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Mol. Cell. Biol., 09 1995, 4930-4938, Vol 15, No. 9
R Zinck, MA Cahill, M Kracht, C Sachsenmaier, RA Hipskind and A Nordheim
Inhibitors of protein synthesis, such as anisomycin and cycloheximide, lead
to superinduction of immediate-early genes. We demonstrate that these two
drugs activate intracellular signaling pathways involving both the
mitogen-activated protein kinase (MAPK) and stress-activated protein kinase
(SAPK) cascades. The activation of either pathway correlates with
phosphorylation of the c-fos regulatory transcription factor Elk-1. In HeLa
cells, anisomycin stabilizes c-fos mRNA when protein synthesis is inhibited
to only 50%. Under these conditions, anisomycin, in contrast to
cycloheximide, rapidly induces kinase activation and efficient Elk-1
phosphorylation. However, full inhibition of translation by either drug
leads to prolonged activation of SAPK activity, while MAPK induction is
transient. This correlates with prolonged Elk-1 phosphorylation and c-fos
transcription. Elk-1 induction and c-fos activation are also observed in KB
cells, in which anisomycin strongly induces SAPKs but not MAPKs. Purified
p54 SAPK alpha efficiently phosphorylates the Elk-1 C-terminal domain in
vitro and comigrates with anisomycin-activated kinases in in-gel kinase
assays. Thus, Elk-1 provides a potential convergence point for the MAPK and
SAPK signaling pathways. The activation of signal cascades and control of
transcription factor function therefore represent prominent processes in
immediate-early gene superinduction.
Copyright © 1995, American Society for Microbiology
Protein synthesis inhibitors reveal differential regulation of mitogen- activated protein kinase and stress-activated protein kinase pathways that converge on Elk-1
Institut f aur Klinische Chemie, Medizinische Hochschule Hannover, Germany.
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