Global Characterization of the SRC-1 Transcriptome Identifies ADAM22 as an ER-Independent Mediator of Endocrine-Resistant Breast Cancer

Abstract

The development of breast cancer resistance to endocrine therapy results from an increase in cellular plasticity that permits the emergence of a hormone independent tumor. The steroid coactivator protein SRC-1, through interactions with developmental proteins and other non-steroidal transcription factors, drives this tumor adaptability. In this discovery study we identified ADAM22, a non-protease member of the ADAM family of disintegrins, as a direct ER-independent target of SRC-1. We confirmed SRC-1 as a regulator of ADAM22 by molecular, cellular and in vivo studies. ADAM22 functioned in cellular migration and differentiation and its levels were increased endocrine resistant tumors compared to endocrine sensitive tumors in a mouse xenograft models of human breast cancer. Clinically ADAM22 was found to serve as an independent predictor of poor disease-free survival. Taken together, our findings suggest that SRC-1 switches steroid-responsive tumors to a steroid resistant state in which the SRC-1 target gene ADAM22 has a critical role, suggesting this molecule as a prognostic and therapeutic drug target that could help improve the treatment of endocrine-resistant breast cancer.

Global Gene Repression by the Steroid Receptor Coactivator SRC-1 Promotes Oncogenesis

“…Its predominant role, however, is as a transcriptional coactivator. In breast cancer, overexpression of SRC-1 confers on the cell the ability to adapt and overcome targeted therapy by upregulating developmental and dedifferentiation genes (7,11). Challenging the classic role of SRC-1 as a transcriptional activator, global analysis of direct SRC-1 targets described here, uncovered a significant number of repressed genes.…”

“…To identify SRC-1 target genes, chromatin immunoprecipitation (ChIP)-seq was conducted in endocrine-resistant LY2 cells that were treated with vehicle or tamoxifen (4-OHT, 10 À7 mol/L) for 45 minutes and immunoprecipitated with anti-SRC-1 (sc-8995; Santa Cruz Biotechnology) and anti-HOXC11 (Ab-37844; AbCam) antibodies as previously described (11). To identify functionally relevant SRC-1 target genes, DNA was hybridized to whole-genome expression arrays as previously described (11).…”

“…To identify functionally relevant SRC-1 target genes, DNA was hybridized to whole-genome expression arrays as previously described (11). Overlapping peaks between the SRC-1 ChIP-seq dataset and the HOXC11 ChIP-seq dataset were identified from ChIP sequencing of SRC-1 immunoprecipitated DNA with a false discovery rate (FDR) of <1 and the identified peaks from the HOXC11 immunoprecipitated DNA with a FDR of <10.…”

“…Overlapping peaks between the SRC-1 ChIP-seq dataset and the HOXC11 ChIP-seq dataset were identified from ChIP sequencing of SRC-1 immunoprecipitated DNA with a false discovery rate (FDR) of <1 and the identified peaks from the HOXC11 immunoprecipitated DNA with a FDR of <10. Genes downregulated by SRC-1 were submitted to DAVID bioinformatic database and arranged by functional annotation (11). Hypergeometric testing as implemented in R through the "phyper" function was used to calculate the P value significance between the SRC-1 ChIP data and SRC-1 downregulated gene from the expression array data.…”

“…Though other members of the p160 family, including SRC-2 (GRIP1/TIF2/NCoA2) and SRC-3 (AIB1/ACTR/RAC-3/pCIP/TRAM-1/NCoA3), have been investigated in endocrine-related cancer (8), a specific role for SRC-1 in the development of metastatic disease has been described (9,10). Global analysis of SRC-1 targets in breast cancer cells has identified pathways involved in growth factor signaling and cellular adaptability (11). Furthermore, molecular and in vivo studies have provided evidence that SRC-1 promotes disease progression and the development of metastasis, through the transcriptional activation of tumorigenic genes, including integrin-a5, ADAM22, and Myc (3,7,12).…”