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Nkx3.1 is a prostate-specific homeobox gene related strongly to prostate development andprostate cancer. To study its regulation of transcription, 1.06 kb 5 ′ flanking region of Nkx3.1 gene and its5 ′deletion mutants (861,617, 417 and 238 bp) were obtained by PCR and cloned into pGL3-basic, apromoter-less luciferase reporter vector, to examine their promoter activities driving the reporter genetranscription, pRL-TK, a Renilla luciferase reporter vector was used as inteal control, and pGL3-controland pGL3-basic were used as positive and negative control respectively. The promoter activities were deter-mined by dual-luciferase reporter assay 48 h after pGL3 constructs were cotransfected with pRL-TK intoprostate cancer cell LNCaP. The results showed that dual-luciferase reporter assay (M1/M2) of pGL3-1.06 kbcotransfection with pRL-TK was 2.7, which was about 1.5-fold higher than that of pGL3-control cotrans-fection with pRL-TK and 50-fold higher than that of pGL3-basic cotransfection with pRL-TK. The resultsalso showed that the relative activities (M1/M2) were 0.71, 0.84, 0.44 and 2.07 respectively for pGL3-861 bp,pGL3-617 bp, pGL3-417 bp, pGL3-238 bp, the last one still had 80% promoter activity compared with pGL3-1.06 kb, which showed that deletion from 1.06 kb to 238 bp had small effects on promoter activity. Theconclusion was that the 238 bp fragment containing a TATA box and two CAAT boxes had strong promoteractivity. However, the deletion from 1.06 kb to 861 bp reduced activity 3.8-fold while the deletion from 417bp to 238 bp enhanced activity 4.7-fold, which indicated that these deleted sequences might contain someimportant positive or negative regulatory elements. It will be important to identify the elements within theNkx3.1 promoter that contribute to regulation of the gene transcription in the future studies.