Abstract B23: Sulfotransferase isoform 1A1 (SULT1A1) gene expression is regulated by transcription factor NF1 in human breast cancer cell lines.

Abstract

Abstract Sulfotransferase isoform 1A1 (SULT1A1), a cytosolic phase II detoxification enzyme, plays a central role in drug metabolism, and breast cancer treatment and prevention drugs such as tamoxifen (TAM) and raloxifene (RAL) are among its substrates. Thus, regulation of this gene in target tissues could influence the efficacy of therapy. SULT1A1 activity varies several-fold in human populations, and genetic variants within the gene only account for a small proportion of the observed variability. Expression also varies with tissue type, with SULT1A1 being more highly expressed in breast tumors than in normal breast tissue. We have identified human nuclear factor 1(NF1) as a potential transcription factor (TF) regulating SULT1A1 gene expression in the ZR-75 breast cancer cell line. The NF1 gene family consists of NF1A, NF1B, NF1C, and NF1X. In order to determine the potential transcriptional regulation of SULT1A1 by NF1 genes in breast cancer in vitro, we measured and compared the mRNA levels of SULT1A1, NF1A, NF1B, NF1C, and NF1X in different human breast cancer cell lines (MCF7, T47D, ZR-75, and MDA-231) and the transformed human epithelial cell line MCF10A. SULT1A1 gene expression in each cell line was highly positively correlated with the gene expression of NF1B (p<0.01), NF1C (p<0.01), and NF1X (p<0.05). To determine if NF1s had a direct effect on SULT1A1 gene expression, ZR-75 cells, which have highest SULT1A1 gene expression among the cell lines tested, were transfected with siRNAs directed against NF1A, NF1B, NF1C, or NF1X for 48 hr. Real-time RT-PCR showed that mRNA levels of NF1A, NF1B, NF1C, and NF1X were decreased 70% ± 0.02, 87% ± 0.08, 81% ± 0.08, and 86% ± 0.12, respectively after transfection. SULT1A1 gene expression decreased 41% ± 0.05 (p=0.05) in siNF1A transfected cells and 64% ± 0.08 (p=0.05) in siNF1C transfected cells. ZR-75 cells were also co-transfected with siNF1A, siNF1B, and siNF1C for 48 hr. SULT1A1 mRNA level was decreased approximately 40%, indicating that there was no additive transcription regulatory effect on SULT1A1 gene expression among those three NF1s. Interestingly, SULT1A1 gene expression was decreased more than four-fold in siNF1B transfected MCF7 cells. In summary, our data demonstrates that SULT1A1 activity is partially regulated at the transcription level by transcription factors NF1A, NF1B, and NF1C. We are currently examining the expression levels of these genes in both normal and breast tumor tissue to identify a mechanistic explanation for the differential expression of SULT1A1 between normal breast tissue and breast tumors. This knowledge will lead to better predictors of therapeutic efficacy for chemopreventive agents that are substrates of SULT1A1. Citation Format: Aiwei Yao-Borengassar, Lora Rogers, Vinay Raj, Susan Kadlubar. Sulfotransferase isoform 1A1 (SULT1A1) gene expression is regulated by transcription factor NF1 in human breast cancer cell lines. [abstract]. In: Proceedings of the Eleventh Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2012 Oct 16-19; Anaheim, CA. Philadelphia (PA): AACR; Cancer Prev Res 2012;5(11 Suppl):Abstract nr B23.