Huntingtin protein (Htt) interplays with a large numbers of proteins and participates in diverse cellular pathways. Wide variety of Htt binding partners have been identified, including the Htt‐Interacting protein‐1 (HIP1) and Htt‐associated protein‐1 (HAP1). Htt has been shown pro‐apoptotic activity, and malfunctioning of Htt may result in cell outgrowth. HIP1 is involved in endocytosis and receptor trafficking and introduced as an oncoprotein. An altered expression of HIP1 has been reported in various cancers including breast cancer. HAP1 maintains the normal level of membrane TrkA by preventing the degradation of internalized TrkA. Recent evidence supports a role of HAP1 in micro‐tubule‐dependent organells transport, but its role in cancer development and progression has not been studied. We propose that the HAP1 and HIP1 may serve as a pair of “Ying‐Yang” modulators on the Htt functions and that the Htt‐HAP1‐HIP1 pathway may play an important role in the development and progression of breast cancer. We further propose that dietary/nutritional components that target this pathway may have chemopreventive effects on breast cancer. The objective of this study was to evaluate the differential expression and epigenetic modification patterns of Htt pathway related genes in normal and cancerous breast cells treated by dietary active components.

Human breast cancer cells were treated with dietary components known to prevent cancer cell growth and the effects of these components on HAP1, HIP1 and HTT expressions and promoter DNA methylations were investigated by using real‐time PCR, Methylation Specific PCR (MSP) and bisulfite sequencing. HAP1 gene was silenced in several breast cancer cell lines including MCF7, MDA‐MB231, MB453, SKBR3 and in much lower extent in immortalized MCF10A cells, but not in normal human mammary epithelial cell line (HMEC). Epigenetic analysis for Htt, HIP1 and HAP1 showed severe HAP1 promoter DNA hypermethylation in breast cancer cell lines, but not in HMEC. When the cells were treated with 5‐AZaC (a DNA demethylating agent) and butyrate (a HDAC inhibitor), we found that 5‐AZaC treatment significantly increased HAP1 expression by over 100 times, but butyrate had little effects. Treatment of the cells with dietary active compounds, sulfuraphane, EGCG, oridonin, tanshinone 2A and cryptotanshinone increased expression of HAP1 and HTT genes and decreased expression of HIP1 gene in HMEC, more significantly in cancer cell lines MCF7 and MB453. Preliminary studies indicate that these dietary components acted through modulation of HAP1 promoter methylation and further experiments are taking place to construct HTT and HAP‐1 expressing plasmids for further in vitro and in vivo gene function studies.

Citation Information: Cancer Prev Res 2010;3(1 Suppl):A60.