Type
Text
Type
Dissertation
Advisor
Obeid, Lina | Cao, Jian | Hannun, Yusuf | Shroyer, Kenneth | Yang, Vincent | Pearl, Michael.
Date
2015-12-01
Keywords
Ezrin, radixin, moesin, Inflammation, Invasion, S1PR2, Sphingosine-1-phosphate, Sphingosine kinase | Oncology
Department
Department of Molecular and Cellular Biology.
Language
en_US
Source
This work is sponsored by the Stony Brook University Graduate School in compliance with the requirements for completion of degree.
Identifier
http://hdl.handle.net/11401/76483
Publisher
The Graduate School, Stony Brook University: Stony Brook, NY.
Format
application/pdf
Abstract
Sphingolipids have emerged as bioactive constituents of eukaryotic cells. The bioactive sphingolipid ceramide mediates cellular senescence, apoptosis and cell cycle arrest. Acted upon by ceramidase, it is transformed to sphingosine that in turn gets phosphorylated by sphingosine kinases (SK1 and SK2) to generate sphingosine-1-phosphate (S1P). This lipid, on the contrary, mediates cellular proliferation, mitogenesis, inflammation, angiogenesis, and cancer metastasis through its actions on specific G-protein coupled receptors (S1PR1-5). ERM (ezrin, radixin, and moesin) proteins are a group of adaptor molecules linking the cortical actin cytoskeleton to the plasma membrane, and are emerging as critical regulators of cancer metastasis and progression via regulation of cell morphology and motility. Recently, we have identified S1P as an acute and potent ERM activator (via phosphorylation) through its action on its receptor S1PR2. We have also demonstrated that S1P-mediated filopodia formation, a first step in cell invasion, is through ERM activation. Growth factors are known activators of ERM proteins; however, it is not known if it involves the newly described S1P/S1PR2 axis, as well as upstream metabolites of the sphingolipid pathway. We demonstrate that SK2, and not SK1, is essential and sufficient in EGF-mediated ERM phosphorylation. Surprisingly, and for the first time, we prove that this event, although strictly dependent on S1PR2 activation, does not require extracellular S1P secretion; therefore introducing a potential novel model of autocrine/intracrine action of S1P that still involves its GPCR receptors. We also establish Spns2 as an essential S1P transporter that is required for S1PR2 activation and subsequent ERM phosphorylation. In addition, we rule out the role of previously established ezrin kinases, and involve the checkpoint kinases, CHK1 and CHK2, as novel mediators of ERM activation downstream of S1PR2; therefore, emphasizing the newly emerging concept stating that a cell need to stop proliferation for it to invade. Finally, we identify SK2, S1PR2 and CHKs as new and potent targets in the pathway of EGF-driven invasion. In fact, inhibiting SK2, S1PR2 or CHKs eradicates EGF-mediated lamellipodia formation, adhesion and extracellular matrix invasion. In conclusion, this body of work uncovers new mechanistic insights for EGF-mediated invasion. More importantly, it sets the stage for novel alternative therapeutic targets that could be of utmost importance especially in patients that become resistant to current EGFR-tyrosine kinase inhibitors. | 284 pages
Recommended Citation
Adada, Mohamad, "The Role and Regulation of Sphingosine Kinases in Cancer Biology" (2015). Stony Brook Theses and Dissertations Collection, 2006-2020 (closed to submissions). 2398.
https://commons.library.stonybrook.edu/stony-brook-theses-and-dissertations-collection/2398