MCPIP1 overexpression in human neuroblastoma cell lines causes cell-cycle arrest by G1/S checkpoint block.

Monocyte chemoattractant protein-1-induced protein 1 (MCPIP1) has a multidomain structure, which assures its pleiotropic activity. The physiological functions of this protein include repression of inflammatory processes and the prevention of immune disorders. The influence of MCPIP1 on the cell cycle of cancer cells has not been sufficiently elucidated. A previous study by our group reported that overexpression of MCPIP1 affects the cell viability, inhibits the activation of the phosphoinositide-3 kinase/mammalian target of rapamycin signalling pathway, and reduces the stability of the MYCN oncogene in neuroblastoma (NB) cells. Furthermore, a decrease in expression and phosphorylation levels of cyclin-dependent kinase (CDK) 1, which has a key role in the M phase of the cell cycle, was observed. On the basis of these previous results, the purpose of our present study was to elucidate the influence of MCPIP1 on the cell cycle of NB cells. It was confirmed that ectopic overexpression of MCPIP1 in two human NB cell lines, KELLY and BE(2)-C, inhibited cell proliferation. Furthermore, flow cytometric analyses and imaging of the cell cycle with a fluorescence ubiquitination cell-cycle indicator test, demonstrated that overexpression of MCPIP1 causes an accumulation of NB cells in the G1 phase of the cell cycle, while the possibility of an increase in G0 phase due to induction of quiescence or senescence was excluded. Additional assessment of the molecular machinery responsible for the transition between the cell-cycle phases confirmed that MCPIP1 overexpression reduced the expression of cyclins A2, B1, D1, D3, E1, and E2 and decreased the phosphorylation of CDK2 and CDK4, as well as retinoblastoma protein. In conclusion, the present results indicated a relevant impact of overexpression of MCPIP1 on the cell cycle, namely a block of the G1/S cell-cycle checkpoint, resulting in arrest of NB cells in the G1 phase.

Downregulation of RUVBL1 inhibits proliferation of lung adenocarcinoma cells by G1/S phase cell cycle arrest via multiple mechanisms.

Lung cancer remains a leading cause of cancer-related mortality and morbidity worldwide, of which non-small cell lung cancer (NSCLC) accounts for 80 %. RUVBL1 is a highly conserved eukaryotic AAA+ adenosine 5'-triphosphatase (ATPase) that has many functions highly relevant to cancer. We therefore attempted to determine the potential role of RUVBL1 in the biogenesis of lung adenocarcinoma and obtained some interesting results. Our study revealed that RUVBL1 expression was higher in lung adenocarcinoma specimens than in those of adjacent non-tumor tissues and in lung cancer cell lines than in normal lung cell lines. RUVBL1 knockdown via siRNA reduced proliferation and caused G1/S phase cell cycle arrest in lung adenocarcinoma cell lines. The G1/S phase cell cycle arrest triggered by RUVBL1 downregulation could be attributed, at least in part, to repression of the AKT/GSK-3ß/cyclin D1 pathway and probably to the activation of IRE1α-mediated endoplasmic reticulum (ER) stress. We thus demonstrated for the first time that a knockdown of RUVBL1 could effectively inhibit the proliferation of lung adenocarcinoma A549 and H292 cells through the induction of G1/S phase cell cycle arrest via multiple mechanisms. These observations strongly suggested that RUVBL1 should be considered a promising target for the prevention or therapy of lung adenocarcinoma.

Downregulation of HSPA2 inhibits proliferation via ERK1/2 pathway and endoplasmic reticular stress in lung adenocarcinoma.

BACKGROUND: To explore the mechanisms of HSPA2 downregulation in inhibiting the proliferation of lung adenocarcinoma. METHODS: We obtained 85 specimens of human lung adenocarcinoma and specimens of adjacent nontumor tissues from the First Affiliated Hospital, School of Medicine, Zhejiang University. We then analyzed the expression of HSPA2 in these tissues and in lung adenocarcinoma and normal lung cell lines. Human lung adenocarcinoma cell lines were transfected with siRNA silencing HSPA2 and subjected to colony forming, Thiazolyl blue tetrazolium bromide (MTT), propidium iodide flow cytometry, immunofluorescence assay and western blotting to explore the causes of the reduction in the proliferation of lung adenocarcinoma cells and the endoplasmic reticulum stress induced by HSPA2 downregulation. Finally, we confirmed these mechanisms via rescue assay. RESULTS: Greater HSPA2 expression was found in the lung adenocarcinoma specimens than in the specimens of adjacent nontumor tissues, and greater expression was found in lung adenocarcinoma cell lines than in normal cell lines. HSPA2 knockdown via siRNA reduced proliferation and led to G1/S phase cell cycle arrest in the lung adenocarcinoma cell lines. G1/S phase cell cycle arrest triggered by HSPA2 downregulation could be attributed, at least in part, to phosphorylation and activation of the Erk1/2 pathway and probably to activation of IRE1α/PERK-mediated endoplasmic reticulum stress. CONCLUSIONS: HSPA2 plays an important role in the origin and development of lung adenocarcinoma. It is thus deserving of further study as a promising clinical therapeutic target.