Effects of PP4 suppression on the proliferation of MCF7 cells

PP4, one of the few protein phosphatases associated with centrosome in cells of many species such as Drosophila, C. elegans and mammals, plays an essential role in the regulation of centrosome functions in Drosophila and C. elegans. In order to explore the role of PP4 in mammalian cells, full-length PP4 gene was obtained by RT-PCR from MCF7 cell total RNA and inserted into eukaryotic expression vector pEGFP-C1. The resultant construct pEGFP-C1-PP4 was transfected into MCF7 cells and immunostaining was carried out to confirm the centrosome localization of PP4. Then we reversely subcloned a non-conserved domain of PP4 into pXJ41 to construct an anti-sense vector pXJ41-as-PP4. By transfecting pXJ41-as-PP4 into MCF7 cells and screening with 6418, we obtained a stable cell line in which PP4 expression was stably suppressed. The cell line was analyzed on cell morphology, cytoskeleton structure, growth characteristics and the mitosis process. It was found that the proliferation rate decreased and serum-dependence increased in PP4-suppressed cells. Furthermore, flow cytometry and mitotic index analysis showed that G2/M transition was prolonged. PP4 suppression resulted in abnormal interphase microtubule, formation of multipolar spindles and an increase in percentage of multinuclear cells. These results suggested that PP4 is required for centrosome function in mammalian cells.