Massachusetts General Hospital Cancer Center and Harvard Medical School, Charlestown, MA.
Broad Institute of Massachusetts Institute of Technology and Harvard, Cambridge, MA.
J Cell Biol. 2022 Mar 7;221(3). doi: 10.1083/jcb.202102144. Epub 2022 Jan 12.
RB restricts G1/S progression by inhibiting E2F. Here, we show that sustained expression of active RB, and prolonged G1 arrest, causes visible changes in chromosome architecture that are not directly associated with E2F inhibition. Using FISH probes against two euchromatin RB-associated regions, two heterochromatin domains that lack RB-bound loci, and two whole-chromosome probes, we found that constitutively active RB (ΔCDK-RB) promoted a more diffuse, dispersed, and scattered chromatin organization. These changes were RB dependent, were driven by specific isoforms of monophosphorylated RB, and required known RB-associated activities. ΔCDK-RB altered physical interactions between RB-bound genomic loci, but the RB-induced changes in chromosome architecture were unaffected by dominant-negative DP1. The RB-induced changes appeared to be widespread and influenced chromosome localization within nuclei. Gene expression profiles revealed that the dispersion phenotype was associated with an increased autophagy response. We infer that, after cell cycle arrest, RB acts through noncanonical mechanisms to significantly change nuclear organization, and this reorganization correlates with transitions in cellular state.
RB 通过抑制 E2F 来限制 G1/S 期进程。在这里，我们表明，持续表达活性 RB 和延长 G1 期停滞会导致染色体结构发生明显变化，而这些变化与 E2F 抑制并无直接关联。我们使用针对两个常染色质 RB 相关区域、两个缺乏 RB 结合位点的异染色质区域以及两个整条染色体探针的 FISH 探针，发现组成性激活的 RB（ΔCDK-RB）促进了更弥散、更分散和更分散的染色质组织。这些变化是 RB 依赖性的，由单磷酸化 RB 的特定同工型驱动，并且需要已知的 RB 相关活性。ΔCDK-RB 改变了 RB 结合基因组位点之间的物理相互作用，但显性负 DP1 对 RB 诱导的染色体结构变化没有影响。RB 诱导的变化似乎广泛存在，并影响核内染色体的定位。基因表达谱显示，分散表型与自噬反应的增加有关。我们推断，在细胞周期停滞后，RB 通过非典型机制作用，显著改变核组织，这种重排与细胞状态的转变相关。
