RESUMO
Adenomatous polyposis coli (APC) is a tumor suppressor involved in the Wnt signaling, the primary driving force of the intestinal epithelium homeostasis. Alterations of components of the Wnt pathway, and in most cases mutations of APC, have been reported to promote colorectal cancer (CRC). During differentiation the enterocytes migrate from the crypt to the tip of the villus where they undergo apoptosis thus ensuring the continual renewal of the intestinal mucosa. The differentiation process is characterized by an activation gradient of the Wnt signaling pathway accompanied by a metabolic switch from glycolysis to mitochondrial oxidative phosphorylation along the crypt-villus axis. In the present work, we study the relationship between the expression of wild type APC protein and mitochondrial oxidative metabolism in HT29 colorectal cancer cells, originally carrying endogenous inactive APC alleles. By generating mtDNA-depleted (rho0) APC-inducible HT29 cells, we demonstrate for the first time that the APC-dependent apoptosis requires the production of reactive oxygen species (ROS) by the mitochondrial respiratory chain. The possible role of mitochondria as putative target in the prevention and/or therapy of colorectal cancer is herein discussed.
RESUMO
We have recently shown that the transcriptional coactivator PGC1α, a master regulator of mitochondrial biogenesis and function, is involved in the control of the intestinal epithelium cell fate. Furthermore, PGC1α protects against colon cancer formation by promoting ROS accumulation and, consequently, mitochondria-mediated apoptosis. Here we provide an additional mechanistic insight into the tumor suppressor activity of PGC1α showing that its pro-apoptotic effect is mediated by Bax. In fact, PGC1α overexpression in HCT116 Bax (-/-) colorectal cancer cells stimulates mitochondrial production and activity, but it fails to induce cell death as well as to oppose tumor growth in the xenograft model. The lack of ROS accumulation in the Bax (-/-) cells strengthens our view that the PGC1α-induced oxidative burst represents one of the main apoptosis-driving factors in colorectal cancer cells.