Phenotypic alterations in breast cancer cells overexpressing the nuclear receptor co-activator AIB1.

Sarah L Anzick,David O Azorsa,S Stoney Simons,Paul S Meltzer

doi:10.1186/1471-2407-3-22

Abstract

BackgroundEstrogen signaling plays a critical role in a number of normal physiological processes and has important implications in the treatment of breast cancer. The p160 nuclear receptor coactivator, AIB1 (amplified in breast cancer 1), is frequently amplified and overexpressed in human breast cancer and has been shown to enhance estrogen-dependent transactivation.MethodsTo better understand the molecular and physiological consequences of AIB1 overexpression in breast cancer cells, an AIB1 cDNA was transfected into the low AIB1 expressing, estrogen-receptor (ER) negative breast cancer cell line, MDA-MB-436. The features of a derivative cell line, designated 436.1, which expresses high levels of AIB1, are described and compared with the parental cell line.ResultsA significant increase in the levels of CREB binding protein (CBP) was observed in 436.1 cells and immunofluorescent staining revealed altered AIB1 and CBP staining patterns compared to the parental cells. Further, transient transfection assays demonstrated that the overall estrogen-dependent transactivation in 436.1 cells is approximately 20-fold higher than the parental cells and the estrogen dose-response curve is repositioned to the right. Finally, cDNA microarray analysis of approximately 7,100 cDNAs identified a number of differentially expressed genes in the 436.1 cells.ConclusionThese observations lend insight into downstream signaling pathways that are influenced by AIB1.

Highlights

Estrogen signaling plays a critical role in a number of normal physiological processes and has important implications in the treatment of breast cancer
MDA-MB-436 cells were transfected with an expression vector containing the full-length human AIB1 cDNA and cultured in the presence of neomycin for the selection of stable transfectants
To determine if the transfected cells expressed the exogenous AIB1 cDNA, RNAs from viable clonal populations were analyzed by Northern blot

Summary

Introduction

Estrogen signaling plays a critical role in a number of normal physiological processes and has important implications in the treatment of breast cancer. Critical to estrogen signaling are the interactions of ER-α with transcriptional coactivators including p/CAF, CREB binding protein (CBP), p300, and the p160 family members (reviewed in [5]). It isthought that the coactivators activate transcription through the modification of histonesand the bridging of (page number not for citation purposes). Transcriptional activation through ER-α depends upon an ordered assembly of coactivator proteins on and off the promoter of the targetgene in a cyclic fashion [6,7] This selective modulation of cofactor assembly potentially contributes to the tightly regulated pattern of tissue-specific estrogen response

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Conclusion