Strain-specific homeostatic responses during early stages of Azoxymethane-induced colon tumorigenesis in mice.
Identifying molecular changes that predict the risk for developing colon cancer is critical for designing effective prevention strategies. In the present study, we determined early-stage molecular alterations within the colonic epithelium of A/J and AKR/J mice that are sensitive and resistant to Azoxymethane (AOM)-initiated tumor development, respectively. Six week-old male mice were injected intraperitoneally with AOM (10 mg/kg body weight) once a week for six weeks. One week after the last injection, distal colons from both strains were analyzed for cell proliferation using a proliferating cell nuclear antigen (PCNA) assay. Unlike AKR/J, a significant increase (2.5-fold, p<0.05) in the number of PCNA-positive cells within the upper third of the crypt compartment was observed in the A/J colons. This proliferative response was associated with a sizeable increase in the levels of c-myc mRNA, quantified by RNase protection assay. cDNA sequencing, protein expression and localization of beta-catenin, an upstream activator of c-myc, however, showed no aberrant changes within AOM-exposed A/J colons. Interestingly, TdT-mediated dUTP nick-end labeling assay revealed a significant increase (4-fold) in the number of apoptotic colonocytes in A/J mice following AOM treatment. Consistent with this finding, a modest increase in the expression of pro-apoptotic Bak was limited to the sensitive A/J colons. In summary, the current study suggests that a significant alteration in the rate of cell turnover in the normal appearing colonic mucosa, as observed in susceptible A/J mice, may be one of the earliest events predisposing the colon to neoplastic growth.
Guda
Kishore
K
Center for Molecular Medicine, University of Connecticut Health Center, Farmington, CT 06030, USA.
Marino
Jillian N
JN
Jung
Yonghwon
Y
Crary
Ken
K
Dong
Mei
M
Rosenberg
Daniel W
DW
D000818:Animals; D017209:Apoptosis; D001397:Azoxymethane / Q000633:toxicity*; D015153:Blotting, Western; D002273:Carcinogens / Q000633:toxicity*; D003106:Colon / Q000187:drug effects* / Q000473:pathology; D003110:Colonic Neoplasms / Q000139:chemically induced* / Q000473:pathology; D004847:Epithelial Cells / Q000187:drug effects; D020287:In Situ Nick-End Labeling; D007413:Intestinal Mucosa / Q000187:drug effects; D008297:Male; D051379:Mice; D008805:Mice, Inbred A; D008806:Mice, Inbred AKR; D011230:Precancerous Conditions / Q000139:chemically induced*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction