Stem Cells and Cell Signaling

Cheng-En LaiBIOE 506: Molecular and Cellular

Bioengineering4/25/2011

Overview• Background

– Stem Cells– Signaling Pathways

• Transforming Growth Factor-β (TGF-β)– SMAD Signaling Pathway– Stem Cell Differentiation Overview– Signaling Examples– TGF-β in various cell types

• Other Signaling Pathways– WNT– Notch– Hedgehog– Fibroblast Growth Factor (FGF)

• Cross-talk– SMAD/WNT– WNT/FGF/Notch/SMAD/Hedgehog

• Conclusions

• Self Renewal• Pluripotency• Source for tissue engineering

and cell replacement therapies

• Similar to cancer cells; stem cells thought to be derived from cancer stem cells

• Understanding stem cells is important for understanding cancer

Adapted from System Biosciences (systembio.com)

Background: Stem Cells

Background: Signaling Pathways

• Abnormalities in pathways may give rise to cancer stem cells and tumors

• Understanding the signaling pathways and identifying important factors helps to understand cancer transformation as well stem cell differentiation for tissue engineering and regenerative medicine applications

Transforming Growth Factor β

• TGF-β proteins and TGF-β related bone morphogenetic proteins (BMPs) are important regulators of stem cell differentiation, maintenance, and self-renewal, as well as carcinogenesis suppression.

• Comprised of 30 related proteins in the SMAD pathway

SMAD Signaling Pathway

OCT3OCT4Nanog

Adapted from Blank et al. (2008)

Stem Cell Differentiation Overview

Adapted from Watabe et al. (2009)

SMAD Signaling Examples

• Nodal and activin cooperate with the WNT pathway to maintain ES cells and keep them undifferentiated and pluripotent.

• Activin and TGF-β confers mesodermal differentiation depending on amount.

• BMP signaling results in mesodermal and ectodermal differentiation in human ES cells.

• Nodal signals are important for OCT3/4 expression and maintenance of ES cells.

• Activin is important for maintenance of pluripotency, which is possibly done through induction of Nanog and OCT-4

TGF-β in Neural Stem Cells

• BMP inhibits neural differentiation

• TGF-β promotes differentiation in committed progenitors

• Inactivation of TGF-β growth-inhibitory functions result in tumor progression

Adapted from Mishra et al. (2005).

TGF-β in other Cell Types

• Hematopoietic Stem cells– Inhibits early progenitors, while enhances differentiation of

committed stem cells• Mesenchymal Stem Cells– Inhibits differentiation and maturation into myoblasts,

osteoblasts, and adipocytes, while stimulating MSC proliferation

– Basis for efficient wound repair in mesenchymal tissue• Gastrointestinal Epithelial Stem Cells– Inactivation with one TGF-β component (Receptor, SMAD

protein) is present in all gastrointestinal cancer

WNT Signaling Pathway

Adapted from Katoh et al. (2007).

WNT Signaling Pathway

• Cell fate determination• Transformation of cancer stem cells due to

disregulation

Notch Signaling Pathway

Adapted from Bray et al. (2009).

Notch Signaling Pathway

• Promotion of neural cell differentiation• Involved in self-renewal of hematopoietic

stem cells

Hedgehog Signaling Pathway

Adapted from Altaba et al. (2002).

Hedgehog Signaling Pathway

• Induces differentiation of hematopoietic progenitors and neural stem cells

• Skin, muscle, and brain cancers develop when pathway is maintained improperly in stem cells

FGF Signaling Pathway

Adapted from Katoh et al. (2006)

FGF Signaling Pathway

• EMT• Cell survival• Proliferation/differentiation• Cross-talk is seen between WNT and FGF via

down-regulation of GSK3β, resulting in tumors with more malignant phenotypes of mammary carcinogenesis

TGF-β1 /WNT Pathway Cross-talk

• SMAD and TCF/LEF associate to cooperatively regulate genes

• Series of experiment by Jian et. al. (2006) show that TGF-β1 addition results in rapid nuclear accumulation of β-catenin in MSCs in a new form of cross-talk.

• β-catenin nuclear accumulation is not due to phosphorylation as from canonical WNT pathway

• Mediated by SMAD3/GSK3β disruption through TGF-β mediated phosphorylation.

TGF-β1 /WNT Pathway Cross-talk

WNT/FGF/Notch/SMAD/Hedgehog Cross-talk

• Balance of all signaling pathways is important for homeostasis and prevention of cancer and congenital diseases

Notch family receptor

Hedgehog pathway induced

SMAD pathway

Notch family receptor

Hedgehog pathway

Conclusions

• Many signaling pathways with cross talk involved in stem cell proliferation, maintenance, and differentiation

• Dependent on differentiation stage, type of cell, local environment, and the identity and amount of particular ligand

• Identification of key regulators has potential for generation of iPS cells and cell replacement therapies

References• Mishra L, Derynck R, & Mishra B. Transforming growth factor-beta signaling in stem cells and

cancer. Science 310, 68-71 (2005).• Blank U, Karlsson G, & Karlsson S. Signaling pathways governing stem-cell fate. Blood. 111(2),

492-503 (2008)• Jian H, et al. Smad3-dependent nuclear translocation of beta-catenin is required for TGF-beta1-

induced proliferation of bone marrow-derived adult human mesenchymal stem cells. Genes Dev 20, 666-674 (2006).

• Katoh M & Katoh M. WNT Signaling Pathway and Stem Cell Signaling Network. Clin. Cancer Res. 13, 4042 (2007).

• Watabe T & Miyazono K. Roles of TGF-beta family signaling in stem cell renewal and differentiation. Cell Research 19, 103-115 (2009).

• Bray S. Notch Signaling: a simple pathway becomes complex. Nature Rev. Mol. Cell Bio. 7, 678-689 (2006).

• Altaba AR, Sanchez P, Dahmane N. Gli and hedgehog in cancer: tumours, embryos and stem cells. Nature Rev. Cancer, 2, 361-372 (2002).

• Katoh M & Katoh M. Cross-talk of WNT and FGF signaling pathways at GSK3-beta to regulate beta-catenin and SNAIL signaling cascades

• Katoh M. Networking of WNT, FGF, Notch, BMP, hedgehog signaling apthways during carcinogenesis. Stem Cell Reviews. 3(1), 30-38 (2007).