Autophagy sustains mitochondrial respiration and determines resistance to BRAF<sup>V600E</sup> inhibition in thyroid carcinoma cells
Creators: name: Díaz-Gago, Sergio
name: Vicente-Gutiérrez, Javier
name: Ruiz-Rodríguez, Jose Manuel
name: Calafell, Josep
name: Álvarez-Álvarez, Alicia
name: Lasa, Marina
name: Chiloeches, Antonio
name: Baquero, Pablo
Publisher: name: Taylor & Francis
Year: 2024
Subjects: subject: Biochemistry
subject: Cell Biology
subject: Genetics
subject: FOS: Biological sciences
subject: Molecular Biology
subject: Physiology
subject: Chemical Sciences not elsewhere classified
subject: Cancer
subject: Hematology

description: BRAF<sup>V600E</sup> is the most prevalent mutation in thyroid cancer and correlates with poor prognosis and therapy resistance. Although selective inhibitors of BRAF<sup>V600E</sup> have been developed, more advanced tumors such as anaplastic thyroid carcinomas show a poor response in clinical trials. Therefore, the study of alternative survival mechanisms is needed. Since metabolic changes have been related to malignant progression, in this work we explore metabolic dependencies of thyroid tumor cells to exploit them therapeutically. Our results show that respiration of thyroid carcinoma cells is highly dependent on fatty acid oxidation and, in turn, fatty acid mitochondrial availability is regulated through macroautophagy/autophagy. Furthermore, we show that both lysosomal inhibition and the knockout of the essential autophagy gene, <i>ATG7</i>, lead to enhanced lipolysis; although this effect is not essential for survival of thyroid carcinoma cells. We also demonstrate that following inhibition of either autophagy or fatty acid oxidation, thyroid tumor cells compensate oxidative phosphorylation deficiency with an increase in glycolysis. In contrast to lipolysis induction, upon autophagy inhibition, glycolytic boost in autophagy-deficient cells is essential for survival and, importantly, correlates with a higher sensitivity to the BRAF<sup>V600E</sup> selective inhibitor, vemurafenib. In agreement, downregulation of the glycolytic pathway results in enhanced mitochondrial respiration and vemurafenib resistance. Our work provides new insights into the role of autophagy in thyroid cancer metabolism and supports mitochondrial targeting in combination with vemurafenib to eliminate BRAF<sup>V600E</sup>-positive thyroid carcinoma cells. <b>Abbreviations</b>: AMP: adenosine monophosphate; ATC: anaplastic thyroid carcinoma; ATG: autophagy related; ATP: adenosine triphosphate; BRAF: B-Raf proto-oncogene, serine/threonine kinase; Cas9: CRISPR-associated protein; CREB: cAMP responsive element binding protein; CRISPR: clustered regularly interspaced short palindromic repeats; 2DG: 2-deoxyglucose; FA: fatty acid; FAO: fatty acid oxidation; FASN: fatty acid synthase; FCCP: trifluoromethoxy carbonyl cyanide phenylhydrazone; LAMP1: lysosomal associated membrane protein 1; LIPE/HSL: lipase E, hormone sensitive type; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; OCR: oxygen consumption rate; OXPHOS: oxidative phosphorylation; PRKA/PKA: protein kinase cAMP-activated; PTC: papillary thyroid carcinoma; SREBF1/SREBP1: sterol regulatory element binding transcription factor 1.