Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, Japan.
Plant Signal Behav. 2011 Sep;6(9):1394-6. doi: 10.4161/psb.6.9.16877.
The proteasome pathway regulates many aspects of biological processes in plants, such as plant hormone signaling, light responses, the circadian clock and regulation of cell division. Key cell-cycle regulatory proteins including B-type cyclins, Cdc6, cyclin-dependent kinase inhibitors and E2Fc undergo proteasome-dependent degradation. We used the proteasome inhibitor MG132 to show that proteolysis of Arabidopsis RETINOBLASTOMA-RELATED 1 (AtRBR1) and three E2Fs is mediated by the proteasome pathway during sucrose starvation in Arabidopsis suspension MM2d cells. We found previously that estrogen-inducible RNAi-mediated downregulation of AtRBR1 leads to a higher frequency of arrest in G2 phase, instead of G1-phase arrest in the uninduced control, after sucrose starvation. Degradation of not only negative (AtRBR1 and E2Fc) but also positive (E2Fa and E2Fb) cell cycle regulators after sucrose starvation may be required for arrest in G1 phase, when cells integrate a variety of nutritional, hormonal and developmental signals to decide whether or not to commit to entry into the cell cycle.
蛋白酶体途径调节植物中许多生物学过程的方面，如植物激素信号转导、光反应、生物钟和细胞分裂的调节。包括 B 型细胞周期蛋白、Cdc6、细胞周期蛋白依赖性激酶抑制剂和 E2Fc 在内的关键细胞周期调节蛋白经历蛋白酶体依赖性降解。我们使用蛋白酶体抑制剂 MG132 表明，在拟南芥悬浮 MM2d 细胞的蔗糖饥饿期间，拟南芥视网膜母细胞瘤相关蛋白 1 (AtRBR1) 和三种 E2F 的蛋白酶体途径介导了它们的降解。我们之前发现，雌激素诱导的 RNAi 介导的 AtRBR1 下调导致蔗糖饥饿后 G2 期阻滞的频率更高，而不是未诱导对照中的 G1 期阻滞。蔗糖饥饿后，不仅负调控（AtRBR1 和 E2Fc），而且正调控（E2Fa 和 E2Fb）细胞周期调节剂的降解，可能是 G1 期阻滞所必需的，此时细胞整合各种营养、激素和发育信号，以决定是否进入细胞周期。
