Abstract
Cells continuously respond to external and internal cues that can initiate signalling cascades that influence cell functions such as cell size, division, proliferation, survival, motility and differentiation. The signal is generally transduced and amplified within the cells by small molecules (e.g., Ca2+i) and proteins, that may also form complexes with other proteins. Dysregulation in cell signalling mechanisms play a key role in proliferative diseases such as cancer. Prostate cancer is the most common cancer in men worldwide with significant morbidity and mortality. Androgen deprivation therapy (ADT) is a first-line treatment for prostate cancer and initially regress the cancer, however, the cancer recurs and is termed castration resistant prostate cancer (CRPC).Androgens and their metabolites (testosterone and 5α-dihydrotestosterone, DHT) are ligands for the androgen receptor (AR), an important cell signalling pathway in prostate cancer. Upon binding with its ligands (e.g., DHT), AR dimerizes and translocate into nucleus to activate gene transcription resulting in evasion of apoptosis. Dysregulation in AR signalling is one explanation for the development of CRPC. Another key cell signalling network is the Wnt pathway. Wnts (Wingless Integration Site) are a large family of secretory glycoproteins that bind to cell membrane receptors and ion channels to initiate an intracellular signal cascade. Free intracellular Ca2+ and β-catenin, a 92kDa cadherin that acts as transcription factor co-activator of genes including proto-oncogenes, act as intracellular transducers of Wnt signalling, regulating proliferation, survival and differentiation. Recently, Cx43 has also been shown as an accessory protein in Wnt signal transduction. Overactivation of Wnt signalling leads to cancer initiation and progression.
Individually, AR and Wnt pathways contribute towards carcinogenesis in prostate and other tissues. Although it is known that AR signalling pathway may be modulated by Wnt signalling, suggesting a close relationship between these key cell signalling mechanisms, little is known about (i) the pattern of co-expression of AR and Wnt related proteins in human prostate (ii) reciprocal activation of AR and Wnt signalling by their respective ligands and (iii) if there is a physical interaction between the transducers of these signalling pathways. Close and reciprocal interaction and co-operativity between AR and Wnt pathways may have important implications for prostate carcinogenesis and therapy.
Here, I have investigated the expression of AR and Wnt related proteins in human prostate tissue and aimed to elucidate the interaction between these two key pathways at molecular and functional levels. I demonstrate, using in situ quantitative expression analysis, that AR expression decreases with increasing Gleason grade diagnosis (normal, Grade 3+3, Grade 4+4 and Grade 4+5/5+4), which is used to signify the aggressiveness of prostate cancer. Conversely, the expression of Wnt related proteins (β-catenin, TCF-1 and PYGO2) increases with increase in Gleason grading. These results indicate an antagonistic co-regulation of AR and Wnt signalling proteins in prostate cancer development. Interestingly, Cx43 expression, like that of AR, decreased in higher grade cancer compared to normal prostate. The expression of both AR and β-catenin show an increase in CRPC tissue compared to normal of different grades of prostate cancer.
Functional and molecular mechanisms of interaction between AR and Wnt signalling were investigated using in vitro cell culture and immunochemical techniques and prostate cancer cell lines LnCAP that expresses AR and PC3 which does not. I demonstrate for the first time that AR ligands induce stabilization and nuclear translocation of β-catenin and reciprocally, Wnt ligands induce translocation of AR into the nucleus. Wnt ligands also activated nuclear translocation of AR in PC3(AR+) (PC3 cells transfected with AR gene), validating the observations in LnCAP cells. Using co-immunoprecipitation, I also show for the first time that there is a physical interaction between androgen receptor and β-catenin.
The novel results presented here, show that in prostate cancer, AR and Wnt signalling pathways interact at functional and molecular levels and there is a reciprocity of signal activation that results in progression of prostate cancer and contributes towards the development of CRPC.
| Date of Award | 1 May 2022 |
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| Original language | English |
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| Supervisor | Aamir Ahmed (Supervisor) & Prokar Dasgupta (Supervisor) |