Transforming Growth Factor-B Signaling in Stem Cells and Cancer Lopa Mishra1,3, Rik Derynck4, Bibhuti Mishra2 1Cancer Genetics and Digestive Diseases, Georgetown University 2Laboratory of CNS Development, Department of Surgery, Medicine

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Transforming Growth Factor-B Signaling in Stem
Cells and CancerLopa Mishra1,3, Rik Derynck4,
Bibhuti Mishra21Cancer Genetics and Digestive
Diseases, Georgetown University2Laboratory of
CNS Development, Department of Surgery, Medicine
Lombardi Cancer Center, Georgetown
University3Department of Veterans
Affairs4Departments of Cell and Tissue biology
and Anatomy, Programs in Cell Biology and
Developmental Biology, University of California
San Franicisco

• David Mahr
• Graduate Student

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Differentiation

• Process in which a less specialized cell becomes
  a more specialized cell
• Cells differentiate into a particular lineage
• From pluripotent cell to mature cell
• Directing differentiation
• Manipulation of cellular environment
• Growth of cells at high density
• Growth of cells on different types of feeder
  cells
• Addition of growth factors
• Growth on crude or defined ECM substrates
• Suspended three dimensional aggregation
• Development of embryoid bodies

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Differentiation Regulation
Feeder Cells
Cell Density
Lineage Direction
Embryoid Bodies
Growth Factors
Cross-talk!
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Differentiation

• Differentiation is regulated by many different
  aspects
• Orchestration by signaling networks
• Growth Factors
• TGF-? Family Proteins
• Gene Expression
• Switch from one form of gene expression to
  another

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Definitions - Potency

• Potency
• Ability to differentiate into a variety of cells
• Pluripotent
• Ability to differentiate into any of the 3 Germ
  Layers (Endoderm, Mesoderm, Ectoderm)
• Multipotent
• Ability to differentiate into a variety of cells
  within own lineage
• Unipotent
• Ability to differentiate into one cell type

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Definitions Germ Layers

• Endoderm
• Central Organs, Interior stomach lining,
  Gastrointestinal tract, Lungs
• Ectoderm
• Epidermal tissues,
• Nervous System
• Mesoderm
• Muscle, Bone,
• Blood

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Embryonic Stem Cell

• Derived from inner cell mass of blastocyst
• (Figure)
• Self Renewal
• Prolonged/Unlimited Proliferation
• (Symmetrical cell division)
• Pluripotent
• Differentiate into many
• cell types

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Definitions Progenitor Cells

• Progenitor Cells
• Characterization
• Limited self-renewal
• Unipotent / Multipotent (as opposed to
  Pluripotent)
• Become mature cell
• Some present in adult tissues (dormant)
• Types (discussed in paper)
• Neural Stem Cell
• Hematopoietic Stem Cell
• Mesenchymal Stem Cell

ESC
Progenitor Cells
Mature Cells
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Differentiation Regulators
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Differentiation Regulators

• Forms of Regulation
• Maintenance of undifferentiated state
• TGF-? family proteins can promote/inhibit cell
  proliferation apoptosis depending on different
  cellular environmental factors
• Specification of differentiation lineage
• Regulation of differentiation also depends on
  cellular environment
• Progression along specific lineage
• Can promote progression along lineage and
  sometime change differentiation pathway depending
  on environmental factors

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TGF-ß Family Signals Smad Pathway
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TGF-ß Family Signals Smad Pathway
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TGF-ß Family Signals Smad Pathway

• Variety of TGF-B Family Proteins can bind the
  serine/threonine-specific protein kinase
  receptors
• Create different downstream effects
• Smad pathway regulated by ubiquitin and SUMO
  ligases, other proteins in transcription
  complexes
• TGF-B can promote/inhibit cell proliferation,
  apoptosis, differentation based on cellular
  environment factors
• Maintenance, Specification, and Progression
  dictated by CROSS-TALK of TGF-B family signals
  and cellular environment factors

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Wnt Pathway
Wnt ligand binds FRZ receptor
Activates DSH protein
DSH inactivates axin/GSK/APC
Increases B-catenin level
B-catenin gene expression
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Wnt Pathway

• Wnt effect as a Stem Growth Factor
• Promotes maintenance and proliferation of Stem
  Cells
• Can also lead to uncontrollable proliferation (if
  unregulated)
• Also been shown to lead to tumorigenesis

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Embryonic Stem Cells TGF-ß Family Signaling

• Maintenance of undifferentiated state
• Promoted by Nodal Activin
• Activate Smad pathway and Wnt signaling
• Maintain undifferentiated state and pluripotency
• Specification of Differentiation lineage
• Mesodermal
• Promoted by Activin TGF-B
• Promoted by BMP
• Ectodermal
• Promoted by BMP
• Neuralectoderm
• Absence of exogenous TGF-B factors
• Endodermal
• Promoted by Activin
• Main-point Presence/Absence of TGF-B family
  signals is a strong regulator of maintenance and
  specification of embryonic stem cells

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Neural Stem Cells TGF-ß Family Signaling
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Neural Stem Cells TGF-ß Family Signaling

• Specification from ES Cells
• Absence of TGF-B family proteins
• Progression along lineage
• Ganglia cells
• Promoted by TBF-B
• Olfactory cells
• Promoted by TGF-B
• Glial Cells (Supporter cells of neural cells)
• Inhibited by TGF-B
• Inhibits uncontrolled growth of glial cells
• Otherwise would lead to malignant gliomas
• Main-point TGF-B accelerates progression of
  neural progenitor cells along neuralectoderm
  lineage.

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Hematopoietic Stem Cells TGF-ß Family Signaling
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Hematopoietic Stem Cells TGF-ß Family Signaling

• Specification from ES Cells
• Promoted by BMPs Cytokines
• Also promotes proliferation
• Inhibited by Smad5
• Progression along lineage
• Myeloid
• Promoted by Smad7
• Inhibits Smad activation
• Lymphoid
• Inhibited by Smad7
• Promotes Smad activation
• Main-point TGF-B family signaling via Smads
  helps regulate the fate of hematopoietic stem
  cells.
• This regulation is also dependent on other
  exogenous effects such as different activiating
  ligands and other pathways. (Cross-talk)

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Mesenchymal Stem Cells TGF-ß Family Signaling

• Specification from ES Cells
• Promoted by TGF-B
• Also induces proliferation
• Example TGF-B levels elevate in the event of
  injury (Wound repair)
• Progression along lineage
• Inhibited by TGF-B
• Mechanism to enhance Mesenchymal Stem Cell
  population? (Maintenance)
• Myoblast
• Inhibited by Myostatin
• Adipocytes
• Promoted by Myostatin
• Osteoblasts
• Promoted by BMPs
• Can cause Mesenchymal SC progressing along one
  lineage to
• trans-differentiate into osteoblasts! (swtich
  differentiation path)
• Main-point (Again) Differentiation regulated
  by TGF-B family members in cooperation with other
  signaling pathways.

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Gastrointestinal Tissue/Cancers TGF-ß Family
Signaling

• Tumor suppressor
• Inhibit cancer growth/development in early stages
• Inactivation of TGF-B receptor, Smad2, Smad4, ELF
  often lead to gastrointestinal tumors
• BMPs
• Suppress Wnt signaling
• Mutations in BMP receptor and Smad4
• Uncontrollable stem cell development Tumor
  development
• Smad2, Smad3, ELF
• Essential for proper hepatocyte development
• Inactviation of Smad2, Smad3, or ELF leads to
  Hepatocellular carcinoma
• Main-point TGF-B family proteins regulate tumor
  progression similar to regulating stem cell
  differentiation.

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Conclusions

• TGF-B family proteins and their signaling
  pathways play key roles in the regulation of
  embryonic stem cells and progenitor cells.
• Embryonic SC Self-renewal, Maintenance of
  undifferentiated state
• Progenitor Cells Specification and Progression
  of differentiation
• Resulting biological effects are dictated by the
  CROSS-TALK of several different pathways and
  factors
• When TGF-B family proteins are deregulated,
  impaired differentiation can occur and lead to
  the formation of cancers.

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Questions?