Graduate School of Science and Technology, Shizuoka University, Ohya 836, Suruga-ku, Shizuoka, 422-8021, Japan.
Course of Biological Science, Department of Science, Graduate School of Integrated Science and Technology, Shizuoka University, Ohya 836, Suruga-ku, Shizuoka, 422-8021, Japan.
Biochem Biophys Res Commun. 2020 Aug 27;529(3):846-853. doi: 10.1016/j.bbrc.2020.05.122. Epub 2020 Jun 15.
The yeast E2F functional homologs MBF (Mbp1/Swi6) and SBF (Swi4/Swi6) complexes are critical transcription factors for G1/S transition. The target of rapamycin complex 1 (TORC1) kinase promotes G1/S transition via upregulation of the G1 cyclin Cln3 that activates MBF and SBF in favorable nutrient conditions. Here, we show evidence that TORC1 directly regulates G1/S transition via MBF and SBF. Various proteins involved in G1/S transition, including Mbp1 and Swi4, but not Swi6, were largely lost after rapamycin treatment. TORC1 inactivation facilitated degradation of Mbp1 and Swi4. Mbp1 degradation was dependent on Skp1-Cullin1-F-box (SCF)-Grr1 and proteasomes. We identified a PEST-like degron in Mbp1. Mutant cells with an unstable Mbp1 protein were hypersensitive to rapamycin and more accumulated G1 cells in the absence and presence of rapamycin. This study revealed that TORC1 directly controls MBF/SBF-mediated G1/S transition in response to nutrient availability.
酵母 E2F 功能同源物 MBF（Mbp1/Swi6）和 SBF（Swi4/Swi6）复合物是 G1/S 转换的关键转录因子。雷帕霉素复合物 1（TORC1）激酶通过上调 G1 周期蛋白 Cln3 促进 G1/S 转换，Cln3 激活有利营养条件下的 MBF 和 SBF。在这里，我们提供了证据表明 TORC1 通过 MBF 和 SBF 直接调节 G1/S 转换。雷帕霉素处理后，各种参与 G1/S 转换的蛋白质，包括 Mbp1 和 Swi4，但不包括 Swi6，大量丢失。TORC1 失活促进了 Mbp1 和 Swi4 的降解。Mbp1 降解依赖于 Skp1-Cullin1-F-box（SCF）-Grr1 和蛋白酶体。我们在 Mbp1 中鉴定了一个 PEST 样降解结构域。具有不稳定 Mbp1 蛋白的突变细胞对雷帕霉素敏感，并且在没有和存在雷帕霉素的情况下，更多地积累 G1 期细胞。这项研究表明，TORC1 直接控制 MBF/SBF 介导的 G1/S 转换，以响应营养物质的可用性。
