Sun Rui, Fisher Robert P
Department of Oncological Sciences, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA.
Department of Oncological Sciences, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA.
Mol Cell. 2025 May 1;85(9):1743-1759.e5. doi: 10.1016/j.molcel.2025.03.021. Epub 2025 Apr 17.
The RNA polymerase II (RNAPII) transcription cycle is regulated throughout its duration by protein phosphorylation. Previously, two regions phosphorylated by cyclin-dependent kinase 9 (CDK9) in elongation factor SPT5-the linker between Kyrpides-Ouzounis-Woese (KOW) x-4 and 5 domains and carboxy-terminal repeat (CTR) 1-were implicated in promoter-proximal pausing and termination, respectively. Here, we show that phosphorylations in the linker, CTR1, and a third region, CTR2, coordinately control pause release, elongation speed, and termination in HCT116 human colon cancer cells. Pausing was unaffected or increased by mutations preventing CTR1 or CTR2 phosphorylation, respectively, but attenuated when both CTRs were mutated. Whereas loss of CTR1 phosphorylation slowed elongation and repressed nascent transcription, simultaneous CTR2 mutation partially reversed both effects. Nevertheless, mutating both CTRs had additive effects on splicing, termination, steady-state mRNA levels, and cell proliferation. Therefore, tripartite SPT5 phosphorylation times pause release and tunes RNAPII elongation rate to ensure productive transcription and cell viability.
RNA聚合酶II（RNAPII）转录周期在其整个过程中都受到蛋白质磷酸化的调控。此前，在延伸因子SPT5中，细胞周期蛋白依赖性激酶9（CDK9）磷酸化的两个区域——基尔皮德斯-乌祖尼斯-沃斯（KOW）结构域x-4和5之间的连接区以及羧基末端重复序列（CTR）1，分别与启动子近端暂停和终止有关。在此，我们表明，连接区、CTR1以及第三个区域CTR2中的磷酸化协同控制HCT116人结肠癌细胞中的暂停释放、延伸速度和终止。分别阻止CTR1或CTR2磷酸化的突变对暂停没有影响或使其增加，但当两个CTR都发生突变时，暂停减弱。虽然CTR1磷酸化的缺失会减缓延伸并抑制新生转录，但同时CTR2突变会部分逆转这两种效应。然而，两个CTR都发生突变对剪接、终止、稳态mRNA水平和细胞增殖具有累加效应。因此，SPT5的三方磷酸化控制着暂停释放的时间，并调节RNAPII的延伸速率，以确保有效的转录和细胞活力。
