| dc.description.abstract | Embryonic development is regulated by a number of signalling pathways, Which are
critical for normal growth. Many of these genes then continue to play an important role
in the regulation of cell growth and differentiation in adult. One such pathway is the
sonic hedgehog (SHH) pathway; SHH protein is secreted which binds to its receptor
patched (PTCH), leading to the activation and repression of target genes via zinc-finger
GLI family transcription factors. Deregulation of this pathway, leads to a number of
human birth defects and diseases such as Basal Cell Carcinoma (BCC) of the skin. In
transgenic mouse model systems activation of GLI1 by SHH-signalling is a key step in
initiating BCC formation. However, there is limited understanding of the molecular
mechanisms involved in response to hedgehog signalling and GLI activity in human
BCC formation and how this pathway interacts with other pathways. The aim of this
thesis was to establish in vitro and in vivo model systems to investigate the molecular
events leading to BCC formation. I have shown that Gl.Il , Gi12, Gi13, PTCH, SMO
and KlF4 were induced and a-TUB was repressed in BCC relative to normal skin. Using
an in vitro model I further showed that Gl.ll , Gi12, Gi13, PTCH, SMO and a-TUB
were induced and KlF4 was repressed in GLII expressing keratinocytes. Collaborative
work with Dr Fritz Aberger's laboratory in Salzburg showed that Gl.Il and FOXEI are
direct targets of GLI2 and I showed that Gl.I? and FOXEI were expressed in the
interfollicular epidermis and the outer root sheath of hair follicles in normal skin as well
as in BCC tumour islands suggesting a possible link between hair follicle and BCe. I
further showed that epidermal growth factor (EGF) signalling reduces transcription
activity of GLI1 by shuttling GLII out of nucleus and altering the expression of PTCH,
SMO, Gil2 and Gl.B SHH genes. In addition, I demonstrated that whilst EGF induced
Vimentin and Snail2 expression and GLII repressed their expression suggesting that
GLI is able to counter epithelial-mesenchymal transition associated with EGF and this
may in part explain why Bee very rarely metastasise. Furthermore, GLI1 appears to
upregulate stem cell like signature and EGF downregulates this signature. Finally, we
were able to generate a KRTI4- Floxed-GFP-Gill transgenic mouse but were unable to
activate the target gene (KRTI4-GFP-GiIl). In conclusion, I have identified possible
targets of GLI activity and shown interactions between EGF signalling and GLI that
will help us to understand the potential molecular actions of SHH signalling with the
goal of developing better therapeutic strategies. | en_US |
