Changes in the gap junctional intercellular communication in renal tubular epithelial cells in vitro treated with renal carcinogens

Connexin43 is associated with the progression of clear cell renal carcinoma and is regulated by tangeretin to sygergize with tyrosine kinase inhibitors

BACKGROUND

The roles of Connexin43 (Cx43) in clear cell renal cell carcinoma (ccRCC) microenviroment remains to be poorly defined.

METHODS

The expression profile, prognosis and immune analysis of Cx43 in various cancers, particularly in ccRCC were performed using TCGA database, and various biological function assays were applied to explore the physiological role of Cx43 and tangeretin in ccRCC. Western blot were applied to examine the protein expression and Kunming mice were used to evaluate preliminary safety or anti-tumor activity of tangeretin and sunitinib.

RESULTS

Compared with the normal group, higher expression levels of Cx43 in ccRCC, and distinct associations between Cx43 expression and ccRCC prognosis or immune infiltration, were found. Notably, the expression of Cx43 was found to be highly correlated with that of receptor tyrosine kinases (RTKs), particularly with VEGFR1, VEGFR2 and VEGFR3. The expression of Cx43 and EGFR was also found to be higher in ccRCC than that in the para-cancerous specimens. Knocking down Cx43 expression decreased RCC cell viability, cell migration, p-EGFR, MMP-9 and survivin expression. Using 14 Chinese medicine monomers, tangeretin was screened and found to inhibit tumor cell viability and Cx43 expression. Tangeretin also enhanced the sensitivity of RCC cells to tyrosine kinase inhibitors (TKIs) sunitinib and sorafenib. However, the same concentration of tangeretin exerted a less prominent effect on normal renal cell viability.

CONCLUSIONS

Cx43 is strongly associated with RTK expression and ccRCC progression, while tangeretin can inhibit RCC cell malignancy by inhibiting Cx43 expression and enhance the sensitivity of RCC cells to TKIs.

Curcuma longa extracts suppress pathophysiology of experimental hepatic parenchymal cell necrosis

The study sought to investigate the protective potentials of Curcuma longa rhizome following potassium bromate-induced liver injury in Wistar rats. Thirty-five male Wistar rats were divided into 7 groups of 5 rats each (n = 5). Control group received normal saline while the other groups received oral administration of 100 mg/kg potassium bromate daily for two weeks to induce hepatic injury. Negative control I rats were sacrificed immediately after induction of hepatic injury, while the test groups were given oral dose of ethanol extract of Curcuma longa rhizome (EECLOR) at 100, 200 and 400 mg/kg for two weeks. Positive control group was treated with Silymarin for two weeks, while negative control II group was observed for the two-week period. At the end of the study, serum biochemical parameters of liver function enzymes, malondialdehyde and histopathological changes were investigated. Necrotic hepatocytes were quantified in H&E-stained liver sections using the morphologic criteria of typical necrotic tissue. Hepatocytes that remained intact were identified as those with round euchromatic nuclei with prominent nucleoli. Histological examination and morphological grading of the stained sections showed massive necrosis across the zones. EECLOR improved liver functions evidenced by reduced activity of serum amino transferases. It also reduced lipid peroxidation. In addition, there was significant reduction of hepatocytes showing morphological criteria of necrosis in EECLOR-treated rats across the zones, with appreciable radial sinusoidal arrangement. In conclusion, the protective actions of EECLOR against potassium bromate liver toxicity in rats, appears to be due to its ability to reduce lipid peroxidation.

Cell adhesion molecules in chemically-induced renal injury

Cell adhesion molecules are integral cell-membrane proteins that maintain cell-cell and cell-substrate adhesion and in some cases act as regulators of intracellular signaling cascades. In the kidney, cell adhesion molecules, such as the cadherins, the catenins, the zonula occludens protein-1 (ZO-1), occludin and the claudins are essential for maintaining the epithelial polarity and barrier integrity that are necessary for the normal absorption/excretion of fluid and solutes. A growing volume of evidence indicates that these cell adhesion molecules are important early targets for a variety of nephrotoxic substances including metals, drugs, and venom components. In addition, it is now widely appreciated that molecules, such as intracellular adhesion molecule-1 (ICAM-1), integrins, and selectins play important roles in the recruitment of leukocytes and inflammatory responses that are associated with nephrotoxic injury. This review summarizes the results of recent in vitro and in vivo studies indicating that these cell adhesion molecules may be primary molecular targets in many types of chemically-induced renal injury. Some of the specific agents that are discussed include cadmium (Cd), mercury (Hg), bismuth (Bi), cisplatin, aminoglycoside antibiotics, S-(1,2-dichlorovinyl)-l-cysteine (DCVC), and various venom toxins. This review also includes a discussion of the various mechanisms, by which these substances can affect cell adhesion molecules in the kidney.

Ochratoxin A alters cell adhesion and gap junction intercellular communication in MDCK cells

Ochratoxin A (OTA) is one of the most potent renal carcinogens studied to date, but the mechanism of tumor formation by ochratoxin A remains largely unknown. Cell adhesion and cell-cell communication participate in the regulation of signaling pathways involved in cell proliferation and growth control and it is therefore not surprising that modulation of cell-cell signaling has been implicated in cancer development. Several nephrotoxicants and renal carcinogens have been shown to alter cell-cell signaling by interference with gap junction intercell communication (GJIC) and/or cell adhesion, and the aim of this study was to determine if disruption of cell-cell interactions occurs in kidney epithelial cells in response to OTA treatment. MDCK cells were treated with OTA (0-50 microM) for up to 24h and gap junction function was analyzed using the scrape-load/dye transfer assay. In addition, expression and intracellular localization of C x 43, E-cadherin and beta-catenin were determined by immunoblot and immunofluorescence analysis. A clear decrease in the distance of dye transfer was evident following treatment with OTA at concentrations/incubation times which did not affect cell viability. Consistent with the functional inhibition of GJIC, treatment with OTA resulted in a dose-dependent decrease in C x 43 expression. In contrast to C x 43, OTA did not alter total amount of the adherens junction proteins E-cadherin and beta-catenin. Moreover, Western blot analysis of Triton X-100 soluble and insoluble protein fractions did not indicate translocation of cell adhesion molecules from the membrane to the cytoplasm. However, a approximately 78 kDa fragment of beta-catenin was detected in the detergent soluble fraction, indicating proteolytic cleavage of beta-catenin. Immunofluorescence analysis also revealed changes in the pattern of both beta-catenin and E-cadherin labeling, suggesting that OTA may alter cell-adhesion. Taken together, these data support the hypothesis that disruption of cell-cell signaling may contribute to OTA toxicity and carcinogenicity.

Expression of connexins in the normal and obstructed developing kidney

Connections between cells are achieved by proteins called connexins that comprise the gap junction. Connexins play a major role in organ development. Our reverse transcription-polymerase chain reaction (RT-PCR) studies demonstrate that Cx30, Cx36, Cx37, Cx40, Cx45, Cx46, and Cx50 are expressed in the kidney. Quantitative RT-PCR indicates that Cx37, Cx45, and Cx46 are preferentially expressed during early renal development. We also explored the expression of connexins in neonatal unilateral ureteral obstruction (UUO). After 12 days of neonatal UUO, the renal mRNA expression of Cx30, Cx37, and Cx40 was significantly elevated. In contrast, there was no change in connexin renal mRNA levels in adult UUO. We conclude that multiple connexins are expressed in the rat kidney and several are aberrantly expressed in neonatal UUO.

Non-genotoxic carcinogens: early effects on gap junctions, cell proliferation and apoptosis in the rat

Non-genotoxic carcinogens are thought to induce tumour formation by disturbing the balance between cell growth and cell death. Gap junctions (GJ) contribute to the maintenance of tissue homeostasis by allowing the intercellular exchange of growth regulatory signals and potential inhibition of GJ intercellular communication through loss of connexin (Cx) plaques has been shown to be involved in the cancer process. We have investigated the time- and dose-dependent effects of the non-genotoxic hepatocarcinogens Wy-14,643, 2,3,7,8-tetrachlorodibenzo-p-dioxin, methapyrilene and hexachlorobenzene and the male rat kidney carcinogens chloroform, p-dichlorobenzene and d-limonene on gap junction plaque expression in relation to proliferation and apoptosis. With the exception of limonene, all non-genotoxic carcinogens significantly reduced the expression of GJ plaques containing Cx32 in their respective target tissue. No dose-dependent, significant effects were seen in non-target organs. Although alteration of Cx32 expression did not appear to correlate with induction of cell proliferation, out data suggest that the interaction of both processes-interference of GJ coupled with a proliferative stimulus (at the carcinogenic dose)-may be important in non-genotoxic carcinogenesis and provide a potential alert for non-genotoxic carcinogens in short-term toxicity tests.

Antioxidant potential and gap junction-mediated intercellular communication as early biological markers of mercuric chloride toxicity in the MDCK cell line

In this study, the early nephrotoxic potential of mercuric chloride (HgCl(2)) has been evaluated in vitro, by exposing a renal-derived cell system, the tubular epithelial Madin-Darby canine kidney (MDCK) cell line, to the presence of increasing HgCl(2) concentrations (0.1-100 microM) for different periods of time (from 4 to 72 h). As possible biological markers of the tubular-specific toxicity of HgCl(2) in exposed-MDCK cultures we analysed: (i) critical biochemical parameters related to oxidative stress conditions and (ii) gap-junctional function (GJIC). HgCl(2) cytotoxicity was evaluated by cell-density assay. The biochemical analysis of the pro-oxidant properties of the mercuric ion (Hg(2+)) was performed by evaluating the effect of the metal salt on the antioxidant status of the MDCK cells. The cell glutathione (GSH) content and the activity of glutathione peroxidase (Gpx) and catalase (Cat), two enzymes engaged in the H(2)O(2) degradation, were quantified. HgCl(2) influence on MDCK GJIC was analysed by the microinjection/dye-transfer assay. HgCl(2)-induced morphological changes in MDCK cells were also taken into account. Our results, proving that subcytotoxic (0.1-10 microM) HgCl(2) concentrations affect either the antioxidant defences of MDCK cells or their GJIC, indicate these critical functions as suitable biological targets of early mercury-induced tubular cell injury.

Cytotoxicity of adenoviral-mediated cytosine deaminase plus 5-fluorocytosine gene therapy is superior to thymidine kinase plus acyclovir in a human renal cell carcinoma model

PURPOSE

An estimated 11,600 Americans will die of renal cell carcinoma in 1998. The lack of effective chemotherapy or radiotherapy requires the investigation of novel treatment modalities. We compared two forms of toxic gene therapy, cytosine deaminase (CD) plus 5-fluorocytosine (5-FC) and thymidine kinase (TK) plus acyclovir (ACV), in pre-clinical models of human renal cell carcinoma.

MATERIALS AND METHODS

Replication-deficient recombinant adenoviral vectors containing the Rous sarcoma virus promoter driving CD (Ad-RSV-CD) or TK (Ad-RSV-TK) gene expression were constructed and tested for in vitro cell-killing assays at various viral multiplicity of infection (MOI) and in vivo for growth inhibition of a human renal cell carcinoma, SK-RC-29 models. Subcutaneous tumors of SK-RC-29 were examined by electron microscopy for presence of intercellular gap junctions. Levels of expression of the gap junctional associated connexin 43 protein in SK-RC-29, 31, 38, 42, 52 human RCC cell lines were examined by western immunoblotting.

RESULTS

In vitro cell-killing assay comparing Ad-RSV-CD/5F-C and Ad-RSV-TK/ACV at a wide range of MOI (2.5 to 20) revealed superior cell-kill by Ad-RSV-CD/5-FC over Ad-RSV-TK/ACV. Consistent with these results, we observed that Ad-RSV-CD/5-FC but not Ad-RSV-TK/ACV demonstrated a significant in vivo tumor growth inhibition. These results are corroborated by the lack of gap junctions in SK-RC-29 subcutaneous tumors by the electron microscopy and the absence of connexin-43 in all five human RCC cell lines by western immunoblotting.

CONCLUSION

We have demonstrated in this study that Ad-RSV-CD/5-FC is superior to Ad-RSV-TK/ACV for the treatment of human RCC in cell culture and animal models. The results are supported by the lack of gap junctional communication between RCC cells assessed by connexin-43 expression.

All-trans retinoic acid enhances gap junctional intercellular communication among renal epithelial cells in vitro treated with renal carcinogens

Epidemiological and clinical studies imply that retinoids have a chemopreventative action against cancer and can suppress the growth of cancer cells. The regulation of connexin (Cx) expression by retinoids varies among tissues and organs. In this study, we investigated whether all-trans retinoic acid (ATRA) upregulates gap junctional intercellular communication (GJIC) in renal epithelial cells exposed to renal carcinogens. Madin Darby canine kidney (MDCK) cells were incubated with ATRA for 3 days, then briefly exposed to 12-O-tetradecanoyl-phorbol-13-acetate (TPA) or renal carcinogens potassium bromate (KBrO3) and dimethylnitrosamine (DMN). ATRA increased the expression of connexin 43 mRNA and protein without affecting Cx 43 phosphorylation and prevented inadequate Cx 43 localisation caused by TPA/KBrO3 or DMN. Consequently, ATRA prevented the disruption of GJIC in MDCK cells. These data suggest that ATRA enhanced GJIC by upregulating Cx 43 expression and that ATRA might be useful for prevention of renal cell carcinoma.

Disruption of gap junctional intercellular communication in human renal cancer cell lines

OBJECTIVES

Gap junctional intercellular communication (GJIC) is believed to play an important role in the maintenance of cell homeostasis, and its disruption may be associated with carcinogenesis. However, GJIC has not been detected in many human cancers. We therefore studied the regulation of GJIC in human renal cancer cell lines.

METHODS

We examined the human renal cancer cell lines, ACHN and NT, as well as Madin-Darby canine kidney (MDCK) cells as a positive control, using GJIC assays, Northern blotting to detect connexin 43 mRNA, immunofluorescent staining, and Western blotting of connexin 43 protein.

RESULTS

GJIC of ACHN and NT was completely blocked. In ACHN cells, connexin 43 mRNA was not altered. However, connexin 43 protein was aberrantly localized and phosphorylated connexin 43 protein had disappeared. Both connexin 43 protein and its mRNA were undetectable in NT cells.

CONCLUSIONS

GJIC in human renal cancer cell lines is impaired and various pathways may inhibit this mechanism in renal cancer. We believe that connexin plays an important role in renal carcinogenesis.