Knockdown of protein phosphatase 4 regulatory subunit 1 inhibits growth of lung cancer cells in vitro

Lung cancer is the leading cause of death from cancer around the world. Cancer patients undertaking chemotherapy or radiotherapy would experience a wide range of distressing side effects. Hence, exploring a promising new and safe therapeutic strategy to fight against cancer was urgent. Protein phosphatase 4 catalytic subunit (PP4c) is a member of the Protein phosphatase 2 (PP2A) family and play an essential role in biological processes of microtubule (MT) growth/organization, apoptosis, and tumor necrosis factor signaling. Protein phosphatase 4 regulatory subunit 1 (PPP4R1), a protein that co-purifying with PP4c from bovine testis extracts, has been reported to be involved in tumor progression. However, its functional role in lung cancer remains unclear. In this study, we firstly evaluated the expression levels of PPP4R1 in three lung cancer cell lines by quantitative real-time PCR (qRT-PCR) analysis and found that PPP4R1 was expressed highest in 95D cells. Then PPP4R1 was knocked down by lentivirus-based system in 95D cells. Proliferation and colony numbers were evaluated in lung cancer 95D cells by tetrazolium (MTT) and colony formation assay, respectively. As a result, stable knockdown of PPP4R1 led to suppression of proliferation and colony-forming ability in 95D cells. Subsequently, the cell cycle analysis showed knockdown of PPP4R1 arrested cell cycle at G0/G1 phase in 95D cells. Further investigation indicated that knockdown of PPP4R1 down-regulated cell-cycle activators, including CDK2, CDK4 and CDK6, as determined by western blot. Our results suggest that PPP4R1 knockdown inhibited lung cancer cell proliferation via down regulating cell-cycle activators. The identification of PPP4R1 may provide a potential therapeutic strategy for lung cancer treatment.