Cyclooxygenase and its derived prostaglandin E 2 (PGE 2 ) have been shown to stimulate the growth of cancer cells and promote tumor angiogenesis. Here, we show that PGE 2 activated the ␤-catenin/T cell factordependent transcription in colon cancer cells through the cAMP/protein kinase A pathway. The expression of cyclin D1 and vascular endothelial growth factor was induced by PGE 2 in LS-174T cells. Moreover, PGE 2 and mutated ␤-catenin stimulated the transcription of cyclin D1 and vascular endothelial growth factor in a synergistic fashion. Mechanistically, PGE 2 increased the phosphorylation of glycogen synthase kinase-3 and consequently accumulated ␤-catenin. In addition, PGE 2 induced the expression of T cell factor-4 transcription factor, which formed transcriptionally active complex with ␤-catenin. In animal experiments, administration of 16,16-dimethyl PGE 2 strongly increased the expression of cyclin D1 and vascular endothelial growth factor in APC min/؉ mouse polyps. Thus, our results provide a novel mechanism, suggesting that cyclooxygenase-2/PGE 2 may exert pro-oncogenic actions through stimulating the ␤-catenin/T cell factor-mediated transcription, which plays critical roles in colorectal carcinogenesis.

ABSTRACT

BackgroundCoactivator-associated arginine methyltransferase 1 (CARM1) functions as a transcriptional coactivator of androgen receptor (AR)-mediated signaling. Correspondingly, overexpression of CARM1 has been associated with the development of prostate cancer (PCa) and its progression to androgen-independent PCa. In our preliminary study, however, the promoting effects of CARM1, with regard to androgen-stimulated AR target gene expression were minimal. These results suggested that the AR target gene expression associated with CARM1 may result primarily from non-hormone dependent activity. The goal of this study was to confirm the pattern of expression of CARM1 in human tumors and determine the mechanism of action in CARM1 overexpressed tumors.MethodsTissue microarray was used to determine the pattern of expression of CARM1 in human cancers by immunohistochemistry. CARM1 expression was also evaluated in prostate and colorectal surgical specimens and the clinical records of all cases were reviewed. In addition, a reporter transcription assay using the prostate-specific antigen (PSA) promoter was used to identify the signaling pathways involved in non-hormone-mediated signal activation associated with CARM1.ResultsThe tissue microarray showed that CARM1 was particularly overexpressed in the colorectal cancers while CARM1 expression was not prevalent in the prostate and breast cancers. Further studies using surgical specimens demonstrated that CARM1 was highly overexpressed in 75% of colorectal cancers (49 out of 65) but not in the androgen-independent PCa. In addition, CARM1's coactivating effect on the entire PSA promoter was very limited in both androgen-dependent and androgen-independent PCa cells. These results suggest that there are other factors associated with CARM1 expression in PSA regulation. Indeed, CARM1 significantly regulated both p53 and NF-κB target gene transcription.ConclusionsThe results of this study suggest that, in addition to its role in activation of steroid receptors, CARM1 functions as a transcriptional modulator by altering the activity of many transcriptional factors, especially with regard to androgen independent PCa and colorectal cancers.

In prostate gland, HOXB13 is highly expressed from the embryonic stages to adulthood. However, the function of HOXB13 in normal cell growth and tumorigenesis is not yet known. We investigated the role of HOXB13 and mechanism by which it functions in HOXB13-negative cells. Expression of HOXB13 was forced in HOXB13-negative PC3 prostate cancer cells using a liposome-mediated gene transfer approach. Compared with the control clones, HOXB13-expressing PC3 cells exhibited significant inhibition of in vitro and in vivo cell growth with G 1 cell cycle arrest mediated by the suppression of cyclin D1 expression. Because cyclin D1 is mainly regulated by ␤-catenin/T-cell factor (TCF), TCF-4 response element was used in a reporter gene transcription assay, demonstrating that HOXB13 significantly inhibits TCF-4-mediated transcriptional activity in both prostate and nonprostate cells. This inhibition occurred in a doseresponsive manner and was specific to TCF-4 response element. Western blot analysis demonstrated that HOXB13 down-regulates the expression of TCF-4 and its responsive genes, c-myc and cyclin D1. HOXB13 also suppressed the activity of natural c-myc promoter. This study suggests that HOXB13, a transcription factor, functions as a cell growth suppressor by negatively regulating the expression of TCF-4, which eventually provides negative signals for cell proliferation. This observation will provide valuable insight into the molecular basis of prostate tumorigenesis.