Fig. 7.

CGS-mediated repression of CT/CGRP enhancer activity. CT/CGRP or TK reporter genes containing the cAMP-responsive region (dotted box), distal cell-specific enhancer HLH–octamer binding motifs (H/O; solid box), and/or noncell-specific elements (striped box) were transfected into CA77 cells treated with 10 μm CGS for 16 hr and then assayed for luciferase activity. CGS responsiveness also was tested by using reporter genes that contain site-directed mutations in the cell-specific enhancer. Insertion of a BamHI linker (1160–920+Bam) or a single adenosine residue (H/O+A) eliminated both cell-specific enhancer activity and repression by CGS. The data in each experiment were normalized to the TK–luciferase reporter activity in the presence (+) or absence (−) of CGS and expressed as the fold change relative to TK–luciferase, the mean for which was set at one. The average activities for CGS-treated and untreated TK–luciferase-transfected cells were 1000 and 2000 light units per 20 μg of protein, respectively. The means and SE from at least three independent experiments with duplicate samples are shown.