Phorbol ester-induced amino-terminal phosphorylation of human JUN but not JUNB regulates transcriptional activation.

Abstract

Phorbol ester tumor promoters activate gene transcription by regulating both the synthesis and posttranslational modification of the activator protein 1 (AP-1) transcription factor. c-Jun and JunB are components of the mammalian AP-1 complex. Here we demonstrate that in U-937 human leukemic cells, phorbol esters stimulate the phosphorylation of the amino terminus of human c-Jun (JUN) but not human JunB (JUNB). Mutational analysis indicates that serine-63 and -73, which reside within the putative regulatory domain of JUN, are required for both constitutive and phorbol 12-myristate 13-acetate-inducible N-terminal JUN phosphorylation. To determine the functional role of this N-terminal phosphorylation, we prepared several chimeric proteins containing the N-terminal 84 amino acids (positions 5-89) of human JUN or murine JUNB fused to the yeast GAL4 DNAbinding domain. This region was found to be sufficient for the phorbol ester-inducible transcriptional activity ofJUN, but not JUNB. This induction was abolished by the mutation of serine-63 and -73 to leucine residues. Thus, we propose that phorbol esters enhance the trans-activation potential of JUN, but not JUNB, by the phosphorylation of the N-terminal

Stimulation of urokinase-type plasminogen activator receptor expression by PMA requires JNK1-dependent and -independent signaling modules

“…Increased transcriptional activity of c-Jun has been ascribed to phosphorylation of residues 63 and 73 in the transactivation domain of this DNAbinding factor and prevailing evidence suggest that this is achieved through the JNKs rather than the ERKs (Hibi et al, 1993;Minden et al, 1994b). Interestingly, in a previous study, it was reported that PMA stimulates the phosphorylation of these serine residues (Wasylyk et al, 1994;Franklin et al, 1992). However, in those studies the authors concluded that the phosphorylation of c-Jun was due to ERK1 and ERK2 (Pulverer et al, 1993).…”

c-Jun, at the crossroad of the signaling network

“…TPA significantly increases the Nterminal phosphorylation, resulting in a robust induction of cJun transactivation activity Lin et al, 1992;Smeal et al, 1992;Nikolakaki et al, 1993). In contrast, Jun B, lacking serine-63 and-73, is irresponsive to TPA induced transcriptional activation (Franklin et al, 1992).…”

Conditional Expression of the Mitogen-activated Protein Kinase (MAPK) Phosphatase MKP-1 Preferentially Inhibits p38 MAPK and Stress-activated Protein Kinase in U937 Cells

“…The resulting expression vector contained a hygromycin B-selectable marker and was driven by the human IIa metallothionein (hMTIIa) promoter. GST-cJun(5-89) and GAL4-cJun(5-89) have been described previously (19,25,26). pCMV-FLAG-p38 MAPK (7) was provided by R. Davis.…”

“…Transient transfections were performed using the DEAE-dextran procedure as described previously (32). Stable transfections were performed by electroporation (26). Two days post-transfection, cells were cultured in selective media containing 200 g/ml hygromycin B (Calbiochem).…”