Cytoplasmic HuR expression correlates with P-gp, HER-2 positivity, and poor outcome in breast cancer

HuR is an ubiquitously expressed RNA-binding protein that stabilizes messenger RNA and regulates translation. This protein has been shown to play an important role in carcinogenesis and cancer progression. P-glycoprotein (P-gp) is the product of the multidrug resistance 1 gene, and the overexpression of P-gp induces multidrug resistance and represents a major obstacle in cancer chemotherapy. The purpose of this study was to determine the expression of HuR and P-gp in human breast cancer tissues and analyze the relationship between HuR or P-gp expression and the clinical-pathological variables and patient outcomes. Immunohistochemistry was used to determine HuR and P-gp expression in 82 human breast cancer tissues and 20 matched adjacent noncancerous tissues. Additionally, 16 benign breast tumor samples were used as controls. The overexpression of cytoplasmic HuR was found in breast cancer but not in the matched adjacent noncancerous tissues or benign breast tumors. The expression levels of cytoplasmic HuR were significantly associated with increased age, high nuclear grade, and the positive expression of the ER, PR, and HER-2/neu. HuR was also associated with the expression of P-gp protein. Furthermore, univariate analysis indicates that patients with high expression levels of cytoplasmic HuR or P-gp had significantly reduced survival compared to patients with low expression levels. A multivariate analysis showed that age at diagnosis, nuclear grade, and cytoplasmic HuR positivity were independent indicators for disease-free survival and overall survival in patients with breast cancer. In conclusion, cytoplasmic HuR expression detected by immunohistochemical staining is a negative prognostic indicator for survival in patients with breast cancer.