Colonic Crypt Changes during Adenoma Development in Familial Adenomatous Polyposis

Abstract

Familial adenomatous polyposis patients, who have a germline APC mutation, develop adenomas in normal-appearing colonic mucosa, and in the process usually acquire a mutation in the other APC allele as well. Nonetheless, the cellular mechanisms that link these initiating genetic changes with the earliest tissue changes (upward shift in the labeling index) in colon tumorigenesis are unclear. Based on the tenet that colorectal cancer originates from crypt stem cells (SCs) and on our kinetic modeling, we hypothesized that overpopulation of mutant colonic SCs is the missing link. Directly testing this hypothesis requires measuring changes in the size of the SC population, but specific markers for human colonic SCs are lacking. Hence, we used immunohistochemical mapping to study crypt base cells, of which SCs are a subset. Using colectomy specimens from 16 familial adenomatous polyposis and 11 control cases, we determined the topographic profiles of various cell populations along the crypt axis and the proportions of each cell type. In the formation of adenomatous crypts, the distribution of cells expressing crypt base cell markers (MSH2, Bcl-2, survivin) expanded toward the crypt surface and showed the greatest proportional increase (fivefold to eightfold). Cells expressing a marker for the upper crypt (p27(kip1)) shifted to the crypt bottom and showed the smallest increase. This suggests that: 1) during adenoma development, APC mutations cause expansion of the crypt base cell population, including crypt SCs; 2) SC overpopulation can explain the shifts in pattern of proliferative crypt cell populations in early colon tumorigenesis, and 3) mutant crypt SCs clonally expand to form colonic adenomas and carcinomas.

Hypoxia induced by benign intestinal epithelial cells is associated with cyclooxygenase-2 expression in stromal cells through AP-1-dependent pathway

“…We also used Intestine-407 cells as a model for 'premalignant (benign)' tumor cells and Caco-2 or DLD-1 cells as a model for 'malignant' tumor cells. During tumor development, the density of tumor cells sometimes shows increase as compared with normal epithelial cells (Sonoshita et al, 2001;Preston et al, 2003;Boman et al, 2004). To examine whether such an increase of tumor cell density affected the COX-2 expression in fibroblasts adjacent to the tumor cells, we performed Western blot analysis for COX-2 protein of NIH3T3 fibroblasts co-cultured with tumor cells in the 'sparse' or 'dense' condition ( Figure 1a and b).…”

“…These data imply a universal regulatory mechanism of COX-2 induction in the stromal cells regardless of the nature of the adjacent epithelial cells. While considering such regulatory mechanisms of COX-2 induction, we noticed one of the common phenomena observed during the growth of intestinal adenomatous polyps and gastric hyperplastic polyps: the increase of epithelial cell number and density (Sonoshita et al, 2001;Preston et al, 2003;Boman et al, 2004). In addition, we are interested in the fact that COX-2 is expressed in the stromal cells that are not in direct contact with adjacent epithelial cells (Oshima et al, 1996;Chapple et al, 2002;Seno et al, 2002;Kawada et al, 2003).…”

“…Thus, a common regulatory mechanism of COX-2 expression appears to be present during neoplastic and non-neoplastic polyp development. Previous reports demonstrated that, in the course of colorectal tumor development, both the number and density of epithelial cells sometimes show remarkable increase compared with normal epithelium (Sonoshita et al, 2001;Preston et al, 2003;Boman et al, 2004), and that the overgrowth of tumor cells may result in hypoxia within the tumor tissues (Nordsmark et al, 1996). Thus, it may be considered that hypoxia within the tumor or polyp tissues induced by densely populated epithelial cells has some role in their own growth.…”

Mitochondrial Targeting of Adenomatous Polyposis Coli Protein Is Stimulated by Truncating Cancer Mutations

“…In sporadic human colorectal cancer and in the base cells of FAP adenomatous crypts, the two primary anti-apoptotic factors Bcl-2 and survivin are overexpressed relative to the normal colonic mucosa (30). Both Bcl-2 and survivin locate at mitochondria where they inhibit apoptosis and promote tumorigenesis (30). We knocked down APC by siRNA and observed a ϳ60% reduction in total Bcl-2 protein levels compared with control cells (Fig.…”

“…To partly address this, we used APC siRNA to investigate the regulation of cell survival factors. In sporadic human colorectal cancer and in the base cells of FAP adenomatous crypts, the two primary anti-apoptotic factors Bcl-2 and survivin are overexpressed relative to the normal colonic mucosa (30). Both Bcl-2 and survivin locate at mitochondria where they inhibit apoptosis and promote tumorigenesis (30).…”