ATF-2 and CREB activity are necessary for the
activity of the cyclin D1 CRE in chondrocytes. MCT cells were
cotransfected with −66CD1LUC or −66 mut CD1LUC, either empty
expression vector or expression vectors for dominant-negative ATF-2
(a), dominant-negative CREB (b), or both
(c), and pRlSV40. After transfection (30 h), cells were
harvested, and firefly luciferase activity was measured and
standardized to Renilla luciferase activity to yield the relative
luciferase activity. Dominant-negative ATF-2 or CREB alone reduced the
activity of −66 CD1LUC 2.5- to 3.5-fold; in combination, they reduced
the activity to the levels of −66 mut CD1LUC. The activity of −66 mut
CD1LUC was not affected by either dominant-negative expression
vector.