Skp2 Regulates Subcellular Localization Of Ppar. By Mek Signaling Pathways In Human Breast Cancer

Nuclear hormone receptor family member PPAR plays an important role in mammary gland tumorigenesis. Previous studies have shown PPAR has cytoplasmic activities upon tetradecanoyl phorbol acetate (TPA) stimulation. However, the clinical pathological significance of cytoplasmic PPAR is not completely understood in human breast cancer. Skp2 is oncogenic, and its frequent amplification and overexpression correlated with the grade of malignancy. In this study, the role of cytoplasmic PPAR and Skp2 expression was investigated in human breast cancer progression. Therefore, immunohistochemical analysis was performed on formalin-fixed paraffin sections of 70 specimens. Furthermore, Western blot and immunofluorescence microscopy analysis were used to study the relationship between expression of cytoplasmic PPAR and Skp2 expression in human breast cancer cells in vitro. Results showed that the expression of cytoplasmic PPAR was positively correlated with Skp2 expression (p < 0.05), and correlated significantly with estrogen receptor (p = 0.026) and pathological grade (p = 0.029), respectively. In addition, Skp2 overexpression can provoke cytoplasmic localization of PPAR upon MEK1-dependent mechanisms in human breast cancer cells by nuclear-cytosolic fractionation technology and immunofluorescence microscopy analysis. Using RNA interference technology, we also found that down-regulated Skp2 reduced the phosphorylation level of MEK1 and significantly reversed TPA-induced nuclear export of PPAR in MDA-MB-231 cells. The changes in the subcellular localization of PPAR may represent a novel target for selective interference in patients with breast cancer.