A novel non-canonical signaling pathway mediates TGF-β1-induced glucocorticoid insensitivity in epithelial cells. A novel non-canonical signaling pathway mediates TGF-β1-induced glucocorticoid insensitivity in epithelial cells

Limited therapeutic responses to glucocorticoids in chronic inflammatory disease are partly attributable to interleukins and transforming growth factor-β1 (TGF-β1). Global inhibition of TGF-β1 carries known risks, including autoimmune disease. Here we elucidate the signaling pathway subserving modulation of glucocorticoid activity by TGF-β1. The proteomic response of airway epithelial cells to TGF-β1 revealed 24 candidate proteins of which 3 were prioritized by exclusion of changes induced by: TGF-β2, which lacks the modulatory activity of TGF-β1 and TGF-β3; and those of TGF-β1 that were prevented by small molecule inhibitors of non-canonical TGF-β1 signaling, that did not prevent glucocorticoid modulation. Pharmacological and genetic approaches establish that TGF-β1-induced glucocorticoid insensitivity is mediated by a novel signaling cascade involving LIM domain kinase 2 mediated phosphorylation of phospho-cofilin1 that activates phospholipase D to generate the effector(s) (lyso)phophatidic acid. This study identifies several promising drug targets that potentially enable safe modulation of TGF-β1 in chronic inflammatory diseases. Overall design: Biological triplicates of BEAS-2B cell lines treated with Dexamethasone, TGFbeta1 and a combination of Dexamethasone +TGFbeta1 were compared among themselves and with an untreated control