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Title: Functional cross-talk between PTEN and PDK1 in normal haematopoiesis and leukaemia development
Author: Lekgetho, Henry Kebafilwe
ISNI:       0000 0004 7232 1196
Awarding Body: King's College London
Current Institution: King's College London (University of London)
Date of Award: 2018
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TEN is a tumour suppressor gene on chromosome 10, which has a central role in regulation of the phosphatidylinositol-3-kinase (PI3K) cell signalling pathway which has been linked to cell proliferation and apoptosis. Previous studies have shown that loss of PTEN induces leukaemogenesis by generating leukaemia stem cells and depleting haematopoietic stem cells. Phosphoinositide-dependent kinase-1(PDK1) is considered as a critical kinase in the PI3K signalling pathway and is responsible for mediating the phosphorylation of AKT and a wide range of other kinases that inhibit apoptosis. Given the important role of PI3K signalling in proliferation and apoptosis, we hypothesized that targeting of key components in this pathway such as PDK1 might be of therapeutic value in the treatment of loss of PTEN driven AML, ALL and other cancers. The main objective of this study is to investigate the role of PTEN and PDK1 in leukaemogenesis and normal haematopoiesis. We generated conditional knockout mice (PTEN fl/fl Rosa-cre-ERT), PDK1 (PDK1 fl/fl Rosa-cre-ERT) and PTEN-PDK1 (PTEN fl/fl PDK1 fl/fl Rosa-cre-ERT) where gene deletion can be mediated by tamoxifen treatment. To restrict the deletions to the haematopoietic compartment, bone marrow cells from the KO mice were transplanted to recipient mice and then treated with tamoxifen. Using these mouse models, we compared the impact of PTEN, PDK1 or both deletions on haematopoietic development from early HSCs to restricted progenitors. Further analysis using two specific knock-in (KI) mice (PDK1 L155e MG and PDK1 K465e) was carried out to further elucidate the activity of PDK1. In these models, PDK1 L155e MG mice have disrupted PDK1-PIF pocket domain whereas the PDK1 K465e have a defective PDK1-PH domain. These two domains are critical for the distinctive function of PDK1. Consistent with previously 5 published data, our data showed that loss of PTEN perturbed the normal haematopoietic development. Simultaneous deletion of PTEN and PDK1 rescued some of the abnormalities caused by PTEN deficiency suggesting that PDK1 may play a crucial role in haematopoiesis. We further demonstrate that loss of PTEN in the haematopoietic compartment results in the development of AML or ALL and in some cases both AML and ALL consistent with previous published data. In addition, we demonstrate that simultaneous deletion of PTEN and PDK1 does not completely reverse the leukaemogenesis induced by PTEN deletion; however it was able to significantly delay the onset of AML. Moreover, deletion of PDK1 in PTEN deficient haematopoietic cells rescued the mice from developing ALL in both PTENfl/fl PDK1fl/fl Rosa-26cre-ERT mice and PTEN fl/fl PDK1 fl/fl Vav-cre mice. PDK1 MGK465 and PDK1L155 mutation did not have any effect on the phenotype of the leukaemia mediated by loss of PTEN, however both mutants significantly reduced the leukemic stem cell frequency of PTEN null ALL stem cells. Our data further suggest that the mechanism of leukaemia in the compound PTEN PDK1 KO might be due the ability to bypass the normal activation of Akt through PDK1 when PTEN is deleted. Further studies need to be carried out to identify the mechanism or cross talk that by passes PDK1 activation of downstream kinases when PTEN is deleted.
Supervisor: Calle, Yolanda ; So, Chi Wai Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available