Fluorescent laser scanning microscopy of F-actin disruption in human endometrial stromal cells expressing the SV40 large T antigen and the EJ ras oncogene

Phospholipase D1 as a key enzyme for decidualization in human endometrial stromal cells

Using primary cell cultures of human endometrial stromal cells (ES cells), we investigated the role of phospholipase D (PLD) in 8-Br-cAMP-induced decidualization, which involves morphological and biological differentiation processes. When treated with 0.5 mM 8-Br-cAMP for 12 days, ES cells were transformed into a decidualized morphology and produced significant amounts of prolactin (PRL) and insulin-like growth factor-binding protein 1 (IGFBP1). Simultaneously, the activity and expression levels of PLD1 increased. In addition, removal of 8-Br-cAMP from decidualized ES cells restored the undifferentiated state, and this was accompanied by decreases in PLD1 promoter activity and PLD1 expression. Overexpression of dominant negative (DN)-PLD1 inhibited the morphological changes induced by 0.5 mM 8-Br-cAMP, whereas PLD1 overexpression induced morphological changes in the absence of 0.5 mM 8-Br-cAMP treatment. Moreover, knockdown of PLD1 by siRNA and blockage of PLD by treatment with 0.3% 1-butanol decreased PRL/IGFBP1 mRNA expression, whereas PLD1 overexpression increased PRL/IGFBP1 mRNA expression. Treatment of ES cells with phosphatidic acid (PA) for 3 days induced PRL mRNA expression and morphological changes, which implies that PA is an end-product of PLD activation-induced decidualization. In addition, pretreatment of ES cells with mepacrine decreased PRL/IGFBP1 expression and inhibited morphological change, whereas pretreatment with propranolol caused no changes, as compared to cAMP-treated cells, which suggests that PA induces decidualization through phospholipase A2 (PLA2G1B). Taken together, these results suggest that PLD1 regulates 8-Br-cAMP-induced decidualization through PLA2G1B, and that PLD1 upregulation is essential for the decidualization of ES cells.

Peroxide resistance in human and mouse lens epithelial cell lines is related to long-term changes in cell biology and architecture

It is well established that the response of the cell to environmental stress is a major basis for cell modification. Such modification is believed to adapt the cell to better survive its environment. Oxidative stress, a major and ubiquitous stressing factor, was selected for investigating the cellular response to stress. Most studies investigating such cellular response have employed examination of the cell either during or shortly after exposure to stress. We have employed a different approach arguing that the short-term response to stress obscures the biological changes that allow the cell to continue to thrive in its new environment. Reflecting this concept, murine and human cell lines capable of surviving regular exposure to toxic levels of H(2)O(2) or TBOOH have been developed. It was found that certain fundamental long-term changes in cell biology had occurred. The peroxide-resistant cells are diploid rather than aneuploid, show fundamental changes in the cytoskeletal cellular structure, suggesting less rigid more flexible cells, express a new lower molecular mass of p53, a key stress protein responder involved in adaptation, and finally have an immunochemical modification in alphaA-crystallin, a small heat-shock protein. Previously, it was found that there is a dramatic increase in catalase and gluthathione S-transferase activity and a remarkable limited change in expression in other antioxidative genes in these cells. The impact of these changes is discussed. It is apparent that evolutionary cell modifications can occur in response to relatively rapid changes in environment over periods ranging from days to months rather than the thousands of years considered in most evolutionary modifications.

U-937 monocyte-mediated c-Jun dephosphorylation and AP-1 activation in human endometrial stromal cells

OBJECTIVE

To determine paracrine effects of monocytes/macrophages on c-Jun dephosphorylation and AP-1 DNA binding activity in human endometrial stromal cells.

STUDY DESIGN

Conditioned medium (CM) was prepared from human monocyte U-937 cells in serum-free medium. Subconfluent immortalized human endometrial stromal N5 cells were serum-starved for 24 h and cultured in the CM or the control medium for 30 min, 1, 3, 8, 16 or 24 h. Nuclear extracts were prepared and phosphorylated and dephosphorylated c-Jun isoforms were detected by Western blot analysis and the DNA binding activity was evaluated by electrophoretic mobility shift assay. Data on protein levels and DNA binding activity were analyzed statistically by ANOVA using SAS programs.

RESULTS

c-Jun was dominantly in the phosphorylated state in N5 cells cultured in the control medium. The CM induced c-Jun accumulation and dephosphorylation and increased AP-1 DNA binding activity in a time-dependent manner.

CONCLUSION

U-937 cells induce c-Jun dephosphorylation and AP-1 activation in human endometrial stromal cells by paracrine factors. Further investigations are needed to characterize the nature of these paracrine factors and their signaling pathways leading to AP-1 activation.

Retinoic acid signaling through PI 3-kinase induces differentiation of human endometrial adenocarcinoma cells

The specific signals required for actin polymerization in response to extracellular factors remain unknown. However, in many cell types, there is a correlation between actin polymerization, activation of phosphatidylinositol 3-kinase (PI 3-kinase), and the production of the second messenger phosphatidylinositol-3,4,5-triphosphate. Increased levels of PI 3-kinase have been detected during cell growth and transformation. However, PI 3-kinase is also activated during differentiation, suggesting that PI 3-kinase and its lipid products also play a role in the regulation of cellular differentiation. The newly characterized CAC-1 cell line established from a poorly differentiated human endometrial adenocarcinoma (Exp. Mol. Pathol. 69 (2000), 175) was used as a model to investigate the role of PI 3-kinase in differentiation induction. CAC-1 cells differentiated upon treatment with pharmacological doses of retinoids (1 micro M of 13-cis or all-trans), evidenced by actin filament reorganization, and cell enlargement. PI 3-kinase staining is primarily localized to perinuclear regions in untreated cells. However, retinoic acid treatment induced PI 3-kinase to relocalize throughout the cytoplasm. Subcellular fractionation and Western blotting confirmed that PI 3-kinase decreased in the particulate fraction, concurrent with retinoid-induced differentiation. Interestingly, pretreatment with the PI 3-kinase inhibitor wortmannin (100 nM) prior to retinoic acid treatment prevented retinoic acid-induced actin reorganization and cell enlargement. To distinuish whether retinoid regulation of PI 3-kinase is mediated through traditional nuclear retinoic acid receptors, the levels of retinoic acid receptor-beta (RAR-beta) protein were evaluated. Retinoid treatment did not alter RAR-beta protein levels compared to controls. These data suggest that PI 3-kinase activity and cytoplasmic relocalization are required for retinoid-induced differentiation of poorly differentiated human endometrial adenocarcinoma cells.

A newly characterized human endometrial adenocarcinoma cell line (CAC-1) differentiates in response to retinoic acid treatment

A new cell line of poorly differentiated human endometrial adenocarcinoma cells termed "CAC-1" cells has been established. These cells are epithelial, as indicated by positive cytokeratin and negative vimentin staining. They are rounded and possess a high nuclear-to-cytoplasmic ratio, desmosomes, surface microvilli, intercelular lumens, and pleomorphic nuclei containing multiple nucleoli. These cells have been in long-term culture for 2 years. Our previous studies demonstrated that moderately differentiated (RL95-2) cells differentiated in response to retinoic acid treatment, illustrated by their reorganization of actin filaments and cell enlargement (Carter et al., 1996; Anticancer Res. 16, 17-24). CAC-1 cells exhibited a similar response because they also organized actin filaments and enlarged in response to retinoic acid treatment. Concurrently, retinoic acid treatment caused a 40% decrease in cell detachment in an in vitro detachment assay compared to controls. A slight lag in cell growth was observed when CAC-1 cells were treated with 1 microM 13-cis or all-trans retinoic acid during a 12-day growth curve. In addition, we examined the effects of retinoic acid on protein kinase C-alpha (PKC-alpha) and myristoylated alanine-rich C-kinase substrate (MARCKS). Treatment with retinoic acid caused cytoplasmic PKC-alpha to increase concomitant with a decrease in PKC-alpha in the membrane. In contrast, MARCKS increased in the membrane in response to retinoic acid treatment. These data indicate that retinoid treatment causes inactivation of PKC-alpha, allowing MARCKS to relocalize to the membrane, where it can cross-link actin filaments. CAC-1 cells represent an ideal model for investigating the effects of retinoids on differentiation induction concomitant with actin reorganization.

Retinoic acid affects the EGF-R signaling pathway during differentiation induction of human endometrial adenocarcinoma cells

We have shown that moderately differentiated endometrial adenocarcinoma (RL95-2) cells differentiate in response to retinoic acid treatment, illustrated by their reorganization of actin filaments and cell enlargement (Carter et al., Anticancer Res. 16, 17-24, 1996). Tyrphostin, an inhibitor of epidermal growth factor receptor (EGF-R)-associated protein tyrosine kinases, caused a dramatic reorganization of actin filaments in RL95-2 cells, similar to retinoic-acid-treated cells (Carter and Bellido, J. Cell. Physiol. 178, 320-332, 1999). We evaluated the possibility that the differentiating effects of retinoids are due to retinoic-acid-induced decreases in phosphorylation of EGF-R and changes in downstream effector proteins. Retinoic acid caused a decrease in tyrosine phosphorylation of EGF-R. Retinoic acid treatment induced a dramatic actin filament reorganization and cell enlargement. Treatment with EGF reversed this effect, because cells treated with retinoic acid followed by EGF only possessed disrupted actin aggregates and appeared small, thus resembling medium controls. Retinoic acid induced a relocalization and decrease in the amount of Shc protein, another actin-binding protein which is an adaptor protein for EGF-R signaling. In addition, retinoic acid induced a relocalization of gelsolin from the plasma membrane to the cytoplasm. Retinoic acid decreased cell detachment in detachment assays; one-half as many retinoic-acid-treated cells detached as in controls. These results are consistent with the idea that retinoic acid induces differentiation of RL95-2 cells by interfering with the EGF-R signaling pathway.

Tyrosine phosphorylation and subcellular localization of focal adhesion proteins during in vitro decidualization of human endometrial stromal cells

Human endometrial stromal cells undergo in vitro decidualization when treated with progesterone and estrogen. Using this model, we previously reported specific changes in the c-Src kinase activity and tyrosine phosphorylation of several proteins during in vitro decidualization. Focal adhesion kinase (FAK) and paxillin are known to form a complex with c-Src at the focal contacts and to participate in the integrin-mediated signal transduction as c-Src substrates. We here examined the tyrosine phosphorylation and subcellular localization of the focal adhesion proteins in stromal cells isolated from human endometrium. We found, however, that the total levels of FAK and paxillin tyrosine phosphorylation were not markedly changed during decidualization or after steroid withdrawal. In our culture system numerous multicellular nodules were developed in cultures of decidualized stromal cells, within whose nodules the focal contacts were found to disappear. Moreover, disruption of the focal contacts was accompanied by disorganization of the actin-based cytoskeleton. These findings suggest that tyrosine phosphorylation of the endometrial paxillin and FAK is not tightly regulated by the kinase activity of c-Src during in vitro decidualization. The escape from regulation by c-Src may be in part due to the dissociation of the focal adhesion proteins/c-Src complex caused by the breakdown of the focal adhesion plaques as well as the loss of the actin-based cytoskeletal architecture.

Decrease in protein tyrosine phosphorylation is associated with F-actin reorganization by retinoic acid in human endometrial adenocarcinoma (RL95-2) cells

Transformed cells often express elevated levels of tyrosine-phosphorylated proteins. Inhibition of protein tyrosine kinases causes reversion of malignant cells to the normal phenotype. In the present study, we evaluated the possibility that the reversion of human endometrial adenocarcinoma RL95-2 cells to a stationary phenotype induced by retinoic acid was associated with inhibition of tyrosine phosphorylation of cellular proteins. We found that retinoic acid decreased the levels of tyrosine-phosphorylated proteins, as assessed by immunostaining and immunoprecipitations using specific anti-phosphotyrosine antibodies. In addition, the inhibitors of tyrosine kinases herbimycin A and tyrphostin mimicked retinoic acid, inducing F-actin reorganization and increasing the size of RL95-2 cells, as determined by measurement of cell perimeters. Because focal adhesions that connect actin filaments with the plasma membrane are major sites of tyrosine phosphorylation, we further investigated whether selected focal adhesion proteins were affected by retinoic acid. We found that retinoic acid altered the localization of focal adhesion kinase. All-trans retinoic acid was effective in reducing the levels of focal adhesion kinase and paxillin protein. Thirteen-cis retinoic acid increased the levels of vinculin protein in the cytosolic fraction of cells. These changes are consistent with actin reorganization and reversion toward a stationary phenotype induced by retinoic acid in endometrial adenocarcinoma RL95-2 cells. Our results indicate that the differentiating effects of retinoids on endometrial cells are associated with decreases in tyrosine phosphorylation and changes in the levels and distribution of focal adhesion proteins. These findings suggest that signaling pathways that involve tyrosine kinases are potential targets for drug design against endometrial cancer.

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.