Signalling mechanisms regulating proliferation and apoptosis in immature and mature B cells

Blair, Derek (2004) Signalling mechanisms regulating proliferation and apoptosis in immature and mature B cells. PhD thesis, University of Glasgow.

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Abstract

Ligation of the antigen receptor (BCR) on B lymphocytes results in differential biological outcomes depending upon the maturation stage of the cell. Thus, mature B lymphocytes become activated and proliferate (clonal expansion) in response to antigen receptor cross linking, whilst immature B cells either become unresponsive, alter the specificity of their BCR, or undergo apoptosis (clonal deletion). These biological responses to antigen are well defined, and many of the membrane proximal signalling events activated upon BCR ligation have been delineated and appear to be similar, despite their differential biological outcomes. The precise molecular events downstream of BCR signalling that are responsible for these distinct responses therefore remain to be established. This project has therefore centred upon identifying the important signalling mechanisms linking BCR ligation with regulation of the cell cycle and the induction of apoptosis in immature and mature B lymphocytes. The murine B cell lymphoma cell line WEHI-231 is widely used as a model for clonal deletion of immature B lymphocytes. This is because it has the cell surface phenotype of an immature B lymphocyte, and as such responds to BCR ligation by undergoing growth arrest and apoptosis, mimicking the processes of clonal deletion. Moreover, WEHI-231 cells can be rescued from BCR-mediated apoptosis by co-stimulation via CD40, conditions mimicking T cell driven rescue of useful clonatypes. This cell line was therefore utilised to further examine the signalling events important for anti-lg induced growth arrest and apoptosis, and CD40 mediated rescue, in immature B lymphocytes. In particular, this investigation has explored the differential roles of the Ras/Erk-MAPKinase pathway and a number of specific PKC isoforms in the regulation of survival of immature B cells. Initial studies examined the activation of the Erk-MAPKinase in both response to apoptotic signalling via the BCR and under conditions of CD40-mediated rescue. These studies indicated that Erk-MAPKinase plays a dual role in WEHI-231 cells, being required both for BCR induced growth arrest and apoptosis and CD40-mediated rescue. The outcome of Erk-MAPKinase activity is determined by the kinetics of activation, with an early, strong, yet transient signal required for BCR induced apoptosis, whilst CD40 signalling induces a more sustained, cycling pattern of Erk-MAPKinase activation. The role of Erk-MAPKinase was further addressed in these cells by expression of constitutively active mutants of the small GTPase, Ras, a key upstream regulator of Erk-MAPKinase as well as PI-3- kinase. Interestingly, cells expressing a mutant form of Ras capable of directly coupling to the activation of PI-3-kinase, but not Erk MAPKinase (RasV12-C40), was found to be better at rescuing the cells from growth arrest than the inverse mutant, which can couple to the Erk-MAPKinase, but not PI-3-kinase pathway (RasV12-S35). (Abstract shortened by ProQuest.).

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: Maggie Harnett
Keywords: Immunology, Cellular biology
Date of Award: 2004
Depositing User: Enlighten Team
Unique ID: glathesis:2004-71081
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 10 May 2019 10:49
Last Modified: 10 May 2019 10:49
URI: http://theses.gla.ac.uk/id/eprint/71081

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