Physiological amounts of ascorbate potentiate phorbol ester-induced nuclear-binding of AP-1 transcription factor in cells of macrophagic lineage

The aim of the reported research was to assess the potential modulatory eff ect exerted by physiological amounts of ascorbate complexed or not to iron on activator protein 1 (AP-1) nuclear binding. The metal-vitamin complex wa s shown able to strongly potentiate AP-1 binding as induced by phorbol 12-m yristate 13-acetate (PMA). Such enhancing activity by ascorbate was not obs erved on PMA-dependent induction of another redox-sensitive transcription f actor nuclear factor kappaB (NF-kappaB). Experiments performed in the prese nce of the metal chelator desferrioxamine (DFO) clearly indicated that asco rbate rather than iron was responsible for the potentiation of PMA effect. The composition of AP-1 heterodimers revealed c-Jun, Jun D, and c-Fos as th e major subunits upon PMA +/- ascorbate stimulation. The change in AP-1 com ponents consequent to such stimuli was mainly dependent upon new synthesis. In fact, protein synthesis inhibitor cycloheximide (CHX) prevented the sti mulation of AP-1 nuclear binding due to PMA and ascorbate, plus PMA. Furthe r, the vitamin was able to amplify the PMA-dependent induction of p38 and p JNK. Thus, a fine modulation of critical thiols by the vitamin along the MA PK pathway is conceivable. (C) 2001 Elsevier Science Inc.