AUTHOR=Trelford Charles B. , Di Guglielmo Gianni M. 

TITLE=Canonical and Non-canonical TGFβ Signaling Activate Autophagy in an ULK1-Dependent Manner

JOURNAL=Frontiers in Cell and Developmental Biology

VOLUME=Volume 9 - 2021

YEAR=2021

URL=https://www.frontiersin.org/journals/cell-and-developmental-biology/articles/10.3389/fcell.2021.712124

DOI=10.3389/fcell.2021.712124

ISSN=2296-634X

ABSTRACT=The mechanism(s) in which TGFβ modulates autophagy in cancer remain unclear. Here, we characterized the TGFβ signalling pathways that induce autophagy in non-small cell lung cancer cells, using cells lines stably expressing GFP-LC3-RFP-LC3DG constructs that measure autophagic flux. We demonstrated that TGFβ1 increases Unc 51-like kinase 1 (ULK1) protein levels, AMPK-dependent ULK1 phosphorylation at serine (S) 555 and decreases mechanistic target of rapamycin (mTOR) activity on ULK1. Further analysis revealed that the TGFβ activated kinase 1/tumour necrosis factor receptor-associated factor 6/P38 mitogen activated protein kinase (TAK1-TRAF6-P38 MAPK) pathway and Smad4 were important for TGFβ1-induced autophagy. The TAK1-TRAF6-P38 MAPK pathway was essential for downregulating mTOR S2448 phosphorylation, AMPK-dependent ULK1 S555 phosphorylation and autophagosome formation. Furthermore, although siRNA-mediated Smad4 silencing did not alter mTOR-dependent ULK1 S757 phosphorylation, it did reduce AMPK-dependent ULK1 S555 phosphorylation and autophagosome formation. Our results suggest that the Smad4 and TAK1-TRAF6-P38 MAPK signalling pathways are essential for TGFβ-induced autophagy and provide specific targets for the inhibition of TGFβ in tumor cells that utilize autophagy in their EMT program.