Abstract
BACKGROUND: Mirk/Dyrk1B contributes to G0 arrest by destabilization of cyclin D1 and stabilization of p27kip1 to maintain the viability of quiescent human cancer cells, and it could be negatively regulated by mitogenic-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) signaling. This study was performed to investigate the effect of Mirk/Dyrk1B on cell cycle and survival of human cancer cells involving MAPK/ERK signaling. METHODS: The correlations between Mirk/Dyrk1B expression and active ERK1/2 detected by western blot in both ovarian cancer and non-small cell lung cancer (NSCLC) cells were analyzed by simple regression. Mirk/Dyrk1B unique phosphopeptides with sites associated with Mirk/Dyrk1B protein were isolated and quantitated by liquid chromatography coupled to tandem mass/mass spectrometry (LC-MS/MS) proteomics analysis. The human cancer cells were treated with small interfering RNAs (siRNAs) and/or U0126, an inhibitor of MEK for indicated duration, followed by investigating the alterations of cell cycle and apoptosis as well as related proteins examined by flow cytometry and Western blot, respectively. RESULTS: Our study demonstrated the widely expressed Mirk/Dyrk1B proteins in the human cancer cells were positively correlated with the levels of activated ERK1/2. Moreover, Mirk/Dyrk1B protein expressions consistent with the tyrosine autophosphorylated levels in the human cancer cells were increased by U0126 or growth factor-depleted culture. Conversely, knockdown of Mirk/Dyrk1B by siRNA led to up-regulated activation of c-Raf-MEK-ERK1/2 pathway and subsequent changes in cell cycle proteins (cyclin D1, p27kip1), accompanied by increased growth rate and cells from G0/G1 into S of cell cycle which could be blocked by U0126 in a dose-dependent manner, indicating Mirk/Dyrk1B may sequester MAPK/ERK pathway, and vice versa. Whereas, combined Mirk siRNA and U0126 induced cell apoptosis in the human cancer cells. CONCLUSIONS: These data together show that Mirk/Dyrk1B mediates cell cycle and survival via interacting with MAPK/ERK signals and simultaneous inhibition of both pathways may be a novel therapeutic target for human cancer.