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M Mesnil

Publications and source records attributed to M Mesnil.

At least 37 records · Page 2Linked to original sources
PubMed1996

Inhibition of gap junctional intercellular communication and delocalization of the cell adhesion molecule E-cadherin by tumor promoters.

The effect of 12-O-tetradecanoylphorbol-13-acetate (TPA) and benzoyl peroxide (BoP) on gap junctional intercellular communication (GJIC) and the amount and localization of E-cadherin was studied in initiated mouse epidermal cells (3PC) and in carcinoma cells (CA3/7) originating from the same cell type. In addition, the localization and phosphorylation of connexin43 was studied in both cell lines and in primary keratinocytes. GJIC inhibition by TPA and BoP was stronger in primary keratinocytes compared with both cell lines. BoP strongly decreased the amount of E-cadherin protein and the level occurring in the membranes in both cell lines, whereas TPA caused a translocation of E-cadherin from the membrane towards the cytosol, without decreasing the total amount of E-cadherin present. The effect of both tumor promoters on connexin43 phosphorylation and localization was agent as well as cell dependent. These results show for the first time that tumor promoters can decrease the quantity and membrane localization of E-cadherin in different cell types.

Animals↗
PubMed1996

Partial regression, yet incomplete eradication of mammary tumors in transgenic mice by retrovirally mediated HSVtk transfer 'in vivo'.

Mice transgenic for the activated rat neu oncogene under the control of the mouse mammary tumor virus long terminal repeat (MMTV-LTR) (neu+ mice), develop breast tumors in 100% of cases. We have previously reported that double transgenic mice obtained from crossing neu+ mice with mice transgenic for the herpes simplex virus thymidine kinase (HSVtk) gene can be used as a suitable model to test the 'suicide gene' strategy for mammary tumor gene therapy in vivo. In the present study, we evaluated the efficacy of the HSVtk/ganciclovir (GCV) system in the neu+ mice by inoculating cells producing a retroviral vector bearing the HSVtk gene in the mammary tumors on one side of the animals, and comparing their weight with that of the contralateral tumors, after systemic GCV administration. A statistically significant effect of this therapy was clearly seen (P < 0.001) but complete eradication of the tumors could not be achieved. This was not due to the inefficient delivery of GCV, as no HSVtk expression was detected in the residual tumors, but could be related to the low transduction efficiency (< 10%) and to inability of the 'bystander effect' (probably due to the absence of functional gap-junctions among mammary tumor cells) to kill nontransduced neoplastic cells. These data suggest that results obtained by in vivo models using transplanted tumor cell lines as targets for gene therapy might not be immediately transferable to spontaneously arising tumors in animals or humans.

Adenocarcinoma↗
PubMed1995

Negative growth control of HeLa cells by connexin genes: connexin species specificity.

In order to examine whether different connexin gene species exert different degrees of tumor-suppressing activity, we characterized growth characteristics of a gap junction-deficient human cancer cell line, HeLa cells, before and after transfection with cDNA for three different connexins, connexin (cx) 26, cx 40, and cx 43. All transfected cell lines (3 clones transfected with the cx 26 gene, 2 clones with cx 40, and 1 with cx 43) showed establishment of gap junctional intercellular communication (GJIC). Two of the cx 26-transfected clones showed significantly slower growth compared with the parental HeLa cells. When transfectants were grown in soft agar, the three cx 26-transfected clones grew much less than the other transfectants and parent HeLa cells. When injected into nude mice, the two cx 26 clones which exhibited the highest amount of cx 26 transcript induced almost no tumors, whereas other transfectants, including the cx 26 clone which exhibited the lowest amount of cx 26 transcript, were tumorigenic. Among transfectants of various connexin genes, there was no good inverse correlation between their GJIC and tumorigenicity. GJIC levels were significantly higher in tumors induced in nude mice by clone cx 26 A and E transfectants. These results suggest that all of the connexin genes examined could induce recovery of GJIC of HeLa cells, but only the cx 26 gene exerts strong negative growth control on HeLa cells; thus, this connexin gene may have different functions from other connexin genes.

Animals↗
PubMed1995

Echinococcus multilocularis protoscoleces and hepatic cell activity in vitro.

E. multilocularis protoscoleces were co-cultured with hepatic cells in the presence of IAR 20 or BALB/c 3T3 cells. Hepatocyte activity was determined by assaying transferrin and albumin secretion in culture media. The level of these 2 plasma proteins is higher in hepatic/BALB/c 3T3 co-culture medium. In the presence of parasites, the transferrin level is unchanged while the production of albumin is stimulated during the first 48 h. Our results suggest that the albumin production could be attributed to a complex cellular cooperation between hepatocytes and activated Kupffer cells as previously observed in the acute inflammatory reaction.

3T3 Cells↗
PubMed1995

Intercellular communication and carcinogenesis.

Two types of intercellular communication (humoral and cell contact-mediated) are involved in control of cellular function in multicellular organisms, both of them mediated by membrane-embedded proteins. Involvement of aberrant humoral communication in carcinogenesis has been well documented and genes coding for some growth factors and their receptors have been classified as oncogenes. More recently, cell contact-mediated communication has been found to have an important role in carcinogenesis, and some genes coding for proteins involved in this type of communication appear to form a family of tumor-suppressor genes. Both homologous (among normal or (pre-)cancerous cells) as well as heterologous (between normal and (pre)cancerous cells) communications appear to play important roles in cell growth control. Gap junctional intercellular communication (GJIC) is the only means by which multicellular organisms can exchange low molecular weight signals directly from within one cell to the interior of neighboring cells. GJIC is altered by many tumor-promoting agents and in many human and rodent tumors. We have recently shown that liver tumor-promoting agents inhibit GJIC in the rat liver in vivo. Molecular mechanisms which could lead to aberrant GJIC include: (1) mutation of connexin genes; (2) reduced and/or aberrant expression of connexin mRNA; (3) aberrant localization of connexin proteins, i.e., intracytoplasmic rather than in the cytoplasmic membrane; and (4) modulation of connexin functions by other proteins, such as those involved in extracellular matrix and cell adhesion. Whilst mutations of the cx 32 gene appear to be rare in tumors, cx 37 gene mutations have been reported in a mouse lung tumor cell line. Our results suggest that aberrant connexin localization is rather common in cancer cells and that possible molecular mechanisms include aberrant phosphorylation of connexin proteins and lack of cell adhesion molecules. Studies on transfection of connexin genes into tumor cells suggest that certain connexin genes (e.g., cx 26, cx 43 and cx 32) act as tumor-suppressor genes.

Animals↗
PubMed1995

Role of blocked gap junctional intercellular communication in non-genotoxic carcinogenesis.

Gap junctional intercellular communication mediates the transfer of small molecules from the cytoplasm of one cell to that of neighbouring cells. Connexins are the proteins that form the channels responsible for this type of communication. Aberrant expression and function of connexins are often found in cells exposed to tumor-promoting agents and during carcinogenesis, both in cell culture systems and in tissues freshly removed directly from patients and exposed animals. Transfection of connexin genes into tumorigenic cells often exerts negative growth control, suggesting that connexins act as a family of tumor-suppressor genes. Connexin gene mutations appear to be the cause of two human diseases, i.e. X-linked Charcot-Marie-Tooth syndrome and visceroatrial heterotaxia. Connexin genes are therefore important for the maintenance of homeostasis and thus their dysfunction could lead to various forms of disease.

Animals↗
PubMed1995

Inhibition of rat liver gap junction intercellular communication by tumor-promoting agents in vivo. Association with aberrant localization of connexin proteins.

BACKGROUND: Gap junctional intercellular communication is believed to play an important role in the maintenance of tissue homeostasis, and disruption of it has been proposed to be involved in carcinogenesis. A number of tumor-promoting agents have been shown to inhibit capacity for intercellular communication in cell culture studies. Recently, we developed a simple dye-transfer technique to evaluate cell-coupling function in fresh liver slices, and we used it to show that inhibition of intercellular communication is associated with rat liver tumor progression. Using this method with analysis of gap junction protein connexin expression, we have examined whether and how different liver-specific tumor-promoting agents inhibit dye-coupling in rat liver in vivo. EXPERIMENTAL DESIGN: Groups of Fischer 344 rats received repeated chronic treatment of phenobarbital (PB), polychlorinated biphenyls (PCB), dichlorodiphenyltrichloroethane (DDT), and clofibrate (CF) for 5 weeks. After 1, 2, and 5 weeks of treatment, intercellular communication via gap junctions was evaluated by the dye-transfer assay in liver slices taken immediately after killing the rats. In parallel, the expression of connexins (cx) 32, 26, and 43 (gap junction proteins expressed in the liver) was studied at the mRNA and protein levels. RESULTS: All four tumor-promoting agents decreased dye-coupling in rat liver. This decrease was associated with a reduced number of gap junctions and aberrant localization of some amount of cx 32 proteins in hepatocytes; cx 32 often was observed in the cytoplasm of hepatocytes instead of at gap junctions in the plasma membrane. Western blot analysis showed only slight changes in the level of cx 32 proteins. Although cx 26 proteins at gap junctions were usually decreased by tumor promoters in rat liver, local induction of cx 26 protein expression in centrolobular groups of hepatocytes after PCB and DDT treatment was observed. The expression of cx 43 was induced in hepatocytes after PCB, DDT, and CF exposure, but this protein was also localized intracytoplasmically, suggesting no functional role. All four tested tumor-promoting agents also increased cell proliferation, as revealed by staining with an anti-Ki 67 antibody. CONCLUSION: The results demonstrate that different types of liver tumor-promoting agents inhibit dye-coupling in rat liver in vivo. This inhibition may be due to aberrant localization of the major liver gap junction protein cx 32, rather than its transcriptional or translational disregulation.

Animals↗
PubMed1994

Altered homologous and heterologous gap-junctional intercellular communication in primary human liver tumors associated with aberrant protein localization but not gene mutation of connexin 32.

Gap-junctional intercellular communication (GJIC) in 20 primary human liver tumors with different degrees of malignancy has been studied at the functional and molecular levels. When GJIC capacity was determined by dye-transfer assay performed directly with freshly removed tumor tissue, significant reduction was found in all samples, regardless of their morphology. In addition, a selective lack of GJIC between tumor and surrounding non-tumorous cells was observed in some cases, probably due to the physical separation between them resulting from encapsulation of tumors. There was, however, no essential change in the level of expression of the major liver gap-junction protein, connexin (cx) 32, in liver tumors as measured by Northern and Western blot analyses. Immunohistochemical study revealed aberrant localization of cx 32 in the majority of malignant liver tumors. Instead of cytoplasmic membrane localization at intercellular contacts, cx 32 was detected mainly either intracytoplasmically or in plasma membrane free from contact with other cells. We did not detect any mutation in the coding sequence of the cx 32 gene from any of the human liver tumors we tested. Thus it is likely that the aberrant localization of cx 32 in tumor cells is due to disruption of the mechanisms for establishment of this protein into gap-junction plaques, rather than to structural abnormality of the cx 32 protein itself. Another member of the connexin family, cx 43, not detectable in non-tumorigenic hepatocytes, was expressed in several tumors, especially in invasive areas, but was detected in only a few tumor cells and was localized intracytoplasmically, suggesting that cx 43 protein is not involved in GJIC in the tumors.

Adult↗
PubMed1994

Echinococcus multilocularis: in vitro interactions between protoscolices and Kupffer cells.

Echinococcus multilocularis protoscolices collected from experimentally infected jirds were incubated for 2 weeks in rat hepatic cell cultures cocultivated with or without feeder cells (BALB/c 3T3 and IAR 20). Scanning and transmission electron microscopy studies were performed during the course of the culture period. Kupffer cells (Kc) were seen adhering to the anterior and posterior ends of the protoscolices. Some protoscolices were fixed to the cell monolayer by a cluster of Kc adhering to the posterior end of the parasite. These cells were phagocytosing the glycocalyx and the electron-dense distal end of the microthrix of the protoscolex tegument. An alteration in the superficial tegumental cytoplasm with extensive mitochondrial damage was also noted. The properties expressed by Kc against protoscolices in vitro might also be relevant for proliferation of metacestodes in vivo.

Animals↗
PubMed1994

Alteration in expression of gap junction proteins in rat liver after treatment with the tumour promoter 3,4,5,3',4'-pentachlorobiphenyl.

Polychlorinated biphenyls (PCBs) are industrial chemicals which are highly persistent and widely distributed in the environment. We have previously shown that 3,4,5,3',4'-pentachlorobiphenyl (PCB 126) is a potent tumour promoter in two separate 20 week initiation-promotion studies. In the present study, rat livers from these two studies were further investigated for connexin expression. The results demonstrated that treatment with PCB 126 caused a decrease in the amount of the two major liver connexins, cx 26 and cx 32, in livers of treated animals. This reduction was also prominent after treatment at low doses, although gamma-glutamyl transpeptidase-positive foci had not developed in these livers. The quantity of cx 26 and cx 32 in immunostained liver sections was determined using a computerized fluorescence image analyzer. Western blot analysis of liver extracts confirmed these results. No changes in the RNA levels in the treated rats were seen, suggesting that the down-regulation of cx 26 and cx 32 is post-transcriptional.

Animals↗
PubMed1994

Growth suppression of transformed BALB/c 3T3 cells by transforming growth factor beta 1 occurs only in the presence of their normal counterparts.

Transforming growth factor beta 1 (TGF-beta 1) enhances the yield of transformed foci of BALB/c 3T3 cells, but the continuous presence of TGF-beta 1 after foci formation inhibits the growth of transformed foci. The focus-forming ability of Ha-ras-, v-src- and PyMT-transformed cells growing on a monolayer of non-transformed cells was completely suppressed by TGF-beta 1, whereas growth of the transformed cells was little inhibited by TGF-beta 1 in the absence of their normal counterparts. The inhibition by TGF-beta 1 of focus formation by transformed BALB/c 3T3 cells on a normal cell monolayer remained when TGF-beta 1 was removed from the culture medium after 2 weeks. However, the transformed cells were not killed, since they grew in culture conditions under which only transformed cells are able to grow (soft agar). These results suggest that TGF-beta 1 suppresses growth of transformed cells in the presence of normal cells. Furthermore, when non-transformed cells were treated with TGF-beta 1 before co-culture with Ha-ras-transformed cells, formation of transformed foci was inhibited. When normal and transformed cells were cultured in the same dish but separated physically, focus formation was still inhibited. On the other hand, TGF-beta 1 enhanced the growth and changed the morphology of non-transformed cells only in the presence of transformed counterparts. The growth inhibitory effect of TGF-beta 1 on transformed cells and its growth stimulatory effect on non-transformed cells in co-culture conditions suggest the induction of reciprocal paracrine growth regulatory factors. As TGF-beta 1 inhibits the growth of transformed BALB/c 3T3 cells only in the presence of their normal counterparts, a paracrine negative growth control mechanism appears to be operating.

3T3 Cells↗
PubMed1994

Non-communicating human and murine carcinoma cells produce alpha 1 gap junction mRNA.

The gap junctional communication capacity of six human carcinoma-derived tumorigenic cell lines (pancreatic, pharyngeal and cervical), two murine carcinoma-derived tumorigenic cell lines (bladder-derived and Ehrlich ascites) and one monkey non-tumorigenic cell line (kidney epithelium) have been compared by the dye-transfer technique. All the tumorigenic cell lines were communication defective, while the non-tumorigenic cell line was not. Moreover, six of the eight tumorigenic cell lines expressed a gap junction transcript coding for the connexin 43 (alpha 1). Finally, gap junction plaques were not detected between tumorigenic cells by immunofluorescence staining. Consequently, these data suggest that communication defects in tumorigenic cells may result from either abnormally low levels of translation of junction mRNA or alterations in the assembly of junction protein into cell surface plaques, and not from failure to produce junction transcripts. Furthermore, since induction of alpha 1 expression has been associated with dedifferentiation processes, the presence of alpha 1 mRNA might be a characteristic property of certain tumorigenic cells that originate from cells that do not normally express alpha 1 mRNA.

Animals↗
PubMed1994

Expression and function of connexin in normal and transformed human keratinocytes in culture.

We have studied the gap junctional intercellular communication (GJIC) of immortalized and tumourigenic human keratinocyte cell lines and of a spontaneously immortalized non-tumourigenic and a highly differentiating keratinocyte cell line (HaCaT) as the control. In homologous cultures, the GJIC capacity of five squamous cell carcinoma-derived cell lines was 1-27% that of the HaCaT cells. Ha-ras-transfected HaCaT cells with tumourigenic potential and an SV40 DNA-immortalized cell line had markedly reduced GJIC capacities. Northern analysis and immunohistochemistry showed that connexin (Cx) 43 is the major gap junction protein expressed in the communicating cells. They do not express Cx 26 or 32. The low or absent communication observed in certain cell lines was due in some to a lack of Cx 43 gene expression, but in others to aberrant localization of the gap junction protein. GJIC of these cell lines, as well as that of primary normal human epidermal keratinocytes, was susceptible to 12-O-tetradecanoylphorbol-13-acetate-mediated inhibition. Moreover, GJIC of HaCaT cells and their tumourigenic derivatives is Ca(2+)-dependent. These results, when compared with those previously obtained for mouse keratinocyte cell lines, reveal that GJIC of human keratinocytes was correlated to the degree of differentiation and is controlled in a similar way to that of murine keratinocytes. Aberrant GJIC seems to be a common feature of human and murine skin carcinogenesis.

Carcinoma, Squamous Cell↗
PubMed1994

Possible molecular mechanism of loss of homologous and heterologous gap junctional intercellular communication in rat liver epithelial cell lines.

We have previously characterized a series of rat liver epithelial cell lines that exhibit levels of gap junctional intercellular communication (GJIC) which are inversely related to their levels of expression of transformed phenotypes. Cells of the non-tumorigenic line do not communicate with their tumorigenic counterparts. We have examined the molecular mechanisms involved in this loss of homologous and heterologous GJIC, employing a non-tumorigenic cell line, IAR 20, and a tumorigenic cell line, IAR 6-1. While both cell lines expressed a transcript coding for the gap junction protein, connexin 43 (cx 43), and similar levels of cx 43 protein, they exhibited different phosphorylation states of this protein, revealed by Western analysis. Immunohistochemical analysis showed that the non-tumorigenic IAR 20 cell line, but not the tumorigenic IAR 6-1 cells, was able to incorporate cx 43 gap junction plaques extensively into their plasma membranes. When IAR 20 and IAR 6-1 cells were co-cultured, cx 43 proteins were abundant in IAR 20 cells but IAR 20/IAR 20 cell boundaries were cx 43-positive, while IAR 20/IAR 6-1 boundaries were negative. The different phosphorylation state of cx 43 may partially explain the low GJIC of the IAR 6-1 cells and inability to communicate with their non-tumorigenic counterparts, but other mechanisms such as cell-cell recognition processes may also be involved.

Animals↗
PubMed1993

Gap junctional intercellular communication and connexin expression in normal and SV 40-transformed human liver cells in vitro.

The gap junction intercellular communication (GJIC) capacity of two normal human liver-derived epithelial cell strains and their SV40 large T oncogene-transformed counterparts was examined. In homologous cultures the GJIC capacity of the transformed cells was considerably less than the parental cells. In heterologous cultures, transformed cells appeared to be able to form GJIC channels with normal cells. Only non-transformed cells expressed connexin (cx) 43 gene and cx 26 or cx 32 transcripts were not detectable in any cell strains tested. When GJIC was assayed in the presence of the phorbol ester tumour promoter 12-O-tetradecanoylphorbol-13- acetate (TPA), all four strains showed a marked sensitivity to TPA in inhibitory activity at 1-10 ng/ml. In contrast to a rat liver epithelial cell line, this effect of TPA did not appear to become refractory even after 24 h exposure. These studies demonstrate that GJIC of human liver cells in culture can be decreased by viral oncogene and tumour promoter action. Such disturbance may be an important component of the carcinogenic activity of these agents.

Adult↗
PubMed1993

An improved long-term culture of rat hepatocytes to detect liver tumour-promoting agents: results with phenobarbital.

Among various cocultures of hepatocytes with other cell types, we found that mouse embryonal cells (BALB/c 3T3) are more effective in maintaining rat hepatocytes in vitro. Because most human cancers are epithelial in origin, we thought that such a hepatocyte culture system could be used for the detection of tumour-promoting agents, most of which are inhibitors of gap-junctional intercellular communication. We, therefore, have examined the effect of the strong rat liver tumour promoter, phenobarbital, on the gap-junctional intercellular communication capacity of hepatocytes in long-term cultures. A single application of phenobarbital drastically inhibited the gap-junctional intercellular communication between hepatocytes in a coculture for only several hours, but treatment for 3 weeks provoked a constant decrease of gap-junctional intercellular communication (50%) throughout the treatment period. This type of long-term culture of rat hepatocytes may be usable in a rapid in vitro assay to detect tumour-promoting agents.

Albumins↗