title: 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.
authors.affiliation: 1] Department of Biology, CBMA - Centre of Molecular and Environmental Biology, University of Minho, Campus de Gualtar, Braga, Portugal [2] ICBAS - Institute of Biomedical Sciences Abel Salazar, University of Porto, Porto, Portugal.
authors.forename: C S F
authors.initials: CS
authors.lastname: Oliveira
authors.affiliation: Department of Biology, CBMA - Centre of Molecular and Environmental Biology, University of Minho, Campus de Gualtar, Braga, Portugal.
authors.forename: H
authors.initials: H
authors.lastname: Pereira
authors.affiliation: Department of Biology, CBMA - Centre of Molecular and Environmental Biology, University of Minho, Campus de Gualtar, Braga, Portugal.
authors.forename: S
authors.initials: S
authors.lastname: Alves
authors.affiliation: Department of Biology, CBMA - Centre of Molecular and Environmental Biology, University of Minho, Campus de Gualtar, Braga, Portugal.
authors.forename: L
authors.initials: L
authors.lastname: Castro
authors.affiliation: 1] Life and Health Sciences Research Institute (ICVS), School of Health Sciences, University of Minho, Braga, Portugal [2] ICVS/3B's - PT Government Associate Laboratory, Braga/Guimarães, Portugal.
authors.forename: F
authors.initials: F
authors.lastname: Baltazar
authors.affiliation: Department of Biology, CBMA - Centre of Molecular and Environmental Biology, University of Minho, Campus de Gualtar, Braga, Portugal.
authors.forename: S R
authors.initials: SR
authors.lastname: Chaves
authors.affiliation: Department of Biology, CBMA - Centre of Molecular and Environmental Biology, University of Minho, Campus de Gualtar, Braga, Portugal.
authors.forename: A
authors.initials: A
authors.lastname: Preto
authors.affiliation: Department of Biology, CBMA - Centre of Molecular and Environmental Biology, University of Minho, Campus de Gualtar, Braga, Portugal.
authors.forename: M
authors.initials: M
authors.lastname: Côrte-Real
mesh_terms: D000085:Acetates / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D001343:Autophagy / Q000502:physiology*; D002402:Cathepsin D / Q000037:antagonists & inhibitors / Q000235:genetics*; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D015179:Colorectal Neoplasms / Q000473:pathology*; D045325:HCT116 Cells; D006801:Humans; D008928:Mitochondria / Q000378:metabolism / Q000473:pathology*; D018384:Oxidative Stress; D010436:Pepstatins / Q000494:pharmacology; D034622:RNA Interference; D034741:RNA, Small Interfering
chemical_list: D000085:Acetates; D010436:Pepstatins; D034741:RNA, Small Interfering; D002402:Cathepsin D; C031375:pepstatin