FIGURE 7.

GADD45β enhances C/EBPβ activity via TAD4. A, mouse C/EBPβ deletion constructs fused with the GAL4-DBD (black bar) are shown. Transactivation domains (TAD1, -2, -3, -4), also known as activation domain modules (ADM1, -2, and -3 for TAD2, -3, and -4, respectively), and repression domains (RD1 and -2) are represented as gray boxes and dashed boxes, respectively. Basic region (BR) and leucine zipper region (LR) are indicated (57). Reporter assays were carried out in ATDC5 cells co-transfected with 300 ng of pRL-TK containing the Gal4 binding site and 50 ng of the GAL4-fused mC/EBPβ constructs, alone or in combination with 25 ng of GADD45β expression vector. Luciferase activities were normalized to pRL-SV40 reporter activities and shown as -fold induction compared with control (empty vector). B, wild-type mouse C/EBPβ (mLAP); mLAPΔSacII-(53–120), and mLIP constructs are represented. Col10a1-(−60/+52) transactivation was analyzed in co-transfection experiments with 25 ng of mLAP, mLIP, or mLAPDSacII, alone or in combination with GADD45β expression plasmid. Luciferase activities were normalized to pRL-TK reporter activities and shown as -fold induction compared with control (mLAP). C, human and mouse TAD1, -2, -3, and -4 homologies among the C/EBP family. SY and FL amino acids are highlighted in boldface type. D, full-length human C/EBPβ (hLAP*), hLAP*ΔSacII(47–182), and point SY and LF mutants are depicted. The Col10a1-(−60/+52) transactivation was analyzed in co-transfection experiments with 25 ng of hLAP*, hLAP*ΔSacII, or SY or LF mutant, alone or in combination with GADD45β expression plasmid. Luciferase activities were normalized to pRL-TK reporter activities and shown as -fold induction compared with control (hLAP*). Means ± S.D. of triplicates from three independent experiments are shown for A, B, and D.