1. A tumor suppressor gene
Smad4 (DPC4)
A tumor suppressor gene

2. Smad4 (DPC4) Smad4: Mothers against decapentaplegic (dpp) homolog 42
Smad4 (DPC4)
Smad4: Mothers against decapentaplegic (dpp) homolog 4
dpp is responsible for dorsal/ventral polarity in the fly
Drosophila melanogaster MADH4: Mothers Against Decapentaplegic Homolog 4
Caenorhabditis elegans sma-4: like MADH4
Human DPC4: Deleted in Pancreatic Carcinoma, locus 4

3. Facts about DPC4 Chromosomal location: 18q21.1 Identified in 19963
Chromosomal location: 18q21.1
Identified in 1996
deleted in 55% of pancreatic cancers (late stage)
deleted in 10% to 35% of colorectal cancers (late stage)
Involved in Familial Juvenile Polyposis
University of Pittsburg Medical Center

4. 4
Endoscopic and colonoscopic appearance of Cowden's syndrome, a rare inherited polyposis syndrome
Charles Donner, M.D. The University of Iowa

5. Department of Biochemistry – University of Toronto5
Smad4 transcription factor changes from a generalized distribution (left) to a nuclear localization (right) following addition of TGF-β
Department of Biochemistry – University of Toronto

6. Big Picture I: the TGF-β signaling pathway6
Big Picture I: the TGF-β signaling pathway

7. The TGF-β signaling pathway7
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 SnoN oncoprotein.

8. 8
SMAD proteins
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

9. X-ray Crystallography DPC4/Smad4 Trimer9
X-ray Crystallography DPC4/Smad4 Trimer
©2005 Memorial Sloan-Kettering Cancer Center
* 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:

10. Smad-mediated TGF-β signaling pathway10
Smad-mediated TGF-β signaling pathway
Michiko Miyakia and Toshio Kuroki, Biochemical and Biophysical Research Communications 306 (2003) 799–804, Role of Smad4 (DPC4) inactivation in human cancer

11. Two normal biological roles for Smad4/DPC411
Two normal biological roles for Smad4/DPC4
Gastrulation and embryogenesis
Initially required for differentiation of visceral endoderm
Secondary involved in anterior/posterior patterning during embryogenesis
Tumor suppressor
Mediates the TGF-β signaling pathway suppressing epithelial cell growth

12. Experiments Smad4-null mice (-/-): lethal12
Experiments
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

13. 13

14. Somatic mutations of the Smad4 gene detected in human cancer14
Somatic mutations of the Smad4 gene detected in human cancer
Michiko Miyakia and Toshio Kuroki, Biochemical and Biophysical Research Communications 306 (2003) 799–804, Role of Smad4 (DPC4) inactivation in human cancer

15. X-ray Crystallography DPC4/Smad4 Trimer15
©2005 Memorial Sloan-Kettering Cancer Center
* 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:

16. Tumors DPC4 is involved in16
Tumors 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

17. Conclusion about Smad4/DPC417
Conclusion about Smad4/DPC4
Involved in TGF-β 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?...

18. A tumor suppressor gene
Smad4 (DPC4)
A tumor suppressor gene