Sphingosine kinase 1 and Sphingosine kinase 2 (SK1 and SK2) are lipid kinases which form the bioactive lipid sphingosine-1-phosphate (S1P). SKs have been widely implicated in human cancers and inflammation. This has been demonstrated to be a consequence of the actions of S1P, which acts as a ligand at five G protein-coupled receptors - termed S1P1-5. S1P is also an intracellular effector which binds to proteins such as HDAC1/2 and TRAF2 to elicit cell responses. Recently, other mediators in the pathway have also emerged as important mediators of autophagic, apoptotic, senescent and proliferative cell processes.This study aims to investigate the molecular pathways which link SK1 and SK2 with senescence in order to identify novel signalling networks which could in turn lead to potential therapeutic approaches to cancer treatment. These aims were achieved by down-regulating SK1 and SK2 using a series of SK inhibitors in an advanced stage castrate resistant prostate cancer cell line (LNCaP AI cells). The current study demonstrated that dual inhibition of SK1 and SK2 as well as knockdown of an additional target up stream in the sphingolipid signalling pathway - dihydroceramide desaturase (Des1) - was responsible for promoting a senescent phenotype in LNCaP AI cells. As an adjunct to these findings it is reported here for the first time that the sphingosine kinase 2 inhibitor, ABC294640 (3-(4-chlorophenyl)-adamantane-1-carboxylic acid (pyridin-4-ylmethyl)amide), which is currently in phase 2 clinical trials for renal cancer and B-cell lymphoma, induces the proteasomal degradation of sphingosine kinase 1; therefore ABC294640 cannot be considered an SK2 selective inhibitor in a cellular context. Also as an adjunct to these findings, Des1 was discovered as a novel target for ABC294640. Thus, this study highlights a role of SKs and the sphingolipid signalling pathway in mediating senescence in human cancer cells which could provide novel therapeutic approaches to cancer treatment. In addition, the study challenged a central dogma in the field and provided useful and previously unknown mechanistic information about a drug which is currently in phase 2 clinical trials. Finally, the study identified a common novel target (Des1) of two existing compounds which, in combination with SK1, is responsible for inducing senescence in LNCaP AI cells. Taken together these findings provide novel and useful information not only regarding the role of SKs in senescence but in a more general context with respect to the mechanisms of action of these inhibitors, which are commonly used as tools to investigate SK signalling in vitro and in vivo.
|Date of Award||8 Jan 2019|
- University Of Strathclyde
|Sponsors||University of Strathclyde|
|Supervisor||Susan Pyne (Supervisor) & Nigel Pyne (Supervisor)|