***** seminarMLから情報転載 *****


日時 : 平成21年 9月 25日 (金曜日) 15:00 ~ 16:00
会場 : (財)東京都医学研究機構 東京都臨床医学総合研究所 2階講堂
演題 :Identification of cellular mechanisms required for the
recovery from DNA replication fork arrest
演者 :Dr. Kenji Shimada&s_comma; Project Leader&s_comma; Friedrich Miescher
Institute for Biomedical Research (FMI)
The mechanisms that control DNA damage repair and genome stability
are highly conserved. They require components of the checkpoint
control pathway&s_comma; including mammalian ATR-ATRIP / S. cerevisiae
Mec1-Ddc2&s_comma; a member of the PI3 kinase family. ATR /Mec1 activates
both S and G2/M checkpoints. A specific Mec1 allele&s_comma; mec1-100&s_comma;
retains the ability to activate the G2/M checkpoint&s_comma; but is deficient
for the S-phase checkpoint response. Stalled replication forks are
partially destabilized in the mec1-100 strain. A parallel pathway
that ensures replication fork stability requires Sgs1 in S.
cerevisiae&s_comma; which is a homologue of conserved RecQ helicase. Cells
bearing both mec1-100 and sgs1_ mutations grow normally but have high
rates of gross chromosomal rearrangements. They show enhanced
sensitivity to hydroxyurea (HU)&s_comma; which inhibits ribonucleotide
reductase&s_comma; and other inhibitors of DNA replication. Recently it has
been shown that evolutionarily conserved TOR (target of rapamycin)
pathway is also involved in the recovery from the replication fork
associated damage. Since the fork associated damage is a hallmark of
many cancer cells&s_comma; we are interested in identifying the pathways that
accentuate the lethality of current cancer drugs that interfere in
fork progression. We screened for and identified a set of compounds
that exhibit hypersensitivity to HU in either mec1-100 or sgs1_
single mutant but not in the wild-type cells. Here we show the effect
of these compounds on the stability of stalled replication fork and
the recovery from the fork arrest. We also examined the effect of
these compounds in combination with other reagents that generate DNA
alkylation (MMS) or double strand breaks; DSBs (Camptothecin&s_comma;
Zeocin). Two compounds exhibited a selective toxicity to mec1-100
only when combined with HU and retarded the fork elongation.
Interestingly we observed that another compound&s_comma; PI3 kinsae -TOR
pathway inhibitor&s_comma; exhibited a strong synergistic toxicity not only
with HU but also with Zeocin. This suggests that TOR pathway is also
required for the efficient recovery from DSBs. We are further
elucidating the mechanism of action of those compounds in mammalian
cells and in S. cerevisiae.
〔世話人:ゲノム動態プロジェクト 正井 久雄〕

Hisao Masai
Genome Dynamics Project&s_comma;
Tokyo Metropolitan Institute of Medical Science&s_comma;
2-1-6 Kamikitazawa&s_comma; Setagaya-ku&s_comma; Tokyo 156-8506&s_comma; JAPAN
Tel: 81-3-5316-3231 Fax: 81-3-5316-3145; E-mail: masai-hs@igakuken.or.jp

正井 久雄
東京都臨床医学総合研究所 ゲノム動態プロジェクト
郵便番号 156-8506
所在地  東京都世田谷区上北沢二丁目1番6号
正井直通電話 03-5316-3231
研究室電話 03-5316-3117
研究室FAX 03-5316-3145
E-mail masai-hs@igakuken.or.jp