PKA-induced phosphorylation of ERα at serine 305 and high PAK1 levels is associated with sensitivity to tamoxifen in ER-positive breast cancer

Marleen Kok (1) , Wilbert Zwart (2) , Caroline Holm (3) , Renske Fles (1) , Michael Hauptmann (4) , Laura J. Van'T Veer (5) , Lodewyk F. A. Wessels (4) , Jacques Neefjes (2) , Olle Stål (6) , Sabine C. Linn (7, 8) , Göran Landberg (3, 9) , Rob Michalides (2)

1 Department of Experimental Therapy
2 Department of Cell Biology
3 Center for Molecular Pathology
4 Department of Bioinformatics and Statistics
5 Department of Pathology
6 Division of Oncology, Department of Clinical and Experimental Medicine
7 Department of Molecular Biology
8 Department of Medical Oncology
9 Breakthrough Breast Cancer Research Unit

Phosphorylation of estrogen receptor α at serine 305 (ERαS305-P) by protein kinase A (PKA) or p21-activated kinase 1 (PAK1) has experimentally been associated with tamoxifen sensitivity. Here, we investigated the clinical application of this knowledge to predict tamoxifen resistance in ER-positive breast cancer patients. Using immunohistochemistry, a score including PAK1 and co-expression of PKA and ERαS305-P (PKA/ERαS305-P) was developed on a training set consisting of 103 patients treated with tamoxifen for metastatic disease, and validated on 231 patients randomized between adjuvant tamoxifen or no treatment. In the training set, PAK1 levels were associated with tumor progression after tamoxifen (HR 1.57, 95% CI 0.99–2.48), as was co-expression of PKA and ERαS305-P (HR 2.00, 95% CI 1.14–3.52). In the validation set, a significant tamoxifen benefit was found among the 73% patients negative for PAK1 and PKA/ERαS305-P (HR 0.54, 95% CI 0.34–0.87), while others (27%) were likely to have no benefit from tamoxifen (HR 0.88, 95% 0.42–1.82). The test for interaction showed a significant difference in recurrence-free survival between groups defined by PAK1 and PKA/ERαS305-P ( = 0.037). Elevated PAK1 and PKA/ERαS305-P appeared to influence tamoxifen sensitivity. Both PAK1 and PKA/ERαS305-P levels were associated with sensitivity to tamoxifen in breast tumors and the combination of these variables should be considered in predicting tamoxifen benefit.

Mots clés: PKA; PAK1; Phosphorylation of ER; Tamoxifen sensitivity; Breast cancer

Marleen Kok, Wilbert Zwart, Caroline Holm, Renske Fles, Michael Hauptmann, et al.. PKA-induced phosphorylation of ERα at serine 305 and high PAK1 levels is associated with sensitivity to tamoxifen in ER-positive breast cancer. Breast Cancer Research and Treatment, 2010, 125 (1), pp.1-12. ⟨10.1007/s10549-010-0798-y⟩. ⟨hal-00554994⟩