Phospho-Serine-118 Estrogen Receptor-α Detection in Human Breast Tumors in Vivo

Purpose: To determine whether estrogen receptor (ER)-α specifically phosphorylated at Ser 118 is detectable in multiple human breast cancer biopsy samples. To gain insight into possible roles for P-Ser 118 -ERα in human breast cancer in vivo . Experimental Design: A specific antibody for P-Ser 118 -ERα was validated for immunohistochemistry (IHC), and Western blot analysis confirmed IHC results. IHC was used to determine the relationship of P-Ser 118 -ERα to known prognostic markers and active mitogen-activated protein kinase (MAPK; erk1/2) expression. Results: P-Ser 118 -ERα was significantly correlated with the expression of total ER, determined by ligand binding assay ( r = 0.442, P = 0.002), but not with progesterone receptor expression or nodal status. P-Ser 118 -ERα was inversely correlated with histological grade ( r = −0.34, P = 0.023), reflecting a similar trend for total ER ( r = −0.287, P = 0.056). Categorical contingency analysis confirmed that P-Ser 118 -ERα was more frequently associated with lower than higher grade breast tumors ( P = 0.038). In addition P-Ser 118 -ERα was significantly associated with detection of active MAPK (Erk1/2; Spearman r = 0.649, P < 0.0001; Fisher’s exact test, P = 0.0004). Conclusions: P-Ser 118 -ERα detection is associated with a more differentiated phenotype and other markers of good prognosis in human breast cancer. P-Ser 118 -ERα is correlated with active MAPK in human breast tumor biopsies, suggesting the possibility that active MAPK either directly or indirectly has a role in the regulation of P-Ser 118 -ERα expression in vivo . These data provide evidence for a role of P-Ser 118 -ERα in human breast cancer in vivo .