Tumors from rats given 1,2-dimethylhydrazine plus chlorophyllin or indole-3-carbinol contain transcriptional changes in β-catenin that are independent of β-catenin mutation status

Abstract

Tumors induced in the rat by 1,2-dimethylhydrazine (DMH) contain mutations in β-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 β-catenin in more than 50 DMH-induced colon tumors and small intestine tumors, and compared this with the concomitant expression of β-catenin mRNA using quantitative real-time RT-PCR analysis. In total, 19/57 (33%) of the tumors harbored mutations in β-catenin, and 14/19 (74%) of the genetic changes substituted amino acids adjacent to Ser33, a key site for phosphorylation and β-catenin degradation. These tumors were found to express a 10-fold range of β-catenin mRNA levels, independent of the β-catenin mutation status and phytochemical exposure, i.e. CHL or I3C given post-initiation. However, β-catenin mRNA levels were strongly correlated with mRNA levels of c-myc, c-jun and cyclin D1, which are targets of β-catenin/Tcf signaling. Tumors with the highest levels of β-catenin mRNA often had over-expressed β-catenin protein, and those with lower β-catenin mRNA typically had low β-catenin protein expression, but there were exceptions (high β-catenin mRNA/low β-catenin protein, or vice versa). We conclude that DMH-induced mutations stabilize β-catenin protein in tumors, which increase c-myc, c-jun and cyclin D1, but there also can be over-expression of β-catenin itself at the mRNA level, contributing to high β-catenin protein levels. Similar findings have been reported in primary human colon cancers and their liver metastases, compared with matched normallooking tissue. Thus, further studies are warranted on the mechanisms that upregulate β-catenin at the transcriptional level in human and rodent colon cancers.

Chemopreventive effects of caraway powder and oils to suppress 1, 2- dimethylhydrazine-induced colon carcinogenesis

“…In regards to the effect of DMH metabolite produced by CYP450 on beta-catenin gene expression [15,16,18,19], the data of this research together with our previous results [34,35] imply that feeding of rats with caraway essential oils and powder could modulate the enzymes interfere with DMH metabolism (GST and CYP1A1) leading to the decreased level of β-catenin gene expression. These entire events, finally leaded to the decreased level of ACF formation terminating in decreased progression of colon…”

“…DMH metabolite produced by CYP450 may alter beta-catenin gene that control the growth and differentiation of the cells [16]. Treatment of rats with diet containing 0.2% caraway essential oils could successfully reverse the β-catenin levels in cooperation with decreased ACF formation ( Table 1, Fig 2-4).…”

“…In the progression of DMH carcinogenesis, the reactive metabolite causes the methylation of DNA in colonic epithelial cell leaded to β-catenin gene mutation [14][15][16][17][18][19]. β-catenin is a cadherin-binding protein that also functions as a transcriptional activator when complexes in the nucleus with members of the TCF/LEF family [20].…”

“…β-catenin is a cadherin-binding protein that also functions as a transcriptional activator when complexes in the nucleus with members of the TCF/LEF family [20]. In normal epithelial cell, cytosolic β-catenin interacts with adenomatous polyposis coli (APC), Axin, glycogen synthase kinase-3β (GSK 3β) and other proteins leading to phosphorylation of Ser and Thr in the N-terminal region of β-catenin, followed by ubiquitination and proteosomal degradation [16,20,21]. Mutation in β-catenin or APC prevents the phosphorylation and consequently β-catenin proteosomal degradation in cytoplasm leading to increased level of cytoplasmic β-catenin.…”

“…Mutation in β-catenin or APC prevents the phosphorylation and consequently β-catenin proteosomal degradation in cytoplasm leading to increased level of cytoplasmic β-catenin. This is resulted in accumulation of β-catenin/TCF/LEF complexes in the nucleolus and activation of downstream target oncogenes such as c-myc, c-jun and cyclin D1 leaded to colon cancer [16].…”