Differential Changes in Expression of Gap Junction Proteins Connexin 26 and 32 during Hepatocarcinogenesis in Rats

Sakamoto, Hirofumi; Oyamada, Masahito; Enomoto, Katsuhiko; Mori, Makoto

doi:10.1111/j.1349-7006.1992.tb02747.x

Cited by 48 publications

(26 citation statements)

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“…30 Furthermore, reduced expression of Gjb2 (Cx26) is known to contribute to the promotion and progression of hepatocarcinogenesis in rats. 31 Of interest, our microarray analysis unveiled the altered expression of genes involved in Wnt/b-catenin signaling; down-regulation of the Wnt antagonist Sox17 (P ¼ 0.009), up-regulation of a Wnt downstream effector Cyclin D1 (P ¼ 0.001), and modestly increased expression of the Wnt receptor Fzd7 (P ¼ 0.098). Wnt/b-catenin signaling is integrally associated with the regulation of stem cells and development of cancer 32 and activated Wnt/b-catenin signaling promotes the proliferation and transformation of hepatic stem/progenitor cells.…”

Section: Discussionmentioning

confidence: 95%

Bmi1promotes hepatic stem cell expansion and tumorigenicity in bothInk4a/Arf-dependent and -independent manners in Mice

et al. 2010

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We previously reported that forced expression of Bmi1 (B lymphoma Moloney murine leukemia virus insertion region 1 homolog) in murine hepatic stem/progenitor cells purified from fetal liver enhances their self-renewal and drives cancer initiation. In the present study, we examined the contribution of the Ink4a/Arf tumor suppressor gene locus, one of the major targets of Bmi1, to stem cell expansion and cancer initiation. Bmi1 2/2 Deltalike protein (Dlk) 1 hepatic stem/progenitor cells showed de-repression of the Ink4a/Arf locus and displayed impaired growth activity. In contrast, Ink4a/Arf 2/2 Dlk 1 cells gave rise to considerably larger colonies containing a greater number of bipotent cells than wild-type Dlk 1 cells. Although Ink4a/Arf 2/2 Dlk 1 cells did not initiate tumors in recipient nonobese diabetic/severe combined immunodeficiency mice, enforced expression of Bmi1 in Ink4a/Arf 2/2 Dlk 1 cells further augmented their self-renewal capacity and resulted in tumor formation in vivo. Microarray analyses successfully identified five downregulated genes as candidate downstream targets for Bmi1 in hepatic stem/progenitor cells. Of these genes, enforced expression of sex determining region Y-box 17 (Sox17) in Dlk 1 cells strongly suppressed colony propagation and tumor growth. Conclusion: These results indicate that repression of targets of Bmi1 other than the Ink4a/Arf locus plays a crucial role in the oncogenic transformation of hepatic stem/progenitor cells. Functional analyses of Bmi1 target genes would be of importance to elucidate the molecular machinery underlying hepatic stem cell system and explore therapeutic approaches for the eradication of liver cancer stem cells.

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Section: Discussionmentioning

confidence: 95%

Bmi1promotes hepatic stem cell expansion and tumorigenicity in bothInk4a/Arf-dependent and -independent manners in Mice

et al. 2010

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“…A recent review of the ability of chemicals with tumor-promoting or tumor-inhibiting activity to modulate GJIC reports that more than 100 substances have been shown to inhibit GJIC (1). The inhibition of GJIC appears to be the most common property of chemicals with tumor-promoting activity; however, phenobarbital (PB), a liver tumor promoter (2, lo), has shown mixed results (negative andlor positive) in iit vitro assays (1).…”

Section: Introduction Gap Junctional Intercellular Communication (Gjimentioning

confidence: 99%

Effect of Phenobarbital on Hepatic Gap Junctional Intercellular Communication in Rats

et al. 1998

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The effects of in v i w exposure to phenobarbital (PB) on hepatic gap junctional intercellular communication (GJIC) and conncxin protein expression in Sprague-Dawley rats were examined by in vivolirn virro dye-transfer assay, immunohistochemical staining, and by Western blot analysis. PB (50 mgkg) was administered orally once a day for up to 6 wk. The average size of the dye spread after injection of Lucifer Yellow decreased at week 1 and remained at the same level until \veek 6. The area and number of connexin 32 (Cx32) spots pcr hcpatocyte in the central zone of liver lobules decreased from week 1 to week 6, but no change of Cx32 spots in thc pcriphcral zone was obscrvcd. Thc average area and number of connexin 26 (Cx26) spots per hepatocytes showed no clear change through thc cxpcrimcntal pcriods. Thc dccrcascd level of Cx32 protein in plasma membranes was observed in the PB group. These results suggest that PB, a liver tumor-promoting agent, inhibits hepatic GJIC in vivo in rats and that aberrant Cx32 protein expression and/or localization may be responsible for this effect.Kejwords. Liver; gap junction; connexin; tumor promoter INTRODUCTION Gap junctional intercellular communication (GJIC) is considered to play an important role in carcinogenesis. A recent review of the ability of chemicals with tumor-promoting or tumor-inhibiting activity to modulate GJIC reports that more than 100 substances have been shown to inhibit GJIC (1). The inhibition of GJIC appears to be the most common property of chemicals with tumor-promoting activity; however, phenobarbital (PB), a liver tumor promoter (2, lo), has shown mixed results (negative andlor positive) in iit vitro assays (1). It was reported that PB (0.05% in diet) diminished the total area and size of rat hepatocyte gap junctions by freeze-fracture analysis in vivo (12). The level of gap junction protein mRNA in rat liver was observed to be markedly reduced at 4 and 11 wk of PB exposure (0.1% in drinking water) (7). However, there have been few studies that examine the hepatic gap junctional functions of rats exposed to PB iii vivo (5). We have studied the effect of DDT on hepatic GJIC in rats and clearly demonstrated that DDT inhibited hepatic GJIC and caused aberrant connexin 32 (Cx32) and connexin 26 (Cx26) protein expression iii vivo (13). This study was conducted to demonstrate the inhibition of hepatic GJIC in rats exposed to PB-iiz vivo and compare these results with the effects of DDT In the present study, the effects of PB on hepatic GJIC of rats treated orally with PB (50 mglkgiday) for up to 6 wk were examined by iit vivoiiit vitro dye-transfer assay using freshly removed liver slices. Localization of the hepatic gap junction proteins, Cx32 and Cx26, and protein levels of

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“…Isolation and Culture of Rat Hepatocytes. Male Sprague-Dawley rats (Shizuoka Laboratory Animal Center, Hamamatsu, Japan) (range, Culture time after treatment was calculated as 0, 3,8,24,48,72,96, and 120 hours from day 10 ( Fig. 1).…”

Section: Dmso Shift Protocol Hepatocytes Used In Dmso Shift Experimementioning

confidence: 99%

“…The cells were scraped, collected in eppendorf tubes, and then sonicated for 30 medium 24 hours before the fixation. The polyclonal anti-Cx32, 8 seconds. The sonicates were centrifuged at 4,500g for 10 minutes.…”

Section: Aid Hepa 0061mentioning

confidence: 99%

“…11,[28][29][30][31] In 1985, EGF with 10 mmol/L nicotinamide for 48 hours, the cells were cultured in Isom et al first reported that adult rat hepatocytes in a chemi-the modified DMEM medium containing EGF with 10 mol/L nicotinamide cally defined medium supplemented with EGF and 2% plus 2% DMSO and 10 07 mol/L glucagon until day 15 (condition 2). Culture time after treatment is calculated as 0, 3,8,24,48,72,96, and 120 hours DMSO survived much longer and synthesized albumin much from day 10 after plating.…”

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Different changes in expression and function of connexin 26 and connexin 32 during DNA synthesis and redifferentiation in primary rat hepatocytes using a DMSO culture system

et al. 1997

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recovery of GJIC measured by lucifer yellow was later thanIn the present study, we determined in detail the changes that of Cx32 expression. These results indicated the different of liver gap junctions, connexin 26 (Cx26), and connexin 32 changes of expression and function of Cx26 and Cx32 in the (Cx32), during DNA synthesis and redifferentiation of hepatohepatocytes during stimulation and re-inhibition of DNA syncytes in vitro. We used primary rat hepatocytes that expressed thesis. This culture system should be useful as a model in the liver gap junction proteins, which were cultured in the which to study liver gap junctions during hepatocyte growth medium containing epidermal growth factor (EGF) with 2% and differentiation in vitro. (HEPATOLOGY 1997;26:585-597.) dimethylsulfoxide (DMSO) and 10 07 mol/L glucagon (a DMSO culture system), as we previously reported. In the present cultures, almost confluent hepatocytes cultured in the medium Gap junctions are intercellular membrane channels that containing EGF with 2% DMSO and 10 07 mol/L glucagon, link neighboring cells and mediate reciprocal exchanges of underwent a nearly synchronous wave of DNA synthesis insmall molecules of less than 1,000 Da and ions, including duced by the removal of 2% DMSO and 10 07 mol/L glucagon, second messengers, such as cyclic adenosine monophosphate and the addition of 10 mmol/L nicotinamide, after which the inositol triphosphate, and Ca 2/ , between adjacent cells in DNA synthesis was completely re-inhibited by the re-addition contact. [1][2][3][4] Gap junctions are composed of proteins termed of 2% DMSO and 10 07 mol/L glucagon. During stimulation of ''connexins (Cxs)''. 5 Both Cx26 and Cx32 are expressed in DNA synthesis, both Cx26 and Cx32 messenger RNA hepatocytes, and it is known that the relative ratios of Cx26 (mRNAs) in hepatocytes transiently increased in the G1 phase protein and messenger RNA (mRNA) in rat livers to those and then markedly decreased before the onset of the S phase, of Cx32 are 1:10 and 1:50, respectively. 6,7 The distribution while only Cx26 messenger RNA (mRNA) increased slightly of these Cx proteins is reported to be different within the in the S/M phase. Furthermore, before the onset of the S phase, liver lobules: Cx26 preferentially localizes in the periportal a disappearance of both Cx26 and Cx32 immunoreactivities zone of the lobules, whereas Cx32 appears in most hepatoand gap junction plaques were observed. Gap junctional intercytes throughout the lobules. 8,9 They have been colocalized cellular communication (GJIC), as measured by lucifer yellow, to the same gap junction plaques in hepatocytes. 6,10,11 Furwhich indicated the function of Cx32, decreased markedly from thermore, more recently, Kumar and Gilula 12 reported that before the onset of the S phase. GJIC measured by propidium gap junction channels in the mouse liver are heterotypic iodide, which indicated the function of Cx26, decreased from channels, which dock among heteromeric connexons combefore the onset of the S phase and then increas...

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Differential Changes in Expression of Gap Junction Proteins Connexin 26 and 32 during Hepatocarcinogenesis in Rats

Cited by 48 publications

References 21 publications

Bmi1promotes hepatic stem cell expansion and tumorigenicity in bothInk4a/Arf-dependent and -independent manners in Mice

Bmi1promotes hepatic stem cell expansion and tumorigenicity in bothInk4a/Arf-dependent and -independent manners in Mice

Effect of Phenobarbital on Hepatic Gap Junctional Intercellular Communication in Rats

Different changes in expression and function of connexin 26 and connexin 32 during DNA synthesis and redifferentiation in primary rat hepatocytes using a DMSO culture system

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