Abstract C21: A germline polymorphism in Necdin causes changes in gene expression and mammary tumor metastasis
Authors: Lee Minnkyong , Beggs Sarah M. , Lichtenberg Jens , Bupp Sujata B. , Trivedi Niraj S. , Hu Ying , Bodine David M. , Crawford Nigel P.S. 
Published: August 2014

Necdin (NDN) is a transcription factor that regulates gene expression by cooperating with chromatin modifying factors. Earlier studies using mouse models of mammary tumorigenesis identified Ndn as a metastasis efficiency modifier that exerts its influence at the germline level. Differential expression of Ndn induces a gene expression signature that accurately predicts prognosis in human breast cancer. Mouse Ndn contains a non-synonymous germline single nucleotide polymorphism (SNP) (T50C; V17A) that distinguishes mouse strains with differing susceptibilities to mammary tumor metastasis. The aim of this study is to characterize how germline variation in Ndn regulates metastasis-associated transcription to enhance our understanding of how hereditary factors influence metastasis in breast cancer. We hypothesize that NDN, a known transcription factor, induces metastasis-predictive gene expression by interacting with chromatin to regulate transcription, and that Ndn coding variants differ in their capacity in regulating the transcription of target genes.

To confirm the role of NDN in human breast cancer, haplotype analysis was performed in a population cohort consisting of 956 breast cancer patients. These analyses revealed that a two marker SNP haplotype in linkage disequilibrium with NDN is significantly associated with survival (P=0.0002). We examined the role of NDN in mammary tumor metastasis and transcriptional regulation by using cells stably over-expressing either the wildtype 17V or the variant 17A Ndn alleles in the highly metastatic Mvt-1 and 4T1 mouse mammary tumor cell lines. Orthotopic implantation of these cells into the mammary fat pad of NU/J and BALB/cJ mice demonstrated that cells expressing the wildtype Ndn 17V allele exhibit a significant decrease in pulmonary metastases compared to cells transduced with an empty vector control. However, these metastasis suppressive properties of Ndn were consistently lost in cells ectopically expressing the variant Ndn 17A allele, demonstrating a prominent role for this SNP in regulation of metastasis efficiency. Soft agar assays confirmed these results in vitro as well as, where a two-fold decrease in cell invasiveness was observed with the wildtype Ndn 17V allele compared to the control and cells over-expressing the variant Ndn 17A allele. Furthermore, microarray analyses revealed that a 71-gene expression signature accurately distinguished cells expressing the two Ndn allelic variants demonstrating that this SNP plays a significant part in gene regulation as well.

These data collectively demonstrate that Ndn functions as a germline metastasis modifier, most likely by regulating gene expression at the transcriptional level. Additionally, our work illustrates that the Ndn V17A SNP plays a significant role in both metastasis and transcriptional regulation. Our ongoing work is focused on defining the mechanism of action of Ndn V17A SNP using ChIP-seq to identify target genes and pathways responsible for the profound influence of Ndn allelic variants on metastatic efficiency.

Citation Format: Minnkyong Lee, Sarah M. Beggs, Jens Lichtenberg, Sujata B. Bupp, Niraj S. Trivedi, Ying Hu, David M. Bodine, Nigel P.S. Crawford. A germline polymorphism in Necdin causes changes in gene expression and mammary tumor metastasis. [abstract]. In: Proceedings of the Third AACR International Conference on Frontiers in Basic Cancer Research; Sep 18-22, 2013; National Harbor, MD. Philadelphia (PA): AACR; Cancer Res 2013;73(19 Suppl):Abstract nr C21.