Zarkowska T, U S, Harlow E, Mittnacht S
Department of Cell and Molecular Biology, Institute of Cancer Research, London, UK.
Oncogene. 1997 Jan 16;14(2):249-54. doi: 10.1038/sj.onc.1200824.
The growth suppressive activity of the retinoblastoma tumour suppressor protein is controlled by cell cycle dependent phosphorylation. However, while many in vivo phosphorylation sites have been mapped, the identities of those residues whose phosphorylation is regulated remain elusive. We have mapped the epitopes of three independent monoclonal antibodies that recognise a distinction between differentially phosphorylated pRB sub-populations. All three antibodies recognise an identical epitope which encompasses an essential serine positioned within a consensus site for proline directed kinase phosphorylation. We provide evidence that this residue, serine 608 of pRB, is an authentic phosphorylation site that can be phosphorylated in vitro by cyclin A-CDK2 and cyclin D1-CDK4 kinases but not by cyclin E-CDK2 kinase or the mitogen activated kinase ERK2. Phosphorylation at this residue seems to be cell cycle regulated, occurring prior to entry into the S phase.
视网膜母细胞瘤肿瘤抑制蛋白的生长抑制活性受细胞周期依赖性磷酸化调控。然而，尽管许多体内磷酸化位点已被定位，但那些磷酸化受调控的残基的身份仍然难以捉摸。我们已经绘制了三种独立单克隆抗体的表位，这些抗体能够识别磷酸化程度不同的pRB亚群之间的差异。所有三种抗体都识别相同的表位，该表位包含位于脯氨酸定向激酶磷酸化共有位点内的一个必需丝氨酸。我们提供的证据表明，这个残基，即pRB的丝氨酸608，是一个真正的磷酸化位点，可在体外被细胞周期蛋白A-CDK2和细胞周期蛋白D1-CDK4激酶磷酸化，但不能被细胞周期蛋白E-CDK2激酶或丝裂原活化激酶ERK2磷酸化。该残基的磷酸化似乎受细胞周期调控，在进入S期之前发生。
