Rapid Degradation of Cdt1 upon UV-induced DNA Damage Is Mediated by SCFSkp2 Complex*
- Takeshi Kondo‡§,
- Masanobu Kobayashi¶,
- Junko Tanaka∥,
- Akiko Yokoyama‡,
- Sachiko Suzuki‡,
- Naoko Kato**,‡‡,
- Masahiro Onozawa‡,
- Kohji Chiba‡,
- Satoshi Hashino‡,
- Masahiro Imamura**,
- Yasuhiro Minami‡‡,
- Naoto Minamino∥ and
- Masahiro Asaka‡
- ‡Department of Gastroenterology and Hematology, Hokkaido University Graduate School of Medicine, Kita 15, Nishi 7, Kita-ku, Sapporo, Hokkaido 060-8638, the ¶Division of Cancer Pathobiology, Institute for Genetic Medicine, Hokkaido University, Kita 15, Nishi 7, Kita-ku, Sapporo, Hokkaido 060-8638, the ∥National Cardiovascular Center Research Institute, 5-7-1 Fujishirodai, Suita, Osaka 565-8565, the **Department of Hematology and Oncology, Hokkaido University Graduate School of Medicine, Kita 15, Nishi 7, Kita-ku, Sapporo, Hokkaido 060-8638, and the ‡‡Department of Genome Sciences, Kobe University Graduate School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe 650-0017, Japan
- ↵§ To whom correspondence should be addressed. Tel.: 81-11-716-1161; Fax: 81-11-706-7867; E-mail: t-kondoh{at}med.hokudai.ac.jp.
Abstract
Cdt1 is a licensing factor for DNA replication, the function of which is tightly controlled to maintain genome integrity. Previous studies have indicated that the cell cycle-dependent degradation of Cdt1 is triggered at S phase to prevent re-replication. In this study, we found that Cdt1 is degraded upon DNA damage induced by either UV treatment or γ-irradiation (IR). Although the IR-triggered degradation of Cdt1 was caffeine-insensitive, the UV-triggered degradation of Cdt1 was caffeine-sensitive. This indicates that the cells treated with UV utilize the checkpoint pathway, which differs from that triggered by IR. A recent study has suggested that Cdt1 is phosphorylated, ubiquitylated, and degraded at the G1/S boundary in the normal cell cycle. Treatment with MG132, a proteasome inhibitor, inhibited the degradation of Cdt1 and resulted in the accumulation of the phosphorylated form of Cdt1 after UV treatment. In the case of UV treatment, phosphorylation of Cdt1 induced the recruitment of Cdt1 to a SCFSkp2 complex. Moreover, ectopic overexpression of Cdt1 after UV treatment interfered the inhibition of DNA synthesis. These results indicate that Cdt1 is a target molecule of the cell cycle checkpoint in UV-induced DNA damage.
- Received December 22, 2003.
- Revision received April 5, 2004.
- The American Society for Biochemistry and Molecular Biology, Inc.
