Comparison of the ability of mammalian eEF1A1 and its oncogenic variant eEF1A2 to interact with actin and calmodulin

Abstract

The question as to why a protein exerts oncogenic properties is answered mainly by well-established ideas that these proteins interfere with cellular signaling pathways. However, the knowledge about structural and functional peculiarities of the oncoproteins causing these effects is far from comprehensive. The 97.5% homologous tissue-specific A1 and A2 isoforms of mammalian translation elongation factor eEF1A represent an interesting model to study a difference between protein variants of a family that differ in oncogenic potential. We propose that the different oncogenic impact of A1 and A2 might be explained by differences in their ability to communicate with their respective cellular partners. Here we probed this hypothesis by studying the interaction of eEF1A with two known partners - calmodulin and actin. Indeed, an inability of the A2 isoform to interact with calmodulin is shown, while calmodulin is capable of binding A1 and interferes with its tRNA-binding and actin-bundling activities in vitro. Both A1 and A2 variants revealed actin-bundling activity; however, the form of bundles formed in the presence of A1 or A2 was distinctly different. Thus, a potential inability of A2 to be controlled by Ca2+-mediated regulatory systems is revealed.

Protein isoforms. Origin, structure and functions.

“…eEF1A1 formed complexes with the multifunctiunal Sgt1 protein in vitro and in cellulo while eEF1A2 did not [74]. eEF1A1 rather than eEF1A2 interacted with calmodulin in Ca 2+dependent way [75]. eEF1A is known to interact with actin [76] probably due to its dimeric form [77].…”

“…eEF1A is known to interact with actin [76] probably due to its dimeric form [77]. Interestingly, the eEF1A1 and eEF1A2 isoforms induced the formation of differently shaped actin bundles [75] which could be important for a supposed role of eEF1A2 in oncogenesis.…”

“…First, as eEF1A2 is found in the excitable tissues (nervous and neuronal) where the processes of the Ca 2+ -mediated signaling involving a number of Ca 2+ binding proteins are very active, it has been suggested that eEF1A2 is less sensitive comparing to eEF1A1 to Ca 2+mediated signaling [75]. This makes translation process more prone to the changes in the concentration of Ca 2+ in these tissues.…”

“…Second, though an oncogenic role of eEF1A2 is still far from being elucidated, one may suggest that eEF1A2 avoids an eEF1A1adapted control in cancer tissues, thus acting in non-controlled or mis-controlled way. It has been proposed that actin-bundling role of A2 should be specially considered as cancer-related one [75] especially taking into account that the dysregulated actin bundling may play a key role in the metastatic processes [78,79].…”

The role of translation elongation factor eEF1 subunits in neurodevelopmental disorders

“…The amino acid residues known to interact with actin are found on the face of the 3D structure of eEF1A, which harbors the majority of amino acid differences between the two isoforms, suggesting that eEF1A1 and eEF1A2 may have different capacities for interacting with actin (Soares, Barlow, Newbery, Porteous, & Abbott, ). Indeed, there is experimental evidence for differences in actin binding and bundling activities between eEF1A1 and eEF1A2 (Novosylna et al., ). One hypothesis, therefore, is the switch occurs so as to modify cytoskeletal interactions in neurons at different developmental stages (Abbott et al., ).…”