Abstract 1835: NFATC1 regulates the long non-coding RNA MALAT1 in breast cancer
Authors: Stone Joshua K. , Kim Jung-Hyun , Tan Ming , Ahn Eun-Young E. 
Published: July 2016

Metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) is a long non-coding RNA overexpressed in many solid tumors such as breast, colorectal, liver, lung, and pancreatic. Its expression progressively increases, first in comparison of adjacent normal tissue to the primary tumor and again from the primary tumor to secondary metastatic sites. It has been reported that MALAT1 controls gene expression through regulation of alternative mRNA splicing as well as chromatin binding and histone modification. These processes result in cell cycle advancement, cell proliferation and migration. In tumor cells, loss of MALAT1 prevents epithelial-mesenchymal transition (EMT), reduces proliferation, invasion, migration, and increases apoptosis. Even though MALAT1 is overexpressed in many tumors, the signaling pathways and transcription factors which regulate its expression are poorly understood.

To identify positive activators of MALAT1, we first selected candidate transcription factors for screening which were identified by ENCODE ChIP-Seq as bound to the MALAT1 promoter and were linked to metastasis. Through small inhibitory RNA (siRNA)-mediated knockdown, we identified NFATC1 (nuclear factor of activated T-cells, cytoplasmic, calcineurin-dependent 1) as a transcription factor that activates MALAT1 expression in multiple breast cancer cell lines. Overexpression of NFATC1 demonstrated an increase in MALAT1, verifying the siRNA results. Our luciferase reporter assay demonstrated that the MALAT1 promoter region is indeed controlled by NFATC1. Furthermore, chromatin immunoprecipitation using an NFATC1 antibody demonstrated enrichment of NFATC1 at multiple sites within the MALAT1 promoter region.

Examination of endogenous levels of NFATC1 and MALAT1 in five breast cancer cell lines indicated those which were HER2-positive had highest expression of both NFATC1 and MALAT1. To determine the effect of HER2 on NFATC1 activity and MALAT1 expression, we ectopically expressed HER2 in HER2-negative cell lines. Interestingly, this increased total and nuclear NFATC1 protein as well as MALAT1 transcript levels.

In conclusion, these results demonstrate that NFATC1 is a positive activator of MALAT1 in breast cancer and HER2 expression can modulate this activity. Notably, NFATC1 is associated with breast cancer EMT, invasion, and migration which match well with those phenotypes ascribed to MALAT1. Furthermore, HER2-positive status is associated with increased tumor proliferation and risk of metastasis. Therefore, our findings demonstrate that the HER2-NFATC1-MALAT1 signaling axis is a novel driver of breast cancer tumorigenesis and represents a potential therapeutic target.

Citation Format: Joshua K. Stone, Jung-Hyun Kim, Ming Tan, Eun-Young E. Ahn. NFATC1 regulates the long non-coding RNA MALAT1 in breast cancer. [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 1835.