Miyakawa Y, Matsushime H
Molecular Oncology Group, Nippon Roche Research Center, 200 Kajiwara, Kamakura, Kanagawa, 247, Japan.
Biochem Biophys Res Commun. 2001 Jun 1;284(1):71-6. doi: 10.1006/bbrc.2001.4950.
DNA damage causes G1 cell cycle arrest through stabilization of p53 and its induction. As this process requires transcription, it takes several hours to achieve cell cycle arrest. We observed that ultraviolet (UV) light induces an immediate G1 arrest by rapid clearance of cyclin D1 in the murine macrophage cell line Bac1.2F5. The rapid disappearance of the cyclin D1 protein after exposure to UV was caused by at least two different mechanisms. In the first mechanism, cyclin D1 mRNA promptly disappeared within 1 min after UV irradiation, although cdk4 mRNA levels were unchanged. In the second mechanism, UV irradiation accelerated the degradation of cyclin D1 protein through the proteasome pathway. The half-life of the cyclin D1 protein was measured by pulse chase analysis and was shortened by UV light. These findings suggest that in the UV-irradiated Bac1.2F5 cells the amount of cyclin D1 protein is regulated at both the mRNA and protein levels. These two clearance mechanisms were also observed in murine bone-marrow-derived macrophages from wild type and p53 -/- mice, indicating that cyclin D1 mRNA and protein levels are independent of p53 function. This machinery might contribute to G1 cell cycle arrest and prevent cells from accumulating further DNA damage.
DNA损伤通过p53的稳定及其诱导导致G1期细胞周期停滞。由于这一过程需要转录，因此需要数小时才能实现细胞周期停滞。我们观察到，紫外线（UV）通过快速清除鼠巨噬细胞系Bac1.2F5中的细胞周期蛋白D1诱导立即的G1期停滞。暴露于紫外线后细胞周期蛋白D1蛋白的快速消失是由至少两种不同机制引起的。在第一种机制中，尽管cdk4 mRNA水平未改变，但细胞周期蛋白D1 mRNA在紫外线照射后1分钟内迅速消失。在第二种机制中，紫外线照射通过蛋白酶体途径加速细胞周期蛋白D1蛋白的降解。通过脉冲追踪分析测量细胞周期蛋白D1蛋白的半衰期，紫外线使其缩短。这些发现表明，在紫外线照射的Bac1.2F5细胞中，细胞周期蛋白D1蛋白的量在mRNA和蛋白水平上均受到调控。在野生型和p53基因敲除小鼠的鼠骨髓来源巨噬细胞中也观察到这两种清除机制，表明细胞周期蛋白D1 mRNA和蛋白水平与p53功能无关。这种机制可能有助于G1期细胞周期停滞，并防止细胞积累更多的DNA损伤。
