Bortezomib Inhibits Lung Fibrosis and Fibroblast Activation without Proteasome Inhibition.

Abstract

The U.S. Food and Drug Administration-approved proteasomal inhibitor bortezomib (BTZ) has attracted interest for its potential antifibrotic actions. However, neither its invivo efficacy in lung fibrosis nor its dependence on proteasome inhibition has been conclusively defined. In this study, we assessed the therapeutic efficacy of BTZ in a mouse model of pulmonary fibrosis, developed an invitro protocol to define its actions on diverse fibroblast activation parameters, determined its reliance on proteasome inhibition for these actions invivo and invitro, and explored alternative mechanisms of action. The therapeutic administration of BTZ diminished the severity of pulmonary fibrosis without reducing proteasome activity in the lung. In experiments designed to mimic this lack of proteasome inhibition invitro, BTZ reduced fibroblast proliferation, differentiation into myofibroblasts, and collagen synthesis. It promoted dedifferentiation of myofibroblasts and overcame their characteristic resistance to apoptosis. Mechanistically, BTZ inhibited kinases important for fibroblast activation while inducing the expression of DUSP1 (dual-specificity protein phosphatase 1), and knockdown of DUSP1 abolished its antifibrotic actions in fibroblasts. Collectively, these findings suggest that BTZ exhibits a multidimensional profile of robust inhibitory actions on lung fibroblasts as well as antifibrotic actions invivo. Unexpectedly, these actions appear to be independent of proteasome inhibition, instead attributable to the induction of DUSP1.