title: Onset of hepatocarcinogen-specific cell proliferation and cell cycle aberration during the early stage of repeated hepatocarcinogen administration in rats.
abstract: We have previously reported that a 28-day treatment of carcinogens evoking target cell proliferation activates G1 /S checkpoint function and apoptosis, as well as induction of aberrant ubiquitin D (Ubd) expression, suggesting disruptive spindle checkpoint function, in rats. The present study aimed to determine the onset time of rat liver cells to undergo carcinogen-specific cell cycle aberration and proliferation. Animals were treated orally with a hepatocarcinogenic dose of methyleugenol or thioacetamide for 3, 7 or 28 days. For comparison, some animals were subjected to partial hepatectomy or treated with noncarcinogenic hepatotoxicants (acetaminophen, α-naphthyl isothiocyanate or promethazine). Carcinogen-specific liver cell kinetics appeared at day 28 as evident by increases of cell proliferation, p21(Cip1+) cells, phosphorylated-Mdm2(+) cells and cleaved caspase 3(+) cells, and upregulation of DNA damage-related genes. Hepatocarcinogens also downregulated Rbl2 and upregulated Cdkn1a and Mdm2, and decreased Ubd(+) cells co-expressing phosphorylated-histone H3 (p-Histone H3) and p-Histone H3(+) cell ratio within the Ki-67(+) proliferating population. These results suggest that it takes 28 days to induce hepatocarcinogen-specific early withdrawal of proliferating cells from M phase due to disruptive spindle checkpoint function as evidenced by reduction of Ubd(+) cells staying at M phase. Disruption of G1 /S checkpoint function reflected by downregulation of Rbl2 as well as upregulation of Mdm2 suggestive of sequestration of retinoblastoma protein is responsible for the facilitation of carcinogen-induced cell proliferation at day 28. Accumulation of DNA damage probably in association with facilitation of p53 degradation by activation of Mdm2 may be a prerequisite for aberrant p21(Cip1) activation, which is responsible for apoptosis.
authors.affiliation: Laboratory of Veterinary Pathology, Tokyo University of Agriculture and Technology, Fuchu-shi, Tokyo, Japan.|Pathogenetic Veterinary Science, United Graduate School of Veterinary Sciences, Gifu University, Gifu-shi, Gifu, Japan.
authors.forename: Masayuki
authors.initials: M
authors.lastname: Kimura
authors.affiliation: Laboratory of Veterinary Pathology, Tokyo University of Agriculture and Technology, Fuchu-shi, Tokyo, Japan.|Pathogenetic Veterinary Science, United Graduate School of Veterinary Sciences, Gifu University, Gifu-shi, Gifu, Japan.
authors.forename: Hajime
authors.initials: H
authors.lastname: Abe
authors.affiliation: Laboratory of Veterinary Pathology, Tokyo University of Agriculture and Technology, Fuchu-shi, Tokyo, Japan.|Pathogenetic Veterinary Science, United Graduate School of Veterinary Sciences, Gifu University, Gifu-shi, Gifu, Japan.
authors.forename: Sayaka
authors.initials: S
authors.lastname: Mizukami
authors.affiliation: Laboratory of Veterinary Pathology, Tokyo University of Agriculture and Technology, Fuchu-shi, Tokyo, Japan.|Pathogenetic Veterinary Science, United Graduate School of Veterinary Sciences, Gifu University, Gifu-shi, Gifu, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Tanaka
authors.affiliation: Laboratory of Veterinary Pathology, Tokyo University of Agriculture and Technology, Fuchu-shi, Tokyo, Japan.|Pathogenetic Veterinary Science, United Graduate School of Veterinary Sciences, Gifu University, Gifu-shi, Gifu, Japan.
authors.forename: Megu
authors.initials: M
authors.lastname: Itahashi
authors.affiliation: Laboratory of Veterinary Pathology, Tokyo University of Agriculture and Technology, Fuchu-shi, Tokyo, Japan.
authors.forename: Nobuhiko
authors.initials: N
authors.lastname: Onda
authors.affiliation: Laboratory of Veterinary Pathology, Tokyo University of Agriculture and Technology, Fuchu-shi, Tokyo, Japan.
authors.forename: Toshinori
authors.initials: T
authors.lastname: Yoshida
authors.affiliation: Laboratory of Veterinary Pathology, Tokyo University of Agriculture and Technology, Fuchu-shi, Tokyo, Japan.
authors.forename: Makoto
authors.initials: M
authors.lastname: Shibutani
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D063646:Carcinogenesis / Q000187:drug effects; D002273:Carcinogens / Q000633:toxicity*; D002453:Cell Cycle / Q000187:drug effects*; D049109:Cell Proliferation / Q000187:drug effects*; D005054:Eugenol / Q000031:analogs & derivatives / Q000633:toxicity; D006498:Hepatectomy / Q000009:adverse effects*; D008099:Liver / Q000187:drug effects* / Q000254:growth & development*; D008297:Male; D051381:Rats; D011916:Rats, Inbred F344; D013853:Thioacetamide / Q000633:toxicity
chemical_list: D002273:Carcinogens; D013853:Thioacetamide; C005223:methyleugenol; D005054:Eugenol
keywords: G1/S checkpoint; apoptosis; cell proliferation; hepatocarcinogen; spindle checkpoint; ubiquitin D