Insulin induces phosphorylation of serine residues of translationally controlled tumor protein in 293T cells

Structural Insights into TCTP and Its Interactions with Ligands and Proteins

The 19-24 kDa Translationally Controlled Tumor Protein (TCTP) is involved in a wide range of molecular interactions with biological and nonbiological partners of various chemical compositions such as proteins, peptides, nucleic acids, carbohydrates, or small molecules. TCTP is therefore an important and versatile binding platform. Many of these protein-protein interactions have been validated, albeit only few received an in-depth structural characterization. In this chapter, we will focus on the structural analysis of TCTP and we will review the available literature regarding its interaction network from a structural perspective.

Structure-Function Relationship of TCTP

The translationally controlled tumor protein (TCTP) is a small, multifunctional protein found in most, if not all, eukaryotic lineages, involved in a myriad of key regulatory processes. Among these, the control of proliferation and inhibition of cell death, as well as differentiation, are the most important, and it is probable that other responses are derived from the ability of TCTP to influence them in both unicellular and multicellular organisms. In the latter, an additional function for TCTP stems from its capacity to be secreted via a nonclassical pathway and function in a non-cell autonomous (paracrine) manner, thus affecting the responses of neighboring or distant cells to developmental or environmental stimuli (as in the case of serum TCTP/histamine-releasing factor in mammals and phloem TCTP in Arabidopsis). The additional ability to traverse membranes without a requirement for transmembrane receptors adds to its functional flexibility. The long-distance transport of TCTP mRNA and protein in plants via the vascular system supports the notion that an important aspect of TCTP function is its ability to influence the response of neighboring and distant cells to endogenous and exogenous signals in a supracellular manner. The predicted tridimensional structure of TCTPs indicates a high degree of conservation, more than its amino acid sequence similarity could suggest. However, subtle differences in structure could lead to different activities, as evidenced by TCTPs secreted by Plasmodium spp. Similar structural variations in animal and plant TCTPs, likely the result of convergent evolution, could lead to deviations from the canonical function of this group of proteins, which could have an impact from a biomedical and agricultural perspectives.

14-3-3 proteins regulate Tctp-Rheb interaction for organ growth in Drosophila

14-3-3 family proteins regulate multiple signalling pathways. Understanding biological functions of 14-3-3 proteins has been limited by the functional redundancy of conserved isotypes. Here we provide evidence that 14-3-3 proteins regulate two interacting components of Tor signalling in Drosophila, translationally controlled tumour protein (Tctp) and Rheb GTPase. Single knockdown of 14-3-3ɛ or 14-3-3ζ isoform does not show obvious defects in organ development but causes synergistic genetic interaction with Tctp and Rheb to impair tissue growth. 14-3-3 proteins physically interact with Tctp and Rheb. Knockdown of both 14-3-3 isoforms abolishes the binding between Tctp and Rheb, disrupting organ development. Depletion of 14-3-3s also reduces the level of phosphorylated S6 kinase, phosphorylated Thor/4E-BP and cyclin E (CycE). Growth defects from knockdown of 14-3-3 and Tctp are suppressed by CycE overexpression. This study suggests a novel mechanism of Tor regulation mediated by 14-3-3 interaction with Tctp and Rheb.

14-3-3 proteins regulate several signalling pathways but often act redundantly; however, the molecular mechanisms behind such redundancy are unclear. Here, the authors show that 14-3-3 proteins regulate two interacting components of Tor signalling in Drosophila, Tctp and Rheb, disrupting organ development.