Upregulation of ATG3 contributes to autophagy induced by the detachment of intestinal epithelial cells from the extracellular matrix, but promotes autophagy-independent apoptosis of the attached cells

Abstract

(2015) Upregulation of ATG3 contributes to autophagy induced by the detachment of intestinal epithelial cells from the extracellular matrix, but promotes autophagy-independent apoptosis of the attached cells, Autophagy, 11:8, 1230-1246, DOI: 10.1080/15548627.2015 Keywords: autophagy, apoptosis, anoikis, ATG3, ATG7, extracellular matrixAbbreviations: ATG, autophagy-related; BCL2L1, Bcl2-like1; CDK4, cyclin-dependent kinase 4; ECM, extracellular matrix; EGFR, epidermal growth factor receptor; GABARAP, GABA(A) receptor-associated protein; GFP, green fluorescent protein; LC3/ MAP1LC3, microtubule-associated protein 1 light chain 3; PE, phosphatidylethanolamine; qPCR, quantitative polymerase chain reaction; SD, standard deviation; SH3GLB1/Bif1, SH3-domain GRB2-like endophilin B1; siRNA, small interfering RNA; UVRAG, UV radiation resistance-associated.Detachment of nonmalignant intestinal epithelial cells from the extracellular matrix (ECM) triggers their growth arrest and, ultimately, apoptosis. In contrast, colorectal cancer cells can grow without attachment to the ECM. This ability is critical for their malignant potential. We found previously that detachment-induced growth arrest of nonmalignant intestinal epithelial cells is driven by their detachment-triggered autophagy, and that RAS, a major oncogene, promotes growth of detached cells by blocking such autophagy. In an effort to identify the mechanisms of detachment-induced autophagy and growth arrest of nonmalignant cells we found here that detachment of these cells causes upregulation of ATG3 and that ATG3 upregulation contributes to autophagy and growth arrest of detached cells. We also observed that when ATG3 expression is artificially increased in the attached cells, ATG3 promotes neither autophagy nor growth arrest but triggers their apoptosis. ATG3 upregulation likely promotes autophagy of the detached but not that of the attached cells because detachment-dependent autophagy requires other detachmentinduced events, such as the upregulation of ATG7. We further observed that those few adherent cells that do not die by apoptosis induced by ATG3 become resistant to apoptosis caused by cell detachment, a property that is critical for the ability of normal epithelial cells to become malignant. We conclude that cell-ECM adhesion can switch ATG3 functions: when upregulated in detached cells in the context of other autophagy-promoting events, ATG3 contributes to autophagy. However, when overexpressed in the adherent cells, in the circumstances not favoring autophagy, ATG3 triggers apoptosis.

PTK2-mediated degradation of ATG3 impedes cancer cells susceptible to DNA damage treatment

“…Recent evidence has shown that overexpressed ATG3 triggers apoptosis in the ECM-attached colorectal cancer cells. 38 However, in our system, we found that there was no difference between ATG3-WT and ATG3 Y203F in the apoptosis process after DNA-damaging drug treatment ( Figure S5). Instead, we found sustained levels of ATG3 were able to enhance DNA damage-induced mitotic catastrophe ( Figure 5), and this might be a new function of ATG3 independent of autophagy and apoptosis.…”

“…In addition to the involvement of ATG3 in autophagy, overexpressed ATG3 induces apoptosis in extracellular matrix (ECM)-attached colorectal cancer cells. 38 To investigate whether ATG3 degradation affects apoptosis, we used the ATG3-WT or ATG3 Y203F -inducible cell lines for flow cytometry analysis. As shown in Figure S5, in response to etoposide treatment, there was no obvious difference in the apoptosis process between the ATG3-WT cell line and ATG3 Y203F cell line.…”

ESRRA (estrogen-related receptor α) is a key coordinator of transcriptional and post-translational activation of autophagy to promote innate host defense

“…Autophagic flux analysis was performed as described previously. [47][48][49] BMDMs were transduced with mCherry-EGFP-LC3B retrovirus for 24 h and stimulated with AICAR or resveratrol. The stimulated cells on coverslips were washed twice with PBS, fixed with 4% paraformaldehyde for 15 min.…”

Oncogenic RAS-induced downregulation of ATG12 is required for survival of malignant intestinal epithelial cells

“…We found that nonmalignant intestinal epithelial cells undergo growth arrest after detachment from the ECM due to the induction of autophagy which is triggered by detachment-dependent upregulation of autophagy mediators ATG3 and ATG7. 29 Furthermore, we observed that RAS blocks autophagy and growth arrest of detached colon cancer cells by downregulating the autophagy mediator BECN1/ Beclin-1. 30 Thus, RAS-induced cellular malignant transformation requires basal autophagy, but RAS-dependent signals prevent such autophagy from exceeding certain levels, and these signals are critical for RAS-driven malignant cellular transformation.…”