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| Author(s): |
Mariana Lemos Duarte
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Conjunto das Químicas (IQ e FCF) (CQ/DBDCQ) |
| Defense date: | 2013-08-02 |
| Examining board members: |
Deborah Schechtman;
Fábio Luís Forti;
Marcelo Damario Gomes;
Jorg Kobarg;
Leticia Labriola
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| Advisor: | Deborah Schechtman |
| Abstract | |
Some of the strategies used to understand stem cell biology are based on the identification of signalling cascades that lead to differentiation and self-renewal of embryonic stem cells (ESC) by selective interference of specific signalling processes. The protein kinase C (PKC) family is known to participate in ESC self-renewal and differentiation, however, the specific role of the different PKC isoenzymes in these cells remains to be determined. Therefore, we investigated the role of atypical PKCs (aPKC) in undifferntiated ESC using a specific inhibitor for these serine/ threonine kinases, pseudo-substrate peptide of aPKCs, and phosphoproteomics. The majority of proteins whose phosphorylation decreased upon aPKC inhibition, are proteins involved in metabolism in particular with the glycolytic pathway. Besides that, inhibiton of aPKCs led to a decrease in glucose uptake and lactate secretion, followed by a decrease in lactate dehydrogenase activity, and an increase in mitochondrial activity as measured by oxygen consumption after treatment with olygomycin and a chemical uncoupler. We also verified that aPKCs are able to directly phosphorylated pyruvate kinase. Aerobic glicolysis seems to be fundamental for the maintainance of undifferentiated ESC, and we demonstrated that aPKCs participte in these processes helping to maintain self-renewal of undifferentiated ESC. We also observed that aPKCs as PKCβI modulate the phosphorylation of α-tubulin, however, while aPKCs interact with α-tubulin during interfase PKCβI interacts with α-tubulin only during mitosis. These results lead to the second part of this thesis. We investigated the role of α-tubulina phosphorylation by PKCβI. Indentifying threonine 253, a conserved residue in several vertebrate species, of localized at the polymerization interface between α- and β-tubulin, as a phosphorylation site of α-tubulin by PKCβI. This site is not in a linear consensus for PKC, however, it is in a structuraly formed consensus, where basic aminoacids distant in the linear sequence are juxtaposed in the three dimentional protein structure. Simulation studies by molecular dynamics show that the interaction between α and β-tubulin increases upon this phosphorylation, once, phosphorylated T253 interacts with com K105, a conserved residue in β-tubulin. The in vitro phosphorylation of α-tubulin increased tubulin polymerization rate and inhibiton of PKCβI in cells reduced repolimeration rate of microtubles upon treatment with nocodazole. Besides that, the importance of this phosphorylation site were demonstrated by the fact that a phosphomimetic mutant GFP-α-tubulina, T253E is more incorporated in mitotic fuses while T253A is less than wild type. Our data support the hypothesis that structural consensus may be important sites recognized and that T253 phosphorylation of α-tubulin afects the polymer stability. In conclusion, using phosphoproteomics methods and selective interference of signal transduction pathways combined with experimental validation studies of the identified targets we can propose roles for aPKCs and PKCβI in undifferentiated ESC. (AU) | |