C/EBPα inhibits JunB expression.
(A) Total cellular protein extracts prepared from 1 × 106 32DPKCδ-αER-1 cells cultured in PMA, estradiol (E2), or both for 0, 8 or 24 hours were subjected to Western blotting for JunB, c-Jun, PU.1, C/EBPβ, and β-actin. (B) The 293 cells were transfected with 5 μg per 100-mm dish of pCMV-c-Jun (cJ) or pCMV-JunB (JB) alone, or 2.5 μg of these DNAs were transfected with 2.5 μg pCMV-c-Fos (cJ:F, JB:F). Then, 2 days later nuclear extracts were prepared and subjected to gel-shift assay with an AP-1 binding site from the macrosialin promoter. Anti–c-Jun antiserum (αcJ) or anti-JunB antiserum (αJB) was included in several samples (left panel). A nuclear extract from 32DPKCδ cells was subjected to gel-shift assay with no antiserum (−), with 1 μL αJB or αcJ antiserum, or with αJB antiserum that had been preincubated with 0.4 μg JunB peptide (pep).
