Protein synthesis inhibitors stimulate MondoA transcriptional activity by driving an accumulation of glucose 6-phosphate

Abstract

<jats:title>Abstract</jats:title> <jats:p>BACKGROUND Protein synthesis is regulated by the availability of amino acids, the engagement of growth factor signaling pathways and ATP levels sufficient to support translation. Crosstalk between these inputs is extensive, yet other regulatory mechanisms remain to be characterized. For example, the translation initiation inhibitor Rocaglamide A (RocA) induces Thioredoxin Interacting Protein (TXNIP). TXNIP is a negative regulator of glucose uptake, thus its induction by RocA links translation to the availability of glucose. MondoA is the principal regulator of glucose-induced transcription and its activity is triggered by the glycolytic intermediate, glucose 6-phosphate (G6P). MondoA responds to G6P generated by cytoplasmic glucose and mitochondrial ATP (mtATP), suggesting a critical role in the cellular response to these energy sources. TXNIP expression is entirely dependent on MondoA, therefore, we investigated how protein synthesis inhibitors impact its transcriptional activity. METHODS We investigated how translation regulates MondoA activity using cell line models and loss-of-function approaches. We examined how protein synthesis inhibitors effect gene expression and metabolism using RNA-sequencing and metabolomics, respectively. The biological impact of RocA was evaluated using cell lines and Patient-Derived xenograft Organoid (PDxO) models. RESULTS We discovered that multiple protein synthesis inhibitors, including RocA, increase TXNIP expression in a manner that depends on MondoA, a functional electron transport chain and mtATP synthesis. Furthermore, RocA increases mtATP and G6P levels and TXNIP induction depends on interactions between the Voltage-Dependent Anion Channel (VDAC) and hexokinase, which generates G6P. RocA treatment impacts the regulation of ~1200 genes and ~250 of those genes are MondoA-dependent. RocA treatment is cytotoxic to Triple Negative Breast Cancer cell lines and shows preferential cytotoxicity against ER- PDxO breast cancer models. Finally, RocA-driven cytotoxicity is partially-dependent on MondoA or TXNIP. CONCLUSIONS Our data suggest that protein synthesis inhibitors rewire metabolism, resulting in an increase in mtATP and G6P, the latter driving MondoA-dependent transcriptional activity. Further, MondoA is a critical component of the cellular transcriptional response to RocA. Our functional assays suggest that RocA or similar translation inhibitors may show efficacy against ER- breast tumors and that the levels of MondoA and TXNIP should be considered when exploring these potential treatment options.</jats:p>

TXNIP: A Double-Edged Sword in Disease and Therapeutic Outlook

“…MondoA binds a double E-box carbohydrate response element (ChoRE) in the TXNIP promotor and promotes the expression of TXNIP, and it is a sensor of a high cellular energy charge. The high intracellular glucose-6-phosphate drives translocation of MondoA from the outer mitochondrial membrane (OMM) to the nucleus where MondoA binds to the promotor of TXNIP and recruits cofactors that initiate transcription [ 100 – 102 ]. Hyperglycemia itself has the ability to affect the level of TXNIP RNA.…”

TXNIP loss expands Myc-dependent transcriptional programs by increasing Myc genomic binding

“…Together, these findings suggest that approaches to ectopically activate MondoA transcriptional activity might be useful cancer therapeutics in that they represent a way to block Myc transcriptional activity. For example, translation initiation inhibitors increase TXNIP expression in a MondoA-dependent manner (55). TXNIP induction is apparently independent of oncogenic burden, suggesting the potential utility of this approach.…”

Thioredoxin-Interacting Protein in Cancer and Diabetes

“…Calcium channel blockers suppress the cardiac expression of Txnip, which may enhance cardiomyocyte survival (23). The translation initiation inhibitor, rocaglamide A, is cytotoxic to triple-negative breast cancer cell lines and induces Txnip in a MondoA-dependent manner (166). Modulatory signals also regulate Txnip gene transcription.…”