Mutational analysis of phosphoinositide-3 kinase (PI3K) genes in high grade glioma cell lines

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Mutational analysis of phosphoinositide-3 kinase (PI3K) genes in high grade glioma cell lines

 

Author: Cheng, Wai-wai
Title: Mutational analysis of phosphoinositide-3 kinase (PI3K) genes in high grade glioma cell lines
Degree: M.Sc.
Year: 2007
Subject: Hong Kong Polytechnic University -- Dissertations.
Gliomas.
Glioblastoma multiforme.
Phosphoinositides.
Department: Dept. of Health Technology and Informatics
Pages: ix, 70 leaves : ill. (some col.) ; 30 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2174227
URI: http://theses.lib.polyu.edu.hk/handle/200/1627
Abstract: Glioblastoma multiforme (GBM) is the most common and aggressive form of glioma. Despite advances in surgical and clinical neuro-oncology, prognosis remains poor. New approaches like molecular targeted therapy are utterly required to tackle this life-threatening disease. Genetic analysis in GBM showed that the PI3K/AKT pathway is the commonly altered pathway. This pathway promotes cell survival, proliferation, invasion and angiogenesis. Molecules like EGRF, CDKN2A and PTEN involved in this pathway were found to be mutated or amplified. PISKs, being one of the central molecules in PI3K/AKT pathway, are a family of enzymes. Class I PISKs are heterodimeric lipid kinases composed of a regulatory subunit and a catalytic subunit. PIK3CA, encodes for the a isoform of the catalytic subunit of class 1A PI3K, was found to be mutated in many cancers. PIK3R1, encodes for the regulatory subunit of class 1A PI3K, was also found to be mutated in some cancers. It is reasonable to postulate that these genes mutations may also occur in GBM. On the other hand, PIK3CD, another isoform of class LA PI3K was highly expressed in several GBM cell lines. Further investigation showed that one of the cell lines with high expression of PIK3CD was apparently functionless towards its downstream effector AKT. Mutations in the gene encodes for the catalytic subunit PIK3CD are the possible reasons for these unusual findings. If mutation was found in either one of the PI3K genes in the cell lines, it may help the investigation into the underlying mechanism of GBM development and provide answers for the high expression and apparently functionless PIK3CD in GBM. Cell lines with mutated gene can also act as a model for molecular targeted drug testing. In this project, mutational analysis using direct sequencing in 11 GBM cell lines was done on selected exons of three PI3K genes (PIK3CA, PIK3R1 and PIK3CD). Two mutations were found in intron 17 (IVS17-41) and 18 (TVS18-30) of PIK3CD while no mutation was found in PIK3CA and PIK3R1. Mutations found hi this project are the same as the one previously reported to the National Centre for Biotechnology Information. They are transitional nucleotide changes. Without further investigations, the nature of IVS17-41 and IVS18-30 cannot be determined. They may reflect polymorphic nature of nucleotide composition, which is usually neutral variation without any association with GBM. Alternatively, it is possible that they cause splicing errors or they regulate expression or function of the protein through unknown mechanisms. No mutation being found in PIK3CA argued against mutated PIK3CA plays a central role in oncogenesis of GBM. No mutation was found in PIK3R1 and other sites of PIK3CD imply that most probably gene mutation hi the investigated sites could not answer the unusual expression and the apparently non-functional PIK3CD. Further investigations like perform sequencing on RNA of PIK3CD or lipid kinase activity assay on PIK3CD may help confirm the importance of the mutations found in this project, hi addition, other genes hi the same altered signaling pathway like AKTand PTEN deserve more than a passing notice.

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