TY  - GEN
Y1  - 2006///
UR  - https://archiv.ub.uni-heidelberg.de/volltextserver/7095/
KW  - PI3K-gamma 
KW  -  Interleukin-2 
KW  -  Jurkat Zellen 
KW  -  Proteinkinase CT-cell receptor 
KW  -  PI3Kgamma 
KW  -  Interleukin-2 
KW  -  Jurkat cells 
KW  -  protein kinase C
AV  - public
ID  - heidok7095
N2  - Phosphoinositide 3-kinases (PI3Ks) are a family of lipid kinases involved in the regulation of diverse important cellular functions. The members of PI3K class I exhibit dual enzymatic specificity both as lipid kinases and protein serine kinases, and they are known to be indispensable for the development and proper functions of T lymphocytes. The involvement of PI3Ks in the activation of T cells is clearly demonstrated and so far mostly related to the PI3K class IA enzymes (alpha, beta and delta isoforms), but it was found that PI3Kgamma, the single member of class IB PI3K, is also involved in the regulation of activation-induced proliferation and cytokine production of T cells. How PI3Kgamma participates in this mechanism is largely elusive. Earlier reports proved that PI3Kgamma KO mice have a reduced number and an impaired differentiation of thymocytes, as well as a reduced number of CD4 T cells in spleen. We confirmed this earlier findings regarding disrupted differentiation of PI3Kgamma KO thymocytes, but in addition results presented here showed that this gene disruption had an even stronger impact on the mouse phenotype, significantly reducing the number of T cells in spleen and lymph nodes and effecting both major subpopulations of mature T cells (CD4 and CD8 cells). In published studies PI3Kgamma KO T cells showed reduced proliferation upon T cell receptor (TCR) stimulation. Costimulation with specific anti-CD28 antibody or activation with Ionomycin and phorbol ester is able to rescue this proliferation, in contrast to subsequent interleukin-2 (IL-2) and interferon-gamma production. In our experiments IL-2 costimulation of TCR-activated PI3Kgamma KO T cells was also sufficient to rescue this impaired proliferation, which clearly implicated that the lack of cytokines may be the major cause of their functional defect. In order to elucidate how PI3Kgamma couples the activation of TCR and IL-2 production in Jurkat cells, we used the PI3Kgamma specific inhibitor AS041164. In our experimental settings AS041164 did not exhibit any detectable cytotoxicity within the applied concentration range. Furthermore, this substance had no significant influence on overall PI3K activity in Jurkat cells proving its selectivity and specificity in our model.  The results obtained by applying AS041164 on Jurkat cells implicated that PI3Kgamma may not be involved in the signalling events in the proximity of activated TCR, and that PI3Kgamma is dispensable for certain aspects of T cell activation, such as CD69 expression. Nevertheless, treatment with AS041164 clearly and reproducibly reduced IL-2 production of activated Jurkat cells in dose-dependent manner. Jurkat cells have constant high level of PIP3, the major product of PI3K lipid-kinase activity; therefore it is most likely that this effect was caused by a lack of PI3Kgamma protein kinase-activity.  PI3Kgamma specifically interactions with several isoforms of protein kinase C (PKC) in Jurkat cells were also proved in this thesis. These interactions seem to be important for the proper function of interacting PKC isoforms upon T cell activation and for the subsequent IL-2 production. Finally, our results showed that PI3Kgamma may be involved in the control of IL-2 production on several levels from transcription to secretion, and one of these levels is apparently PKC-related. In conclusion, results from this thesis clearly demonstrate that PI3Kgamma is an important modulator of thymocyte proliferation and differentiation. Moreover, PI3Kgamma is necessary for the TCR-induced IL-2 production, a process known to be crucial for the normal proliferation of T cells after antigen receptor activation. PI3Kgamma  interacts with several PKC isoforms and modulate their activity upon TCR engagement, which is necessary for the IL-2 production. Described interactions depend on overall PI3K lipid-kinase activity as well as PI3Kgamma protein-kinase activity. This various modes of protein-protein interactions and kinase activity clearly show the PI3Kgamma is a multifunctional enzyme important for proper development and function of lymphocytes.
TI  - Signalling reactions of PI3Kgamma in T cells
A1  - Kitanovic, Igor
ER  -