3Background: Stem Cells Self RenewalPluripotencySource for tissue engineering and cell replacement therapiesSimilar to cancer cells; stem cells thought to be derived from cancer stem cellsAdapted from System Biosciences (systembio.com)Understanding stem cells is important for understanding cancer
4Background: Signaling Pathways Abnormalities in pathways may give rise to cancer stem cells and tumorsUnderstanding the signaling pathways and identifying important factors helps to understand cancer transformation as well stem cell differentiation for tissue engineering and regenerative medicine applications
5Transforming 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
6SMAD Signaling Pathway The downstream canonical signaling pathway for TGF-β proteins, including activin, nodal, and BMP. Also called the nodal signaling pathway and TGF-beta signaling pathway.Bind to type 1/type II serine/theonine kinase receptors.A number of SMAD proteins are activated via phosphorylationReceptor SMADs complex with common-partner SMAD4 to translocate to the nucleusInhibitory SMADs inactivate R-Smads and function as a negative feedback loop.Signaling cascade resulting in activation and suppression of genes, such as OCT3/4 and Nanog.OCT3 OCT4 NanogAdapted from Blank et al. (2008)
7Stem Cell Differentiation Overview BMP-4 is important for proliferation and is mediated by its inhibitory effect on neural differentiationShows how changes in signal levels drive differentiation. IE. BMP signals alone are required for formation of the posterior primitive streak, and eventually giving rise to mesodermal tissueM=maintenanceD=differentiationAdapted from Watabe et al. (2009)
8SMAD 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-4OCT4 and Nanog are important transcription factors in generation of IPS cellsBMP and leukemia-inhibiting factor keep mouse ES cells in the undifferentiated state.[Mishra]
9TGF-β in Neural Stem Cells BMP inhibits neural differentiationTGF-β promotes differentiation in committed progenitorsInactivation of TGF-β growth-inhibitory functions result in tumor progressionAdapted from Mishra et al. (2005).
10TGF-β in other Cell Types Hematopoietic Stem cellsInhibits early progenitors, while enhances differentiation of committed stem cellsMesenchymal Stem CellsInhibits differentiation and maturation into myoblasts, osteoblasts, and adipocytes, while stimulating MSC proliferationBasis for efficient wound repair in mesenchymal tissueGastrointestinal Epithelial Stem CellsInactivation with one TGF-β component (Receptor, SMAD protein) is present in all gastrointestinal cancerBMP’s and cytokines promote specification, differentiation and proliferation of human ES cellsDeregulation of TGF-β can result in cancer progression as well.BMPs activate osteoblast differentiation.
11WNT Signaling Pathway Adapted from Katoh et al. (2007). Frizzled receptors and LRP coreceptors receive canonical WNT signals, which in turn activate disheveled proteins (DVL).DVL proteins inhibit the formation of the axin/GSK-3/APC complex, which acts to phosphorylate beta-catenin, tagging it for polyubiquitination and eventual degradation.Nuclear accumulation of beta-catenin complexes with TCF/LEF transcription factors which activate FGF20, DKK1, WISP1, MYC, and CCND1 genes.Adapted from Katoh et al. (2007).
12WNT Signaling Pathway Cell fate determination Transformation of cancer stem cells due to disregulationMYC is a transcription factor involved in generation of IPS cells.
13Notch Signaling Pathway Delta or jagged ligands bind to Notch receptors.Gamma-secretase causes the release of the intracellular domain (NICD)Forms a complex with CSL and MAM and activate genes involved in neural differentiation.Adapted from Bray et al. (2009).
14Notch Signaling Pathway Promotion of neural cell differentiationInvolved in self-renewal of hematopoietic stem cells
15Hedgehog Signaling Pathway Shh binds to Patched-1 which stops inhibition of Smoothened.Smo activates Gli proteins in the nucleus resulting in regulation of genes.Adapted from Altaba et al. (2002).
16Hedgehog Signaling Pathway Induces differentiation of hematopoietic progenitors and neural stem cellsSkin, muscle, and brain cancers develop when pathway is maintained improperly in stem cells
17FGF Signaling Pathway Adapted from Katoh et al. (2006) FGF signals are transduced through FGF receptorsVarious signaling cascades result in EMT, cell survival, and proliferation/differentiationEMT is caused by downregulation of E-cadherinAdapted from Katoh et al. (2006)
18FGF 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
19TGF-β1 /WNT Pathway Cross-talk SMAD and TCF/LEF associate to cooperatively regulate genesSeries 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 pathwayMediated by SMAD3/GSK3β disruption through TGF-β mediated phosphorylation.MSCs act differently with TGF-β.SMAD3 acts as a chaperone for beta-catenin
20TGF-β1 /WNT Pathway Cross-talk MSCs act differently with TGF-β.SMAD3 acts as a chaperone for beta-catenin
21WNT/FGF/Notch/SMAD/Hedgehog Cross-talk Balance of all signaling pathways is important for homeostasis and prevention of cancer and congenital diseasesHedgehog pathwaySMAD pathwayNotch family receptorNotch family receptorHedgehog pathway induced
22ConclusionsMany signaling pathways with cross talk involved in stem cell proliferation, maintenance, and differentiationDependent on differentiation stage, type of cell, local environment, and the identity and amount of particular ligandIdentification of key regulators has potential for generation of iPS cells and cell replacement therapies
23ReferencesMishra L, Derynck R, & Mishra B. Transforming growth factor-beta signaling in stem cells and cancer. Science 310, (2005).Blank U, Karlsson G, & Karlsson S. Signaling pathways governing stem-cell fate. Blood. 111(2), (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, (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, (2009).Bray S. Notch Signaling: a simple pathway becomes complex. Nature Rev. Mol. Cell Bio. 7, (2006).Altaba AR, Sanchez P, Dahmane N. Gli and hedgehog in cancer: tumours, embryos and stem cells. Nature Rev. Cancer, 2, (2002).Katoh M & Katoh M. Cross-talk of WNT and FGF signaling pathways at GSK3-beta to regulate beta-catenin and SNAIL signaling cascadesKatoh M. Networking of WNT, FGF, Notch, BMP, hedgehog signaling apthways during carcinogenesis. Stem Cell Reviews. 3(1), (2007).