Longworth Michelle S, Herr Anabel, Ji Jun-Yuan, Dyson Nicholas J
Massachusetts General Hospital Cancer Center and Harvard Medical School, Charlestown, Massachusetts 02129, USA.
Genes Dev. 2008 Apr 15;22(8):1011-24. doi: 10.1101/gad.1631508. Epub 2008 Mar 26.
The Drosophila retinoblastoma family of proteins (RBF1 and RBF2) and their mammalian homologs (pRB, p130, and p107) are best known for their regulation of the G1/S transition via the repression of E2F-dependent transcription. However, RB family members also possess additional functions. Here, we report that rbf1 mutant larvae have extensive defects in chromatin condensation during mitosis. We describe a novel interaction between RBF1 and dCAP-D3, a non-SMC component of the Condensin II complex that links RBF1 to the regulation of chromosome structure. RBF1 physically interacts with dCAP-D3, RBF1 and dCAP-D3 partially colocalize on polytene chromosomes, and RBF1 is required for efficient association of dCAP-D3 with chromatin. dCap-D3 mutants also exhibit chromatin condensation defects, and mutant alleles of dCap-D3 suppress cellular and developmental phenotypes induced by the overexpression of RBF1. Interestingly, this interaction is conserved between flies and humans. The re-expression of pRB into a pRB-deficient human tumor cell line promotes chromatin association of hCAP-D3 in a manner that depends on the LXCXE-binding cleft of pRB. These results uncover an unexpected link between pRB/RBF1 and chromatin condensation, providing a mechanism by which the functional inactivation of RB family members in human tumor cells may contribute to genome instability.
果蝇视网膜母细胞瘤蛋白家族（RBF1和RBF2）及其哺乳动物同源物（pRB、p130和p107）最为人所知的是它们通过抑制E2F依赖性转录来调控G1/S期转换。然而，RB家族成员还具有其他功能。在此，我们报道rbf1突变体幼虫在有丝分裂期间的染色质凝聚方面存在广泛缺陷。我们描述了RBF1与dCAP-D3之间的一种新相互作用，dCAP-D3是凝聚素II复合物的非SMC组分，它将RBF1与染色体结构的调控联系起来。RBF1与dCAP-D3发生物理相互作用，RBF1和dCAP-D3在多线染色体上部分共定位，并且RBF1是dCAP-D3与染色质有效结合所必需的。dCap-D3突变体也表现出染色质凝聚缺陷，并且dCap-D3的突变等位基因可抑制由RBF1过表达诱导的细胞和发育表型。有趣的是，这种相互作用在果蝇和人类之间是保守的。将pRB重新表达至pRB缺陷的人类肿瘤细胞系中，以一种依赖于pRB的LXCXE结合裂隙的方式促进hCAP-D3与染色质的结合。这些结果揭示了pRB/RBF1与染色质凝聚之间意想不到的联系，提供了一种机制，通过该机制人类肿瘤细胞中RB家族成员的功能失活可能导致基因组不稳定。
