Intracellular sphingosine kinase 2‐derived sphingosine‐1‐phosphate mediates epidermal growth factor‐induced ezrin‐radixin‐moesin phosphorylation and cancer cell invasion

Abstract

The bioactive sphingolipid sphingosine-1-phosphate (S1P) mediates cellular proliferation, mitogenesis, inflammation, and angiogenesis. These biologies are mediated through S1P binding to specific GPCRs [sphingosine-1-phosphate receptor (S1PR)1-5] and some other less well-characterized intracellular targets. Ezrin-radixin-moesin (ERM) proteins, a family of adaptor molecules linking the cortical actin cytoskeleton to the plasma membrane, are emerging as critical regulators of cancer invasion via regulation of cell morphology and motility. Recently, we identified S1P as an acute ERM activator (via phosphorylation) through its action on S1PR2. In this work, we dissect the mechanism of S1P generation downstream of epidermal growth factor (EGF) leading to ERM phosphorylation and cancer invasion. Using pharmacologic inhibitors, small interfering RNA technologies, and genetic approaches, we demonstrate that sphingosine kinase (SK)2, and not SK1, is essential and sufficient in EGF-mediated ERM phosphorylation in HeLa cells. In fact, knocking down SK2 decreased ERM activation 2.5-fold. Furthermore, we provide evidence that SK2 is necessary to mediate EGF-induced invasion. In addition, overexpressing SK2 causes a 2-fold increase in HeLa cell invasion. Surprisingly, and for the first time, we find that this event, although dependent on S1PR2 activation, does not generate and does not require extracellular S1P secretion, therefore introducing a potential novel model of autocrine/intracrine action of S1P that still involves its GPCRs. These results define new mechanistic insights for EGF-mediated invasion and novel actions of SK2, therefore setting the stage for novel targets in the treatment of growth factor-driven malignancies.

Sphingolipid metabolism in cancer signalling and therapy

“…In tumour cells, S1PR2 signalling induced AML growth and/or proliferation 113 and was shown to activate ezrin–radixin–moesin (ERM) proteins to induce motility and invasion of HeLa cells in culture 114 , consistent with S1PR2-mediated tumour metastasis of bladder cancer and melanoma cells in mouse models 107 . By contrast, systemic S1PR2 signalling, mainly in endothelial cells and bone-marrow-derived cells (BMDCs), was reported to inhibit tumour angiogenesis in mouse models 115 .…”

An intrinsic lipid-binding interface controls sphingosine kinase 1 function

“…Activity was measured by the production of a fluorescent sphingosine-1-phosphate as previously described [57,58].…”

Recent advances in the development of sphingosine kinase inhibitors

“…Upregulation of SK1 expression has been shown in a wide array of human solid cancers and hematological malignancies with this elevated expression correlating with the severity of malignancy and shorter patient survival (reviewed in [18,22]). While less is known about the role of SK2 in cancer, its elevated expression in human non-small cell lung cancer has recently been correlated with poorer patient survival [23] and has been shown to regulate cancer cell invasion via modulation of epidermal growth factor (EGF) signalling through activation of ezrin-radixin-moesin adaptor proteins [24].…”