Eukaryotic Elongation Factor 1A2 Cooperates with Phosphatidylinositol-4 Kinase III β To Stimulate Production of Filopodia through Increased Phosphatidylinositol-4,5 Bisphosphate Generation

Abstract

Eukaryotic elongation factor 1 alpha 2 (eEF1A2) is a transforming gene product that is highly expressed in human tumors of the ovary, lung, and breast. eEF1A2 also stimulates actin remodeling, and the expression of this factor is sufficient to induce the formation of filopodia, long cellular processes composed of bundles of parallel actin filaments. Here, we find that eEF1A2 stimulates formation of filopodia by increasing the cellular abundance of cytosolic and plasma membrane-bound phosphatidylinositol-4,5 bisphosphate [PI(4,5)P 2 ]. We have previously reported that the eEF1A2 protein binds and activates phosphatidylinositol-4 kinase III beta (PI4KIII␤), and we find that production of eEF1A2-dependent PI(4,5)P 2 and generation of filopodia require PI4KIII␤. Furthermore, PI4KIII␤ is itself capable of activating both the production of PI(4,5)P 2 and the creation of filopodia. We propose a model for extrusion of filopodia in which eEF1A2 activates PI4KIII␤, and activated PI4KIII␤ stimulates production of PI(4,5)P 2 and filopodia by increasing PI4P abundance. Our work suggests an important role for both eEF1A2 and PI4KIII␤ in the control of PI(4,5)P 2 signaling and actin remodeling.Filopodia are fingerlike projections from the plasma membrane that are the first cellular structures to reach new spaces during cell migration. Filopodia are composed of bundled actin filaments and actin-associated proteins (9, 13). Transmembrane receptors within filopodia respond to extracellular cues and guide directional movement toward chemoattractants (26). In addition, filopodia contain abundant adhesion molecules that regulate cellular attachment to growth substrates and cell-cell interactions (37). As such, filopodia regulate several key physiological processes, including cell migration, wound healing, and development. For example, filopodia are essential for neurogenesis in mice and for cell-cell adhesion during Drosophila melanogaster embryogenesis (9, 13).We have previously described a role for eukaryotic elongation factor 1 alpha 2 (eEF1A2) in the initiation and maintenance of filopodia (1). In several types of mammalian cells, eEF1A2 expression is sufficient to stimulate formation of filopodia (1). eEF1A2 is one of two members of the eEF1A family of proteins, eEF1A1 and eEF1A2. During the elongation phase of protein synthesis, GTP-bound eEF1A proteins interact with amino-acylated tRNA and recruit them to the ribosome (18). While eEF1A1 and eEF1A2 are believed to have equivalent roles in protein translation, their tissue-specific expression patterns are each markedly different. eEF1A1 is expressed ubiquitously, whereas eEF1A2 is detectably expressed only in normal tissues of mammalian heart, brain, and skeletal muscle (24a, 24b, 28). Homozygous deletion of eEF1A2 occurs in the wasted mouse (7). These mice develop normally but suffer from neuromuscular abnormalities and immunodeficiency and die at approximately 1 month of age (35,36). Importantly, eEF1A2 is likely to be a human oncogene, it is highly expressed, and its gene is...

The role of translation elongation factor eEF1A in intracellular alkalinization-induced tumor cell growth

“…These non-canonical roles of eEF1A based on the strong relation of eEF1A with actin, and furthermore, eEF1A actually binds to actin. [26][27][28] It is interesting to note that the binding of eEF1A to F-actin has pH-dependent kinetics. For example, Dictyostelium eEF1A showed a K d value of 0.2 mM at pH 6.5, and this value increases greatly to a K d of 42.2 mM at pH 7.8.…”

eEF1A: Thinking Outside the Ribosome

“…Together, these data suggest that there exists a complex relationship in eukaryotic cells between the function of eEF1A in translation and actin organization that may be influenced by the availability of its binding factors. Finally, in addition to the direct interaction between eEF1A and actin described above, certain isoforms of eEF1A in human cells (see "To Die or Not to Die, eEF1A and Apoptosis") may also influence the actin cytoskeleton indirectly (27,28).…”

FiloDetect: automatic detection of filopodia from fluorescence microscopy images

“…We were interested in this question because of several lines of evidence implicating a role for PI4KIII β in breast cancer and filopodia production: it is activated by eEF1A2 (eukaryotic elongation factor 1 alpha 2) [14], which is amplified in approximately two-thirds of breast tumours [15,16]; it was recently identified as a putative breast cancer driver gene, in a large-scale copy number and gene expression analysis of 2000 breast tumours [17]; and ectopic expression of PI4KIII β in fibroblast cells increases filopodia number and length [5,14]. Thus, we hypothesized that PI4KIII β may drive filopodia formation in breast cancer cells, potentially enhancing their invasivenes.…”