TY - JOUR
T1 - Regulation of heme synthesis and proteasomal activity by copper
T2 - Possible implications for Wilson's disease
AU - Hait-Darshan, Ravit
AU - Babushkin, Tania
AU - Malik, Zvi
PY - 2009
Y1 - 2009
N2 - Wilson's disease (Wd) is a genetic disorder resulting in Cu2+ accumulation, and is caused by mutations in the ATP7B gene, the copper transporter. In vivo studies show a correlation between Cu2+ accumulation and malfunction of the heme biosynthesis pathway. In this study, we describe multiple effects of Cu2+ accumulation on heme synthesis, which, in turn, affect proteasomal activity. Cu2+ toxicity was examined in two hepatocellular carcinoma cell lines, HepG2 and Hep3B, with Hep3B cells containing an integrated hepatitis B virus genome. Exposure of HepG2 and Hep3B cells to Cu2+ inhibited the enzymes PBGD and ALAD of the heme synthesis pathway and, in parallel, upregulated heme oxygenase-1 (HO-1). Proto-porphyrin IX (PpIX) and the heme pool were reduced as a result of these processes. PpIX synthesis was found to be lower in cells expressing the mutant ATP7B (P1134P), compared to those expressing the WT enzyme. Proteasomal activity was inhibited under Cu2+ treatment in HepG2 cells; however, Cu 2+ induced marked proteosomal acceleration in Hep3B cells. Under these conditions, Ub-conjugated proteins were gradually accumulated, whereas treatment with bathocuproine disulfonic acid (BCS), a Cu2+ chelator, reversed this effect. In conclusion, our data suggest that copper downregulates the heme synthesis pathway in hepatocellular cells and further reduces it in the presence of mutated ATP7B.
AB - Wilson's disease (Wd) is a genetic disorder resulting in Cu2+ accumulation, and is caused by mutations in the ATP7B gene, the copper transporter. In vivo studies show a correlation between Cu2+ accumulation and malfunction of the heme biosynthesis pathway. In this study, we describe multiple effects of Cu2+ accumulation on heme synthesis, which, in turn, affect proteasomal activity. Cu2+ toxicity was examined in two hepatocellular carcinoma cell lines, HepG2 and Hep3B, with Hep3B cells containing an integrated hepatitis B virus genome. Exposure of HepG2 and Hep3B cells to Cu2+ inhibited the enzymes PBGD and ALAD of the heme synthesis pathway and, in parallel, upregulated heme oxygenase-1 (HO-1). Proto-porphyrin IX (PpIX) and the heme pool were reduced as a result of these processes. PpIX synthesis was found to be lower in cells expressing the mutant ATP7B (P1134P), compared to those expressing the WT enzyme. Proteasomal activity was inhibited under Cu2+ treatment in HepG2 cells; however, Cu 2+ induced marked proteosomal acceleration in Hep3B cells. Under these conditions, Ub-conjugated proteins were gradually accumulated, whereas treatment with bathocuproine disulfonic acid (BCS), a Cu2+ chelator, reversed this effect. In conclusion, our data suggest that copper downregulates the heme synthesis pathway in hepatocellular cells and further reduces it in the presence of mutated ATP7B.
KW - ALAD
KW - ATP 7B
KW - PBGD
KW - Proteasome
KW - Protoporphyrin IX
KW - Ubiquitin
UR - http://www.scopus.com/inward/record.url?scp=70449507981&partnerID=8YFLogxK
U2 - 10.1615/jenvironpatholtoxicoloncol.v28.i3.20
DO - 10.1615/jenvironpatholtoxicoloncol.v28.i3.20
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C2 - 19888908
AN - SCOPUS:70449507981
SN - 0731-8898
VL - 28
SP - 209
EP - 221
JO - Journal of Environmental Pathology, Toxicology and Oncology
JF - Journal of Environmental Pathology, Toxicology and Oncology
IS - 3
ER -