at the University of Pécs and at the University of Debrecen
Identification number: TÁMOP-4.1.2-08/1/A-2009-0011
WNT SIGNALING
Tímea Berki and Ferenc Boldizsár Signal transduction
at the University of Pécs and at the University of Debrecen
Identification number: TÁMOP-4.1.2-08/1/A-2009-0011
Discovery of Wnts
Wnt genes:
• Wingless gene in Drosophila melanogaster
• Int gene in mice
• 24 has been discovered
• 19 are expressed in mammals
• 10 receptor genes - Frizzleds
Wnt family proteins
Comprises of 19 secreted glycoproteins controlling a variety of developmental processes:
• Cell fate specification
• Cell proliferation
• Cell polarity and cell migration
• Different types of cancers
• Various processes of aging
Frizzled (Fz) family receptors
• They are 7-TM receptors; however, assembly of an active Wnt-Fz receptor complex also requires the presence of a co- receptors, the low-density lipoprotein related protein 5 and 6 (LRP5/6)
• Canonical pathway activators: Wnt1, Wnt3, Wnt3a, Wnt7a,
Wnt7b, Wnt8
• Non-canonical pathway activators: Wnt5a, Wnt4, Wnt11
Canonical pathway
• In developing thymocytes or in thymic epithelium
• Signals from the Wnt-Fz-LRP6 complex lead to the phosphorylation of three domains of Dishevelled (Dvl), a family of cytosolic signal
transducer molecules.
• Activation of Dvl ultimately leads to phosphorylation and consequently inhibition of GSK-3
• Inhibition of GSK-3 results in stabilisation and consequent cytosolic accumulation of -catenin, which then translocates into the nucleus,
• -catenin forms active transcription complexes with members of the T- Cell Factor (LEF1, TCF1, TCF3, TCF4) transcription factor family and transcription initiator p300.
• Successful assembly of the transcription complex leads to the activation of various target genes including cyclin-D1, c-myc, c-jun , Fra-1 VEGFR, etc.
Non-canonical pathways
• Independent from -catenin
• Branches into the:
1 Polar cell polarity (PCP) or c-Jun-N Terminal
Kinase (JNK)/Activating Protein (AP1) dependent 2 Ca
2+or Protein kinase C (PKC)/Calmodulin
Kinase (CaMKII)/Nuclear Factor of Activating T-
cells (NFAT) dependent pathways
Wnt signaling pathways
Canonical pathway Wnt/Ca2+
Cytoskeletal rearrangment
Planar cell polarity
Gene transcription Nucleus
PKC PLC
NFAT Ca2+
Calcineurin
Rac RhoA
JNK G proteins?
CaMKII
P NFAT Cytoplasm
Plasma membrane
DIX PDZ DEP
Daam1
ROCK
Prickle LRP5/6
-catenin
DIX PDZ DEP
Axin GSK3
APC
-TrCP
-catenin LEF/
TCF
-catenin
Dsh Dsh
Wnt
Frizzled
Axin
Wnt5a
Frizzled
Wnt11
Frizzled Stbm
No Wnt signal
?
?
Canonical Wnt pathway
Nucleus
Wnt8
Cytoplasm Plasma membrane LRP5/6
Frizzled
-catenin
Axin DIX PDZ DEP
TCF3
Dsh Dkk1
Krm
Anterior genes
-catenin in cellular adhesion
Cytoplasm
-catenin Axin
GSK3
APC
-catenin degradation Wnt
Frizzled
No Wnt signal Dsh
Nucleus
-catenin
LEF/TCF Transcription
-catenin
P
P
-catenin
Cadherin
-catenin -catenin
Cadherin
-catenin
-catenin
Cadherin
-catenin
-catenin
Cadherin
-catenin
Adherens junction
+ Wnt signal Plasma membrane
Alzheimer’s disease I
Development of NFTs Apoptosis
NO
Activated microglia
DNA damage Excitotoxicity
Cell-cycle activation
Abnormal DNA synthesis
AP
p53
Fast AP toxicity Wnt Delayed AP toxicity
Dkk1 Bax
- +
Alzheimer’s disease II
Late stage
↓Phosphorylation of tau GSK3
Wnt
Frizzled
Akt PI3K Dkk1
Krm
↑Phosphorylation of tau GSK3
Wnt
Frizzled
Akt PI3K Dkk1
Krm
Early stage
P
GD3 synthase- cyclin D1
-catenin GSK3
Wnt
Frizzled
Dsh
Nucleus
-catenin LEF/
TCF bAP
Akt
the canonical pathway
Growth
-catenin GSK3
Wnt
Frizzled
Dsh
Nucleus -catenin
TCF4 Frat
PP2A
Axin APC
b-TrCP
TCF4
Frp
Nkd 1 and 2
Dominant negative Dsh-s Dominant negative Frizzleds
ICAT CK-1,2
PKC isoforms in Wnt signalling
• PKC
• PKCd
• PKCz
independent Wnt signalling pathways
1 The canonical pathway is the first and best characterized Wnt pathway. Signals are coming through the 7
transmembrane domains of Frizzled-receptors, than Dsh is phosphorylated and signal is transmitted via -catenin to TCF/LEF in the nucleus.
2 Ca-dependent Wnt signaling is transmitted by Frizzled-s
and G-proteins and the intracellular signaling molecules are CaMKII and different izotypes of PKCs. Inhibitory signals can use TAK and NLK to get into the nucleus. One of the key targets is NF-AT.
3 Planar cell polarity pathway is Ca dependent and using JNK
as well as PKCs to transduce signals to the AP1 complex.
pathways involved ?
• Inflammation
• Fibrosis
• Cancer
Wnt Target genes
Canonical pathway
(-catenin/TCF) Cyclin D1, MMP-s, c-myc, Cox-2, c-jun, Fra-1, VEGFR, EGFR
Ca2+ pathway (NFAT, NFkB)
IL-1, IL-2, IL-3, IL-4, IL-5, IL-6, IL-8, IL-15, IFN-, GMCSF, TNF-, ICAM-1
PCP pathway (AP1)
Cyclin D1, MMP-s, FasL, Bim, Bcl3, FL1, GMCSF
INFLAMMATION TISSUE REPAIR AND
REMODELLING
IL-1, Il-8, IL-6, MMP-s FGF10, TGFb, BMP4, MMP-s
Wnt target genes
Rheumatoid arthritis
CD34+ bone marrow progenitorcell infiltration
Inflammatory stimuli
Leukocyte infiltration
Increased Wnt5a
IL6, IL8, IL15, metallo-proteinases
Joint destruction
Wnt1 Wnt5a Wnt11 Wnt13
Fz-2 Fz-5 Fz-7
Synoviocytes
in the aging thymus
• Wnt4 uses mainly the -catenin dependent canonical signaling pathway
• Wnt4 expression is decreasing during aging in the thymus
• The receptors of Wnt4 signaling are Frizzled-4 and Frizzled-6
• The expression pattern of Wnt4 receptors is changing during thymic senescence
• During aging the balance moves towards the Fz-6, transducing negative Wnt signals
• PKCd is modulating intracellularly the Wnt4 signaling mechanism
• CTGF - a target gene of Wnt4 signals- expression is increasing
• CTGF is a negative regulator of b-catenin dependent signaling
• CTGF and its recently described receptor Fz-8 is functioning as a secondary negative feedback mechanism of Wnt4 signaling
