Download Role of Smad4 (DPC4) inactivation in human cancer.

SMAD4/DPC4:
A Tumor Suppressor
James Brooks
March 23rd, 2006
Found on chromosome 18 in humans, encodes 11 exons
A 552 amino acid protein found in the cytoplasm
SMAD Structure: MH1 and MH2 Domains
SMAD proteins exist as homo-oligomers
• The quaternary structure
of SMADs consists of
three monomers attached
at their MH2 domains
(homo-oligomers)
• MH2 domains are also
responsible for heterooligomerization
SMAD4 is expressed at all
stages of development
Above: Northern blot (RNA) of SMAD4 (3.8 kb) at various stages
of development in mouse (L32 is a loading control)
SMAD4 mutant mouse embryos exhibit early embryonic
lethality
• By day 6.5, SMAD4 mutant
mouse embryos appear much
smaller than wild type ones;
the difference in size is
attributed to reduced cell
proliferation
• By day 7.5, SMAD4 mutant
mouse embryos are lethal
SMAD4 is the convergence point of several TGF-β pathways
SMAD4 activity regulates cell proliferation in the TGF-β
signaling pathway
Left: SMAD4 distribution in absence of TGF-β
Right: SMAD4 after translocation into nucleus following stimulation by TGF-β
SMAD4 activity regulates cell proliferation in the TGF-β
signaling pathway
The Smad4 gene is often mutated in the MH2 domain
Familial Juvenile Polyposis (FJP)
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Clinical manifestation of germline
SMAD4 mutation, phenotypically
similar to that of familial
adenomatous polyposis (FAP)
from loss of APC function
Autosomal Dominant inheritance
pattern
SMAD4 is mutated in
approximately 50% of FJP cases
Agrees with Knudson’s two-hit
model
Above: A juvenile polyp
Smad4 mutation is often seen in late-stage malignancies
that have metastasized
This makes sense!
To sum things up…
• SMAD4 is a tumor suppressor that regulates cell
proliferation through interaction with transcription
factors
• When inactive, it is located in the cytosol. It is
translocated into the nucleus once activated
• Loss of SMAD4 is associated with familial
juvenile polyposis, and is often absent in
malignant pancreatic and colon carcinomas
References
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Karyotype: http://www.amnh.org/learn/musings/FA01/ia/HW_01.jpg
SMAD4 Crystal Structure: Shi et. al. A structural basis for the mutational inactivation of the tumour
suppressor Smad4. 3 Jul 1997. Nature.
SMAD MH1 and MH2 Domain Structure:
http://ethesis.helsinki.fi/julkaisut/laa/haart/vk/roth/discussion.html
Smad Mediated TGF-Beta Signaling Pathway: Miyaki et. al. Role of Smad4 (DPC4) inactivation in
human cancer. 2003. Biochemical and Biophysical Research Communications.
Smad4 Northern Blot: Sirard et. al. The tumor suppressor gene Smad4/DPC4 is required for
gastrulation and later for anterior development of the mouse embryo. 1998. Genes and
Development.
Wild-type and Smad Mutant embryos: Sirard et. al. The tumor suppressor gene Smad4/DPC4 is
required for gastrulation and later for anterior development of the mouse embryo. 1998. Genes
and Development.
TGF-Beta Superfamily Signaling Pathway: Waite and Eng. From developmental disorder to
heritable cancer: it’s all in the BMP/TGF-β family. 2003. Nature.
TGF-Beta Signaling Pathway: Lodish et. al. Molecular Cell Biology p. 957
SMAD4 Localization Photos:
http://biochemistry.utoronto.ca/research/signal_transduction_and_regulation.html
References, Continued
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Mutations in SMAD4: Miyaki et. al. Role of Smad4 (DPC4) inactivation in human cancer. 2003.
Biochemical and Biophysical Research Communications.
Juvenile Polyp: http://www.surgery.uiowa.edu/surgery/physpubs/familialjuvenilepolyposis.html
SMAD4 in Cancer: Miyaki et. al. Role of Smad4 (DPC4) inactivation in human cancer. 2003.
Biochemical and Biophysical Research Communications.