A structural basis for mutational inactivation of the tumour suppressor Smad4.
The Smad4/DPC4 tumour suppressor is inactivated in nearly half of pancreatic carcinomas and to a lesser extent in a variety of other cancers. Smad4/DPC4, and the related tumour suppressor Smad2, belong to the SMAD family of proteins that mediate signalling by the TGF-beta/activin/BMP-2/4 cytokine superfamily from receptor Ser/Thr protein kinases at the cell surface to the nucleus. SMAD proteins, which are phosphorylated by the activated receptor, propagate the signal, in part, through homo- and hetero-oligomeric interactions. Smad4/DPC4 plays a central role as it is the shared hetero-oligomerization partner of the other SMADs. The conserved carboxy-terminal domains of SMADs are sufficient for inducing most of the ligand-specific effects, and are the primary targets of tumorigenic inactivation. We now describe the crystal structure of the C-terminal domain (CTD) of the Smad4/DPC4 tumour suppressor, determined at 2.5 A resolution. The structure reveals that the Smad4/DPC4 CTD forms a crystallographic trimer through a conserved protein-protein interface, to which the majority of the tumour-derived missense mutations map. These mutations disrupt homo-oligomerization in vitro and in vivo, indicating that the trimeric assembly of the Smad4/DPC4 CTD is critical for signalling and is disrupted by tumorigenic mutations.
Shi
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Cellular Biochemistry and Biophysics Program, Memorial Sloan-Kettering Cancer Center, New York 10021, USA.
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Massagué
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Pavletich
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D000595:Amino Acid Sequence; D018360:Crystallography, X-Ray; D004268:DNA-Binding Proteins; D004926:Escherichia coli; D005786:Gene Expression Regulation; D016147:Genes, Tumor Suppressor; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry; D017386:Sequence Homology, Amino Acid; D051901:Smad4 Protein; D015534:Trans-Activators / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism
D004268:DNA-Binding Proteins; D011994:Recombinant Proteins; C497796:SMAD4 protein, human; D051901:Smad4 Protein; D015534:Trans-Activators