The effects of purified
Wnt proteins on prostate cell growth and differentiation
Work in my laboratory
focuses on the involvement of the Wnt signalling pathway in prostate
cancer. The NCRI Pilot Award will provide us with funding for consumables
to purify Wnt proteins and assess their effects on cultured primary
Wnts are secreted growth/differentiation
factors that play significant roles during development (for recent
reviews see the Wnt homepage http://www.stanford.edu/~rnusse/wntwindow.html).
They can be grouped into two classes: canonical and noncanonical.
Canonical Wnts stabilise beta-catenin and activate gene expression;
noncanonical Wnts affect other pathways, for example, involving
PKC and JNK activation, thereby regulating cell survival, cell motility
and cell polarity. Importantly, there are instances when noncanonical
Wnts inhibit the actions
of canonical Wnts (Saneyoshi
et al., 2002; Topol et al., 2003), suggesting that the balance of
Wnt family members expressed in a tissue will be an important determinant
of beta-catenin activation. We have identified Wnts
from both classes that are
expressed to different degrees in primary prostate cells and in
prostate cancer cell lines. These are therefore candidates for factors
that regulate prostate stem cell growth and differentiation.
Research in the Wnt field
has been hampered by the inability to purify active Wnt proteins,
and, until recently, all studies used conditioned medium from cells
transfected with Wnt expression plasmids. This problem, which resulted
from the high hydrophobicity of Wnts, has now been solved for at
least three Wnts. It has been shown that purified Wnt3A
maintains hematopoietic stem
cells in an undifferentiated state to a greater extent than Wnt3A-conditioned
medium (Willert et al., 2003; Reya et al., 2003). Thus cell-conditioned
medium might contain factors that induce stem and/or progenitor
cell differentiation, and any meaningful studies of the effects
of Wnts on prostate cell growth and differentiation will ultimately
require the use of purified proteins.
It has been suggested that
prostate cancer arises from abnormal prostate stem cells. If Wnt
proteins are found to regulate prostate stem cell development, then
they might also play a primary role in the origins of prostate cancer.
There is circumstantial evidence to support this idea. Wnt
proteins, foir example, play
important roles in stem cell maintenance in several other organs
(reviewed in Taipale and Beachy, 2001 and in Fuchs et al., 2001),
and activation of the Wnt signalling pathway occurs during androgen-induced
regrowth of the rat prostate (Chesire et al., 2002).
Moreover, even though only
5% of prostate tumours contain activating mutations in the beta-catenin
gene, beta-catenin is 'activated' (that is, found in the nucleus
and cytoplasm rather than solely at cell-cell junctions) in up to
38% of advanced prostate tumours (Chesire et al., 2002;
de la Taille, 2003). We
hope that by exploring the effects of Wnts on prostate cell growth
and differentiation we will be able to shed light on any link between
stem cells and prostate cancer.
- Chesire DR, Ewing CM, Gage WR, Isaacs WB. In vitro evidence
for complex modes of nuclear beta-catenin signaling during prostate
growth and tumorigenesis. Oncogene. 2002 Apr 18;21(17):2679-94.
- De La Taille A, Rubin MA, Chen MW, Vacherot F, De Medina SG,Burchardt
M, Buttyan R, Chopin D. beta-Catenin-related Anomalies in Apoptosis-resistant
and Hormone-refractory Prostate Cancer Cells. Clin Cancer Res.
- Fuchs E, Merrill BJ, Jamora C, DasGupta R. At the roots of
a never-ending cycle. Dev Cell. 2001 Jul;1(1):13-25.
- Hudson DL, Masters JR. Prostate epithelial stem cell isolation
and culture. Methods Mol Med. 2003;81:59-67.
- Saneyoshi T, Kume S, Amasaki Y, Mikoshiba K. The Wnt/calcium
pathway activates NF-AT and promotes ventral cell fate in Xenopus
embryos. Nature. 2002 May 16;417(6886):295-9.
- Taipale J, Beachy PA. The Hedgehog and Wnt signalling pathways
in cancer. Nature. 2001 May 17;411(6835):349-54.
- Topol L, Jiang X, Choi H, Garrett-Beal L, Carolan PJ, Yang
Y. Wnt-5a inhibits the canonical Wnt pathway by promoting GSK-3-independent
beta-catenin degradation. J Cell Biol. 2003 Sep 1;162(5):899-908.
- Wodarz A, Nusse R. Mechanisms of Wnt signaling in development.
Annu Rev Cell Dev Biol. 1998;14:59-88.