An acidic environment leads to p53 dependent induction of apoptosis in human adenoma and carcinoma cell lines: implications for clonal selection during colorectal carcinogenesis

Abstract

As tumours are known to acidify their microenvironment and¯uctuations in lumenal pH have been reported in a number of colonic disease conditions, we investigated whether loss of p53 function, commonly associated with the adenoma to carcinoma transition in human colorectal epithelium, was implicated in the cellular response to changes in extracellular pH. Human colonic adenoma and carcinoma derived cell lines were incubated at an inital pH range of 5.5 ± 8.0 and the attached cell yield and apoptotic cell yield determined after 4 days. Exposure of all cell lines to an acidic growth environment was associated with a G1 arrest, down regulation of the retinoblastoma protein (pRb) protein and switch to the hypophosphorylated form of the protein, and increased expression of the p21 protein. However, induction of apoptosis, associated with increased p53 protein expression but not with changes in Bcl-2 expression, was only detected in the adenoma derived BH/C1 and AA/C1 cell lines which express wild type p53 activity. Furthermore, this induction of apoptosis was inhibited in the transfected cell line AA/ 273p53/B, in which the wild type p53 function has been abrogated. These results suggest that acidi®cation of the microenvironment would provide a selective growth advantage for cells that have lost wild type p53 function, leading to clonal expansion of aberrant cell populations.

Metabolic reprogramming of the tumor

“…Equally important is the H þ extrusion and the extracellular acidification brought not only by MCT4 (Gallagher et al, 2007) but also by Na þ /H þ exchangers (Reshkin et al, 2000) and other transmembrane channels whose levels are orchestrated in cancer cells (Pouyssegur et al, 2006). This strategy maintains intracellular alkalinization, exerting a positive feedback loop on glycolysis, through activation of 6-phosphofructo-1-kinase (Erecinska et al, 1995), whereas extracellular acidification triggers apoptosis in neighboring cells with normal p53 levels (Williams et al, 1999).…”

Transcriptional down-regulation of the retinoblastoma protein is associated with differentiation and apoptosis in human colorectal epithelial cells

“…Western samples of 1 × 10 6 cells were prepared by the method described in Williams et al (1999). Proteins were resolved on 7.5% polyacrylamide gels and transferred onto Immobilon-P polyvinylidene difluoride membranes (Millipore, MA).…”

“…Triplicate flasks of cells were grown to 50% confluency, 100% confluency, one week post-confluent and two weeks post-confluent. At these timepoints the cell monolayers were trypsinized to single cells, and samples prepared for Western blotting by the method described in Williams et al (1999). …”

Induction of the adenoma-carcinoma progression and Cdc25A-B phosphatases by the trefoil factor TFF1 in human colon epithelial cells

“…In order to further investigate on this concept, we examined the status and functional role of TFF1 at the adenoma and adenocarcinoma transitions in human colorectal tumors and in vitro, using as model the premalignant adenomatous PC/AA/C1 cell line (designated PC) isolated from a patient with familial adenomatous polyposis FAP (Williams et al, 1994). Several biological and molecular parameters were also investigated in premalignant and tumorigenic colorectal and kidney cancer cells, including anchorage-independent growth, cell survival and invasion, growth of tumor xenografts, and identification of TFF1 target genes.…”