DISTINCT SUBPOPULATIONS OF THE RETINOBLASTOMA PROTEIN SHOW A DISTINCT PATTERN OF PHOSPHORYLATION
DISTINCT SUBPOPULATIONS OF THE RETINOBLASTOMA PROTEIN SHOW A DISTINCT PATTERN OF PHOSPHORYLATION
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DOI：
10.1002/j.1460-2075.1994.tb06241.x
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发表时间：
1994-01-01
期刊：
影响因子：
11.4
通讯作者：
WEINBERG, RA
中科院分区：
文献类型：
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作者：
MITTNACHT, S;LEES, JA;WEINBERG, RA
视网膜母细胞瘤蛋白（pRB）的磷酸化被认为是调节其生长控制功能。此外，pRB的低磷酸化和高磷酸化形式可以通过它们与细胞核结合的不同亲和力来区分。该性质允许鉴定含有一种或另一种形式的pRB的单个细胞核。我们在此表明，细胞从静止（G（0））状态出现后，其pRB补体转化为过度磷酸化形式发生在G（1）晚期，在进入S期之前数小时。因此，与早期的报道相反，pRB磷酸化与G（1）-S转换不协调，可能不直接调节它。一组独特的磷酸肽专门存在于那些表现出pRB过度磷酸化形式的松散核缔合特征的pRB形式中。另一组磷酸肽被发现具有低磷酸化和高磷酸化形式。这表明存在与pRB分子的不同子集相关的不同磷酸化模式。我们的结论是，即使在过度磷酸化点之前，G（1）中也存在大量的pRB磷酸化。细胞周期蛋白依赖性激酶可以导致pRB从体外细胞核中释放。因此，该激酶家族成员的磷酸化可能直接参与体内核亲和力的变化和pRB功能的相关变化。
Phosphorylation of the retinoblastoma protein (pRB) is assumed to regulate its growth-controlling function. Moreover, hypophosphorylated and hyperphosphorylated forms of pRB can be distinguished by virtue of the distinct affinities with which they bind to the cell nucleus. This property allows the identification of individual cell nuclei that contain pRB in one or the other form. We show here that after cells emerge from a quiescent (G(0)) state, conversion of their complement of pRB into a hyperphosphorylated form occurs in late G(1), preceding entry into S phase by several hours. Thus, contrary to earlier reports, pRB phosphorylation is not co-ordinated with the G(1)-S transition and may not directly regulate it. A distinct set of phosphopeptides is found exclusively in those forms of pRB that show the loose nuclear association characteristic of the hyperphosphorylated form of pRB. Another set of phosphopeptides is found with both hypophosphorylated and hyperphosphorylated forms. This suggests the existence of distinct patterns of phosphorylation that are associated with different subsets of pRB molecules. We conclude that substantial phosphorylation of pRB exists in G(1) even prior to the hyperphosphorylation point. Cyclin-dependent kinases can cause a liberation of pRB from cell nuclei in vitro. Phosphorylation by members of this kinase family is therefore likely to be directly involved in the change in nuclear affinity in vivo and the associated changes in pRB functioning.