Deciphering the Role of TFEB in Echinococcus granulosus larval stage

Abstract

Autophagy and lysosomal activity are adaptation mechanisms used by the Echinococcus granulosus in response to different metabolic contexts or stressors. Cestode lack of excretory and digestive systems, therefore they required high lysosomal activity to cope with their metabolism. In this line evidence, previously we demonstrated the occurrence of a single functional ortholog of the MiT/TFE family transcription factors in Echinococcus larval stages, Eg-TFEB, a bHLH-ZIP-type protein with a modular sequence involved in lysosomal biogénesis, autophagy and exocytosis. Based on Eg-TFEB conserved structure and its high level of endogenous expression, in situ immunodetection resulted appropriate as a method to verify its subcellular localization in the parasite. Eg-TFEB conserve a Ser199 residue phosphorylatable by TOR (equivalent to Ser211 of Homo sapiens TFEB), through which can to inhibit its activity by promoting its retention in the cytoplasm. During starvation and mTOR inactivation, TFEB is dephosphorylated and translocated to the nucleus, where it can promote the expression of its target genes. Rapamycin, hydroxychloroquine and metformin act as Eg-TFEB activators, promoting its nuclear localization. In this scenario, Eg-TFEB binds to palindromic CLEAR motifs (GTCACGTGAC) present in promoters of target genes, activating transcriptional expression and favoring processes such as autophagy (atg5, atg7, atg8.2 and atg12), lysosomal (lal-1, lal-2, atp6V1 and clcn7), metabolic activity (glut-1 and glut1-4), and even its own transcription. Contrarily to expectations, calcineurin is not involved in the activation of Eg-TFEB, due to its subcellular localization unchanged in presence of cyclosporine A. Finally, this work describes the in vitro dose-dependent anti-echinococcal effects exerted by eltrombopag (FDA-approved drug) on metacestodes, drug that specifically binds to helix-loop-helix region disrupting the TFEB-DNA interaction, highlighting TFEB as a druggable target for autophagy, a promising strategy for anti-cestodal therapy.