Maff, A New Hypoxia Target Gene Involving Tumor Invasion And Metastasis

Activation of hypoxia‐inducible factor (HIF) under hypoxia is significantly correlated with tumor progression and treatment resistance by regulating target genes involved in invasion, metastasis, angiogenesis, apoptosis, and metabolism. This important role of HIF and hypoxia in promoting tumor progression provides a strong rationale to develop therapies that disrupt or target critical effectors of these pathways. V-Musculoaponeurotic Fibrosarcoma homolog F (MAFF) is a basic leucine zipper (bZIP) transcription factor that regulates antioxidative responses, hematopoiesis, and inflammation. However, its role in tumor hypoxia has not been well studied. In this study, we demonstrated that hypoxia specifically regulated MAFF in various tumor cell types and it was specifically induced by HIF-1 but not HIF-2. To determine the role of MAFF in tumor progression, we investigated tumor cells by both gain and loss of function studies. Knocking down MAFF in metastatic cancer cell lines, MDAMB-231 and OVCAR-8, resulted in reduced tumor cell invasion and metastasis both in vitro and in vivo. In contrast, overexpressing MAFF in non-metastatic cell lines, MCF7 and A549 increased tumor cell invasion. To elucidate the underlying mechanisms of MAFF-mediated tumor progression, we performed RNA sequencing in MDAMB-231 cells, which were exposed to either 20% O2 or 0.5% O2 with or without genetic inhibition of MAFF using siRNA. After performing a functional annotation using DAVID (Database for Annotation, Visualization, and Integrated Discovery) analysis, we observed genes involved in “blood vessel development” and “cell motility” were dysregulated in the absence of MAFF expression. In addition, genes relevant to “apoptosis”, “transcription”, and “inflammatory response” were altered when MAFF was inhibited. These observations suggest novel aspects of MAFF-mediated gene regulation. To further determine genes which were directly regulated by MAFF, we performed ChIP-sequencing with cells treated under normoxia or hypoxia. By combining profiles from RNA-sequencing and ChIP-sequencing, we highlighted 45 genes under normoxia and 44 genes under hypoxia. Among these, eight genes were regulated both under normoxia and hypoxia. Future studies will determine the set of genes that are responsible for tumor invasion and metastasis as well as other aspects of tumor progression. In conclusion, our study identifies MAFF as a novel HIF-1 target gene and also demonstrates its role in cell invasion and metastasis, which has not previously been described in cancer. This work may point towards a new therapeutic strategy to target tumor progression. Citation Format: Eui Jung Moon, Stephano S. Mello, Jen-Tsan Chi, Adam J. Krieg, Amato Giaccia. MAFF, a new hypoxia target gene involving tumor invasion and metastasis. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1628.