TCTP regulates genotoxic stress and tumorigenicity via intercellular vesicular signaling.

Oncogenic intercellular signaling is regulated by extracellular vesicles (EVs), but the underlying mechanisms remain mostly unclear. Since TCTP (translationally controlled tumor protein) is an EV component, we investigated whether it has a role in genotoxic stress signaling and malignant transformation. By generating a Tctp-inducible knockout mouse model (Tctp-/f-), we report that Tctp is required for genotoxic stress-induced apoptosis signaling via small EVs (sEVs). Human breast cancer cells knocked-down for TCTP show impaired spontaneous EV secretion, thereby reducing sEV-dependent malignant growth. Since Trp53-/- mice are prone to tumor formation, we derived tumor cells from Trp53-/-;Tctp-/f- double mutant mice and describe a drastic decrease in tumori-genicity with concomitant decrease in sEV secretion and content. Remarkably, Trp53-/-;Tctp-/f- mice show highly prolonged survival. Treatment of Trp53-/- mice with sertraline, which inhibits TCTP function, increases their survival. Mechanistically, TCTP binds DDX3, recruiting RNAs, including miRNAs, to sEVs. Our findings establish TCTP as an essential protagonist in the regulation of sEV-signaling in the context of apoptosis and tumorigenicity.

TCTP contains a BH3-like domain, which instead of inhibiting, activates Bcl-xL.

Translationally Controlled Tumor Protein (TCTP) is anti-apoptotic, key in development and cancer, however without the typical Bcl2 family members' structure. Here we report that TCTP contains a BH3-like domain and forms heterocomplexes with Bcl-xL. The crystal structure of a Bcl-xL deletion variant-TCTP11-31 complex reveals that TCTP refolds in a helical conformation upon binding the BH3-groove of Bcl-xL, although lacking the h1-subregion interaction. Experiments using in vitro-vivo reconstituted systems and TCTP(+/-) mice indicate that TCTP activates the anti-apoptotic function of Bcl-xL, in contrast to all other BH3-proteins. Replacing the non-conserved h1 of TCTP by that of Bax drastically increases the affinity of this hybrid for Bcl-xL, modifying its biological properties. This work reveals a novel class of BH3-proteins potentiating the anti-apoptotic function of Bcl-xL.