Leslie N R, Bennett D, Gray A, Pass I, Hoang-Xuan K, Downes C P
Division of Signal Transduction Therapy, Department of Biochemistry, University of Dundee, Dundee DD1 5EH, Scotland, UK.
Biochem J. 2001 Jul 15;357(Pt 2):427-35. doi: 10.1042/0264-6021:3570427.
The tumour suppressor protein PTEN (phosphatase and tensin homolog deleted on chromosome 10) is a lipid phosphatase which can antagonize the phosphoinositide 3-kinase (PI 3-kinase) signalling pathway, promoting apoptosis and inhibiting cell-cycle progression and cell motility. We show that very little cellular PTEN is associated with the plasma membrane, but that artificial membrane-targeting of PTEN enhances its inhibition of signalling to protein kinase B (PKB). Evidence for potential targeting of PTEN to the membrane through PDZ domain-mediated protein-protein interactions led us to use a PTEN enzyme with a deletion of the C-terminal PDZ-binding sequence, that retains full phosphatase activity against soluble substrates, and to analyse the efficiency of this mutant in different cellular assays. The extreme C-terminal PDZ-binding sequence was dispensable for the efficient down-regulation of cellular PtdIns(3,4,5)P3 levels and a number of PI 3-kinase-dependent signalling activities, including PKB and p70S6K. However, the PDZ-binding sequence was required for the efficient inhibition of cell spreading. The data show that a PTEN mutation, similar to those found in some tumours, affects some functions of the protein but not others, and implicate the deregulation of PTEN-dependent processes other than PKB activation in the development of some tumours. Significantly, this hypothesis is supported by data showing low levels of PKB phosphorylation in a glioblastoma sample carrying a mutation in the extreme C-terminus of PTEN compared with tumours carrying phosphatase-inactivating mutations of the enzyme. Our data show that deregulation of PKB is not a universal feature of tumours carrying PTEN mutations and implicate other processes that may be deregulated in these tumours.
肿瘤抑制蛋白PTEN（第10号染色体缺失的磷酸酶和张力蛋白同源物）是一种脂质磷酸酶，它可以拮抗磷酸肌醇3激酶（PI 3激酶）信号通路，促进细胞凋亡并抑制细胞周期进程和细胞运动。我们发现，细胞内与质膜相关的PTEN极少，但人工将PTEN靶向膜可增强其对蛋白激酶B（PKB）信号传导的抑制作用。有证据表明PTEN可能通过PDZ结构域介导的蛋白质-蛋白质相互作用靶向膜，这促使我们使用一种缺失C末端PDZ结合序列的PTEN酶，该酶对可溶性底物仍保留完全的磷酸酶活性，并在不同的细胞分析中分析该突变体的效率。极端C末端的PDZ结合序列对于有效下调细胞内磷脂酰肌醇（3,4,5）三磷酸（PtdIns(3,4,5)P3）水平以及许多PI 3激酶依赖性信号活性（包括PKB和p70S6K）并非必需。然而，PDZ结合序列对于有效抑制细胞铺展是必需的。数据表明，与某些肿瘤中发现的类似的PTEN突变会影响该蛋白的某些功能，但不会影响其他功能，并且暗示在某些肿瘤的发生发展中，除了PKB激活外，PTEN依赖性过程的失调也有作用。重要的是，这一假设得到了数据支持，即与携带该酶磷酸酶失活突变的肿瘤相比，在携带PTEN极端C末端突变的胶质母细胞瘤样本中，PKB磷酸化水平较低。我们的数据表明，PKB失调并非携带PTEN突变肿瘤的普遍特征，并暗示这些肿瘤中可能失调的其他过程。
