SUMMARY
Limited supply and catabolism restrict the essential amino acid tryptophan (Trp) in tumors. How tumors sustain translation under Trp stress remains unclear. Unlike other amino acids, Trp stress activates the EGFR, which enhances macropinocytosis and RAS signaling to the MTORC1 and p38/MAPK kinases, sustaining translation. The AHR forms part of the Trp stress proteome and promotes autophagy to sustain Trp levels, and ceramide biosynthesis. Thus, Trp restriction elicits pro-translation signals enabling adaptation to nutrient stress, placing Trp into a unique position in the amino acid-mediated stress response. Our findings challenge the current perception that Trp restriction inhibits MTORC1 and the AHR and explain how both cancer drivers remain active. A glioblastoma patient subgroup with enhanced MTORC1 and AHR displays an autophagy signature, highlighting the clinical relevance of MTORC1-AHR crosstalk. Regions of high Trp or high ceramides are mutually exclusive, supporting that low Trp activates the EGFR-MTORC1-AHR axis in glioblastoma tissue.
Under Trp stress,
EGFR-RAS signaling activates macropinocytosis, MTORC1 and p38.
MTORC1 and p38 driven translation induces AHR levels and activity.
AHR enhances ceramides and autophagy, sustaining intracellular Trp.
In glioblastoma, ceramides localize to low Trp areas, and high AHR associates with MTORC1 activity and autophagy.
Competing Interest Statement
AS, ST and CO are founders and AS and CO are managing directors of cAHRmeleon Bioscience GmbH. VIK is a Scientific Advisor for Longaevus Technologies. Authors of this manuscript have patents on AHR inhibitors in cancer (WO2013034685, CO); A method to multiplex tryptophan and its metabolites (WO2017072368, CO); A transcriptional signature to determine AHR activity (WO2020201825, AS, ST, CO); Interleukin-4-induced gene 1 (IL4I1) as a biomarker (WO2020208190, AS, ST, LFSP, MPT, CO) Interleukin-4-induced gene 1 (il4i1) and its metabolites as biomarkers for cancer (WO2021116357, AS, ST, LFSP, CO).
