Regulation of cellular invasion and matrix metalloproteinase activity in HepG2 cell by connexin 26 transfection

Oxytocin inhibits ovarian cancer metastasis by repressing the expression of MMP-2 and VEGF

Breastfeeding is associated with a decreased risk of ovarian cancer. However, the mechanism underlying this apparent clinical benefit is unknown. Oxytocin (OXT), a hypothalamic nonapetide, plays a crucial role in many reproductive and behavioural functions. In recent year, OXT acts as a growth regulator in many kind of tumor tissues, through the activation of a specific G-coupled transmembrane receptor, the oxytocin receptor (OXTR). OXT has been proved to inhibit the proliferation, migration and invasion of ovarian cancer SKOV3 cells in vitro. But, the underlying mechanisms remain unknown. Here, we found OXT inhibited proliferation, and critically migration and invasion of human ovarian cancer cells SKOV3 and A2780. Strikingly, OXT inhibited ovarian cancer metastasis by repressing the expressions of MMP-2 and VEGF. Moreover, OXT inhibited vascular endothelial cell tube formation by reducing the VEGF production from ovarian cancer cells. Our findings may provide a possible explanation for breastfeeding-associated protective effects and suggest new therapeutic opportunities for ovarian cancer.

Multifaceted Roles of Connexin 43 in Stem Cell Niches

Purpose of Review

Considerable progress has been made in the field of stem cell research; nonetheless, the use of stem cells for regenerative medicine therapies, for either endogenous tissue repair or cellular grafts post injury, remains a challenge. To better understand how to maintain stem cell potential in vivo and promote differentiation ex vivo, it is fundamentally important to elucidate the interactions between stem cells and their surrounding partners within their distinct niches.

Recent Findings

Among the vast array of proteins depicted as mediators for cell-to-cell interactions, connexin-comprised gap junctions play pivotal roles in the regulation of stem cell fate both in vivo and in vitro.

Summary

This review summarizes and illustrates the current knowledge regarding the multifaceted roles of Cx43, specifically, in various stem cell niches.

Cx32 suppresses extrinsic apoptosis in human cervical cancer cells via the NF‑κB signalling pathway

Tumour necrosis factor α (TNFα) and TNF‑related apoptosis inducing ligand (TRAIL) usually trigger either survival or apoptosis signals in various cell types, and nuclear factor κB (NF‑κB) is a key factor that regulates their biological effects. Connexin 32 (Cx32) is a gap junction (GJ) protein that plays vital roles in tumourigenesis and tumour progression. Our previous study explored abnormal Cx32 expression in para‑nuclear areas, exacerbated prognostic parameters and suppressed streptonigrin/cisplatin-induced apoptosis in human cervical cancer (CaCx) cells. In this study, we investigated the role of Cx32 in the extrinsic apoptosis pathway of CaCx cells. In transgenic HeLa cells and C-33A cells, Cx32 expression was manipulated using doxycycline or Cx32 siRNA. GJ inhibitors or low density culturing was used to change the status of gap junction intracellular communication (GJIC). We found that apoptosis induced by TNFα and TRAIL was suppressed by Cx32 expression despite the presence or absense of GJIC. We also found that Cx32 upregulated the expression of nuclear NF‑κB and its downstream targets c-IAP1, MMP‑2, and MMP‑9 in HeLa‑Cx32 and C-33A cells. Following our previous study design, our clinical data showed that NF‑κB and MMP‑2 levels increased in human CaCx specimens with high Cx32 expression compared to levels in para‑carcinoma of cervical specimens. SC75741 and JSH-23, NF‑кB signalling pathway inhibitors, inhibited the anti-apoptotic effects of Cx32. In conclusion, Cx32 suppressed TNFα /TRAIL-induced extrinsic apoptosis by upregulating the NF‑κB signalling pathway. This study demonstrates a novel mechanism for Cx32's anti-apoptotic effect and provides a reasonable explanation for the pro-tumour effect of Cx32 in human CaCx cells.

Models and methods for in vitro testing of hepatic gap junctional communication

Inherent to their pivotal roles in controlling all aspects of the liver cell life cycle, hepatocellular gap junctions are frequently disrupted upon impairment of the homeostatic balance, as occurs during liver toxicity. Hepatic gap junctions, which are mainly built up by connexin32, are specifically targeted by tumor promoters and epigenetic carcinogens. This renders inhibition of gap junction functionality a suitable indicator for the in vitro detection of nongenotoxic hepatocarcinogenicity. The establishment of a reliable liver gap junction inhibition assay for routine in vitro testing purposes requires a cellular system in which gap junctions are expressed at an in vivo-like level as well as an appropriate technique to probe gap junction activity. Both these models and methods are discussed in the current paper, thereby focusing on connexin32-based gap junctions.

Connexins, gap junctions and tissue invasion

Formation of metastases negatively impacts the survival prognosis of cancer patients. Globally, if the various steps involved in their formation are relatively well identified, the molecular mechanisms responsible for the emergence of invasive cancer cells are still incompletely resolved. Elucidating what are the mechanisms that allow cancer cells to evade from the tumor is a crucial point since it is the first step of the metastatic potential of a solid tumor. In order to be invasive, cancer cells have to undergo transformations such as down-regulation of cell-cell adhesions, modification of cell-matrix adhesions and acquisition of proteolytic properties. These transformations are accompanied by the capacity to "activate" stromal cells, which may favor the motility of the invasive cells through the extracellular matrix. Since modulation of gap junctional intercellular communication is known to be involved in cancer, we were interested to consider whether these different transformations necessary for the acquisition of invasive phenotype are related with gap junctions and their structural proteins, the connexins. In this review, emerging roles of connexins and gap junctions in the process of tissue invasion are proposed.

Cx31.1 acts as a tumour suppressor in non-small cell lung cancer (NSCLC) cell lines through inhibition of cell proliferation and metastasis

Reduced connexin expression and loss of gap junction function is a characteristic of many cancers, including lung cancer. However, there are little reports about the relation between Cx31.1 and lung cancer. This study was conducted to investigate the effect of Cx31.1 on non-small cell lung cancer (NSCLC). We found that the Cx31.1 was down-regulated in NSCLC cell lines, and the expression levels were reversely related with their metastatic potential. We ectopically expressed Cx31.1 in H1299 NSCLC cell line to examine the influence of Cx31.1 overexpression. The results showed that overexpression of Cx31.1 in H1299 cells reduced cell proliferation, induced a delay in the G₁ phase, inhibited anchorage-independent growth and suppressed cell migration and invasion. The cell cycle delay and cell migration and invasion suppressive effects of Cx31.1 were partially reversed by siRNA targeting mRNA of Cx31.1. Moreover, xenografts of Cx31.1 overexpressing H1299 cells showed reduced tumourigenicity. These results suggested that Cx31.1 has tumour-suppressive properties. Further investigation indicated that cyclin D3 may be responsible for Cx31.1-induced G₁ phase delay. Importantly, Cx31.1 increased the expression of epithelial markers, such as cytokeratin 18, and decreased expression of mesenchymal markers, such as vimentin, indicating a Cx31.1-mediated partial shift from a mesenchymal towards an epithelial phenotype. We concluded that Cx31.1 inhibit the malignant properties of NSCLC cell lines, the mechanisms under this may include regulation of EMT.

Biological role of connexin intercellular channels and hemichannels

Gap junctions (GJ) and hemichannels (HC) formed from the protein subunits called connexins are transmembrane conduits for the exchange of small molecules and ions. Connexins and another group of HC-forming proteins, pannexins comprise the two families of transmembrane proteins ubiquitously distributed in vertebrates. Most cell types express more than one connexin or pannexin. While connexin expression and channel activity may vary as a function of physiological and pathological states of the cell and tissue, only a few studies suggest the involvement of pannexin HC in acquired pathological conditions. Importantly, genetic mutations in connexin appear to interfere with GJ and HC function which results in several diseases. Thus connexins could serve as potential drug target for therapeutic intervention. Growing evidence suggests that diseases resulting from HC dysfunction might open a new direction for development of specific HC reagents. This review provides a comprehensive overview of the current studies of GJ and HC formed by connexins and pannexins in various tissue and organ systems including heart, central nervous system, kidney, mammary glands, ovary, testis, lens, retina, inner ear, bone, cartilage, lung and liver. In addition, present knowledge of the role of GJ and HC in cell cycle progression, carcinogenesis and stem cell development is also discussed.

Contact stimulation of prostate cancer cell migration: the role of gap junctional coupling and migration stimulated by heterotypic cell-to-cell contacts in determination of the metastatic phenotype of Dunning rat prostate cancer cells

BACKGROUND INFORMATION

Motile activity of tumour cells is regarded as a critical factor determining their metastatic potential. We have shown previously that contrary to the majority of normal cells, homotypic contacts between some tumour cells, among them low metastatic (AT-2) and highly metastatic (MAT-LyLu) rat prostate cancer cells, increase the speed of their movements. The aim of the present study was to determine the effect of heterotypic cell-to-cell contacts on the migration of rat prostate cancer cells differing in metastatic potential, and to correlate it with the intensity of homo- and heterologous gap junctional coupling.

RESULTS

MAT-LyLu and AT-2 cells moving on the surface of fibroblasts displayed significantly greater cell displacement than those moving on plastic substrata. This effect correlated with the polarization (contact guidance) and increased speed of cell movements. However, in contrast with the migration on plastic substrata, where MAT-LyLu cells displayed considerably higher motility than AT-2 cells, no differences between both cell lines were observed on the surface of fibroblasts. On the other hand, in contrast with AT-2, Mat-LyLu cells displayed extensive homologous coupling mediated by connexin43 and were able to couple with normal fibroblasts.

CONCLUSION

Heterotypic contacts between migrating prostatic cancer cells and normal fibroblasts can strongly stimulate their migration during invasion; however, this effect does not correlate with the gap junctional coupling between cancer cells and normal fibroblasts.

Non-channel functions of connexins in cell growth and cell death

Cellular communication mediated by gap junction channels and hemichannels, both composed of connexin proteins, constitutes two acknowledged regulatory platforms in the accomplishment of tissue homeostasis. In recent years, an abundance of reports has been published indicating functions for connexin proteins in the control of the cellular life cycle that occur independently of their channel activities. This has yet been most exemplified in the context of cell growth and cell death, and is therefore as such addressed in the current paper. Specific attention is hereby paid to the molecular mechanisms that underpin the cellular non-channel roles of connexin proteins, namely the alteration of the expression of tissue homeostasis determinants and the physical interaction with cell growth and cell death regulators. This article is part of a Special Issue entitled: The Communicating junctions, composition, structure and characteristics.

Reconstitution of secreted frizzled-related protein 1 suppresses tumor growth and lung metastasis in an orthotopic model of hepatocellular carcinoma

BACKGROUND

Secreted Frizzled-related protein 1 (sFRP1) is frequently silenced in many types of cancer, including hepatocellular carcinoma (HCC), leading to aberrant activation of Wnt signaling and thereby facilitating tumor development. In this study, we aimed to investigate whether restoration of sFRP1 affected HCC growth and metastasis.

METHODS

We generated stable cell lines overexpressing sFRP1 in MHCC97-H cells, which naturally do not express detectable sFRP1 messenger RNA (mRNA) and have high metastatic properties. The effects of sFRP1 reexpression on tumor growth and metastasis were assessed in vitro and in vivo. It was also tested whether β-catenin signaling mediated the function of sFRP1 in tumor progression.

RESULTS

Overexpression of sFRP1 substantially diminished the proliferation and invasion potentials of MHCC97-H cells. Furthermore, sFRP1 expression significantly inhibited MHCC97-H xenograft growth and metastasis in vivo, which was accompanied by decreased angiogenesis and increased tumor cell apoptosis. Moreover, sFRP1 overexpression caused less expression of β-catenin and its downstream effector genes cyclin D1 and matrix metalloproteinase (MMP)-2.

CONCLUSION

Together these findings demonstrate that sFRP1 reconstitution suppresses tumor growth, angiogenesis, and metastasis in MHCC97-H xenografts, which may be associated with inactivation of β-catenin signaling, thus providing a possible therapeutic strategy against HCC.

Connexins: sensors and regulators of cell cycling

It is nowadays well established that gap junctions are critical gatekeepers of cell proliferation, by controlling the intercellular exchange of essential growth regulators. In recent years, however, it has become clear that the picture is not as simple as originally anticipated, as structural precursors of gap junctions can affect cell cycling by performing actions not related to gap junctional intercellular communication. Indeed, connexin hemichannels also foresee a pathway for cell growth communication, albeit between the intracellular compartment and the extracellular environment, while connexin proteins as such can directly or indirectly influence the production of cell cycle regulators independently of their channel activities. Furthermore, a novel set of connexin-like proteins, the pannexins, have lately joined in as regulators of the cell proliferation process, which they can affect as either single units or as channel entities. In the current paper, these multifaceted aspects of connexin-related signalling in cell cycling are reviewed.

Cell Adhesion Dynamics and Actin Cytoskeleton Reorganization in HepG2 Cell Aggregates

The temporal dependence of cytoskeletal remodelling on cell-cell contact in HepG2 cells has been established here. Cell-cell contact occurred in an ultrasound standing wave trap designed to form and levitate a 2-D cell aggregate, allowing intercellular adhesive interactions to proceed, free from the influences of solid substrata. Membrane spreading at the point of contact and change in cell circularity reached 50% of their final values within 2.2 min of contact. Junctional F-actin increased at the interface but lagged behind membrane spreading, reaching 50% of its final value in 4.4 min. Aggregates had good mechanical stability after 15 min in the trap. The implication of this temporal dependence on the sequential progress of adhesion processes is discussed. These results provide insight into how biomimetic cell aggregates with some liver cell functions might be assembled in a systematic, controlled manner in a 3-D ultrasound trap.

Changes in expression of Connexin and Par-3 in colorectal cancer

AIM: To study the expression change and characteristics of Connexin and protease activated receptor 3 (Par-3) and to investigate their clinical significance in colorectal tumor.

METHODS: The 51 tissue samples were collected and divided into three groups: tumor tissue group, tissue adjacent to tumor group (2.0 cm), and normal tissue group (apart from tumor >5.0 cm) respectively. Morphological changes of cells were observed using electronic microscopy, histopathological changes were detected using HE staining, and the expressions of Connexin and Par-3 were detected immunohistochemistry and Western blot.

RESULTS: The tumor tissue was deformed and epithelium polarity was vanished, compared with normal tissue. On electronic microscopy, the organelles of the tumor epithelium was in disorder and the structure of cell junctions, such as tight junction, intermediate junction were disarranged or disappeared. For normal tissue group, epithelial cells were regular in shape, the cell polarity was clear, and the cell junction structure was integrated. Immunohistochemistry showed the expression levels of Connexin and Par-3 were gradually decreased, in such order as normal tissue group (0.572 ± 0.051, 0.485 ± 0.042), tissue adjacent to tumor group (0.432 ± 0.049, 0.367 ± 0.035), and tumor tissue of colorectum group (0.290 ± 0.041, 0.227 ± 0.031). There had been significant difference among them (P < 0.05).

CONCLUSION: Down-regulation of Connexin and Par-3 expression is premonition for cancer cell aggravation and metastasis.

Biology and pathobiology of gap junctional channels in hepatocytes

The present review provides the state of the art of the current knowledge concerning gap junctional channels and their roles in liver functioning. In the first part, we summarize some relevant biochemical properties of hepatic gap junctional channels, including their structure and regulation. In the second part, we discuss the involvement of gap junctional channels in the occurrence of liver cell growth, liver cell differentiation, and liver cell death. We further exemplify their relevance in hepatic pathophysiology. Finally, a number of directions for future liver gap junctional channel research are proposed, and the up-regulation of gap junctional channel activity as a novel strategy in (liver) cancer therapy is illustrated.

Peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1alpha) upregulated E-cadherin expression in HepG2 cells

Peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1alpha), a highly inducible transcriptional coactivator regulating energy homeostasis, is down-regulated in hepatoma tissues. To dissect its role in hepato-tumorigenesis, Ingenuity Pathway Analysis was applied to construct pathways affected by PGC-1alpha upregulation in HepG2 hepatoma cells based on our microarray data. Interestingly, migration of these cells was markedly diminished by PGC-1alpha overexpression in consistency with Ingenuity results. Moreover, a deduced expression increase of E-cadherin was also observed in PGC-1alpha-overexpressing HepG2 cells. Finally, transient transfection and chromatin-immunoprecipitation assays suggested that increased histone acetylation might be responsible for PGC-1alpha-mediated transactivation of a minimal E-cadherin promoter.

A redox-silent analogue of tocotrienol inhibits hypoxic adaptation of lung cancer cells

We have previously reported that a redox-silent analogue of alpha-tocotrienol (T3), 6-O-carboxypropyl-alpha-tocotrienol (T3E) shows more potential anti-carcinogenic property than T3 in a lung cancer cell (A549 cell). However, the mechanisms by which T3E exerts its potential anti-carcinogenic effect is still unclear. As tumor malignancy is associated with hypoxia adaptation, in this study, we examined whether T3E could suppress survival and invasion in A549 cells under hypoxia. Hypoxia treatment drastically-induced activation of the protein tyrosine kinase, Src, and its regulated signaling required for hypoxia adaptation of A549 tumor cells. The survival and invasion capacity of the tumor cells under hypoxia was suppressed by T3E via the inactivation of Src. More specifically, T3E-dependent inhibition of Src-induced Akt activation contributed to suppression of cell survival under hypoxia, and the reduction of fibrinolytic factors such as plasminogen activator-1(PAI-1) via the decrease of hypoxia-inducible factor-2alpha by T3E led to inhibition of hypoxic invasion. Overall these results suggest that T3E suppresses hypoxia adaptation of A549 cells by the inhibition in hypoxia-induced activation of Src signaling.

Enhancing effect of connexin 32 gene on vinorelbine-induced cytotoxicity in A549 lung adenocarcinoma cells

PURPOSE

Connexin (Cx) genes exert negative growth effects on tumor cells with certain cell specificity, and tumor-suppressive effects of the Cx genes contribute to enhancement of chemotherapeutical agents-induced cytotoxicity in some cancer cells. Since we and others have been reported that Cx32 acts as a tumor suppressor gene in lung adenocarcinomas, this study was undertaken to estimate if the combination of Cx32-dependent tumor-suppressive effect and vinorelbine (VBN), a chemotherapeutic agent which has been utilized for clinical lung adenocarcinoma treatment, could be effective in enhancing the sensitivity of the lung cancer to VBN treatment.

METHODS

We established the A549 cells (a human lung adenocarcinoma cell line) which had stable expression of Cx32 and estimated effect of Cx32 on VBN-induced cytotoxicity in the established cells.

RESULTS

Cx32 expression in A549 cells significantly potentiated VBN-induced cytotoxicity on the cells due to enhancement of apoptosis induction. The enhancing cytotoxicity in A549 cells by Cx32 mainly depended on a decrease in expression of multi-drug resistance-1 (MDR-1) gene responsible for reduction of VBN accumulation into the cells. We also observed that silencing of Cx32 by siRNA treatment elevated the expression level of MDR-1 mRNA in A549 cells and that inhibition of MDR-1 gene product-dependent function enhanced VBN-induced cytotoxicity in the cells.

CONCLUSION

These results suggest that Cx32 contributes to the enhancement of VBN-induced cytotoxicity in A549 cells via the reduction of MDR-1 expression.

Connexin 32 potentiates vinblastine-induced cytotoxicity in renal cell carcinoma cells

We have reported that connexin (Cx) 32 gene, a member of gap junction protein family, acts as a tumor suppressor gene in human renal cell carcinoma (RCC). Of solid tumors, RCC is one of the most chemoresistant cancers, and there is no effective cancer chemotherapy against RCC at present. In this study, we examined if the combination of Cx32-dependent tumor-suppressive effect and vinblastine (VBL), a chemotherapeutic agent which has been utilized for clinical RCC treatment, could be effective in enhancing the sensitivity of RCC to VBL treatment. Cx32 expression in a human metastatic RCC cell (Caki-1 cell) significantly enhanced in vitro and in vivo VBL-induced cytotoxicity on the cell. Cx32 expression in the RCC cells potentiated VBL-induced apoptosis compared to the Cx32-negative RCC cells in vitro as well as in vivo. The enhancing apoptosis in the RCC cells by Cx32 mainly depended on the decrease of P-glycoprotein (P-gp), a multidrug resistance gene-1 (MDR-1) product responsible for reduction of VBL accumulation into the cells. We also observed that silencing of Cx32 by short interfering RNA (siRNA) treatment elevated the level of P-gp in Caki-1 cells and that inhibition of P-gp function enhanced VBL-induced apoptosis in the RCC cells. These results suggest that Cx32 is effective to enhance VBL-induced cytotoxicity in Caki-1 cells via the reduction of P-gp. Overall, it seems that the combination of Cx32-dependent tumor-suppressive effect and VBL is promising as a new cancer therapy against RCC.

Involvement of cell junctions in hepatocyte culture functionality

In liver, like in other multicellular systems, the establishment of cellular contacts is a prerequisite for normal functioning. In particular, well-defined cell junctions between hepatocytes, including adherens junctions, desmosomes, tight junctions, and gap junctions, are known to play key roles in the performance of liver-specific functionality. In a first part of this review article, we summarize the current knowledge concerning cell junctions and their roles in hepatic (patho)physiology. In a second part, we discuss their relevance in liver-based in vitro modeling, thereby highlighting the use of primary hepatocyte cultures as suitable in vitro models for preclinical pharmaco-toxicological testing. We further describe the actual strategies to regain and maintain cell junctions in these in vitro systems over the long-term.

Connexin 32 as an anti-invasive and anti-metastatic gene in renal cell carcinoma

Cellular homeostasis in many organs is maintained via gap junctions composed of connexin (Cx), a large protein family with a number of isoforms. In fact, gap junctional intercellular communication (GJIC) is actively involved in all aspects of the cellular life cycle, ranging from cell growth to cell death. It has been well known that Cx gene acts as a tumor suppressor gene due to the maintenance of cellular homeostasis via GJIC. On the other hand, recent data show that GJIC-independent function for Cx gene contributes to tumor-suppressive effect of the gene with cell certain specificity. However, the mechanistic aspect of the GJIC-independent function remains largely unknown. In this review, we briefly summarize the tumor-suppressive effects of Cx genes, refer to a new aspect of Cx32 as an anti-invasive and anti-metastatic gene against renal cell carcinoma in a GJIC-independent function and establishment of a new cancer therapy based on the new function of Cx32.

Gata3 is required for early morphogenesis and Fgf10 expression during otic development

Inner ear develops from an induced surface ectoderm placode that invaginates and closes to form the otic vesicle, which then undergoes a complex morphogenetic process to form the membranous labyrinth. Inner ear morphogenesis is severely affected in Gata3 deficient mouse embryos, but the onset and basis of the phenotype has not been known. We show here that Gata3 deficiency leads to severe and unique abnormalities during otic placode invagination. The invagination problems are accompanied often by the formation of a morphological boundary between the dorsal and ventral otic cup and by the precocious appearance of dorsal endolymphatic characteristics. In addition, the endolymphatic domain often detaches from the rest of the otic epithelium during epithelial closure. The expression of several cell adhesion mediating genes is altered in Gata3 deficient ears suggesting that Gata3 controls adhesion and morphogenetic movements in early otic epithelium. Inactivation of Gata3 leads also to a loss of Fgf10 expression in otic epithelium and auditory ganglion demonstrating that Gata3 is an important regulator of Fgf-signalling during otic development.

Connexin32 as a tumor suppressor gene in a metastatic renal cell carcinoma cell line

Connexin genes expressing gap junction proteins have tumor-suppressive effects on primary cancers with certain cell specificity, but the suppressive effects on metastatic cancers are still conflicting. In this study, we show that connexin32 (Cx32) has a strong tumor-suppressive effect on a human metastatic renal cell carcinoma cell line (Caki-1 cell). Cx32 expression in Caki-1 cells reduced in vitro malignant phenotypes of the cells such as anchorage independency and invasion capacity. Furthermore, the Cx32 expression drastically reduced the development of Caki-1 cells in nude mice. We also determined that Cx32 reduced the malignant phenotypes in Caki-1 cells mainly through the inactivation of Src signaling. Especially, Cx32-dependent inactivation of Src decreased the production of vascular epithelial growth factor (VEGF) via the suppression of signal transducers and activators of transcription 3 (Stat3) activation, and we confirmed this result using short interfering RNA. In nude mice, Cx32-transfected Caki-1 cells showed lower serum level of VEGF comparing mock transfectant, and the development of the cells in nude mice positively related to the VEGF level. These data suggest that Cx32 acts as a tumor suppressor gene in Caki-1 cells and that the tumor-suppressive effect partly depends on the inhibition of Src-Stat3-VEGF signal pathway.

Oxytocin inhibits the progression of human ovarian carcinoma cells in vitro and in vivo

The neurohypophyseal nonapeptide oxytocin (OT) is involved in many biologic functions and regulation of cell proliferation under both physiologic and neoplastic conditions. In some cases, OT exhibits an oxytocin receptor (OTR)-mediated antiproliferative effect on cancer cells. In this study, we examined the effects of OT on ovarian carcinoma progression in vitro and in vivo. We investigated the inhibitory effects of OT on cell growth, invasion and migration in vitro. Furthermore, we examined the OT effects in vivo ovarian carcinoma model. We demonstrated OTR expressions in the large majority of ovarian carcinoma tissues, and OT inhibited not only proliferation but also migration and invasion in ovarian carcinoma cells in vitro. Furthermore, we examined the mechanisms of the antiinvasive ability of OT. Secretion of matrix metalloproteinase 2 was slightly inhibited by 10(-7) M OT, while treatment with 10(-7) M OT for 24 hr remarkably enhanced the expression of E-cadherin. In addition, our in vivo study showed that intraperitoneal administration of OT resulted in the reduction of intraperitoneal dissemination of ovarian carcinoma cells. Mean tumor burden in the OT-treated group (0.2 +/- 0.11 g) was significantly (p < 0.05) less than that of physiologic saline-treated group (0.5 +/- 0.54 g). This evidence implies that OT may functionally suppress peritoneal dissemination in ovarian carcinoma.

Down-regulation of connexin 32 gene expression through DNA methylation in a human renal cell carcinoma cell

BACKGROUND

We have recently reported that connexin (Cx) 32 is down-regulated in a human renal cell carcinoma (RCC) cell (Caki-2 cell).

HYPOTHESIS

We postulated that the down-regulation of Cx32 gene in the RCC cell is due to hypermethylation of its promoter region.

METHODS

We estimated methylation status in the promoter region of Cx32 gene in the RCC cell by DNA digestion with methylation-sensitive restriction enzyme and PCR, and methylation-specific PCR (MSP). We also checked the recovery of Cx32 gene expression in the RCC cell treated with a DNA methyltranferase inhibitor, 5-Aza-2'-deoxycytidine (5-Aza-CdR).

RESULTS

Treatment with 5-Aza-CdR resulted in induction of Cx32 expression in the RCC cell. Hypermethylation of the Cx32 promoter region in the RCC cell was confirmed by DNA digestion with methylation-sensitive restriction enzyme and PCR, and MSP.

CONCLUSION

We suggest that hypermethylation in the promoter region is a mechanism for the Cx32 gene repression in the RCC cell.