Estrogens Correlate with <i>PELP1</i> Expression in ER Positive Breast Cancer

<div><p>The Proline-, glutamic acid- and leucine-rich protein 1 (<i>PELP1</i>) is an estrogen receptor (ER) coactivator and a proto-oncogene known to be deregulated in endocrine cancers. In breast cancer, <i>PELP1</i> overexpression has been associated with endocrine therapy resistance. Although <i>PELP1</i> is known to be regulated by estrogens <i>in vitro</i>, its association with estrogen levels within the tissue of breast cancer patients has not previously been assessed. Here, we determined <i>PELP1</i> mRNA expression levels in paired samples of normal and malignant breast tissue obtained from 32 postmenopausal and 11 premenopausal women. In the total sample set, <i>PELP1</i> levels were higher in tumors compared to normal breast tissue (<i>P</i> = 0.041). Among postmenopausal women, <i>PELP1</i> tumor levels correlated positively with estrone (E₁) and estradiol (E₂) levels in both normal tissue (r = 0.543, <i>P</i> = 0.003 and r = 0.601, <i>P</i> = 0.001, respectively) and plasma (r = 0.392, <i>P</i> = 0.053 and r = 0.403, <i>P</i> = 0.046, respectively). Analyzing all ER+ tumors (n = 26), <i>PELP1</i> correlated positively with E₁ and E₂ in tumor tissue (r = 0.562, <i>P</i> = 0.003 and r = 0.411, <i>P</i> = 0.037, respectively) and normal tissue (r = 0.461, <i>P</i> = 0.018 and r = 0.427, <i>P</i> = 0.030, respectively) in addition to plasma E₁, E₂ and estrone sulphate (E₁S) concentrations (r = 0.576, <i>P</i> = 0.003, r = 0.456, <i>P</i> = 0.025 and r = 0.406, <i>P</i> = 0.049, respectively). Finally, <i>PELP1</i> correlated positively with ER mRNA (<i>ESR1)</i> (r = 0.553, <i>P</i> = 0.026) in ER+ tumors, whereas a negative association between <i>PELP1</i> and <i>ESR1</i> (r = -0.733, <i>P</i> = 0.010) was observed in ER- breast tumors. Taken together, tumor <i>PELP1</i> mRNA expression is associated with estrogen levels in breast cancer, suggesting a potentially important role of <i>PELP1</i> in ER+ breast cancer growth <i>in vivo</i>.</p>