Silencing of Wnt5a during colon cancer metastasis involves histone modifications

Colorectal cancer (CRC) is the third most common cancer in the United States. Approximately 90% of colon cancer deaths arise from the metastasis of primary tumors. Aberrant expression of Wnt5a, one of the WNT signaling factors, has been reported during colon cancer development and progression. We found that both mRNA and protein expression of Wnt5a were decreased in the highly metastatic human colon cancer cell line SW620 compared with the non-metastatic human colon cancer cell SW480. This study tested the hypothesis that the silencing of Wnt5a in metastatic human colon cancer cells is related to altered epigenetic modifications. Wnt5a expression was not responsive to DNA methyltransferase inhibitor 5-aza-cytidine treatment. However, histone deacetylase (HDAC) inhibitors trichostatin A (TSA) and sodium butyrate (NaBt) significantly increased Wnt5a mRNA expression in SW620. Importantly, lower transcription of Wnt5a in SW620 than SW480 corresponded to multiple histone modifications, including lower levels of acetylated histone H3, H4 and H3K4me2 and higher levels of H3K27me3 in the promoter region. The increase of H3Ac, H4Ac and H3K4me2 after NaBt treatment in SW620 confirmed the involvement of histone modifications in the transcriptional regulation of Wnt5a. Additionally, NaBt treatment increased β-catenin signaling and diminished the difference in cell adhesion ability between non-metastatic SW480 and metastatic SW620, suggesting that the HDAC inhibitor plays critical roles in the WNT signaling pathway and cell physiology that relate to metastasis. In conclusion, our study suggests the importance of Wnt5a in colon cancer metastasis and also indicates that Wnt5a silencing in the highly invasive human colon cancer cell line might result from transcriptional regulation of the gene by histone modifications.