Steroidogenesis-inducing protein, isolated from human ovarian follicular fluid, is a potent mitogen for cell lines derived from ovarian surface epithelial carcinomas

DING Proteins Extend to the Extremophilic World

The DING proteins are ubiquitous in the three domains of life, from mesophiles to thermo- and hyperthermophiles. They belong to a family of more than sixty members and have a characteristic N-terminus, DINGGG, which is considered a "signature" of these proteins. Structurally, they share a highly conserved phosphate binding site, and a three dimensional organization resembling the "Venus Flytrap", both reminding the ones of PstS proteins. They have unusually high sequence conservation, even between distantly related species. Nevertheless despite that the genomes of most of these species have been sequenced, the DING gene has not been reported for all the relative characterized DING proteins. Identity of known DING proteins has been confirmed immunologically and, in some cases, by N-terminal sequence analysis. Only a few of the DING proteins have been purified and biochemically characterized. DING proteins are heterogeneous for their wide range of biological activities and some show different activities not always correlated with each other. Most of them have been originally identified for different biological properties, or rather for binding to phosphate and also to other ligands. Their involvement in pathologies is described. This review is an update of the most recent findings on old and new DING proteins.

Mutagenic, surviving and tumorigenic effects of follicular fluid in the context of p53 loss: initiation of fimbria carcinogenesis

Ovulation is the strongest risk factor for ovarian high-grade serous carcinoma (HGSC) that largely originates from the fallopian tube fimbriae and always carries loss-of-function mutations of TP53 in both early and late lesions. Mature ovarian follicle contains high level of reactive oxygen species (ROS). When released from ovulation, follicular fluid (FF) bathes the fimbriae and may lead to DNA double-strand break (DSB) and neoplastic transformation. In this study, we examined the mutagenic and tumorigenic activities of human pre-ovulatory FFs. A subset (6/11) of FFs was found with high levels of ROS whereas the antioxidant capacities were indifferent. These ROS(high) FFs induced intracellular ROS and DSBs in the secretory cell population of fimbriae epithelium. When p53 and Rb were turned down, the FF-exposed secretory cells overcame apoptosis and expanded the population carrying ROS and DSB. The cancer initiation and promotion effects of FF were further recapitulated in Trp53 (-/-) mice. When introduced into the mammary fat pad, ROS(high) but not ROS(low) FFs induced early-onset B-cell lymphoma. Cotreatment with physiological concentration of melatonin, a potent antioxidant, ameliorated the mutagenic and tumorigenic effect of ROS(high) FF in vitro and in vivo. The study revealed ROS and mitogens in mature ovarian follicles could initiate the transformation of fimbria epithelium in the context of p53 loss and melatonin is a potent preventive agent.

Human X-DING-CD4 mediates resistance to HIV-1 infection through novel paracrine-like signaling

X-DING-CD4 is a novel phosphatase mediating antiviral responses to HIV-1 infection. This protein is constitutively expressed and secreted by HIV-1 resistant CD4(+) T cells and its mRNA transcription is up-regulated in peripheral blood mononuclear cells from HIV-1 elite controllers. The secreted/soluble X-DING-CD4 protein form is of particular importance because it blocks virus transcription when added to HIV-1 susceptible cells. The present study aimed to determine the contribution of this factor to the induction of the antiviral response in target cells. We found that soluble X-DING-CD4 enters cells by endocytosis and that influx of this protein induced transcription of interferon-α and endogenous X-DING-CD4 mRNA in transformed CD4(+) T cells and primary macrophages. Treatment of HIV-1 susceptible cells with exogenous X-DING-CD4 caused depletion of phosphorylated p50 and p65 nuclear factor kappa β subunits and a significant reduction in p50/p65 nuclear factor kappa β binding to the HIV-1 long terminal repeat. Taken together, these findings indicate a novel antiviral mechanism mediated by the influx of soluble X-DING-CD4, its signaling to promote self-amplification, and functional duality as an endogenous innate immunity effector and exogenous factor regulating gene expression in bystander cells.

DING proteins from phylogenetically different species share high degrees of sequence and structure homology and block transcription of HIV-1 LTR promoter

Independent research groups reported that DING protein homologues isolated from bacterial, plant and human cells demonstrate the anti-HIV-1 activity. This might indicate that diverse organisms utilize a DING-mediated broad-range protective innate immunity response to pathogen invasion, and that this mechanism is effective also against HIV-1. We performed structural analyses and evaluated the anti-HIV-1 activity for four DING protein homologues isolated from different species. Our data show that bacterial PfluDING, plant p38SJ (pDING), human phosphate binding protein (HPBP) and human extracellular DING from CD4 T cells (X-DING-CD4) share high degrees of structure and sequence homology. According to earlier reports on the anti-HIV-1 activity of pDING and X-DING-CD4, other members of this protein family from bacteria and humans were able to block transcription of HIV-1 and replication of virus in cell based assays. The efficacy studies for DING-mediated HIV-1 LTR and HIV-1 replication blocking activity showed that the LTR transcription inhibitory concentration 50 (IC₅₀) values ranged from 0.052–0.449 ng/ml; and the HIV-1 replication IC₅₀ values ranged from 0.075–0.311 ng/ml. Treatment of cells with DING protein alters the interaction between p65-NF-κB and HIV-1 LTR. Our data suggest that DING proteins may be part of an innate immunity defense against pathogen invasion; the conserved structure and activity makes them appealing candidates for development of a novel therapeutics targeting HIV-1 transcription.

The level of DING proteins is increased in HIV-infected patients: in vitro and in vivo studies

DING proteins constitute an interesting family, owing to their intriguing and important activities. However, after a decade of research, little is known about these proteins. In humans, at least five different DING proteins have been identified, which were implicated in important biological processes and diseases, including HIV. Indeed, recent data from different research groups have highlighted the anti-HIV activity of some DING representatives. These proteins share the ability to inhibit the transcriptional step of HIV-1, a key step of the viral cycle that is not yet targeted by the current therapies. Since such proteins have been isolated from humans, we undertook a comprehensive study that focuses on the relationship between these proteins and HIV-infection in an infectious context. Hence, we developed a home-made ELISA for the quantification of the concentration of DING proteins in human serum. Using this method, we were able to determine the concentration of DING proteins in healthy and HIV-infected patients. Interestingly, we observed a significant increase of the concentration of DING proteins in non treated and treated HIV-infected patients compared to controls. In addition, cell cultures infected with HIV also show an increased expression of DING proteins, ruling out the possible role of antiretroviral treatment in the increase of the expression of DING proteins. In conclusion, results from this study show that the organism reacts to HIV-infection by an overexpression of DING proteins.

Regulation of the proliferative activity of ovarian surface epithelial cells by follicular fluid

Despite critical roles of the ovarian surface epithelium (OSE) in ovulation and post-ovulatory wound repair, little is known about the physiological mechanism regulating OSE proliferation. A role of follicles and corpora lutea in locally regulating the proliferative activity of OSE has been suggested. In this study, the effects of follicular and luteal products on proliferation of cultured OSE cells were tested using cells obtained from seasonally anoestrous ewes. Follicular fluid but not luteal extracts induced OSE cell proliferation (2.5-fold relative to untreated controls; P<0.0001). The response of OSE cells was not affected by follicle size or previous charcoal-extraction of follicular fluid (P>0.1). Treatment with IGF-1 (2.2-fold; P<0.01), EGF (1.9-fold; P<0.01) and, to a lesser extent, FSH (P<0.05) also induced OSE cell proliferation. In contrast, oestradiol or progesterone did not induce cell proliferation or enhance the effects of FSH on proliferation (P>0.1). It was concluded that follicular fluid can directly stimulate ovine OSE cell proliferation and that this effect is attributable to non-steroidal mitogens.

Fibroblast growth factor (FGF), intracellular adhesion molecule (sICAM-1) level in serum and follicular fluid of infertile women with polycystic ovarian syndrome, endometriosis and tubal damage, and their effect on ICSI outcome

PROBLEM

The objective of this study was to determine the concentration of fibroblast growth factor (FGF) and soluble intracellular adhesions molecule (sICAM-1) in serum and follicular fluid (FF) of polycystic ovary (PCO), endometriosis and tubal factor infertility and male factor infertility patients, and to investigate the relationship between these parameters and the outcome of intracytoplasmic sperm injection (ICSI).

METHOD OF STUDY

The concentration of FGF and sICAM-1 in serum and FF were determined in patients undergoing controlled ovarian hyperstimulation (COH) for ICSI therapy for various etiology of infertility and the results of cytokines concentration and ICSI outcome were compared between the groups. Twenty patients with PCO (G.I), 17 with endometriosis (G.II), 19 with tubal damage (G.III) and 19 with male factor infertility (G.IV) were enrolled in this study. Quantitative determination of levels of FGF and sICAM-1 was performed using enzyme-linked immunosorbent assays (ELISAs).

RESULTS

The FGF level in serum of PCO patients (G.I) were 4.8 +/- 2.3 and in FF were 104.0 +/- 39.0 pg/mL. The corresponding values in the endometriosis patients group (G.II) were 5.9 +/- 3.1 and 125.4 +/- 74.9 pg/mL. The concentration of FGF in tubal factor infertility group (G.III) in serum was significantly higher (P = 0.009) than those observed in the PCO group (G.I) 7.4 +/- 4.5 pg/mL, whereas the concentration in FF was at the same level like the other groups investigated, 128.7 +/- 75.9 pg/mL. Besides, the sICAM-1 (pg/ml) concentration in FF showed a significant difference between the groups investigated (G.I, 175.3 +/- 52.8; G.II 194.4 +/- 32.2; G.III 233.1 +/- 54.3; and G.IV 215.1 +/- 54.4 ng/mL; P = 0.003). The sICAM-1 levels in serum were not significantly different between the groups (217.0 +/- 42.9; 216.3 +/- 73.6; 254.8 +/- 79.6; 237.56 +/- 78.4 ng/ml; P = 0.267). The fertilization rate was significantly higher in G.III (66.0 +/- 23.89%) in comparison to G.II (38.8 +/- 33.9%; P = 0.014) or G.IV (38.7 +/- 22.7%; P = 0.012). The pregnancy rates were similar in all groups (30, 35.3 and 35.0, 38.6%, respectively).

CONCLUSION

Both, FGF and sICAM-1 are present in serum and FF of patients undergoing controlled ovarian hyperstimulation for ICSI therapy. The FGF concentration in serum differs significantly between the groups investigated, whereas, no significant difference could be observed in the FF concentration of FGF. On the other hand, the sICAM in serum showed no significant difference between the groups, whereas, sICAM in FF demonstrated a significant difference between the patient groups investigated. On the whole, the ICSI outcome was not related to serum or FF concentrations of FGF or sICAM-1. Therefore, the mean concentration of FGF and sICAM-1 in serum and in FF could not be used to predict the fertilization rate in an ICSI program.

Transforming growth factor-beta inhibits DNA synthesis in immature rat Leydig cells in vitro

TGFbeta isoforms and its receptors are present in the testis and regulate in vitro function of various testicular cells. We have investigated the effects of TGFbeta on basal and mitogen stimulated in vitro proliferation of immature rat Leydig cells. Leydig cells were cultured with TGFbeta1, either alone or in combination with hCG, steroidogenesis-inducing protein (SIP), interleukin-1beta (IL-1beta), insulin or TGFalpha, and the incorporation of [3H]thymidine into DNA was determined. TGFbeta1 blocked the stimulatory effects of hCG, SIP, IL-1beta, insulin and TGF-alpha on DNA synthesis. Since G1- to S-phase transition depends upon cyclins and their associated kinases (cdks), we investigated the effects of TGFbeta on cdks. Immunoreactive levels of cdc2 (or cdk1) and cdk2 were significantly decreased in Leydig cells treated with TGFbeta1. We conclude that TGFbeta1 inhibits proliferation of immature rat Leydig cells and this effect may be mediated, at least in part, through down-regulation of cdc2 and cdk2 synthesis.

Mitogenic activity of steroidogenesis-inducing protein (SIP) during hypoxic stress of human ovarian carcinoma cells

Steroidogenesis-inducing protein (SIP) is a novel growth factor isolated from human ovarian follicular fluid. While the steroidogenic and mitogenic effects appear to be restricted towards gonadal cell types, we have recently demonstrated that SIP is also a potent mitogen for cell lines derived from ovarian surface epithelial carcinomas. Here, we demonstrate that SIP reverses hypoxia-induced cell proliferation arrest of the human ovarian carcinoma cell line SKA, as determined by flow cytometry and cell proliferation assays. Concomitant with this reversal of proliferation arrest is an increase in expression of cyclins D and E and a reduction in expression of the cyclin-dependent kinase inhibitor p27. Pretreatment of hypoxic SKA cells with SIP is also shown to increase Taxol sensitivity of these cells by two-fold. These studies further characterize the mitogenic activity of SIP at the molecular level and suggest that this protein may be an effective biological response modifier for ovarian carcinoma cells.

CD44 splice variant expression in clear cell carcinoma of the ovary

OBJECTIVE

CD44 is a surface glycoprotein widely distributed among different tissues. Malignant tumors may show a more complex pattern of CD44 expression, indicating a loss of splice control. The aim of our study is to investigate the expression of CD44 splice variants (CD44v) and its metastatic potential in clear cell carcinoma of the ovary.

METHODS

Twenty-two cases of clear cell carcinoma of the ovary were evaluated for CD44 standard form (CD44s) and splice variants: -4v, -6v, and -9v expression by immunocytochemistry.

RESULTS

Twenty-one primary ovarian tumors and 23 metastatic sites were available for evaluation. Eighteen of 21 (86%) of ovarian sections studied expressed CD44s; 15/21 (71%) expressed CD44-4v; 14/21 (67%) expressed CD44-6v; and 12/21 (57%) expressed CD44-9v. Of 23 metastatic sites evaluated, 87% expressed CD44s. In contrast, only 5 (22%) metastases had CD44-4v and CD44-6v expression and 8 (35%) had CD44-9v immunoreactivity. None of 10 normal contralateral ovaries expressed CD44s or any splice variants. In 2 cases we had tumor available from the primary surgery, and subsequent recurrences. Both recurrences showed decreased expression of CD44-4v and CD44-6v.

CONCLUSIONS

Clear cell carcinoma of the ovary shows an abnormal pattern of CD44s expression and mRNA splicing when compared to the contralateral normal ovary in the same patient. Metastases of clear cell carcinoma show a downregulation in expression of some splice variants. Furthermore, we have data that suggest that as the tumors recur, CD44s and its isoforms are downregulated. Our results suggest that alternative mRNA splicing of CD44 may be important in the development of metastases from clear cell carcinoma of the ovary.

Activation of Fas ligand/receptor system kills ovarian cancer cell lines by an apoptotic mechanism

The majority of ovarian cancers originate from the surface epithelium of the ovary and from inclusion cysts derived from the epithelium that becomes sequestered in the stroma. To identify naturally occurring ligands that could activate mechanisms by which these ovarian neoplasms could be eliminated, we have examined the ability of anti-Fas mAb to induce apoptosis in two cell lines, HEY and Caov-3, derived from ovarian carcinomas of surface epithelial origin. Treatment of each cell line with anti-Fas mAb caused chromatin condensation, nuclear segmentation, and apoptotic body formation, indicative of apoptosis. Furthermore we have shown that anti-Fas mAb activates the sphingomyelin-ceramide signal transduction pathway. Sphingomyelin levels were measured by normal-phase high-performance liquid chromatography interfaced with electrospray mass spectrometry. The six most abundant sphingomyelin species identified in Caov-3 cells were 34:1 (d18:1/16:0), 36:1 (d18:1/18:0), 40:1 (d18:1/22:0), 41:1 (d18:1/23:0), 42:1 (d18:1/24:0), and 42:2 (d18:1/24:1). Treatment of Caov-3 cells for 30 min caused a 40% decrease in the total sphingomyelin content. Specifically three of these species, 34:1, 40:1, and 42:2, were reduced to 44, 70, and 54% of control values, respectively. The decrease was attributed to the hydrolysis of sphingomyelin. Treatment of these cell lines with ceramide, a product of sphingomyelin hydrolysis, using a cell-permeable synthetic ceramide analogue C2-ceramide, also caused the above cells to undergo apoptosis. Thus, the Fas ligand/receptor system, acting through the sphingomyelin-ceramide pathway, provides a mechanism by which ovarian surface epithelial cancer cells can be induced to undergo apoptosis.