Cloning of human XAF1 gene promoter and assay of its transcription activity in a variety of cell lines

To investigate the regulation of tumor sup-pressor XAF1 gene expression in digestive system cancers,we studied XAF1 gene promoter transcription activity and mRNA level in digestive system cancer cell lines(human hepatoma cell line HepG2,human colon cancer cell line LoVo,and human gastric cancer cell line AGS)and nontumor cell lines(human embryonic liver cell line L02(L02 cells)and human embryonic kidney 293 cells[HEK293 cells])as controls.1395-bp-promoter fragment of XAF1 gene was amplified by polymerase chain reaction(PCR)and cloned into pGL3-basic vector and pEGFP-1 vector to assay its promoter transcription activity.The plasmids were transfected into a variety of cell lines by lipofectamine 2000.The promoter transcription activity was determined by dual-luciferase report assay,and enhanced greenfluorescent protein(EGFP)-positive cells were detected byfluorescence microscope.The expression of XAF1 mRNA in HEK293 and L02 were significantly higher than that in any of the three digestive system cancer cell lines.The dual-luciferase reporter assay showed that the promoter transcription activity in digestive system tumor cell lines transfected with pGL3-XAF1p promoter was apparently lower than that of both HEK293 and L02 cells.Expression of greenfluorescent protein(GFP)under the control of XAF1 promoter in the three digestive system cancer cell lines was lower than that of both HEK293 and L02 cells.The activities of pGL3-XAF1p in the three digestive system cancer cell lines after treatment with heat stress were significantly lower than those in the unstressed cells.The results suggested that remarkably down-regulated XAF1 mRNA expression in digestive system cancer cell lines may be due to loss of transcription activity of XAF1 promoter.

Construction and expression of hepatitis B virus vector encoding TC-tagged core protein

Virus tagged with greenfluorescent protein(GFP)contributes to the visualization and study of the virus in living cells.However,the hepatitis B virus(HBV)particle,which is a compact virion with limited internal space,cannot be incorporated with GFP tag as a large fragment.It was recently reported that protein genetically inserted with a smaller size tetracysteine(TC)tag could be specially labeled by a biarsenicalfluorescent dye in living cells.In this study,we constructed a recombinant HBV vector encoding TC-tagged core protein for biarsenical labeling of HBV virion.TC tag was genetically inserted near the immunodominant c/e1 site of HBV core protein by mutagenesis.Western blot and enzyme-linked immu-nosorbent assay(ELISA)analysis showed that the TC-tagged core protein,hepatitis B surface antigen(HBsAg)and hepatitis B e antigen(HBeAg)could be expressed in cells transfected with the recombinant HBV vector,which is similar to the cells transfected with wild-type HBV vector.Reverse transcription-polymerase chain reaction(RT-PCR)and Southern blot analysis showed that HBV virion formation was affected by the genetic insertion of TC tag into core protein in some degree,but cells transfected with the HBV vector could still produce HBV virions incorporated with TC-tagged core proteins.Taken together,the recombinant HBV vector can serve as a useful tool to produce HBV virions incorporated with TC-tagged core proteins to befluorescently labeled by biarsencial dye for visualizing and studying HBV in living cells.