Abstract
Abstract CD44, a major hyaluronic acid (HA) receptor, is involved in cell migration, metastasis and tumor progression. While in normal ovarian epithelium CD44 is not expressed, ovarian carcinoma cells express multiple CD44 isoforms as the tumor progresses and eventually CD44 expression is abrogated in advanced ovarian cancer metastatic sites. We as well as others have observed that the levels of CD44 mRNA transcript not always correspond to the CD44 protein expression levels. This observation suggests that CD44 is post-transcriptionally regulated. To test this hypothesis we first analyzed the CD44 3’ untranslated region (3’ UTR) sequence and found numerous AU-rich elements (ARE) in this region. Some of these sequences are known HuR binding site consensus sequences. HuR is an RNA binding protein that is known to stabilize transcripts. HuR is expressed in the nucleus and is transported to the cytoplasm where it functions as an mRNA stabilizer. We performed mRNA half-life experiments that showed a two-fold reduction in the stability of CD44 transcript in siHuR transfected ovarian cancer cells. Consistent with this result, treatment of these cells with inhibitors of DNA methylation and histone deacetylation (i.e., 5-azacytidine and Trichostatin A, respectively) known to diminish the presence of HuR in the cytoplasm, also decreased the stability of CD44 mRNA. Western blot analysis showed the expected reduction in cytoplasmic HuR as well as down-regulation in CD44 protein expression. A direct interaction of HuR with the CD44 3’ UTR was detected by biotin pulldown assays. These results indicate that HuR posttranscriptionally stabilizes the expression of CD44 in the cytoplasm. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3078. doi:10.1158/1538-7445.AM2011-3078
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