Smad4 (DPC4)Smad4 (DPC4)

A tumor suppressor gene

Smad4 (DPC4)Smad4 (DPC4)• Smad4Smad4: Mothers against decapentaplegic (dpp) : Mothers against decapentaplegic (dpp)

homolog 4homolog 4

• dppdpp is responsible for dorsal/ventral polarity in the is responsible for dorsal/ventral polarity in the flyfly

• Drosophila melanogasterDrosophila melanogaster MADH4MADH4: : MMothers others AAgainst gainst DDecapentaplegic ecapentaplegic HHomolog omolog 44

• Caenorhabditis elegansCaenorhabditis elegans sma-4sma-4: like MADH4: like MADH4

• Human Human DPC4DPC4: : DDeleted in eleted in PPancreatic ancreatic CCarcinoma, arcinoma, locus locus 44

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Facts about DPC4Facts about DPC4

• Chromosomal location: 18q21.1

• Identified in 1996Identified in 1996

• deleted in 55% of pancreatic deleted in 55% of pancreatic cancers (late stage)cancers (late stage)

• deleted in 10% to 35% of deleted in 10% to 35% of colorectal cancers (late stage)colorectal cancers (late stage)

• Involved in Familial Juvenile Involved in Familial Juvenile PolyposisPolyposis

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University of Pittsburg Medical Center http://colonpolyps.upmc.com/Overview.htm

Endoscopic and colonoscopic appearance of Cowden's Endoscopic and colonoscopic appearance of Cowden's syndrome, a rare inherited polyposis syndromesyndrome, a rare inherited polyposis syndrome

Charles Donner, M.D. The University of Iowa http://www.vh.org/adult/provider/internalmedicine/GIAtlas/Organ/pages/3-Duodenum/OtherPolypImage2.html

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Smad4 transcription factor changes from a Smad4 transcription factor changes from a generalized generalized distributiondistribution (left) to a (left) to a nuclear localizationnuclear localization (right) following (right) following

addition of TGF-addition of TGF-ββ

Department of Biochemistry – University of Torontohttp://biochemistry.utoronto.ca/research/signal_transduction_and_regulation.html

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Big Picture I:the TGF-β signaling pathway

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The TGF-β signaling pathwayThe TGF-β signaling pathway

Stroschein SL, Wang W, Zhou S, Zhou Q, Luo K. Science 1999 Oct Stroschein SL, Wang W, Zhou S, Zhou Q, Luo K. Science 1999 Oct 22;286(5440):771-4, Negative feedback regulation of TGF-beta signaling by the 22;286(5440):771-4, Negative feedback regulation of TGF-beta signaling by the SnoN oncoprotein.SnoN oncoprotein.

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SMAD proteinsSMAD proteins8

• Two domains: Mad Homology 1 and 2 (MH1 and MH2) domains, separated by a linker region

• MH1: at the amino-terminal, involved in DNA binding

• MH2: at the carboxy-terminal, involved in homo- and hetero-oligomerization

• Molecular weight: 60.4 kDa

• Number of amino acids: 552

X-ray CrystallographyX-ray CrystallographyDPC4/Smad4 TrimerDPC4/Smad4 Trimer

©2005 Memorial Sloan-Kettering Cancer Centerhttp://www.mskcc.org/mskcc/html/10859.cfm

* Shi Y, Hata A, Lo RS, Massague J, Pavletich NP. (1997) A structural basis for mutational inactivation of the tumour suppressor Smad4. Nature. 1997;388:87-93.* Shi Y, Wang YF, Jayaraman L, Yang H, Massague J, Pavletich NP. (1998) Crystal structure of a Smad MH1 domain bound to DNA: insights on DNA binding in TGF-beta signaling. Cell. 1998;94:585-594.

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Smad-mediated TGFSmad-mediated TGF-β signaling signaling pathwaypathway

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Michiko Miyakia and Toshio Kuroki, Biochemical and Biophysical Research Communications 306 (2003) 799–804, Role of Smad4 (DPC4) inactivation in human cancer

Two normal biological roles for Two normal biological roles for Smad4/DPC4Smad4/DPC4

Gastrulation and embryogenesis• Initially required for differentiation of visceral

endoderm• Secondary involved in anterior/posterior

patterning during embryogenesis

Tumor suppressor• Mediates the TGF-ββ signaling pathway

suppressing epithelial cell growth

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ExperimentsExperiments

• Smad4-null mice (-/-): lethal

• Heterozygotes of Smad4 (+/-): fertile but develop polyps after the age of 1 year (loss of the wild-type allele)

• Heterozygote intercrosses: the lethality phase of Smad4 mutant embryos is E7.5

Smad4 is essential for postimplantation development

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Somatic mutations of the Smad4 Somatic mutations of the Smad4 gene detected in human cancergene detected in human cancer

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Michiko Miyakia and Toshio Kuroki, Biochemical and Biophysical Research Communications 306 (2003) 799–804, Role of Smad4 (DPC4) inactivation in human cancer

X-ray CrystallographyX-ray CrystallographyDPC4/Smad4 TrimerDPC4/Smad4 Trimer

©2005 Memorial Sloan-Kettering Cancer Centerhttp://www.mskcc.org/mskcc/html/10859.cfm

* Shi Y, Hata A, Lo RS, Massague J, Pavletich NP. (1997) A structural basis for mutational inactivation of the tumour suppressor Smad4. Nature. 1997;388:87-93.* Shi Y, Wang YF, Jayaraman L, Yang H, Massague J, Pavletich NP. (1998) Crystal structure of a Smad MH1 domain bound to DNA: insights on DNA binding in TGF-beta signaling. Cell. 1998;94:585-594.

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Tumors DPC4 is involved inTumors DPC4 is involved in• Pancreatic carcinoma (late stage)

• Colorectal carcinoma (late stage)

• Juvenile Intestinal Polyposis (jip): Hamartomatous lesions in the gastrointestinal tract (increased risk of colon and other gastrointestinal cancers)

Hamartoma: a focal growth that resembles a neoplasm (tumor) but results from faulty development in an organ

• Juvenile Polyposis/Hereditary Hemorrhagic Telangiectasia syndrome (jp/hht): coexistence of the two diseases

HHT: tendency to form blood vessels that lack the capillaries between an artery and vein

Telangiectasia: tendency to rupture a normal blood vessel

and bleed

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Conclusion about Smad4/DPC4Conclusion about Smad4/DPC4

• Involved in TGF-ββ pathway• Smad4/DPC4 trimer creates a complex with Smad2 in

the cytoplasm and then binds to the DNA

• Tumor suppressor • Also involved in gastrulation and embryogenesis

• Homozygous deletion (at the MH2 region, especially)• Treatment?...

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Smad4 (DPC4)Smad4 (DPC4)

A tumor suppressor gene