Tumors from rats given 1,2-dimethylhydrazine plus chlorophyllin or indole-3-carbinol contain transcriptional changes in beta-catenin that are independent of beta-catenin mutation status.
Tumors induced in the rat by 1,2-dimethylhydrazine (DMH) contain mutations in beta-catenin, but the spectrum of such mutations can be influenced by phytochemicals such as chlorophyllin (CHL) and indole-3-carbinol (I3C). In the present study, we determined the mutation status of beta-catenin in more than 50 DMH-induced colon tumors and small intestine tumors, and compared this with the concomitant expression of beta-catenin mRNA using quantitative real-time RT-PCR analysis. In total, 19/57 (33%) of the tumors harbored mutations in beta-catenin, and 14/19 (74%) of the genetic changes substituted amino acids adjacent to Ser33, a key site for phosphorylation and beta-catenin degradation. These tumors were found to express a 10-fold range of beta-catenin mRNA levels, independent of the beta-catenin mutation status and phytochemical exposure, i.e. CHL or I3C given post-initiation. However, beta-catenin mRNA levels were strongly correlated with mRNA levels of c-myc, c-jun and cyclin D1, which are targets of beta-catenin/Tcf signaling. Tumors with the highest levels of beta-catenin mRNA often had over-expressed beta-catenin protein, and those with lower beta-catenin mRNA typically had low beta-catenin protein expression, but there were exceptions (high beta-catenin mRNA/low beta-catenin protein, or vice versa). We conclude that DMH-induced mutations stabilize beta-catenin protein in tumors, which increase c-myc, c-jun and cyclin D1, but there also can be over-expression of beta-catenin itself at the mRNA level, contributing to high beta-catenin protein levels. Similar findings have been reported in primary human colon cancers and their liver metastases, compared with matched normal-looking tissue. Thus, further studies are warranted on the mechanisms that upregulate beta-catenin at the transcriptional level in human and rodent colon cancers.
Wang
Rong
R
Linus Pauling Institute, Oregon State University, Corvallis, OR 97331, USA.
Dashwood
W Mohaiza
WM
Bailey
George S
GS
Williams
David E
DE
Dashwood
Roderick H
RH
D019813:1,2-Dimethylhydrazine / Q000633:toxicity*; D000818:Animals; D016588:Anticarcinogenic Agents / Q000494:pharmacology; D002273:Carcinogens / Q000633:toxicity; D002735:Chlorophyllides / Q000494:pharmacology*; D003110:Colonic Neoplasms / Q000139:chemically induced / Q000235:genetics; D019938:Cyclin D1 / Q000235:genetics; D004252:DNA Mutational Analysis / Q000379:methods; D007211:Indoles / Q000494:pharmacology*; D008297:Male; D009154:Mutation / Q000235:genetics*; D009374:Neoplasms, Experimental / Q000139:chemically induced / Q000235:genetics*; D016755:Proto-Oncogene Proteins c-jun / Q000235:genetics; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014158:Transcription, Genetic / Q000187:drug effects; D051176:beta Catenin / Q000235:genetics*
D016588:Anticarcinogenic Agents; D002273:Carcinogens; D002735:Chlorophyllides; D007211:Indoles; D016755:Proto-Oncogene Proteins c-jun; D016271:Proto-Oncogene Proteins c-myc; D012333:RNA, Messenger; D051176:beta Catenin; D019938:Cyclin D1; C016517:indole-3-carbinol; C007020:chlorophyllin; D019813:1,2-Dimethylhydrazine