Objectives: We previously demonstrated the regulation of epithelial ovarian cancer (EOC) cell invasiveness by the bioactive phospholipid sphingosine 1-phosphate (S1P). Low-dose S1P stimulated invasion like lysophosphatidic acid (LPA), while high-dose S1P inhibited invasion. Here we investigate how cell attachment status affects response to S1P and examine the effects of S1P and LPA on cell-cell and cell-extracellular matrix (ECM) adhesion.
Methods: EOC Dov13 cell invasion, ECM attachment and cell adhesion were tested through in vitro assays of Matrigel invasion and attachment to Matrigel, collagen or cell monolayer. Fractionated membrane and cytoplasmic proteins and biotin-labeled surface proteins were analyzed by western analysis. Actin cytoskeleton and FAK were visualized by immunofluorescence.
Results: S1P (20 muM) inhibited invasion of sustained, attached cells but enhanced that of invading cells. Membrane N-cadherin was depleted upon reattachment to ECM. S1P pretreatment (20 muM) accelerated N-cadherin recovery, while 40 muM LPA or 0.5 muM S1P delayed recovery. Cell-cell adhesion and stress fibers were decreased by LPA and by 0.5 muM S1P but increased by 20 muM S1P. While S1P increased cellular attachment to Matrigel and collagen-I, LPA inhibited attachment to Matrigel. Surface N-cadherin, gamma- and beta-catenins, FAK and integrinbeta1 were altered by both reattachment and treatment with S1P or LPA.
Conclusions: S1P inversely affects invasion of attached and invading cells, switching from inhibition to stimulation. This switch is associated with depletion of N-cadherin and membrane FAK. The recovery of membrane N-cadherin, change in cell-cell adhesion and actin stress fibers intensity in response to LPA and S1P inversely correlate with their effects on cellular invasiveness.