Signalling pathways involved in multisite phosphorylation of the transcription factor ATF-2

Area of Science:

• Molecular Biology
• Cell Signaling
• Transcription Factor Regulation

Background:

• Multisite phosphorylation of transcription factors like ATF-2 is critical for regulating gene expression.
• Mitogen-activated protein kinases (MAPKs), including JNK, p38 MAPK, and ERK, play key roles in cellular signaling pathways.
• Understanding the specific roles of different MAPKs in ATF-2 phosphorylation is essential for deciphering downstream cellular responses.

Purpose of the Study:

• To investigate the roles of c-Jun N-terminal kinases (JNK)1 and 2, p38 MAPK, and ERK1/2 in the multisite phosphorylation of ATF-2.
• To determine the rate-limiting kinases for specific phosphorylation sites (Thr69, Thr71, Ser90) on ATF-2.
• To examine the compensatory roles of p38 MAPK and ERK1/2 in JNK-deficient cells for ATF-2 phosphorylation.

Main Methods:

• Utilized transformed embryonic fibroblasts from wild-type and JNK1/2-deficient mice.
• Employed inhibitors for p38 MAPK and the classical MAP kinase cascade (ERK).
• Analyzed the phosphorylation status of ATF-2 at specific sites (Thr69, Thr71, Ser90) under various kinase inhibition conditions.

Main Results:

• In wild-type cells, p38 MAPK and ERK1/2 were not rate-limiting for Thr69, Thr71, or Ser90 phosphorylation.
• In JNK-deficient cells, p38 MAPK partially substituted for JNK in Thr69 phosphorylation.
• p38 MAPK or ERK1/2 could substitute for JNK in Thr71 phosphorylation, while JNK was the sole kinase for Ser90 phosphorylation.

Conclusions:

• JNK is the primary kinase responsible for ATF-2 phosphorylation at Ser90.
• p38 MAPK and ERK1/2 exhibit partial functional redundancy with JNK for Thr69 and Thr71 phosphorylation, particularly in the absence of JNK.
• These findings elucidate the specific and overlapping roles of different MAPK pathways in regulating ATF-2 activity.