Ellis James, Yao Shuyuan
Developmental Biology Program, Hospital for Sick Children, Toronto, Ontario, Canada.
Curr Gene Ther. 2005 Aug;5(4):367-73. doi: 10.2174/1566523054546233.
An obstacle confronting gene therapy in stem cells is transcriptional silencing of the vector. Here, we discuss recent data indicating that oncoretrovirus and lentivirus vectors are silenced by multiple epigenetic pathways that result in DNA methylation and histone modifications. Both vector types can be variegated in stem cells and expression is often extinguished during differentiation. We propose a novel model of retrovirus silencing in which epigenetic pathways compete to recruit histone deacetylases, de novo methyltransferases, histone H1 and MeCP2 to the provirus. These chromatin modifications may act in concert with heterochromatin at or near the integration site to establish silencing or variegation respectively. Retrovirus vector designs for stem cells should delete virus silencer elements, incorporate strong positive regulatory elements and insulators, and avoid non-mammalian reporter genes. In addition, cancer stem cells that continually repopulate a growing tumour may share silencing pathways with normal stem cells. Ultimately, optimized vector designs may prove to be valuable tools for gene therapy of both normal and cancer stem cells.
干细胞基因治疗面临的一个障碍是载体的转录沉默。在此，我们讨论近期的数据，这些数据表明，致癌逆转录病毒和慢病毒载体通过多种表观遗传途径被沉默，这些途径导致DNA甲基化和组蛋白修饰。两种载体类型在干细胞中都可能呈现斑驳状态，且在分化过程中表达常常会熄灭。我们提出了一种逆转录病毒沉默的新模型，其中表观遗传途径竞争招募组蛋白脱乙酰酶、从头甲基转移酶、组蛋白H1和MeCP2至原病毒。这些染色质修饰可能分别与整合位点处或其附近的异染色质协同作用，以建立沉默或斑驳状态。用于干细胞的逆转录病毒载体设计应删除病毒沉默元件，纳入强阳性调控元件和绝缘子，并避免使用非哺乳动物报告基因。此外，不断补充生长中肿瘤的癌症干细胞可能与正常干细胞共享沉默途径。最终，优化的载体设计可能被证明是用于正常和癌症干细胞基因治疗的有价值工具。
