Elevated protein expression of cyclin D1 and Fra‐1 but decreased expression of c‐Myc in human colorectal adenocarcinomas overexpressing β‐catenin

Abstract

Mutations of the adenomatous polyposis coli tumor suppressor gene, or its downstream target ␤-catenin, have been implicated in the initiation of most sporadic human colorectal epithelial neoplasms. These mutations, in turn, lead to aberrant nuclear accumulation of ␤-catenin and subsequent activation of the ␤-catenin/Tcf transcription factor complex. In vitro studies utilizing cultured human colon cancer cell lines have identified c-myc, cyclin D1 and fra-1 as target genes of ␤-catenin/Tcf signaling. In our study, 12 cases of human colorectal adenocarcinomas were examined by Western immunoblotting analysis and immunohistochemical staining to specifically investigate whether the protein expression of these target genes was indeed altered in vivo by ␤-catenin dysregulation. The results show that the protein level of ␤-catenin was significantly increased in all 12 tumors (3.4 ؎ 1.0-fold increase compared to the control normal mucosa by Western immunoblotting, p < 0.05), and this increase was associated with positive nuclear staining by immunohistochemistry in 10 cases. Increased levels of expression of cyclin D1 and Fra-1 proteins were also demonstrated in every tumor (9.0 ؎ 2.7 and 3.3 ؎ 0.9-fold increases compared to normal mucosa, respectively). Surprisingly, the protein level of c-Myc was significantly decreased in all tumors examined by 49 ؎ 19% (p < 0.05), but the c-myc mRNA level was increased in 8 of 12 tumors when compared to that in normal mucosa by RT-PCR. Immunohistochemical staining performed on these carcinomas and additional 27 colorectal carcinomas further demonstrated that the protein expression level of c-Myc and ␤-catenin nuclear localization were not correlated. Moreover, 15 of 20 colorectal adenomas exhibited positive nuclear ␤-catenin immunostaining, among which 11 also exhibited increased c-Myc protein expression. These data thus support the notion that upregulation of cyclin D1 and Fra-1 in human colorectal adenocarcinomas is driven by abnormally expressed ␤-catenin. However, the regulation of c-myc expression in colorectal tumors appears to be more complex. While dysregulated ␤-catenin may cause a transcriptional upregulation of the c-myc gene, the c-Myc protein expression appears to be further regulated by a posttranscriptional mechanism(s) during the process of neoplastic progression.

Immunohistochemical investigation of tumorigenic pathways in small intestinal adenocarcinoma: a comparison with colorectal adenocarcinoma

“…Thus, lack of immunoreactivity in tumor cells in the presence of positive staining in non-neoplastic cells would indicate the presence of gene mutations. 13,14 Our study demonstrates a significant lower frequency of negative immunostaining for adenomatous polyposis coli in small intestinal adenocarcinoma than in colorectal adenocarcinoma (31 vs 71%). However, this frequency appears to be somewhat higher than those reported by others using genetic or molecular approaches.…”

PAX2 Protein Induces Expression of Cyclin D1 through Activating AP-1 Protein and Promotes Proliferation of Colon Cancer Cells

“…AP-1 has been implicated in the pathogenesis of cancer in various tissues and plays a critical role in tumor promotion (25,(33)(34)(35). Increased expression of c-Jun has been reported in human colorectal carcinoma (36). A previous study revealed the role of AP-1 in the proliferation of the colon cancer HT29 cells (37).…”

Induction of HSF1 expression is associated with sporadic colorectal cancer

“…There are four signal transduction pathways described by Potter [3,4] to be involved in the oncogenesis of hereditary CRC: APC-β-catenin-TCF-myc (Wnt) pathway [5] , microsatellite unstable pathway [6] , p53 pathway and estrogen receptor hypermethylation pathway. However, the signal transduction pathways involved in sporadic CRC remain unclear.…”