c-Jun N-terminal phosphorylation antagonises recruitment of the Mbd3/NuRD repressor complex

Area of Science:

• Molecular Biology
• Cell Biology
• Cancer Research

Background:

• Activator protein 1 (AP-1) activity, regulated by transcription factors like c-Jun, is crucial for intestinal cell proliferation and tumorigenesis.
• Jun amino-terminal kinases (JNKs) phosphorylate c-Jun, enhancing AP-1 transcriptional activity, but the underlying molecular mechanisms remain unclear.

Purpose of the Study:

• To elucidate the molecular mechanism by which N-terminal phosphorylation of c-Jun regulates AP-1 target gene transcription.
• To investigate the role of Mbd3 and the NuRD repressor complex in c-Jun-mediated gene regulation within the intestinal context.

Main Methods:

• Co-immunoprecipitation assays to assess protein interactions between c-Jun, Mbd3, and NuRD components.
• Chromatin immunoprecipitation sequencing (ChIP-seq) to identify AP-1 target genes and assess histone modifications.
• Conditional gene deletion in mice (Mbd3 and c-Jun) to study in vivo function.
• Analysis of colon cancer cell lines and mouse models of colitis-induced tumorigenesis.

Main Results:

• Unphosphorylated c-Jun, but not N-terminally phosphorylated c-Jun, interacts with Mbd3 to recruit the NuRD repressor complex.
• Mbd3 depletion in colon cancer cells leads to increased histone acetylation and expression of AP-1 target genes, including the stem cell marker lgr5.
• Gut-specific deletion of Mbd3 in mice enhances c-Jun activity, promotes progenitor cell proliferation, and increases susceptibility to colitis-induced intestinal tumorigenesis.
• Inactivation of one c-Jun allele in Mbd3-deficient mice reverses hyperproliferation and reduces tumorigenesis.

Conclusions:

• The transactivation domain of c-Jun recruits Mbd3/NuRD to repress AP-1 target gene expression.
• JNK-mediated N-terminal phosphorylation of c-Jun relieves Mbd3/NuRD-mediated repression, thereby increasing target gene transcription.
• This regulatory axis involving c-Jun, Mbd3, and NuRD plays a critical role in controlling intestinal progenitor proliferation and tumorigenesis, particularly in response to inflammation.