Nuclear Receptors Are Differentially Expressed and Activated in KAIMRC1 Compared to MCF7 and MDA-MB231 Breast Cancer Cells

Abstract

We recently established a KAIMRC1 cell line that has unique features compared to the known breast cancer cell lines, MCF7 and MDA-MB231. To characterize it further, we investigated the expression profile of nuclear receptors and their respective co-factors in these cell lines. We confirm that in contrast to the triple negative cell line MDA-MB231, the MCF7 and KAIMRC1 are estrogen receptor alpha (ERa) and progesterone receptor alpha (PRa) positive, with significant lower expression of these receptors in KAIMRC1. KAIMRC1 cell is a vitamin D receptor (VDR) negative and V-ErbA-Related Protein 2 (EAR2) positive in contrast to MCF7 and MDA-MB231. Remarkably, the histone deacetylases (HDACs) are highly expressed in KAIRMC1 with HDAC6 and HDAC 7 are exclusively expressed in KAIMRC1 while thyroid hormone receptor-associated protein 80 (TRAP80), telomeric DNA binding protein 1 (TBP1) and TGF-beta receptor interacting protein (TRIP1) are absent in KAIMRC1 but present in MCF7 and MDA-MB231. In a luciferase reporter assay, the ERa coexpression is needed for estrogen receptor element (ERE)-luciferase activation by estradiol in KAIMRC1 but not in MCF7. The co-expression of exogenous Liver X receptor alpha (LXRa)/retinoid X receptor alpha (RXRa) are necessary for LXR responsive element (LXRE) activation by the GW3696 in the three cell lines. However, the activity of peroxisome proliferator-activated receptor response element (PPARE)-tk-luciferase reporter increased when peroxisome proliferator-activated receptors alpha (PPARa)/RXRa were coexpressed but the addition of PPARa agonist (GW7647) did not stimulate further the reporter. The signal of the PPARE reporter increased in a dose-dependent manner with rosiglitazone (PPARg agonist) in KAIMRC1, MCF7, and MDA-MB231 when the proliferator-activated receptors gamma (PPARg)/RXRa receptors were cotransfected. Retinoic acid-induced activation of retinoic acid receptor response element (RARE)-tk-luciferase is dependent on exogenous expression of retinoic acid receptor alpha (RARa)/RXRa heterodimer in MDA-MB 231 but not in MCF7 and KAIMRC1 cell lines. In the three cell lines, Bexarotene-induced retinoid X receptor response element (RXRE)-luciferase reporter activation was induced only if the RXRa/LXRa heterodimer were co-expressed. The vitamin D receptor response element (VDRE)-luciferase reporter activity showed another distinct feature of KAIMRC1, where only co-expression of exogenous vitamin D receptor (VDR)/RXRa heterodimer was sufficient to reach the maximum rate of activation of VDRE reporter. In the proliferation assay, nuclear receptors ligands showed a distinct effect on KAIMRC1 compared to MCF7 and MDA-MB231. Growth inhibition effects of used ligands suggest that KAIMRC1 correlate more closely to MDA-MB231 than MCF7. Vitamin D3, rosiglitazone, novel RXR compound (RXRc) and PPARa compound (GW6471) have the most profound effects. In conclusion, we showed that nuclear receptors are differentially expressed, activated and also their ligand produced distinct effects in KAIMRC1 compared to MCF7 and MDA-MB231. This finding gives us confidence that KAIMRC1 has a unique biological phenotype.