Contribution of MAP kinase pathways to the activation of ATF-2 in human neuroblastoma cells.

Activated Transcription Factor-2 (ATF-2) is important during development of and during injury to the brain. Both Jun N-terminal Kinases (JNKs) and p38 Mitogen-Activated Protein Kinases (p38MAPKs) may phosphorylate ATF-2, but the contribution of these two pathways in cells has never been investigated. We have assayed endogenous p38MAPK activity in SK-N-MC and SH-SY5Y human neuroblastoma cells for activation of a GAL4/ATF-2 fusionprotein, by means of titrations of transfected expression plasmids and by using the p38MAPK inhibitor SB203580. It was found that basal activation of ATF-2 was independent of p38MAPK and that whereas MAPK kinase-3 (MKK3) was a weak inducer of ATF-2 activation, it was a potent activator of the stress activated transcription factor CHOP. In contrast, ATF-2 was very potently activated by the JNK pathway activator MAPK kinase kinase-1 (MEKK1). Thus, kinases downstream of MEKK1 appear relevant, but it is unlikely that p38MAPKs contribute quantitatively to activation of ATF-2 in these cells.