Abstract 4256: Neuroendocrine, stem, and stromal cell interactions involved in the organization of the normal colonic stem cell niche which become disorganized during colon tumorigenesis

In development of colorectal cancer (CRC), stem cell (SC) overpopulation underlies tumor initiation and progression, but it is incompletely understood which dysregulated mechanisms cause SC overpopulation. Because neuroendocrine cell (NEC) and SC populations both reside in the SC niche at the normal crypt bottom, we hypothesized that i) NECs play a role in maintaining the SC population, and ii) changes in the NEC population contributes to SC overpopulation and altered epithelial: stromal interactions during tumorigenesis. Immunofluorescence mapping and flow cytometry were used to analyze SC niche structure and cell-cell interactions in normal and neoplastic colonic tissues from Caucasian and African-American patients. In normal colonic crypts, most cells (77%) staining positively for the colonic SC marker ALDH1, also co-stained for the NE cell marker chromogranin-A (CGA). In the progression from normal to normal-appearing FAP to adenomatous to malignant colonic tissue, the proportion of ALDH1+/CGA+ cells progressively diminished while the proportion of ALDH1+/CGA- cells increased. The epithelial phenotype of tumor cells was confirmed by co-staining for pancytokeratin. These data suggest that colonic SC express a NE phenotype, and loss of this phenotype is associated with an increased number of SC during colon tumorigenesis. Our studies using flow cytometry and CRC cell lines (COLO320, DiFi, LIM1863, LoVo, SW480, HCT116 & HT29) revealed that each line is characterized by the proportion of cells having a SC phenotype (ALDEFLUOR+) and NEC phenotype (SSTR+ or GLPR2+). have a low proportion. These findings suggest that these proportions are maintained constant through feedback mechanisms involving SC and NEC subpopulations. Our studies of epithelial-stromal interactions used immunofluorescence mapping of basement membrane proteins (Perlecan; collagen IV), inflammation markers (Cox2; Caveolin 1), pericryptal fibroblasts (smooth muscle actin), endothelial cells (CD34) and macrophages (CD68). Our results show that the stroma undergoes progressive disorganization (particularly pericryptal fibroblasts & basement membrane) in parallel with increasing size of the SC population during colon tumorigenesis. These results suggest that genetic changes occurring during colon tumorigenesis lead to breakdown of stromal-epithelial interactions that are crucial to the maintenance of the stem cell niche, which contributes to colonic tissue disorganization that is a cardinal feature of cancer. Taken together, our investigations yield insights into: (i) the control of normal SC populations (including how the SC niche is maintained), (ii) molecular mechanisms underlying SC overpopulation in tumorigenesis, and (iii) potential targets for novel anti-cancer therapeutic strategies. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4256.