Abstract : During my PhD I studied two genes, TSAP6 and TCTP that are differentially regulated in tumor reversion. The proteins encoded by these two genes interact and form a complex both in vitro and in vivo. My goal was to better understand the biological function of these two genes. Different approaches were used, namely crystallography (TCTP), knockout mice (TSAP6 and TCTP) and site-directed mutagenesis (TSAP6 and TCTP).
The TSAP6 knockout mice display a microcytic anemia. We have shown that this anemia is due to a delay in the maturation of the reticulocytes and a default in the secretion of the Transferrin-Receptor by the exosomes. Since TSAP6 is a direct transcriptional target gene of p53, we analyzed the secretion of exosomes following activation of p53 by irradiation or Actinomicine D. We demonstrate that in the absence of TSAP6, there is no induction in the secretion of exosomes. More generally, we show that the TSAP6 gene has a major role in vivo in the secretion of exosomes, including following activation of p53.
We studied the TCTP gene in its antiapoptotic role. The deletion of TCTP in knockout mice is lethal. This loss of TCTP causes an increase of apoptosis during embryogenesis. This embryonic lethality occurs between days 6,5 and 9,5 of the development.
The crystal structure of TCTP at 2A resolution shows a strong homology with the one of s.pombe protein. Furthermore, we observed a homology between the H2-H3 helices of TCTP and the H5-H6 helices of BAX, a proapoptotic protein involved in mitochondrial membrane permeability. We demonstrated that these two helices are responsible for the antiapoptotic function of TCTP, which inhibits the dimerization of BAX in the mitochondrial membrane, preventing this way cell death.
We also show that Sertraline and Thioridazine, that kill tumor cells by decreasing the level of intracellular TCTP, bind directly to TCTP and prevent the formation of a complex between TSAP6 and TCTP.