| Popis: |
Expression of the chorionic gonadotropin alpha-subunit (alpha CG) gene is regulated differently in human tumor cell lines derived from trophoblastic and nontrophoblastic tissues. This is based, at least in part, on the observations that production of alpha CG is increased by cAMP but not by sodium butyrate in choriocarcinoma cells (JEG-3), whereas production of alpha CG is increased by butyrate but not by cAMP in cervical carcinoma cells (HeLa). Data presented herein confirm that the steady-state levels of alpha CG mRNA are increased approximately 10-fold by cAMP in JEG-3 cells, but additionally demonstrate that these levels can be further increased (to 25-fold) by sodium butyrate in conjunction with the cyclic nucleotide. Similar effects were achieved with the phorbol ester 12-0-tetradecanoylphorbol-13-acetate, which also acted synergistically with cAMP to increase alpha CG mRNA levels (24-fold). Butyrate and 12-0-tetradecanoylphorbol-13-acetate had little or no effect when added alone (1.5-fold and 2.5-fold, respectively) or in combination with one another (3.8-fold). Induction of the alpha CG gene by cAMP was independent of protein synthesis, as mRNA levels were comparable when JEG-3 cells were treated with cAMP in the absence and presence of cycloheximide (CHX). Unexpectedly, alpha CG mRNA levels were also elevated 8- to 10-fold in response to a combination of butyrate and CHX, but CHX alone or in combination with 12-0-tetradecanoylphorbol-13-acetate had no effect. Gel mobility shift assays demonstrated changes in the pattern of proteins binding to a cAMP response element and to a trophoblast-specific element with nuclear extracts from cells treated with CHX but not with cAMP or sodium butyrate. Together, these results suggest that induction patterns of the alpha CG gene by butyrate and cAMP in trophoblast- and nontrophoblast-derived tumor cell lines are less distinct than suggested previously and indicate that CHX, which is permissive for induction by butyrate, causes a significant shift in electrophoretic mobility of trans-acting factors involved in alpha CG gene expression. |
