Abstract 3058: miRNA networks mediate the tumor suppressive function of FOXO proteins.

FOXO transcription factors, as regulators of a variety of cellular functions, including promotion of apoptotic cell death, are negatively regulated by various oncogenic signaling cascades and have emerged as bona fide tumor suppressors. Indeed, studies by others and us have shown that the suppression of FOXO function is critical in promoting evasion of apoptosis and is a significant occurrence in several hematological malignancies. Consequently, FOXO proteins signify an important therapeutic target in hematopoietic malignancies as well as other types of cancer, where repression of FOXO plays a key role in malignancy. Since transcription factors are not yet easily “druggable," it is vital to identify mediators of FOXO function that can be readily targeted. It is now apparent that aberrant miRNA expression plays a major role in cell and tissue-specific manner in the pathogenesis of various types of cancers including hematological malignancies. Both miRNA loss of function and miRNA overexpression have been shown to target key cellular proteins and contribute to cancer pathogenesis. Conversely, miRNA genes themselves have been shown to be direct targets of transcription factors that are known as important tumor suppressors or oncogenic proteins. Through a systematic screening approach, we have identified members of three miRNA clusters that are dependent on FOXO transcription factors for expression. We have observed that the level of these miRNAs is dependent on BCR-ABL status of hematopoeitc cells and they their levels are changed in specimens from Leukemia patients. Our studies indicates a mechanism of action for FOXO tumor suppressors whereby members of two miRNA families are direct transcriptional targets of FOXO3. Moreover, these miRNAs target and reduce the expression of two key oncogenic factors, the serine/threonine kinase mTOR, and proto-onocogene c-myc, to keep cell growth at bay and prevent tumorigenesis. Our investigations have unraveled the miRNA arm of the FOXO tumor suppression network. Citation Format: Monica Nadler, Robin Zabolian, Kenneth Ndebele, thierry bertomeu, Octavian Bucur, Bodvael Pennarun, Roya Khosravi-Far. miRNA networks mediate the tumor suppressive function of FOXO proteins. [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 3058. doi:10.1158/1538-7445.AM2013-3058 Note: This abstract was not presented at the AACR Annual Meeting 2013 because the presenter was unable to attend.