Preventive effect of germanium dioxide on the inhibition of gap junctional intercellular communication by TPA.
Gap junctional intercellular communication (GJIC) is thought to be essential for maintaining cellular homeostasis and growth control. In order to detect any protective agent against tumor formation, we examined the anticarcinogenic effect of a germanium dioxide (GeO(2)) using a model system of GJIC in F344 rat liver epithelial cells, named WB cells. 12-O-tetradecanoylphorbol-13-acetate (TPA), known as tumor promoters, inhibited GJIC in the epithelial cells as determined by the scrape loading/dye transfer (SL/DT) assay. And GeO(2) recovered this inhibition of GJIC. Immunostaining of connexin 43 (Cx43) protein in WB cells indicated that TPA caused a loss of Cx43 protein from the cell membranes. However, GeO(2) treatment showed re-appearance of Cx43 protein on the membrane. Reverse transcription-polymerase chain reaction (RT-PCR) and Western blots were analyzed to determine whether the test compounds might have altered the steady-state levels of gap junction mRNA and/or connexin protein levels or phosphorylation. The inhibition of GJIC by TPA in WB cells was correlated with the hyperphosphorylation of Cx43 as measured by mobility shifts of the western blot bands of Cx43. TPA induced hyperphosphorylation of Cx43 protein, while GeO(2) appeared to partially block this hyperphosphorylation. Here, we showed that pre- and co-incubation with GeO(2) in TPA-treated WB-cells abolished down-regulation of GJIC by TPA. These data suggest that GeO(2) may inhibit tumor promotion by enhancing GJIC.
Kang
K S
KS
Department of Veterinary Public Health, College of Veterinary Medicine and School of Agricultural Biotechnology, Seoul National University, 103 Seodun-dong, Kwonsun-ku, 441-744, Suwon, South Korea.
Yun
J W
JW
Yoon
B
B
Lim
Y K
YK
Lee
Y S
YS
D000818:Animals; D016588:Anticarcinogenic Agents / Q000494:pharmacology*; D002450:Cell Communication / Q000187:drug effects*; D002460:Cell Line; D018031:Connexin 43 / Q000032:analysis; D017630:Connexins / Q000032:analysis; D004847:Epithelial Cells / Q000187:drug effects; D005455:Fluorescent Antibody Technique; D017629:Gap Junctions / Q000187:drug effects*; D005857:Germanium / Q000494:pharmacology*; D010766:Phosphorylation; D051381:Rats; D011916:Rats, Inbred F344; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013755:Tetradecanoylphorbol Acetate / Q000037:antagonists & inhibitors*
D016588:Anticarcinogenic Agents; D018031:Connexin 43; D017630:Connexins; D005857:Germanium; C040516:germanium oxide; D013755:Tetradecanoylphorbol Acetate