Cathepsin D protects colorectal cancer cells from acetate-induced apoptosis through autophagy-independent degradation of damaged mitochondria

Abstract

Acetate is a short-chain fatty acid secreted by Propionibacteria from the human intestine, known to induce mitochondrial apoptotic death in colorectal cancer (CRC) cells. We previously established that acetate also induces lysosome membrane permeabilization in CRC cells, associated with release of the lysosomal protease cathepsin D (CatD), which has a well-established role in the mitochondrial apoptotic cascade. Unexpectedly, we showed that CatD has an antiapoptotic role in this process, as pepstatin A (a CatD inhibitor) increased acetate-induced apoptosis. These results mimicked our previous data in the yeast system showing that acetic acid activates a mitochondria-dependent apoptosis process associated with vacuolar membrane permeabilization and release of the vacuolar protease Pep4p, ortholog of mammalian CatD. Indeed, this protease was required for cell survival in a manner dependent on its catalytic activity and for efficient mitochondrial degradation independently of autophagy. In this study, we therefore assessed the role of CatD in acetate-induced mitochondrial alterations. We found that, similar to acetic acid in yeast, acetate-induced apoptosis is not associated with autophagy induction in CRC cells. Moreover, inhibition of CatD with small interfering RNA or pepstatin A enhanced apoptosis associated with higher mitochondrial dysfunction and increased mitochondrial mass. This effect seems to be specific, as inhibition of CatB and CatL with E-64d had no effect, nor were these proteases significantly released to the cytosol during acetate-induced apoptosis. Using yeast cells, we further show that the role of Pep4p in mitochondrial degradation depends on its protease activity and is complemented by CatD, indicating that this mechanism is conserved. In summary, the clues provided by the yeast model unveiled a novel CatD function in the degradation of damaged mitochondria when autophagy is impaired, which protects CRC cells from acetate-induced apoptosis. CatD inhibitors could therefore enhance acetate-mediated cancer cell death, presenting a novel strategy for prevention or therapy of CRC.

Apoptotic effect of sodium acetate on a human gastric adenocarcinoma epithelial cell line

“…It has been established that acetate induces mitochondrial apoptotic death, as well as MP in RCs. Caspase-3 plays a crucial role in the cell death process (Jan et al, 2002;Marques et al, 2013;Oliveira et al, 2015). In this study, caspase-8 activity changed weakly after 6 h, while caspase-9 activity increased by 11% after 6 h in the presence of 50 mM sodium acetate.…”

Characterization of acetate transport in colorectal cancer cells and potential therapeutic implications

“…The cellular and molecular mechanisms underlying acetate-induced apoptosis in CRC cells have been studied [5, 9, 31], however the reason for acetate selectivity towards transformed colon and CRC cells is still elusive. To exert its effects and access the cellular targets, acetate has to be transported across the plasma membrane of colon cells.…”

Tissue metabolic profiling of lymph node metastasis of colorectal cancer assessed by 1H NMR

“…Moreover, Marques et al reported that acetate-induced apoptosis in CRC cells involved lysosomal membrane permeabilization and cathepsin D release (54). However, another study demonstrated that cathepsin D protected CRC cells from acetate-induced apoptosis through autophagy-independent degradation of damaged mitochondria (55). Thus, acetate has been proven to play a critical role in CRC development and metastasis, although the exact mechanism needs to be further investigated.…”