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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Role of Protein Kinase C-iota in Neuroblastoma and the Effect of ICA-1, a Novel Protein Kinase C-iota Inhibitor on the Proliferation and Apoptosis of Neuroblastoma Cells

Pillai, Prajit P 01 January 2011 (has links)
Protein Kinase C-iota (PKC-é), an atypical protein kinase C isoform manifests its potential as an oncogene by targeting various aspects of cancer cells such as growth, invasion and survival. PKC-é confers resistance to drug-induced apoptosis in cancer cells. The acquisition of drug resistance is a major obstacle to good prognosis in neuroblastoma. The focus of the dissertation was three-fold: First to study the role of PKC-é in the proliferation of neuroblastoma. Secondly, to identify the efficacy of [4-(5-amino-4-carbamoylimidazol-1-yl)-2,3-dihydroxycyclopentyl] methyl dihydrogen phosphate (ICA-1) as a novel PKC-é inhibitor in neuroblastoma cell proliferation and apoptosis. Finally, to analyze whether PKC-é could self-regulate its expression. Cyclin dependent kinase 7 (Cdk7) phosphorylates cyclin dependent kinases (cdks) and promotes cell proliferation. Our data shows that PKC-é is an in-vitro Cdk7 kinase and that neuroblastoma cells proliferate via a PKC-é/Cdk7/cdk2 cell signaling pathway. ICA-1 specifically inhibits the activity of PKC-é but not that of PKC-zeta (PKC-æ), the closely related atypical PKC family member. The IC50 for the kinase activity assay was approximately 0.1µM which is 1000 times less than that of aurothiomalate, a known PKC-é inhibitor. The phosphorylation of Cdk7 by PKC-é was potently inhibited by ICA-1. ICA-1 mediates its antiproliferative effects on neuroblastoma cells by inhibiting the PKC-é/Cdk7/cdk2 signaling pathway. ICA-1 (0.1µM) inhibited the in-vitro proliferation of BE(2)-C neuroblastoma cells by 58% (P=0.01). Additionally, ICA-1 also induced apoptosis in neuroblastoma cells. Interestingly, ICA-1 did not affect the proliferation of normal neuronal cells suggesting its potential as chemotherapeutic with low toxicity. Hence, our results emphasize the potential of ICA-1 as a novel PKC-é inhibitor and chemotherapeutic agent for neuroblastoma. Bcr-Abl has been shown to regulate the activation of the transcription factor ELK-1 which in turn regulates the expression of PKC-é. Alternatively, we hypothesize that PKC-é can self regulate its expression by indirectly regulating the activity of Elk-1 in an ERK1 dependent manner. Our preliminary data shows that there was robust increase in the expression as well as association of PKC-é and Elk-1 in actively proliferating neuroblastoma cells suggesting a potential role of PKC-é in regulating the activity of Elk-1. Analysis of the subcellular fractions also presented a similar increase in the association between PKC-é and Elk-1 in the nuclear fraction of actively proliferating cells as compared to cytoplasm. Interestingly, the nuclear expression of PKC-é was also found to be higher in these cells, suggesting that PKC-é translocated to the nucleus in actively proliferating cells and regulated the transcriptional activity of Elk-1. However, our data from in-vitro kinase activity demonstrated that PKC-é was not an Elk-1 kinase but that it increased the phosphorylation of Elk-1 in the presence of ERK1, an upstream kinase of Elk-1 in the Bcr-Abl mediated regulatory pathway of PKC-é. This suggested that ERK1 was integral to the self-regulatory activity of PKC-é. In conclusion, we hypothesize that the self-regulatory mechanism of PKC-é is initiated by the translocation PKC-é into the nucleus where it activates ERK1. This promotes the activation of its downstream target Elk-1 which subsequently upregulates the expression of PKC-é

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