Mechanisms of elF4E mediated transformation

描述（由申请人提供）：真核起始因子eIF4E是细胞生长的关键调节因子，elF4E在几种癌症中过表达。它的过表达导致多种细胞系的致癌转化。该蛋白在翻译起始的限速步骤中起作用，在该步骤中，它结合在所有mRNA上发现的7甲基鸟苷帽片段（m7G帽），从而允许给定的mRNA被翻译。eIF4E对翻译的影响并不均匀，其中eIF4E过表达对特定转录物翻译的上调作用强于其他转录物。具有复杂非翻译区（utr）的转录本对eIF4E水平尤其敏感。一般来说，管家基因没有复杂的utr，然而，一些生长控制蛋白，如细胞周期蛋白，有。传统上，elF4E通过不适当的转录本翻译来转化细胞，从而促进生长。然而，令人兴奋的新发现表明，相当一部分（高达68%）的eIF4E形成核小体，并且这一部分促进特定转录本（如细胞周期蛋白D1）从细胞核到细胞质的运输，而不影响GAPDH和肌动蛋白等家政基因的运输。再次，特异性似乎是由UTR结构介导的。我们的研究表明，突变破坏了eIF4E在翻译中的作用能力，但不会破坏其转化细胞的能力。这些发现代表了一个重大的范式转变，即eIF4E可以独立于其翻译功能转化细胞。我们假设eIF4E促进转化至少部分是通过其促进生长特异性mrna运输的能力，eIF4E核体与含有早幼粒细胞白血病蛋白PML的核体共定位。PML是eIF4E转运和转化活性的有效负调控因子。PML的RING结构域直接与eIF4E结合，改变其构象，降低m7G cap mRNA亲和力，抑制转运和转化。此外，在造血中起作用的髓系特异性脯氨酸富同源结构域蛋白PRH直接与eIF4E结合，降低其对m7G帽的亲和力，减少cyclin D1 mRNA的转运。PRH利用保守的eIF4E结合位点直接结合eIF4E。数据库分析表明，大约有200种同源结构域蛋白具有该位点。因此，我们假设eIF4E通过与这些蛋白质的相互作用在分化中起着关键作用。我们提议……确定eIF4E的核功能在其转化潜能方面的作用，2。确定eIF4E是否通过与PRH和3的相互作用在造血中发挥作用。确定其他同域是否调节eIF4E功能。我们相信，阐明elF4E功能的调控网络将对正常生长控制和分化产生广泛的见解。

DESCRIPTION (provided by applicant): The eukaryotic initiation factor eIF4E is a key regulator of cellular growth elF4E is overexpressed in several cancers. Its overexpression results in oncogenic transformation of a variety of cell lines. This protein functions in the rate limiting step of translation initiation where it binds the 7 methyl guanosine cap moiety (m7G cap) found on all mRNAs thereby allowing the given mRNA to be translated. The effects of eIF4E on translation are not uniform, where eIF4E overexpression upregulates translation of specific transcripts more so than others. Transcripts with complex untranslated regions (UTRs) in particular are more sensitive to eIF4E levels. In general housekeeping genes do not have complex UTRs, however, several growth control proteins, such as the cyclins, do. Traditionally, elF4E transforms cells by inappropriate translation of transcripts that promote growth. However, exciting new findings indicate that a substantial fraction (up to 68%) of eIF4E forms nuclear bodies and that this fraction promotes the transport of specific transcripts, such as cyclin D1, from the nucleus to the cytoplasm without affecting transport of housekeeping genes such as GAPDH and actin. Again, the specificity appears to be mediated by the UTR structure. Our studies indicate that mutations, which disrupt the ability of eIF4E to act in translation do not disrupt its ability to transform cells. These findings represent a major paradigm shift in that eIF4E can transform cells independently of its translation functions. We hypothesize that eIF4E promotes transformation at least in part through its ability to promote the transport of growth specific mRNAs, eIF4E nuclear bodies co-localize with those containing the promyelocytic leukemia protein PML. PML is a potent negative regulator of the transport and transformation activity of eIF4E. The RING domain of PML binds directly to eIF4E, alters its conformation, reduces m7G cap mRNA affinity and suppresses transport and transformation. In addition, the myeloid specific proline rich homeodomain protein PRH, which functions in hematopoiesis binds directly to eIF4E, reduces its affinity for the m7G cap and decreases cyclin D1 mRNA transport. PRH uses a conserved eIF4E, binding site to directly bind eIF4E. Data base analysis indicates that about 200 homeodomain proteins have this site. Thus, we hypothesize that eIF4E, through interactions with these proteins plays a key rote in differentiation. We propose to 1. Determine the role of nuclear functions of eIF4E in terms of its transformation potential, 2. Determine whether eIF4E plays a role in hematopoiesis through its interactions with PRH and 3. Determine whether other homeodomains modulate eIF4E function. We believe that elucidation of the regulatory network in which elF4E functions will yield broad insights into normal growth control and differentiation.