Regulation of PTEN Activity in Cancer Cells

描述（由申请人提供）：正常和癌细胞中PTEN活性和易位的调节。PTEN（phosphatase and tensin homolog deleted on chromosome ten）是最近发现的一种肿瘤抑制因子，在胶质母细胞瘤、前列腺癌、子宫癌、膀胱癌、乳腺癌和恶性黑色素瘤等人类肿瘤中存在缺失/突变。PTEN使磷脂酰肌醇（PdtIns）-3-磷酸的3-位去磷酸化，从而防止Akt被PtdIns-3-激酶激活。PTEN还使粘着斑激酶（p125 FAK）和Shc去磷酸化，Shc是将酪氨酸激酶与Ras信号传导和MAP激酶途径连接的SH 2-磷酸酪氨酸结合衔接蛋白。PTEN在其C-末端含有C2脂质结合结构域，其负责以Ca 2+非依赖性方式与质膜内小叶处的磷脂酰胆碱结合。最近我们发现一种小的氧化还原蛋白硫氧还蛋白（thioredoxin）直接与PTEN的C2结构域结合，从而能够负调节PTEN的脂质活性。硫氧还蛋白与PTEN的Cys 212结合形成稳定的复合物，该复合物可以以氧化还原依赖性方式调节。此外，已知增加硫氧还蛋白还原酶活性的硒添加到细胞中能够恢复PTEN活性，因此，我们的研究所基于的假设是：1）PTEN活性由小氧化还原蛋白和硒间接地变构调节，以及2）PTEN活性可以由其C2结构域间接地调节。我们提出的研究的目的是为了更好地了解C2结构域在PTEN易位中的作用，以及通过与其他蛋白质的相互作用调节PTEN的活性。

DESCRIPTION (provided by applicant): Regulation of PTEN activity and translocation in normal and cancer cells. PTEN (phosphatase and tensin homolog deleted on chromosome ten) is a recently identified tumor suppressor, which is deleted/mutated in human tumors including glioblastomas, carcinomas of the prostate, uterus, bladder and breast and malignant melanomas. PTEN dephosphorylates the 3-position of phosphatidylinositol (Pdtlns)-3-phosphates, thus, preventing activation of Akt by Ptdlns-3-kinase. PTEN also dephosphorylates focal adhesion kinase (p125FAK) and Shc, a SH2-phosphotyrosine-binding adapter protein that links tyrosine kinases to Ras signaling and the MAP kinase pathway. PTEN contains a C2 lipid binding domain at its C-terminal end, which is responsible for its' binding to phosphatidylcholine at the inner leaflet of the plasma membrane in a Ca2+-independent manner. It has been suggested that this domain may influence the activity of the protein, but no clear-cut role for the C2 domain of PTEN has been proposed.We have recently found that a small redox protein, thioredoxin, binds directly to the C2 domain of PTEN and thereby is able to negatively regulate the lipid activity of PTEN. Thioredoxin binds to the Cys212 of PTEN forming a stable complex, which can be regulated in a redox dependent manner. Moreover, the addition of selenium to cells, which is know to increase thioredoxin reductase activity, is able to restore PTEN activity.Hence, the hypotheses upon which our studies are based are that 1) PTEN activity is allosterically regulated by a small redox protein and indirectly by selenium and that 2) PTEN activity can be regulated indirectly by its C2 domain. The objectives of our proposed studies are directed towards a better understanding of the role of the C2 domain in the translocation of PTEN and in the regulation of the activity of PTEN via its interaction with other proteins.