Abstract 4204: miR-205 functions as a tumor suppressor in breast cancer by targeting HMGB3.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Breast cancer is the most commonly diagnosed cancer and the second leading cause of death among women. Triple Negative Breast Cancer (TNBC) represents 10-20% of breast cancer patients. It is considered the most aggressive and challenging type of breast cancer due to the lack of effective targeted therapies. Metastatic TNBC commonly migrates to the lung, brain and liver. Chemotherapy is the only option for these patients and it is hard to predict the success of chemotherapy. It is crucial to investigate the molecular changes leading to TNBC and develop new therapies targeting the molecular changes that cause this disease. microRNA (miRNA) has been implicated in many cancers by deregulating the expression of genes having key roles in cancer initiation and/or progression. We measured the mature levels of miR-205 in five breast cell lines: MCF10A non-tumorigenic normal like epithelial cell line, MCF7 cancer cell line expressing both estrogen and progesterone receptors (ER+/PR+); MDA-MB-436, MDA-MB-231 and BT549 TNBC cell lines (ER-/PR-/HER2-). We also assayed miR-205 in 33 human breast tissues (benign, tumor and metastatic). miR-205 levels were significantly down regulated in breast cancer cell lines compared to normal-like breast epithelial cells and in tumor and metastatic tissues compared to benign. We identified two miR-205 predicted binding sites in the 3’ untranslated region of the high mobility group gene, HMGB3. Both Dual-luciferase reporter assay and Western blotting confirmed that miR-205 regulates HMGB3. To explore the function of miR-205 and HMGB3 in breast cancer, WST-1 proliferation and Matrigel invasion assays were done using the TNBC cell lines MDA-MB-231 and BT549 transiently transfected with precursor miR-205 oligonucleotide (pre-miR-205 oligo) or HMGB3 small interfering RNA (siRNA). Both treatments reduced the proliferation and invasion of the cancer cells, demonstrating that knockdown of HMGB3 with miRNA or siRNA is effective in reducing the malignant phenotype of this protein. The messenger RNA (mRNA) levels of HMGB3 significantly increased in the tumor and metastatic groups in a stage dependent manner suggesting a tumor initiating and progression role. Western blotting of HMGB3 protein from 5 matched pairs of breast tissue showed that HMGB3 protein was not detected in benign tissues but was present in tumor. In conclusion, regulation of HMGB3 by miR-205 reduced both proliferation and invasion of breast cancer cells. Since the down regulation of miR-205 in patients’ tumor specimens correlate with the high HMGB3 protein levels in tumor, our findings suggest that reintroducing miR-205 and targeting HMGB3 are potential therapies for TNBC. Citation Format: Ola Elgamal, Jong-Kook Park, Thomas D. Schmittgen. miR-205 functions as a tumor suppressor in breast cancer by targeting HMGB3. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4204. doi:10.1158/1538-7445.AM2013-4204