Sapkota, G. | bioRxiv Science

bioRxiv2024

AMPK activation promotes transcriptional activation of TFEB through its dephosphorylation

Transcription Factor EB (TFEB) is a critical regulator of lysosomal biogenesis, autophagy and energy homeostasis through controlling expression of genes belonging to the coordinated lysosomal expression and regulation network. AMP-activated protein kinase (AMPK) has been reported to phosphorylate TFEB at three conserved C-terminal serine residues (S466, S467, S469) and these phosphorylation events were essential for transcriptional activation of TFEB. In sharp contrast to this proposition, here we demonstrate that AMPK activation leads to dephosphorylation of the C-terminal sites, and that AMPK is dispensable for mTORC1-mediated/torin1-sensitive TFEB activation. We show that a synthetic peptide encompassing C-terminal serine residues of TFEB is a poor substrate of AMPK. Treatment of cells with AMPK activator (MK-8722) or mTOR inhibitor (torin1) robustly dephosphorylated TFEB not only at mTORC1-targeted N-terminal serine sites, but also at the C-terminal sites. Loss of function of AMPK abrogated MK-8722-but not torin1-induced dephosphorylation and induction of the vast majority of TFEB target genes.

biochemistry↗

bioRxiv2024

Zebrafish reveal new roles for Fam83f in hatching and the DNA damage-mediated autophagic response

The FAM83 (Family with sequence similarity 83) family is highly conserved in vertebrates, but little is known of the functions of these proteins beyond their association with oncogenesis. Of the family, FAM83F is of particular interest because it is the only membrane-targeted FAM83 protein. When over-expressed, FAM83F activates the canonical Wnt signalling pathway and binds to and stabilizes p53; it therefore interacts with two pathways often dysregulated in disease. Insights into gene function can often be gained by studying the roles they play during development, and here we report the generation of fam83f knock-out (KO) zebrafish, which we have used to study the role of Fam83f in vivo. We show that endogenous fam83f is most strongly expressed in the hatching gland of developing zebrafish embryos, and that fam83f KO embryos hatch earlier than their wild-type (WT) counterparts, despite developing at a comparable rate. We also demonstrate that fam83f KO embryos are more sensitive to ionizing radiation than WT embryos--an unexpected finding, bearing in mind the previously-reported ability of FAM83F to stabilize p53. Transcriptomic analysis shows that loss of fam83f leads to downregulation of phosphatidylinositol-3-phosphate (PI(3)P) binding proteins and impairment of cellular degradation pathways, particularly autophagy, a crucial component of the DNA damage response. Finally, we show that Fam83f protein is itself targeted to the lysosome when over-expressed in HEK293T cells, and that this localization is dependent upon a C terminal signal sequence. The zebrafish lines we have generated suggest that Fam83f plays an important role in autophagic/lysosomal processes, resulting in dysregulated hatching and increased sensitivity to genotoxic stress in vivo.

developmental biology↗