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Steroid receptor RNA activator protein (SRAP) expression as a prognostic factor in ER+ human breast tumors

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Abstract

Background

The steroid receptor RNA activator protein (SRAP) is a newly described protein modulating the activity of multiple transcription factors including the estrogen receptor (ER). We have recently reported the immunodetection by Western blot of multiple SRAP peptides in breast tissue. High expression of these peptides, assessed by tissue micro-array (TMA) analysis, was associated with poor prognosis in patients whose primary tumors were ER positive (ER+). In such studies, it is recognized that intensity as well as specificity of the signal detected directly depends upon the antibody used as well as the position of the epitope recognized. To confirm the potential relevance of SRAP as a new prognostic factor, it is critical to establish whether similar results are obtained with independent antibodies.

Methods

Two commercial anti-SRAP antibodies (742A and 743A), respectively, recognizing the N- and C-terminal extremity of the protein, were first used to analyze by Western blot SRAP expression in protein extracts from frozen breast tumor tissue sections. These antibodies were further used to investigate by immunohistochemistry (IHC) SRAP location in paraffin-embedded breast tumors. Comparative TMA analysis of 170 ER+ tumors was eventually performed in order to establish the potential associations existing between SRAP expression and clinical outcome.

Results

Multiple SRAP peptides were differentially detected by Western blot. Both antibodies led to similar nuclear and cytoplasmic staining in breast tissue section. A solid correlation was found (Spearman r = 0.46, P < 0.001) between 742A and 743A IHC scores. Results from both antibodies independently showed that dividing expression levels into lower 25 percentile, 26–75 percentile, and highest 25 percentile demonstrated a hazard ratio (HR) of 1.82 (P = 0.0042) for 742A antibody and 1.35 (P = 0.14) for 743A antibody. When both scores are combined, double high expressor (by 742A and 743A) was associated with a poor prognosis of breast-cancer-specific survival (Mantel–Cox: P = 0.005, HR = 2.24).

Conclusion

Overall, our data suggest the existence in breast tumor tissue of multiple SRAP-like peptides. Assessing their expression in primary breast tumors can predict clinical outcome in ER+ breast cancer patients.

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Acknowledgments

This work was supported by grants from the Canadian Institute of Health Research (CIHR), the CancerCare Manitoba Foundation (CCMF), the Manitoba Health Research Council (MHRC), and the Canadian Breast Cancer Foundation (CBCF). Y.Y. received a CIHR Graduate Studentship Award.

Conflict of interest

No competing interests to be declared.

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Authors and Affiliations

  1. Manitoba Institute of Cell Biology, 675 McDermot Ave., Winnipeg, MB, R3E0V9, Canada

    Yi Yan, Carla C. Penner, George P. Skliris, Charlton Cooper, Zoann Nugent, Anne Blanchard, Mohammad K. Hamedani, Xuemei Wang, Yvonne Myal, Leigh C. Murphy & Etienne Leygue

  2. Department of Biochemistry and Medical Genetics, University of Manitoba, 770 Bannatyne Avenue, Winnipeg, MB, R3E0W3, Canada

    Yi Yan, George P. Skliris, Mohammad K. Hamedani, Xuemei Wang, Leigh C. Murphy & Etienne Leygue

  3. Department of Physiology, University of Manitoba, 770 Bannatyne Avenue, Winnipeg, MB, R3E0W3, Canada

    Anne Blanchard & Yvonne Myal

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  1. Yi Yan
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  2. Carla C. Penner
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  3. George P. Skliris
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  4. Charlton Cooper
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  7. Mohammad K. Hamedani
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  8. Xuemei Wang
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  9. Yvonne Myal
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  10. Leigh C. Murphy
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  11. Etienne Leygue
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Correspondence to Etienne Leygue.

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432_2013_1485_MOESM1_ESM.eps

Supplementary material Fig. 1 Nuclear and cytoplasmic extracts from MCF7 cells were prepared as described in Materials and Methods and analyzed by Western blot using 742A and 743A (anti-SRAP) antibodies, anti-GAPDH antibody (cytoplasmic protein marker) and SP3 antibody (nuclear protein marker). A 30-Kd SRAP peptide was detected in both nuclear and cytoplasmic fraction. (EPS 1247 kb)

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Yan, Y., Penner, C.C., Skliris, G.P. et al. Steroid receptor RNA activator protein (SRAP) expression as a prognostic factor in ER+ human breast tumors. J Cancer Res Clin Oncol 139, 1637–1647 (2013). https://doi.org/10.1007/s00432-013-1485-2

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  • DOI: https://doi.org/10.1007/s00432-013-1485-2

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