Autophagy is the process of “cell self-eating” which has been implicated both in cell survival and cell death. Sphingosine kinase 1 (SphK1) regulates the intracellular balance between ceramide and sphingosine, bioactive lipids associated with cell death, and sphingosine-1-phosphate (S1P), whose actions are associated with survival and proliferation. Previous studies have implicated upregulation of SphK1 in the induction of autophagy. In this study, SK1-I, a SphK1 specific competitive inhibitor, induced autophagy in a concentration and time dependent manner in HCT116 colorectal carcinoma cells. This autophagic response was observed to be more intense in wild type p53 expressing HCT116 cells than in p53 null cells and ultimately led to non-apoptotic death in wild type and apoptotic death in p53 null cells. In agreement, cell death in wild type cells was not accompanied by cleavage of polyADP ribose polymerase, a hallmark of apoptosis. Knockdown of Beclin 1 demonstrated that it and its binding partners do not have a significant role in the induction of autophagy in response to SK1-I treatment. Similarly, mTORC1 signaling was not observed. In contrast, SK1-I markedly decreased Akt phosphorylation. However, this might not be the sole factor important for SK1-I induced autophagy, as pharmacological inhibition of Akt only led to a comparatively weak autophagic response. Indeed, phosphorylation of the endoplasmic reticulum (ER) stress marker eIF2 α, was greatly reduced, suggesting that an ER mediated mechanism also contributes to SK1-I induced autophagy. Thus, SK1-I induced autophagy was likely triggered by ER stress signaling and led to non-apoptotic cell death in the more highly autophagic wild type 53 expressing cells. These results suggest that an isotype specific SphK1 inhibitor might be a useful adjunct for the treatment of cancer or other diseases in which enhancement of cytotoxicity or autophagy is desirable.
| Identifer | oai:union.ndltd.org:vcu.edu/oai:scholarscompass.vcu.edu:etd-2870 |
| Date | 09 July 2009 |
| Creators | Meza, Daniel |
| Publisher | VCU Scholars Compass |
| Source Sets | Virginia Commonwealth University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Theses and Dissertations |
| Rights | © The Author |
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