Investigation into class II P-glycoprotein messenger RNA decay in normal liver and liver tumours

Class II P-glycoprotein (Pgp2) is a plasma membrane protein associated with multidrug resistance. This protein and its corresponding mRNA are over expressed in many tumours, including liver tumours. Pgp2 has also been found to be overexpressed in all models of rat and mouse liver carcinogenesis. Over expression of Pgp2 in liver tumours is predominantly due to an increase in stability of Pgp2 mRNA. The main objective of this thesis was to compare the degradation pathway of rat Pgp2 mRNA in normal liver and liver tumours, with the goal of understanding why Pgp2 is more stable in liver tumours compared to normal liver. Considerable effort was spent developing the Yeast Poly (A) tailing RT-PCR method in the hope of identifying Pgp2 mRNA degradation product(s) in vivo. This study concluded that although in-vitro transcribed RNA can be detected, the Yeast Poly (A) tailing RT-PCR method is not suitable for detecting in vivo mRNA degradation product(s). This study has introduced key issues related to Pgp2 mRNA that were previously unknown. Primer extension identified that endonucleolytic pathway is at least one mechanism for degradation of Pgp2 mRNA in vivo. However, the presence of an endonucleolytic cleaved product in normal liver and liver tumour suggests that endonucleolytic decay is unlikely to contribute to increased stability of Pgp2 mRNA in liver tumours. In summary, the work presented in this thesis does not provide answers as to why Pgp2 mRNA is more stable in liver tumours in comparison with normal liver. It does, however, enhance our knowledge regarding the molecular mechanisms occurring during the processing of Pgp2 mRNA in liver tumours and normal liver.