Hypo-phosphorylation of the retinoblastoma protein (pRb) by cyclin D:Cdk4/6 complexes results in active pRb
Hypo-phosphorylation of the retinoblastoma protein (pRb) by cyclin D:Cdk4/6 complexes results in active pRb
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DOI：
10.1073/pnas.94.20.10699
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发表时间：
1997-09-30
影响因子：
11.1
通讯作者：
Dowdy, SF
中科院分区：
文献类型：
--
作者：
Ezhevsky, SA;Nagahara, H;Dowdy, SF
在循环细胞中，视网膜母细胞瘤蛋白（pRb）在G早期(1)处于非磷酸化和/或低磷酸化状态，在G晚期(1)变为超磷酸化状态。低磷酸化的作用和相关激酶的身份仍然未知。我们在这里表明，低磷酸化的pRb在体内与E2F相关，因此具有活性。通过转化生长因子β处理角质形成细胞，增加细胞内Cdk4/6特异性抑制剂p15（INK4b）的浓度，导致G(1)阻滞和低磷酸化pRb的丧失，同时增加未磷酸化的pRb。相反，p15（INK4b）独立的转化生长因子β介导的G(1)阻滞肝癌细胞导致Cdk2激酶活性的丧失，而Cdk6激酶活性持续，pRb仅保持低磷酸化。通过融合Cdk4/6抑制剂p16（INK4a）蛋白进入细胞的蛋白转导结构域也可以防止pRb的低磷酸化，增加未磷酸化的pRb。我们得出结论，细胞周期蛋白D:Cdk4/6复合物在G早期低磷酸化pRb(1)，允许持续的E2F结合。
In cycling cells, the retinoblastoma protein (pRb) is un- and/or hypo-phosphorylated in early G(1) and becomes hyper-phosphorylated in late G(1). The role of hypophosphorylation and identity of the relevant kinase(s) remains unknown. We show here that hypo-phosphorylated pRb associates with E2F in vivo and is therefore active. Increasing the intracellular concentration of the Cdk4/6 specific inhibitor p15(INK4b) by transforming growth factor beta treatment of keratinocytes results in G(1) arrest and loss of hypo-phosphorylated pRb with an increase in unphosphorylated pRb, Conversely, p15(INK4b)-independent transforming growth factor beta-mediated G(1) arrest of hepatocellular carcinoma cells results in loss of Cdk2 kinase activity with continued Cdk6 kinase activity and pRb remains only hypo-phosphorylated, Introduction of the Cdk4/6 inhibitor p16(INK4a) protein into cells by fusion to it protein transduction domain also prevents pRb hypo-phosphorylation with an increase in unphosphorylated pRb. We conclude that cyclin D:Cdk4/6 complexes hypo-phosphorylate pRb in early G(1) allowing continued E2F binding.