PurposeProtein phosphatase 4 regulatory subunit 1 (PP4R1), as an interaction partner of the catalytic serine/threonine-protein phosphatase 4 catalytic subunit has been shown to involve in cellular processes and nuclear factor κB signaling. However, the functions of PP4R1 in human breast cancers remain unclear. This study is designed to explore the effect of PP4R1 knockdown on the biological characteristics of breast cancer cells.MethodsA lentivirus-mediated short hairpin RNA (shRNA) was designed to knockdown the expression of PP4R1 in ZR-75-30 breast cancer cells. The efficiency of lentivirus-mediated shRNA infection was determined using fluorescence microscopy to observe lentivirus-mediated green fluorescent protein expression and confirmed to be over 80%. PP4R1 expression in infected ZR-75-30 cells was detected by quantitative real-time polymerase chain reaction and western blot analysis. Cell proliferation and colony formation ability were measured by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT) assay and colony formation assay, respectively. Flow cytometry was used to measure cell cycle progression and cell apoptosis. In addition, apoptosis makers, including poly-ADP-ribose polymerase (PARP) and caspase-3, were investigated in PP4R1-silenced ZR-75-30 cells by western blot assay.ResultsWe successfully constructed lentivirus-mediated shRNA to target PP4R1 in ZR-75-30 cells. MTT assay and colony formation assay showed the loss of PP4R1 suppressed the proliferation of ZR-75-30 cells. Flow cytometry analysis indicated cell cycle arrest and increased cell apoptosis in PP4R1 knockdown cells. Further, the apoptosis response in cells depleted of PP4R1 was illustrated by downregulation of PARP and upregulation of caspase-3.ConclusionOur results suggest that PP4R1 could promote breast cancer cell proliferation and might play a vital role in breast cancer occurrence.

Expression of Krüppel-like factor 9 (KLF9) in breast cancer tissue and its influence on prognosis was investigated. Sixty-eight patients with breast cancer admitted in Ningde Hospital Affiliated to Fujian Medical University from February 2014 to August 2015 were collected, and the expression level of KLF9 in cancerous tissue (n=68) and normal tissue (n=68) of the patients was measured by quantitative real-time PCR (RT-qPCR). The relationship between the expression and clinical pathological features and prognosis of patients was analyzed. The expression level of KLF9 in cancerous tissue was significantly lower than that in normal tissue (P<0.05). The expression in breast cancer tissue was not significantly correlated with age, height, menstrual status, lymph node metastasis or pathological differentiation (P>0.05), but was significantly correlated with tumor size and clinical stage (P<0.05). The 1-, 2-, and 3-year survival rates in the high expression group were significantly higher than those in the low expression group (P<0.001). Univariate Cox regression analysis was carried out according to the 3-year survival of the patients, and the results showed that tumor size (P= 0.009), lymph node metastasis (P= 0.002), pathological differentiation (P=0.015), clinical stage (P=0.013), and KLF9 (P=0.018) were factors affecting the survival of breast cancer patients. Subsequently, multivariate Cox regression analysis of the indicators with differences showed that those indicators were independent predictors of survival of breast cancer patients. In conclusion, KLF9 expression is low in breast cancer tissue, and its expression level is related to tumor size and clinical stage. Moreover, tumor size >5 cm, lymph node metastasis, low pathological differentiation, high clinical stage and low expression of KLF9 are all important factors that cause death of patients.

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