Mittnacht S, Weinberg R A
Whitehead Institute for Biomedical Research, Massachusetts Institute of Technology, Cambridge 02142.
Cell. 1991 May 3;65(3):381-93. doi: 10.1016/0092-8674(91)90456-9.
Hyperphosphorylation of the retinoblastoma protein (pRB) is assumed to be a regulatory event leading to the inactivation of its growth-repressing functions. We demonstrate a functional alteration linked to the phosphorylation status of the protein. The un- or under-phosphorylated species are tightly associated with the nuclear structure. The association is resistant to digestion with nucleases, and release requires elevated salt concentrations. In contrast, the hyperphosphorylated species are eluted under hypotonic buffer conditions. The conversion from low salt-resistant to low salt-extractable pRB occurs with transition through the G1/S boundary of the cell cycle and thus parallels the reported onset of pRB phosphorylation. The ability to form a tight nuclear association is impaired in several naturally occurring pRB mutants, all of which show alterations within the binding region for viral oncoproteins. We suggest that the tight nuclear interaction is essential for the growth-regulating functions of pRB and may be preempted by viral oncoproteins.
视网膜母细胞瘤蛋白（pRB）的过度磷酸化被认为是一种导致其生长抑制功能失活的调节事件。我们证明了一种与该蛋白磷酸化状态相关的功能改变。未磷酸化或磷酸化不足的蛋白与核结构紧密结合。这种结合对核酸酶消化具有抗性，且需要高盐浓度才能释放。相反，过度磷酸化的蛋白在低渗缓冲液条件下被洗脱。从低盐抗性的pRB转变为低盐可提取的pRB发生在细胞周期的G1/S边界过渡时，因此与报道的pRB磷酸化起始过程平行。在几种天然存在的pRB突变体中，形成紧密核结合的能力受损，所有这些突变体在病毒癌蛋白的结合区域内均表现出改变。我们认为紧密的核相互作用对于pRB的生长调节功能至关重要，并且可能被病毒癌蛋白抢先占据。
