. Transfection and gel shift experiments showed that a sequence located at +36/+50 in the first exon permitted induction of expression of this gene by estradiol acting via ERalpha. This sequence (GGGTCAACGTGACGT) differs only by one base pair from the consensus estrogen response element ERE (GGGTCAACGTGACCT). It can be concluded that the ERE located in the first exon encoding the 5'-untranslated region is sufficient for E2 activation of gec1/GABARAPL1 transcription.

Onset of direct 17-β estradiol effects on proliferation and c-fos expression during oncogenesis of endometrial glandular epithelial cells

In normal endometrial glandular epithelial cells (GEC), 17beta-estradiol (E2) enhances proliferation and c-fos expression only in the presence of growth factors. On the contrary, growth factors are not required for the E2 effects in cancerous cells. Thus, a repression of E2 action could exist in normal cells and be turned off in cancerous cells, allowing a direct estrogen-dependent proliferation. To verify this hypothesis, we established immortalized and transformed cell models, then investigated alterations of E2 effects during oncogenesis. SV40 large T-antigen was used to generate immortalized GEC model (IGEC). After observation of telomerase reactivation, IGEC model was transfected by activated c-Ha-ras to obtain transformed cell lines (TGEC1 and TGEC2). The phenotypic, morphological, and genetic characteristics of these models were determined before studying the E2 effects. In IGEC, the E2 action on proliferation and c-fos expression required the presence of growth factors, as observed in GECs. In TGECs, this action arose in the absence of growth factors. After IGEC transformation, the activation of ras pathway would substitute the priming events required for the release of repression in GEC and IGEC and thus permit direct E2 effects. Our cell models are particularly suitable to investigate alterations of gene regulation by E2 during oncogenesis.

Improved TRAP-silver staining versus conventional radioactive TRAP assays: quantification of telomerase activity during immortalization and in pathological human endometrium

OBJECTIVES

To develop a sensitive telomeric repeat amplification protocol (TRAP)-silver staining assay for telomerase activity quantification.

DESIGN AND METHODS

TRAP assays were performed by using a TRAPeze telomerase kit with or without [alpha-32P]-dCTP. Amplification products were electrophoresed in polyacrylamide gels and detected by autoradiography or a modified silver staining protocol. Telomerase activity was quantified from radioactive counts or optical density of telomerase products from test extracts and controls.

RESULTS

TRAP-silver staining assay was at least as sensitive as radioactive TRAP assay and quantified telomerase activity within linearity from 10 to 3,000 cell equivalents. Both methods quantified a weak telomerase activity in normal endometrial glandular epithelial cells (GEC) and a strong increase in immortalized GEC. In human pathologic endometria (n=24), telomerase activity was correlated with lesion seriousness and distinguished simple hyperplasias from nonhyperplasic or cancerous lesions.

CONCLUSIONS

TRAP-silver staining assay is suitable for cell and tissue telomerase activity routine quantification.

Expression of dioxin-responsive genes in human endometrial cells in culture

To investigate expression of dioxin-responsive genes in human endometrial cells with exposure to 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD), human endometrial stromal cells immortalized with temperature-sensitive SV40 T antigen were used for the experiments. Cells were treated with 0.1% DMSO or 0.1, 1, 10, or 100 nM TCDD for 24 h. Induction of interleukin-1beta (IL-1beta) and plasminogen activator inhibitor-2 (PAI-2) mRNAs was analyzed by reverse-transcription polymerase chain reaction. Expression of IL-1beta or PAI-2 mRNA in response to TCDD was increased in a dose-dependent fashion. The maximum increases of PAI-2 and IL-1beta mRNAs were observed at 100 and 10 nM TCDD, respectively. While cycloheximide treatment did not show a significant difference of PAI-2 mRNA levels between control and TCDD-treated cells, mRNA stability assay using actinomycin D showed that PAI-2 mRNA in TCDD-treated cells was about twofold more stable than the control cells. While expression of CYP1A1 mRNA was not detected and levels of ARNT mRNA were not altered by TCDD exposure, the amount of AhR mRNA was decreased dose dependently. The present study represents an initial attempt to determine the responses of dioxin-responsive genes in human endometrial cells following TCDD exposure. The results demonstrated that IL-1beta and PAI-2 genes are induced dose dependently in human endometrial cells with exposure to TCDD and expression of PAI-2 mRNA is controlled at the posttranscriptional level.

Can ends justify the means?: telomeres and the mechanisms of replicative senescence and immortalization in mammalian cells

Finite replicative lifespan, or senescence, of mammalian cells in culture is a phenomenon that has generated much curiosity since its description. The obvious significance of senescence to organismal aging and the development of cancer has engendered a long-lasting and lively debate about its mechanisms. Recent discoveries concerning the phenotypes of telomerase knockout mice, the consequences of telomerase reexpression in somatic cells, and genes that regulate senescence have provided striking molecular insights but also have uncovered important new questions. The objective of this review is to reconcile old observations with new molecular details and to focus attention on the key remaining puzzles.

Endothelial cell expression of testican mRNA

By screening random cDNAs from a continuous vascular endothelial cell line, EA.hy926, we identified a 5 kb mRNA that is expressed at high levels by this human cell line and by an early passage umbilical vein endothelial cell line. It is detected at lower levels in certain stromal cell lines, but it is not detected in most other cell lines tested, indicating that it represents a differentially expressed function rather than a ubiquitous or housekeeping function. This mRNA was readily detected in samples derived from most human organs as might be expected for a gene expressed in the vascular wall. Sequencing of the 5 kb mRNA reveals its identity with 3.5 kb of previously published testis-derived cDNA sequence called testican (Alliel et al., 1993). Differential expression of this gene by endothelial cells contributes a new perspective on the potential function of testican.

Diethylstilbestrol-induced immortalization of human endometrial cells: alterations in p53 and estrogen receptor

Carcinogenesis is a process requiring multiple steps. Immortalization is one step in this process and may be rate limiting. To further our understanding of estrogen-induced carcinogenesis, we evaluated diethylstilbestrol (DES)-induced immortalization of human endometrial stromal cells. This was achieved by assessing at the restrictive temperature the colony-forming efficiency of cells that were conditionally immortalized with a temperature-sensitive simian virus 40 large T antigen. Treatment with DES for 1 wk did not increase the immortalization frequency; however, cultures that were treated for 20 wk had a twofold increase in immortalization frequency, and continued treatment for a total of 44 wk produced a threefold increase in immortalization frequency that was dose dependent. DES-treated restrictive temperature variants (RTVs) but not spontaneous RTVs lost the temperature-sensitive phenotype. DES-RTVs also had a shorter doubling time than spontaneous RTVs did. p53 expression was increased in DES-RTVs, and its localization within the cell was altered. Conversely, expression of the estrogen receptor was decreased in DES-immortalized cells. These changes in gene expression often occur in estrogen-related malignancies, and our results are consistent with a causal role for estrogens in these p53 and the estrogen receptor alterations. Immortalization of human cells may be analogous to initiation of rodent cells, and our results suggest that estrogen-induced alterations in p53 or other genes that regulate life span could contribute to estrogen-induced initiation.

Estrogen-induced anchorage-independence in human endometrial stromal cells

Estrogens are important etiologic agents for most gynecologic malignancies, and chronic exposure to estrogen that is unopposed by progestins conveys the greatest risk. Treatments with estrogen facilitate the process of malignant transformation in rodents, but relatively few studies of estrogen-induced carcinogenesis have been performed using human cells. Most malignancies in estrogen-responsive tissues arise from epithelial cells, but an increasing body of evidence emphasizes the role of stromal cells as mediators of the effects of estrogens on epithelial cells. Our studies were designed to assess estrogens as carcinogens for human endometrial stromal cells and to provide a basis for studies of the role of stroma in estrogen-induced carcinogenesis in humans. Acute treatments with the estrogens diethylstilbestrol (DES), 17 beta-estradiol (E2) and beta-dienestrol enhance anchorage-independent proliferation (AIP) of SV40-immortalized human endometrial stromal cells in the rank order of DES > E2 > beta-dienestrol. The anti-estrogenic compound tamoxifen inhibits DES-induced AIP. The magnitude of DES-induced AIP increases with prolonged duration of treatment. After 11 months of chronic treatment with 0.1 nM DES, AIP was 20-fold higher than in vehicle-treated control cultures. Expression of the estrogen receptor was altered by treatments with DES in parallel with increased capacity for AIP. These conditionally immortal human endometrial stromal cells appear to be a good model for estrogen-induced transformation of human cells.

Differential effects of dioctanoylglycerol on fibronectin localization in normal, partially transformed, and malignant human endometrial stromal cells

In this study, we describe the effects of direct activation of PKC by dioctanoylglycerol (DiC8) on cellular morphology and the localization of fibronectin (Fn) in normal, oncogene-transfected, and malignant human endometrial stromal cells. We questioned whether DiC8, an endogenous specific activator of PKC, would function as a second oncogene in partially transformed human endometrial stromal cells (HESC). Cells utilized were (1) normal HESC, (2) HESC transfected with a plasmid containing an origin-defective temperature-sensitive SV40 large T antigen alone or (3) in combination with an EJ ras oncogene, and (4) an endometrial sarcoma cell line (S7). Cell cultures were treated for 1 h with sn-dioctanoylglycerol (DiC8) and stained with a monoclonal fluorescein-labeled anti-Fn antibody. In normal HESC, DiC8 induced cell rounding and caused Fn localization to revert from the perinuclear region to the cell periphery. All experiments in this investigation were performed when cells were maintained at the permissive temperature for SV40 large T antigen function. In HESC expressing the SV40 large T antigen alone, Fn was localized to the perinuclear region and also occurred as parallel strands between cells. When these cells were treated with DiC8, Fn localization changed to intense punctate regions at the cell periphery or to matrix-like patterns between cells. Also, in these cells, DiC8 induced greater detachment of cells from the substrate than from other cells, resulting in an apparent piling up of cells. Control and treated SV40/EJ ras cells and uterine sarcoma cells expressed Fn in a matrix-like pattern between cells. The rounded cellular morphology of treated HESC and treated cells expressing SV40 resembled the morphology of control or treated SV40/EJ ras cells and uterine sarcoma cells. Thus, treated cells expressing the SV40 large T antigen resembled the SV40/EJ ras cells and uterine sarcoma cells with respect to Fn localization and cellular morphology. DiC8 did not appear to further transform HESC expressing SV40 and EJ ras. However, with regard to cell shape and Fn localization, our results suggest that DiC8 may function as a second oncogene in the signal transduction pathway, in cells expressing SV40 alone. It appears that, with regard to Fn localization, DiC8 may alter signal transduction analogously to that caused by the activated Ha-ras oncogene in HESC expressing the SV40 large T antigen.

Mechanism of induction of cellular DNA synthesis by the adenovirus E1A 12S cDNA product

The mechanism of induction of DNA synthesis in quiescent rat 3Y1 cells by the adenovirus E1A gene was investigated using the 3Y1 derivative cell lines g12-21, gn12RB1, and gn12RB2. The g12-21 cells express the E1A 12S cDNA and the latter two cells express both the E1A 12S cDNA and the human retinoblastoma susceptibility (Rb) gene at different levels in response to dexamethasone (dex). The cDNA sequences of E1A-inducible cell cycle-dependent genes, clone 3 and clone 16, were isolated by differential screening of a cDNA library constructed from dex-treated g12-21 cells. The quiescent 3Y1 cells induced c-fos and c-myc expression within 2 h after serum stimulation and expressed clone 16 and clone 3 transiently at around 8 h before the onset of DNA synthesis (10 h). In contrast, the quiescent g12-21 cells treated with dex expressed a high level of E1A at 6 to 8 h after treatment and expressed clone 16 and clone 3 at around 8 h without stimulation of c-fos and c-myc expression, suggesting that E1A bypasses the cell cycle early in G1. The half-maximal rate of DNA synthesis was reached in a much shorter time in dex-treated g12-21 cells (12 h) than in serum-treated 3Y1 cells (18 h), suggesting that E1A also bypasses the cell cycle at the G1/S boundary. The gn12RB1 and gn12RB2 cells were unable to induce DNA synthesis in response to dex presumably due to lower levels of E1A expression, although gn12RB2 but not gn12RB1 cells could express clone 16 and clone 3. These results suggest that the level of E1A required for bypass at the G1/S boundary is higher than that required early in G1.

Porcine endometrial epithelial cells immortalized by transfection with origin-defective, temperature-sensitive simian virus 40 DNA

The purpose of this study was to immortalize porcine endometrial cells and to characterize the transformed cells. Primary porcine endometrial cells were transfected with the plasmid vector (pmk16) containing SV40 DNA using a liposome-mediated method. The viral DNA was from a replication-defective, origin-minus, temperature-sensitive mutant strain (A58). One clone, designated PE-1, has been propagated for over 120 passages. PE-1 cells grown at 33C (33C cells) exhibit spindle-shaped morphology; when cultured at 40C (40C cells), they took on a polygonal or spherical shape. Morphology of 40C cells returned to the spindle shape after culture flasks were shifted back to 33C. During a 2-week period, 33C cells propagated approximately 30-fold faster than 40C cells, whereas protein concentration was higher in 40C cells. Southern blot analysis of PE-1 cells demonstrated successful integration of the ts-SV40 DNA sequence into the porcine endometrial cells, possibly at multiple sites. The presence of cytokeratin on PE-1 cell membranes was shown by immunocytochemical studies, suggesting that the PE-1 cell clone was of epithelial origin. Reverse phase (RP)-HPLC analysis of PE-1 cell extract indicated that the majority of immunoreactive beta-endorphin (ir-BEND) eluted with a hydrophobicity similar to that of synthetic BEND and alpha-N-acetylated BEND (Nac-BEND). These results demonstrate that a porcine endometrial cell line has been established, and that this cell line possesses characteristics of temperature sensitivity in cell morphology, growth rate, and protein synthesis.

Polyomavirus large and small T antigens cooperate in induction of the S phase in serum-starved 3T3 mouse fibroblasts

The induction of an S phase in the host cell is a prerequisite for the lytic replication cycle of polyomavirus. This function was attributed to proteins coded for by the early region of the viral DNA, the T antigens. A consideration of the role of the T antigens in the initiation of a mitogenic response of the host cell has to take into account the recent discovery that virus adsorption is sufficient to induce the synthesis of proteins which are known to appear early after quiescent cells are stimulated by the addition of serum, namely fos, jun, and myc (J. Zullo, C.D. Stiles, and R.L. Garcea, Proc. Natl. Acad. Sci. USA 84:1210-1214, 1987; G. M. Glenn and W. Eckhart, J. Virol. 64:2193-2201, 1990). This induction is followed by an initiation of DNA synthesis. It is therefore important to dissociate the effects of the T antigens on the host cell from those of virus adsorption. To do so, we used dexamethasone-regulated versions of the large and small T antigens of polyomavirus stably integrated into the genome of Swiss 3T3 cells to study their function in S-phase induction. When the production of the large or small T antigen in serum-starved 3T3 mouse fibroblasts was activated, only a small fraction of cells was able to leave G0/G1 despite the synthesis of considerable amounts of the respective T antigen. Activation of both T antigens within the same cell, on the other hand, resulted in S-phase induction in a notable percentage of cells, suggesting that the two proteins cooperate in this activity. Polyomavirus T antigens appear to bypass the pathway of growth regulation involving the activation of c-fos. These results are discussed in relation to other known functions of the two virally coded proteins.

Methionine-enkephalin in a porcine endometrial cell line and its responsiveness to potassium depolarization

Immunoreactive methionine-enkephalin (ir-MENK) has been identified in the porcine uterine fluid and endometrium. Previously, we have established a porcine endometrial cell line of epithelial origin (PE-1) by transfecting primary endometrial cells with temperature sensitive SV40 DNA. The current study was conducted to identify and characterize ir-MENK present in PE-1 cells, and to investigate the effect of KCl depolarization on the kinetics of ir-MENK secretion. PE-1 cells were cultured at 33C until confluency was reached (33C cells), after which they were incubated at 40C for 2 days (40C cells). Ir-MENK in PE-1 cells was analyzed by Sephadex G-15 gel filtration and reverse phase (RP)-HPLC. Analysis of 40C cell extract by Sephadex G-15 and RP-HPLC indicated that the major portion of ir-MENK present in PE-1 cells was eluted at a position similar to that of synthetic MENK. The effect of temperature on ir-MENK synthesis in PE-1 cells was examined by measuring ir-MENK content in 33C and 40C cells over a 14-day culture period. Compared to 33C cells, 40C cells maintained higher and steadier levels of ir-MENK, suggesting that synthesis of ir-MENK is temperature sensitive. KCl stimulated ir-MENK secretion at all concentrations tested (5-60 mM for 60 min), with 30 mM being the optimal concentration. Temporal analysis of ir-MENK secretion showed that incubation for 60 min with 30 mM KCl allowed maximal secretion. Secretion of ir-MENK from PE-1 cells resulted in depletion of ir-MENK in cell content. These results demonstrate that PE-1 cells contain ir-MENK which is biochemically similar to synthetic MENK, PE-1 cells synthesize ir-MENK in a temperature sensitive manner, and these cells secrete ir-MENK upon KCl stimulation.