The article under consideration is Growth Properties of Colonic Tumor Cells Are a Function of the Intrinsic Mitochondrial Membrane Potential by Barbara Heerdt, Michele Houston, and Leonard Augenlicht. In this article, the researchers explore the role of the ∆φm in the development and progression of cancer tumors. In their earlier studies, the authors have discovered that the changes in mitochondrial membrane potential of colonic mucosal cells may result in the transformation of a cell into a malignant one. In this study, they deal with the ∆φm trying to prove that it can initiate apoptosis of colonic carcinoma cells, as well as the cell cycle arrest. The main hypothesis of the authors is that the cell composition or shifts in biochemical pathways may have a certain effect on the formation of cancer tumors. To study this question, the researchers used isogenic colonic carcinoma cell lines that allowed them to trace differences in the cells’ intrinsic ∆φm.
A particular question that the researchers are trying to answer in this study is whether the differences in the ∆φm have any relation to those properties of the cells that are responsible for the formation and the expansion of the colonic tumor. These differences in the intrinsic ∆φm were developed by the researchers earlier in the isogenic carcinoma cell lines. Owing to this, the researchers have discovered that ∆φm may be connected with certain tumorigenic properties of a cell. Such an increased interest in these properties is explained by the authors’ earlier findings that colonic epithelial cells that have been transformed into the malignant ones were characterized by the mitochondrial genome with depressed expression and that other kinds of mutations in the mitochondrial genome, as well as certain modifications in the mitochondrial enzymatic activity, are also related to the progression of colonic tumors. This is why in this study theirs they wished to explore the relation of the ∆φm and differences within its structure to the development of the tumors in question. Thus, this study attempts to find out whether the mitochondrial gene expression is in any way affected by the differences within the cells’ intrinsic ∆φm.
Specifically, in this study, the authors compared the cells with elevated ∆φm with those that had lower ∆φm. This was done to determine whether the former has more capacity to avoid apoptosis (this was checked by measuring the cells’ response to hypoxia), start growing in the independent conditions, and, in this way, escape anoikis, and whether such cells can succeed in invading the basement membrane. To do all this, the researchers observed the determination of ∆φm in the cells, the response of the cells to the deficiency of oxygen (hypoxia), the cell invasion, and the growth of the cells in the conditions that were created for them by the researchers. In more detail, the authors started with determining the ∆φm in the cells. To do this, they stained the cells with propidium iodide, a fluorescent dye dependent on the ∆φm. This allowed the researchers to identify the cells that had the ∆φm and could be used for further analysis. After this, the researchers needed to analyze flow cytometry. For this, they stained the cells with Red-LEHD-FMK, which allowed them to determine the quantity of the active caspase-9. Then, to observe the cells’ response to hypoxia, the researchers have added CoCl2 to the cells they have grown, and in 24 hours the number of viable cells was determined. These cells were again stained for the determination on the ∆φm. The vascular endothelial growth factor was counted afterward. And lastly, the researchers have determined the cell invasion. The cell lines were placed on the basement membrane layer and left for 24 hours under the temperature of 37oC. Then the researchers stained and quantified those cells that managed to get through the basement membrane. So, as it can be seen, the researchers have utilized different techniques to measure the ability of the cells with the elevated intrinsic ∆φm to avoid apoptosis and to continue growing under the anchorage-independent conditions.
All these procedures and techniques led to the obtaining of three major results. First of all, the researchers have discovered that isogenic cell lines can be successfully used in studying the influence of the ∆φm on the functioning of the colonic carcinoma cells. The study has revealed that these lines allow tracing the relationship between the differences in the cells’ intrinsic ∆φm and, thus, identifying the cells’ viability and the function of the colonic carcinoma cell. Secondly, another result of the research was that non-adherent conditions, as well as the response of the cell to hypoxia, make it possible to observe more differences in the ∆φm. The expansion of any tumor makes certain areas within this tumor more in need of oxygen as compared to the healthy cells (with no treatment, the areas that obtain little oxygen become hypoxic). The experiment has shown that the exposure of the cells to hypoxia can favor the development of those cells that are able to survive in the oxygen-poor environment. And, thirdly, the researchers have discovered that the presence of the ∆φm in the cell largely increases its ability to invade the basement membrane. This is extremely important because a cell that can cross the basement membrane has more chances to avoid anoikis. So, one of the major findings of the researchers was that the cells that have an increased ∆φm show non-adherent growth, which means that there is much connection between the ability of a cell to cross the basement membrane and the intrinsic ∆φm of this cell.
Based on the results, the researchers make corresponding conclusions. They admit that their hypothesis was correct and that certain changes in biochemical pathways and composition of the cells may account for the differences in the cells’ ∆φm. They conclude that these differences might be affected by certain biochemical or molecular processes that are controlled by certain environmental factors and the nuclear genome. Consequently, future research should be dedicated to these processes and their effect on the growth properties of the colonic tumor cells.
It is hard to disagree with the conclusions which the authors make because they are based on a thorough research that was explained by the authors in detail. Besides, they are presented in more or less understandable way, though people not involved into this area of studies may experience difficulties in understanding specific vocabulary and concepts which the authors use and never explain.
Though the article has good references and supplements, there is one thing missing from it, namely, the glossary of the terms used. The comprehension of the article will be easier if the authors included formulae, abbreviations, and basic terms that they utilized throughout the paper. Moreover, there is no separate conclusion section; the authors present their conclusions in the discussion section. On the whole, however, the study is quite impressive.