Molecular Basis for the Mechanism of Constitutive CBP/p300 Coactivator Recruitment by CRTC1-MAML2 and Its Implications in cAMP Signaling

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• 作者：Michael David Clark ; Ganesan Senthil Kumar ; Ryan Marcum ; Qianyi Luo ; Yongbo Zhang ; Ishwar Radhakrishnan
• 刊名：Biochemistry
• 出版年：2015
• 出版时间：September 8, 2015
• 年：2015
• 卷：54
• 期：35
• 页码：5439-5446
• 全文大小：516K
• ISSN：1520-4995

文摘

The cyclic AMP response element-binding protein (CREB) is a signal-dependent transcription factor that exerts its positive effects on gene transcription of a broad range of genes by recruiting coactivators, including CREB-binding protein (CBP), its paralog, p300, and the family of CRTC (CREB-regulated transcriptional coactivators) proteins. Whereas recruitment of CBP/p300 is dependent on CREB phosphorylation at Ser133, recruitment of CRTCs is not. Here we describe how both mechanisms could concurrently drive transcription of CREB targets in a subset of head and neck cancers featuring chromosomal translocations that fuse portions of CRTC1 and CRTC3 genes with that of the Mastermind-like transcriptional coactivator MAML2. We show that a peptide derived from transactivation domain 1 (TAD1) of MAML2 binds to the CBP KIX domain with micromolar affinity. An 鈭?0-residue segment within this peptide, conserved in MAML2 orthologs and paralogs, binds directly to a KIX surface previously shown to bind to MLL1. The 20-residue MAML2 segment shares sequence similarity with MLL1, especially at those positions in direct contact with KIX, and like MLL1, the segment is characterized by the presence of an 鈭?0-residue helix. Because CRTC1/3-MAML2 fusion proteins are constitutively nuclear, like CREB, our results suggest constitutive recruitment of CBP/p300 to CREB targets that could be further enhanced by signals that cause CREB Ser133 phosphorylation.