PMID:27614840

Citation	Wen, G, Pachner, LI, Gessner, DK, Eder, K and Ringseis, R' (2016) Sterol regulatory element-binding proteins are regulators of the sodium/iodide symporter in mammary epithelial cells. J. Dairy Sci. '
Abstract	The sodium/iodide symporter (NIS), which is essential for iodide concentration in the thyroid, was reported to be transcriptionally regulated by sterol regulatory element-binding proteins (SREBP) in rat FRTL-5 thyrocytes. The SREBP are strongly activated after parturition and throughout lactation in the mammary gland of cattle and are important for mammary epithelial cell synthesis of milk lipids. In this study, we tested the hypothesis that the NIS gene is regulated also by SREBP in mammary epithelial cells, in which NIS is functionally expressed during lactation. Regulation of NIS expression and iodide uptake was investigated by means of inhibition, silencing, and overexpression of SREBP and by reporter gene and DNA-binding assays. As a mammary epithelial cell model, the human MCF-7 cell line, a breast adenocarcinoma cell line, which shows inducible expression of NIS by all-trans retinoic acid (ATRA), and unlike bovine mammary epithelial cells, is widely used to investigate the regulation of mammary gland NIS and NIS-specific iodide uptake, was used. Inhibition of SREBP maturation by treatment with 25-hydroxycholesterol (5 µM) for 48 h reduced ATRA (1 µM)-induced mRNA concentration of NIS and iodide uptake in MCF-7 cells by approximately 20%. Knockdown of SREBP-1c and SREBP-2 by RNA interference decreased the mRNA and protein concentration of NIS by 30 to 50% 48 h after initiating knockdown, whereas overexpression of nuclear SREBP (nSREBP)-1c and nSREBP-2 increased the expression of NIS in MCF-7 cells by 45 to 60%, respectively, 48 h after initiating overexpression. Reporter gene experiments with varying length of NIS promoter reporter constructs revealed that the NIS 5'-flanking region is activated by nSREBP-1c and nSREBP-2 approximately 1.5- and 4.5-fold, respectively, and activation involves a SREBP-binding motif (SRE) at -38 relative to the transcription start site of the NIS gene. Gel shift assays using oligonucleotides spanning either the wild-type or the mutated SRE at -38 of the NIS 5'-flanking region showed that in vitro-translated nSREBP-1c and nSREBP-2 bind only the wild-type but not the mutated SRE at -38 of NIS. Collectively, the present results from cell culture experiments with human mammary epithelial MCF-7 cells and from genetic studies show for the first time that the NIS gene and iodide uptake are regulated by SREBP in cultured human mammary epithelial cells. Future studies are necessary to clarify if the regulation of NIS expression and iodide uptake by SREBP also applies to the lactating bovine mammary epithelium.
Links	PubMed Online version:10.3168/jds.2016-11174
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
HUMAN:SRBP1		GO:0032933: SREBP signaling pathway	ECO:0000315:		P		Figure 2B. RNA interference-mediated knockdown of (SREBP)-1c reduces expression of sodium/iodide symporter (NIS) in MCF-7 cells.	complete CACAO 12104
HUMAN:SRBP1		GO:0032933: SREBP signaling pathway	ECO:0000314:		P		Figure 4B and 4C. nSREBP-1c Transcriptionally Activates the 5′-Flanking Region of hNIS in MCF-7 Cells	complete CACAO 12106
HUMAN:SRBP2		GO:0032933: SREBP signaling pathway	ECO:0000315:		P		Figure 2B. RNA interference-mediated knockdown of SREBP-2 decreases the expression of sodium/iodide symporter (NIS) in human MCF-7 cells.	complete CACAO 12107
HUMAN:SRBP2		GO:0032933: SREBP signaling pathway	ECO:0000314:		P		Figure 4B and 4C. nSREBP-2 transcriptionally activates the 5′-Flanking Region of hNIS in human MCF-7 Cells	complete CACAO 12108

References

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