Metabolic remodeling in human colorectal cancer and surrounding tissues: alterations in regulation of mitochondrial respiration and metabolic fluxes

Abstract

The aim of the work was to evaluate whether or not there is glycolytic reprogramming in the neighboring cells of colorectal cancer (CRC). Using postoperative material we have compared the functional capacity of oxidative phosphorylation (OXPHOS) in CRC cells, their glycolytic activity and their inclination to aerobic glycolysis, with those of the surrounding and healthy colon tissue cells. Experiments showed that human CRC cannot be considered a hypoxic tumor, since the malignancy itself and cells surrounding it exhibited even higher rates of OXPHOS than healthy large intestine. The absence of acute hypoxia in colorectal carcinomas was also confirmed by their practically equal glucose-phosphorylating capacity as compared with surrounding non-tumorous tissue and by upregulation of VEGF family and their ligands. Studies indicated that human CRC cells in vivo exert a strong distant effect on the energy metabolism of neighboring cells, so that they acquire the bioenergetic parameters specific to the tumor itself. The growth of colorectal carcinomas was associated with potent downregulation of the creatine kinase system. As compared with healthy colon tissue, the tumor surrounding cells display upregulation of OXPHOS and have high values of basal and ADP activated respiration rates. Strong differences between the normal and CRC cells in the affinity of their mitochondria for ADP were revealed; the corresponding Km values were measured as 93.6±7.7 µM for CRC cells and 84.9±9.9 µM for nearby tissue; both these apparent Km (ADP) values were considerably (by almost 3 times) lower in comparison with healthy colon tissue cells (256±34 µM).

Comparative analysis of the bioenergetics of human adenocarcinoma Caco-2 cell line and postoperative tissue samples from colorectal cancer patients

“…We have recently demonstrated that the mitochondrial VDAC, a binding partner for HK2, was overexpressed in HCC tissue. An increased binding of hexokinase to mitochondria may be responsible for elevated rates of aerobic glycolysis in HCC cells (Chekulayev et al 2015). The presence of mitochondrially-bound HK2 was also revealed in cultured Caco-2 cells (Fig.…”

“…Our study was approved by the Medical Research Ethics Committee (National Institute for Health Development, Tallinn) and it was in full accordance with Helsinki Declaration and Convention of the Council of Europe on Human Rights and Biomedicine. Normal colon tissue samples were controlled for the presence of malignant cells; they were normal according to histopathology and cytochemical studies (Chekulayev et al 2015). Immediately after the surgery, the excised tissues were placed into precooled medium-A.…”

“…The coupling of HK-catalyzed processes with the OXPHOS system in permeabilized Caco-2 cells, tumor and non-tumorous tissue samples was assayed by oxygraphy through stimulation of mitochondrial respiration by locally-generated ADP (Chekulayev et al 2015). This effect of glucose on mitochondrial respiration was expressed by glucose index (I GLU ) that was calculated according to the equation: I GLU (%) = [(V GLU -V ATP )/(V ADP -V ATP )]*100.…”

“…Tumor cells can also shifts the metabolism of surrounding stromal cells toward aerobic glycolysis to use metabolic substrates donated by these cells (L-lactate, ketone bodies, and L-glutamine) for cellular energy generation via OXPHOS (Martinez-Outschoorn et al 2014;Pavlides et al 2009;Whitaker-Menezes et al 2011). We have previously reported that HCC tissue exhibited obvious signs of stimulated mitochondrial biogenesis (Chekulayev et al 2015) and it was recently proposed that suppression of mitochondrial function may serve as an efficient strategy for the treatment of this type of cancer (Zhang et al 2014). The insufficient elucidation of HCC pathogenesis and its metabolic features is probably due to the limited access to patient samples and the lack of reliable model organisms.…”

“…The main aim of our work was therefore to provide a comprehensive characterization of the human colon cancer derived Caco-2 cell line growing under standard conditions with respect to their phenotype and bioenergetic function of mitochondria -the main source of ATP in HCC tissue (Chekulayev et al 2015). Oxygraphy together with metabolic control analysis (MCA) were applied to characterize the function of OXPHOS system in cultured Caco-2 cells and HCC tissue samples.…”