Fig. 3. Modulation of AP-1 and MAPK activity in Hodgkin and non-Hodgkin cell lines. (A) Phorbolester-induction of a distinct AP-1 DNA-binding activity in HRS and non-Hodgkin cells. Cells were left untreated or stimulated with PMA, as indicated. Extracts were assayed by EMSA with or without preincubation with antibodies against c-Fos or c-Jun. Supershifted protein–DNA complexes are indicated (ss). The PMA-induced AP-1 complex (**) migrates slower than the constitutive complex in HRS cells (*). n.s., non-specific. (B) Extracts of unstimulated or stimulated cells were analyzed in a western blot for c-Fos induction. (C) MAPK pathways are not constitutively activated in HRS cells, as revealed by mitogen and UV-light induction. The HRS cell lines L428 and L1236 or control cell lines were stimulated with PMA (P), UV-irradiated (UV) or left untreated. Whole-cell extracts were analyzed in western blots for MAPK activation and c-Jun N-terminal phosphorylation with phosphospecifc antibodies (pERK1/2, pp38, pJNK, pc-Jun), and for expression of the kinases and c-Jun with the respective antibodies, as indicated.