Prolonged proteasome inhibition antagonizes TGFβ1-dependent signalling by promoting the lysosomal-targeting of TGFβ receptors

Impairing autophagy disrupts transforming growth factor beta 1 (TGFβ1) signalling and epithelial-mesenchymal transition (EMT) in non-small cell lung cancer (NSCLC). Since autophagy and proteasome-mediated degradation are interdependent, we investigated how prolonged downregulation of proteasomal cat...

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Bibliographic Details
Published in:Cellular signalling 2022-10, Vol.98, p.110414-110414, Article 110414
Main Authors: Trelford, Charles B., Di Guglielmo, Gianni M.
Format: Article
Language:English
Subjects:
Autophagy
Endocytosis
Epithelial-mesenchymal transition
Lysosome
p62/SQSTM1
Proteasome
Transforming growth factor beta
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Summary:Impairing autophagy disrupts transforming growth factor beta 1 (TGFβ1) signalling and epithelial-mesenchymal transition (EMT) in non-small cell lung cancer (NSCLC). Since autophagy and proteasome-mediated degradation are interdependent, we investigated how prolonged downregulation of proteasomal catalytic activity affected TGFβ1-dependent signalling and EMT. Proteasome-dependent degradation was inhibited in A549 and H1299 NSCLC cells using MG132 and lactacystin, which are reversible and irreversible proteasome inhibitors, respectively. We observed that inhibiting proteasomal activity for 24 h decreased TGFβ-dependent nuclear accumulation of Smad2/3. Time course studies were then carried out to characterize the time frame of this observation. Short-term (< 8 h) proteasome inhibition resulted in increased receptor regulated Smad (R-Smad) phosphorylation and steady-state TGFβ receptor type II (TGFβRII) levels. However, prolonged (8–24 h) proteasome inhibition decreased TGFβ1-dependent R-Smad phosphorylation and steady-state TGFβRI and TGFβRII levels. Furthermore, proteasome inhibition blunted TGFβ-dependent E- to N-Cadherin shift, stress fiber formation, and increased cellular apoptosis via the TAK-1-TRAF6-p38 MAPK pathway. Interestingly, proteasome inhibition also increased autophagic flux, steady-state microtubule-associated protein light chain 3B-II and active uncoordinated 51-like autophagy activating kinase 1 levels, and co-localization of lysosomes with autophagy cargo proteins and autophagy-related proteins. Finally, we observed that proteasome inhibition increased TGFβRII endocytosis and trafficking to lysosomes and we conclude that prolonged proteasome inhibition disrupts TGFβ signalling outcomes through altered TGFβ receptor trafficking. •Short term proteasome inhibition increased TGFβ signalling.•Long term proteasome inhibition depleated TGFβ type II receptor levels.•TGFβRII endocytosis and trafficking is altered by prolonged proteasome inhibition.
ISSN:0898-6568
1873-3913
DOI:10.1016/j.cellsig.2022.110414