Bohnacker, Thomas. PI3Kγ adapter subunits in mast cells. 2009, PhD Thesis, University of Basel, Faculty of Science.
Official URL: http://edoc.unibas.ch/diss/DissB_8743
). In line with PI3Kγ’s predominant expression in immune
cells, genetic ablation of the catalytic subunit p110γ causes defects in inflammatory and allergic responses, such as leukocyte chemotaxis, mast cell migration, and the synergistic amplification of IgE and antigen mediated degranulation. While the requirement of class IB PI3K activity in mast cell function was proven in murine disease models, there is still a lack of knowledge on the physiologic function of its adapter subunits, dubbed p101 and p84. Based on in vitro experiments both adapters support p110γ activity by sensitizing p110γ for the Gβγmediated activation downstream of GPCRs. Expression analysis performed here determined mast cells most appropriate to study the physiologic requirement of p84. Mast cells have high abundance of p84 and p110γ protein, while p101 protein was undetectable. In particular the observed destabilization of p84 protein in p110γ null mast cells was beneficial to conduct elegant complementation experiments. To this end, p84 complexed with the catalytic subunit p110γ (p84:p110γ), was essential for all PI3Kγ dependent cell responses, such as adenosine driven PtdIns(3,4,5)P3 production, phosphorylation of PKB/Akt, cell migration and the adenosine enforced degranulation. Of note, increased abundance of p110γ was ineffective in compensating lack of p84.
Moreover, the replacement of p84 by p101 in complex with p110γ (p101:p110γ) unraveled a non-redundant function for the two adapter subunits, as p101:p110γ failed to support degranulation, while cell migration and phosphorylation of PKB/Akt were intact. A possible explanation was provided by adapter dependent spatiotemporal differences of PtdIns(3,4,5)P3 production. Both PI3Kγ complexes produced PtdIns(3,4,5)P3 at the plasma membrane, which was however rapidly endocytosed via microtubule dependent process, when derived from p101:p110γ signaling. Especially during co-stimulation with adenosine and IgE and antigen, p84:p110γ derived PtdIns(3,4,5)P3 significantly prolonged localization to the plasma membrane was observed as compared to PtdIns(3,4,5)P3 of p101:p110γ origin. Moreover the two PI3Kγ complexes have differential sensitivity to cholesterol depleting agents. Altogether this implies adapter dependent production of distinct pools of PtdIns(3,4,5)P3 at the plasma membrane, eliciting specific cell responses. Thus it is exclusively the p84:p110γ complex, that amplifies mast degranulation and allergic responses. This adds an additional pathway for specific treatment of allergic diseases, e.g. by particular disruption of this complex.
|Advisors:||Wymann, Matthias Paul|
|Committee Members:||Huber, Michael|
|Faculties and Departments:||03 Faculty of Medicine > Departement Biomedizin > Division of Biochemistry and Genetics > Cancer- and Immunobiology (Wymann)|
|Bibsysno:||Link to catalogue|
|Number of Pages:||123|
|Last Modified:||30 Jun 2016 10:41|
|Deposited On:||25 Aug 2009 14:16|
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