The role of axin in the degradation of B-catenin in human oesophageal squamous cell carcinoma
Date
2009-04-23T05:16:14Z
Authors
Bezuidenhout, Belinda Catherine
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Abstract
Axin, in combination with adenomatous polyposis coli (APC), forms the scaffold of
the β-catenin degradation-targeting complex. Intricate interactions within this
complex lead to the phosphorylation and subsequent ubiquitination of β-catenin,
followed by proteosome-mediated degradation. Low density lipoprotein receptorrelated
protein 5 (LRP5), the canonical Wnt coreceptor, is able to function in axin
inhibition, by recruiting it to the plasma membrane in response to canonical Wnt/β-
catenin signalling. This study investigates the influences of each of these proteins
within the context of human oesophageal squamous cell carcinoma (HOSCC).
Western immunoblotting, and subsequent densitometric analysis of whole cell protein
lysates revealed the presence of differing levels of β-catenin, axin and APC in five
oesophageal carcinoma cell lines. Furthermore, both β-catenin and axin were able to
associate with the plasma membrane, and, along with APC, were shown to localize to
the nucleus. Immunofluorescence experiments confirmed this distribution pattern for
β-catenin. APC and β-catenin were co-immunoprecipitated, displaying the interaction
between components of the degradation-targeting complex. Relatively high levels of
axin were detected at the plasma membrane, and so studies on LRP5 were
commenced. LRP5 was detected in all five cell lines, and unexpectedly low levels of
LRP5 at the plasma membrane were confirmed by indirect immunofluorescence. In
response to EGF (10 ng/ml) treatment, there were a number of differences observed in the different cell lines, but average levels of LRP5 “peaked” at 3 hours. Further
investigation revealed that each cell line had an almost unique response to EGF
treatment when it came to axin plasma membrane-localization. These results confirm
the influence of growth factors on HOSCC, as well as indicate that axin and its role in
oesophageal tumourogenesis must, therefore, be influenced by additional
intermediates not assayed in this study.