Fig. 5. Involvement of MAP kinase activation in the inhibitory effects of the AhR on adipogenesis. (A) Cells expressing AhR sense mRNA (S) and cells expressing vector mRNA (V) were treated with differentiation cocktail (MDI). Cell lysates were prepared at the indicated day. The lysates obtained were immunoprecipitated with anti-phospho p42/p44 MAP kinase antibody and the kinase activity was assayed as described in Materials and Methods. (B) The lysates obtained as described above were resolved by electrophoresis on 10% SDS/polyacrylamide gel. Western blot analysis of p42/p44 MAP kinase was performed with the specific antibodies against p42/p44 MAP kinase, which detect total p42/p44 MAP kinase (phosphorylation-state independent) protein. (C) On day 0, cells expressing AhR sense mRNA (S) and cells expressing vector mRNA (V) were treated with differentiation cocktail (MDI) and 10 µM PD98059, 1 µM U0126 or 10 µM SB203580. On day 6, cells were fixed and stained with oil red O. Similar results were obtained with independent clones.