| Summary: | Astrocytic tumours are the most common form of primary brain tumour in humans. The disease is notoriously refractive to treatment because of tumour heterogeneity and invasive propensity. Dynamic changes to the actin cytoskeleton are crucial to cancer cell invasion, but the specific mechanisms that underlie the invasive phenotype of astrocytic tumour cells are unclear. Protein interacting with C kinase 1 (PICK1) is a PDZ and BAR domain containing protein that inhibits actin related protein 2/3 (Arp2/3) complex-dependent actin polymerisation, and is involved in regulating the trafficking of a number of cell-surface receptors. There are reports that PICK1 is upregulated in a number of cancers but previous to this thesis, PICK1 had not been studied in astrocytic tumours. In this thesis, a combination of Western blotting and quantitative PCR techniques has revealed that PICK1 expression is downregulated in astrocytic tumour cell lines and clinical cases, particularly in secondary grade IV tumours. Exogenous expression of PICK1 in a grade IV astrocytic cell line reduced the cells capacity for anchorageindependent growth, 20 migration, and invasion through a 3D matrix, strongly suggesting that low PICK1 expression plays an important role in astrocytic tumourigenicity. PDZ domain interactions of PICK1 have been identified as crucial in PICK1 mediated inhibition of neoplastic characteristics. Using mass spectrophotometry proteomics analysis a number of potential binding partners of the PICK1 PDZ domain have been isolated. It has also been found that exogenous expression of PICK1 increases Rac1 activity, implicating Rac1 involvement in the mechanism that underlies PICK1 tumour suppression. The data from this thesis indicates that PICK1 negatively regulates neoplastic growth and infiltration of astrocytic tumours, thereby suggesting that manipulation of PICK1 is an attractive possibility for therapeutic intervention.
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