Proteasome activator PA200 regulates myofibroblast differentiation

Abstract

The proteasome is essential for the selective degradation of most cellular proteins and is fine-tuned according to cellular needs. Proteasome activators serve as building blocks to adjust protein turnover in cell growth and differentiation. Understanding the cellular function of proteasome activation in more detail offers a new strategy for therapeutic targeting of proteasomal protein breakdown in disease. The role of the proteasome activator PA200 in cell function and its regulation in disease is unknown. In this study, we investigated the function of PA200 in myofibroblast differentiation and fibrotic tissue remodeling. PA200 was upregulated in hyperplastic basal cells and myofibroblasts of fibrotic lungs from patients with idiopathic pulmonary fibrosis. Increased expression of PA200 and enhanced formation of PA200-proteasome complexes was also evident in experimental fibrosis of the lung and kidney in vivo and in activated primary human myofibroblasts of the lung in vitro. Transient silencing and overexpression revealed that PA200 functions as a negative regulator of myofibroblast differentiation of human but not mouse cells. Our data thus suggest an unexpected and important role for PA200 in adjusting myofibroblast activation in response to pro-fibrotic stimuli, which fails in idiopathic pulmonary fibrosis.

Exploring the proteasome system: A novel concept of proteasome inhibition and regulation

“…Dysregulation of PA200-proteasome complexes in disease has only recently been described by our lab. We observed elevated levels of PA200 in lungs of patients with idiopathic pulmonary fibrosis as well as in experimental models of fibrosis of the lung and kidney (Welk et al, 2019). Enhanced formation of PA200-proteasome complexes was induced upon TGFβ-induced myogenic differentiation.…”

“…On the transcriptional level PA200 is regulated upon proteotoxic stress after proteasome inhibition by the transcription factor NRF1 (Sha & Goldberg, 2014). We have recently shown that PA200 is also transcriptionally induced by transforming growth factor (TGF) β (Welk et al, 2019). On the posttranscriptional level, PA200 is regulated by miRNA29b via its 3'UTR region .…”

“…Enhanced formation of PA200-proteasome complexes was induced upon TGFβ-induced myogenic differentiation. Knockdown experiments of PA200, however, revealed an adaptive function of PA200 in myofibroblast activation (Welk et al, 2019). Protein atlas data analysis indicates that increased RNA expression of PA200 in tumors might be associated with poor prognosis in liver and endometrial cancers based on TCGA data (www.proteinatlas.org).…”

Bortezomib inhibits lung fibrosis and fibroblast activation without proteasome inhibition

“…Indeed, increased activity of this proteolytic complex has been reported in fibrotic lung (4)(5)(6) and other organs (7), and in Fibs treated with pro-fibrotic mediators (6,8,9). At the molecular level, increased expression of ubiquitin ligases as well as proteasome subunits and their activators has been reported in fibrotic tissue and Fibs, including those from IPF patients (10)(11)(12). These findings provide a potential therapeutic rationale for proteasome inhibition in fibrosis.…”

The proteasome regulator PSME4 drives immune evasion and abrogates anti-tumor immunity in NSCLC

“…MISSION shRNA targeting mouse or human PSME4 or RFP were obtained from Sigma (TRCN0000176569, TRCN0000178428, TRCN0000158223, TRCN0000157073). pcDNA3.1_PSME4 (Welk et al, 2019) was transfected into A549/KP1.9 cells with Lipofectamine 2000 (Thermo Fisher). Cell culture and drug treatments A549 were originally obtained from ATCC grown in DMEM and used as model systems for cell biology studies including western blot, biochemistry, and imaging.…”