R. Zinck et al., C-FOS TRANSCRIPTIONAL ACTIVATION AND REPRESSION CORRELATE TEMPORALLY WITH THE PHOSPHORYLATION STATUS OF TCF, EMBO journal, 12(6), 1993, pp. 2377-2387
EGF-induction of human astrocytoma and A431 cells leads to c-fos trans
criptional activation and then repression. This could be correlated wi
th changes in the DNA binding characteristics of the c-fos regulatory
protein ternary complex factor (TCF) present in nuclear extracts from
these cells. Band shifts showed the appearance of induction-related sl
owly migrating protein-DNA complexes, detected as ternary complexes on
the c-fos SRE using a truncated SRF molecule and by direct binding to
the Drosophila E74 Ets-protein recognition sequence. By several crite
ria both types of complexes represented TCF. The appearance of the slo
w ternary and direct complexes correlated with c-fos transcriptional a
ctivation, and their disappearance coincided with the ensuing c-fos sh
ut-off. Blocking c-fos transcriptional repression with the phosphatase
inhibitor okadaic acid led to their continued presence. They were sen
sitive to protein phosphatase 2A but not 1alpha, and similar slow comp
lexes were formed by partially purified p62TCF phosphorylated by a cop
urifying kinase activity. Thus the phosphorylation state of TCF correl
ated strongly with c-fos promoter activity. Since ternary complex form
ation mediated by full-sized SRF was only slightly affected under comp
arable conditions, we propose a model for c-fos regulation involving m
odification of constitutively bound TCF.