Differential regulation of glucocorticoid receptor signaling in luminal, triple negative and HER2+ breast cancer cells

Abstract

Background: Glucocorticoids (GC) are frequently used in the adjuvant treatment of breast cancer (BC). However, they develop numerous side effects including survival of resistant tumor subclones and promotion of metastasis. Biological response to GCs is mediated by glucocorticoid receptor (GR) regulating gene expression via transactivation (TA) associated with side effects of GC, and transrepression (TR), negative interaction between GR and transcription factors. The aims of this study were to investigate: 1) mechanisms of different GC treatment response in different BC cells subtypes; 2) effects of novel selective GR agonist Compound A (CpdA) on BC cells. Methods: MCF-7,MDA-MB-231,MDA-MB-453 cell lines and their subclones withGR knockdown were used as model cells. Cellswere treated with Dexamethasone (Dex) and CpdA. Effects on cell growth were evaluated by trypan blue exclusion analysis and by flow cytometry with PI staining. Migration and invasion were determined by the transwell assay. Gap junction entirety was measured by scrape-load dye transfer assay. Expression of TA/TR specific genes as well as 15 genes associatedwith epithelial-mesenchymal transition andmetastasis of BC (ANXA1, CJUN, COL1A1, COX2, CSF1, FIBL1, ICAM1, IL-6, IL-8, iNOS, KLF4,MKP1,MMP9, RHOB, SK1) were evaluated by q-PCR. Results: Dex and CpdA induced GR-mediated G1-phase arrest and suppressed cell proliferation by 50-70% in BC cells. CpdA shifted GR function towards therapeutically important TR. CpdA as opposed to Dex did not lead to loss of gap junctions. CpdA had a favorable therapeutic effect on 9/15 genes in luminal and 7/15 genes in HER2+BC cells, down-regulating several mesenchymal markers associated with poor prognosis, in particular, on ANXA1, CJUN, ICAM1, IL-6, IL-8, iNOS, KLF4, RHOB, SK1 in luminal BC cells and on COL1A1, CJUN, COX2, IL-8, MMP9, RHOB, SK1 in HER2+ BC cells. Conclusions: Dex has stimulated cell motility and migration potential of all BC cells types, the most therapeutically unfavorable effect on metastasis promotion was observed for triple negative BC cells. CpdA keeps all benefits of GC with no effects on TA and migration potential of BC cells.