Glucocorticoid receptors drive breast cancer cell migration and metabolic reprograming via PDK4.

Corticosteroids act on the glucocorticoid receptor (GR; NR3C1) to resolve inflammation and are routinely prescribed to breast cancer patients undergoing chemotherapy treatment to alleviate side effects. Triple negative breast cancers (TNBCs) account for 15-20% of diagnoses and lack expression of estrogen and progesterone receptors as well as amplified HER2, but often express high GR levels. GR is a mediator of TNBC progression to advanced metastatic disease, however the mechanisms underpinning this transition to more aggressive behavior remain elusive. We previously showed that tissue/cellular stress (hypoxia, chemotherapies) as well as factors in the tumor microenvironment (TGFβ, HGF) activate p38 MAPK, which phosphorylates GR on Ser134. In the absence of ligand, p-Ser134-GR further upregulates genes important for responses to cellular stress, including key components of the p38 MAPK pathway. Herein, we show that p-Ser134-GR is required for TNBC metastatic colonization to the lungs of female mice. To understand the mechanisms of p-Ser134-GR action in the presence of GR agonists, we examined glucocorticoid-driven transcriptomes in CRISPR knock-in models of TNBC cells expressing wild-type or phospho-mutant (S134A) GR. We identified dexamethasone- and p-Ser134-GR-dependent regulation of specific gene sets controlling TNBC migration (NEDD9, CSF1, RUNX3) and metabolic adaptation (PDK4, PGK1, PFKFB4). TNBC cells harboring S134A-GR displayed metabolic reprogramming that was phenocopied by PDK4 knockdown. PDK4 knockdown or chemical inhibition also blocked cancer cell migration. Our results reveal a convergence of GR agonists (i.e., host stress) with cellular stress signaling whereby pSer134-GR critically regulates TNBC metabolism, an exploitable target for the treatment of this deadly disease.