BACKGROUNDApoptosis is closely related to development of lung cancer. It is a strategy of lung cancer therapy to induce apoptosis. The aim of this study is to explore the effects of growth arrest-specific homeobox (Gax) transfection on apoptosis and expression of Bcl-2 and Bax proteins of human lung adenocarcinoma A549 cells.

METHODSA549 cells were transfected with Gax gene by a replication-deficient adenovirus expressing the hemagglutinin-tagged Gax cDNA (Ad-Gax). Apoptosis of A549 cells was observed by transmission electronic microscope and terminal-deoxynucleotidyl transferase mediated nick end labeling (TUNEL) positive staining. Apoptotic rate of A549 cells was evaluated by flow cytometry. Expressions of Bcl-2 and Bax proteins in A549 cells were detected by immunocytochemistry.

RESULTSBefore Ad-Gax transfection, none or few of TUNEL-positive A549 cells were detected. After Ad-Gax transfection, a marked increase in TUNEL-positive staining occurred, especially at 24 h later. The ratio of apoptosis of A549 cellsin non-transfection group and transfection groups at 12 h, 24 h, 48 h were 0.25%, 12.57%, 17.29%, 15.03%, respectively. Compared with non-transfection group, the apoptotic rates of transfection groups increased significantly (Chi-square value was 7.357, 11.126 and 9.943 respectively, P < 0.01). The average optical density (AOD) of Bcl-2 protein in A549 cells in non-transfection group and transfection groups at 12 h, 24 h, 48 h were 2.02±0.07, 1.79±0.02, 1.25±0.51 and 1.21±0.24 respectively. Compared with non-transfection group, AOD of Bcl-2 protein in A549 cells in transfection groups decreased significantly (t value was 6.651, 7.089 and 7.438 respectively, P < 0.01). On the other hand, Bax protein expression in transfection groups increased, the AODs of Bax were 4.49±0.61, 4.24±0.37 and 3.95±0.43, respectively. Compared with non-transfection group (3.12±0.42), AOD of Bax protein in A549 celle in transfection groups increased significantly (t value was 7.469, 7.287 and 6.473 respectively, P < 0.01). In the Ad-Gax transfection groups the lower Bcl-2/Bax ratio was, the higher the apoptotic rate of A549 cells was (r=-0.49, P < 0.01).

CONCLUSIONSAd-Gax transfection can induce A549 cells apoptosis. Possible mechanism is that Gax can downregulate Bcl-2 protein expression and upregulate Bax protein expression, and A549 cells apoptosis is related to the Bcl-2/Bax ratio.

Gax gene is a newly found negative transcriptional regulator of cells proliferation. This paper introduces the detection and structural features of Gax, details the inhibitory effect of Gax on the proliferation of vascular smooth muscle cells, vascular endothelial cells and cancer cells, and explains the putative mechanisms therein involved. The potential for providing therapeutic insights into human diseases by modulating Gax activity is prospected.
Cell Proliferation ; drug effects ; Cells, Cultured ; Endothelial Cells ; cytology ; Gene Expression ; Homeodomain Proteins ; genetics ; metabolism ; Humans ; Muscle, Smooth, Vascular ; cytology